1000MPa级高延伸率Q&P钢的实验室研究

以C-Si-Mn系TRIP钢成分为基础,设计了四种不同Si和Mn含量的合金成分,并采用不同两相区奥氏体化温度的淬火—配分(QP)工艺进行处理,得到了兼具高强度和高塑性的QP钢。其中,当奥氏体化温度为820℃时,0.18C-1.8Si-2.2Mn(质量分数,%)钢和0.18C-1.8Si-2.5Mn钢在抗拉强度达到1 000 MPa以上的同时断后延伸率仍不低于20%,显示了极佳的强塑性结合。利用SEM和XRD等对热处理材料的显微组织进行了表征,结果显示,其显微组织为铁素体、板条马氏体和一定量的残余奥氏体,残余奥氏体多呈块状且被铁素体所包围,且奥氏体化温度为820℃时,材料中的残余奥氏体含量和平均碳浓度均较高。更多且稳定的残余奥氏体在变形过程中发生TRIP效应,可以在不显著降低材料强度的情况下更有效地改善材料的塑性,这也是四种试验用钢经820℃的QP工艺处理后显示出更佳强塑性结合的主要原因。

Development of 1 000 MPa grade quenched and partitioned steels with high elongation

Based on C -Si-Mn TRIP steel, four types of steels with different contents of Si and Mn were designed and subjected to quenching and partitioning ( Q&P) processes with variable austenizing temperatures .The as-treated steels exhibited good combination of high strength and substantial elongation .Particularly, with austenizing at 820℃, 0.18C-1.8Si-2.2Mn (%) steel and 0.18C -1.8Si -2.5Mn (%) steel possessed high elongation ( more than 20%) with the tensile strength over 1 000 MPa.The microstructures of the as-treated steels were observed by SEM , and the volume fraction and carbon content of retained austenite were quantified by XRD .As a result , the designed Q&P steels contained a multi-phase microstructure including ferrite , lath martensite and retained austenite , the volume fraction and carbon content of which is higher in those steels treated by Q&P processes with austenizing at 820 ℃.By TRIP effect during the deformation , more retained austenite with better stability can more effectively improve the formability of steels with slightly decreasing the strength , contributing to a better performance .