低碳多相钢的组织调控与力学性能

采用优化后的临界区再加热-淬火中温等温(T1、T2)热处理工艺,对具有不同前躯体组织的(0.22/0.17)C-(1.91/1.85)Mn-(1.32/0.94)Si两类热轧6 mm钢板分别进行处理,获得了具有铁素体、贝氏体、马氏体以及弥散分布于原奥氏体晶界、相界等处的残余奥氏体所构成的多相组织.利用扫描电镜、X射线衍射以及电子背散射衍射分析技术等对不同热处理阶段钢的微观组织进行了表征.结果证实,采用不同的前躯体组织设计可以很好地调控临界区再加热逆转变奥氏体的组织形貌、比例以及碳含量,进而通过后续处理来实现对钢中多相组织的调控.前躯体为马氏体的0.22C钢,经T1工艺后获得了以针状铁素体为基体的多相组织,其强塑积超过了30 GPa·%;前躯体为铁素体+马氏体的0.17C钢经T2工艺后获得了以块状铁素体为基体的多相组织,其强塑积超过了27 GPa·%.

Microstructure regulation and mechanical properties of low-carbon multiphase steels

Two kinds of 6 mm hot rolled plate steels, (0.22/0.17)C-(1.91/1.85)Mn-(1.32/0.94)Si, which have different precursor microstructures were heat treated by the critical region reheating, quenching and medium temperature isothermal processes (named T1 and T2). After the processes, a multiphase microstructure, which is composed of ferrite, bainite, martensite and well-distributed retained austenite (primarily distributed in prior austenitic grain boundaries and phase boundaries), was obtained for both of the steels, The microstructures of the steels in different heat treatment stages were characterized by scanning electron microscopy, X-ray diffraction and electron backscatter diffraction. It is found that making use of different precursor microstructures can well lead to the regulation of morphology, proportion and carbon content of the reversed austenite during the process of critical region reheating, and then achieve the regulation and control of the multiphase microstructure by the subsequent quenching and medium temperature isothermal processes. After the process of T1, 0.22C steel which has a martensite precursor microstructure can obtain a multiphase mierostructure with acicular-like ferrite as the matrix, and its product of strength and elongation is greater than 30 GPa.%. After the process of T2, 0.17C steel which has a ferrite + martensite precursor microstructure can obtain a multiphase microstructure with block-like ferrite as the matrix, and its product of strength and elongation is greater than 27 GPa.%.