一种低成本高强塑积汽车用钢及其制备方法

专利号：CN201110005359．4专利权人：钢铁研究总院一种低成本高强塑积汽车用钢及其制备方法,属于汽车用钢技术领域。基于合理化学成分设计和合金元素的配分,关键在于控制马氏体相变、C／Mn等溶质再次配分和奥氏体逆相变,获得多相、亚稳、及多尺度的M3型组织结构。其特征为：主要通过w（C）0．02％～0．509／6和zv（Mn）3．50％～9．00％使钢板、钢卷等在工业生产冷却过程中获得马氏体组织,且在Acl以下100℃到Acl的保温过程中通过Mn和C配分,获得超细尺寸的逆转变奥氏体和α相基体。可实现汽车用高强塑积热轧和冷轧钢板的工业生产。     

Ti、V、Nb元素对DH36焊接热影响区显微组织的影响

结合Ti、V、Nb元素对焊接热影响区微观组织的影响,添加不同微合金元素,进行实验室真空冶炼-轧制DH36高强船板钢。利用Gleeble3500试验机,针对加入不同微合金元素的DH36船板钢进行线能量为50 k J/cm和100 k J/cm的焊接热模拟试验,研究微合金元素V、Ti、Nb对焊接热影响区组织性能的影响。结果表明,在DH36焊接热影响区中,Ti生成了氧化物,该氧化物诱发了针状铁素体,钉扎了奥氏体晶界,而V、Nb并未生成夹杂物。     

第3代汽车钢的组织与性能调控技术

  介绍了第3代汽车钢的基础研究与工业试制工作。对国内外高性能汽车钢进行了回顾总结,在以“多相（Multi phase）、亚稳（Meta stable）、多尺度（Multi scale）”（简称M3）为特征的组织调控理论的指导下,提出了高强塑积第3代汽车钢的超细晶基体与亚稳相的组织调控思路,采用了新型中锰合金化和逆转变奥氏体(Austenite Reverted Transformation, ART)退火的技术思路。详细介绍了第3代汽车钢的基础研究进展及工业试制结果,内容包括奥氏体逆转变退火机制,超细铁素体与亚稳奥氏体的双相形成规律,高强塑积汽车钢的力学行为及其强塑化机制,第3代汽车钢的工业试制流程及其服役性能和在汽车上应用技术与前景。本研究结果形成了以高强度和高塑性为特征的高塑积第3代汽车钢的原型钢技术,为汽车轻量化与碰撞安全性能的提高奠定了材料技术基础。     

稀土在汽车用先进高强钢中的研究现状

成分设计与优化是先进高强钢增强、增塑以及增韧的关键技术之一。随着钢质高纯化装备和技术的进步与发展,稀土元素在钢中的应用已由净化、夹杂物改性逐步向微合金化过渡。从第一代铁素体基软钢和高强低合金钢向第二代奥氏体基超高强钢,再到多相、亚稳和多尺度组织调控的第三代高强韧性钢,先进高强钢的微合金化技术一直是控制组织和性能的有效举措。稀土原子具备较大原子半径以及与O、S的高亲和力等优异特性,可从控制凝固与固态相变,影响碳元素与合金元素的扩散等多方面影响先进高强钢的组织结构,从而对其力学性能、成形性能以及耐腐蚀等服役性能产生显著影响。本文阐述了稀土元素分别在第一代、第二代和第三代典型先进高强钢中的作用机理,并展望了稀土元素在未来汽车钢中的应用前景。      

汽车用冷轧低合金高强钢HC340LA的开发

介绍柳钢开发汽车用冷轧低合金高强钢HC340LA,采用的在低碳钢中添加Nb、Ti微合金元素的成分设计、冷热轧工艺、再结晶温度、罩式退火工艺等以及产品性能,并实现批量供货。     

微合金元素对低合金高强钢焊缝及热影响区组织性能的影响

介绍了新一代低合金高强结构钢发展过程中可焊接性及接头性能的重要性。焊接接头性能的优劣取决于接头的微观组织。焊接接头微观组织是在焊接凝固以及随后的固态相变过程中生成的,组织种类与很多因素有关,其中,焊缝金属中微合金元素的影响非常大。综述了微合金元素Ti,V,Ni,Cr,Nb,B,稀土等对低合金高强钢焊缝及热影响区组织和性能的影响,着重论述了针状铁素体形成过程中上述微合金元素及一些非金属夹杂物的作用机制与影响途径,并对该领域的发展进行了展望。     

超高强热轧贝氏体双相钢中的亚稳组织与成型性

贝氏体双相钢具有强度高、初时加工硬化率高以及强度和韧性良好配合等优点,应用于运输机械可节能减排。本文在对高强钢的合金元素减量化的前提下,采用超快冷为核心的TMCP技术开发了强韧性较好的抗拉强度为450MPa的双相钢,其组织主要为贝氏体+铁素体。由于超快冷保留了较多的形变亚结构,使得组织中存在亚稳奥氏体。用平底凸模法测定扩孔率达到120%,亚稳奥氏体对钢的扩孔性能有影响。     

退火工艺对Nb-V微合金化双相钢组织性能的影响

为了进一步提升双相钢性能、探究Nb-V元素复合添加对双相钢组织性能的影响,在实验室研发了Nb-V微合金化的冷轧双相钢。利用连退模拟试验机、扫描电镜等设备,系统地研究了退火温度和过时效温度对双相钢组织性能的影响。结果表明,抗拉强度和伸长率随着退火温度的升高变化不大,屈服强度在组织中铁素体含量明显减少后有显著提升;Nb、V元素的添加细化了组织,可以提高综合性能。随着过时效温度的升高,试验钢主要组织由起初低温时的淬火马氏体+回火马氏体变为高温时的粒状贝氏体,残余奥氏体比例也逐渐增大。高温过时效时,试验钢强度的降低主要由回火马氏体的软化造成;低温过时效时,V析出量的增加也对试验钢的强化起到了重要作用。     

退火工艺对Nb-V微合金化双相钢组织性能的影响

为了进一步提升双相钢性能、探究Nb-V元素复合添加对双相钢组织性能的影响,在实验室研发了Nb-V微合金化的冷轧双相钢。利用连退模拟试验机、扫描电镜等设备,系统地研究了退火温度和过时效温度对双相钢组织性能的影响。结果表明,抗拉强度和伸长率随着退火温度的升高变化不大,屈服强度在组织中铁素体含量明显减少后有显著提升;Nb、V元素的添加细化了组织,可以提高综合性能。随着过时效温度的升高,试验钢主要组织由起初低温时的淬火马氏体+回火马氏体变为高温时的粒状贝氏体,残余奥氏体比例也逐渐增大。高温过时效时,试验钢强度的降低主要由回火马氏体的软化造成;低温过时效时,V析出量的增加也对试验钢的强化起到了重要作用。     

中国汽车发展趋势及汽车用钢面临的机遇与挑战

 首先对中国汽车发展的现状与趋势进行了分析预测,2020年中国汽车产量可能达到3 600万辆。伴随汽车迅速发展的同时,汽车用钢也面临安全、环境、资源、能源及成本等方面的挑战。中国汽车的高速增长和庞大的市场为汽车用钢的发展带来重大机遇,同时冶金行业也面临来自非钢材料的激烈竞争和用户方面的挑战。文章就汽车用钢的发展潜力和钢铁行业可能采取的应对方案进行了讨论,分析了近年汽车用高强钢合金含量的发展、新型高强钢的组织性能精细控制及应用技术、超高强双相钢及新型淬火配分钢的精细组织、冷轧高强钢中的纳米粒子析出控制、热成形钢的工艺与组织性能以及先进高强钢的成形应用技术等。最后,举例介绍了汽车用钢供应商的先期介入（EVI）服务体系的加强与完善。     

Unexpected Effect of Nb Addition as a Microalloying Element on Mechanical Properties of δ-TRIP Steels

The concept of microalloying was applied to the δ-TRIP(transformation-induced plasticity)steel to investigate the feasibility of increasing the mechanical properties and understanding the effect of microalloying on the morphology and structure of the steel.A hot rolled δ-TRIP steel with three different contents of Nb(0,0.03,0.07 mass%)was subjected to the microstructural and mechanical examination.The high Al and Si concentration in these steels guaranteed the presence of the considerable δ-ferrite phase in the microstructure after the casting and the subsequent hot rolling.The obtained results showed that Nb dramatically affects the microstructure,the dynamic recovery and recrystallization behavior,as well as the grain shape and thus the stability of austenite after the thermomechanical process of hot rolling.The results also revealed an unexpected effect of Nb on the mechanical properties.The addition of Nb to theδ-TRIP steel led to a significant decrease in the ultimate strength(from 1 144 to 917 MPa)and an increase in ductility(from 24% to 28%).These unconventional results could be explained by the change in the steel microstructure.The work-hardening behaviors of all samples exhibit three stages of the work-hardening rate evolution.At the stage 2,the work-hardening rate of the studied steels increased,being attributed to the TRIP effect and the transformation of austenite to martensite.     

Effects of Niobium Addition on Microstructures and Formability in Si‐Al‐Mn TRIP Cold‐rolled Steels

The effects of Nb addition on microstructures and formability in Si‐Al‐Mn TRIP cold‐rolled steels were investigated. These steels were intercritical annealed at 770 °C for 5 min, and isothermally treated at 400 °C for 3 min. Microstructural observation, tensile tests and forming limit diagram (FLD) tests were conducted, and the changes of retained austenite volume fraction as a function of tensile strain were measured by using an X‐ray diffractometer. The results showed that Nb addition makes grain size refined, the volume fraction of ferrite increase and that of bainite decrease, however, obviously it does not affect the volume fraction and carbon content of retained austenite. The Nb addition increased the stability of retained austenite owing to grain refinement. With Nb addition, increase in strength, ductility, strain hardening exponent and formability could be achieved simultaneously. These findings indicate that Nb addition can be a new direction of microalloying design for the low carbon TRIP steels with excellent formability and high stability of retained austenite.     

Advanced Cold Rolled Steels for Automotive Applications

Advanced high‐strength steels offer a great potential for the further development of automobile bodies‐in‐white due to their combined mechanical properties of high formability and strength. They represent the first choice in material selection for strength and crash‐relevant parts with challenging geometries. The intensive development of multiphase steels by ThyssenKrupp Steel has led to hot dip galvanizing concepts with an outstanding forming potential. Hot rolled, hot dip galvanized complex‐phase steels are currently produced in addition to cold rolled dual phase (DP) and retained austenite (RA) or transformation induced plasticity (TRIP) steels. New continuously annealed grades of steel are being developed with tensile strength levels of up to 1000 MPa in combination with sufficient ductility for the high demands of structural automobile components. These steels make use of the classic advantages of microalloying as well as the principles of DP steels and RA / TRIP steels. Further improvement of properties will be reached by the new class of high manganese alloyed steels.     

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The beneficial effects of the elements Nb, V, Ti and N in microalloyed forging steels was reviewed. Among these elements, the vanadium is the most effective and commonly used strengthening element for non-quenched and tempered steels due to its high solubility in the steels. The effects of grain refinement and precipitation strengthening can be achieved in non-quenched and tempered steels through micro-alloying elements Nb, V and Ti inhibiting the recrystallization of deformed austenites and grain growth, and enchancing strain induction precipitation during hot processing. Although the Nb, V and Ti are all strengthening elements, their strengthening effect and strengthening mechanism vary with the C and N content of these steels. Therefore, it would be the most effective way to improve strength and toughness of the ferrite-pearlite non-quenched and tempered steels through making use of the microalloying characteristics of the elements Nb, V, Ti and N and meanwhile applying the proper forging process.     

Effect of Nb on Microstructure Evolution in Cold Rolled Dual-Phase Steels:Interaction of Recovery,Recrystallization and Phase Transformations

The effects of Nb addition,individually and in combination with Ti,were evaluated over a range of coiling temperatures.Coiling temperature influences the ratio of soluble and precipitated Nb in the hot rolled steel containing 0.08 % C and 2.2 % Mn.Nb bearing precipitates can co-precipitate on TiN and impact the microstructure and mechanical properties of the steel after annealing treatment.Microstructure characterization revealed that recovery and recrystallization processes preceded austenite formation.The effects of Nb on austenite formation in cold rolled steels during heating and isothermal holding and on austenite decomposition during subsequent cooling were investigated using dilatometry.The addition of Nb retarded ferrite recrystallization starting temperature,but had no significant effect on the starting temperature of austenite formation during heating.The Nb addition also accelerated austenite formation once the transformation started,and was beneficial for the formation of a finer and homogeneous microstructure.     

Effect of Nb Microalloying and Hot Rolling on Microstructure and Properties of Ultrathin Cast Strip Steels Produced by the CASTRIP<Superscript>®</Superscript> Process

The microstructure and corresponding tensile properties of both plain and Nb-microalloyed grades of ultrathin cast strip (UCS) low alloy steel produced using the CASTRIP^® process were studied. Both as-cast and hot-rolled strip cast steels with various levels of Nb microalloying were manufactured and investigated in this study. Hot rolling had little effect on the yield strength of Nb microalloyed UCS specimens for a given chemical composition, but resulted in a slightly finer microstructure. The effect of Nb microalloying was significant, and this is attributable to the promotion of finer, tougher austenite transformation products such as bainite and acicular ferrite at the expense of large polygonal ferrite grains. A fine dispersion of Nb solute clusters was observed in all Nb-containing steels following hot rolling, and it is suggested that this also contributes to the observed strengthening.     

高性能汽车钢组织性能特点及未来研发方向

 介绍了先进汽车用钢的组织和性能特点,认为具有较低强塑积的第一代汽车钢主要是通过铁素体、马氏体等多种基体组织的选取和配合对强度和塑性进行调控,第二代汽车钢通常具有单相奥氏体组织,表现出超高的强塑积,在汽车轻量化和安全性方面都有明显促进作用,但是其高合金质量分数提高了生产成本和难度,不利于规模化生产和应用。而第三代汽车钢则是通过在马氏体或超细晶铁素体基体上引入大量的亚稳奥氏体来提高汽车钢的强度和塑性,从而大幅度提高钢的强塑积。第三代汽车钢综合性能比第一代汽车钢提高1倍以上,其强塑积达到了25～50 GPa·%,接近或达到了第二代汽车钢的强塑积。新型合金化设计、高强度基体组织调控和大量亚稳奥氏体控制是第三代汽车钢的重要研究内容。基于轻量化与高安全性要求,低密度化与高强化将是未来第三代汽车钢的一个主要发展方向。     

鞍钢先进高强汽车用钢的研制开发

介绍了鞍钢先进高强汽车用钢开发研制情况,包括以980 MPa级DP钢、TRIP钢、TWIP钢和QP钢为代表的热轧、冷轧和热镀锌先进高强钢系列产品,以及鞍钢开发的先进高强钢热镀锌生产技术,并对鞍钢先进高强汽车钢未来的发展方向进行了展望。