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

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。

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

Microstructure and mechanical properties of 0.2C-5.0Mn-0.5Si-1.0Al 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.