WO2018036346A1 - 用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢及生产方法 - Google Patents

用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢及生产方法 Download PDF

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WO2018036346A1
WO2018036346A1 PCT/CN2017/095492 CN2017095492W WO2018036346A1 WO 2018036346 A1 WO2018036346 A1 WO 2018036346A1 CN 2017095492 W CN2017095492 W CN 2017095492W WO 2018036346 A1 WO2018036346 A1 WO 2018036346A1
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mpa
production line
steel
thin
temperature
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French (fr)
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毛新平
潘利波
胡宽辉
汪水泽
葛锐
李立军
彭涛
段小平
方芳
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武汉钢铁有限公司
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Priority to KR1020197002739A priority Critical patent/KR20190021451A/ko
Priority to US16/322,108 priority patent/US11124851B2/en
Publication of WO2018036346A1 publication Critical patent/WO2018036346A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • 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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • 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
    • 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
    • C21D2211/008—Martensite
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous 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
    • 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
    • C21D8/0231—Warm rolling

Definitions

  • the invention relates to a steel for automobile parts and a production method thereof, in particular to a thin hot-formed steel with a tensile strength ⁇ 1900 MPa and a production method thereof, which are directly rolled by a thin slab, and is suitable for the production of a product having a thickness of 0.8 to 2 mm. .
  • stamping equipment that is, it requires a large-tonnage punching machine and a high-wearing mold, and has a great influence on the life cycle of the mold.
  • stamping equipment there is no cold forming stamping equipment and mold capable of forming more than 1900 MPa in China.
  • the tensile strength of existing hot-formed steels at home and abroad cannot reach 1900 MPa and above, and all of them are pre-coated by cold-rolled annealed or cold-rolled annealed.
  • the production process is: desulfurization of molten iron ⁇ converter smelting ⁇ refining outside the furnace ⁇ continuous casting ⁇ slab heating ⁇ hot continuous rolling ⁇ pickling + cold continuous rolling ⁇ continuous annealing ⁇ (pre-coating) ⁇ finishing packaging ⁇ blanking ⁇ Heating ⁇ die stamping and quenching.
  • For some anti-collision or load-bearing parts multiple parts are used to improve the anti-collision and load-bearing capacity, which leads to greatly increased raw material cost and processing cost.
  • the medium and thin slab continuous casting and rolling process can directly produce >2.0 ⁇ 10mm specification steel plates and steel strips. Some of them can only be used cold.
  • the thin gauge parts of high-strength steel or the construction of multiple parts for increasing strength have been gradually replaced by direct-rolling ultra-high-strength steel sheets by continuous casting and rolling.
  • a high-strength steel for engineering structures with yield strength (R eL ) ⁇ 700 MPa and tensile strength (R m ) ⁇ 750 MPa is developed.
  • the component percentage is: C: 0.15 to 0.25%.
  • the production process is smelting and continuous casting into a billet, performing soaking, controlling the soaking temperature at 1200-1300 ° C, soaking time is 20-60 min; rolling, and controlling the rolling temperature not lower than 1200 ° C
  • the final rolling temperature is 870-930 ° C; laminar cooling is performed, and the cooling temperature is not lower than 20 ° C / s to the coiling temperature; the coiling is performed, and the coiling temperature is controlled at 580 to 650 ° C.
  • CN 103658178A invents a short-flow method for producing high-strength thin strip steel.
  • the percentages are: C: 0.02 to 0.15%, Si: 0.20 to 0.6%, Mn: 0.2 to 1.50%, P: 0.02 to 0.3%, S ⁇ 0.006%, Cr: 0.40 to 0.8%, and Ni: 0.08 to 0.40%, Cu: 0.3 to 0.80%, Nb: 0.010 to 0.025%, Ti: 0.01 to 0.03%, Al: 0.01 to 0.06%, Re: 0.02 to 0.25%; the balance is Fe and inevitable impurities, and cast into 1.0 to 2.0 after smelting.
  • the invention overcomes the defects of the prior art that the strength level is low, can not meet the user's demand for high-strength parts, and provides a requirement that can satisfy the requirements of the ultra-high-strength mechanical performance of the automobile design, and can smoothly complete the complex deformation and deformation. After the rebound, the dimensional accuracy of the parts is high, the tensile strength is ⁇ 1900MPa hot-formed steel and the production method.
  • a method for producing a thin hot-formed steel having a tensile strength of ⁇ 1900 MPa directly rolled by a thin slab wherein:
  • the mold is stamped and formed, and the pressure is maintained in the mold for 10 to 20 s;
  • the rolling process of the medium and thin slab is in the form of a 6F production line or a 1R+6F production line, or a 2R+6F production line, or a 7F production line, or a 3R+4F production line, or 2R+5F.
  • the production line, or the 1R+5F production line is arranged in any form of short-flow production line.
  • Carbon is a strong solid solution strengthening element, which plays a decisive role in the acquisition of ultra-high strength.
  • the carbon content has a great influence on the microstructure and properties of the final product, but the content is too high, and it is easy to form a large amount in the cooling process after finish rolling.
  • the pearlite or bainite or martensite the higher the content, the higher the strength, resulting in a decrease in plasticity, and difficulty in blanking before forming. Therefore, under the premise of ensuring heat treatment strengthening, the carbon content is not easy to be too high. Therefore, the content is limited to the range of 0.31 to 0.40%.
  • Si Silicon has a strong solid solution strengthening effect, which can improve the strength of steel. At the same time, silicon can improve the hardenability of steel and reduce the volume change of austenite to martensite transformation, thus effectively controlling quenching cracks.
  • the production of low temperature tempering can hinder the diffusion of carbon, delay the decomposition of martensite and the growth rate of carbide accumulation, so that the hardness of steel decreases slowly during tempering, which significantly improves the tempering stability and strength of steel. Therefore, the content is limited to the range of 0.36 to 0.44%.
  • Mn Manganese acts as a solid solution strengthening agent, and at the same time, it can remove FeO from steel and significantly improve the quality of steel. It can also form MnS with high melting point with sulfide. In thermal processing, MnS has sufficient plasticity to prevent the steel from generating hot brittleness, reduce the harmful effects of sulfur, and improve the hot workability of steel. Manganese can reduce the phase change driving force, make the "C" curve shift to the right, improve the hardenability of steel, enlarge the ⁇ phase region, and reduce the Ms point of steel, so it can ensure the martensite at a suitable cooling rate. . Therefore, the content is limited to the range of 1.6 to 2.0%.
  • Chromium can reduce the phase change driving force and also reduce the nucleation growth of carbides during phase transformation, so the hardenability of steel is improved. In addition, chromium can improve the tempering stability of steel. Therefore, the content is limited to the range of 0.36 to 0.49%.
  • B Boron is a substance that strongly enhances hardenability.
  • the addition of trace amounts of boron to the steel can significantly improve the hardenability of the steel.
  • its content is less than 0.0005%, or more than 0.0050%, and the effect on improving hardenability is not obvious. Therefore, in order to consider the actual production and hardenability effects, the content is limited to the range of 0.004 to 0.005%.
  • Als which deoxidizes in steel, should ensure that there is a certain amount of acid-soluble aluminum in the steel, otherwise it will not exert its effect, but too much aluminum will cause aluminum inclusions in the steel, which is not conducive to steel smelting and casting. .
  • the addition of an appropriate amount of aluminum in the steel can eliminate the adverse effects of nitrogen and oxygen atoms on the properties of the steel. Therefore, the content is limited to the range of 0.015 to 0.060%.
  • Phosphorus is a harmful element in steel, which tends to cause segregation in the center of the slab. In the subsequent hot rolling heating process, it tends to be segregated to the grain boundary, so that the brittleness of the steel is significantly increased. At the same time based on cost considerations and does not affect the performance of the steel, the content is controlled at 0.006% under.
  • S Sulfur is a very harmful element.
  • Sulfur in steel is often present in the form of manganese sulfides. This sulfide inclusion can deteriorate the toughness of the steel and cause anisotropy in properties. Therefore, it is necessary to control the sulfur content in the steel as low as possible.
  • the sulfur content in the steel is controlled to be less than 0.004% based on consideration of manufacturing cost.
  • N Nitrogen can be combined with titanium to form titanium nitride in titanium-added steel. This second phase precipitated at a high temperature is advantageous for strengthening the matrix and improving the weldability of the steel sheet.
  • the nitrogen content is higher than 0.005%, and the solubility product of nitrogen and titanium is higher.
  • coarse titanium nitride is formed in the steel, which seriously damages the plasticity and toughness of the steel; in addition, the higher nitrogen content will cause The amount of microalloying elements required to stabilize the nitrogen element is increased, thereby increasing the cost. Therefore, the content is controlled to be less than 0.005%.
  • Titanium is a strong C and N compound forming element.
  • the purpose of adding Ti to steel is to fix the N element in the steel, but the excess Ti will combine with C to reduce the hardness and strength of the martensite after quenching of the test steel.
  • the addition of titanium contributes to the hardenability of steel. Therefore, the content is limited to the range of 0.036 to 0.045%.
  • Nb, V: niobium and vanadium are also strong C and N compounds forming elements, which can refine the austenite grains.
  • a small amount of niobium or vanadium can be added to the steel to form a certain amount of niobium carbon and nitride. Therefore, the austenite grain growth is hindered, and therefore, the size of the martensite lath after quenching is small, and the strength of the steel is greatly improved. Therefore, the content is controlled between 0.036 and 0.045%.
  • Molybdenum can significantly improve the hardenability of steel, and the stacking fault energy of molybdenum is high. Adding steel can improve the low temperature ductility and toughness of steel. Therefore, the content is controlled between 0.26 and 0.35%.
  • the reason why the invention adopts three descaling in the whole production process is that the scale of the steel strip can be maximally removed by controlling the descaling pass and the appropriate descaling water pressure, thereby ensuring good surface quality of the strip steel. .
  • the uniformity of the strip steel and the stable performance can be achieved.
  • the invention has high strength, short manufacturing process, good product surface quality and high thickness precision, and the thickness precision can be controlled within ⁇ 0.03 mm, which can meet the quality requirements of cold rolled products and greatly save energy.
  • the strength is much higher than that of the existing products, which is of great significance for realizing light weight of automobiles.
  • Figure 1 is a metallographic structure of the product of the present invention.
  • Table 1 is a list of chemical composition values of various examples and comparative examples of the present invention.
  • Table 2 is a list of values of main process parameters of various embodiments and comparative examples of the present invention.
  • Table 3 is a list of performance detection cases of various embodiments and comparative examples of the present invention.
  • the mold is stamped and formed, and the pressure is maintained in the mold for 10 to 20 s;
  • the rolling process of the thin slab is in the form of a 6F production line or a 1R+6F production line, or a 2R+6F production line, or a 7F production line, or a 3R+4F production line, or a 2R+5F production line, or
  • the 1R+5F production line can be carried out in any form of short-flow production line.

Abstract

用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢，其组分及wt％：C：0.31～0.40％，Si：0.36～0.44％,，Mn：1.6～2.0％，P≤0.006％，S≤0.004％，Als：0.015～0.060％，Cr：0.36～0.49％，Ti：0.036～0.045％或Nb：0.036～0.045％或V：0.036～0.045％或其中两种以上以任意比例的混合，B：0.004～0.005％，Mo：0.26～0.35％，N≤0.005％。生产步骤：铁水脱硫；电炉或转炉冶炼及精炼；连铸；入均热炉前的除鳞处理；均热；加热；进轧机之前的高压水除鳞；轧制；冷却；卷取；奥氏体化；模具冲压成形；淬火。热成形钢强度高，制造流程短，产品表面质量好，其厚度精度可控制在±0.03mm以内，大幅节约了能源消耗。

Description

用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢及生产方法 技术领域
本发明涉及一种汽车零部件用钢及其生产方法，具体地属于一种用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢及生产方法，且适用于生产的产品厚度0.8至2mm。
背景技术
随着汽车工业发展及汽车行业对汽车设计和制造逐渐向节能、环保、安全方向发展，汽车轻量化成为当前和今后相当长一段时间汽车设计的主流方向。
研究发现，汽车的整车重量和能源消耗成线性关系。据统计，汽车重量每降低10％则燃油效率可提高6％～8％。汽车轻量化最重要的途径之一是采用高强度和超高强度钢，从而能使在不降低碰撞安全性和舒适性的同时，采能大幅降低汽车整备重量。但随着强度的不断提高，钢板的成形性能会越来越差，尤其是1900MPa以上的超高强度钢，在成形过程中会存在开裂、回弹和零件尺寸达不到要求的精度等问题，并同时也对冲压设备提出了更高的要求，即需要大吨位的冲压机和高耐磨模具，并且对模具的使用周期还有较大的影响。目前国内也没有能成形1900MPa以上的冷成形冲压设备和模具。
当前，国内外现有热成形钢的抗拉强度均不能到达1900MPa及以上，且全部采用冷轧退火态或冷轧退火后预涂层。其生产工艺流程为：脱硫铁水→转炉冶炼→炉外精炼→连铸→板坯加热→热连轧→酸洗+冷连轧→连续退火→(预涂层)→精整包装→落料→加热→模具冲压淬火。存在生产工艺流程较长，成本较高的不足。对于有些抗碰撞或承载部件均采用多个零件组合构件来提高抗碰撞和承载能力，而又导致大大提高原材料成本和加工成本。
随着钢铁工业的发展，中薄板坯连铸连轧工艺得到了长足发展，采用中薄板坯连铸连轧工艺可以直接轧制生产＞2.0～10mm规格钢板及钢带，一些原来只能使用冷轧高强钢的薄规格零件或为增加强度采用多个零件组成的构建已逐步采用连铸连轧工艺直接轧制超高强度钢板所代替。如申请号为CN 102965573A的专利开发了屈服强度(ReL)≥700MPa，抗拉强度 (Rm)≥750MPa的工程结构用高强度钢，其组分百分含量为：C:0.15～0.25％，Si:≤0.10％，Mn:1.00～1.80％，P:≤0.020％，S≤0.010％，Ti:0.09～0.20％，Als:0.02～0.08％,N≤0.008％，其余为Fe及不可避免的夹杂；其生产步骤为冶炼并连铸成坯，进行均热，控制均热温度在1200～1300℃，均热时间为20～60min；进行轧制，并控制开轧温度不低于1200℃，终轧温度在870～930℃；进行层流冷却，在冷却速度为不低于20℃/s下冷却到卷取温度；进行卷取，并控制卷取温度在580～650℃。专利号为CN 103658178A的专利发明了一种短流程生产高强度薄带钢的方法，所发明的带钢屈服强度(ReL)≥550MPa，抗拉强度(Rm)≥600MPa，其化学成分质量百分比为：C:0.02～0.15％，Si:0.20～0.6％，Mn:0.2～1.50％，P:0.02～0.3％，S≤0.006％，Cr:0.40～0.8％，Ni:0.08～0.40％，Cu:0.3～0.80％，Nb:0.010～0.025％，Ti:0.01～0.03％，Al:0.01～0.06％，Re:0.02～0.25％；其余为Fe和不可避免杂质，冶炼后浇铸成1.0～2.0mm厚的铸带，浇铸速度60～150m/min，进行轧制，控制终轧温度850～1000℃；采用雾化冷却，冷却速度50～100℃/s，进行卷取，控制卷取温度为520～660℃。上述两文献的抗拉强度均很低，不能满足高端汽车车身对1900MPa以上超高强度的需求。
发明内容
本发明在于克服现有技术存在的强度级别低，不能满足用户对高强度零件需求的不足，提供一种既可以满足汽车设计对超高强度力学性能的要求，又能顺利完成复杂变形，且变形后无回弹，零件的尺寸精度高的抗拉强度≥1900MPa热成形钢及生产方法。
实现上述目的的措施：
用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢，其组分及重量百分比含量为：C：0.31～0.40％，Si：0.36～0.44％,，Mn：1.6～2.0％，P≤0.006％，S≤0.004％，Als：0.015～0.060％，Cr：0.36～0.49％，Ti：0.036～0.045％或Nb：0.036～0.045％或V：0.036～0.045％或其中两种以上以任意比例的混合，B：0.004～0.005％，Mo：0.26～0.35％，N≤0.005％，余为Fe及不可避免的杂质；淬火后的金相组织为全板条马氏体；力学性能：屈服强度≥1300MPa，抗拉 强度≥1900MPa，伸长率A80mm≥5％。
生产用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢的方法，其在于：其步骤：
1)铁水脱硫，并控制S≤0.002％，扒渣后铁水裸露面不低于96％；
2)常规电炉或转炉冶炼，及常规精炼；
3)进行连铸，控制中包钢水过热度在15～30℃，铸坯厚度在48～52mm，拉坯速度在4.0～7.0m/min；
4)进行铸坯入均热炉前的除鳞处理，并控制除鳞水的压力在300～400bar；
5)对铸坯进行常规均热，控制均热炉内呈弱氧化气氛，即使炉内残氧量在0.5～5.0％；
6)对铸坯入进行加热，并控制铸坯入炉温度在850～1050℃，出炉温度为1210～1230℃；
7)进行进轧机之前的高压水除鳞，并控制除鳞水压力在280～420bar；
8)轧制，并控制第一道次压下率为：52～63％，第二道次压下率为：50～60％，末道次压下率为：10～16％；控制轧制速度在8～12m/s；并在第一道次及第二道次之间进行中压水除鳞，除鳞水压力为200～280bar；控制终轧温度在870～910℃；
9)进行冷却，冷却方式为层流冷却、或水幕冷却、或加密冷却的方式冷却到卷取温度；
10)进行卷取，并控制卷取温度为605～635℃；
11)进行开卷落料后的奥氏体化，控制奥氏体化温度在850～920℃，并保温3～5min；
12)模具冲压成形，并在模具内保压10～20s；
13)进行淬火，控制淬火冷却速度在20～40℃/s；后自然冷却至室温。
其在于：所述中薄板坯的轧制过程在轧机布置形式为6F产线或1R+6F产线、或2R+6F产线、或7F产线、或3R+4F产线、或2R+5F产线、或1R+5F产线任意一种布置形式的短流程产线进行。
本发明中各元素及主要工艺的作用及机理
C：碳是强固溶强化元素，对超高强度的获得起决定作用，碳含量对最终产品的组织形态和性能有较大影响，但是含量太高，在精轧后的冷却过程中易形成大量的珠光体或贝氏体、马氏体，其含量愈高，强度愈高，从而造成塑性降低，进行成形前的落料困难。所以在保证热处理强化的前提下，碳含量不易过高。故将其含量限定在0.31～0.40％范围。
Si：硅有较强的固溶强化效果，可提高钢的强度，同时，硅能提高钢的淬透性，有减少奥氏体向马氏体转变时体积变化的作用，从而有效控制淬火裂纹的产生；在低温回火时能阻碍碳的扩散，延缓马氏体分解及碳化物聚集长大的速度，使钢在回火时硬度下降较慢，显著提高钢的回火稳定性及强度。所以，将其含量限定在0.36～0.44％范围。
Mn：锰起固溶强化作用，同时能清除钢中的FeO，显著改善钢的质量。还能与硫化物生成高熔点的MnS，在热加工时，MnS有足够的塑性，使钢不产生热脆现象，减轻硫的有害作用，提高钢的热加工性能。锰能降低相变驱动力，使“C”曲线右移，提高钢的淬透性，扩大γ相区，另它可降低钢的Ms点，故可保证在合适的冷却速度下得到马氏体。所以，将其含量限定在1.6～2.0％范围。
Cr：铬能降低相变驱动力，也降低相变时碳化物的形核长大，所以提高钢的淬透性。另外，铬能提高钢的回火稳定性。所以，将其含量限定在0.36～0.49％范围。
B:硼是强烈提高淬透性元素，钢中加入微量的硼元素能显著提高钢的淬透性。但是其含量低于0.0005％，或者高于0.0050％，对提高淬透性的作用不明显。所以，为考虑生产实际及淬透性效果，将其含量限定在0.004～0.005％范围。
Als，其在钢中起脱氧作用，应保证钢中有一定量的酸溶铝，否则不能发挥其效果，但过多的铝也会使钢中产生铝系夹杂，且不利于钢的冶炼和浇铸。同时钢中加入适量的铝可以消除钢中氮、氧原子对性能的不利影响。故将其含量限定在0.015～0.060％范围。
P：磷是钢中的有害元素，易引起铸坯中心偏析。在随后的热连轧加热过程中易偏聚到晶界，使钢的脆性显著增大。同时基于成本考虑且不影响钢的性能，将其含量控制在0.006％以 下。
S：硫是非常有害的元素。钢中的硫常以锰的硫化物形态存在，这种硫化物夹杂会恶化钢的韧性，并造成性能的各向异性，因此，需将钢中硫含量控制得越低越好。基于对制造成本的考虑，将钢中硫含量控制在0.004％以下。
N：氮在加钛的钢中可与钛结合形成氮化钛，这种在高温下析出的第二相有利于强化基体，并提高钢板的焊接性能。但是氮含量高于0.005％，氮与钛的溶度积较高，在高温时钢中就会形成颗粒粗大的氮化钛，严重损害钢的塑性和韧性；另外，较高的氮含量会使稳定氮元素所需的微合金化元素含量增加，从而增加成本。故将其含量控制在0.005％以下。
Ti：钛是强C、N化物形成元素，钢中加入Ti的目的是固定钢中的N元素，但是过量的Ti会与C结合从而降低试验钢淬火后马氏体的硬度和强度。另外，钛的加入对钢的淬透性有一定的贡献。所以，将其含量限定在0.036～0.045％范围。
Nb、V:铌和钒也是强C、N化物形成元素，能起到细化奥氏体晶粒的作用，钢中加入少量的铌或钒就可以形成一定量的铌的碳、氮化物，从而阻碍奥氏体晶粒长大，因此，其淬火后的马氏体板条尺寸较小，大大提高钢的强度。故将其含量均控制在0.036～0.045％之间。
Mo：钼能显著提高钢的淬透性，并且钼的层错能较高，加入钢中可提高钢的低温塑性和韧性。故将其含量控制在0.26～0.35％之间。
本发明之所以在整个生产过程中采取三次除鳞，是由于通过控制除鳞道次和合适的除鳞水压力，能最大化去除带钢表面的氧化铁皮，从而保证带钢具有良好的表面质量。另外通过一、二道及末道次压下率控制，可实现带钢的组织均匀和性能稳定。
本发明与现有技术相比，其强度高，制造流程短，产品表面质量好，厚度精度高,其厚度精度可控制在±0.03mm以内，能够达到冷轧产品的质量要求，大幅节约了能源消耗；另外，与现有中薄板坯直接轧制产品相比，其强度远远高于现有产品，对于实现汽车轻量化具有重大意义。
附图说明
图1为本发明产品金相组织图。
具体实施方式
下面对本发明予以详细描述：
表1为本发明各实施例及对比例的化学成分取值列表；
表2为本发明各实施例及对比例的主要工艺参数取值列表；
表3为本发明各实施例及对比例的性能检测情况列表。
本发明各实施例均按以下工艺生产：
1)铁水脱硫，并控制S≤0.002％，扒渣后铁水裸露面不低于96％；
2)常规电炉或转炉冶炼，及常规精炼；
3)进行连铸，控制中包钢水过热度在15～30℃，铸坯厚度在48～52mm，拉坯速度在4.0～7.0m/min；
4)进行铸坯入均热炉前的除鳞处理，并控制除鳞水的压力在300～400bar；
5)对铸坯进行常规均热，控制均热炉内呈弱氧化气氛，即使炉内残氧量在0.5～5.0％；
6)对铸坯入进行加热，并控制铸坯入炉温度在850～1050℃，出炉温度为1210～1230℃；
7)进行进轧机之前的高压水除鳞，并控制除鳞水压力在280～420bar；
8)轧制，并控制第一道次压下率为：52～63％，第二道次压下率为：50～60％，末道次压下率为：10～16％；控制轧制速度在8～12m/s；并在第一道次及第二道次之间进行中压水除鳞，除鳞水压力为200～280bar；控制终轧温度在870～910℃；
9)进行冷却，冷却方式为层流冷却、或水幕冷却、或加密冷却的方式冷却到卷取温度；
10)进行卷取，并控制卷取温度为605～635℃；
11)进行开卷落料后的奥氏体化，控制奥氏体化温度在850～920℃，并保温3～5min；
12)模具冲压成形，并在模具内保压10～20s；
13)进行淬火，控制淬火冷却速度在20～40℃/s；后自然冷却至室温。
所述薄板坯的轧制过程在轧机布置形式为6F产线或1R+6F产线、或2R+6F产线、或7F产线、或3R+4F产线、或2R+5F产线、或1R+5F产线任意一种布置形式的短流程产线进行即可。
表1本发明各实施例及对比例的化学成分(wt.％)
Figure PCTCN2017095492-appb-000001
表2本发明各实施例及对比例的主要工艺参数取值列表
Figure PCTCN2017095492-appb-000002
表3本发明各实施例及对比例的的力学性能情况列表
Figure PCTCN2017095492-appb-000003
从表3可以看出，通过薄板坯直接轧制的短流程工艺，实现了发明钢的强度达到了2100MPa以上，能够达到以热代冷的目的，为推进汽车轻量化发展具有重要意义。
本具体实施方式仅为最佳例举，并非对本发明技术方案的限制性实施。

Claims (3)

  1. 用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢，其组分及重量百分比含量为：C:0.31～0.40％，Si：0.36～0.44％,，Mn：1.6～2.0％，P≤0.006％，S≤0.004％，Als：0.015～0.060％，Cr：0.36～0.49％，Ti：0.036～0.045％或Nb：0.036～0.045％或V：0.036～0.045％或其中两种以上以任意比例的混合，B：0.004～0.005％，Mo：0.26～0.35％，N≤0.005％，余为Fe及不可避免的杂质；淬火后的金相组织为全板条马氏体；力学性能：屈服强度≥1300MPa，抗拉强度≥1900MPa，伸长率A80mm≥5％。
  2. 生产权利要求1所述的用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢的方法，其特征在于：其步骤：
    1)铁水脱硫，并控制S≤0.002％，扒渣后铁水裸露面不低于96％；
    2)常规电炉或转炉冶炼，及常规精炼；
    3)进行连铸，控制中包钢水过热度在15～30℃，铸坯厚度在48～52mm，拉坯速度在4.0～7.0m/min；
    4)进行铸坯入均热炉前的除鳞处理，并控制除鳞水的压力在300～400bar；
    5)对铸坯进行常规均热，控制均热炉内呈弱氧化气氛，即使炉内残氧量在0.5～5.0％；
    6)对铸坯入进行加热，并控制铸坯入炉温度在850～1050℃，出炉温度为1210～1230℃；
    7)进行进轧机之前的高压水除鳞，并控制除鳞水压力在280～420bar；
    8)轧制，并控制第一道次压下率为：52～63％，第二道次压下率为：50～60％，末道次压下率为：10～16％；控制轧制速度在8～12m/s；并在第一道次及第二道次之间进行中压水除鳞，除鳞水压力为200～280bar；控制终轧温度在870～910℃；
    9)进行冷却，冷却方式为层流冷却、或水幕冷却、或加密冷却的方式冷却到卷取温度；
    10)进行卷取，并控制卷取温度为605～635℃；
    11)进行开卷落料后的奥氏体化，控制奥氏体化温度在850～920℃，并保温3～5min；
    12)模具冲压成形，并在模具内保压10～20s；
    13)进行淬火，控制淬火冷却速度在20～40℃/s；后自然冷却至室温。
  3. 如权利要求2所述的生产用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢的方法，其特征在于：所述中薄板坯的轧制过程在轧机布置形式为6F产线或1R+6F产线、或2R+6F产线、或7F产线、或3R+4F产线、或2R+5F产线、或1R+5F产线任意一种布置形式的短流程产线进行。
PCT/CN2017/095492 2016-08-24 2017-08-01 用薄板坯直接轧制的抗拉强度≥1900MPa薄热成形钢及生产方法 WO2018036346A1 (zh)

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