新型Q-P-T钢性能及其微观组织

为了提高钢的综合强塑性能,根据徐祖耀提出的淬火-分配-回火(Q-P-T)热处理新工艺,即在Fe-Mn-Si-C钢中加入合金元素Nb和V,利用碳化物弥散析出强化,开发出了性能比QP钢更为优越的Q-P-T钢,证实了Q-P-T工艺设想的预期结果。通过微观结构和力学性能表征着重研究了淬火温度对残留奥氏体含量和性能的影响,从而获得了试验钢最佳的淬火温度。     

Control of Austenite Characteristics and Ferrite Formation Mechanism by Multiple-Cyclic Annealing in Quenching and Partitioning Steel

Quenching and partitioning (Q&P) treatment is a novel method to produce advanced high strength steel with excellent mechanical properties. In this study, combination of multiple-cyclic annealing and Q&P process was compared with traditional cold-rolled Q&P steel to investigate the microstructural characteristics and austenite retention. The results showed that retained austenite in traditional Q&P sample was principally located in the exterior of austenite transformation products, while those in multiple-cyclic annealing samples were mainly distributed inside the transformation products. With the increase in cyclic annealing number, both of austenite fraction and austenite carbon content increased, attributing to higher initial austenite carbon content and larger number of austenite/neighbored phase interface to act as carbon partitioning channel. In traditional Q&P sample, the deformed ferrite was recrystallized by sub-grain coalescence, while the austenite was newly nucleated and grew up during annealing process. As a comparison, the ferrite in multiple-cycle annealing samples was formed by means of three routes: tempered martensite that completely recovered with retention of interior martensite variant, epitaxial ferrite that formed on basis of tempered martensite, ferrite that newly nucleated and grew up during the final annealing process. Both of lath martensite and twin martensite were formed as initial martensite and then tempered during partitioning process to precipitate ε carbide with C enrichment, Mn enrichment and homogeneous Si distribution. Compared with the traditional cold-rolled Q&P steel, the Q&P specimens after multiple-cyclic annealing show smaller strength and much larger elongation, ascribing to the coarser microstructure and more efficient transformation induced plasticity (TRIP) effect deriving from retained austenite with high carbon content and larger volume fraction. The application of double annealing treatment can optimize the mechanical properties of Q&P steel to show a striking product of strength and elongation as about 29 GPa%, which efficiently exploit the potential of mechanical performance in low carbon steel.     

残余奥氏体增强低碳Q-P-T钢塑性的新效应

低碳Fe-0.25C-1.48Mn-1.20Si-1.51Ni-0.05Nb(质量分数,%)钢通过新型Q-P-T工艺处理后获得高的抗拉强度和良好延伸率的综合性能.对该低碳Q-P-T钢在拉伸过程中残余奥氏体含量的XRD测定和形变孪晶马氏体的TEM观测,证明了相变诱发塑性(TRIP)效应的存在.基于形变过程中马氏体和残余奥氏体中的平均位错密度测定和TEM的观察,验证了在中碳钢中最新发现的残余奥氏体吸收位错(DARA)新效应在低碳钢中同样存在,由此提出了DARA效应产生的条件,阐明了残余奥氏体增强高强度钢塑性的机制.     

Dynamic Compression Behavior and Microstructure of a Novel Low-Carbon Quenching-Partitioning-Tempering Steel

A 0.2C-1.5Mn-1.5Si-0.6Cr-0.05Nb （wt%） steel is treated respectively by novel quenching-partitioning-tempering （Q-P-T） process and traditional quenching and tempering （Q＆T） process for comparison. X-ray diffraction analysis indicates that Q-P-T steel has about 10% retained austenite, but Q＆T steel hardly has one. With the increase of com- pression strain rate from 7 × 10^2 to 5 × 10^3 s^-1, the flow stress of Q-P-T steel increases, which demonstrates the positive strain rate effect, but does not exist in Q＆T steel. The characterization of scanning electron microscopy indicates that a large number of long, straight martensite laths in Q-P-T steel will bend or be destroyed by large compressive strain of 35% at 5 × 10^3 s^-1. However, relative small compressive s~xain of about 5% at 7× 10^2 s^-1 almost does not have any effect on the original lath morphology. The characterization of transmission electron microscopy further reveals the origin of the positive strain rate effect and the microstructural evolution during dynamic compressive deformation.     

Nb对Fe-28Mn-10Al-C低密度钢组织与机械性能的影响

开发制备了一种汽车用含0.5％Nb(质量分数)的Fe-28Mn-10Al-C-0.5Nb 低密度钢,旨在研究Nb 在奥氏体Fe-Mn-Al-C低密度钢中的存在形态,以及Nb 添加对Fe-Mn-Al-C 低密度钢组织与力学性能影响.结果表明,Fe-28Mn-10Al-C 低密度钢中加入Nb 后,奥氏体晶粒平均尺寸由39....     

30CrMo钢Q-P-T及深冷处理后的组织与性能

利用光学显微镜(OM),扫描电镜(SEM),X射线衍射仪(XRD)和力学性能测试等研究了不同深冷处理工艺对经Q-P-T工艺处理后30CrMo钢组织和力学性能的影响。结果表明,30CrMo钢最佳的Q-P-T+深冷工艺为:260℃淬火温度,400℃碳配分温度、60 s碳配分时间、-100℃深冷温度、1 h深冷保温时间和一次深冷。经最优的Q-P-T+深冷工艺处理后,30CrMo钢的碳化物的平均尺寸较小,残留奥氏体含量明显增加,残留奥氏体的体积分数约为7.9%,显微硬度约为482 HV,抗拉强度约为1629 MPa,强塑积约为20525 MPa·%,伸长率约为12.6%,其综合力学性能得到了较大幅度提高。     

用于超高强度钢的淬火-碳分配-回火（沉淀）（Q-P-T）工艺

为进一步提高钢的强度,改造淬火-碳分配（Q—P）工艺,在超高强度钢的成分设计中加入碳化物形成元素Nb或（和）Mo,使在马氏体基体上析出碳化物,提出淬火-碳分配-回火（沉淀）（Q—P—T）工艺。将按设计超高强度钢大致成分的钢进行Q—P—T处理后,得钢的抗拉强度高达〉2000MPa,总断后伸长率〉10％。和迄今发展的各类含碳小于0．5％钢的综合力学性能相比,Q—P—T钢可能成为优异的超高强度钢。     

淬火-分配-回火工艺和多循环淬火-分配-回火工艺

综述了由徐祖耀院士提出的淬火-分配-回火（Q-P-T）新工艺的背景和发展现状。总结了先进Q-P-T钢从超高强度到高强塑性的发展,重点论述了在形变中残留奥氏体增强超高强度钢的塑性的微观机制。鉴于单循环Q-P-T工艺对大尺寸工件和不同尺寸热轧板（或H型钢）处理的局限性,提出了多循环淬火-分配-回火（MQ-P-T）工艺及其在冶金行业热轧板（或H型钢）的工程应用。最后列举了MQ-P-T工艺在机械行业的应用实例。     

Nb对高Ti耐候钢连续冷却后显微组织及硬度的影响

采用Gleeble热模拟试验机研究了微合金元素Nb对高Ti耐候钢奥氏体连续冷却转变行为的影响,通过光学显微镜(OM)、透射电镜(TEM)以及硬度测试等手段比较了0.050%Nb和无Nb试验钢连续冷却转变后显微组织和硬度的变化。结果表明,Nb能抑制铁素体相变,促进贝氏体相变。冷却速度由5 ℃/s提高到10 ℃/s,两种试验钢的晶粒细化效果均最显著,无Nb钢和0.050%Nb钢硬度分别增加了22 HV0.2和25 HV0.2。冷却速度为40 ℃/s时,无Nb试验钢中析出物主要为6～13 nm球形Ti(C, N)复合析出物;含Nb试验钢中主要为5～12 nm球形(Ti, Nb)(C, N)和10～15 nm方形(Ti, Nb)(C, N)复合析出物,含Nb试验钢析出物较多,因此析出强化作用更强。在高Ti耐候钢中,Nb产生的晶粒细化作用并不显著。在相同冷速下,0.050%Nb试验钢的硬度略高于无Nb试验钢,最大差值仅为11 HV0.2。     

低碳微量铌钢形变强化相变的组织演变

利用热模拟压缩变形实验研究了含Nb钢过冷奥氏体形变强化相变的组织演变规律,探讨了微量Nb对形变强化相变的影响,并对转变动力学和晶体取向进行了分析.结果表明,含Nb钢在A3-Ar3之间的形变过程中主要以形变强化相变为主.与低碳钢相比,含Nb钢形变强化相变的孕育期变长,完成相变所需的应变量也相应增加,使得其转变动力学曲线向高应变方向平移.含Nb钢的转变动力学曲线可划分成两个阶段,其中第一阶段固溶Nb阻碍铁素体相变,使孕育期推迟,而第二阶段形变过程中动态析出的Nb(C,N)既为铁素体相变提供了大量的形核位置,又钉扎铁索体晶界,阻碍铁索体晶粒的长大.在这种以形核为主的过程中出现了<111>和<001>两种织构的交替变化.     

不同成分体系罩退高强IF钢的组织与性能

研究了不同成分体系含P高强IF钢在罩式退火条件下的析出物、组织与性能差异。结果表明,微合金元素Nb和Ti是影响试验钢析出物、组织和性能的关键因素。添加Ti的Ti-HIF和Nb+Ti-HIF两种成分体系的试验钢FeTiP析出物数量多,r值较差;添加Nb可以细化钢板组织,使钢板析出强化、细晶强化、固溶强化效果更显著,有利于提高抗拉强度;Nb-HIF成分体系试验钢性能最优,适合罩式退火工艺条件下生产。     

35CrMo钢强韧化工艺研究

研究了35CrMo钢经不同工艺热处理后的组织和力学性能。结果表明,与经常规调质处理的35CrMo钢相比较,经790℃亚温淬火+高温回火或常规调质处理后再经790℃亚温淬火+高温回火的35CrMo钢具有更好的强韧性,特别是后者,其抗拉强度、屈服强度、断后伸长率、断面收缩率和冲击韧度分别达到了986MPa、923MPa、18%、41%和156J/cm2。钢的塑性和韧性的提高是由于组织均匀细小、具有少量游离铁素体存在所致。     

Nb对热轧低碳贝氏体钢组织与性能的影响

为开发600 MPa级热轧贝氏体钢,设计了两种钢种成分,以C-Si-Mn系贝氏体钢为基础,添加一定合金元素Nb,经冶炼、轧制后进行了组织观察、析出沉淀分析以及性能测试试验,研究Nb元素在热轧贝氏体钢中的作用。结果表明,添加0.025wt%的Nb,能细化贝氏体板条,贝氏体板条短小,有利于提高钢的强度与韧性。弥散的含Nb碳氮化物颗粒析出,起到析出强化作用,提高钢的强度。Nb可明显改善低碳高强贝氏体钢的综合性能。     

Nb元素对含Ti低碳微合金钢连续冷却转变及析出行为的影响

采用热模拟试验机研究了Nb元素对含Ti低碳微合金钢的动态连续冷却转变行为的影响,利用OM和TEM对等温淬火工艺处理后实验钢的显微组织和析出行为进行观察和分析。结果表明：Nb元素使得含Ti低碳微合金钢的动态CCT曲线整体向右下方移动,大大减小了先共析铁素体和珠光体相变区,同时扩大了针状铁素体和贝氏体相变区,在较低冷速时能得到较多的针状铁素体;含Nb- Ti和含Ti两种实验钢经等温淬火工艺处理后的显微组织均由铁素体和马氏体两相组成,铁素体相中析出物平均尺寸分别为6.8、4.2 nm,利用Orowan机制对析出强化量进行计算得出析出强化量分别为90.6、142.3 MPa。     

铌对高强度51CrV钢组织及性能的影响

借助光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)与万能拉伸试验机等研究了铌元素的添加对51CrV钢奥氏体晶粒尺寸、淬火和回火组织以及力学性能的影响.结果表明:0Nb和0.02wt％Nb试验钢的奥氏体平均晶粒尺寸分别为10.0μm和3.1μm,添加0.02wt％Nb的51CrV钢奥氏体晶粒尺寸显著细化、板条...     

第3代先进高强度钢AHSS汽车板的开发

为满足汽车轻量化、节能减排和抗冲撞安全对高强塑性车身结构材料的需求,各国钢铁业与汽车业合作开发应用第3代先进高强度钢AHSS汽车板取得重要进展。由于金属晶体结构的本质特征,任何提高强度的方法均会导致其塑性的降低,因此第3代AHSS钢超高强度汽车板的开发,面临着金属晶体材料强塑化机理的难题：在大幅度提高汽车板强度的同时如何获得必要的塑性延伸能力及其相应的显微组织？以抗拉强度TS 1 000~1 500 MPa级超高强度汽车板在强塑化机理研究方面取得的两次突破性进展为线索,讨论了第3代AHSS汽车板在淬火碳分配（Quenching Partitioning）QP处理钢、非均质性纳米组织钢（Heterogeneous Nanostructure Steel）和高强塑性热成形钢（Ductile Press Hardened Steel）在研究开发与生产应用方面的国际前沿进展。     

热处理工艺对SM570钢叉车横梁力学性能的影响

通过试验对比了正火和调质热处理工艺对SM570钢叉车横梁力学性能的影响。结果表明,有效厚度为40 mm的横梁在900 ℃×3 h水淬+550 ℃×4 h回火的调质处理后才能完全满足力学性能的要求。而正火后试样的抗拉强度和屈服强度都较低,尤其屈服强度比技术要求低很多。SM570钢叉车横梁若要在正火态下交货,除了Si、Mn的固溶强化,还必须通过微合金化进行细晶强化,从而提高正火态下的屈服强度,提升屈强比。     

Achieving Excellent Strength–Ductility and Impact Toughness Combination by Cyclic Quenching in Medium Mn TRIP-Aided Steel

A novel heat treatment process combined cyclic quenching (CQ) with austenite reversion treatment (ART) is proposed to obtain high strength–ductility and high-impact toughness combination in Fe-0.18C-8.92Mn-3.43Al (in mass%) steel. The process referred as CQ-ART was designed for accomplishing the following objectives: (i) refine the prior austenite grains during cyclic quenching process, (ii) further obtain the refined austenite–ferrite block and (iii) improve the stabilities of retained austenite with Mn/C enrichment during ART process. The outstanding product of tensile strength and total elongation of CQ-ART-treated steels was 41.53 and 37.39 GPa%, respectively, and higher than the ART steel of 27.45 GPa%. The highest Charpy impact toughness of CQ-ART steel can reach to 221 J, which is mainly attributed to the refined grains and discontinuous transformation-induced plasticity (TRIP) effect.     

淬火温度对Nb微合金化齿轮钢18CrNiMo7-6组织演变及力学性能的影响

通过Thermo-calc热力学计算软件、扫描电镜、光学显微镜、冲击试验及拉伸试验等,研究了淬火温度对Nb微合金化齿轮钢18CrNiMo7-6组织及力学性能的影响。结果表明:随着淬火温度的升高,Nb微合金化齿轮奥氏体平均晶粒尺寸增加,但保持在20 μm 以下,晶界稳定性较高;根据Thermo-calc热力学计算结果可知,主要存在的碳氮化物为Cr₇C₃、Cr₂₃C₆、NbC以及AlN,其中Cr₇C₃、Cr₂₃C₆固溶温度较低,分别为730 ℃和749 ℃,NbC、AlN固溶温度较高,分别为1180 ℃和1070 ℃,NbC和AlN为主要钉扎晶界、细化晶粒的碳氮化物;NbC中存在少量的N元素,在一定温度下,NbC有向Nb(C,N)转变的趋势。随着淬火温度的升高,屈服强度呈降低趋势,抗拉强度在860 ℃出现平台,冲击性能先升高后降低。含Nb齿轮钢18CrNiMo7-6具有较宽的工艺设计窗口,最佳热处理工艺为860 ℃淬火+180 ℃低温回火,此时抗拉强度为1455 MPa,屈服强度为1229 MPa,冲击吸收能量为100 J,硬度约为44 HRC。     

热处理对高强度捆带钢的组织和性能的影响

实验室研究了一种高强捆带钢的热处理工艺、组织和性能的关系.结果表明:含031%C-0.23%Si-1.43%Mn的冷轧板,经735～745℃的两相区迅速淬火+470℃中温同火后可达到1100 MPa以上的抗拉强度和10%以上的伸长率,用此工艺生产的捆带钢比传统的铅浴等温淬火工艺具有更高的强度.