控轧控冷TRIP钢的微观相组成及其与力学性能的关系

采用电子背散射衍射技术等实验方法,研究了控轧控冷工艺制备的铌钒微合金化C-Mn-Si系热轧TRIP钢的显微组织及相组成,并分析了与其对应的力学性能.奥氏体轧制过程中的热变形及随后的冷却工艺对最终各相组织的形貌、大小和分布都有直接影响,并决定TRIP钢最终的力学性能.对TRIP钢卷取温度的模拟结果显示,与450和350℃模拟卷取温度相比,400℃模拟卷取温度能使该钢获得更好的综合力学性能.     

控轧控冷工艺对SCM435钢盘条组织和性能的影响

试验钢SCM435（/%:0.33~0.38C,0.15~0.35Si,0.60~0.85Mn,≤0.025P,≤0.025S,0.90~1.20Cr,0.15~0.30Mo）盘条的生产流程为80t BOF-LF-280 mm×325 mm铸坯-160 mm×160 mm热轧坯-热连轧成Φ16 mm盘条。试验研究了160 mm×160 mm热轧坯由常规轧制工艺（开轧1060℃,精轧930~950℃,吐丝860~900℃,冷却速度0.5~0.6℃/s）和控轧控冷工艺（开轧1060℃,精轧820~850℃,吐丝780~820℃,冷却速度0.4~0.5℃/s）对SCM435钢热轧盘条组织和力学性能的影响。结果表明,随着精轧温度的降低和冷却速度的减小,钢热轧盘条的组织得到改善,抗拉强度明显降低;常规工艺轧制SCM435钢热轧盘条的抗拉强度平均952 MPa,组织为铁素体+珠光体+贝氏体+马氏体,控轧控冷工艺轧制的SCM435钢热轧盘条的抗拉强度平均817 MPa,组织为均匀的铁素体+珠光体。结合控轧控冷工艺原理对钢的组织和性能变化进行了分析。     

含铌微合金化热轧多相钢的控轧控冷工艺

通过热轧试验研究了两阶段轧制+层流冷却、空冷、超快冷的TMCP工艺对高硅铌钢、高硅Nb-Ti钢、低硅Nb-Ti钢显微组织和力学性能的影响。结果表明,控轧控冷后的试验钢含有铁素体、贝氏体、马氏体以及少量残余奥氏体的混合组织。在控轧控冷工艺参数相近的情况下,高硅铌钢、高硅Nb-Ti钢、低硅Nb-Ti钢的抗拉强度依次减小,其伸长率和强塑积依次增大。低硅Nb-Ti钢的伸长率和强塑积分别达到了41%、25 256 MPa.%的最大值。     

锰含量对奥氏体TRIP/TWIP钢低温冲击行为的影响

对3种不同锰含量的高锰奥氏体钢进行了低温冲击实验,分析了其冲击变形行为.实验结果表明:在-196～20℃温度区间冲击时,w(Mn)=14.8%(1号)的高锰钢均为脆性断裂,冲击过程中发生了形变诱发塑性(TRIP效应);w(Mn)=33.0%(3号)的高锰钢,即使在-196℃冲击时,仍呈现出韧性断裂,冲击过程中出现了形变诱导孪晶(TWIP效应);w(Mn)=18.8%(2号)的高锰钢有韧脆转变区间,韧脆转变温度约为-80℃,在冲击过程中同时存在TRIP和TWIP效应.随冲击温度降低,TRIP和TWIP效应更显著.     

600 MPa级热轧双相钢的研制与开发

为了满足汽车制造轻量化的行业需求,针对微合金化作用及控轧控冷工艺对双相钢组织和性能的影响展开研究,成功开发抗拉强度600 MPa级的热轧双相钢。生产实践表明,采用低C-Mn钢添加微合金元素Nb、Ti、Cr的成分优化设计,并结合控轧控冷工艺,所生产的600 MPa级热轧双相钢具有铁素体和马氏体两相组织结构,各项力学性能满足汽车用600 MPa级热轧双相钢要求。     

H08Mn2SiA拉拔断裂问题的探讨

主要针对H08Mn2SiA钢在拉拔中的断裂问题进行探讨，分析了化学成分和控轧控冷工艺参数对拉拔性能的影响。     

热轧双相钢DP600关键工艺技术

在热轧双相钢中,终轧温度、卷曲温度、控冷时间和控冷温度对铁素体晶粒的大小和马氏体的形态、分布和含量都有重要影响,直接影响双相钢力学性能。通过对双相钢动态CCT曲线的模拟,制定出了合理的工艺制度,系统分析了热轧双相钢DP600热轧生产过程中终轧温度、卷取温度、控冷时间和控冷温度对双相钢的影响,对热轧双相钢的关键技术参数进行了研究,最终确定了合适的双相钢热轧生产工艺。     

铁 素 体 贝 氏 体 钢 的 扩 孔 性 能

 通过力学拉伸实验和扩孔实验对铌、钛复合微合金化低碳热轧铁素体贝氏体钢板的力学性能和成形性能进行了研究,以了解控轧控冷工艺参数和微观组织对其性能的影响,并分析了影响扩孔率的因素以及铁素体贝氏体钢的裂纹扩展机制。研究结果可为开发高强度、高扩孔性能的汽车底盘用钢板提供实验依据。     

超高强铁素体/贝氏体双相钢的控轧控冷

通过实验室热轧机组的控轧控冷试验,研究了控轧控冷参数对超高强铁素体/贝氏体双相钢组织性能的影响。结果表明,采用不同温度终轧,轧后不同方式冷却,抗拉强度几乎都在1 000MPa以上,屈强比在0.54～0.62之间,伸长率在13%～17%之间。铁素体晶粒随终轧温度降低和冷却速度加快而细化;终冷温度降低,贝氏体量增多。经800℃终轧后层流冷却至560℃左右空冷,由于铁素体晶粒细化,组织中大量的粒状贝氏体、无碳化物贝氏体、少量的孪晶马氏体以及残余奥氏体的存在使抗拉强度达1 130MPa,伸长率达16%,强塑积达到18 080MPa.%的最高值。控轧控冷获得以铁素体/贝氏体双相组织为主并含有少量残余奥氏体+马氏体的复相组织,使试验钢具有了优异的力学性能。     

采用优化成分及控轧控冷降低15MnV钢含锰量的研究

在实验室条件下,研究了15MnV钢降锰的可能性和有效途径。通过试验得出,采用优化碳、钒含量和控轧控冷工艺,将15MnV钢的锰含量降至1.2％仍满足原钢种机械性能要求是可能的。降锰15MnV钢能达到规定强韧性的较佳碳含量为0.12～0.14％、钒含量为0.08～0.12％;合适的控轧控冷工艺为加热温度1150℃、道次变形量14～21％、终轧温度900℃、轧后冷迷4℃/s、终冷温度800℃。     

Microstructures and Mechanical Properties of Fe-Mn-（Al, Si） TRIP/TWIP Steels

The mechanical properties and microstructure of two low carbon high manganese steels with 23.8% （No. 1） and 33% （No. 2） （mass percent） of manganese were investigated. The results showed that No. 1 steel possesses high strength and high plasticity, and No. 2 steel has a relatively high strength and extraordinary plasticity. The No. 1 steel exhibits both TRIP （transformation induced plasticity） and TWIP （twin induced plasticity） effects during the deformation; while only TWIP effect appeared under the same deformation condition for No. 2 steel. The comparison between the microstructures and mechanical properties of two steels was made, and the strengthening mechanisms were also analyzed.     

Study on Microstructures and Mechanical Properties of High Manganese Steels with TRIP/TWIP Effects

In the present work, advanced high strength and high ductility TRIP/TWIP steels with different manganese concentrations were studied. The microstructures of these steels were evaluated prior to and after deformation and the mechanical properties of these steels were determined. The microstructure analysis indicated that both TRIP and TWIP effects appeared in the steel with lower Mn content, while the TWIP effect was the dominant deformation mechanism in the steel with a higher Mn content, with many deformation twins formed during the deformation. In addition, the forming limit diagrams of these steels were recorded and the results showed an excellent formability.     

Formability of TRIP/TWIP Steel Containing Manganese of 18.8%

 The mechanical property and forming limit experiments were carried out on a high manganese TRIP/TWIP steels with 18.8% manganese. And the forming limit diagram was obtained. This high manganese steel shows outstanding mechanical properties combining high strength and good formability. Its FLD0 is about 38%. The effects of conventional mechanical property on the FLD0 were analyzed. With the contents of Mn increasing, FLD0 increases, which indicates TWIP effect is advantageous to enhance formability. Combining with three classical models and volume invariable principle, a FLD model was established, which fits high manganese steels very well.     

Partial Inverse Grain Size Dependence of Strength in High Mn Steels Microalloyed With Nb

 Two steels without and with Nb addition were chosen to investigate the effects of Nb on the microstructures and the mechanical properties of Fe-Mn-Al-Si steels. The results revealed that Nb refined the grains markedly and both TRIP and TWIP effects occurred during deformation process. The Nb containing steel possesses higher yield strength and much lower tensile strength, the latter being explained by the suppression of TRIP effect due to the increase of stacking fault energy. This indicates grain refining is secondary for strengthening of steels when TRIP or TWIP effect exists during the deformation of low carbon and high Mn steels.     

Effect of Controlled Cooling After Hot Rolling on Mechanical Properties of Hot Rolled TRIP Steel

A three-step cooling pattern on the runout table（ROT）was conducted for the hot rolled TRIP steel.Microstructural evolution during thermomechanical controlled processing（TMCP）was investigated.Processing condition of controlled cooling on a ROT in the laboratory rolling mill was discussed.The results indicated that the microstructure containing polygonal ferrite,granular bainite and a significant amount of the stable retained austenite can be obtained through three-step cooling on the ROT after hot rolling.TMCP led to ferrite grain refinement.Controlled cooling after hot rolling resulted in the stability of the remaining austenite and a satisfactory TRIP effect.Excellent mechanical properties were obtained through TMCP for the hot rolled TRIP steel.     

Static Tensile Deformation Behaviors of an Fe-30Mn-3Al-3Si TWIP Steel Studied by In-Situ Neutron Diffraction

TWIP (TWinning Induced Plasticity) steel is one of the advanced steels with attractive mechanical properties.The typical composition of TWIP steel includes a large amount of manganese with some aluminum and silicon.Previous study has shown that TWIP steel exhibits high strength with adequate elongation at high strain rates,so that TWIP steel is desired to be applied for automotive use.However,there are few studies concerning the deformation behaviors aimed to make clear the TWIP effect in TWIP steel.In this study,static tensile deformation behaviors of an Fe-30Mn-3Al-3Si TWIP steel and a SUS310S one were studied by in situ neutron diffraction during tensile deformation.In terms of mechanical properties obtained by the static tensile tests,the TWIP steel showed better balance of tensile strength and uniform elongation than the 310S steel.The angular dispersion neutron diffraction with a wavelength of 0.16 nm was performed during stepwise tensile testing by using a neutron diffractometer for residual stress analysis (RESA) at the Japan Atomic Energy Agency.A specimen was extended in a step by step manner and neutron diffraction profiles of (111),(200) and (311) for austenite were obtained at each step.The diffraction peak,lattice plane spacing,lattice plane strain and so on were determined by the profile analysis as a function of applied stress.The changes of lattice plane strain for austenite in the TWIP and 310S steels indicated several deformation stages in the tensile deformation and can be discussed the difference of intergranular stress between the two samples.     

高锰奥氏体TRIP/TWIP钢的组织和力学性能

研究了两种不同锰含量的高锰奥氏体钢在室温拉伸变形过程中力学性能和组织的变化.结果表明,随着钢中锰含量的变化,实验钢在流变应力的作用下出现相变诱导塑性的TRIP效应和孪晶诱导塑性的TWIP效应.在1×10-3 s-1的初始应变速率条件下,锰的质量分数为23.8%的实验钢可达到666 MPa的抗拉强度和67%的伸长率,而锰的质量分数为33%的实验钢可达到540 MPa的抗拉强度和97%的伸长率.并且在10-3～10-1 s-1的初始应变速率范围内,实验钢的抗拉强度对于流变应力不敏感,而实验钢的塑性则表现出一定的应变速率敏感性.由于该钢具有较好的综合力学性能,有望作为新一代高强度、高塑性汽车用钢.     

中锰钢的研究进展与前景

总结了国内外中锰钢研究现状, 对文献中中锰钢的成分设计、成型工艺、热处理工艺、组织性能调控等进行汇总分析, 得到了合金元素、成型工艺、微观组织结构和热处理对力学性能的影响规律, 并对中锰钢的性能例如lüders带和PLC带对加工硬化率的影响、氢致延迟开裂性能给予了重点关注和讨论; 同时提出借鉴第二代先进高强钢(纯奥氏体相)"层错能"这一控制形变模式的概念, 对中锰钢中奥氏体相的形变模式提出预测; 最后对目前中锰钢研究的争议问题、发展前景及未来可能面对的问题进行阐述.      

Martensite Transformation and Its Control in DP,TRIP and TWIP Steels

Designing of alloy concept and process for DP,TRIP and TWIP steels stressing at martensite transformation are analyzed.For DP steel,austenite volume percent and its carbon content at different intercritical temperatures are calculated as well as the tensile strength of the steel,which meet well with the experimental result.The condition for dissolution of carbide is discussed by experiments and predicted by kinetic estimation.Several sample TRIP steels are prepared and their concentration profiles are calculated showing different diffusion characteristics of elements.Calculation also shows carbon enrichment is successful in this stage through the quick diffusion of carbon from ferrite to austenie.In order to maintain the austenite stability or to prevent precipitation of cementite,minimum cooling rate from the intercritical zone to over aging stage is obtained through kinetic simulation.Bainite transformation is estimated,which indicates the carbon rerichment from ferrite of bainite structure to austenite in this stage is also successful.Thermal HCP martensite transformation and the strain induced martensite transformation in TWIP steel is introduced.Relationship between transformation and mechanical properties in the steel is also mentioned.     

Mn和Si对中锰热轧高强钢组织和性能的影响

为了研究Mn和Si元素对中锰热轧高强钢显微组织和力学性能的影响,设计了不同Mn、Si含量C-Si-Mn系试验用钢.利用热膨胀仪、扫描电镜、透射电镜、X射线衍射和单向拉伸等实验方法对试验用钢的相变点、显微组织、残余奥氏体含量和力学性能进行了测定与分析.结果表明：Mn和Si对中锰热轧高强钢的显微组织影响较大,对于低Si高Mn的试验钢,其显微组织主要由粒状贝氏体组成;对于高Si高Mn的试验钢,主要由贝氏体铁素体、马氏体和残余奥氏体组成;对于高Si低Mn的试验钢,则由块状铁素体、贝氏体、马氏体和残余奥氏体组成.高Si高Mn试验钢获得最高的综合力学性能,抗拉强度达1200 MPa以上,总伸长率为16%,强塑积接近20 GPa·%.分析认为,试验钢这种高强度和较高的塑性是由超细晶组织和TRIP效应共同决定的.