含Al中锰TRIP钢原始组织对临界退火后组织与力学性能的影响

Effect of original microstructure of medium manganese TRIP steel containing Al on microstructure and mechanical properties after intercritical annealing

利用Factsage软件、SEM、XRD等研究了不同原始组织的0.2C-5.0Mn-0.5Si-1.0Al中锰TRIP钢经临界区退火处理后的显微组织与力学性能。结果表明,经热力学计算、设计的不同预处理工艺处理后试验钢的组织分别为:铁素体+块状残留奥氏体(700℃预处理10 min)、铁素体+马氏体+少量残留奥氏体(800℃预处理5 min)和马氏体+少量碳化物(900℃预处理5 min)。不同预处理工艺处理后试样能获得不同形貌的残留奥氏体,700℃预处理+临界退火试样得到块状残留奥氏体,其他两种工艺下为膜状残留奥氏体。800℃预处理+临界退火试样拥有最佳力学性能,屈服强度为840 MPa,抗拉强度为1121.5 MPa,伸长率为33.25%,强塑积达到37.29 GPa·%。残留奥氏体形貌对中锰钢的加工硬化性能有显著影响,700℃预处理+临界退火试样的块状残留奥氏体稳定性较差,表现出高的加工硬化率,但持续区间较短;而800℃预处理+临界退火试样的膜状残留奥氏体稳定性更好,试样呈现较高的加工硬化率且持续区间较长。

Microstructure and mechanical properties of 0.2 C-5.0 Mn-0.5 Si-1.0 Al TRIP steel with different original microstructure after intercritical annealing were studied by Factsage software,SEM,XRD,etc.The results show that the microstructure of the steel treated by different pretreatment processes are as follows:ferrite+blocky type retained austenite(pretreatment at 700℃for 10 min),ferrite+martensite+small amount of retained austenite(pretreatment at 800℃for 5 min),and martensite+small amount of carbides(pretreatment at 900℃for 5 min).The residual austenite with different morphologies can be obtained by different pretreatment processes.By pretreatment at 700℃and intercritical annealing,blocky-type retained austenite is obtained,and the film-type one can be obtained by the other processes.The specimen pretreated at 800℃+intercritical annealing has the best mechanical properties with the yield strength of 840 MPa,the tensile strength of 1121.5 MPa,the elongation of 33.25%,and the product of strength and plasticity of 37.29 GPa·%.The morphology of retained austenite has a significant impact on the work hardening performance.The blocky-type retained austenite pretreated at 700℃and intercritical annealing has poor stability,showing high work hardening rate,but the continuous interval is short.However,the stability of film retained austenite pretreated at 800℃and intercritical annealing is better,showing higher work hardening rate and longer duration.