不同工艺下低碳Mn--Si钢的组织与力学性能

Microstructure and mechanical properties of low carbon Mn-Si steel by different processes

通过Gleeble--1500热模拟压缩试验,借助光学显微镜、扫描电镜、X射线衍射及拉伸试验等,研究一种低碳Mn--Si钢在基于热轧动态相变的热轧TRIP钢工艺和基于贝氏体等温处理工艺下的组织与力学性能,比较了通过两种工艺获得的不同复相组织状态对材料的加工硬化能力的影响.结果表明:实验钢在基于动态相变的热轧TRIP钢工艺下获得了以细晶铁素体为基体和贝氏体、残余奥氏体组成的复相组织,而在基于贝氏体等温处理工艺下得到了以板条贝氏体为基体和残余奥氏体组成的复相组织,前者中残余奥氏体含量较高且其碳含量也较高.实验钢具有以板条贝氏体为基体的复相组织时屈服强度和抗拉强度较高;但由于残余奥氏体稳定性较差,实验钢的加工硬化能力较弱,导致其均匀延伸率和总延伸率较小.

The microstructure and mechanical properties of a low-carbon Mn-Si multiphase steel treated by two different thermal-mechanical processes, the hot-rolling process for TRIP steel based on dynamic transformation of undercooled austenite and the process based on bainitic isothermal treatment, were investigated by hot uniaxial compression tests on a Gleeble-1500 hot simulator, in combi-nation with optical microscopy, scanning electron microscopy, X-ray diffraction and tensile testing. A comparison was carried out to analyze the influence of multiple-phase microstructure states by the two processes on the work-hardening behaviors of the steel. The multiple-phase microstructure consisting of fine-grained ferrite matrix, bainite, and retained austenite is formed by the hot-rolling process for TRIP steel based on dynamic transformation of undercooled austenite, but the multiple-phase microstructure which is composed of lath bainite matrix and retained austenite is formed by the process based on bainitic isothermal treatment. The volume frac-tion of retained austenite and the mass fraction of carbon in retained austenite in the former are higher than those in the latter. The yield strength and tensile strength of the steel with the multiple-phase microstructure consisting of lath bainite matrix and retained austenite are higher;but the steel has lower uniform elongation and total elongation, which should be attributed to its lower work-hardening capa-bility resulting from the lower stability of retained austenite.