冷轧中锰钢的再结晶调控及其对力学性能的影响

Recrystallization Controlling in a Cold-Rolled Medium Mn Steel and Its Effect on Mechanical Properties

为探究铁素体再结晶对冷轧中锰钢微观组织与力学性能的影响规律,以0.15C-5Mn(质量分数,%)冷轧中锰钢为研究对象,采用两步临界区退火的热处理方法,利用SEM、TEM和EBSD等表征手段和力学性能测试方法,研究了铁素体再结晶调控对冷轧中锰钢多样化残余奥氏体形成及其力学性能的影响。结果表明,通过在不同温度预先调控冷轧中锰钢中的铁素体再结晶,可获得由不同比例的等轴状再结晶铁素体和马氏体组成的双相细晶组织。经常规退火处理后,在终态组织中形成了不同体积分数的超细晶再结晶铁素体和呈等轴状/板条状形貌的多样化细晶残余奥氏体,使中锰钢在拉伸变形过程中表现出多样化的TRIP效应,在提升冷轧中锰钢强塑性能的同时,其Lüders变形也获得改善。

Owing to the excellent combination of specific strength and ductility,medium Mn steels(MMSs)with Mn contents of 3%-12%(mass fraction)are considered the most promising candidates for the third-generation advanced high-strength steel.The combination of excellent strength-ductility is mainly attributed to the active transformation-induced plasticity effect of the metastable retained austenite during deformation.Therefore,producing a considerable amount of retained austenite with reasonable stabilities in the steel by various heat treatment schedules is always important.In this study,granular-and lamellar-structured retained austenites were developed in a cold-rolled 0.15C-5Mn MMS by introducing a technical process of precontrolling ferrite recrystallization in the annealing schedule.The microstructures of the annealed samples were analyzed using SEM,EBSD,and TEM.The results show that duplex microstructures comprising various amounts of recrystallized ferrite and fresh martensite can be obtained in the cold-rolled MMS when controlling the occurrence of recrystallization at different intercritical temperatures by a preannealing process.When this microstructure is used for the final austenite reverted transformation annealing,the resultant ultrafine duplex microstructure with recrystallized ferrite and two types of heterogeneous retained austenite,i.e.,lamellar and granular,is produced.The heterogeneous-structured austenite shows more sensitivity to increasing strain,i.e.,various mechanical stabilities,which enable an excellent strength-ductility combination and reduced Lüders strain in the cold-rolled medium Mn steel.