相变时间对CSP热轧TRIP钢组织和性能的影响

利用OM、SEM、XRD、EBSD和室温拉伸试验机等研究了CSP热轧TRIP钢中间缓冷时间及贝氏体等温时间对组织和力学性能的影响。结果表明,随着中间缓冷时间的延长,试验钢中的铁素体和残余奥氏体体积分数增加,贝氏体体积分数减少;抗拉强度基本不变,屈服强度逐渐降低,断后伸长率和强塑积变化不明显。中间缓冷时间为6 s时,可满足CSP产线的要求。对贝氏体相变时间的研究表明,当等温时间为15 min时,试验钢中的残余奥氏体主要分布于铁素体/铁素体界面、铁素体/贝氏体界面以及贝氏体中,体积分数约为7.1%,表现出良好的TRIP效应。其抗拉强度、屈服强度、断后伸长率和强塑积分别达到744.0 MPa、522.5 MPa、29.3%和21.8 GPa·%,力学性能最优。当等温时间延长至50 min时,试验钢中的贝氏体含量增加,残余奥氏体体积分数减少至2.7%,强塑积明显下降。

Effect of phase transformation time on microstructure and mechanical properties of hot rolled TRIP steel produced by CSP process

The effects of intermediate cooling time and isothermal bainite transformation time on microstructure and mechanical properties of hot rolled TRIP steel produced by CSP process were investigated by using OM, SEM, XRD, EBSD and tensile testing machine. The results indicate that with an increase in the intermediate cooling time, the volume fraction of ferrite and retained austenite in experimental steel increases, but the volume fraction of bainite decreases. And the tensile strength basically remains constant, the yield strength gradually decreases, the total elongation and product of tensile strength and ductility change very little. It is found that the intermediate cooling time of hot-rolled TRIP steel produced by CSP process can be set as 6s. Moreover, when the isothermal bainite transformation time is 15min, the retained austenite is found in experimental steel which is mainly distributed in the ferrite/ferrite interface, the ferrite/bainite interface and bainite with the volume fraction of 7.1%. It exhibits a good TRIP effect. Correspondingly, the excellent mechanical properties are obtained. The tensile strength, yield strength, total elongation and product of tensile strength and ductility are 744.0MPa, 522.5MPa, 29.3% and 21.8GPa·%, respectively. When the isothermal bainite transformation time further increases to 50 min, the amount of retained austenite decreases to 2.7%, resulting in the product of tensile strength and ductility of experimental steel significantly decreasing.