Multiphase advanced high strength low alloy steels having a refined microstructure of hard bainite and/or martensite laths, interspersed with finely divided retained austenite films, are the potential candidate materials for futuristic industrial applications, such as automotive industry, structural parts, crankshafts and shafts, and powertrain components. In this study, a silicon-bearing, medium-carbon low alloy steel grade of DIN 1.5025 was subjected to both quenching and bainitic holding (Q&B), as well as quenching and partitioning (Q&P) isothermal heat treatments at temperatures closely above and below the martensite start temperature (M_s), respectively. The mechanical response of heat treated samples was evaluated by conducting hardness and tensile tests, corroborated by XRD analysis and metallography using both scanning electron microscopy combined with electron backscatter diffraction as well as transmission electron microscopy. The experimental results showed that a number of Q&B heat treated samples displayed a superior combination of high strength levels with good ductility and work hardening capacity in comparison to that of Q&P ones, akin to the requirements for third generation high strength multiphase steels. It was also found that the superior mechanical response of Q&B heat treated samples was rationalized in respect of the formation of tough strong multiphase microstructures involving a fine mixture of hard bainite and/or martensite laths along with thin films of mostly interlath retained austenite that imparted superior combination of ductility and tensile strength through TRIP phenomenon. Moreover, limited tensile test results conducted in this study, supported by XRD and electron microscopy analyses, suggested that the TRIP response was quite effective in the Q&B multiphase samples containing more than 18 vol.% of retained austenite.

具有精细贝氏体和/或马氏体板条的精细组织的多相高级高强度低合金钢，并散布有细分的残余奥氏体薄膜，是未来工业应用（例如汽车工业，结构件，曲轴和轴）的潜在候选材料，和动力总成组件。在这项研究中，对DIN 1.5025的含硅，低碳的中碳低合金钢进行了淬火和贝氏体保温（Q＆B）以及淬火和分配（Q＆P）等温热处理，热处理温度分别接近或低于该温度。马氏体起始温度（M _s）， 分别。热处理样品的机械响应通过进行硬度和拉伸测试进行评估，通过XRD分析和金相学证实，使用扫描电子显微镜与电子背散射衍射以及透射电子显微镜相结合。实验结果表明，与第三代高强度多相钢相比，许多经过Q＆B热处理的样品与Q＆P相比具有高强度水平，良好的延展性和加工硬化能力的优异组合。还发现了Q＆B热处理的样品在形成坚韧的坚固多相微结构方面是合理的，该结构涉及硬贝氏体和/或马氏体板条的精细混合物，以及大部分夹层保留奥氏体的薄膜，通过TRIP现象赋予延展性和拉伸强度优异的组合。而且，在XRD和电子显微镜分析的支持下，这项研究进行的有限拉伸试验结果表明，TRIP响应在含有18％（体积）以上残留奥氏体的Q＆B多相样品中非常有效。