摘要:
将C-Si-Mn钢加热至800℃保温120 s后,分别快速冷却至350℃保温100~1 000 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时间对超高强冷轧相变诱导塑性钢(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。随着贝氏体等温时间增加,促进了过冷奥氏体向贝氏体转变,固溶C原子充分向剩余奥氏体中富集。因此,过冷奥氏体中的平均碳含量增加,使得冷轧TRIP钢残余奥氏体分数提高,马氏体体积分数下降。贝氏体等温时间由100 s延长至1 000 s时,冷轧TRIP钢屈服强度由596 MPa提高至692 MPa,抗拉强度由1 455 MPa降低至1 138 MPa,屈强比由0.41提高至0.61,伸长率(A80)由6.3%提高至18.9%。贝氏体等温时间为1 000 s时,冷轧超高强TRIP钢具有优良的综合力学性能,最大强塑积达到21 510 MPa·%。
Abstract:
In the paper, C-Si-Mn steels were soaked at 800℃ for 120 s, and then rapidly cooled to 350℃ and held for 100~1 000 s to simulate the bainite isothermal transformation process. The influence of bainite isothermal time 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 com-posed of ferrite, bainite, martensite and retained austenite. The bainite and retained austenite formed in the isothermal stage, and the martensite isl and formed in the final cooling stage after isothermal process.With an increase in the bainite isothermal time, the solute C atoms fully diffused into the retained austen-ite due to the transformation of the supercooled austenite into bainite. Therefore, the average solute C content in the austenite increased due to the enrichment of solute C atoms and the decrease of the austen-ite volume fraction. And the martensite volume fraction reduced, and the retained austenite volume frac-tion increased. As a result, with an increase in the isothermal time from 100 s to 1 000 s, the yield strength increased from 596 MPa to 692 MPa, the tensile strength decreased from 1 455 MPa to 1 138 MPa, the YS/UTS ratio increased from 0.41 to 0.60, and the elongation decreased from 6.2% to 18.9%.The cold-rolled ultra-high strength TRIP steel with excellent comprehensive mechanical properties(Rm×A=21 510 MPa·%) was obtained at 1 000 s of bainitic isothermal holding.
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