The processing of advanced multiphase high strength steels often includes isothermal treatments around the martensite start temperature (M_s) for achieving a refined microstructure comprising bainite-austenite and/or bainite-martensite-austenite phase constituents. The objective of this research work was to investigate the structure-property relationship for a medium carbon, high-silicon DIN 1.5025 steel (Fe-0.529C-1.67 Si-0.72Mn-0.12Cr (in wt.%)) following isothermal holding close to the M_s temperature (~275°C) to enable low temperature austenite decomposition. For realizing multiphase microstructures, DIN 1.5025 steel samples were austenitized at 900°C for 5 min and then quenched to the isothermal holding temperatures 350 and 250°C for various times ranging from 5 to 3600 s. Microstructural investigation corroborated the formation of multiphase microstructure comprising tempered martensite, bainite, retained austenite, and fresh martensite in both the samples isothermally held above (350°C) and below the M_s (250°C) temperature. The sample isothermally held at 250°C showed a much more refined microstructure in comparison to that held at 350°C due to the presence of a fraction of initial martensite laths which acted as potential sites for bainite nucleation. Also, the evaluation of mechanical behaviour showed that the best tensile properties in terms of high tensile strength and good ductility were achieved in samples with high volume fractions of both interlath and blocky retained austenite, particularly those isothermally treated at 350°C for 200 s and at 250°C for 600 s, respectively.

先进的多相高强度钢的加工通常包括在马氏体起始温度（M _s）附近进行等温处理，以实现包含贝氏体-奥氏体和/或贝氏体-马氏体-奥氏体相成分的精细组织。这项研究工作的目的是研究等温保温关闭后中碳，高硅DIN 1.5025钢（Fe-0.529C-1.67 Si-0.72Mn-0.12Cr（wt。％））的结构-性能关系于M_小号温度（〜275°C）使低温奥氏体分解。为了实现多相微结构，将DIN 1.5025钢样品在900°C下奥氏体化5分钟，然后在5至3600 s的不同时间内淬火至350和250°C的恒温。显微组织研究证实了等温保持在高于（350°C）和低于M _s的样品中包括回火马氏体，贝氏体，残余奥氏体和新鲜马氏体的多相组织的形成_。（250°C）温度。与在350°C下等温相比，等温保持在250°C下的样品的微观结构要细得多，这是因为存在一部分初始马氏体板条，它们可能作为贝氏体成核的可能部位。此外，对机械性能的评估表明，在具有高体积分数的层间和块状残余奥氏体的样品中，尤其是在350°C等温处理200 s和200 s的样品中，可以获得高拉伸强度和良好延展性方面的最佳拉伸性能。在250°C下分别持续600 s。