铁素体—马氏体复相组织对20MnSi钢回火脆性的影响

20MnSi钢经不同双相处理得到的铁素体和马氏体复相组织，具有比常规处理高10％以上的强塑积，且对高温回大脆性有抑制作用，其中马氏体一针状铁索体复相组织可以达到完全抑制的水平。     

马氏体钢双相区奥氏体组织特征及形成机理

采用双相区再加热-淬火（IQ）工艺,研究了马氏体钢在双相区再加热过程中奥氏体的组织特征及形成机理。结果表明,经890 ℃奥氏体化900 s后淬火处理获得板条马氏体组织的试验钢,经随后的双相区750 ℃再加热-淬火处理,在马氏体组织的基础上获得了由亚温铁素体和块状或针状马氏体组成的双相组织。马氏体钢在双相区再加热过程中,针状奥氏体的形成过程可以分为3个阶段：以板条马氏体间碳化物（Fe₃C）为奥氏体形核点及C元素在奥氏体内的扩散控制奥氏体在板条界间生长;板条马氏体内C向奥氏体内扩散控制其沿板条方向长大;Mn向奥氏体扩散并控制铁素体-奥氏体两相达到最终的平衡状态。钢在750 ℃再加热过程中,C、Mn元素由铁素体向奥氏体相中扩散,其扩散过程控制着奥氏体的形核与长大,扩散的结果是C、Mn元素在奥氏体内富集,实现C、Mn元素在两相之间的配分。     

不锈钢相变的研究进展

综述了各类不锈钢相变的研究进展以及主要合金元素对相变的影响.铁素体不锈钢高温加热时,有碳化物和氮化物析出,降低耐蚀性、韧性;马氏体不锈钢加热过程中发生马氏体向奥氏体的转变:奥氏体不锈钢加热到1300℃以上时,发生高温8相变,产生高温铁索体,冷却或经受冷变形时,发生马氏体相变.相变产物为ε和a'组织;双相不锈钢中由于奥氏体的存在,相变与奥氏体不锈钢相似.     

Mn-Mo-Nb-B低碳微合金钢中温转变组织的演化

利用金相、电子背散射衍射(EBSD)技术结合纳米压痕仪研究了低碳Mn-Mo-Nb-B微合金钢的组织转变、晶粒的晶体学取向及其纳米力学性能.由1℃/s冷速连续冷却到室温所得组织主要是贝氏体铁素体和粒状贝氏体.以1℃/s冷速连续冷却到560℃淬水所得组织为针状铁素体和淬水时形成的马氏体/贝氏体,其中相邻针状铁索体之间为小角晶界;前一试样中粒状贝氏体的平均纳米压痕硬度(2.31 GPa)与后一试样中针状铁素体的平均纳米压痕硬度(2.22 GPa)极为接近.取向差较小的针状铁素体组织在1℃/s冷速下连续冷却过程中碰撞,接合成粒状贝氏体.     

热轧双相钢的发展

1 前言热轧双相钢是由一定成分的低碳或低合金钢经控轧和控冷而得到具有铁素体和马氏体双相组织的钢。这种钢有75％～85％的铁索体及15％～25％的弥散于铁素体基体的岛状马氏体。同时,保留少量的残余奥氏体。     

变形条件对Mn-Cr齿轮钢连续冷却相变的影响

使用Gleeble 1500热模拟实验机研究了Mn—Cr齿轮钢在奥氏体再结晶区不同温度变形后的连续冷却相变行为及相变组织．实验结果表明，变形温度降低，促进了多边形铁索体及珠光体相变，获得多边形铁索体加珠光体混合组织的临界冷速增大．贝氏体与针状铁索体之间存在相互竞争机制，随着变形温度及冷速的降低，大量的晶界仿晶型铁索体占据了奥氏体晶界，中温相变产物由贝氏体向针状铁索体转变．降低变形温度，奥氏体在中温相变区稳定性增加，相变结束温度下降，室温组织中马氏体／奥氏体岛的数量增多．     

C、Mn元素配分对淬火-配分贝氏体钢摩擦磨损的影响

采用淬火-配分-贝氏体区等温(QPB)和双相区保温-淬火-配分-贝氏体区等温(IQPB)两种热处理工艺并进行对比,通过摩擦磨损试验来研究C、Mn元素对残留奥氏体稳定性的影响。采用扫描电镜(SEM)、X射线衍射仪(XRD)、电子探针(EPMA)对试样的显微组织、残留奥氏体含量及C、Mn元素分布进行表征。结果表明:在双相区保温过程中,C、Mn元素发生配分,在奥氏体中富集。摩擦磨损试验后,QPB试样中的残留奥氏体体积分数从7. 24%减少到4. 36%,维氏硬度从417 HV0. 02增加到526 HV0. 02,磨损体积为0. 252 mm~3。IQPB试样中的残留奥氏体体积分数从9.11%减少到7.58%,维氏硬度从384 HV0.02增加到413 HV0. 02,磨损体积为0. 268 mm~3。IQPB试样在摩擦磨损试验前后残留奥氏体体积分数、维氏硬度没有QPB试样变化明显,表明在摩擦磨损过程中,C、Mn元素使残留奥氏体稳定性提高,残留奥氏体不易向马氏体转变。     

川崎钢铁公司开发高强度热轧钢板

日本川崎钢铁公司为使汽车车轮部分零部件轻量化，开发了成形性和疲劳强度好的540～780MPa级高强度热轧钢板“RH540DH～RllA780DH”。该种钢板选用最佳化学成分和采用最佳热轧条件轧制，得到微细T江析出强化的铁索体和马氏体双相组织。该显微组织对热轧钢板有以下作用。1）这一双相组织司提高均匀延伸性能和降低屈服比。2）由于铁素体相的析出强化，缩小了与第2相马氏体的硬度差，抑制了加工应变集中到铁素体扫过程，提高了局部变形能．3）由于存在析出强化铁索体相，句抑制由疲劳引起的裂纹及裂纹传播，提高了疲劳强度．RHA780DH热…     

新型热成形-淬火碳分配工艺

基于变形、相变、和碳分配同时实现的高强度钢设计思想,利用奥氏体区变形来细化晶粒,利用淬火与分配工艺使钢发生相变且进行碳分配来实现对硬相马氏体和软相残余奥氏体的调控,既一种新型热成形-淬火碳分配碳分配工艺,最终获得纳米级含有错位型马氏体和残余奥氏体的双相复合组织,这种工艺在不损害高强度钢强度的前提下,提高其力学性能,值得推广。     

低碳钢IQ&P工艺下元素配分行为及对组织性能影响

采用双相区再加热-淬火-碳配分(IQP)工艺,研究了双相区不同等温时间下低碳钢中元素配分行为,并分析其对组织形貌、残余奥氏体及力学性能的影响。结果表明:在IQP工艺中,在750℃随等温时间的延长,Mn元素向逆转奥氏体内富集现象逐渐明显,等温时间超过300s后,C元素在两相之间的配分效果不随时间的延长而改变;在750℃等温处理过程中,原奥氏体晶界生成块状逆转奥氏体,马氏体板条界间生成针状逆转奥氏体;随等温时间的延长,钢的最终组织中针状铁素体体积分数不断减小,而块状及针状马氏体体积分数不断增大,同样残余奥氏体体积分数也不断增大;在C、Mn元素的综合作用下,钢的抗拉强度不断增大,断后伸长率先减小而后增大,等温1800s时,钢的强塑积达到最大值21GPa%。     

Development of a Plane Strain Tensile Geometry to Assess Shear Fracture in Dual Phase Steels

A geometrically modified sample capable of generating a triaxial stress state when tested on a standard uniaxial tensile frame was developed to replicate shear fractures observed during stretch bend tests and industrial sheet stamping operations. Seven commercially produced dual phase (DP) steels were tested using the geometrically modified sample, and the modified sample successfully produced shear fractures on a unique shear plane for all steels. For each steel, void densities were determined, based on metallographic analyses, as a function of imposed displacement. Microstructural properties of ferrite and martensite grain size, martensite volume fraction (MVF), retained austenite content, Vickers hardness, average nanoindentation hardness, average ferrite and martensite constituent hardness, and tensile properties were obtained in order to evaluate potential correlations with void data. A linear correlation was observed between Vickers hardness and the average nanoindentation hardness, verifying the ability of nanoindentation to produce data consistent with more traditional hardness measurement techniques. A linear relationship was observed between the number of voids present at 90% failure displacement and the martensite/ferrite hardness ratio, indicating that a decrease in relative hardness difference in a microstructure can suppress void formation, and potentially extend formability limits. The void population appeared independent of MVF, grain size, and tensile properties suggesting that constituent hardness may be a dominant parameter when considering suppression of void nucleation in DP steels.     

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.     

双相区轧制对铁素体/马氏体双相钢组织性能的影响

采用双相区(α+γ)轧制及双相区短时保温处理相结合的方式,制备了一种高强高韧性低碳低合金铁素体/马氏体双相钢,并采用SEM、室温拉伸试验和维氏硬度检测等手段研究了不同轧制工艺对铁素体/马氏体双相钢组织和性能的影响。结果表明:相对于普通的连续轧制工艺,等温轧制和道次之间短时保温处理相结合的工艺对铁素体/马氏体双相钢的相比例、形貌和尺寸有重要影响。等温轧制及短时保温处理的双相钢的组织明显细化,马氏体相比例增加,组织均匀性显著改善,屈服强度提升了34%,达到1229 MPa,屈强比高达0.78,断口为韧性断口特征,呈细小韧窝状,具有良好的综合力学性能。     

退火温度对铁素体/马氏体双相钢组织及性能的影响

利用扫描电镜、室温拉伸、冲击测试等试验方法,采用两相区退火,研究了退火温度对铁素体/马氏体双相钢组织和性能的影响。结果表明:试验钢热轧态组织为铁素体+马氏体,铁素体含量为32.8%;随着两相区退火温度由720 ℃逐渐提高至830 ℃,铁素体含量由45.7%降低到23.6%,马氏体含量逐渐提高;试验钢的屈强比由热轧态的50%,提高至830 ℃退火后的60%;试验钢的冲击吸收能量与铁素体含量成线性关系。     

Effect of carbon on the plastic strain ratio of low carbon dual-phase steels

The effect of carbon on the plastic strain ratio of low-carbon dual-phase steels was investigated in a series of low C-1.6 Mn-0.3Cr-0.2Mo-0.001B steels with carbon contents ranging from 0.021 to 0.048%. The r_m value of dual-phase steel could be increased by controlling both the carbon content and the martensite morphology. The highest r_m value of 1.23 was obtained in 0.021% C steel annealed at 790 °C according to the typical galvannealing heat cycle. The martensite volume fraction was 5.4%, which was sufficient to eliminate the yieldpoint elongation in as-annealed steel, and this had little deteriorating effect on the r_m value. The fine martensite particles between 0.5 μm and 2.0 μm in size were desirable for a high r_m value in dual-phase steel.     

Role of Martensite Structural Characteristics on Corrosion Features in Ni-Advanced Dual-Phase Low-Alloy Steels

The relationship between the corrosion resistance and martensite structure of Ni-advanced dual-phase weathering steel was studied using transmission electron microscopy, scanning electron microscopy, electrochemical analysis, and atomic force microscopy. The investigations indicate that the final microstructure of the dual-phase weathering steel was composed of a large amount of low-carbon lath martensite distributed in the ferrite matrix. The potential of the martensite phase is higher than that of ferrite, which acts as a microcathode. As the martensite volume fraction in the Ni-advanced dual-phase weathering steel increased, the corrosion rate increased owing to the greater galvanic couple formed between the ferrite and martensite from the increasing ratio of the cathode area to the anode area. In addition, this work provides a method to obtain advanced weathering steel with improved mechanical properties and corrosion resistance.     

纤维双相钢的回复与再结晶

研究了两次淬火纤维双相钢的组织结构特点和８４％冷压缩形变后的回复再结晶过程，ＳＥＭ、ＴＥＭ观察，硬度测量和再结晶过程激活能的计算结果表明，在其他条件相同时，钢中硅含量的增多推迟了形变纤维双相钢的再结晶过程。     

Phase field simulation of the carbon redistribution during the quenching and partitioning process in a low-carbon steel

Phase-field modelling is used to simulate the quenching and partitioning process in a low-carbon transformation-induced plasticity (TRIP) steel, in order to understand the carbon redistribution in the microstructure during the heat treatment. The simulations show that, depending on local characteristics of the microstructure, including phase distributions and carbon-concentration gradients, different features in the carbon evolution during the partitioning step occur that are physically and practically relevant, but are not accessible for experimental observation. The overall carbon partitioning from martensite to austenite occurs not only by direct diffusion from martensite to austenite, but also through the bulk ferrite grains. The simulations also show interface migration driven by the free-energy difference between austenite and martensite, which affects the fractions of phases and the dimensions of the austenite grains. The carbon content of individual austenite, martensite and ferrite grains as well as average values are analysed, showing that the carbon concentration within the austenite grains is strongly inhomogeneous at short partitioning times, which contributes to a variable mechanical stability of individual austenite grains, affecting the occurrence of TRIP.     

A DYNAMIC OBSERVATION OF MICROSCOPIC DEFORMATION BEHAVIOR IN DUAL-PHASE STEELS

<正> 在备有拉伸台的S-550扫描电镜下直接观察了铁素体加马氏体双相钢拉伸变形的全过程,分析了马氏体含量,马氏体含碳量,铁素体性能等因素对两相变形特别是屈服行为的影响。材料及试验方法 试验用料为国产10号(C     

A nanoindentation study on the micromechanical characteristics of API X100 pipeline steel

The hardness characteristics of constituent micro-phases (ferrite and bainite) in a dual-phase API X100 pipeline steel were analyzed by nanoindentation experiments. The measured nano-hardness of the bainite phase is from 3.8 GPa to 4.9 GPa, which is much higher than that of the ferrite phase, which ranged from 1.75 GPa to 2.3 GPa. With the hardness and volume fraction of each micro-phase, attempts were made to predict the overall hardness by applying a simple rule-of-mixture. A comparison between the predicted overall hardness value and the experimentally measured value revealed that the rule-of-mixture can be successfully applied for prediction purposes. The results are discussed in terms of the grain boundary strengthening effect and the indentation size effect.