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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·%。
The C-Si-Mn steel was heated to 800 ℃ for 120 s and then rapidly cooled to 350 ℃ for 100 to 1 000 s respectively to simulate the isothermal transformation process of bainite. The influence of bainite isothermal time on the microstructure and mechanical properties of TRIP steel was investigated by scanning electron microscopy (SEM) and tensile testing. The results show that the microstructure of cold-rolled TRIP steel consists of ferrite, bainite, martensite and retained austenite. Bainite and retained austenite form in the isothermal transformation stage, while martensite forms in the isothermal cold stage. With the increase of bainite isothermal time, the transformation from supercooled austenite to bainite was promoted, and the solid solution C atoms were enriched in the remaining austenite. As a result, the average carbon content in the supercooled austenite increases, causing the retained austenite fraction in the cold-rolled TRIP steel to increase and the martensite volume fraction to decrease. When the bainite isothermal time extended from 100 s to 1000 s, the yield strength of cold rolled TRIP steel increased from 596 MPa to 692 MPa, the tensile strength decreased from 1 455 MPa to 1 138 MPa, and the yield ratio increased from 0.41 to 0.61 , Elongation (A80) increased from 6.3% to 18.9%. When the isothermal time of bainite is 1 000 s, the TRIP steel with super high strength has excellent mechanical properties and the maximum plastic modulus reaches 21 510 MPa ·%.