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WO2015020028A1 - Tôle d'acier doux à teneur élevée en carbone - Google Patents

Tôle d'acier doux à teneur élevée en carbone Download PDF

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Publication number
WO2015020028A1
WO2015020028A1 PCT/JP2014/070570 JP2014070570W WO2015020028A1 WO 2015020028 A1 WO2015020028 A1 WO 2015020028A1 JP 2014070570 W JP2014070570 W JP 2014070570W WO 2015020028 A1 WO2015020028 A1 WO 2015020028A1
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steel
steel sheet
carbon steel
crystal grains
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PCT/JP2014/070570
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English (en)
Japanese (ja)
Inventor
梶原　桂
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Kobe Steel Ltd
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Kobe Steel Ltd
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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
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C21D1/32—Soft annealing, e.g. spheroidising
    • 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
    • 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
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/06—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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • 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
    • C21D2201/00—Treatment for obtaining particular effects
    • C21D2201/05—Grain orientation
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • 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

Definitions

  • the present invention relates to a soft high carbon steel sheet, and more particularly, to a soft high carbon steel sheet that is excellent in cold workability in a softened state and contributes to improvement of component accuracy.
  • High carbon steel plates are widely used as materials for chains, gears, clutches, etc.
  • the softened high carbon steel plate is usually cured by heat treatment such as quenching and tempering after forming and punching. For this reason, high carbon steel sheets are required to have workability that can withstand complicated and severe processing.
  • steel materials that are hot-forged steel bars are used as steel materials that are generally used.
  • hot forging has been used so far.
  • the high carbon steel sheet used for gears and elements is processed into a part shape by cold working or cold rolling and subsequent punching after the cold-rolled material is spheroidized carbide contained therein, Furthermore, it is used by introducing a tempered martensite structure in which a certain amount of undissolved carbide is dispersed by quenching and tempering from a temperature equal to or higher than the Acm point on the equilibrium diagram. Since gears and elements are sliding parts, they are particularly required to be excellent in wear resistance and fatigue resistance. Abrasion resistance is better as the hardness after quenching and tempering into the martensite structure is higher and contains more undissolved carbides, that is, as the amount of carbon increases. It is said that impact resistance and fatigue resistance are reduced by precipitation of carbides along the boundaries.
  • high carbon steel sheets used for gears and elements are formed in a softened state before quenching, but there are cases where parts forming with a step in the plate surface, irregular shape processing, and rolling are performed, which is very high. Parts accuracy is required.
  • Patent Document 1 finds that the punchability is remarkably improved by introducing voids into the steel structure by a combination of annealing conditions and cooling conditions, mainly for the purpose of improving punchability.
  • C 0.70 to 0.95%
  • Si 0.05 to 0.4%
  • Mn 0.5 to 2.0%
  • P 0.005 to 0.03%
  • S 0.0001 to 0.006%
  • Al 0.005 to 0.10%
  • N 0.001 to 0.01%
  • Cr 0.05 to 1.0%
  • the balance being Fe and inevitable impurities
  • a soft high carbon steel sheet having an excellent punching property in which the structure has 100 or more voids per 1 mm 2 of the observed structure has been proposed.
  • Patent Document 2 for the purpose of improving punching burrs, C: 0.65 to 0.85%, Si: 0.05 to 0.4%, Mn: 0.5 to 2 in mass%. 0.0%, P: 0.005 to 0.03%, S: 0.0001 to 0.006%, Al: 0.005 to 0.10%, and N: 0.001 to 0.01%. And the balance is Fe and unavoidable impurities, (i) hardness is 170 HV or less, and (ii) the area of carbide of 0.5 ⁇ m 2 or less in the plate thickness section of the structure before final cold rolling
  • a soft high-carbon steel sheet with a small punching strength that is within 15% of the total area of carbide has been proposed.
  • Patent Document 3 discloses a high-carbon steel sheet that is soft and has good formability before heat treatment and that has excellent wear resistance compared to hardness after heat treatment. And by controlling the size distribution of the spheroidized carbide, it has been found that it is possible to make the alloy softer than the content of the alloy element compared to the conventional material, and C: 0.50 to 1.00%, Si: 0.35% or less, Mn: 0.60 to 0.90%, P: 0.015% or less, S: 0.0030% or less, Cr: 0.30 to 0.60%, sol. Al: 0.005 to 0.080%, N: 0.0050% or less, balance Fe and impurities, and Cr content and Mn content satisfy the following formula (1).
  • Patent Document 4 aims to provide a steel material that is excellent in wear resistance even when the amount of undissolved carbide is reduced while improving fatigue resistance, in particular, fatigue resistance of low and medium cycles.
  • the mass% of the element M is [M], 10.8 [C] +5.6 [Si] +2.7 [Mn] +0.3 [Cr] ⁇ 13
  • Patent Document 5 discloses a high-carbon steel strip having both cold workability and hardenability for thin plate products such as automobile parts and electrical parts, and a method for producing the same in terms of weight ratio.
  • C 0.15 to 0.75%
  • Si 0.30% or less
  • Mn 0.20 to 1.60%
  • sol. Al less than 0.05%
  • N 0.0060% or less
  • Spheroidization rate represented by the occupation ratio of the spherical structure in which the average particle size of carbide in steel is 0.5 to 2.0 ⁇ m and the major axis / minor axis is ⁇ 5.
  • a high carbon steel strip excellent in cold forgeability and hardenability has been proposed.
  • Carbide dispersion interval ⁇ sp ( ⁇ m) ⁇ 10 6 /(3.14 ⁇ average ⁇ n) ⁇ 0.5 ⁇ 2.3 (1)
  • ⁇ n is a region of a depth of 1 ⁇ 4 depth from the surface of the steel strip, corroded with nital after cross-section polishing, and magnified by 2000 times with a scanning electron microscope, and has a field of view of 100 ⁇ 100 ⁇ m.
  • the numerical value of the number of carbide particles divided and measured is converted to the number in a 1 mm 2 region, the unit is n / mm 2 , and the average value of 16 fields is the average ⁇ n (n / mm 2 ).
  • Patent Document 6 C: 0.1 to 1.5% by weight, Si: 2.0 is provided for the purpose of providing a high carbon steel sheet having no difference in mechanical properties in the rolling direction and the orthogonal direction. Less than wt%, Mn: 0.2 to 2.5 wt%, S: less than 0.002 wt%, composition of balance Fe and inevitable impurities, direction perpendicular to rolling direction with respect to elongation and impact value in rolling direction
  • the average length of inclusions in the rolling direction is 6 ⁇ m or less so that the in-plane anisotropy index defined by the ratio between the elongation and the impact value is 0.9 to 1.0.
  • a high carbon steel sheet having a small in-plane anisotropy has been proposed in which the number of inclusions having a length of 4 ⁇ m or less is 80% or more of all inclusions.
  • Japanese Patent No. 4903839 Japanese Unexamined Patent Publication No. 2011-12317 Japanese Patent No. 4371702 Japanese Unexamined Patent Publication No. 2012-1794 Japanese Patent No. 3468172 Japanese Patent No. 3910242
  • the present invention has been made paying attention to the above circumstances, and an object of the present invention is to provide a soft high-carbon steel sheet that is excellent in cold workability in a softened state and contributes to improvement of component accuracy.
  • the present invention provides the following (1) to (4).
  • Each having a component composition consisting of iron and inevitable impurities Regarding ferrite crystal grains present at a position of depth t / 4 when the plate thickness is represented by t, The area ratio of ferrite crystal grains whose plate plane orientation is within 10 ° from the (123) plane is 20% or more,
  • a soft high carbon steel sheet characterized in that an average grain size of ferrite crystal grains existing at a position of the depth t / 4 is 3 to 50 ⁇ m.
  • the area ratio of the ferrite crystal grains having a plane orientation within 10 ° from the (001) plane is 20% or less (1)
  • the component composition is further mass%, Ca: more than 0% and 0.05% or less, REM: more than 0% and 0.05% or less, Mg: more than 0% and 0.02% or less, Li: more than 0% and 0.02% or less, Pb: more than 0% and 0.5% or less, Bi: The soft high carbon steel plate according to (1) or (2), which includes at least one selected from the group consisting of more than 0% and 0.5% or less.
  • the component composition is further mass%, Cr: 0.05 to 1.0%,
  • the present invention it is possible to provide a soft high-carbon steel sheet that is excellent in cold workability in a softened state and contributes to improvement in component accuracy by more strictly controlling the texture form.
  • the steel sheet of the present invention will be described.
  • the steel sheet of the present invention is characterized in that the texture form in the steel is more strictly controlled.
  • the deep drawing workability of a thin steel sheet used for a car body outer plate of an automobile is determined by the plastic anisotropy (r value (rankford value): tensile
  • r value crankford value
  • tensile The greater the ratio between the plate width strain and the plate thickness strain in the test), the higher the workability, and the stronger the ⁇ 111 ⁇ plane parallel to the plane orientation in the recrystallized texture, the ⁇ 100 ⁇ plane orientation
  • the soft high carbon steel sheet of the steel sheet of the present invention is a structural form mainly based on a ferrite phase and spheroidized cementite, and in particular, the plate surface orientation of ferrite crystal grains and the size thereof are controlled within a specific range.
  • the formation of the texture differs depending on the processing method even if the crystal system is the same.
  • a rolled material it is expressed by the rolling surface and the rolling direction. That is, as shown below, the rolling surface is represented by ⁇ xxx ⁇ and the rolling direction is represented by ⁇ >.
  • delta) have shown the integer.
  • the expression of each of these directions is described in, for example, edited by Junichi Nagashima: “Aggregation” (published by Maruzen Co., Ltd.).
  • the ferrite crystal grains present at the position of the depth t / 4 are soft by controlling the area ratio of ferrite crystal grains whose plate plane orientation is within 10 ° from the (123) plane to 20% or more.
  • the cold workability of the high-carbon steel sheet can be improved.
  • t represents the thickness of the softened high carbon steel plate.
  • the ferrite crystal grains present at the position of the depth t / 4 are further softened by controlling the area ratio of ferrite crystal grains whose plate plane orientation is within 10 ° from the (001) plane to 20% or less.
  • the cold workability of the high carbon steel sheet can be further improved.
  • the ferrite crystal grains having the (123) plane as the plate surface orientation have the effect of improving the cold workability in the softened state, and in order to effectively exhibit such an effect, An area ratio of 20% or more is required.
  • the area ratio is preferably 22% or more, more preferably 24% or more, and particularly preferably 26% or more.
  • the (001) plane causes in-plane anisotropy by molding and deteriorates moldability. Therefore, it is preferable to limit the area ratio to 20% or less, further 18% or less, and particularly 15% or less.
  • the structure form was defined with a depth position of 1/4 of the sheet thickness as a representative position.
  • the ferrite crystal grains whose plate surface orientation is within 10 ° from each of the above ideal surface orientations ((123) plane, (001) plane) are considered to have substantially the same action, they have a plate plane orientation within that range. Each area is defined by the area ratio of ferrite crystal grains.
  • the average grain size of ferrite crystal grains constituting the ferrite structure is 3 to 50 ⁇ m in order to improve the workability (drawing workability, bending workability, press workability) of the steel sheet and to satisfy the surface properties after working. It must be in range. If the ferrite crystal grains become too fine, the deformation resistance becomes too high, so the average grain size is 3 ⁇ m or more, preferably 4 ⁇ m or more, and more preferably 5 ⁇ m or more. On the other hand, if the ferrite crystal grains become too coarse, the toughness, fatigue characteristics, etc.
  • the average particle size is 50 ⁇ m or less, preferably 45 ⁇ m or less, and more preferably 40 ⁇ m or less. Similar to the above, there is a size distribution of ferrite crystal grains in the plate thickness direction, but the average grain size of ferrite crystal grains is defined with a depth position of 1/4 of the plate thickness as a representative position.
  • the plate surface orientation of the ferrite crystal grains is measured and analyzed by SEM-EBSP [Electron Back Scattering Pattern and EBSD (Electron Back Scattering Diffraction).
  • SEM-EBSP Electromagnetic Pattern and EBSD (Electron Back Scattering Diffraction).
  • SEM-EBSP Electromagnetic Pattern and EBSD (Electron Back Scattering Diffraction).
  • SEM apparatus for example, SEM (JEOLJSM5410) manufactured by JEOL Ltd. is used, and for example, EBSP: manufactured by TSL (OIM) is used as the EBSP measurement / analysis system.
  • the measurement area of the sample is 300 to 1000 ⁇ m ⁇ 300 to 1000 ⁇ m, and the measurement step interval is 1 to 3 ⁇ m, for example. From the crystal orientation of each ferrite crystal grain thus identified, the total area is calculated by summing the orientations within 10 ° from each ideal surface orientation, and divided by the area of the measurement region. The area ratio for each direction was determined.
  • the average grain size of the ferrite crystal grains is determined by measuring the maximum diameter of each ferrite crystal grain observed in a predetermined measurement region using the SEM-EBSP and measurement conditions thereof, and calculating the average value of the average grain diameters. Obtained as the diameter.
  • the component composition constituting the steel sheet of the present invention will be described.
  • the unit of the content of chemical components is all mass%.
  • the percentage based on mass (% by mass) is the same as the percentage based on weight (% by weight).
  • “X% or less (not including 0%)” may be expressed as “over 0% and X% or less”.
  • Component composition of the steel sheet of the present invention C: 0.65 to 1.0%
  • C is an important element for securing the strength of the steel sheet, and is contained by 0.65% or more to ensure the required strength. In the parts targeted in the present invention, if the C content is less than 0.65%, the hardenability is lowered and the strength as a high-strength steel sheet for machine structures cannot be obtained, so the lower limit is made 0.65%. . If the C content exceeds 1.0%, a long time is required for heat treatment to ensure toughness and workability, so the upper limit is made 1.0%.
  • the content of C is preferably 0.68 to 0.95%, more preferably 0.70 to 0.90%.
  • Si 0.10 to 0.60% Si acts as a deoxidizer and is an effective element for improving hardenability. In the parts targeted by the present invention, if the Si content is less than 0.10%, the effect of addition cannot be obtained, so the lower limit is made 0.10%. If the Si content exceeds 0.60%, the surface properties are deteriorated due to scale defects during hot rolling, so the upper limit is made 0.60%.
  • the Si content is preferably 0.15 to 0.55%, more preferably 0.20 to 0.50%.
  • Mn 0.10 to 1.0%
  • Mn is an element having a deoxidizing and desulfurizing action in the steel making process. Furthermore, it is an element effective for improving hardenability. If the Mn content is less than 0.10%, the addition effect cannot be obtained, so the lower limit is made 0.10%. If the Mn content exceeds 1.0%, impact properties after quenching and tempering are promoted, and the amount of Mn-based inclusions increases, thereby deteriorating cold workability and fatigue resistance. The upper limit is 1.0%.
  • the Mn content is preferably 0.15 to 0.9%, more preferably 0.2 to 0.85%.
  • Al 0.01 to 0.1%
  • Al is an element effective for deoxidation in the steelmaking process, and is an element effective for fixing N. Moreover, it is an additive substance required in order to control the form of the inclusion in this invention. In order to obtain these effects, it is essential that the Al content in the steel material be 0.01% or more, preferably 0.015% or more, and more preferably 0.02% or more. On the other hand, if the Al content exceeds 0.1%, the toughness is lowered and cracking tends to occur, which is unsuitable, preferably 0.09% or less, and more preferably 0.08% or less.
  • P 0.03% or less (excluding 0%)
  • P is an inevitable impurity element, and segregates at the grain boundaries to deteriorate the cold workability. Therefore, it is desirable to reduce the P content as much as possible from the viewpoint of cold workability. However, since extreme reduction leads to an increase in steelmaking cost, considering the process capability, it is 0.03% or less (0%). Not containing), preferably 0.02% or less (not including 0%).
  • S 0.01% or less (excluding 0%) S, like P, is an unavoidable impurity and is an element that precipitates in the form of a film at the grain boundary as FeS and degrades workability. Moreover, S forms a nonmetallic inclusion and becomes a cause of inhibiting workability and toughness after heat treatment. It also has the effect of causing hot brittleness. Therefore, from the viewpoint of improving the deformability, in the present invention, the S content is 0.01% or less, preferably 0.005% or less. However, it is industrially difficult to reduce the S content to zero. In addition, since S also has the effect of improving the punching workability and machinability, it is preferable to contain 0.0003% or more from that viewpoint, and more preferably 0.0005% or more.
  • the steel of the present invention basically contains the above components, and the balance is iron and inevitable impurities, but the following permissible components can be added as long as the effects of the present invention are not impaired.
  • These elements all have the effect of spheroidizing inclusions and reducing the deterioration of cold workability and fatigue resistance. is there.
  • each of them may contain one kind alone or two or more kinds at the same time. The content of these elements is selected within the following range.
  • Ca 0.05% or less (excluding 0%) Ca is an element that spheroidizes sulfide compound inclusions such as MnS to improve the deformability of steel and contribute to the improvement of punching workability and machinability.
  • the Ca content is preferably 0.0005% or more, and more preferably 0.001% or more.
  • the upper limit of the Ca content is preferably 0.05%, more preferably 0.03%. Particularly preferably, it is 0.01%.
  • REM 0.05% or less (excluding 0%) REM is an element that contributes to the improvement of punching workability and machinability as well as Ca by spheroidizing sulfide compound inclusions such as MnS to improve the deformability of steel.
  • content of REM shall be 0.0005% or more, More preferably, it is 0.001% or more.
  • the content of REM is preferably 0.05%, more preferably 0.03%. Particularly preferably, it is 0.01%.
  • REM means a lanthanoid element (15 elements from La to Ln), Sc (scandium) and Y (yttrium).
  • Y yttrium
  • Mg 0.02% or less (excluding 0%) Mg, like Ca, is an element that spheroidizes sulfide compound inclusions such as MnS to enhance the deformability of steel and contribute to the improvement of punching workability and machinability.
  • content of Mg shall be 0.0002% or more, More preferably, it is 0.0005% or more.
  • the upper limit of the Mg content is preferably 0.02%, more preferably 0.015%. Particularly preferably, it is 0.01%.
  • Li 0.02% or less (excluding 0%) Li, like Ca, can spheroidize sulfide compound inclusions such as MnS to improve the deformability of steel, and lower the melting point of Al-based oxides to make them harmless. It is an element that contributes to improved machinability.
  • the Li content is preferably 0.0002% or more, and more preferably 0.0005% or more.
  • the upper limit of the Li content is preferably 0.02%, more preferably 0.015%. Particularly preferably, it is 0.01%.
  • Pb 0.5% or less (excluding 0%)
  • Pb is an effective element for improving machinability.
  • the steel material of this invention contains Pb, Preferably it is 0.005% or more, More preferably, 0.01% or more can be contained. However, if excessively contained, problems in production such as generation of rolling defects occur, so the upper limit of the Pb content is preferably 0.5%, preferably 0.4%, more preferably 0.3%.
  • Bi 0.5% or less (excluding 0%) Bi, like Pb, is an effective element for improving the punching workability and machinability.
  • the steel material of this invention contains Bi, Preferably it is 0.005% or more, More preferably, 0.01% or more can be contained.
  • the upper limit of the Bi content is preferably 0.5%, preferably 0.4%, more preferably 0.3%. %.
  • the steel material of the present invention may further contain at least one selected from the following groups (a) to (e) as necessary, in addition to the above essential components and allowable components. .
  • the content of these elements is selected within the following range.
  • Cr 0.05 to 1.0% Cr is an element effective for improving hardenability, and is an element having an action of improving the deformability of steel by increasing the strength of the grain boundary. As needed, Preferably it is 0.05% or more, More preferably, it can be made to contain 0.06% or more. However, when Cr is excessively contained, deformation resistance increases and cold workability may be lowered. Therefore, the content is preferably 1.0% or less, and more preferably 0.9%. % Or less, particularly preferably 0.8% or less.
  • Cu 0.2% or less (excluding 0%) Cu is an element effective for ensuring hardenability, but the smaller the better in the present invention. If the Cu content exceeds 0.2%, it becomes too hard and the cold workability deteriorates, so the upper limit is made 0.2%. Preferably, it is 0.19% or less, more preferably 0.18% or less.
  • Sn 0.1% or less (excluding 0%) Sn is an inevitable impurity, and the smaller the better in the present invention. If the Sn content exceeds 0.1%, it becomes too hard and cold workability deteriorates, so the upper limit is made 0.1%. Preferably, it is 0.09% or less, more preferably 0.08% or less.
  • Ni 0.2% or less (excluding 0%) Ni is an element effective in improving toughness and hardenability, but the smaller the better in the present invention, the better. If the Ni content exceeds 0.2%, the number of inclusions increases and the performance deteriorates, so the upper limit is made 0.2%. Preferably, it is 0.18% or less, more preferably 0.15% or less.
  • Mo 0.1% or less (excluding 0%) Mo is an effective element having the effects of improving hardenability, improving temper softening resistance, and increasing the hardness and deformability of the steel material after processing, but the smaller the better in the present invention. If Mo is excessively contained, cold workability may be deteriorated. Therefore, the Mo content is preferably 0.1% or less (excluding 0%), and more preferably 0.09% or less. Especially preferably, it is 0.08% or less.
  • Nb 0.1% or less (excluding 0%) Nb is an element that forms carbonitride and is effective in preventing coarsening of crystal grains and improving toughness, but the smaller the better in the present invention. If the Nb content exceeds 0.1%, cold workability and fatigue resistance are deteriorated, so the upper limit is made 0.1%. Preferably, it is 0.08% or less.
  • V 0.01% or less
  • V like Nb, forms a carbonitride and is an element effective for preventing coarsening of crystal grains and improving toughness, but the smaller the better in the present invention, the better. If the V content exceeds 0.01%, carbides are generated and the quenching hardness is lowered, so the upper limit is made 0.01%. Preferably, it is 0.009% or less.
  • B 0.005% or less (excluding 0%)
  • B has a strong affinity with N, coexists with N to form an N compound, refines the crystal grains of steel, improves the toughness of the processed product obtained after cold working, and although it is an element having a role of improving crack resistance, in the present invention, since it is necessary to reduce the amount of the compound, the content of B is preferably as small as possible, and is 0.005% or less (not including 0%). The content is preferably 0.0001 to 0.0035%, more preferably 0.0002 to 0.002%.
  • N 0.01% or less (excluding 0%) N is an element that forms a nitride, and it is necessary to reduce it as much as possible in the present invention. Further, when nitride precipitates during slab bending correction in continuous casting, the slab may break, so the upper limit of the N content is 0.01%. The smaller the N content, the better. However, the reduction to less than 0.001% leads to an increase in refining costs, so the lower limit is made 0.001%. Preferably, it is 0.004 to 0.007%.
  • Ti, Co, and the like may be inevitably included, but in the present invention, all are elements that generate inclusions, and it is preferable that they are not added or reduced as much as possible. .
  • the total amount is preferably 0.01% or less, and more preferably 0.005% or less.
  • a desired oxide can be generated by adding a predetermined alloy element in a predetermined order to molten steel in which the dissolved oxygen amount and the total oxygen amount are adjusted. Particularly in the present invention, it is extremely important to adjust the total oxygen amount after adjusting the dissolved oxygen amount so that coarse oxides are not formed.
  • Dissolved oxygen means oxygen in a free state that does not form oxides and exists in molten steel. Total oxygen means the sum of all oxygen contained in molten steel, that is, free oxygen and oxygen forming oxides.
  • the dissolved oxygen content of the molten steel is adjusted to a range of 0.0010 to 0.0060%.
  • the amount of dissolved oxygen in the molten steel is less than 0.0010%, the amount of dissolved oxygen in the molten steel is insufficient, so that a predetermined amount of Al—O-based oxide cannot be secured, and a desired size distribution cannot be obtained.
  • the amount of dissolved oxygen is set to 0.0010% or more.
  • the amount of dissolved oxygen is preferably 0.0013% or more, more preferably 0.0020% or more.
  • the amount of dissolved oxygen should be suppressed to 0.0060% or less.
  • the amount of dissolved oxygen is preferably 0.0055% or less, more preferably 0.0053% or less.
  • the amount of dissolved oxygen in molten steel primarily refined in a converter or electric furnace usually exceeds 0.010%. Therefore, in the production method of the present invention, it is necessary to adjust the amount of dissolved oxygen in the molten steel to the above range by some method.
  • Examples of the method for adjusting the amount of dissolved oxygen in the molten steel include a method of vacuum C deoxidation using an RH type degassing refining device, a method of adding a deacidifying element such as Si, Mn, and Al.
  • the amount of dissolved oxygen may be adjusted by appropriately combining these methods.
  • a method of adding a deacidifying element such as Si may be adopted to adjust the amount of dissolved oxygen.
  • the deoxidizing element may be added when steel is removed from the converter to the ladle.
  • the molten steel is stirred, and the oxides in the molten steel are floated and separated so that the total oxygen content in the molten steel is 0.0010 to 0.00. Adjust to 0070%.
  • the molten steel in which the amount of dissolved oxygen is appropriately controlled is stirred to remove unnecessary oxides, and then generation of coarse oxides, that is, coarse inclusions can be prevented.
  • the total oxygen amount is set to 0.0010% or more.
  • the total oxygen amount is preferably 0.0015% or more, more preferably 0.0018% or more.
  • the total oxygen amount should be suppressed to 0.0070% or less.
  • the total oxygen amount is preferably 0.0060% or less, more preferably 0.0050% or less.
  • the total amount of oxygen in the molten steel changes generally in correlation with the stirring time of the molten steel, it can be controlled by adjusting the stirring time. Specifically, the total amount of oxygen in the molten steel is appropriately controlled while appropriately measuring the total amount of oxygen in the molten steel after stirring the molten steel and removing the floating oxide.
  • the desired oxide can be obtained by adding the above elements to the molten steel with the total oxygen content adjusted.
  • the form of REM added to the molten steel is not particularly limited.
  • REM pure La, pure Ce, pure Y, etc.
  • pure Ca Fe—Si—La alloy, Fe—Si—Ce alloy, Fe— A Si—Ca alloy, a Fe—Si—La—Ce alloy, a Fe—Ca alloy, a Ni—Ca alloy, or the like may be added.
  • Misch metal is a mixture of cerium group rare earth elements, and specifically contains about 40 to 50% Ce and about 20 to 40% La.
  • misch metal often contains Ca as an impurity, when the misch metal contains Ca, it is necessary to satisfy the preferred range defined in the present invention.
  • the stirring time is preferably within 40 minutes.
  • the stirring time is more preferably within 35 minutes, and further preferably within 30 minutes.
  • the lower limit of the stirring time of the molten steel is not particularly limited, but if the stirring time is too short, the concentration of the additive element becomes non-uniform, and the desired effect cannot be obtained as a whole steel material. Accordingly, a desired stirring time corresponding to the container size is required.
  • molten steel with an adjusted composition can be obtained. It casts using the obtained molten steel, and obtains a steel piece.
  • manufacturing is performed by heating, hot rolling including finish rolling, rapid cooling after hot rolling, slow cooling after quenching stop, rapid cooling after slow cooling, and winding.
  • Heating before hot rolling is performed at 1150 to 1300 ° C.
  • An austenite single phase is obtained by this heating.
  • solid solution elements including impurities such as V and Nb
  • the heating temperature is less than 1150 ° C., it cannot be dissolved in austenite, and coarse carbides are formed, so that the effect of improving fatigue characteristics cannot be obtained.
  • temperatures exceeding 1300 ° C. are difficult to operate.
  • TiC solution solution temperature or higher and 1300 ° C. or lower are necessary also in terms of solid solution of Ti having the highest solution temperature among carbides.
  • the preferable lower limit of the heating temperature is 1150 ° C, and the more preferable lower limit is 1200 ° C.
  • Hot rolling is performed so that the finish rolling temperature is 800 ° C. or higher. If the finish rolling temperature is too low, ferrite transformation occurs at a high temperature and the precipitated carbides in the ferrite are coarsened, so that a certain finish rolling temperature is required.
  • the finish rolling temperature is more preferably 850 ° C. or higher in order to coarsen austenite grains and increase the grain size of bainite.
  • the upper limit of the finish rolling temperature is set to 1000 ° C. because it is difficult to secure the temperature.
  • the quenching stop temperature is preferably 600 to 650 ° C, more preferably 610 to 640 ° C.
  • the slow cooling rate is less than 5 ° C./s, the amount of pro-eutectoid ferrite is increased and coarse grains are produced, and coarse grains are produced in the final steel plate, resulting in a non-uniform state of carbides, resulting in cold workability. Deteriorate.
  • annealing is performed for softening and carbide spheroidization before cold rolling.
  • Softening annealing is performed by heating the steel sheet from room temperature to Ac1 to Ac1 + 50 ° C. in an atmosphere of H 2 : 15 to 20% by volume and holding for 10 hours or more. This holding for 10 hours or more promotes the spheroidization of carbides and dissolves the fine lamellae in austenite. After holding for 10 hours or more, the steel sheet is cooled to about 400 ° C. at 10 ° C./h or more.
  • Softening (spheroidizing) annealing After cold rolling, annealing is performed for softening and carbide spheroidization. Softening annealing is performed in an atmosphere of H 2 : 15 to 20% by volume, after heating the steel sheet from room temperature to Ac1 to Ac1-50 ° C. and holding for 10 hours or more, or after heating to Ac1 to Ac1 + 50 ° C. Hold for 5 hours or more. Depending on the plate thickness and the size of the coil, it is selected depending on the required spheroidization, softening degree, and uniformity in the coil. This heat treatment promotes spheroidization of carbides and dissolves fine lamellae in austenite.
  • the steel sheet After holding for 10 hours or more, the steel sheet is cooled to 600 ° C. at a rate of 10 ° C./h or less. In this way, spheroidization of carbide is promoted, and cooling is performed at a rate of 15 ° C./h or less up to 600 to 400 ° C. This is to stabilize the shape such as coil collapse by cooling the inside of the coil uniformly. Thereafter, at a temperature of 400 ° C. or lower, cooling can be performed at a high cooling rate (such as about 50 ° C. to 100 ° C./h or higher) by water cooling or the like if the temperature distribution in the coil can be uniformly cooled.
  • a high cooling rate such as about 50 ° C. to 100 ° C./h or higher
  • a test steel containing chemical components shown in Table 1 below was melted, cast into a 150 kg ingot, and cooled.
  • the components are adjusted for elements other than Al, REM, and Ca, and deoxidized using at least one element selected from C, Si, and Mn.
  • the amount of dissolved oxygen in the molten steel was adjusted.
  • the total amount of oxygen in the molten steel was adjusted by stirring the molten steel in which the amount of dissolved oxygen was adjusted for about 1 to 10 minutes to float and separate oxides in the molten steel.
  • the molten steel which adjusted the component was obtained by adding to the molten steel which adjusted the total amount of added oxygen.
  • REM was added in the form of a misch metal containing about 25% La and about 50% Ce
  • Ca was added in the form of a Ni—Ca alloy, a Ca—Si alloy, or a Fe—Ca compact. .
  • the obtained ingot was hot-rolled under the conditions shown in Table 2 below to produce a hot-rolled sheet having a thickness of 4 mm.
  • the cooling rate until the quenching stop after the finish rolling was finished was 20 ° C./s or more.
  • the hot-rolled sheet is heated from room temperature to 700 ° C. in 20 hours, maintained at 700 ° C. ⁇ 25 hours, and annealed in a pattern of cooling from 700 ° C. to 500 ° C. in 10 hours, followed by cold rolling.
  • a cold-rolled sheet having a thickness of 2 mm was manufactured.
  • ⁇ Surface hardness> Using a Vickers hardness tester, the load is 1000 g, the measurement position is the surface of the steel sheet, the number of measurements is 5 times, and the Vickers hardness (Hv) is measured. When the hardness deteriorates and the hardness becomes too high, the workability deteriorates.
  • ⁇ Punching workability> A shearing test of the steel sheet was performed, and when the crack occurred at the fracture surface, ⁇ , when a visible crack of about 1 mm was seen ⁇ , no crack was generated, but a burr exceeding 30 ⁇ m was generated The case where the occurrence of burr was small (30 ⁇ m or less) was evaluated as “ ⁇ ”, and the case where “ ⁇ ” or “ ⁇ ” was passed.
  • Yield ratio is defined by [Yield point] / [Tensile strength].
  • the low “yield ratio” means that the difference between tensile strength and yield point is large and the range of stress showing uniform elongation is Since it is wide, it means that it is easy to be plastically processed, that is, it is excellent in cold workability.
  • a product having a yield ratio in the rolling direction of 0.80 or less was accepted. Preferably it is 0.78 or less, More preferably, it is 0.76 or less.
  • the in-plane anisotropy is also small. It is recommended that the difference between the yield ratio in the rolling direction and the yield ratio in the direction perpendicular to the rolling direction (the direction perpendicular to the rolling direction) is less than 0.1, further 0.08 or less, and particularly 0.06 or less.
  • Reference numerals 1,3,4,6,10,15,19-26 are comparative steels that do not satisfy at least one of the compositional composition and the structural requirements specified in the present invention, and the surface hardness, punching workability and rolling direction. At least one of the yield ratios does not meet the acceptance criteria.
  • sample no. 2, 5, 7 to 9, 11 to 14, and 16 to 18 are all manufactured using the steel grade satisfying the range of the composition of the present invention under the recommended production conditions. It is a satisfactory invention steel, and the surface hardness, punching workability and yield ratio in the rolling direction all meet the acceptance criteria, excellent cold workability in the softened state, and contributing to improved component accuracy It was confirmed that a carbon steel plate was obtained.

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Abstract

　La présente invention concerne une tôle d'acier doux à teneur élevée en carbone comprenant de 0,65 à 1,0 % de C, de 0,10 à 0,60 % de Si, de 0,10 à 1,0 % de Mn, de 0,01 à 0,1 % d'Al, plus de 0 % et jusqu'à 0,03 % de P, et plus de 0 % et jusqu'à 0,01 % de S (pourcentages donnés en masse), le complément comprenant du fer et des impuretés inévitables. La surface des grains de cristaux de ferrite, présents à une profondeur de t/4 (t : épaisseur de la tôle) et ayant une orientation de surface de tôle inférieure ou égale à 10° par rapport au plan (123), est supérieure ou égale à 20 %, et le diamètre moyen des grains de cristaux de ferrite présents à la profondeur de t/4 est compris entre 3 et 50 µm.
PCT/JP2014/070570 2013-08-07 2014-08-05 Tôle d'acier doux à teneur élevée en carbone Ceased WO2015020028A1 (fr)

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JP6443126B2 (ja) * 2015-02-26 2018-12-26 新日鐵住金株式会社 フェライト系薄鋼板
JP7606070B2 (ja) * 2020-09-18 2024-12-25 日本製鉄株式会社 高炭素鋼板

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AU2021425738B2 (en) * 2021-02-02 2024-05-23 Tata Steel Limited A method for producing spheroidized or non-lamellar microstructure steels

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