摘要:
将C-Si-Mn钢加热至800℃保温120 s后,分别快速冷却至350~410℃保温600 s以模拟贝氏体等温转变工艺。通过扫描电镜(SEM)和拉伸测试的方法研究了贝氏体等温温度对超高强相变诱导塑性钢(TRIP钢)微观组织和力学性能的影响规律。结果表明,冷轧TRIP钢的微观组织由铁素体、贝氏体、马氏体和残余奥氏体组成;贝氏体和残余奥氏体形成于等温转变阶段,而马氏体形成于等温后的终冷阶段。随着贝氏体等温温度增加,固溶C原子扩散系数提高,促进残余奥氏体中碳化物的析出。因此,奥氏体中的平均固溶C含量降低,使得TRIP钢残余奥氏体分数降低,马氏体体积分数增加。贝氏体等温温度由350℃增加至410℃时,TRIP钢屈服强度由720 MPa降低至573 MPa,抗拉强度由1 195 MPa提高至1 312 MPa,伸长率A80由17.8%降低至12.5%。贝氏体等温温度为350℃时,冷轧TRIP钢具有优良的综合力学性能,强塑积达到21 270 MPa·%。
Abstract:
In this paper,C-Si-Mn steels were soaked at 800 ℃ for 120 s,and then rapidly cooled to 350～410 ℃ and held for 600 s to simulate the bainite transformation process.The influence of bainite isothermal temperature on the microstructure and mechanical properties of ultra-high strength cold rolled transformation induced plasticity（TRIP）steel was investigated by means of scanning electron microscopy（SEM）and tensile test.The results showed that the microstructure of cold rolled TRIP steel was composed of ferrite,bainite,martensite and retained austenite.The bainite and retained austenite were formed in the isothermal stage,and the martensite island was formed in the final cooling stage after isothermal process.With an increase in the bainite isothermal temperature,the carbide precipitated fully due to the increase of diffusion coefficient.Therefore,the average solute C content in the supercooled austenite decreased due to the precipitation of solute C atoms.The martensite volume fraction increased,and the retained austenite volume fraction reduced.As a result,with an increase in the isothermal temperature from 350 ℃ to 410 ℃,the yield strength decreased from 720 MPa to 573 MPa,the tensile strength increased from 1 195 MPa to 1 312 MPa,and the elongation A80decreased from 17.8% to 12.5%.Therefore,the cold rolled TRIP steel with excellent comprehensive mechanical properties(Rm×A80=21 270 MPa·%)was obtained by bainite isothermal holding at 350 ℃.
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