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WO2016159011A1 - Stainless steel sheet for exhaust system component having excellent intermittent oxidation characteristics, and exhaust system component - Google Patents

Stainless steel sheet for exhaust system component having excellent intermittent oxidation characteristics, and exhaust system component Download PDF

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Publication number
WO2016159011A1
WO2016159011A1 PCT/JP2016/060249 JP2016060249W WO2016159011A1 WO 2016159011 A1 WO2016159011 A1 WO 2016159011A1 JP 2016060249 W JP2016060249 W JP 2016060249W WO 2016159011 A1 WO2016159011 A1 WO 2016159011A1
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Prior art keywords
stainless steel
exhaust system
oxidation
oxidation resistance
system component
Prior art date
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Ceased
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PCT/JP2016/060249
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French (fr)
Japanese (ja)
Inventor
慎一 寺岡
井上　宜治
濱田　純一
敦久 矢川
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Stainless Steel Corp
Original Assignee
Nippon Steel and Sumikin Stainless Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel and Sumikin Stainless Steel Corp filed Critical Nippon Steel and Sumikin Stainless Steel Corp
Priority to US15/563,159 priority Critical patent/US20180080106A1/en
Priority to KR1020177026809A priority patent/KR101988150B1/en
Priority to PL16772892T priority patent/PL3279359T3/en
Priority to ES16772892T priority patent/ES2890333T3/en
Priority to JP2017510057A priority patent/JP6239192B2/en
Priority to EP16772892.2A priority patent/EP3279359B1/en
Priority to CN201680018828.7A priority patent/CN107429358B/en
Publication of WO2016159011A1 publication Critical patent/WO2016159011A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features
    • F01N13/16—Selection of particular materials
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main catalyst
    • F01N3/106—Auxiliary oxidation catalysts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/30—Honeycomb supports characterised by their structural details
    • F01N2330/40—Honeycomb supports characterised by their structural details made of a single sheet, foil or plate
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
    • F01N2370/00—Selection of materials for exhaust purification
    • F01N2370/02—Selection of materials for exhaust purification used in catalytic reactors

Definitions

  • the present invention relates to a heat-resistant stainless steel plate excellent in intermittent oxidation characteristics, and an exhaust system component.
  • the exhaust system component of the present invention is particularly suitable as a component that is used in an environment where it is repeatedly heated to a high temperature of 1000 ° C. or higher, such as an exhaust manifold or turbocharger component of an automobile engine.
  • austenitic stainless steel SUS310S 25Cr-20Ni-0.5Si
  • SUS302B 18Cr-8Ni-2Si
  • XM15J1 (20Cr-12Ni-3Si)
  • DIN1.4828 (19Cr-11Ni-2Si)
  • ferritic stainless steel It is more expensive than ferritic stainless steel, and the steel type is selected from environmental factors such as availability and molding technology in each region.
  • ferritic stainless steel has insufficient strength
  • austenitic stainless steel has problems such as thermal fatigue and scale peeling, which cannot be used.
  • Patent Document 1 heat-resistant cast steel and stainless steel cast as shown in Patent Document 1 are also used for exhaust manifolds and turbocharger parts, but there is a great need for weight reduction of automobile parts, and efforts to replace cast parts with plate-formed press-formed parts Has been done.
  • Patent Document 2 discloses a material that ensures heat resistance at 950 ° C. by adding Mo, Nb, Cu, W, or the like to SUS444, which is a ferritic stainless steel, to increase the high-temperature strength.
  • SUS444 which is a ferritic stainless steel
  • Patent Document 3 in a repetitive heating and cooling environment of 900 ° C. or more, the Mo content is reduced as much as possible, a trace amount of V is added, and the crystal grain size and surface roughness of the hot-rolled sheet are controlled, thereby improving the heat resistance. It is disclosed that a hot-rolled steel sheet having excellent properties is obtained. However, it is difficult to produce the plate thickness required for automobile exhaust system parts by hot rolling, and the required plate thickness accuracy cannot be obtained.
  • exhaust manifolds and turbocharger parts are also made into double pipe structures. Specifically, by using austenitic stainless steel on the inner side and ferritic stainless steel on the outer side, the restraint of the inner austenitic stainless steel member is relaxed and thermal strain is reduced. This makes it possible to lower the temperature by not letting the outer ferritic stainless steel directly touch the high-temperature exhaust gas.
  • Such a double structure part is expensive, but is often used for an exhaust manifold having an exhaust gas temperature of 1000 ° C. or less. Even when the exhaust gas temperature is 900 ° C. or lower, it may be used to suppress the oxidation of the outer surface of the exhaust manifold and improve the design.
  • the present invention can be suitably used as an automobile exhaust system part such as a double pipe inner pipe of an exhaust manifold or a turbocharger part (including a case of a double pipe structure), has no surface flaws, and has high high temperature strength and corrosion resistance.
  • Another object of the present invention is to provide a stainless steel plate that does not cause embrittlement at high temperatures and exhibits high oxidation resistance. It is another object of the present invention to provide an automobile exhaust system component that uses the stainless steel plate and has excellent base material and welded portion oxidation resistance.
  • the present inventors first reviewed the component composition.
  • austenitic stainless steel having good oxidation resistance stainless steel with increased Si and stainless steel with REM added, such as SUS302B, XM15J1, and DIN1.4828, are generally used.
  • the inventors conducted an intermittent oxidation test in an atmosphere gas simulating an automobile exhaust gas environment. The weight loss due to oxidation was noticeable, and it was judged that there was no oxidation resistance at 1050 ° C.
  • the present inventors have made various studies in order to clarify the material composition that can withstand an environment of 1050 ° C.
  • a stainless steel sheet having oxidation resistance capable of withstanding 1050 ° C. can be obtained by a method for forming a highly protective scale even in an intermittent oxidation environment by ensuring the amount of the product and controlling the precipitation form. I found out.
  • an oxide scale mainly composed of Cr 2 O 3 that hardly causes diffusion of oxygen ions and metal atoms in the scale is formed.
  • An internal oxide layer is formed so that the scale does not peel due to thermal expansion and contraction of the base material during heating and cooling.
  • An internal oxide layer refers to Si oxide formed in an austenite grain boundary. If a scale mainly composed of Cr 2 O 3 having a high protective property is not formed on the surface, this grain boundary oxidation becomes shallow, and it is difficult to prevent scale peeling. In addition, when austenite grains grow, grain boundary oxidation is suppressed by the movement of grain boundaries, and thus oxidation resistance is impaired. Therefore, precipitates are dispersed in order to suppress grain growth.
  • FIG. 1 shows the results of examining the influence of Cr, Mo and Si, C, N on the oxidation resistance in intermittent oxidation.
  • the test method is as follows.
  • Austenitic stainless steels of various compositions are melted in the laboratory, heated to 1250 ° C for 1 hour, hot-rolled to a plate thickness of 3 mm, hot-rolled sheet annealed at 1100 ° C for 20 seconds, immediately water-cooled, shot After blasting, the scale was removed with sulfuric acid and nitric hydrofluoric acid.
  • FIG. 2 shows the cross-sectional shape of the sample welded by lap fillet and the reduction of the plate thickness after the oxidation test.
  • the oxidation became prominent in the heat affected zone, and as a result of the increase in plate thickness reduction, the sample was sometimes separated (upper left of the lower photograph in FIG. 2). ). Therefore, it was found that the weld heat affected zone dominates the life of the exhaust system parts.
  • the scale mainly composed of Cr 2 O 3 was not uniformly formed on the surface, and it was found that the grain boundary oxidation did not occur much. I understood.
  • the “gradient of plate thickness change (toe angle)” means the angle at which the surface of the base material and the surface tangent of the weld bead (welded metal) intersect in the cross-sectional observation of the side surface of the weld. When expressed in degrees, it refers to an angle of (180-X). The toe angle is usually displayed in the range of 0 to 90 degrees.
  • the toe angle in the present invention is defined as the largest angle in the cross-sectional view.
  • a large toe angle means that the gradient at which the plate thickness changes due to the swelling (swelling) of the surface of the weld bead is steep.
  • 24Cr-12Ni-0.1C-0.02N-2.0Si-1Mn-0.5Mo-0.05Al-0.05V steel was melted in the laboratory, heated to 1250 ° C for 1 hour, After rolling to a sheet thickness of 3 mm, hot-rolled sheet annealing was performed at 1100 ° C. for 20 seconds, immediately cooled with water, shot blasted, and the scale was removed with sulfuric acid and nitrohydrofluoric acid. Subsequently, it was cold-rolled to a thickness of 1.2 mm.
  • an intermittent oxidation test was performed in 2000 cycles of heating and cooling between 200 ° C. and 1050 ° C. in an automobile exhaust gas environment.
  • the thickness reduction of the weld heat affected zone was measured, and the thickness reduction of 0.4 mm or less was accepted.
  • the scale peeling of the weld heat affected zone can be reduced by setting the gradient of the plate thickness change to 15 degrees or less. It was.
  • the effect of butt welding was also investigated.
  • the oxidation of the weld heat affected zone is further reduced by reducing the gradient of the plate thickness change, and when the gradient of the plate thickness change is eliminated, it has the same oxidation resistance as the base material, but at over 15 degrees. It was found that the effect of improving oxidation resistance was small.
  • the type of welding method is not limited, but good results can be obtained particularly in the case of arc welding. Even in other welding methods, the same effect can be obtained based on the technical mechanism disclosed in the present invention.
  • the durability as an exhaust system component can be made durable at 1050 ° C. by optimizing the component design of the base metal and controlling the shape of the weld metal.
  • the present invention has been made on the basis of the above findings, and the gist thereof is as follows.
  • W 0.01 to 3.00%
  • Zr 0.05 to 0.30%
  • Sn 0.01 to 0.10%
  • Co 0.01 to 0.30 %
  • Mg 0.0002% to 0.010% of one or more kinds
  • the present invention it is possible to improve the oxidation resistance of the stainless steel plate for exhaust system parts and the exhaust system parts, and since surface flaws are less likely to occur in the steel sheet, the surface grinding process ( CG) can be omitted or simplified.
  • the surface grinding process CG
  • FIG. 1 is a graph showing the influence of components on the resistance to intermittent oxidation at 1050 ° C. of a thin plate.
  • FIG. 2 shows the thickness change shape in the cross section of the weld metal welded by lap fillet. The upper row shows the case where the gradient of the plate thickness change at the welded portion is 11 degrees, and the lower row shows the case where the gradient is 25 degrees.
  • FIG. 3 is a graph showing the influence of the gradient of the plate thickness change on the oxidation resistance (plate thickness reduction) at 1050 ° C.
  • C 0.05 to 0.15% C is effective for increasing the stability of the austenite structure and the high temperature strength. In addition, it forms carbides with Cr and suppresses the growth of austenite grains, moderately grows grain boundary oxidation, and improves the scale peeling resistance. Since this effect appears at 0.05% or more of C, the lower limit is made 0.05%. In order to suppress grain growth stably, it is desirable to make it 0.10% or more. If it exceeds 0.15%, the amount of Cr carbide increases, and the chromium-deficient layer at the grain boundary increases. Even in high Cr austenitic stainless steel such as this steel, exhaust manifold parts and turbocharger parts for automobiles However, the required corrosion resistance cannot be maintained, so the upper limit is made 0.15% or less. From the viewpoint of corrosion resistance, it is desirable to make it 0.12% or less.
  • Si 1.0% to 4.0% Si is effective in oxidation resistance, and is particularly effective in preventing scale peeling during intermittent oxidation. In order to form grain boundary oxidation in an environment exceeding 1000 ° C. and suppress scale peeling on the surface, 1.0% or more of Si is required. In order to improve oxidation resistance, it is desirable to make it 2.0% or more. Si is a ferrite stabilizing element and increases the amount of ⁇ -ferrite in the solidified structure, so that the hot workability is deteriorated in hot rolling. In addition, since Si promotes the formation of a sigma layer and there is a risk of embrittlement when used at a high temperature for a long time, it is preferably 3.5% or less.
  • Mn 0.5 to 3.5%
  • Mn is an element added as a deoxidizer, and contributes to the stabilization of the structure by expanding the austenite single phase region. The effect appears clearly at 0.5% or more, so 0.5% or more.
  • it since it has the effect of improving hot workability by forming sulfides and reducing the amount of solute S in the steel, it is desirable to set it to 1.0% or more.
  • excessive addition reduces the corrosion resistance, so it is made 3.5% or less.
  • an oxide mainly composed of Cr 2 O 3 is desirable, and an oxide of Mn is not preferable.
  • P 0.010 to 0.040%
  • P is an element contained as an impurity in the main raw material such as hot metal or ferrochrome. Since it is an element harmful to hot workability, it is set to 0.040% or less. In addition, Preferably it is 0.030% or less. Excessive reduction leads to an increase in cost, such as making it necessary to use a high-purity raw material, so 0.010% or more. Economically preferably 0.020% or more is desirable.
  • the upper limit of the content is preferably as small as 0.010%. Further, the smaller the S content, the better the corrosion resistance. However, since the desulfurization load increases and the production cost increases for lowering the S content, the lower limit is preferably made 0.0001%. Preferably, the content is 0.001 to 0.008%.
  • Cr 20-30%
  • Cr is an essential element for ensuring oxidation resistance and corrosion resistance. If it is less than 20%, these effects are not exhibited. On the other hand, if it exceeds 30%, the austenite single phase region is reduced and the hot workability at the time of production is impaired, so 20-30%. From the viewpoint of oxidation resistance, it is desirable to make it 24% or more. Further, if the amount of Cr is increased, embrittlement occurs due to the formation of a sigma phase.
  • Ni 8-25%
  • Ni is an element that stabilizes the austenite phase, and unlike Mn, is an element that is effective in oxidation resistance. Since these effects are obtained at 8% or more, the lower limit is made 8% or more. Since it also has an effect of suppressing the formation of sigma phase, it is desirable to make it 10% or more. On the other hand, excessive addition increases the susceptibility to solidification cracking and lowers the hot workability, so the content is made 25% or less. Furthermore, in order to suppress scale peeling in intermittent oxidation, it is desirable to make it 15% or less.
  • Mo 0.01 to 1.5% Mo, together with Si and Cr, is effective for forming a protective scale on the surface, and the effect is obtained at 0.01%, so the lower limit is made 0.01% or more. Further, since it is an element effective for improving corrosion resistance, it is desirable to add 0.3% or more. On the other hand, it is also a ferrite stabilizing element, and as the amount of Mo added increases, it is necessary to increase the amount of Ni added. Further, since the formation of the sigma phase is promoted to cause embrittlement, the content is made 1.5% or less. Since the effect of improving corrosion resistance and oxidation resistance is almost saturated at 0.8% or more, it is desirable to make it 0.8% or less.
  • Al 0.001 to 0.10%
  • Al is an element that improves oxidation resistance. Since the effect is obtained at 0.001% or more, the lower limit is made 0.001% or more. In order to improve deoxidation efficiency, it is desirable to make it 0.003% or more.
  • excessive addition forms a nitride to reduce the amount of dissolved N and lowers the high temperature strength, so the upper limit is made 0.10% or less. Considering the weldability, it is desirable to make it 0.05% or less.
  • N 0.13-0.50% N is one of the very important elements in the present invention.
  • increasing Ni austenite stability also makes it possible to reduce Ni.
  • a larger amount than C can be added.
  • the content is made 0.13% or more.
  • the reduction effect of Ni it is desirable to make it 0.25% or more.
  • the upper limit is made 0.50% or less.
  • the strength at normal temperature is too high, the load during cold rolling becomes high and the productivity is impaired, so it is desirable to make it 0.30% or less.
  • the stainless steel plate of the present invention includes Cu: 0.1 to 3.0%, V: 0.03 to 0.5%, Ti: 0.001 to 0.3%, Nb One or two or more of: 0.001 to 0.3%, B: 0.0001 to 0.0050%, and Ca: 0.001 to 0.010% may be optionally added.
  • Cu 0.1 to 3.0%
  • Cu is a relatively inexpensive element that substitutes for Ni as an austenite stabilizing element. Furthermore, it is effective in suppressing the progress of crevice corrosion and pitting corrosion. To that end, it is desirable to add 0.1% or more.
  • Cu is often mixed from raw materials such as scrap and is inevitably contained in an amount of about 0.2% as an impurity. However, if it exceeds 3.0%, the hot workability is lowered, so the content is made 3.0% or less.
  • V 0.03-0.5%
  • V is generally contained in a range of 0.01 to 0.10% because it is mixed as an inevitable impurity in the alloy raw material of stainless steel and is difficult to remove in the refining process. Moreover, since it forms fine carbonitride and has the effect of suppressing grain growth, it is an element that is intentionally added as necessary. The effect is stably manifested when 0.03% or more is added, so the lower limit is made 0.03%. Since it is not preferable that the crystal grain size changes due to the variation of V, 0.08% or more is desirable in order to make the crystal grain size within a certain range. On the other hand, if added excessively, the precipitates may be coarsened. As a result, the toughness after quenching decreases, so the upper limit is made 0.5%. In view of manufacturing cost and manufacturability, it is desirable to set it to 0.2% or less.
  • Ti 0.001 to 0.3%
  • Ti is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride similarly to Nb.
  • the upper limit is made 0.3% or less.
  • Ti may not be contained.
  • Nb 0.001 to 0.3%
  • Nb is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride.
  • the upper limit is made 0.3%.
  • Nb may not be contained.
  • B 0.0001 to 0.0050% B is an element effective for improving the hot workability. Since the effect is manifested at 0.0001% or more, 0.0001% or more may be added. In order to improve the hot workability in a wider temperature range, the content is preferably 0.0005% or more. On the other hand, excessive addition causes surface flaws due to a decrease in hot workability, so 0.0050% is made the upper limit. In consideration of corrosion resistance, 0.0025% or less is desirable.
  • Ca 0.001 to 0.010%
  • Ca is added as a desulfurization element, and has the effect of reducing S in steel and improving hot workability.
  • CaO is added to slag during melting and refining, and a part of this is dissolved as Ca in steel.
  • a composite oxide such as CaO—SiO 2 —Al 2 O 3 —MgO is also contained in the steel. Since the effect of improving hot workability is obtained from 0.001%, it is desirable to make it 0.001% or more.
  • a relatively coarse water-soluble inclusion CaS is precipitated, so that the content is preferably 0.010% or less in order to reduce the corrosion resistance.
  • W 0.01 to 3.00%
  • Zr 0.05 to 0.30%
  • Sn 0.01 to 0.10%
  • Co 0.01 to 0.30 %
  • Mg 0.0002 to 0.010%, or two or more of them may be optionally added.
  • W 0.01-3.0% W is an element that improves the corrosion resistance like Cr and Mo. There is also an effect of increasing the high temperature strength by solid solution strengthening. In order to exhibit these effects, it is desirable to add 0.01% or more. On the other hand, it is an element that promotes precipitation of the sigma phase, and in order to cause a reduction in the strength of the material due to aging embrittlement, it is desirable to make it 3.0% or less. Moreover, since it is an expensive element like Mo and Nb, it is more preferable to make it 1.5% or less.
  • Zr 0.05-0.30%
  • Zr is an element that suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitrides similarly to Ti and Nb.
  • the upper limit is made 0.30% or less. Considering the improvement in high temperature strength by securing the amount of dissolved C and N, it is desirable to make it 0.1% or less. Zr may not be contained.
  • Sn 0.01-0.10% Sn is an element effective for improving the corrosion resistance after quenching, and it is preferable to add 0.02% or more as necessary. However, excessive addition promotes ear cracking during hot rolling, so it is preferable to make it 0.10% or less.
  • Co 0.01 to 0.30%
  • Co is an element that is easily mixed as an inevitable impurity from alloy raw materials in austenitic stainless steel. Moreover, since it is an element effective in improving high temperature strength, it is desirable to add 0.01% or more. However, excessive addition causes surface flaws due to a decrease in hot workability, so it is desirable to make it 0.30% or less.
  • Mg 0.0002 to 0.010%
  • Mg is added as a desulfurization element in the same manner as Ca, and in general, a parallel amount is dissolved in the molten steel from the slag and may be contained as MgO in the composite oxide.
  • MgO in the refractory may be dissolved into the molten steel. Since the desulfurization effect appears at 0.0002% or more, it is desirable to set the lower limit to 0.0002%. On the other hand, excessive addition causes the water-soluble inclusion MgS to precipitate coarsely and lowers the corrosion resistance, so it is desirable to make it 0.010% or less.
  • the balance of the component composition is Fe and inevitable impurities.
  • the inevitable impurities are not intentionally included from the raw materials and production environment, etc., but are inevitably mixed when the stainless steel plate having the component composition defined in the present invention is industrially produced. Say.
  • the above-described optional added element may be mixed as an unavoidable impurity even if it is not intended to be contained, but there is no particular problem as long as it is below the upper limit of the content described above. Moreover, elements other than those described above can also be contained within a range not impairing the effects of the present invention.
  • a stainless steel plate exhibiting high oxidation resistance can be obtained by having the above-described component composition. Furthermore, by having the above-described welded shape, an exhaust system component that is excellent in both oxidation resistance of the base material and the welded portion can be obtained.
  • steel having the composition shown in Table 1 was melted and cast into a 200 mm thick slab. This slab is heated to 1200 ° C, then hot-rolled steel plate with a thickness of 4 mm after rough hot rolling and finish hot rolling, and inserted into an 800 ° C heat treatment furnace to simulate winding in the temperature range of 800 ° C. After holding for 1 hour, it was air cooled. Subsequently, hot-rolled sheet annealing was performed at 1100 ° C. for 20 seconds, followed by water cooling. Then, it was shot blasted and pickled to remove scale. The presence or absence of surface wrinkles was evaluated by observing with the naked eye and a magnifier with a magnification of 10 times. Those in which surface wrinkles could be confirmed by either naked eye observation or loupe observation were rejected.
  • the high temperature strength of the cold-rolled sheet was measured at 1000 ° C., and the one with 0.2% proof stress of 30 MPa or more was regarded as acceptable. Moreover, after oxidizing at 700 degreeC for 300 hours, the thin plate which grind
  • this thin plate was subjected to a JIS salt spray test, and a product in which rust occurred was regarded as a corrosion resistance failure.
  • the oxidation resistance was evaluated using a test piece in which a flat plate as pickled and a flat plate were stacked and welded on the fillet.
  • the atmosphere for the oxidation test was an atmosphere in which H 2 O was 5 to 10%, O 2 was 0.2 to 1.0%, and the balance was nitrogen.
  • the atmospheric gas composition was changed periodically by simulating automobile exhaust gas.
  • the test piece was heated and held at 1050 ° C., cooled to 200 ° C. as one cycle, tested up to 2500 cycles, the appearance was recorded, and the weight change was measured. The location where oxidation was most advanced was recorded and the thickness of the portion was evaluated, and 0.8 mm or more was regarded as having good oxidation resistance (O).
  • the base material has good oxidation resistance, and surface defects, high-temperature strength and high-temperature embrittlement are acceptable. There was also good corrosion resistance. In particular, NO. 1 to NO. As a result of controlling the shape of the weld bead within the range of the present invention, not only the base material but also the oxidation resistance of the welded portion was satisfactory. On the other hand, in the component composition that departs from the present invention, the oxidation resistance is poor, and it is difficult to achieve both surface flaws, high temperature strength, high temperature embrittlement, corrosion resistance and oxidation resistance, Any property was rejected. Thereby, it turns out that a comparative example is inferior to the example of this invention in a characteristic.
  • test NO. 31 is low in C, so NO. No. 33 is low in Si, so NO. No. 36 has a high Mn, so NO. 43 is low in Mo, so NO. 45 has a high V, so NO. Since Nos. 49 and 53 had low Cr + 20Mo or low Si + 20C + 15N, both the base metal and the welded portion had poor oxidation resistance. NO. No. 32 had poor corrosion resistance due to high C.
  • NO. 34 is high in Si, so NO. 35 has a low Mn, so NO. 37 has a high P, so NO. 42 is high in Ni, so NO. No. 48 was defective because surface defects occurred because N was high.
  • NO. No. 38 had high S and low Al, so the surface flaws were poor and the corrosion resistance was also poor.
  • NO. No. 39 had a low Cr and a low Cr + 20Mo, so the surface defects were poor and the oxidation resistance of the base metal and the welded part was also poor.
  • NO. 40 is high in Cr, NO. No. 41 has low Ni and NO. Since No. 44 had high Mo, high temperature embrittlement was bad.
  • NO. 46 is high in Al, NO. No. 47 had a poor high temperature strength because N was low.
  • NO. No. 49 does not contain Mo, and because of this, Cr + 20Mo is low, so that the oxidation resistance of the base metal and the welded part was both poor.
  • NO. Nos. 50 to 52 used A23 satisfying the provisions of the present invention as the test steel. Therefore, NO. For 50 to 52, only the oxidation resistance of the welded part is poor, but other properties and performance including the base metal oxidation resistance were satisfactory, so it is applicable to parts that do not require welding. Is possible.
  • test steel used was B20, and the value of Cr + 20C + 15N was 5.60, which was lower than the lower limit defined in the present invention, so that the oxidation resistance of the base metal and the welded part was poor. .
  • the stainless steel plate for exhaust system parts and the exhaust system parts with excellent intermittent oxidation characteristics of the present invention can improve the oxidation resistance of the heat affected zone by controlling the shape of the welded part as well as the component design that improves the oxidation resistance. is there. Moreover, since there are few surface wrinkles, the surface grinding process (CG) at the time of thin plate manufacture can be omitted or simplified. Furthermore, by improving the oxidation resistance, it is possible to reduce the thickness of the exhaust system parts, and by reducing the weight of the parts, the effect of improving the fuel efficiency of the automobile can also be obtained. The industrial applicability of the invention is great.

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Abstract

Provided is a stainless steel sheet which can be appropriately used as an automotive exhaust system component, such as the inner tube of a double tube in an exhaust manifold, or a turbocharger component, and which is free from surface flaws, has high high-temperature strength and corrosion resistance, does not experience embrittlement at high temperatures, and exhibits high oxidation resistance, wherein the stainless steel sheet has a prescribed elemental composition, and satisfies the conditions Cr + 20 Mo ≥ 24.0% and Si + 20C + 15N ≥ 5.8%. Also provided is an exhaust system component in which both the base material in which the stainless steel sheet is used and the weld exhibit excellent oxidation resistance, wherein the gradient of the change in thickness of the weld metal and the stainless steel sheet serving as the base material is 15 degrees or less.

Description

断続酸化特性に優れた排気系部品用ステンレス鋼板及び排気系部品Stainless steel plate for exhaust system parts and exhaust system parts with excellent intermittent oxidation characteristics

　本発明は、断続酸化特性に優れた耐熱ステンレス鋼板、及び排気系部品に関する。本発明の排気系部品は、とくに自動車エンジンのエキゾーストマニホールドやターボチャージャー部品のように、１０００℃以上の高温に繰り返し加熱される環境下で使用される部品として好適である。 The present invention relates to a heat-resistant stainless steel plate excellent in intermittent oxidation characteristics, and an exhaust system component. The exhaust system component of the present invention is particularly suitable as a component that is used in an environment where it is repeatedly heated to a high temperature of 1000 ° C. or higher, such as an exhaust manifold or turbocharger component of an automobile engine.

　自動車の排気系部品に用いられる材料は、高温の排ガス雰囲気にさらされ、繰り返し加熱冷却されるため、高い熱疲労特性が必要になるとともに、高温における耐酸化性、酸化スケールの耐剥離性に優れることが要求されている。たとえば、従来、エキゾーストマニホールド、フロントパイプ、コンバーターシェル用に、ＳＵＨ４０９、ＳＵＳ４２９、ＳＵＳ４３０Ｊ１Ｌ、ＳＵＳ４３６Ｌ、ＳＵＳ４４４などのフェライト系ステンレス鋼が用いられてきた。これらの鋼は、７００～９００℃程度の耐熱性を有し、かつ比較的安価であるためである。必要な耐熱温度に応じて、この中のより高合金のステンレス鋼が適用される。 Materials used for automobile exhaust system parts are exposed to high-temperature exhaust gas atmosphere and repeatedly heated and cooled, so high thermal fatigue characteristics are required, and high temperature oxidation resistance and oxide scale exfoliation resistance are excellent. It is requested. For example, conventionally, ferritic stainless steels such as SUH409, SUS429, SUS430J1L, SUS436L, and SUS444 have been used for exhaust manifolds, front pipes, and converter shells. This is because these steels have a heat resistance of about 700 to 900 ° C. and are relatively inexpensive. Depending on the required heat-resistant temperature, higher alloy stainless steels are applied.

　また、エキゾーストマニホールドにはオーステナイト系ステンレス鋼ＳＵＳ３１０Ｓ（２５Ｃｒ－２０Ｎｉ－０．５Ｓｉ）やＳＵＳ３０２Ｂ（１８Ｃｒ－８Ｎｉ－２Ｓｉ）、ＸＭ１５Ｊ１（２０Ｃｒ－１２Ｎｉ－３Ｓｉ）、ＤＩＮ１．４８２８（１９Ｃｒ－１１Ｎｉ－２Ｓｉ）等も用いられている。フェライト系ステンレス鋼に比べて高価であり、地域ごとの入手性や成形技術などの環境要因から鋼種選択がなされている。 For the exhaust manifold, austenitic stainless steel SUS310S (25Cr-20Ni-0.5Si), SUS302B (18Cr-8Ni-2Si), XM15J1 (20Cr-12Ni-3Si), DIN1.4828 (19Cr-11Ni-2Si), etc. Are also used. It is more expensive than ferritic stainless steel, and the steel type is selected from environmental factors such as availability and molding technology in each region.

　しかし、９００℃を超える温度では、フェライト系ステンレス鋼では強度が不足し、オーステナイト系ステンレス鋼では熱疲労やスケール剥離が問題になり、いずれも使用できない問題があった。 However, at temperatures exceeding 900 ° C., ferritic stainless steel has insufficient strength, and austenitic stainless steel has problems such as thermal fatigue and scale peeling, which cannot be used.

　また、エキゾーストマニホールドやターボチャージャー部品には耐熱鋳鋼や、特許文献１に示すようなステンレス鋳鋼も用いられているが、自動車部品の軽量化ニーズは高く、鋳物部品を板材のプレス成型部品に置き換える取り組みが行われている。 In addition, heat-resistant cast steel and stainless steel cast as shown in Patent Document 1 are also used for exhaust manifolds and turbocharger parts, but there is a great need for weight reduction of automobile parts, and efforts to replace cast parts with plate-formed press-formed parts Has been done.

　最近では自動車の燃費向上ニーズが極めて高くなり、燃費向上手段の一つとして、エンジンの小型高出力化が進められており、排ガス温度が上昇する傾向にある。特許文献２では、フェライト系ステンレス鋼であるＳＵＳ４４４にさらにＭｏやＮｂ、Ｃｕ、Ｗ等を添加して高温強度を上げることで９５０℃における耐熱性を確保する材料が開示されている。しかしながら、室温での加工性や製造性に課題があり、エキゾーストマニホールドの様な複雑形状に加工する際には問題があった。また、薄板を製造する際にも板破断などの問題があった。 Recently, the need for improving the fuel efficiency of automobiles has become extremely high, and as one of the means for improving the fuel efficiency, the engine is becoming smaller and higher in output, and the exhaust gas temperature tends to rise. Patent Document 2 discloses a material that ensures heat resistance at 950 ° C. by adding Mo, Nb, Cu, W, or the like to SUS444, which is a ferritic stainless steel, to increase the high-temperature strength. However, there are problems in processability and manufacturability at room temperature, and there has been a problem when processing into a complicated shape such as an exhaust manifold. In addition, when manufacturing a thin plate, there is a problem such as plate breakage.

　一方、オーステナイト系ステンレス鋼を適用する場合、強度面では問題ないが、熱疲労の問題が大きい。特許文献３では、９００℃以上の繰り返し加熱冷却環境において、Ｍｏ含有量を可能な限り低減し、微量のＶを添加し、熱延板の結晶粒径と表面粗度を制御することで、耐熱性に優れた熱延鋼板とすることが開示されている。しかし自動車排気系部品に必要な板厚を熱延で造ることは難しく、必要な板厚精度が得られない問題があった。 On the other hand, when austenitic stainless steel is applied, there is no problem in strength, but the problem of thermal fatigue is large. In Patent Document 3, in a repetitive heating and cooling environment of 900 ° C. or more, the Mo content is reduced as much as possible, a trace amount of V is added, and the crystal grain size and surface roughness of the hot-rolled sheet are controlled, thereby improving the heat resistance. It is disclosed that a hot-rolled steel sheet having excellent properties is obtained. However, it is difficult to produce the plate thickness required for automobile exhaust system parts by hot rolling, and the required plate thickness accuracy cannot be obtained.

　また、耐熱性を排気系部品の構造から改善すべく、エキゾーストマニホールドやターボチャージャー部品を２重管構造にすることも行われている。具体的には、内側にオーステナイト系ステンレス鋼、外側にフェライト系ステンレス鋼を使うことで、内側のオーステナイト系ステンレス鋼部材の拘束を緩和して熱歪を低減する。これにより、外側のフェライト系ステンレス鋼を直接高温の排ガスに触れさせないことで、温度を下げることが可能になる。このような二重構造部品は高価であるが、排ガス温度が１０００℃以下のエキゾーストマニホールドにしばしば使われている。また、９００℃以下の排ガス温度であっても、エキゾーストマニホールド外面の酸化を抑制し、意匠性を高めるために用いられる場合もある。しかしながら、これらの取り組みも、１０００℃を超える温度に排ガス温度が上昇すると、効果が失われ、十分な耐熱性を得ることができない。そのため、１０００℃以上の排ガス環境で耐熱性を有する排気系部品が求められていた。 Also, in order to improve heat resistance from the structure of exhaust system parts, exhaust manifolds and turbocharger parts are also made into double pipe structures. Specifically, by using austenitic stainless steel on the inner side and ferritic stainless steel on the outer side, the restraint of the inner austenitic stainless steel member is relaxed and thermal strain is reduced. This makes it possible to lower the temperature by not letting the outer ferritic stainless steel directly touch the high-temperature exhaust gas. Such a double structure part is expensive, but is often used for an exhaust manifold having an exhaust gas temperature of 1000 ° C. or less. Even when the exhaust gas temperature is 900 ° C. or lower, it may be used to suppress the oxidation of the outer surface of the exhaust manifold and improve the design. However, in these approaches, if the exhaust gas temperature rises to a temperature exceeding 1000 ° C., the effect is lost and sufficient heat resistance cannot be obtained. Therefore, an exhaust system part having heat resistance in an exhaust gas environment of 1000 ° C. or higher has been demanded.

特開２００６－１１８０４８号公報Japanese Patent Laid-Open No. 2006-118048 特開平９－８７８０９号公報JP-A-9-87809 特開２０１２－２０７２５２号公報JP 2012-207252 A

　本発明は、エキゾーストマニホールドの二重管内管やターボチャージャー部品（二重管構造の場合を含む）等の自動車排気系部品として好適に使用できる、表面疵がなく、高い高温強度、耐食性を有し、高温での脆化が生じず、さらに、高い耐酸化性を発揮するステンレス鋼板を提供することを目的とする。また、本発明は、さらに、上記ステンレス鋼板を用いて、母材と溶接部の耐酸化性がともに優れる自動車排気系部品を提供することを目的とする。 The present invention can be suitably used as an automobile exhaust system part such as a double pipe inner pipe of an exhaust manifold or a turbocharger part (including a case of a double pipe structure), has no surface flaws, and has high high temperature strength and corrosion resistance. Another object of the present invention is to provide a stainless steel plate that does not cause embrittlement at high temperatures and exhibits high oxidation resistance. It is another object of the present invention to provide an automobile exhaust system component that uses the stainless steel plate and has excellent base material and welded portion oxidation resistance.

　本発明者らは、上記課題を解決するため、まず成分組成の見直しを行った。耐酸化性の良いオーステナイト系ステンレス鋼としては、前述のＳＵＳ３０２Ｂ、ＸＭ１５Ｊ１、ＤＩＮ１．４８２８のように、Ｓｉを高めたステンレス鋼やＲＥＭを添加したステンレス鋼が一般に使用されている。 In order to solve the above problems, the present inventors first reviewed the component composition. As the austenitic stainless steel having good oxidation resistance, stainless steel with increased Si and stainless steel with REM added, such as SUS302B, XM15J1, and DIN1.4828, are generally used.

　本発明者らは、上記のオーステナイト系ステンレス鋼が１０５０℃の環境に耐え得るか確認するために、自動車排気ガス環境を模擬した雰囲気ガス中での断続酸化試験を行ったが、いずれの鋼種も酸化による重量減少が顕著に現れ、１０５０℃における耐酸化性は無いと判断された。 In order to confirm whether the above-mentioned austenitic stainless steel can withstand an environment of 1050 ° C., the inventors conducted an intermittent oxidation test in an atmosphere gas simulating an automobile exhaust gas environment. The weight loss due to oxidation was noticeable, and it was judged that there was no oxidation resistance at 1050 ° C.

　そこで、本発明者らは、１０５０℃の環境に耐え得る材料組成を明らかにすべく、種々の検討を重ねた。 Therefore, the present inventors have made various studies in order to clarify the material composition that can withstand an environment of 1050 ° C.

　その結果、Ｃｒ、Ｍｏ、Ｓｉ量を適正量に制御しつつ、オーステナイト母相を安定させるために、Ｎｉ、Ｃ、Ｎを所定の量添加する際に、オーステナイト相の粒成長を抑制する炭窒化物の量の確保、及び析出形態を制御することで、断続酸化環境に於いても保護性の高いスケールを形成させる方法により、１０５０℃に耐え得る耐酸化性を有するステンレス鋼板が得られることを知見した。 As a result, in order to stabilize the austenite matrix phase while controlling the Cr, Mo, and Si amounts to appropriate amounts, carbonitriding that suppresses the grain growth of the austenite phase when adding a predetermined amount of Ni, C, and N. A stainless steel sheet having oxidation resistance capable of withstanding 1050 ° C. can be obtained by a method for forming a highly protective scale even in an intermittent oxidation environment by ensuring the amount of the product and controlling the precipitation form. I found out.

　具体的には、Ｃｒ、Ｍｏ量を所定の範囲に制御することで、スケール中の酸素イオンの拡散、金属原子の拡散が起こり難いＣｒ２Ｏ３を主体とする酸化物スケールを形成させる。 Specifically, by controlling the amounts of Cr and Mo within a predetermined range, an oxide scale mainly composed of Cr 2 O 3 that hardly causes diffusion of oxygen ions and metal atoms in the scale is formed.

　このスケールが加熱冷却時の母材の熱膨張収縮によって剥離しないように内部酸化層を形成させる。内部酸化層は、オーステナイト粒界に形成されるＳｉ酸化物を指すものである。表面に保護性の高いＣｒ２Ｏ３を主体とするスケールが形成されないとこの粒界酸化が浅くなり、スケール剥離を防止することが困難である。また、オーステナイト粒が成長すると、粒界の移動により、粒界酸化が抑制されるため、耐酸化性が損なわれることから、粒成長を抑制するために析出物を分散させる。 An internal oxide layer is formed so that the scale does not peel due to thermal expansion and contraction of the base material during heating and cooling. An internal oxide layer refers to Si oxide formed in an austenite grain boundary. If a scale mainly composed of Cr 2 O 3 having a high protective property is not formed on the surface, this grain boundary oxidation becomes shallow, and it is difficult to prevent scale peeling. In addition, when austenite grains grow, grain boundary oxidation is suppressed by the movement of grain boundaries, and thus oxidation resistance is impaired. Therefore, precipitates are dispersed in order to suppress grain growth.

　図１は、Ｃｒ、ＭｏとＳｉ、Ｃ、Ｎが断続酸化に於ける耐酸化性に及ぼす影響を調べた結果を示したものである。試験方法は以下のとおりである。 FIG. 1 shows the results of examining the influence of Cr, Mo and Si, C, N on the oxidation resistance in intermittent oxidation. The test method is as follows.

　各種組成のオーステナイト系ステンレス鋼をラボ溶解し、１２５０℃に１時間加熱し、熱間圧延して板厚３ｍｍにした後、熱延板焼鈍を１１００℃で２０秒行い、すぐに水冷し、ショットブラストした後、硫酸と硝弗酸でスケールを除去した。 Austenitic stainless steels of various compositions are melted in the laboratory, heated to 1250 ° C for 1 hour, hot-rolled to a plate thickness of 3 mm, hot-rolled sheet annealed at 1100 ° C for 20 seconds, immediately water-cooled, shot After blasting, the scale was removed with sulfuric acid and nitric hydrofluoric acid.

　引き続き冷間圧延して、板厚１．２ｍｍにした。さらに１１００℃で２０秒の焼鈍を行った後、水冷し、ソルトでスケール改質を行った後、酸洗した。 Subsequently, it was cold-rolled to a thickness of 1.2 mm. Further, after annealing at 1100 ° C. for 20 seconds, it was cooled with water, scale-modified with salt, and then pickled.

　表面をＳｉＣ紙で＃６００研磨した後、自動車排ガス雰囲気下で、１０５０℃と２００℃の間で加熱冷却を繰り返す断続酸化試験を行った。繰り返しサイクル数２０００サイクルにおいて、板厚減少が０．４ｍｍ超であるものを不合格、０．４ｍｍ以下を合格とした。この試験結果をまとめると図１に示すように、表面の酸化抑制にはＣｒとＭｏが、スケールの剥離抑制にはＳｉ、Ｃ、Ｎが、図中に示す係数で効果を示すことが明らかになった。なお、図１において、白抜きのプロットが合格を表し、黒抜きのプロットが不合格を表す。 After the surface was # 600 polished with SiC paper, an intermittent oxidation test was repeated in which heating and cooling were repeated between 1050 ° C. and 200 ° C. in an automobile exhaust gas atmosphere. When the number of repeated cycles was 2,000, the sheet thickness reduction exceeding 0.4 mm was rejected, and 0.4 mm or less was determined acceptable. When this test result is summarized, as shown in FIG. 1, it is clear that Cr and Mo are effective for suppressing surface oxidation, and Si, C, and N are effective for suppressing scale peeling with the coefficients shown in the figure. became. In FIG. 1, a white plot represents a pass and a black plot represents a failure.

　これらの成分的な対策により、薄板では１０５０℃に耐え得る耐酸化性が得られる。しかしながら、排気系部品のように溶接構造になると、それだけでは不十分である。図２に重ね隅肉溶接したサンプルの断面形状と、酸化試験後の板厚減少を示した。このサンプルを断続酸化試験に供したところ、溶接熱影響部において酸化が顕著になり、板厚減少が大きくなった結果、サンプルが分離してしまう場合も見られた（図２下写真の左上部）。そのため、溶接熱影響部が排気系部品の寿命を支配することが分かった。溶接熱影響部が選択的に酸化する実態を調査したところ、この部分には表面にＣｒ２Ｏ３を主体とするスケールが均一に形成されておらず、粒界酸化もあまり起こっていないことが分かった。 With these component measures, oxidation resistance that can withstand 1050 ° C. can be obtained with a thin plate. However, when it comes to a welded structure like an exhaust system component, it is not enough. FIG. 2 shows the cross-sectional shape of the sample welded by lap fillet and the reduction of the plate thickness after the oxidation test. When this sample was subjected to an intermittent oxidation test, the oxidation became prominent in the heat affected zone, and as a result of the increase in plate thickness reduction, the sample was sometimes separated (upper left of the lower photograph in FIG. 2). ). Therefore, it was found that the weld heat affected zone dominates the life of the exhaust system parts. When the actual state of selective oxidation of the weld heat affected zone was investigated, the scale mainly composed of Cr 2 O 3 was not uniformly formed on the surface, and it was found that the grain boundary oxidation did not occur much. I understood.

　そこで、溶接熱影響部と母材の組成を調べたところ、差異が認められなかったことから、母材と溶接熱影響部の酸化挙動の違いは、熱膨張、収縮による歪が影響していると考えられた。すなわち、溶接金属と母材の板厚により、加熱、冷却時に溶接金属と母材の間に温度差が生じ、この温度差による熱膨張収縮応力により、境目にある溶接熱影響部でスケールが剥離しやすくなるものと思われた。 Therefore, when the composition of the weld heat-affected zone and the base metal was examined, no difference was observed. Therefore, the difference in the oxidation behavior between the base metal and the weld heat-affected zone was affected by strain due to thermal expansion and contraction. It was considered. In other words, due to the thickness of the weld metal and the base metal, a temperature difference occurs between the weld metal and the base metal during heating and cooling, and the scale peels off at the weld heat affected zone at the boundary due to the thermal expansion and contraction stress due to this temperature difference. It seemed to be easy to do.

　このサンプルの溶接部における板厚変化の勾配（止端角度）を測定したところ、酸化が小さかったサンプルは止端角度が約１０度と小さいのに対して、耐酸化性が劣ったサンプルでは止端角度が２０度と大きいことが分かった。なお、本発明において、「板厚変化の勾配（止端角度）」とは、溶接部側面の断面観察において、母材の面と、溶接ビード（溶接金属）の表面接線とが交わる角度をＸ度（degree）とするとき、（１８０－Ｘ）の角度で表したものを指す。止端角度は通常０から９０度の範囲で表示される。一般的に溶接ビードは複数の止端を有するので、複数の止端の角度が存在するが、本発明における止端角度は、その断面視野の中で最も大きい角度のものと定義する。止端角度が大きいということは、溶接ビード表面の膨らみ（盛り上がり）によって板厚が変化する勾配が急峻であることを意味する。 When the gradient of the plate thickness change (toe angle) at the welded part of this sample was measured, the sample with less oxidation had a toe angle of about 10 degrees, whereas the sample with poor oxidation resistance stopped. It was found that the end angle was as large as 20 degrees. In the present invention, the “gradient of plate thickness change (toe angle)” means the angle at which the surface of the base material and the surface tangent of the weld bead (welded metal) intersect in the cross-sectional observation of the side surface of the weld. When expressed in degrees, it refers to an angle of (180-X). The toe angle is usually displayed in the range of 0 to 90 degrees. In general, since a weld bead has a plurality of toes, there are a plurality of toe angles, but the toe angle in the present invention is defined as the largest angle in the cross-sectional view. A large toe angle means that the gradient at which the plate thickness changes due to the swelling (swelling) of the surface of the weld bead is steep.

　そこで、以下の試験により、溶接金属と母材の板厚差が耐酸化性に及ぼす影響を調べたところ、特定の板厚差以上になると溶接熱影響部でスケール剥離を生じ耐酸化性が低下することが分かった。 Therefore, the effect of the difference in thickness between the weld metal and the base metal on the oxidation resistance was investigated by the following test. When the difference between the thicknesses exceeds a certain thickness, scale peeling occurred at the weld heat affected zone and the oxidation resistance decreased. I found out that

　具体的には、２４Ｃｒ-１２Ｎｉ-０．１Ｃ-０．０２Ｎ－２．０Ｓｉ－１Ｍｎ－０．５Ｍｏ－０．０５Ａｌ－０．０５Ｖ鋼をラボ溶解し、１２５０℃に１時間加熱し、熱間圧延して板厚３ｍｍにした後、熱延板焼鈍を１１００℃で２０秒行い、すぐに水冷し、ショットブラストした後、硫酸と硝弗酸でスケールを除去した。引き続き冷間圧延して板厚１．２ｍｍにした。 Specifically, 24Cr-12Ni-0.1C-0.02N-2.0Si-1Mn-0.5Mo-0.05Al-0.05V steel was melted in the laboratory, heated to 1250 ° C for 1 hour, After rolling to a sheet thickness of 3 mm, hot-rolled sheet annealing was performed at 1100 ° C. for 20 seconds, immediately cooled with water, shot blasted, and the scale was removed with sulfuric acid and nitrohydrofluoric acid. Subsequently, it was cold-rolled to a thickness of 1.2 mm.

　さらに１１００℃で２０秒の焼鈍を行った後、水冷し、ソルトでスケール改質を行った後、硝酸と弗酸の混酸中で浸漬酸洗した。この板をＴｉｇ溶接で重ね隅肉溶接した。溶接は裏ビードが出る条件で行い、溶接ワイヤにはＳＵＳ３１０Ｓを用いた。溶接入熱と溶接速度を変えることで、溶接ビード形状を変化させ、板厚変化の勾配を変えた。 Further, after annealing at 1100 ° C. for 20 seconds, it was cooled with water, scale-modified with salt, and then pickled in a mixed acid of nitric acid and hydrofluoric acid. This plate was overlapped and welded by Tig welding. Welding was performed under the condition that the back bead appeared, and SUS310S was used as the welding wire. By changing the welding heat input and welding speed, the weld bead shape was changed and the gradient of the plate thickness change was changed.

　溶接線を試験片の中心に置いて、酸化試験片を作成した後、自動車排ガス環境下で、２００℃と１０５０℃の間を加熱冷却する断続酸化試験を２０００サイクル行った。溶接熱影響部の板厚減少を測定し、板厚減少が０．４ｍｍ以下を合格とした。その結果、溶接金属と母材との板厚差があってもその板厚変化の勾配を１５度以下にすることで、溶接熱影響部のスケール剥離を軽減することが可能になることが分かった。 After the weld line was placed at the center of the test piece to create an oxidation test piece, an intermittent oxidation test was performed in 2000 cycles of heating and cooling between 200 ° C. and 1050 ° C. in an automobile exhaust gas environment. The thickness reduction of the weld heat affected zone was measured, and the thickness reduction of 0.4 mm or less was accepted. As a result, even if there is a difference in plate thickness between the weld metal and the base metal, it is understood that the scale peeling of the weld heat affected zone can be reduced by setting the gradient of the plate thickness change to 15 degrees or less. It was.

　重ね隅肉溶接以外に、突合せ溶接についてもその効果を調べたが、いずれの場合でも板厚変化の勾配を１５度以下にすることで溶接熱影響部の酸化を大きく軽減することが可能であることが分かった。さらに、板厚変化の勾配を低減することにより溶接熱影響部の酸化はより軽減し、板厚変化の勾配が無くなると母材と同じ耐酸化性を有するようになるが、１５度超での耐酸化性改善効果は小さいことがわかった。なお、本発明では溶接方法の種類を限定しないが、特にアーク溶接の場合に良好な結果が得られる。他の溶接方法でも本発明が開示する技術的メカニズムに基づき遜色のない効果が得られる。 In addition to lap fillet welding, the effect of butt welding was also investigated. In any case, it is possible to greatly reduce the oxidation of the heat affected zone by setting the gradient of the plate thickness change to 15 degrees or less. I understood that. Furthermore, the oxidation of the weld heat affected zone is further reduced by reducing the gradient of the plate thickness change, and when the gradient of the plate thickness change is eliminated, it has the same oxidation resistance as the base material, but at over 15 degrees. It was found that the effect of improving oxidation resistance was small. In the present invention, the type of welding method is not limited, but good results can be obtained particularly in the case of arc welding. Even in other welding methods, the same effect can be obtained based on the technical mechanism disclosed in the present invention.

　上述のとおり、母材の成分設計の最適化と溶接金属の形状制御により、排気系部品としての耐久性を１０５０℃で耐えられるものにすることを可能であることが分かった。 As described above, it has been found that the durability as an exhaust system component can be made durable at 1050 ° C. by optimizing the component design of the base metal and controlling the shape of the weld metal.

　本発明は上記の知見に基づきなされたものであって、その要旨は以下のとおりである。 The present invention has been made on the basis of the above findings, and the gist thereof is as follows.

　（１）質量％で、Ｃ：０．０５～０．１５％、Ｓｉ：１．０％～４．０％、Ｍｎ：０．５～３．５％、Ｐ：０．０１０～０．０４０％、Ｓ：０．０００１～０．０１０％、Ｃｒ：２０～３０％、Ｎｉ：８～２５％、Ｍｏ：０．０１～１．５％、Ａｌ：０．００１～０．１０％、及びＮ：０．１３～０．５０％を含有し、残部がＦｅ及び不可避的不純物であり、Ｃｒ、Ｍｏ、Ｓｉ、Ｃ、及びＮの含有量がＣｒ+２０Ｍｏ≧２４．０％、及びＳｉ＋２０Ｃ＋１５Ｎ≧５．８％を満たすことを特徴とする断続酸化特性に優れた排気系部品用ステンレス鋼板。 (1) By mass%, C: 0.05 to 0.15%, Si: 1.0% to 4.0%, Mn: 0.5 to 3.5%, P: 0.010 to 0.040 %, S: 0.0001 to 0.010%, Cr: 20 to 30%, Ni: 8 to 25%, Mo: 0.01 to 1.5%, Al: 0.001 to 0.10%, and N: contains 0.13 to 0.50%, the balance is Fe and inevitable impurities, and the contents of Cr, Mo, Si, C, and N are Cr + 20Mo ≧ 24.0%, and Si + 20C + 15N ≧ A stainless steel plate for exhaust system parts having excellent intermittent oxidation characteristics characterized by satisfying 5.8%.

　（２）さらに、質量％で、Ｃｕ：０．１～３．０％、Ｖ：０．０３～０．５％、Ｔｉ：０．００１～０．３％、Ｎｂ：０．００１～０．３％、Ｂ：０．０００１～０．００５０％、及びＣａ：０．００１～０．０１０％の１種又は２種以上を含有することを特徴とする前記（１）の断続酸化特性に優れた排気系部品用ステンレス鋼板。 (2) Further, by mass, Cu: 0.1 to 3.0%, V: 0.03 to 0.5%, Ti: 0.001 to 0.3%, Nb: 0.001 to 0.00. 3), B: 0.0001 to 0.0050%, and Ca: 0.001 to 0.010%, or one or more, excellent in intermittent oxidation characteristics of (1) above Stainless steel sheet for exhaust system parts.

　（３）さらに、質量％でＷ：０．０１～３．００％、Ｚｒ：０．０５～０．３０％、Ｓｎ：０．０１～０．１０％、Ｃｏ：０．０１～０．３０％、及びＭｇ：０．０００２％～０．０１０％の１種又は２種以上を含有することを特徴とする前記（１）又は（２）の断続酸化特性に優れた排気系部品用ステンレス鋼板。 (3) Further, in terms of mass%, W: 0.01 to 3.00%, Zr: 0.05 to 0.30%, Sn: 0.01 to 0.10%, Co: 0.01 to 0.30 %, And Mg: 0.0002% to 0.010% of one or more kinds, (1) or (2) stainless steel plate for exhaust system parts having excellent intermittent oxidation characteristics .

　（４）前記（１）～（３）のいずれかのステンレス鋼板を母材として用いた溶接構造を有し、溶接部における板厚変化の勾配が１５度以下であることを特徴とする排気系部品。 (4) An exhaust system having a welded structure using the stainless steel plate of any one of (1) to (3) as a base material, wherein the gradient of the plate thickness change at the welded portion is 15 degrees or less. parts.

　本発明によれば、排気系部品用ステンレス鋼板及び排気系部品の耐酸化性を高めることが可能であり、また、鋼板に表面疵が生じることが少ないために、薄板製造時の表面研削工程（ＣＧ）を省略、あるいは簡略化することが可能である。耐酸化性を高めることにより、排気系部品の板厚を薄くすることが可能になり、部品の軽量化により、自動車の燃費向上の効果も得られる。 According to the present invention, it is possible to improve the oxidation resistance of the stainless steel plate for exhaust system parts and the exhaust system parts, and since surface flaws are less likely to occur in the steel sheet, the surface grinding process ( CG) can be omitted or simplified. By increasing the oxidation resistance, it is possible to reduce the thickness of the exhaust system parts, and the weight reduction of the parts can also improve the fuel efficiency of the automobile.

図１は、薄板の１０５０℃の耐断続酸化特性に及ぼす成分の影響を示すグラフである。FIG. 1 is a graph showing the influence of components on the resistance to intermittent oxidation at 1050 ° C. of a thin plate. 図２は、重ね隅肉溶接された溶接金属の断面における板厚変化形状を示す。上段は溶接部における板厚変化の勾配が１１度、下段は同勾配が２５度の場合を示す。FIG. 2 shows the thickness change shape in the cross section of the weld metal welded by lap fillet. The upper row shows the case where the gradient of the plate thickness change at the welded portion is 11 degrees, and the lower row shows the case where the gradient is 25 degrees. 図３は、板厚変化の勾配が１０５０℃の耐酸化性（板厚減少）に及ぼす影響を示すグラフである。FIG. 3 is a graph showing the influence of the gradient of the plate thickness change on the oxidation resistance (plate thickness reduction) at 1050 ° C.

　以下、本発明の実施の形態について説明する。まず、本実施形態のステンレス鋼板の鋼組成を限定した理由について説明する。なお、組成についての％の表記は、特に断りのない場合は、質量％を意味する。 Hereinafter, embodiments of the present invention will be described. First, the reason which limited the steel composition of the stainless steel plate of this embodiment is demonstrated. In addition, the description of% about a composition means the mass% unless there is particular notice.

　Ｃ：０．０５～０．１５％
　Ｃは、オーステナイト組織の安定と高温強度を高めるために有効である。また、Ｃｒと炭化物を形成しオーステナイト粒の成長を抑制して粒界酸化を適度に成長させ、耐スケール剥離特性を向上させる。この効果は０．０５％以上のＣで発現することから、下限を０．０５％とする。粒成長を安定的に抑制するためには０．１０％以上にすることが望ましい。０．１５％超では、Ｃｒ炭化物の量が増えて、粒界のクロム欠乏層が増加し、本鋼の様な高Ｃｒオーステナイト系ステンレス鋼であっても、自動車のエキゾーストマニホールド部材やターボチャージャー部品としても必要とされる耐食性が維持できなくなるため、上限を０．１５％以下とする。耐食性の観点からは０．１２％以下にすることが望ましい。 C: 0.05 to 0.15%
C is effective for increasing the stability of the austenite structure and the high temperature strength. In addition, it forms carbides with Cr and suppresses the growth of austenite grains, moderately grows grain boundary oxidation, and improves the scale peeling resistance. Since this effect appears at 0.05% or more of C, the lower limit is made 0.05%. In order to suppress grain growth stably, it is desirable to make it 0.10% or more. If it exceeds 0.15%, the amount of Cr carbide increases, and the chromium-deficient layer at the grain boundary increases. Even in high Cr austenitic stainless steel such as this steel, exhaust manifold parts and turbocharger parts for automobiles However, the required corrosion resistance cannot be maintained, so the upper limit is made 0.15% or less. From the viewpoint of corrosion resistance, it is desirable to make it 0.12% or less.

　Ｓｉ：１．０％～４．０％
　Ｓｉは耐酸化性に効果があり、とくに断続酸化におけるスケール剥離の防止に効果がある。１０００℃を超える環境で粒界酸化を形成し、表面のスケール剥離を抑制するためには１．０％以上のＳｉが必要である。耐酸化性を高めるためには２．０％以上にすることが望ましい。またＳｉはフェライト安定化元素であり、凝固組織におけるδフェライト量を増加させ、熱間圧延において熱間加工性の低下が問題になるため、４．０％以下にする。そのほか、Ｓｉはシグマ層の生成も促進し高温長時間使用時の脆化も危惧されるため３．５％以下にすることが望ましい。 Si: 1.0% to 4.0%
Si is effective in oxidation resistance, and is particularly effective in preventing scale peeling during intermittent oxidation. In order to form grain boundary oxidation in an environment exceeding 1000 ° C. and suppress scale peeling on the surface, 1.0% or more of Si is required. In order to improve oxidation resistance, it is desirable to make it 2.0% or more. Si is a ferrite stabilizing element and increases the amount of δ-ferrite in the solidified structure, so that the hot workability is deteriorated in hot rolling. In addition, since Si promotes the formation of a sigma layer and there is a risk of embrittlement when used at a high temperature for a long time, it is preferably 3.5% or less.

　Ｍｎ：０．５～３．５％
　Ｍｎは、脱酸剤として添加される元素であるとともに、オーステナイト単相域を拡大し組織の安定化に寄与する。その効果は０．５％以上で明確に現れるため０．５％以上とする。また硫化物を形成し、鋼中の固溶Ｓ量を低減することで熱間加工性を向上させる効果もあることから、１．０％以上とすることが望ましい。一方、過度の添加は耐食性を低下させることから３．５％以下とする。また耐酸化性の点ではＣｒ2Ｏ3主体の酸化物が望ましく、Ｍｎの酸化物は好ましくないため、２．０％以下にすることが望ましい。 Mn: 0.5 to 3.5%
Mn is an element added as a deoxidizer, and contributes to the stabilization of the structure by expanding the austenite single phase region. The effect appears clearly at 0.5% or more, so 0.5% or more. Moreover, since it has the effect of improving hot workability by forming sulfides and reducing the amount of solute S in the steel, it is desirable to set it to 1.0% or more. On the other hand, excessive addition reduces the corrosion resistance, so it is made 3.5% or less. Further, from the viewpoint of oxidation resistance, an oxide mainly composed of Cr 2 O 3 is desirable, and an oxide of Mn is not preferable.

　Ｐ：０．０１０～０．０４０％
　Ｐは、原料である溶銑やフェロクロム等の主原料中に不純物として含まれる元素である。熱間加工性に対しては有害な元素であるため、０．０４０％以下とする。なお、好ましくは０．０３０％以下である。過度な低減は高純度原料の使用を必須にするなど、コストの増加に繋がるため、０．０１０％以上とする。経済的に好ましくは、０．０２０％以上にすることが望ましい。 P: 0.010 to 0.040%
P is an element contained as an impurity in the main raw material such as hot metal or ferrochrome. Since it is an element harmful to hot workability, it is set to 0.040% or less. In addition, Preferably it is 0.030% or less. Excessive reduction leads to an increase in cost, such as making it necessary to use a high-purity raw material, so 0.010% or more. Economically preferably 0.020% or more is desirable.

　Ｓ：０．０００１～０．０１０％
　Ｓは、硫化物系介在物を形成し、鋼材の一般的な耐食性（全面腐食や孔食）を劣化させるため、その含有量の上限は少ないほうが好ましく、０．０１０％とする。また、Ｓの含有量は少ないほど耐食性は良好となるが、低Ｓ化には脱硫負荷が増大し、製造コストが増大するので、その下限を０．０００１％とするのが好ましい。なお、好ましくは０．００１～０．００８％である。 S: 0.0001 to 0.010%
S forms sulfide inclusions and degrades the general corrosion resistance (entire corrosion and pitting corrosion) of the steel material. Therefore, the upper limit of the content is preferably as small as 0.010%. Further, the smaller the S content, the better the corrosion resistance. However, since the desulfurization load increases and the production cost increases for lowering the S content, the lower limit is preferably made 0.0001%. Preferably, the content is 0.001 to 0.008%.

　Ｃｒ：２０～３０％
　Ｃｒは、本発明において、耐酸化性や耐食性確保のために必須な元素である。２０％未満では、これらの効果は発現せず、一方で、３０％超ではオーステナイト単相域が縮小し、製造時の熱間加工性を損ねるため、２０～３０％とする。なお、耐酸化性の観点からは２４％以上にすることが望ましい。また、Ｃｒ量を高くするとシグマ相の形成により脆化するため、２７％以下にすることが望ましい。 Cr: 20-30%
In the present invention, Cr is an essential element for ensuring oxidation resistance and corrosion resistance. If it is less than 20%, these effects are not exhibited. On the other hand, if it exceeds 30%, the austenite single phase region is reduced and the hot workability at the time of production is impaired, so 20-30%. From the viewpoint of oxidation resistance, it is desirable to make it 24% or more. Further, if the amount of Cr is increased, embrittlement occurs due to the formation of a sigma phase.

　Ｎｉ：８～２５％
　Ｎｉは、オーステナイト相を安定化させる元素であり、Ｍｎと異なって耐酸化性に有効な元素である。これらの効果は８％以上で得られるため、下限を８％以上とする。シグマ相の生成を抑制する効果もあるので１０％以上にすることが望ましい。一方、過度な添加は凝固割れ感受性を高めると共に、熱間加工性も低下させるために、２５％以下とする。更に、断続酸化におけるスケール剥離を抑制するためには、１５％以下にすることが望ましい。 Ni: 8-25%
Ni is an element that stabilizes the austenite phase, and unlike Mn, is an element that is effective in oxidation resistance. Since these effects are obtained at 8% or more, the lower limit is made 8% or more. Since it also has an effect of suppressing the formation of sigma phase, it is desirable to make it 10% or more. On the other hand, excessive addition increases the susceptibility to solidification cracking and lowers the hot workability, so the content is made 25% or less. Furthermore, in order to suppress scale peeling in intermittent oxidation, it is desirable to make it 15% or less.

　Ｍｏ：０．０１～１．５％
　ＭｏもＳｉやＣｒと共に、表面の保護性スケール形成に有効であり、その効果は０．０１％で得られることから、その下限を０．０１％以上とする。また耐食性の向上にも有効な元素であることから、０．３％以上添加することが望ましい。一方、フェライト安定化元素でもあり、Ｍｏ添加量が増えるとＮｉの添加も増やす必要が生じるため、過度な添加は好ましくない。また、シグマ相の形成を促進して脆化を生じることがあるため、１．５％以下とする。耐食性や耐酸化性の向上効果は０．８％以上でほぼ飽和するために、０．８％以下にすることが望ましい。 Mo: 0.01 to 1.5%
Mo, together with Si and Cr, is effective for forming a protective scale on the surface, and the effect is obtained at 0.01%, so the lower limit is made 0.01% or more. Further, since it is an element effective for improving corrosion resistance, it is desirable to add 0.3% or more. On the other hand, it is also a ferrite stabilizing element, and as the amount of Mo added increases, it is necessary to increase the amount of Ni added. Further, since the formation of the sigma phase is promoted to cause embrittlement, the content is made 1.5% or less. Since the effect of improving corrosion resistance and oxidation resistance is almost saturated at 0.8% or more, it is desirable to make it 0.8% or less.

　Ａｌ：０．００１～０．１０％
　Ａｌは、脱酸元素として添加される他、耐酸化性を向上させる元素である。その効果は０．００１％以上で得られるため、下限を０．００１％以上にする。脱酸効率を高めるためには０．００３％以上にすることが望ましい。一方、過度な添加は窒化物を形成して固溶Ｎ量を低下させ、高温強度が低下するために、上限を０．１０％以下とする。溶接性も考慮すると０．０５％以下とすることが望ましい。 Al: 0.001 to 0.10%
In addition to being added as a deoxidizing element, Al is an element that improves oxidation resistance. Since the effect is obtained at 0.001% or more, the lower limit is made 0.001% or more. In order to improve deoxidation efficiency, it is desirable to make it 0.003% or more. On the other hand, excessive addition forms a nitride to reduce the amount of dissolved N and lowers the high temperature strength, so the upper limit is made 0.10% or less. Considering the weldability, it is desirable to make it 0.05% or less.

　Ｎ：０．１３～０．５０％
　Ｎは、本発明において非常に重要な元素のひとつである。Ｃと同様に高温強度を上げるほか、オーステナイト安定度を上げることで、Ｎｉの低減も可能になる。またＣよりも鋭敏化による耐食性低下影響が小さいため、Ｃよりも多量の添加が可能である。高温環境に耐える高温強度を得るために、０．１３％以上とする。Ｎｉの低減効果も考慮すると、０．２５％以上にすることが望ましい。一方多量に添加すると、製鋼工程で凝固時に気泡系欠陥が生じるために、上限を０．５０％以下とする。その他にも、常温における強度が高すぎて冷間圧延時の負荷が高くなり、生産性を損なうため、０．３０％以下にすることが望ましい。 N: 0.13-0.50%
N is one of the very important elements in the present invention. In addition to increasing the high temperature strength as in C, increasing Ni austenite stability also makes it possible to reduce Ni. Moreover, since the influence of the corrosion resistance reduction due to sensitization is smaller than that of C, a larger amount than C can be added. In order to obtain a high temperature strength that can withstand a high temperature environment, the content is made 0.13% or more. Considering the reduction effect of Ni, it is desirable to make it 0.25% or more. On the other hand, if added in a large amount, a bubble defect occurs during solidification in the steel making process, so the upper limit is made 0.50% or less. In addition, since the strength at normal temperature is too high, the load during cold rolling becomes high and the productivity is impaired, so it is desirable to make it 0.30% or less.

　［Ｃｒ+２０Ｍｏ≧２４．０％、かつＳｉ＋２０Ｃ＋１５Ｎ≧５．８％］
　１０５０℃で耐酸化性を発揮するためには、表面に保護性の高い酸化スケールを形成するとともに、断続酸化時のスケール剥離を抑制するために、スケール下のオーステナイト相に於いて、Ｓｉ酸化物による粒界酸化を形成させることが必要である。そのためには、各元素を先の条件範囲にするだけでは不十分であり、保護性の高いスケールを形成させるために、Ｃｒ及びＭｏの含有量をＣｒ＋２０Ｍｏを２４％以上とし、オーステナイトの粒成長を抑制し、かつ粒界酸化を形成させるためにはＳｉ、Ｃ、及びＮの含有量を、Ｓｉ＋２０Ｃ＋１５Ｎを５．８％以上とすることが必要である。Ｃｒ＋２０Ｍｏは２７．０％以上がより好ましく、３０．０％以上がさらに好ましい。Ｓｉ＋２０Ｃ＋１５Ｎは７．０％以上がより好ましく、８．５％以上がさらに好ましい。 [Cr + 20Mo ≧ 24.0% and Si + 20C + 15N ≧ 5.8%]
In order to exhibit oxidation resistance at 1050 ° C., a highly protective oxide scale is formed on the surface, and in order to suppress scale peeling during intermittent oxidation, in the austenite phase under the scale, Si oxide It is necessary to form grain boundary oxidation due to. For that purpose, it is not sufficient to make each element within the above condition range. In order to form a highly protective scale, the content of Cr and Mo should be 24% or more of Cr + 20Mo, and the grain growth of austenite should be increased. In order to suppress and form grain boundary oxidation, it is necessary that the content of Si, C, and N is Si + 20C + 15N of 5.8% or more. Cr + 20Mo is more preferably 27.0% or more, and further preferably 30.0% or more. Si + 20C + 15N is more preferably 7.0% or more, and further preferably 8.5% or more.

［母材と溶接金属との板厚変化の勾配を１５度以下］
　自動車のエキゾーストマニホールドやターボチャージャーなどの排気系部品の多くが溶接構造を有している。母材と溶接金属の板厚差が大きいと、加熱冷却時の温度差により熱歪を生じ、高温時に表面に生成したスケールが剥離しやすくなり、繰り返し加熱時に表面が保護されず酸化による板厚減少が進行する。母材と溶接金属との板厚変化の勾配が小さいほど熱歪が緩和するが、板厚変化の勾配が１５度以下になると、耐酸化性の改善効果が大きくなるため、１５度以下とした。耐酸化性をより高めるためには、板厚変化の勾配を１０度以下に低減することが望ましい。 [Gradient of thickness change between base metal and weld metal is 15 degrees or less]
Many exhaust system parts such as automobile exhaust manifolds and turbochargers have a welded structure. If the plate thickness difference between the base metal and the weld metal is large, thermal distortion will occur due to the temperature difference during heating and cooling, the scale generated on the surface will easily peel off at high temperatures, and the surface will not be protected during repeated heating, resulting in plate thickness due to oxidation. Decrease proceeds. The thermal strain is reduced as the slope of the thickness change between the base metal and the weld metal is smaller. However, if the slope of the thickness change is 15 degrees or less, the effect of improving oxidation resistance is increased. . In order to further improve the oxidation resistance, it is desirable to reduce the gradient of the plate thickness change to 10 degrees or less.

　また、本発明のステンレス鋼板には、上記元素に加えて、Ｃｕ：０．１～３．０％、Ｖ：０．０３～０．５％、Ｔｉ：０．００１～０．３％、Ｎｂ：０．００１～０．３％、Ｂ：０．０００１～０．００５０％、Ｃａ：０．００１～０．０１０％の１種又は２種以上を任意で添加してもよい。 In addition to the above elements, the stainless steel plate of the present invention includes Cu: 0.1 to 3.0%, V: 0.03 to 0.5%, Ti: 0.001 to 0.3%, Nb One or two or more of: 0.001 to 0.3%, B: 0.0001 to 0.0050%, and Ca: 0.001 to 0.010% may be optionally added.

　Ｃｕ：０．１～３．０％
　Ｃｕは、オーステナイト安定化元素としてＮｉを代替する、相対的に安価な元素である。さらに、隙間腐食や孔食の進展抑制に効果があり、そのためには０．１％以上添加することが望ましい。ただし、オーステナイト系ステンレス鋼の製造において、Ｃｕはスクラップ等の原料から混入することが多く、不可避的に不純物として０．２％程度含まれることが多い。ただし、３．０％を超えると熱間加工性を低下させるため３．０％以下とする。 Cu: 0.1 to 3.0%
Cu is a relatively inexpensive element that substitutes for Ni as an austenite stabilizing element. Furthermore, it is effective in suppressing the progress of crevice corrosion and pitting corrosion. To that end, it is desirable to add 0.1% or more. However, in the production of austenitic stainless steel, Cu is often mixed from raw materials such as scrap and is inevitably contained in an amount of about 0.2% as an impurity. However, if it exceeds 3.0%, the hot workability is lowered, so the content is made 3.0% or less.

　Ｖ：０．０３～０．５％
　Ｖは、ステンレス鋼の合金原料に不可避的不純物として混入し、精錬工程における除去が困難であるため、一般的に０．０１～０．１０％の範囲で含有される。また、微細な炭窒化物を形成し、粒成長抑制効果を有するため、必要に応じて、意図的な添加も行われる元素である。その効果は０．０３％以上の添加で安定して発現するため、下限を０．０３％とする。Ｖの変動により、結晶粒径が変化することは好ましくないので、結晶粒径の一定範囲に造りこむためには、０．０８％以上にすることが望ましい。一方、過剰に添加すると、析出物の粗大化を招くおそれがあり、その結果、焼入れ後の靭性が低下してしまうため、上限を０．５％とする。なお、製造コストや製造性を考慮すると、０．２％以下にとすることが望ましい。 V: 0.03-0.5%
V is generally contained in a range of 0.01 to 0.10% because it is mixed as an inevitable impurity in the alloy raw material of stainless steel and is difficult to remove in the refining process. Moreover, since it forms fine carbonitride and has the effect of suppressing grain growth, it is an element that is intentionally added as necessary. The effect is stably manifested when 0.03% or more is added, so the lower limit is made 0.03%. Since it is not preferable that the crystal grain size changes due to the variation of V, 0.08% or more is desirable in order to make the crystal grain size within a certain range. On the other hand, if added excessively, the precipitates may be coarsened. As a result, the toughness after quenching decreases, so the upper limit is made 0.5%. In view of manufacturing cost and manufacturability, it is desirable to set it to 0.2% or less.

　Ｔｉ：０．００１～０．３％
　Ｔｉは、Ｎｂと同様に炭窒化物を形成することで、ステンレス鋼におけるクロム炭窒化物の析出による鋭敏化や耐食性の低下を抑制する元素である。しかしながら、大型の製鋼介在物を形成することで、表面疵の原因になりやすいため、その上限は０．３％以下とする。固溶Ｃ、Ｎ量の確保による高温強度向上を考慮すると、０．０１％以下にすることが望ましい。Ｔｉは含有していなくても良い。 Ti: 0.001 to 0.3%
Ti is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride similarly to Nb. However, since the formation of large steel-making inclusions tends to cause surface flaws, the upper limit is made 0.3% or less. Considering the improvement in high-temperature strength by securing the amount of dissolved C and N, it is desirable to make it 0.01% or less. Ti may not be contained.

　Ｎｂ：０．００１～０．３％
　Ｎｂは、炭窒化物を形成することで、ステンレス鋼におけるクロム炭窒化物の析出による鋭敏化や耐食性の低下を抑制する元素である。しかしながら、大型の製鋼介在物を形成することで、表面疵の原因になりやすいため、その上限は０．３％とする。固溶Ｃ、Ｎ量の確保による高温強度向上を考慮すると、０．０１％以下にすることが望ましい。Ｎｂは含有していなくても良い。 Nb: 0.001 to 0.3%
Nb is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. However, since the formation of large steel-making inclusions tends to cause surface defects, the upper limit is made 0.3%. Considering the improvement in high-temperature strength by securing the amount of dissolved C and N, it is desirable to make it 0.01% or less. Nb may not be contained.

　Ｂ：０．０００１～０．００５０％
　Ｂは、熱間加工性の向上に有効な元素であり、その効果は０．０００１％以上で発現するため、０．０００１％以上添加してもよい。より広い温度域における熱間加工性を向上させるためには、０．０００５％以上とすることが望ましい。一方、過度な添加は熱間加工性の低下により、表面疵の原因となるため、０．００５０％を上限とする。耐食性も考慮すると０．００２５％以下が望ましい。 B: 0.0001 to 0.0050%
B is an element effective for improving the hot workability. Since the effect is manifested at 0.0001% or more, 0.0001% or more may be added. In order to improve the hot workability in a wider temperature range, the content is preferably 0.0005% or more. On the other hand, excessive addition causes surface flaws due to a decrease in hot workability, so 0.0050% is made the upper limit. In consideration of corrosion resistance, 0.0025% or less is desirable.

　Ｃａ：０．００１～０．０１０％
　Ｃａは、脱硫元素として添加され、鋼中のＳを低減して熱間加工性を向上させる効果がある。一般には、溶解精錬時のスラグ中にＣａＯとして添加させ、この一部が鋼中にＣａとして溶解する。また、ＣａＯ－ＳｉＯ2－Ａｌ2Ｏ3－ＭｇＯなどの複合酸化物としても鋼中に含有される。熱間加工性の改善効果は０．００１％から得られるために、０．００１％以上にすることが望ましい。一方、多量に含有すると比較的粗大な水溶性介在物ＣａＳが析出し、耐食性を低下させるために０．０１０％以下にすることが望ましい。 Ca: 0.001 to 0.010%
Ca is added as a desulfurization element, and has the effect of reducing S in steel and improving hot workability. In general, CaO is added to slag during melting and refining, and a part of this is dissolved as Ca in steel. Further, a composite oxide such as CaO—SiO 2 —Al 2 O 3 —MgO is also contained in the steel. Since the effect of improving hot workability is obtained from 0.001%, it is desirable to make it 0.001% or more. On the other hand, when it is contained in a large amount, a relatively coarse water-soluble inclusion CaS is precipitated, so that the content is preferably 0.010% or less in order to reduce the corrosion resistance.

　さらに、上記元素に加えて、Ｗ：０．０１～３．００％、Ｚｒ：０．０５～０．３０％、Ｓｎ：０．０１～０．１０％、Ｃｏ：０．０１～０．３０％、Ｍｇ：０．０００２～０．０１０％の１種又は２種以上を任意で添加してもよい。 In addition to the above elements, W: 0.01 to 3.00%, Zr: 0.05 to 0.30%, Sn: 0.01 to 0.10%, Co: 0.01 to 0.30 %, Mg: 0.0002 to 0.010%, or two or more of them may be optionally added.

　Ｗ：０．０１～３．０％
　Ｗは、ＣｒやＭｏと同様に耐食性を向上させる元素である。また固溶強化により高温強度を高める効果もある。これらの効果を発現するためには、０．０１％以上添加することが望ましい。一方、シグマ相の析出を促進する元素であり、時効脆化による材料の強度低下を生じるために、３．０％以下にすることが望ましい。また、Ｍｏ、Ｎｂと同様に高価な元素であるため、１．５％以下にすることがより好ましい。 W: 0.01-3.0%
W is an element that improves the corrosion resistance like Cr and Mo. There is also an effect of increasing the high temperature strength by solid solution strengthening. In order to exhibit these effects, it is desirable to add 0.01% or more. On the other hand, it is an element that promotes precipitation of the sigma phase, and in order to cause a reduction in the strength of the material due to aging embrittlement, it is desirable to make it 3.0% or less. Moreover, since it is an expensive element like Mo and Nb, it is more preferable to make it 1.5% or less.

　Ｚｒ：０．０５～０．３０％
　Ｚｒは、Ｔｉ、Ｎｂと同様に炭窒化物を形成することで、ステンレス鋼におけるクロム炭窒化物の析出による鋭敏化や耐食性の低下を抑制する元素である。しかしながら、大型の製鋼介在物を形成することで、表面疵の原因になりやすいため、その上限は０．３０％以下とする。固溶Ｃ、Ｎ量の確保による高温強度向上を考慮すると、０．１％以下にすることが望ましい。Ｚｒは含有していなくても良い。 Zr: 0.05-0.30%
Zr is an element that suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitrides similarly to Ti and Nb. However, since the formation of large steelmaking inclusions tends to cause surface flaws, the upper limit is made 0.30% or less. Considering the improvement in high temperature strength by securing the amount of dissolved C and N, it is desirable to make it 0.1% or less. Zr may not be contained.

　Ｓｎ：０．０１～０．１０％
　Ｓｎは、焼入れ後の耐食性向上に有効な元素であり、必要に応じて０．０２％以上添加する事が好ましい。ただし、過度な添加は熱延時の耳割れを促進するため、０．１０％以下にすることが好ましい。 Sn: 0.01-0.10%
Sn is an element effective for improving the corrosion resistance after quenching, and it is preferable to add 0.02% or more as necessary. However, excessive addition promotes ear cracking during hot rolling, so it is preferable to make it 0.10% or less.

　Ｃｏ：０．０１～０．３０％
　Ｃｏは、オーステナイト系ステンレス鋼においては、合金原料から不可避的不純物として混入しやすい元素である。また高温強度の向上に有効な元素であるために、０．０１％以上添加することが望ましい。ただし、過度な添加は熱間加工性の低下による表面疵の原因となるために、０．３０％以下にすることが望ましい。 Co: 0.01 to 0.30%
Co is an element that is easily mixed as an inevitable impurity from alloy raw materials in austenitic stainless steel. Moreover, since it is an element effective in improving high temperature strength, it is desirable to add 0.01% or more. However, excessive addition causes surface flaws due to a decrease in hot workability, so it is desirable to make it 0.30% or less.

　Ｍｇ：０．０００２～０．０１０％
　Ｍｇは、Ｃａと同様に脱硫元素として添加され、一般にはスラグ中から溶鋼中に平行量が固溶するほか、複合酸化物中にＭｇＯとして含有される場合もある。また耐火物中のＭｇＯが溶鋼中に溶け出す場合もある。脱硫効果は０．０００２％以上で現われるため、下限を０．０００２％とすることが望ましい。一方、過度な添加は、水溶性介在物ＭｇＳが粗大析出し、耐食性を低下させるため、０．０１０％以下にすることが望ましい。 Mg: 0.0002 to 0.010%
Mg is added as a desulfurization element in the same manner as Ca, and in general, a parallel amount is dissolved in the molten steel from the slag and may be contained as MgO in the composite oxide. In addition, MgO in the refractory may be dissolved into the molten steel. Since the desulfurization effect appears at 0.0002% or more, it is desirable to set the lower limit to 0.0002%. On the other hand, excessive addition causes the water-soluble inclusion MgS to precipitate coarsely and lowers the corrosion resistance, so it is desirable to make it 0.010% or less.

　成分組成の残部は、Ｆｅ及び不可避的不純物である。不可避的不純物とは、本発明で規定する成分組成を有するステンレス鋼板を工業的に製造する際に、原料や製造環境等から、意図的に含有させたものではなく、不可避的に混入するものをいう。 The balance of the component composition is Fe and inevitable impurities. The inevitable impurities are not intentionally included from the raw materials and production environment, etc., but are inevitably mixed when the stainless steel plate having the component composition defined in the present invention is industrially produced. Say.

　上述した任意で添加される元素も、含有を意図しなくとも不可避的不純物として混入する場合があるが、上述した含有量の上限以下であれば特に問題はない。また、上述した以外の元素も、本発明の効果を損なわない範囲で含有させることが出来る。 The above-described optional added element may be mixed as an unavoidable impurity even if it is not intended to be contained, but there is no particular problem as long as it is below the upper limit of the content described above. Moreover, elements other than those described above can also be contained within a range not impairing the effects of the present invention.

　上述した成分組成を有することにより高い耐酸化性を発揮するステンレス鋼板を得ることができる。さらに、上述した溶接形状を有することにより、母材と溶接部の耐酸化性がともに優れる排気系部品を得ることができる。 A stainless steel plate exhibiting high oxidation resistance can be obtained by having the above-described component composition. Furthermore, by having the above-described welded shape, an exhaust system component that is excellent in both oxidation resistance of the base material and the welded portion can be obtained.

　以下、実施例により本発明の効果を説明するが、本発明は、以下の実施例で用いた条件に限定されるものではない。 Hereinafter, the effects of the present invention will be described with reference to examples, but the present invention is not limited to the conditions used in the following examples.

　まず、表１に示す成分組成の鋼を溶製して２００ｍｍ厚のスラブに鋳造した。このスラブを１２００℃に加熱後、粗熱延、仕上熱延を経て板厚４ｍｍの熱延鋼板とし、８００℃の温度域での巻取りをシミュレーションするために、８００℃の熱処理炉に挿入し、１時間保持後空冷した。引き続き、熱延板焼鈍を、１１００℃で２０秒行った後、水冷した。その後、ショットブラストし、酸洗してスケールを除去した。表面疵の有無を肉眼及び倍率１０倍のルーペで観察して評価した。肉眼又はルーペ観察のいずれかで表面疵が確認できるものを不合格とした。 First, steel having the composition shown in Table 1 was melted and cast into a 200 mm thick slab. This slab is heated to 1200 ° C, then hot-rolled steel plate with a thickness of 4 mm after rough hot rolling and finish hot rolling, and inserted into an 800 ° C heat treatment furnace to simulate winding in the temperature range of 800 ° C. After holding for 1 hour, it was air cooled. Subsequently, hot-rolled sheet annealing was performed at 1100 ° C. for 20 seconds, followed by water cooling. Then, it was shot blasted and pickled to remove scale. The presence or absence of surface wrinkles was evaluated by observing with the naked eye and a magnifier with a magnification of 10 times. Those in which surface wrinkles could be confirmed by either naked eye observation or loupe observation were rejected.

　その後、冷間圧延を行って板厚を１．２ｍｍにした後、冷延板焼鈍を１１００℃で２０秒行った。表面の酸化皮膜をソルトで改質し、硝弗酸で酸洗して酸洗肌とした。 Then, after cold-rolling to a plate thickness of 1.2 mm, cold-rolled sheet annealing was performed at 1100 ° C. for 20 seconds. The oxide film on the surface was modified with salt and pickled with nitric hydrofluoric acid to form a pickled skin.

　冷延板の高温強度を１０００℃で測定し、０．２％耐力が３０ＭＰａ以上であるものを合格とした。また、７００℃で３００時間酸化させたあと、表面を研磨した薄板を作成し、割れが生じたものを高温脆化で不合格とした。 The high temperature strength of the cold-rolled sheet was measured at 1000 ° C., and the one with 0.2% proof stress of 30 MPa or more was regarded as acceptable. Moreover, after oxidizing at 700 degreeC for 300 hours, the thin plate which grind | polished the surface was created, and the thing which the crack produced was made rejected by high temperature embrittlement.

　また、この薄板をＪＩＳの塩水噴霧試験に供して、さびが発生したものを耐食性不合格とした。耐酸化性の評価には、酸洗ままの平板と平板を重ね隅肉溶接した試験片で行った。酸化試験の雰囲気は、Ｈ２Ｏが５～１０％、Ｏ２が０．２～１．０％で残部が窒素となる雰囲気で行った。雰囲気ガス組成は、自動車排気ガスを模擬して周期的な変化を加えた。試験片を１０５０℃に加熱、保持、２００℃まで冷却を１サイクルとして２５００サイクルまで試験を行って、外観を記録するとともに、重量変化を測定した。最も酸化が進んだ場所を記録するとともに、その部分の板厚を評価し、０．８ｍｍ以上を耐酸化性が良好（○）とした。 In addition, this thin plate was subjected to a JIS salt spray test, and a product in which rust occurred was regarded as a corrosion resistance failure. The oxidation resistance was evaluated using a test piece in which a flat plate as pickled and a flat plate were stacked and welded on the fillet. The atmosphere for the oxidation test was an atmosphere in which H 2 O was 5 to 10%, O 2 was 0.2 to 1.0%, and the balance was nitrogen. The atmospheric gas composition was changed periodically by simulating automobile exhaust gas. The test piece was heated and held at 1050 ° C., cooled to 200 ° C. as one cycle, tested up to 2500 cycles, the appearance was recorded, and the weight change was measured. The location where oxidation was most advanced was recorded and the thickness of the portion was evaluated, and 0.8 mm or more was regarded as having good oxidation resistance (O).

　比較例として、組成及び溶接部形状が本発明外になるサンプルについても同様の評価を行った。 As a comparative example, the same evaluation was performed for a sample whose composition and welded portion shape are outside the scope of the present invention.

Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001

Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002

　表１、２から明らかなように、本発明で規定する成分組成、成分パラメータを有する本発明例では、母材の耐酸化性が良好であり、表面疵、高温強度及び高温脆化が合格であり、耐食性も良好であった。特に、ＮＯ．１～ＮＯ．３０は溶接ビード形状を本発明範囲に制御した結果、母材のみならず、溶接部の耐酸化性も良好な結果となった。一方、本発明から外れる成分組成では、耐酸化性が不良であるほか、表面疵、高温強度、高温脆化、耐食性及び耐酸化性の各特性を両立させることが困難であり、比較例において、いずれかの特性が不合格であった。これにより、比較例は本発明例よりも特性が劣ることが分かる。 As is clear from Tables 1 and 2, in the present invention examples having the component composition and component parameters defined in the present invention, the base material has good oxidation resistance, and surface defects, high-temperature strength and high-temperature embrittlement are acceptable. There was also good corrosion resistance. In particular, NO. 1 to NO. As a result of controlling the shape of the weld bead within the range of the present invention, not only the base material but also the oxidation resistance of the welded portion was satisfactory. On the other hand, in the component composition that departs from the present invention, the oxidation resistance is poor, and it is difficult to achieve both surface flaws, high temperature strength, high temperature embrittlement, corrosion resistance and oxidation resistance, Any property was rejected. Thereby, it turns out that a comparative example is inferior to the example of this invention in a characteristic.

　具体的には、試験ＮＯ．３１はＣが低いため、ＮＯ．３３はＳｉが低いため、ＮＯ．３６はＭｎが高いため、ＮＯ．４３はＭｏが低いため、ＮＯ．４５はＶが高いため、ＮＯ．４９、５３はＣｒ＋２０Ｍｏが低いか、Ｓｉ＋２０Ｃ＋１５Ｎが低いために、母材、溶接部共に耐酸化性不良であった。ＮＯ．３２はＣが高いために耐食性が不良であった。 Specifically, test NO. 31 is low in C, so NO. No. 33 is low in Si, so NO. No. 36 has a high Mn, so NO. 43 is low in Mo, so NO. 45 has a high V, so NO. Since Nos. 49 and 53 had low Cr + 20Mo or low Si + 20C + 15N, both the base metal and the welded portion had poor oxidation resistance. NO. No. 32 had poor corrosion resistance due to high C.

　ＮＯ．３４はＳｉが高いため、ＮＯ．３５はＭｎが低いため、ＮＯ．３７はＰが高いため、ＮＯ．４２はＮｉが高いため、ＮＯ．４８はＮが高いために、表面疵が発生し、不良であった。ＮＯ．３８はＳが高く、Ａｌが低いために表面疵が不良であり、耐食性も不良であった。ＮＯ．３９はＣｒが低く、Ｃｒ＋２０Ｍｏが低いために、表面疵が不良であり、母材と溶接部の耐酸化性も不良であった。 NO. 34 is high in Si, so NO. 35 has a low Mn, so NO. 37 has a high P, so NO. 42 is high in Ni, so NO. No. 48 was defective because surface defects occurred because N was high. NO. No. 38 had high S and low Al, so the surface flaws were poor and the corrosion resistance was also poor. NO. No. 39 had a low Cr and a low Cr + 20Mo, so the surface defects were poor and the oxidation resistance of the base metal and the welded part was also poor.

　ＮＯ．４０はＣｒが高く、ＮＯ．４１はＮｉが低く、ＮＯ．４４はＭｏが高いために、高温脆化が不良であった。ＮＯ．４６はＡｌが高く、ＮＯ．４７はＮが低いために、高温強度が不良であった。 NO. 40 is high in Cr, NO. No. 41 has low Ni and NO. Since No. 44 had high Mo, high temperature embrittlement was bad. NO. 46 is high in Al, NO. No. 47 had a poor high temperature strength because N was low.

　また、ＮＯ．４９は、Ｍｏを含まず、これにも起因して、Ｃｒ＋２０Ｍｏが低いために、母材と溶接部の耐酸化性が、共に不良であった。
　ＮＯ．５０～５２、５４、５５は溶接部における板厚変化の勾配が大きかったために、溶接部の耐酸化性が不良であった。 In addition, NO. No. 49 does not contain Mo, and because of this, Cr + 20Mo is low, so that the oxidation resistance of the base metal and the welded part was both poor.
NO. In 50 to 52, 54, and 55, the gradient of the plate thickness change in the welded portion was large, so the oxidation resistance of the welded portion was poor.

　これらのうち、ＮＯ．５０～５２は、供試鋼として本発明の規定を充足しているＡ２３を使用した。そのため、ＮＯ．５０～５２は溶接部の耐酸化性のみが不良であるが、母材の耐酸化性をはじめとする他の性状、性能は満足できるものであったので、溶接が不要である部品には適用が可能である。 Of these, NO. Nos. 50 to 52 used A23 satisfying the provisions of the present invention as the test steel. Therefore, NO. For 50 to 52, only the oxidation resistance of the welded part is poor, but other properties and performance including the base metal oxidation resistance were satisfactory, so it is applicable to parts that do not require welding. Is possible.

　また、ＮＯ．５５は、使用した供試鋼がＢ２０であって、Ｃｒ＋２０Ｃ＋１５Ｎの値が５．６０となり、本発明で規定する下限値に満たないことから、母材と溶接部の耐酸化性に関して不良であった。 Also, NO. In No. 55, the test steel used was B20, and the value of Cr + 20C + 15N was 5.60, which was lower than the lower limit defined in the present invention, so that the oxidation resistance of the base metal and the welded part was poor. .

　ＮＯ．５４、５５は溶接部における板厚変化の勾配が大きい上に、供試鋼Ｂ３のＳｉが低かったために、溶接部に加えて、母材の耐酸化性も不良であった。 NO. In Nos. 54 and 55, the gradient of the plate thickness change in the welded portion was large and the Si of the test steel B3 was low, so that in addition to the welded portion, the base material had poor oxidation resistance.

　これらの結果から、上述した知見を確認することができ、また、上述した各鋼組成及び校正を限定する根拠を裏付けることができた。 From these results, the above-mentioned knowledge could be confirmed, and the grounds for limiting the above-described steel composition and calibration could be supported.

　本発明の断続酸化特性に優れた排気系部品用ステンレス鋼板及び排気系部品は、耐酸化性を高める成分設計とともに、溶接部の形状制御により溶接熱影響部の耐酸化性を高めることが可能である。また、表面疵が少ないために薄板製造時の表面研削工程（ＣＧ）を省略、あるいは簡略化することが可能である。さらに、耐酸化性を高めることで、排気系部品の板厚を薄くすることが可能になり、部品の軽量化により、自動車の燃費向上の効果も得られるので、社会的な意味合いは大きく、本発明の産業上の利用可能性は大きい。 The stainless steel plate for exhaust system parts and the exhaust system parts with excellent intermittent oxidation characteristics of the present invention can improve the oxidation resistance of the heat affected zone by controlling the shape of the welded part as well as the component design that improves the oxidation resistance. is there. Moreover, since there are few surface wrinkles, the surface grinding process (CG) at the time of thin plate manufacture can be omitted or simplified. Furthermore, by improving the oxidation resistance, it is possible to reduce the thickness of the exhaust system parts, and by reducing the weight of the parts, the effect of improving the fuel efficiency of the automobile can also be obtained. The industrial applicability of the invention is great.

Claims (4)

　質量％で、
　　Ｃ　：０．０５～０．１５％、
　　Ｓｉ：１．０％～４．０％、
　　Ｍｎ：０．５～３．５％、
　　Ｐ　：０．０１０～０．０４０％、
　　Ｓ　：０．０００１～０．０１０％、
　　Ｃｒ：２０～３０％、
　　Ｎｉ：８～２５％、
　　Ｍｏ：０．０１～１．５％、
　　Ａｌ：０．００１～０．１０％、及び
　　Ｎ：０．１３～０．５０％
を含有し、残部がＦｅ及び不可避的不純物であり、
　Ｃｒ、Ｍｏ、Ｓｉ、Ｃ、及びＮの含有量が
　　Ｃｒ+２０Ｍｏ≧２４．０％、及び
　　Ｓｉ＋２０Ｃ＋１５Ｎ≧５．８％
を満たすことを特徴とする断続酸化特性に優れた排気系部品用ステンレス鋼板。 % By mass
C: 0.05 to 0.15%,
Si: 1.0% to 4.0%,
Mn: 0.5 to 3.5%
P: 0.010 to 0.040%,
S: 0.0001 to 0.010%,
Cr: 20-30%,
Ni: 8-25%,
Mo: 0.01 to 1.5%,
Al: 0.001 to 0.10%, and N: 0.13 to 0.50%
And the balance is Fe and inevitable impurities,
Cr, Mo, Si, C, and N contents are Cr + 20Mo ≧ 24.0%, and Si + 20C + 15N ≧ 5.8%
Stainless steel sheet for exhaust system parts with excellent intermittent oxidation characteristics characterized by satisfying 　さらに、質量％で、
　　Ｃｕ：０．１～３．０％、
　　Ｖ　：０．０３～０．５％、
　　Ｔｉ：０．００１～０．３％、
　　Ｎｂ：０．００１～０．３％、
　　Ｂ：０．０００１～０．００５０％、及び
　　Ｃａ：０．００１～０．０１０％
の１種又は２種以上を含有することを特徴とする請求項１に記載の断続酸化特性に優れた排気系部品用ステンレス鋼板。 Furthermore, in mass%,
Cu: 0.1 to 3.0%,
V: 0.03-0.5%,
Ti: 0.001 to 0.3%,
Nb: 0.001 to 0.3%,
B: 0.0001 to 0.0050%, and Ca: 0.001 to 0.010%
The stainless steel plate for exhaust system parts having excellent intermittent oxidation characteristics according to claim 1, comprising one or more of the following. 　さらに、質量％で
　　Ｗ　：０．０１～３．００％、
　　Ｚｒ：０．０５～０．３０％、
　　Ｓｎ：０．０１～０．１０％、
　　Ｃｏ：０．０１～０．３０％、及び
　　Ｍｇ：０．０００２％～０．０１０％
の１種又は２種以上を含有することを特徴とする請求項１又は２に記載の断続酸化特性に優れた排気系部品用ステンレス鋼板。 Further, in terms of mass%, W: 0.01 to 3.00%,
Zr: 0.05 to 0.30%,
Sn: 0.01 to 0.10%,
Co: 0.01 to 0.30%, and Mg: 0.0002% to 0.010%
The stainless steel plate for exhaust system parts having excellent intermittent oxidation characteristics according to claim 1 or 2, characterized by containing one or more of the following. 　請求項１～３のいずれか一項に記載のステンレス鋼板を母材として用いた溶接構造を有し、溶接部における板厚変化の勾配が１５度以下であることを特徴とする排気系部品。 An exhaust system part having a welded structure using the stainless steel plate according to any one of claims 1 to 3 as a base material, wherein a gradient of plate thickness change at a welded portion is 15 degrees or less.
PCT/JP2016/060249 2015-03-31 2016-03-29 Stainless steel sheet for exhaust system component having excellent intermittent oxidation characteristics, and exhaust system component Ceased WO2016159011A1 (en)

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KR1020177026809A KR101988150B1 (en) 2015-03-31 2016-03-29 Exhaust system parts
PL16772892T PL3279359T3 (en) 2015-03-31 2016-03-29 Exhaust system part having stainless steel sheet having excellent intermittent oxidation characteristics
ES16772892T ES2890333T3 (en) 2015-03-31 2016-03-29 Stainless steel sheet for use in an exhaust system part with excellent intermittent rust characteristics and an exhaust system part
JP2017510057A JP6239192B2 (en) 2015-03-31 2016-03-29 Exhaust system parts
EP16772892.2A EP3279359B1 (en) 2015-03-31 2016-03-29 Exhaust system part having stainless steel sheet having excellent intermittent oxidation characteristics
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