Classifications

• • 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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
• • 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
  • 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
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • 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
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/4998—Combined manufacture including applying or shaping of fluent material
  • Y10T29/49988—Metal casting
  • Y10T29/49991—Combined with rolling

Definitions

• the invention relates to a dual-phase steel, the structure of which consists essentially of martensite and ferrite or bainite, wherein shares of retained austenite may be present and the dual-phase steel has a tensile strength of more than 950 MPa.
• the invention likewise relates to a flat product produced from such a dual-phase steel and to a process for producing a flat product.
• the generic term "flat product" typically includes steel strips and sheets of the type according to the invention.
• the known steel contains, in addition to iron and the unavoidable impurities (in% by weight) 0.05-0.3% C, up to 1.5% Si, 0.01-0.3% Mn, up to 0.02 % P, 0.02% S, up to 0.01% N and 0, 01 - 3.0% Al.
• the known steel should have a retained austenite content of not more than 7% and have Mg precipitates with a particle diameter of 0.01-5.0 ⁇ m at a distribution determined in more detail in this document.
• the from the EP 1 637 618 A1 known steel to further increase its strength in addition to other optionally added alloying elements also contain contents of Cr and Mo of 0.005 - 5 wt .-% and 0.0051 - 2 wt .-% Cu, the contents of Cu should additionally reduce the risk of breakage ,
• the Martenistanteil of the steel in question is about 5% to 20% of the predominantly martensitic-ferritic microstructure.
• a flat product produced in this way has strengths of at least 500 N / mm 2 and at the same time good formability, without requiring particularly high contents of certain alloying elements.
• JP-A-2000282175 discloses a steel, the structure of which consists of 60-90 vol.% Bainite and the remainder of ferrite, martensite and retained austenite for bodywork.
• the object of the invention was to develop a steel and a flat product produced therefrom which has a strength of at least 950 MPa and good deformability.
• the steel should be one Having a surface finish that allows using a simple manufacturing process, a flat product produced from this steel in the uncoated or provided with a corrosion-protective coating state to deform a complex-shaped component, such as a part of an automobile body.
• a method should also be given that allows in a simple manner to produce in the above-mentioned manner manufactured flat products.
• a the above-mentioned object solving flat product according to claim 21 according to the invention characterized in that it consists of a composite according to the invention and procured steel.
• a steel according to the invention is characterized by high strengths of at least 950, in particular 980 MPa, with regular strengths of 1000 MPa and more being achieved. At the same time, the steel according to the invention has a yield strength of at least 580 MPa, in particular at least 600 MPa, and has an elongation A 80 of at least 10%.
• steel according to the invention is particularly suitable for the production of complex shaped, highly loaded in practical use components, such as those required in the field of bodywork for automobiles.
• the advantageous combination of properties of a steel according to the invention is achieved inter alia by possessing a dual-phase structure despite its high strengths.
• the alloy of a steel according to the invention is composed to have a martensite content of at least 20% to a maximum of 70%.
• residual austenite contents of up to 8% may be advantageous, with generally lower residual austenite contents of not more than 7% or less being preferred.
• the remainder of the microstructure of a dual-phase steel according to the invention consists respectively of ferrite and / or bainite (bainitic ferrite + carbides).
• the high strengths, good elongation properties and optimized surface textures are due to the adjustment of the dual-phase structure according to the invention achieved. This has been made possible by a narrow selection of the individual contents of the alloying elements present in a steel according to the invention besides iron and unavoidable impurities.
• the invention provides a C content of 0.050-0.105% by weight.
• the inventively provided levels of C have been chosen in view of the best possible weldability of the steel.
• the advantageous effect of carbon in a steel according to the invention can be used particularly reliably if the C content of a steel according to the invention is 0.060-0.090% by weight, in particular 0.070-0.080% by weight.
• Si is used in a steel according to the invention to increase the strength by hardening the ferrite or bainite.
• a minimum content of Si of 0.10 wt .-% is provided, the effect of Si is particularly safe when the Si content of a steel according to the invention at least 0.2 wt .-%, in particular at least 0.25 wt .-% is.
• adherence to this upper limit minimizes the risk of grain boundary oxidation.
• the upper limit of the Si content has at the same time been set at 0.6% by weight. In this case, an unfavorable influence of Si on the properties of the steel according to the invention can be avoided with even greater certainty that the Si content of the steel according to the invention is limited to 0.4% by weight, in particular 0.35% by weight.
• the Mn content of a steel according to the invention is in the range of 2.10-2.80% by weight in order to use, on the one hand, the strength-increasing effect and, on the other hand, the positive influence of Mn on martensite formation.
• Mn also has a positive effect with regard to the lowering of the critical cooling rate after annealing, since it hinders the formation of perlite.
• the positive effects of the presence of Mn in a steel according to the invention can be used with particular certainty if the Mn content is at least 2.20% by weight, in particular at least 2.45% by weight.
• Negative effects of Mn on a steel according to the invention such as a reduction in elongation, deterioration of weldability or poorer suitability for hot-dip galvanizing, can be excluded with increased certainty that the Mn content to 2.70 wt .-%, in particular 2, 60 wt .-% is limited.
• Cr also strengthens in a dual-phase steel according to the invention in contents of 0.2-0.8% by weight.
• the effect of Cr is comparable to the effect of Mn.
• the advantageous effects of Cr occur in particular when the Cr content is at least 0.3% by weight, in particular at least 0.55% by weight.
• the Cr content of a steel according to the invention is limited to 0.8% by weight in order to reduce the risk of occurrence of grain boundary oxidation and to avoid a negative influence on the ductility of the steel according to the invention. This is especially ensured when the upper limit of the Chromium content of a steel according to the invention to at most 0.7 wt .-%, in particular 0.65 wt .-%, is set.
• the presence of titanium at levels of at least 0.02% by weight also contributes to increasing the strength of a steel according to the invention by forming fine precipitates of TiC or Ti (C, N) and contributing to grain refining.
• Another positive effect of Ti is the setting of possibly present nitrogen, so that the formation of boron nitrides in the steel according to the invention is prevented. These would have a strong negative impact on the elongation properties and, consequently, on the formability of a flat product according to the invention.
• the presence of Ti thus ensures, in the case of an addition of boron to increase the strength, that the boron can fully develop its effect.
• Ti is added in an amount which is more than 5.1 times the respective N content (ie Ti content> 1.5 (3.4 ⁇ N content)).
• too high Ti contents lead to unfavorably high recrystallization temperatures, which has a negative effect, in particular, when cold-rolled flat products are produced from steel according to the invention, which are finally annealed. Therefore, the upper limit of the Ti content has been limited to 0.10 wt%.
• the positive influence of Ti on the properties of a steel according to the invention can be used particularly reliably if its Ti content is 0.060-0.090% by weight, in particular 0.070-0.085% by weight.
• the strength of the steel according to the invention is also increased by the amounts of B, which are optionally provided according to the invention, of up to 0.002% by weight and, as in the case of the addition of Mn, Cr and Mo in the case of the production of cold strip of steel according to the invention, the critical cooling rate lowered after annealing. Therefore, according to a particularly preferred embodiment of the invention, the B content is at least 0.0005 wt .-%. At the same time, however, excessively high contents of B can reduce the deformability of the steel according to the invention and adversely affect the expression of the dual-phase structure desired according to the invention. Optimized effects of boron can be used in a steel according to the invention in that the B content is limited to 0.0007-0.0016% by weight, in particular 0.0008-0.0013% by weight.
• the inventively optional contents of molybdenum of at least 0.05% by weight also contribute to increasing the strength of a steel according to the invention.
• the presence of Mo does not adversely affect the coatability of the flat product with a metallic coating and its ductility.
• Practical experiments have shown that the positive effects of Mo up to contents of 0.25% by weight, in particular 0.22% by weight, can be used particularly effectively, even from a cost point of view.
• contents of Mo of at least 0.05% by weight have a positive effect on the properties of a steel according to the invention.
• the desired effect of molybdenum occurs a steel according to the invention, in particular if its Mo content is 0.065-0.18% by weight, in particular 0.08-0.13% by weight.
• Mo content is 0.065-0.18% by weight, in particular 0.08-0.13% by weight.
• Cr contents of less than 0.3% by weight it is advantageous to add 0.05-0.22% by weight of Mo to secure the required strength of the steel according to the invention.
• Aluminum is used in the melting of a steel according to the invention for deoxidizing and for setting nitrogen which may be present in the steel.
• Al may be added to the steel according to the invention in contents of less than ⁇ 0.1% by weight, the desired effect of Al occurring particularly safely if its contents in the range of 0.01-0.06 wt .-%, in particular 0.020 - 0.050 wt .-%, are.
• the steel according to the invention may, to further increase its strength, have copper in contents of up to 0.20% by weight.
• a copper content has a particularly favorable effect when it is in the range of 0.08 to 0.12 wt .-%.
• nickel may be added to the steel according to the invention in order to further improve the hardenability and, accordingly, the strength of a steel according to the invention.
• Ca can be used for deoxidation like Al in steelmaking.
• the presence of Ca in amounts of up to 0.005 wt .-%, in particular from 0.002 to 0.004 wt .-%, also favor the formation of a fine-grained structure.
• Nitrogen is allowed in inventive steel only in amounts of up to 0.012 wt .-%, in order to avoid the formation of boron nitrides especially in the simultaneous presence of B.
• the N content is preferably limited to 0.007% by weight.
• the P content is according to the invention preferably limited to ⁇ 0.1, in particular ⁇ 0.02 wt .-%, with particularly good results at levels of less than 0.010 wt .-% can be achieved.
• a dual phase steel composed according to the invention is first melted, then the melt to a precursor, such as slab or thin slab, cast, then reheated the precursor at a hot rolling start temperature of 1100 - 1300 ° C. or held, then the precursor hot rolled at a hot rolling end temperature of 800 - 950 ° C to a hot strip and finally the hot strip at a reel temperature of up to 650 ° C, in particular 500 - 650 ° C, reeled.
• hot strip composed according to the invention reacts insensitive to the change in the coiler temperature and can always achieve strengths which are in the range of 1000 MPa and yield strengths of 750 to 890 MPa.
• the reel temperature can be varied over a wide range in order to influence the respective desired properties and microstructural characteristics in a targeted manner.
• particularly suitable reel temperatures are in the range of 500-650 ° C, with reel temperatures of 530-580 ° C as have proved particularly favorable, since at temperatures of more than 580 ° C with increasing reel temperature, the risk of grain boundary oxidation increases and lying below 500 ° C reel temperatures, the strength of the hot strip increases so much that a subsequent deformation can be difficult.
• the hot strip obtained in the manner according to the invention should remain uncoated or be electrolytically coated with a metallic coating as a hot strip, no annealing of the flat product is required.
• the hot-rolled strip is to be coated with a metallic coating by hot-dip galvanizing, then it is first annealed at a maximum annealing temperature of 600 ° C. and then cooled to the temperature of the coating bath, which may be, for example, a zinc bath. After passing through the zinc bath, the coated hot strip can be conventionally cooled to room temperature.
• cold rolled strips can also be produced from composite steel.
• a composite according to the invention dual-phase steel melted, then cast the melt into a precursor, such as slab or thin slab, then reheated or held the precursor at a hot rolling start temperature of 1100-1300 ° C, then the hot rolled at a final hot rolling temperature of 800-950 ° C to a hot strip, the pre-product obtained hot strip at a reel temperature of up to 650 ° C, in particular 500 - 650 ° C, reeled, then the hot strip cold rolled into a cold strip, then the cold strip annealed at a 700 - 900 ° C amount annealing temperature and finally cooled the cold strip controlled
• the cold strip thus produced can also be provided with a protective coating against corrosion.
• the cold strip to be cold rolled to cold strip is preferably at least 500 ° C, in particular at least 530 ° C or at least 550 ° C, reeled.
• Such cold-rolled Cold rolled strip according to the invention typically has thicknesses of 0, 8-2.5 mm.
• the flat product according to the invention is provided with a metallic protective coating, this can be done, for example, by hot-dip galvanizing, galvannealing or electrolytic coating. If necessary, a pre-oxidation can be carried out before the coating in order to ensure a secure connection of the metallic coating to the respective substrate to be coated.
• the cold strip produced according to the invention remains uncoated or is to be electrolytically coated, an annealing treatment in a continuous annealing anneal takes place as a separate working step.
• the maximum annealing temperatures achieved are in the range of 700-900 ° C at heating rates of 1-50 K / s.
• the annealed cold strip for the targeted setting of the desired property combination according to the invention is preferably cooled in such a way that in the temperature range of 550-650 ° C cooling rates of at least 10 K / s are achieved in order to suppress the formation of perlite.
• the strip can be held for a period of 10-100 s or cooled directly to room temperature at a cooling rate of 0.5-30 K / s.
• the cold strip is to be coated by hot dip galvanizing, then the steps of annealing and coating can be combined.
• the cold strip in continuous sequence through different furnace sections of a fire-coating plant, wherein in the individual furnace sections have different temperatures, the maximum in the range of 700 - 900 ° C, with heating rates in the range of 2 - 100 K / s should be selected.
• the strip is then held at this temperature for 10-200 seconds.
• the strip is then cooled to the temperature of the respective coating bath, which is typically below 500 ° C., which is typically a zinc bath, the cooling rate also being more than 10 K in the temperature range 550-650 ° C. in this case / s should be.
• the cold strip can be kept at the respective temperature for 10 - 100 s. Then the annealed cold strip passes through the respective coating bath, which is preferably a zinc bath. This is followed by either cooling to room temperature to obtain a conventionally hot-dip galvanized cold-rolled strip or rapid heating followed by cooling to room temperature to produce a galvanized cold-rolled strip.
• the respective coating bath which is preferably a zinc bath. This is followed by either cooling to room temperature to obtain a conventionally hot-dip galvanized cold-rolled strip or rapid heating followed by cooling to room temperature to produce a galvanized cold-rolled strip.
• the cold-rolled strip in the coated or uncoated state after the annealing treatment may be subjected to a skin pass rolling in which the skin passages ranging up to 2% are adjusted.
• the hot rolled strips thus obtained were rewound at a coiler temperature of 550 ° C., adjusted to an accuracy of +/- 30 ° C., before being cold rolled to a thickness of 50%, 65% and 70%, respectively from 0.8 mm to 2 mm cold rolled.
• Table 2 shows the microstructural state, the mechanical properties as well as the respectively set cold rolling degrees and strip thicknesses for the cold strips produced in the first test series from melts 1 to 16.
• the hot strips produced from melts 1 to 16 in the manner described above were rewound at a reel temperature lower than 100 ° C, at 500 ° C, at 600 ° C and at 650 ° C.
• the hot strips thus obtained were not intended for cold rolling, but have been supplied as hot strips - possibly after application of a metallic protective coating - the further processing to components.
• Table 1 melt C Si Mn al Not a word Ti Cr B P S N 1 0.087 0.18 2.22 0,007 0,100 0,050 0.60 0.001 0,007 0,004 0.0045 2 0,069 0.28 2.62 0.04 0.092 0,080 0.58 0.0015 0,008 0.0015 0.0031 3 0,095 0.23 2.27 0.031 0.10 0,075 0.62 0.0012 0,013 0,002 0.0051 4 0,089 0.22 2.31 0.034 0,050 0.081 0.64 0.0017 0,012 0.0021 0.0036 5 0.091 0.31 2.52 0.034 0,150 0,052 0.42 0.0011 0.009 0,003 0.0046 6 0,060 0.26 2.15 0,041 0,250 0,051 0.25 0.001 0,012 0.0019 0.0052 7 0,102 0.15 2.26 0,038 0,050 0,090 0.80 0.0018 0.009 0.0021 0.0049 8th 0,065 0.60 2.64 0.032 0,095 0,025 0.45 0.0012 0,0

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Coating With Molten Metal (AREA)
• Heat Treatment Of Steel (AREA)

Priority Applications (8)

Applications Claiming Priority (1)

Publications (2)

Family

ID=38654974

Family Applications (1)

Country Status (8)

Cited By (2)

Families Citing this family (29)

Family Cites Families (12)

• 2007
  • 2007-08-15 AT AT07114399T patent/ATE516380T1/de active
  • 2007-08-15 PL PL07114399T patent/PL2031081T3/pl unknown
  • 2007-08-15 EP EP07114399A patent/EP2031081B1/de active Active
  • 2007-08-15 ES ES07114399T patent/ES2367713T3/es active Active
• 2008
  • 2008-08-07 US US12/673,279 patent/US20110220252A1/en not_active Abandoned
  • 2008-08-07 JP JP2010520537A patent/JP5520221B2/ja active Active
  • 2008-08-07 CN CN2008801034281A patent/CN101802237B/zh active Active
  • 2008-08-07 WO PCT/EP2008/060382 patent/WO2009021898A1/de not_active Ceased

Also Published As

Similar Documents

Legal Events