WO2020259531A1 - 一种厚向变强度硬度冷轧带钢及其制造方法 - Google Patents

一种厚向变强度硬度冷轧带钢及其制造方法 Download PDF

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WO2020259531A1
WO2020259531A1 PCT/CN2020/097893 CN2020097893W WO2020259531A1 WO 2020259531 A1 WO2020259531 A1 WO 2020259531A1 CN 2020097893 W CN2020097893 W CN 2020097893W WO 2020259531 A1 WO2020259531 A1 WO 2020259531A1
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cold
hardness
steel strip
strength
rolled steel
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PCT/CN2020/097893
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English (en)
French (fr)
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朱晓东
薛鹏
李伟
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宝山钢铁股份有限公司
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Priority to CA3144242A priority Critical patent/CA3144242A1/en
Priority to US17/619,345 priority patent/US20220235429A1/en
Priority to JP2021576725A priority patent/JP7479407B2/ja
Priority to EP20833231.2A priority patent/EP3988681A4/en
Publication of WO2020259531A1 publication Critical patent/WO2020259531A1/zh

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    • C—CHEMISTRY; METALLURGY
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    • 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
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    • 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
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    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
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    • C21D6/00—Heat treatment of ferrous alloys
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    • C21D6/00—Heat treatment of ferrous alloys
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    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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    • 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
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    • 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
    • C21D8/0236—Cold rolling
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    • 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
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    • 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
    • C21D8/0294—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a localised treatment
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0062—Heat-treating apparatus with a cooling or quenching zone
    • 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
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    • 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
    • C22C38/04—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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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    • 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
    • C21D2221/00—Treating localised areas of an article
    • 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
    • C21D2221/00—Treating localised areas of an article
    • C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively

Definitions

  • the invention relates to a strip steel and a manufacturing method thereof, in particular to a cold rolled strip steel and a manufacturing method thereof.
  • the automobile industry requires the use of higher-strength steel plates for weight reduction and safety requirements.
  • the manufacture of cold-rolled advanced high-strength steel sheets for automobiles generally relies on rapid cooling in the continuous annealing process. Rapid cooling is conducive to the transformation of austenite to martensite, bainite and other structures to obtain high strength.
  • high-strength steel plates are mostly obtained by the traditional uniform rapid cooling method, that is, the temperature at which the rapid cooling of the steel plate starts and the temperature at which the rapid cooling ends is the same, and the cooling rate of the two surfaces of the steel plate is also the same. Obtain a steel plate with uniform strength.
  • the publication number is CN102822375A
  • the publication date is December 12, 2012
  • the Chinese patent document entitled "Ultra-high-strength cold-rolled steel sheet and its manufacturing method” discloses an ultra-high-strength cold-rolled steel sheet and its manufacturing method.
  • the chemical composition is C: 0.05-0.4%, Si: 2.0% or less, Mn: 1.0-3.0%, P: 0.05% or less, S: 0.02% or less, Al: 0.01- 0.05%, N: less than 0.005%
  • the steel involved in this document is continuously annealed from Ac3 to a cooling rate of 20°C/s or more (gas cooling) to the range of Ms point-Ms point + 200°C, After maintaining for 0.1-60s, at a cooling rate of 100°C/s or more (water cooling), cooling to below 100°C, a high-strength steel with a tensile strength of 1320MPa or more is obtained, and the flatness of the steel plate is below 10mm.
  • the technical solution disclosed in the patent document uses a uniform rapid cooling process.
  • the publication number is CN102953002A
  • the publication date is March 6, 2013,
  • the Chinese patent document entitled "High-strength steel sheet with excellent seam weldability" discloses a high-strength steel sheet with excellent seam weldability.
  • C 0.12-0.4%
  • Si 0.003-0.5%
  • Mn 0.01-1.5%
  • P 0.02% or less
  • S 0.01% or less
  • Al 0.032-0.15%
  • N 0.01% or less
  • Ti 0.01-0.2%
  • B 0.0001% to 0.001%
  • the steel structure is a single martensite structure.
  • the tensile strength of the steel is above 1180 MPa, and it also uses a uniform rapid cooling process.
  • phase-change-strengthened high-strength steel sheets in the prior art although they belong to different strength levels and adopt different quenching processes, all use uniformly cooled quenching processes, so their final
  • the obtained steel plate has uniform properties, and the strength and hardness in the thickness direction are basically the same.
  • One of the objectives of the present invention is to provide a method for manufacturing a thickness-variable strength/hardness cold-rolled strip steel, which realizes the asymmetric mechanical properties of the strip steel by performing an asymmetric quenching and cooling process on the strip steel Distribution, so as to obtain a gradual hardness/strength gradient along the thickness direction, so as to obtain the combined properties of high hardness, high strength and excellent ductility and formability at the same time.
  • the present invention proposes a method for manufacturing cold-rolled steel strip with variable strength hardness in the thickness direction, which includes the steps of smelting, continuous casting, hot rolling, cold rolling and continuous annealing; wherein, the continuous annealing step is performed During quenching, an asymmetric quenching cooling process is performed on the two surfaces of the strip.
  • austenite is transformed into martensite or bainite, thereby achieving hardening of the steel.
  • the two surfaces of the strip are cooled from the same initial cooling temperature at the same cooling rate to the same quenching termination temperature at the same time. It is completely the same and symmetrical, and the mechanical properties of the obtained quenched steel plates are also completely symmetrical and uniform).
  • This technical solution designs an asymmetric quenching cooling technology, so that the strip can obtain a thickness-wise asymmetric strip mechanical properties.
  • the thickness-direction variable-strength hardness cold-rolled strip steel in this case is the thickness-direction variable strength (or hardness), that is, the upper and lower surfaces of the strip have different strengths (or hardness). Between the two surfaces of the strip, the strength (or hardness) from one surface of the strip to the other surface of the strip changes and transitions gradually.
  • the side with higher hardness can be used for anti-friction and indentation resistance, while the side with lower hardness along the thickness direction and the transition part have strength and hardness.
  • the continuous decrease, along with the continuous improvement of toughness and elongation, is conducive to the improvement of the formability and toughness of strip steel.
  • this case utilizes the characteristics of quenching and hardening of phase-change-strengthened steel, and adopts an asymmetric quenching and cooling process on the two surfaces of the strip during the quenching rapid cooling process of continuous annealing. Therefore, the thickness-variable strength/hardness cold-rolled steel strip finally obtained by the manufacturing method of the present invention can be suitable for demanding applications with high requirements on strength, hardness, plasticity, and formability.
  • the cold-rolled strip steel with variable strength hardness can provide high hardness of a single surface, high friction and indentation resistance, and the overall strip formability and toughness are relatively high.
  • the asymmetric quenching and cooling process includes at least one of the following items:
  • the cooling start temperature of the two surfaces of the strip is asymmetrical
  • the cooling termination temperature of the two surfaces of the strip is asymmetrical
  • the cooling rate of the two surfaces of the strip is asymmetrical.
  • the use of different strip steel surfaces with asymmetric cooling start temperatures, or asymmetric cooling end temperatures on the two surfaces of the strip steel, or asymmetric cooling speeds on the two surfaces of the strip can make the Different cooling paths are formed on both sides of the strip, or any combination of these three conditions, so that the final thickness-variable-strength cold-rolled strip steel contains a difference in ferrite and martensite/bainite content Different, so that the difference in the thickness strength of the two sides of the strip is different.
  • the cooling medium used can be water mist cooling (for example, gas-water mixed injection) or gas cooling.
  • a gas medium a gas containing nitrogen and optional hydrogen can be used, wherein the gas volume percentage of hydrogen is 0-75%.
  • a mixed gas of hydrogen and nitrogen is used, wherein the gas volume percentage of hydrogen is greater than 0% to less than or equal to 75%.
  • the difference between the cooling onset temperature of the two surfaces of the strip is 20-100°C.
  • the initial cooling temperature of both sides is in the range of 650-750°C.
  • the difference in the cooling start temperature is less than 20°C
  • the difference in the strength or hardness of the cold-rolled steel strip with variable strength hardness in the thickness direction is not obvious enough, and if the difference in the cooling start temperature is If the temperature is higher than 100°C, the strength or hardness of one side of the strip may be too low, and the overall strength or hardness may be too low.
  • the difference in the cooling start temperature of the two surfaces can be preferably controlled within the range of 20-100°C.
  • the cooling onset temperature of the two surfaces of the strip is asymmetric
  • the cooling onset temperature is 25-100°C.
  • the difference between the cooling termination temperature of the two surfaces of the strip is 40 -200°C.
  • the cooling termination temperature of both surfaces is in the range of 50-400°C.
  • the difference in cooling termination temperature is less than 40°C
  • the difference in strength or hardness of the thickness direction variable strength hardness cold-rolled steel strip in the thickness direction is not obvious enough, and if the cooling termination temperature difference is higher than 200 °C, will cause the strength or hardness of one side of the strip to be too low, which may result in the overall strength or hardness of the strip being too low.
  • the difference between the cooling termination temperatures of the two surfaces can be preferably controlled within the range of 40-200°C.
  • the difference between the cooling termination temperature of the two surfaces of the steel strip is 50-180°C.
  • the difference between the cooling rates of the two surfaces of the steel strip is 25-200 °C/s.
  • the cooling rate of the two sides is ⁇ 30°C/s, which can be in the range of 30-500°C.
  • the difference in cooling rate is less than 25°C/s, the difference in strength or hardness of the strip in the thickness direction is not obvious enough, and if the difference in cooling rate is higher than 200°C/s, it will If the strength or hardness of one side of the strip is too low, the overall strength or strength of the strip may be too low.
  • the difference between the cooling rates of the two surfaces can be preferably controlled within the range of 25-200°C/s.
  • the difference between the cooling rates of the two surfaces of the steel strip is 40- 200°C/s.
  • the cooling rate of the side with the higher initial cooling temperature can be higher than the cooling rate of the other side, or lower than the cooling rate of the other side.
  • the cooling start temperature of the two surfaces the difference, the cooling rate, and the difference between them, the cooling end temperature of the side with the higher cooling start temperature is usually higher than the cooling end temperature of the other side, or lower than the cooling end temperature of the other side. Termination temperature.
  • the side with a higher cooling start temperature has a higher cooling rate than the other side, and the cooling end temperature is lower than the other side.
  • another object of the present invention is to provide a cold-rolled steel strip with variable-strength hardness in the thick direction, which can be used for anti-friction and indentation resistance on the side with higher hardness.
  • the strength and hardness continue to decrease, while the toughness and elongation continue to increase, which is conducive to the improvement of the formability and toughness of the strip, making the overall formability and toughness of the strip Relatively high.
  • the present invention proposes a thick-direction variable-strength hardness cold-rolled steel strip which is produced by the above-mentioned manufacturing method.
  • the thickness of the cold rolled steel strip with variable strength hardness in the thickness direction is 1.0 mm and above.
  • the inventor of this case found through research that when the thickness of the strip steel is less than 1.0 mm, due to the heat transfer performance of the strip steel itself, it is difficult to obtain a more obvious difference in the asymmetric strength in the thickness direction. Therefore, the greater the thickness of the strip, the better the degree of asymmetry in the thickness direction can be obtained. From this point of view, it is preferable to set the thickness of the cold-rolled strip with variable strength hardness in the thickness direction to 1.0mm and above, so that it is easier to obtain a higher degree of asymmetry. Good thickness-wise hardness asymmetric effect.
  • the thickness of the thick-direction variable-strength hardness cold-rolled steel strip is 1.4-2.5 mm.
  • the mass percentage of chemical elements is: C 0.06-0.3wt%, Si 0.01-2.5wt%, Mn 0.5-3wt%, Al 0.02-0.08wt%, the balance is Fe and other unavoidable impurities.
  • the present invention provides a cold-rolled steel strip with variable strength and hardness in the thickness direction
  • the mass percentage of chemical elements is: C 0.06-0.3wt%, Si 0.01-2.5wt%, Mn 0.5-3wt%, Al 0.02-0.08wt%, the remainder is Fe and other unavoidable impurities
  • the yield strength of the cold-rolled steel strip with variable strength hardness in the thickness direction is ⁇ 420MPa, tensile strength ⁇ 800MPa, elongation ⁇ 11%, two
  • the difference in surface hardness is at least 20HV.
  • the thickness-direction variable strength hardness cold-rolled steel strip further contains at least one of Cr, Mo and B, wherein the content of Cr is ⁇ 0.2%, the content of Mo is ⁇ 0.2%, and the content of B is ⁇ 0.0035%.
  • the B content of the cold-rolled steel strip with variable strength hardness in the thickness direction is less than 0.0005 wt%, and Cr+Mn+Mo ⁇ 3.5 wt%.
  • the B content of the thickness-variable-strength hardness cold rolled steel strip ranges from 0.0005 to 0.0035 wt%, and Cr+Mn+Mo ⁇ 2.5 wt%.
  • the thickness-direction variable-strength hardness cold-rolled steel strip further contains at least one of V, Ti, Nb and W, the content of which satisfies V+Ti+Nb+W ⁇ 0.2wt%; preferably, V ⁇ 0.1%, Ti ⁇ 0.05%, Nb ⁇ 0.05%, W ⁇ 0.2%.
  • the thickness of the cold-rolled steel strip with variable strength hardness in the thickness direction is above 1.0 mm, preferably 1.4-2.5 mm.
  • the mass percentage ratio of chemical elements of the cold-rolled steel strip with variable strength hardness in any one of the embodiments is: C 0.09-0.2wt%, Si 0.3-1.2wt%, Mn 1.5-2.5wt%, Al 0.02-0.08wt%, the balance is Fe and other unavoidable impurities.
  • the yield strength of the cold-rolled steel strip with variable strength hardness in any of the embodiments is 435-900MPa
  • the tensile strength is 820-1260MPa
  • the elongation is 11-20%
  • the hardness difference between the two faces is 35-80HV.
  • the inventor of the present case considered that the thickness-variable-strength cold-rolled steel strip needs to have certain hardenability. Therefore, in the thickness-variable-strength cold-rolled steel strip of the present invention, the above-mentioned various The mass ratio of chemical elements, and the design principles of each chemical element are as follows:
  • the strength is improved by affecting the martensite hardness. If the carbon content is too low, the martensite cannot be hardened, or the strength itself after quenching is low, and the contradiction between toughness and plasticity is not prominent; however, if the carbon content is too high, the martensite is harder, the toughness is too low, and delayed cracking tends to occur. Based on this, in order to obtain a good thickness-variable hardness effect, the mass percentage of C of the cold-rolled steel strip with thickness-variable strength hardness according to the present invention can be controlled within 0.06-0.3wt%. In some preferred embodiments, the mass percentage of C is controlled within 0.09-0.2%.
  • Si has little effect on hardenability. Based on this, the mass percentage of Si in the thickness-variable-strength cold-rolled steel strip according to the present invention can be controlled at 0.01-2.5 wt%. In some preferred embodiments, the mass percentage of Si is controlled at 0.3-1.2%.
  • Mn is the main element to improve the hardenability of steel.
  • the content of Mn needs to match the cooling capacity of the selected cooling method to obtain good thickness asymmetric strength results. If the mass percentage of Mn is too low, the strip cannot Hardening can not obtain the effect of changing the strength in the thickness direction; but if the mass percentage of Mn is too high and the hardenability is too high, the effect of changing the strength in the thickness direction cannot be obtained as well.
  • the mass percentage of Mn in the thickness-variable-strength hardness cold-rolled steel strip according to the present invention can be controlled at 0.5-3wt%. In some preferred embodiments, the mass percentage of Mn is controlled at 1.5-2.5%.
  • Al The role of Al is to deoxidize and refine austenite grains. Therefore, in the technical solution of the present invention, the mass percentage of Al is controlled to be 0.02-0.08 wt%.
  • unavoidable impurity elements mainly include P, S and N.
  • the impurity elements should be controlled as little as possible.
  • P 0.015%, S ⁇ 0.005%, and N ⁇ 0.03%.
  • the cold-rolled steel strip with variable strength hardness according to the present invention further contains at least one of Cr, Mo and B, wherein: when B ⁇ 0.0005wt%, Cr+Mn+Mo ⁇ 3.5 wt%; when the B content ranges from 0.0005 to 0.0035wt%, Cr+Mn+Mo ⁇ 2.5wt%.
  • the content of Cr does not exceed 0.2%, preferably not more than 0.15%; when contained, the content of Mo does not exceed 0.2%, preferably not more than 0.1%; when contained, the content of B does not exceed 0.0035% ,
  • the content of Cr does not exceed 0.2%, preferably not more than 0.15%
  • Mo does not exceed 0.2%, preferably not more than 0.1%
  • the content of B does not exceed 0.0035% ,
  • the range of 0.0005 to 0.0035 wt% or 0.001 to 0.002 wt% is preferably in the range of 0.0005 to 0.0035 wt% or 0.001 to 0.002 wt%.
  • the thickness-variable-strength hardness cold-rolled steel strip according to the present invention further contains at least one of V, Ti, Nb and W, and its content satisfies V+Ti+Nb+W ⁇ 0.2wt%.
  • the content of V does not exceed 0.1%, preferably not more than 0.05%
  • the content of Ti does not exceed 0.05%, preferably not more than 0.03%
  • the content of Nb does not exceed 0.05%
  • when contained, the content of W does not exceed 0.2%, preferably does not exceed 0.1%
  • V+Ti+Nb+W ⁇ 0.2wt% when contained, the content of V does not exceed 0.1%, preferably not more than 0.05%; when contained, the content of Ti does not exceed 0.05%, preferably not more than 0.03%
  • the content of Nb does not exceed 0.05%
  • the content of W does not exceed 0.2%, preferably does not exceed 0.1%
  • V+Ti+Nb+W ⁇ 0.2wt% when
  • the thickness-variable-strength-hardness cold-rolled steel strip and its manufacturing method according to the present invention have the following advantages and beneficial effects:
  • the manufacturing method of the present invention adopts the thickness-wise asymmetric cooling technology to obtain the asymmetrical thickness (hardness) distribution of the phase-change-strengthened steel strip, so that it has one side strength and high hardness, and the other side is shaped , Good toughness.
  • the hardness or strength along the thickness direction is gradually changed, which makes the obtained thickness-direction variable-strength hardness cold-rolled strip suitable for single
  • the surface hardness is high, the anti-friction and anti-indentation performance is good, and the overall application needs good toughness.
  • the yield strength of the cold-rolled steel strip with variable strength hardness in the present invention is ⁇ 420MPa, tensile strength ⁇ 800MPa, elongation ⁇ 11%, hardness on one side ⁇ 220HV, and hardness on the other side ⁇ 200HV. More specifically, in some preferred embodiments, the yield strength of the cold-rolled steel strip with variable strength hardness in the present invention is 435-900MPa, the tensile strength is 820-1260MPa, and the elongation is 11-20%. , The hardness of one side is 235-380HV, and the hardness of the other side is 200-330HV.
  • the hardness difference between the two faces of the cold rolled steel strip with variable strength hardness in the present invention is at least 30HV, preferably at least 35HV.
  • the hardness difference between the two sides of the cold rolled steel strip with variable strength hardness of the present invention is in the range of 35-80HV, which is beneficial to obtain better practical performance, as well as strength, plasticity and toughness. balance.
  • Fig. 1 schematically shows the cooling process of the thick-direction variable-strength hardness cold-rolled steel strip according to the present invention in some embodiments.
  • Fig. 2 schematically shows the cooling process of the thick-direction variable-strength hardness cold-rolled steel strip according to the present invention in other embodiments.
  • Fig. 3 schematically shows the cooling process of the thick-direction variable-strength hardness cold-rolled steel strip according to the present invention in other embodiments.
  • the thickness-direction variable-strength hardness cold-rolled steel strips of the foregoing Examples 1-6 are prepared by the following steps:
  • the slab heating temperature can be 1170-1230°C
  • the final rolling temperature can be 850-910°C
  • the coiling temperature can be 570-630°C, and then pickling can be carried out to remove surface oxide scale.
  • the strip steel after the hot rolling, can be cold rolled, and the cold rolling reduction rate can be controlled at 30-65%, and then the continuous annealing described in the above step (4) is performed.
  • Table 1 lists the mass percentage ratio of each chemical element of the cold rolled steel strip with variable strength hardness in the thickness direction of Examples 1-6.
  • Table 2 lists the specific process parameters in the continuous annealing step of the thickness-variable-strength hardness cold-rolled steel strips of Examples 1-6.
  • Comparative Example 1 uses the mass ratio of each chemical element shown in Example 1 for smelting
  • Comparative Example 2 uses the mass ratio of each chemical element shown in Example 3 for smelting.
  • Comparative Example 3 The mass ratio of each chemical element shown in Example 5 was used for smelting.
  • Example 7 the mass ratio of each chemical element of Example 1 shown in Table 1 was used for smelting.
  • Example 8 the mass ratio of each chemical element of Example 2 shown in Table 1 was used for smelting.
  • one of the surfaces is called the I surface, and the other surface opposite to the I surface is the II surface.
  • Table 3 lists the performance test results of the cold-rolled steel strips with variable thickness and hardness in Examples 1-8 of this case.
  • the strip steel of Comparative Examples 1-3 adopts the existing technology, so the cooling on both sides of the strip steel is completely the same and symmetrical, and the mechanical properties of the quenched steel plate obtained are also completely symmetrical and symmetrical. average.
  • the thickness-variable hardness cold-rolled steel strips of each embodiment 1-8 of this case realized the asymmetrical mechanical property distribution of the strip steel through the asymmetrical quenching and cooling process of the strip steel, thereby obtaining a gradual change along the thickness direction.
  • the strength/hardness gradient in order to obtain the combined properties of high hardness, high strength and excellent ductility and formability at the same time.
  • Figures 1 to 3 show that different embodiments adopt different asymmetric quenching and cooling processes.
  • FIG. 1 schematically shows the cooling process of the thick-direction variable-strength hardness cold-rolled steel strip according to the present invention in some embodiments.
  • the initial cooling temperature of the two sides of the strip is different.
  • the I surface is first sprayed and cooled by the nozzle of the cooling template 2, and the II surface is subsequently sprayed by the cooling nozzle. Therefore, different cooling paths can be formed on both sides of the strip.
  • the rapid cooling start temperature and cooling length of different surfaces are different, which leads to different rapid cooling termination temperatures, and ultimately leads to different surfaces of ferrite and martensite/ The difference in bainite content ultimately leads to the difference in the strength of the strip in the thickness direction.
  • the use of the asymmetric cooling process shown in Figure 1 makes the steel surface I have high hardness, less ferrite content, more martensite content, and less bainite content, while the II side hardness is lower and less ferrite content. , The content of martensite is less, and the content of bainite is more.
  • Fig. 2 schematically shows the cooling process of the thick-direction variable-strength hardness cold-rolled steel strip according to the present invention in other embodiments.
  • the cooling start temperature of both sides of the strip is the same, but the ending temperature is different.
  • the cooling nozzle of the corresponding cooling module 2 on the II side of the strip is The cooling process ends first, and the cooling nozzles corresponding to the I surface continue to cool to a lower temperature, thereby forming different cooling paths on both sides of the strip, and finally leading to a difference in the cooling termination temperature of the I and II surfaces of the strip. This in turn leads to the difference in ferrite and martensite/bainite content, and ultimately to the difference in the strength of the strip in the thickness direction.
  • Fig. 3 schematically shows the cooling process of the thick-direction variable-strength hardness cold-rolled steel strip according to the present invention in other embodiments.
  • the cooling start temperature on both sides of the strip steel is the same, and the ending time is also the same, but due to the cooling of the cooling modules 2 arranged on both sides of the strip steel
  • the cooling capacity of the nozzles is different.
  • the cooling speed of the nozzle corresponding to the I surface of the strip is faster, and the cooling speed of the nozzle corresponding to the II surface is relatively slow.
  • different cooling paths are formed on both sides of the strip, that is to say, the cooling rate is different, resulting in a difference in the content of ferrite and martensite/bainite, and finally a difference in the strength of the strip in the thickness direction.
  • the difference in cooling speed can be caused by the different cooling medium sprayed through the nozzle or by adjusting the spraying speed or flow rate of the cooling medium, resulting in different cooling speeds on the I and II sides.
  • the medium with high thermal energy either has a higher ejection speed or a higher flow rate, so as to achieve a faster cooling rate.
  • cooling processes illustrated in FIG. 1, FIG. 2 or FIG. 3 described above may also be combined to realize an asymmetric quenching cooling method.
  • the manufacturing method of the present invention adopts the thickness-wise asymmetric cooling technology to obtain the phase-change-strengthened steel thickness-wise asymmetrical strip strength (hardness) distribution, so that it has one-sided strength, The hardness is high, and the other side has the advantages of good plasticity and toughness.
  • the hardness along the thickness direction changes gradually. This makes the obtained cold-rolled steel strip with variable strength and hardness in the thickness direction very suitable for high single-sided hardness and resistance. Friction, indentation resistance, and the overall need for toughness applications.

Abstract

一种厚向变强度硬度冷轧带钢（1）的制造方法，其包括步骤：冶炼、连铸、热轧、冷轧和连续退火；在连续退火步骤中进行淬火时，对带钢两个表面进行不对称的淬火冷却工艺。此外，还公开了一种厚向变强度硬度冷轧带钢（1），其采用上述的制造方法制得。该制造方法通过对带钢进行非对称式的淬火冷却工艺，实现了带钢非对称式的力学性能分布，从而得到沿厚度方向渐变式的硬度梯度，以同时获得高硬度、高强度和优良的韧塑性和成形性的组合性能，有效应对超高强钢强度和塑性、韧性之间的矛盾。

Description

一种厚向变强度硬度冷轧带钢及其制造方法 技术领域
本发明涉及一种带钢及其制造方法，尤其涉及一种冷轧带钢及其制造方法。
背景技术
汽车工业出于减重和安全性的需要，要求使用更高强度的钢板。汽车用冷轧先进高强钢板的制造一般都依赖连续退火过程中的快速冷却，快速冷却有利于奥氏体向马氏体、贝氏体等组织的转变，从而获得高强度。
在现有技术中，高强度钢板多采用传统的均一的快速冷却方式而获得，即钢板开始快速冷却的温度和结束快速冷却的温度相同，钢板两个表面的冷却速度也相同，照此方式可以获得强度均一的钢板。
例如：公开号为CN102822375A，公开日为2012年12月12日，名称为“超高强度冷轧钢板及其制造方法”的中国专利文献公开了一种超高强度冷轧钢板及其制造方法。在该专利文献所公开的技术方案中，化学成分为C：0.05-0.4％，Si：2.0％以下，Mn：1.0-3.0％，P：0.05％以下，S：0.02％以下，Al：0.01-0.05％，N：小于0.005％，并且该文献所涉及的钢在连续退火中，从Ac3，以20℃/s以上(气体冷却)的冷速，冷却到Ms点-Ms点+200℃范围，保持0.1-60s后，以100℃/s以上的冷速(水冷)，冷却到100℃以下，得到抗拉强度1320MPa以上的高强钢，并且钢板的平坦度在10mm以下。然而，该专利文献所公开的技术方案采用的是均一的快速冷却工艺。
又例如：公开号为CN102953002A，公开日为2013年3月6日，名称为“缝焊性优异的高强度钢板”的中国专利文献公开了一种缝焊性优异的高强度钢板。在该专利文献所公开的技术方案中，C：0.12-0.4％，Si：0.003-0.5％，Mn：0.01-1.5％，P：0.02％以下，S：0.01％以下，Al：0.032-0.15％，N：0.01％以下，Ti：0.01-0.2％，B：0.0001-0.001％，钢的组织为单一马氏体组织。在该专利文献所公开的技术方案中，该钢抗拉强度在1180MPa以上，其采用的也是均一的快速冷却工艺。
综上所述可以看出，现有技术中的相变强化高强度钢板，虽然分属不同的强度级别，采用了不同的淬火工艺，但其采用的都是均一冷却的淬火工艺，因此其最终 获得的钢板具有均一性能，在厚向的强度、硬度也基本相同。
基于此，期望获得一种不同于现有技术的带钢，其上下表面的硬度不同，并且可以沿着厚度方向逐步变化。
发明内容
本发明的目的之一在于提供一种厚向变强度/硬度冷轧带钢的制造方法，该制造方法通过对带钢进行非对称式的淬火冷却工艺，实现了带钢非对称式的力学性能分布，从而得到沿厚度方向渐变式的硬度/强度梯度，以同时获得高硬度、高强度和优良的韧塑性和成形性的组合性能。
为了实现上述目的，本发明提出了一种厚向变强度硬度冷轧带钢的制造方法，其包括步骤：冶炼、连铸、热轧、冷轧和连续退火；其中，在连续退火步骤中进行淬火时，对带钢两个表面进行不对称的淬火冷却工艺。
在本发明所述的制造方法中，在淬火过程中，奥氏体转变成为马氏体或者贝氏体，从而实现钢的硬化。不同于现有技术中的淬火工序同时使带钢的两个表面从相同的起始冷却温度以同样的冷却速度冷却到同样的淬火终止温度结束快冷(通过该冷却技术对带钢两面的冷却是完全相同和对称的，得到的淬火钢板的力学性能也是完全对称和均匀的)，本技术方案设计了非对称式淬火冷却技术，从而使得带钢获得厚向非对称式的带钢力学性能。具体来说，本案的厚向变强度硬度冷轧带钢最重要的特点就是厚向变强度(或硬度)，即带钢的上下两个表面具有不同的强度(或硬度)，可由此，在带钢两个表面之间，从带钢的一个表面到带钢的另外一个表面的强度(或硬度)是逐渐变化和过渡的。这种厚向变强度(或硬度)的带钢，其硬度较高的一面可以用于抗摩擦、抗压痕的使用目的，而沿厚度方向硬度较低的一面以及过渡的部位则强度、硬度不断降低，伴随着韧性和延伸率不断提高，有利于带钢的成形性和韧性的提高。
基于此，本案利用相变强化钢淬火硬化的特点，在连续退火的淬火快速冷却过程中，采用对带钢两个表面进行不对称的淬火冷却工艺。由此，通过本发明所述的制造方法最终获得的厚向变强度/硬度冷轧带钢，可以适用于对强度、硬度和塑性、成形性要求都高的苛刻的应用场合，所述的厚向变强度硬度冷轧带钢可以提供单个表面的高硬度，具有较高的抗摩擦和抗压痕性能，同时整体上带钢成形性和韧性都比较高。
进一步地，在本发明所述的厚向变强度硬度冷轧带钢的制造方法中，不对称的 淬火冷却工艺包括下述各项的至少其中之一：
带钢两个表面的冷却起始温度不对称；
带钢两个表面的冷却终止温度不对称；
带钢两个表面的冷却速度不对称。
上述方案中，采用不同的带钢两个表面的冷却起始温度不对称，或是带钢两个表面的冷却终止温度不对称，又或是带钢两个表面的冷却速度不对称可以使得在带钢的两面形成不同的冷却路径，或者这三个条件的任意组合，从而使得最终所获得的厚向变强度硬度冷轧带钢所含的铁素体和马氏体/贝氏体含量差异不同，以使得带钢两面的厚向强度的差异有所区别。
需要说明的是，在本技术方案中，冷却采用的介质可以是水雾冷却(例如：气水混合喷射)或气体冷却。其中当采用气体介质进行冷却时，可以采用含有氮气和任选的氢气的气体，其中氢气的气体体积百分比在0-75％。在一些实施方案中，采用氢气与氮气的混合气体，其中，氢气的气体体积百分比为大于0％到小于等于75％。
进一步地，在本发明所述的厚向变强度硬度冷轧带钢的制造方法中，当带钢两个表面的冷却起始温度不对称时，带钢两个表面的冷却起始温度的差为20-100℃。通常，两个面的起始冷却温度在650-750℃的范围内。
在上述优选的技术方案中，考虑到冷却起始温度的差低于20℃，厚向变强度硬度冷轧带钢在厚度方向上的强度或硬度差异不够明显，而若冷却起始温度的差高于100℃，会导致带钢一面的强度或硬度过低可能导致整体强度或硬度过低，可以优选地将两个表面的冷却起始温度的差控制在20-100℃范围内。
更进一步地，在本发明所述的厚向变强度硬度冷轧带钢的制造方法中，当带钢两个表面的冷却起始温度不对称时，带钢两个表面的冷却起始温度的差为25-100℃。
进一步地，在本发明所述的厚向变强度硬度冷轧带钢的制造方法中，当带钢两个表面的冷却终止温度不对称时，带钢两个表面的冷却终止温度的差为40-200℃。通常，两个表面的冷却终止温度在50-400℃的范围内。
在上述优选的技术方案中，考虑到冷却终止温度的差低于40℃，厚向变强度硬度冷轧带钢在厚度方向的强度或硬度差异不够明显，而若冷却终止温度的差高于200℃，会导致带钢一面的强度或硬度过低进而可能导致带钢整体强度或硬度过低，可以优选地将两个表面的冷却终止温度的差控制在40-200℃范围内。
更进一步地，在本发明所述的厚向变强度硬度冷轧带钢的制造方法中，当带钢两个表面的冷却终止温度不对称时，带钢两个表面的冷却终止温度的差为50-180℃。
进一步地，在本发明所述的厚向变强度硬度冷轧带钢的制造方法中，当带钢两个表面的冷却速度不对称时，带钢两个表面的冷却速度的差为25-200℃/s。通常，两个面的冷却速度≥30℃/s，可在30-500℃的范围内。
在上述优选的技术方案中，考虑到若冷却速度的差异低于25℃/s，带钢在厚度方向上的强度或硬度差异不够明显，而若冷却速度的差高于200℃/s，会导致带钢一面的强度或硬度过低可能导致带钢整体强度或强度过低，可以优选地将两个表面的冷却速度的差控制在25-200℃/s范围内。
更进一步地，在本发明所述的厚向变强度硬度冷轧带钢的制造方法中，当带钢两个表面的冷却速度不对称时，带钢两个表面的冷却速度的差为40-200℃/s。
在上述方案中，冷却起始温度高的那一面，其冷却速度可高于另一面的冷却速度，也可低于另一面的冷却速度。根据两个面冷却起始温度、其差值、冷却速度及其差值，冷却起始温度高的那一面的冷却终止温度通常高于另一面的冷却终止温度，也可低于另一面的冷却终止温度。优选地，冷却起始温度高的那一面，其冷却速度高于另一面，且冷却终止温度低于另一面。
相应地，本发明的另一目的还在于提出一种厚向变强度硬度冷轧带钢，该厚向变强度硬度冷轧带钢的硬度较高一面可以用于抗摩擦、抗压痕的目的，而沿厚向硬度较低的一面过渡的部位则强度、硬度不断降低，而韧性和延伸率不断提高，有利于带钢的成形性和韧性的提高，使得整体上带钢成形性和韧性都比较高。
为了达到上述发明目的，本发明提出了一种厚向变强度硬度冷轧带钢，其采用上述的制造方法制得。
进一步地，在本发明所述的厚向变强度硬度冷轧带钢中，厚向变强度硬度冷轧带钢的厚度在1.0mm及以上。
本案发明人通过研究发现，当带钢的厚度低于1.0mm时，由于带钢本身的传热性能，厚向非对称的强度将难以得到较明显的差异。因此，带钢厚度越大，获得厚向非对称的程度越好，从这个角度出发，优选地可以将厚向变强度硬度冷轧带钢的厚度设置在1.0mm及以上，从而更容易获得较好的厚向硬度非对称效果。
更进一步地，在本发明所述的厚向变强度硬度冷轧带钢中，厚向变强度硬度冷轧带钢的厚度在1.4-2.5mm。
进一步地，在本发明所述的厚向变强度硬度冷轧带钢中，其化学元素质量百分配比为：C 0.06-0.3wt％，Si 0.01-2.5wt％，Mn 0.5-3wt％，Al 0.02-0.08wt％，余量为Fe和其他不可避免的杂质。
在一些实施方案中，本发明提供一种厚向变强度硬度冷轧带钢，其化学元素质量百分配比为：C 0.06-0.3wt％，Si 0.01-2.5wt％，Mn 0.5-3wt％，Al 0.02-0.08wt％，余量为Fe和其他不可避免的杂质；且所述厚向变强度硬度冷轧带钢的屈服强度≥420MPa、抗拉强度≥800MPa、延伸率≥11％、两个面的硬度差至少为20HV。
优选地，所述厚向变强度硬度冷轧带钢还含有Cr、Mo和B中的至少一种，其中，Cr含量≤0.2％，Mo含量≤0.2％，B含量≤0.0035％。
在一些实施方案中，所述厚向变强度硬度冷轧带钢的B含量＜0.0005wt％，且Cr+Mn+Mo≤3.5wt％。
在一些实施方案中，所述厚向变强度硬度冷轧带钢的B含量范围为0.0005-0.0035wt％，且Cr+Mn+Mo≤2.5wt％。
在一些实施方案中，所述厚向变强度硬度冷轧带钢还含有V、Ti、Nb和W中的至少一种，其含量满足V+Ti+Nb+W≤0.2wt％；优选地，V≤0.1％，Ti≤0.05％，Nb≤0.05％，W≤0.2％。
在一些实施方案中，所述厚向变强度硬度冷轧带钢的厚度在1.0mm以上，优选厚度为1.4-2.5mm。
优选地，任一实施方案所述的厚向变强度硬度冷轧带钢的化学元素质量百分配比为：C 0.09-0.2wt％，Si 0.3-1.2wt％，Mn 1.5-2.5wt％，Al 0.02-0.08wt％，余量为Fe和其他不可避免的杂质。
优选地，任一实施方案所述的厚向变强度硬度冷轧带钢的屈服强度为435-900MPa、抗拉强度为820-1260MPa、延伸率为11-20％，两个面的硬度差为35-80HV。
上述方案中，本案发明人考虑到厚向变强度硬度冷轧带钢需要具有一定淬硬性，因此，在本发明所述的厚向变强度硬度冷轧带钢中，设计了如上所述的各化学元素质量配比，而各化学元素的设计原理如下所述：
C：通过影响马氏体硬度来提高强度。含碳量过低，马氏体无法淬硬，或者淬火后强度本身较低，韧塑性矛盾不突出；然而，含碳量过高，马氏体越硬，韧性过低且发生延迟开裂的倾向越大，基于此，为了获得良好的厚向变硬度效果，可以将本发明所述的厚向变强度硬度冷轧带钢的C的质量百分比控制在0.06-0.3wt％。在 一些优选的实施方案中，C的质量百分比控制在0.09-0.2％。
Si：Si对淬硬性影响较小，基于此，可以将本发明所述的厚向变强度硬度冷轧带钢的Si的质量百分比控制在0.01-2.5wt％。在一些优选的实施方案中，Si的质量百分比控制在0.3-1.2％。
Mn：Mn是提高钢的淬硬性的主要元素，Mn的含量需要和选取的冷却方式的冷却能力相匹配，以获得良好的厚向非对称强度结果，若Mn的质量百分比过低，带钢无法淬硬，无法获得厚向变强度的效果；但若Mn的质量百分比过高，淬硬性过高，则同样无法获得厚向变强度的效果。为了和淬火冷却段的冷却能力相匹配，获得理想的厚向变强度效果，可以将本发明所述的厚向变强度硬度冷轧带钢中的Mn的质量百分比控制在0.5-3wt％。在一些优选的实施方案中，Mn的质量百分比控制在1.5-2.5％。
Al：Al的作用为脱氧，并能细化奥氏体晶粒，因此，在本发明所述的技术方案中，控制Al的质量百分比在0.02-0.08wt％。
需要说明的是，在本发明所述的技术方案中，其他不可避免的杂质元素主要包括P、S和N，为了使得带钢获得较好的性能，应当将杂质元素控制得越少越好。在优选的实施方案中，P≤0.015％，S≤0.005％，N≤0.03％。
进一步地，在本发明所述的厚向变强度硬度冷轧带钢中，还含有Cr、Mo和B中的至少一种，其中：当B＜0.0005wt％时，Cr+Mn+Mo≤3.5wt％；当B含量范围为0.0005-0.0035wt％时，Cr+Mn+Mo≤2.5wt％。优选地，当含有时，Cr的含量不超过0.2％，优选不超过0.15％；当含有时，Mo的含量不超过0.2％，优选不超过0.1％；当含有时，B的含量不超过0.0035％，例如在0.0005-0.0035wt％或0.001-0.002wt％的范围内。
发明人通过研究发现，为了提高钢的淬透性，并同时与Mn元素的质量百分比适配，从而使得最终带钢的淬透性和冷却能力相匹配，避免无法淬硬或者淬硬性过高，造成对冷却工艺变化不敏感的情况，优选地，可以将Cr、Mo以及的添加控制在：当B＜0.0005wt％时，Cr+Mn+Mo≤3.5wt％；当B含量范围为0.0005-0.0035wt％时，Cr+Mn+Mo≤2.5wt％。
进一步地，在本发明所述的厚向变强度硬度冷轧带钢中，还含有V、Ti、Nb和W中的至少一种，其含量满足V+Ti+Nb+W≤0.2wt％。优选地，当含有时，V的含量不超过0.1％，优选不超过0.05％；当含有时，Ti的含量不超过0.05％，优选不超过0.03％；当含有时，Nb的含量不超过0.05％，优选为0.01-0.03％；当含有 时，W的含量不超过0.2％，优选不超过0.1％；且优选地，V+Ti+Nb+W≤0.2wt％。
综上所述可以看出，相较于现有技术，本发明所述的厚向变强度硬度冷轧带钢及其制造方法具有如下所述的优点以及有益效果：
本发明所述的制造方法通过厚向非对称式冷却技术，从而可以得到相变强化钢厚向非对称的带钢强度(硬度)分布，使之具有一面强度、硬度高，而另外一面塑形、韧性好的优点。此外，由于带钢的两个表面的性能是有差异的，这就使得其沿厚度方向的硬度或强度是逐步变化的，这使得所获得的厚向变强度硬度冷轧带钢适用于需要单面硬度高，抗摩擦、抗压痕性能好，而整体需要韧性好的应用场合。
在优选的实施方案中，本发明所述的厚向变强度硬度冷轧带钢的屈服强度≥420MPa、抗拉强度≥800MPa、延伸率≥11％、一面的硬度≥220HV、另一面的硬度≥200HV。更具体而言，在一些优选的实施方案中，本发明所述的厚向变强度硬度冷轧带钢的屈服强度为435-900MPa、抗拉强度为820-1260MPa、延伸率为11-20％、一面的硬度为235-380HV、另一面的硬度为200-330HV。优选地，本发明厚向变强度硬度冷轧带钢两个面的硬度差至少为30HV，优选至少35HV。在优选的实施方案中，本发明厚向变强度硬度冷轧带钢两个面的硬度差在35-80HV的范围内，从而有利于获得较好的实际使用性能，以及强度、塑性和韧性的平衡。
附图说明
图1示意性地显示了本发明所述的厚向变强度硬度冷轧带钢在一些实施方式中的冷却工艺。
图2示意性地显示了本发明所述的厚向变强度硬度冷轧带钢在另一些实施方式中的冷却工艺。
图3示意性地显示了本发明所述的厚向变强度硬度冷轧带钢在又一些实施方式中的冷却工艺。
具体实施方式
下面将结合附图说明和具体的实施例对本发明所述的厚向变强度硬度冷轧带钢及其制造方法做进一步的解释和说明，然而该解释和说明并不对本发明的技术方案构成不当限定。
实施例1-6
上述实施例1-6的厚向变强度硬度冷轧带钢采用以下步骤制得：
(1)按照表1所示的化学成分进行冶炼和铸造；
(2)连铸；
(3)热轧：板坯加热温度可以为1170～1230℃，终轧温度可以为850～910℃，卷取温度可以为570～630℃，然后可以进行酸洗，去除表面氧化皮。
(4)连续退火：将带钢先加热到保温温度，保持40-120s，然后以2-10℃/s的冷却速度冷却，接着进行非对称式的淬火冷却工艺，淬火冷却工艺结束后进行回火，回火结束后水冷到室温，带钢干燥后进行平整。
在另外的一些实施方式中，在热轧后，带钢还可以进行冷轧，冷轧压下率可以控制在30～65％，然后接着进行上述步骤(4)所述的连续退火。
表1列出了实施例1-6的厚向变强度硬度冷轧带钢的各化学元素的质量百分配比。
表1.(wt％，余量为Fe和除了P、S以及N以外的其他不可避免的杂质)
Figure PCTCN2020097893-appb-000001
表2列出了实施例1-6的厚向变强度硬度冷轧带钢的连续退火步骤中的具体工艺参数。
表2
Figure PCTCN2020097893-appb-000002
Figure PCTCN2020097893-appb-000003
需要说明的是，对比例1采用的是实施例1所示的各化学元素质量配比进行冶炼，对比例2采用的是实施例3所示的各化学元素质量配比进行冶炼，对比例3采用的是实施例5所示的各化学元素质量配比进行冶炼。实施例7采用的是表1所示的实施例1的各化学元素质量配比进行冶炼。实施例8采用的是表1所示的实施例2的各化学元素质量配比进行冶炼。
此外，为了便于区分带钢厚度方向的两个表面，将其中的一个面称为I面，而相对I面的另一面为II面。
表3列出了本案实施例1-8的厚向变强硬度冷轧带钢的各项性能测试结果。
表3
Figure PCTCN2020097893-appb-000004
Figure PCTCN2020097893-appb-000005
注：通过制备金相试样，采用显微硬度仪在厚度方向上分别检测两面和中间的硬度。
由表2和表3可以看出，对比例1-3的带钢由于采用现有技术，因而，对带钢两面的冷却是完全相同和对称的，得到的淬火钢板的力学性能也是完全对称和均匀的。而本案各实施例1-8的厚向变硬度冷轧带钢由于通过对带钢进行非对称式的淬火冷却工艺，实现了带钢非对称式的力学性能分布，从而得到沿厚度方向渐变式的强度/硬度梯度，以同时获得高硬度、高强度和优良的韧塑性和成形性的组合性能。
图1至图3则示意了不同的实施例采用不同的非对称的淬火冷却工艺。
其中，图1示意性地显示了本发明所述的厚向变强度硬度冷轧带钢在一些实施方式中的冷却工艺。
如图1所示，冷轧带钢1沿着前进方向F1进入连续退火后，带钢两面冷却起始温度不同，I面首先受到冷却模板2的喷嘴喷射冷却，II面随后受到冷却喷嘴喷射，从而可以在带钢的两面形成不同的冷却路径，不同表面的快冷开始温度有差异，冷却长度有差异，从而导致快冷终止温度也不同，最终导致不同表面的铁素体和马氏体/贝氏体含量的差异，最终导致带钢厚向强度的差异。
采用图1所示的不对称冷却工艺，使得带钢I面的硬度高，铁素体含量少，马 氏体含量多，贝氏体含量少，而II面硬度较低，铁素体含量少，马氏体含量少，贝氏体含量多。
图2示意性地显示了本发明所述的厚向变强度硬度冷轧带钢在另一些实施方式中的冷却工艺。
如图2所示，冷轧带钢1沿着前进方向F1进入连续退火后，带钢两面冷却起始温度相同，但终止的温度不同，带钢II面的对应的冷却模块2的冷却喷嘴在冷却过程率先结束，而I面所对应的冷却喷嘴则继续冷却到较低温度，从而在带钢的两面形成不同的冷却路径，并最终导致带钢I、II面的冷却终止温度有所差异，进而导致铁素体和马氏体/贝氏体含量的差异，最终导致带钢厚向强度的差异。
采用这种不对称的冷却工艺，使得带钢I面的硬度高，马氏体含量多，而II面硬度较低，马氏体含量少，贝氏体含量多。
图3示意性地显示了本发明所述的厚向变强度硬度冷轧带钢在又一些实施方式中的冷却工艺。
如图3所示，冷轧带钢1沿着前进方向F1进入连续退火后，带钢两面的冷却起始温度相同，终止的时间也相同，但由于带钢两侧布置的冷却模块2的冷却喷嘴的冷却能力不同，带钢I面对应的喷嘴冷却速度快，II面所对应的喷嘴冷却速度相对较慢。从而在带钢的两面形成不同的冷却路径，也就是说冷却速度有差异，导致铁素体和马氏体/贝氏体含量的差异，最终导致带钢厚向强度的差异。
采用这种不对称的冷却工艺，使得带钢I面的硬度高，马氏体含量多，而II面硬度较低，铁素体含量多，马氏体含量少，贝氏体含量多。
需要说明的是，冷却速度的不同可以通过喷嘴喷出的冷却介质不同或是通过调整冷却介质喷出的速度或是流量的不同从而造成I、II面的冷却速度不同，例如可以I面采用换热能量高的介质或是喷出速度更高或是流量更高，从而实现较快的冷却速度。
此外，在一些其他的实施方式中，也可以将上述图1、图2或图3示意的冷却工艺进行组合，从而实现非对称的淬火冷却方式。
综上所述可以看出，本发明所述的制造方法通过厚向非对称式冷却技术，从而可以得到相变强化钢厚向非对称的带钢强度(硬度)分布，使之具有一面强度、硬度高，而另外一面塑形、韧性好的优点，沿厚度方向的硬度则是逐步变化的看，这使得所获得的厚向变强度硬度冷轧带钢非常适于需要单面硬度高，抗摩擦、抗压痕，而整体需要韧性好的应用场合。
需要说明的是，本发明的保护范围中现有技术部分并不局限于本申请文件所给出的实施例，所有不与本发明的方案相矛盾的现有技术，包括但不局限于在先专利文献、在先公开出版物，在先公开使用等等，都可纳入本发明的保护范围。
此外，本案中各技术特征的组合方式并不限本案权利要求中所记载的组合方式或是具体实施例所记载的组合方式，本案记载的所有技术特征可以以任何方式进行自由组合或结合，除非相互之间产生矛盾。
还需要注意的是，以上所列举的实施例仅为本发明的具体实施例。显然本发明不局限于以上实施例，随之做出的类似变化或变形是本领域技术人员能从本发明公开的内容直接得出或者很容易便联想到的，均应属于本发明的保护范围。

Claims (20)

  1. 一种厚向变强度硬度冷轧带钢，其特征在于，其化学元素质量百分配比为：C 0.06-0.3wt％，Si 0.01-2.5wt％，Mn 0.5-3wt％，Al 0.02-0.08wt％，余量为Fe和其他不可避免的杂质；且所述厚向变强度硬度冷轧带钢的屈服强度≥420MPa、抗拉强度≥800MPa、延伸率≥11％、两个面的硬度差至少为30HV。
  2. 如权利要求1所述的厚向变强度硬度冷轧带钢，其特征在于，所述厚向变强度硬度冷轧带钢还含有Cr、Mo和B中的至少一种，其中，Cr含量≤0.2％，Mo含量≤0.2％，B含量≤0.0035％。
  3. 如权利要求2所述的厚向变强度硬度冷轧带钢，其特征在于，所述厚向变强度硬度冷轧带钢的B含量＜0.0005wt％，且Cr+Mn+Mo≤3.5wt％；或所述厚向变强度硬度冷轧带钢的B含量范围为0.0005-0.0035wt％，且Cr+Mn+Mo≤2.5wt％。
  4. 如权利要求1所述的厚向变强度硬度冷轧带钢，其特征在于，所述厚向变强度硬度冷轧带钢还含有V、Ti、Nb和W中的至少一种，其含量满足V+Ti+Nb+W≤0.2wt％。
  5. 如权利要求1所述的厚向变强度硬度冷轧带钢，其特征在于，所述厚向变强度硬度冷轧带钢的化学元素质量百分配比为：C 0.09-0.2wt％，Si 0.3-1.2wt％，Mn 1.5-2.5wt％，Al 0.02-0.08wt％，余量为Fe和其他不可避免的杂质。
  6. 如权利要求1所述的厚向变强度硬度冷轧带钢，其特征在于，所述厚向变强度硬度冷轧带钢的屈服强度为435-900MPa、抗拉强度为820-1260MPa、延伸率为11-20％，两个面的硬度差为35-80HV。
  7. 一种厚向变强度硬度冷轧带钢的制造方法，其包括步骤：冶炼、连铸、热轧、冷轧和连续退火；其特征在于：在连续退火步骤中进行淬火时，对带钢两个表面进行不对称的淬火冷却工艺。
  8. 如权利要求7所述的厚向变强度硬度冷轧带钢的制造方法，其特征在于，所述不对称的淬火冷却工艺包括下述各项的至少其中之一：
    带钢两个表面的冷却起始温度不对称；
    带钢两个表面的冷却终止温度不对称；
    带钢两个表面的冷却速度不对称。
  9. 如权利要求8所述的厚向变强度硬度冷轧带钢的制造方法，其特征在于，当带钢两个表面的冷却起始温度不对称时，带钢两个表面的冷却起始温度的差为 20-100℃。
  10. 如权利要求9所述的厚向变强度硬度冷轧带钢的制造方法，其特征在于，当带钢两个表面的冷却起始温度不对称时，带钢两个表面的冷却起始温度的差为25-100℃。
  11. 如权利要求8所述的厚向变强度硬度冷轧带钢的制造方法，其特征在于，当带钢两个表面的冷却终止温度不对称时，带钢两个表面的冷却终止温度的差为40-200℃。
  12. 如权利要求11所述的厚向变强度硬度冷轧带钢的制造方法，其特征在于，当带钢两个表面的冷却终止温度不对称时，带钢两个表面的冷却终止温度的差为50-180℃。
  13. 如权利要求8所述的厚向变强度硬度冷轧带钢的制造方法，其特征在于，当带钢两个表面的冷却速度不对称时，带钢两个表面的冷却速度的差为25-200℃/s。
  14. 如权利要求13所述的厚向变强度硬度冷轧带钢的制造方法，其特征在于，当带钢两个表面的冷却速度不对称时，带钢两个表面的冷却速度的差为40-200℃/s。
  15. 一种厚向变强度硬度冷轧带钢，其采用如权利要求7-14中任意一项所述的制造方法制得。
  16. 如权利要求15所述的厚向变强度硬度冷轧带钢，其特征在于，所述厚向变强度硬度冷轧带钢的厚度在1.0mm以上。
  17. 如权利要求16所述的厚向变强度硬度冷轧带钢，其特征在于，所述厚向变强度硬度冷轧带钢的厚度在1.4-2.5mm。
  18. 如权利要求15-17中任意一项所述的厚向变强度硬度冷轧带钢，其特征在于，其化学元素质量百分配比为：C 0.06-0.3wt％，Si 0.01-2.5wt％，Mn 0.5-3wt％，Al 0.02-0.08wt％，余量为Fe和其他不可避免的杂质。
  19. 如权利要求18所述的厚向变强度硬度冷轧带钢，其特征在于，还含有Cr、Mo和B中的至少一种，其中：当B＜0.0005wt％时，Cr+Mn+Mo≤3.5wt％；当B含量范围为0.0005-0.0035wt％时，Cr+Mn+Mo≤2.5wt％。
  20. 如权利要求18或19所述的厚向变强度硬度冷轧带钢，其特征在于，还含有V、Ti、Nb和W中的至少一种，其含量满足V+Ti+Nb+W≤0.2wt％。
PCT/CN2020/097893 2019-06-24 2020-06-24 一种厚向变强度硬度冷轧带钢及其制造方法 WO2020259531A1 (zh)

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