卷取温度和退火工艺对热轧中锰钢组织和力学性能的影响

Effects of Coiling Temperatures and Annealing Processes on Microstructure and Mechanical Properties of Hot-rolled Medium-manganese Steel

冶炼了含1.0%~1.5%C、5.0%Mn(质量分数)的中锰钢,热轧后水冷至600、630和660℃保温1 h炉冷以模拟卷取工序,并进行了在600、640、680和730℃保温1~16 h后炉冷的退火处理。通过金相分析、X射线衍射(XRD)、电子背散射衍射(EBSD)和拉伸试验研究了模拟的卷取温度和退火工艺对钢的微观组织和力学性能的影响。结果表明:模拟不同温度卷取的中锰钢组织均由马氏体、少量贝氏体和4.5%(体积分数)左右的残留奥氏体组成,力学性能变化不明显;退火后钢中残留奥氏体含量显著增加,且随着退火温度的升高和保温时间的延长,残留奥氏体由片条状转变为块状,钢的屈服强度降低,抗拉强度先升高后降低,断后伸长率升高。经680℃保温10 h炉冷退火的钢中残留奥氏体最稳定,力学性能最佳,抗拉强度为890 MPa,断后伸长率达29%。提高退火温度和缩短保温时间使钢中残留奥氏体稳定性降低,TRIP效应减弱,力学性能降低。

One type of medium-manganese steel containing 1.0%to 1.5%C and 5.0%Mn by mass was smelted,hot-rolled,and water cooled to 660℃,635℃and 600℃and held for 1 h then furnace cooled to simulate coiling operation,as well as was annealed by soaking at 600℃,640℃,680℃,and 730℃for 1 h to 16 h followed by furnace-cooling.The effects of simulated coiling temperatures and annealing cycles on microstructure and mechanical properties of the steel were investigated by means of metallographic examination,XRD,EBSD and tensile test.The results showed that the steel subjected to simulated coiling at different temperatures all exhibited microstructure which consisted of martensite,a small amount of bainite and about 4.5%by volume retained austenite,and mechanical properties which did not change obviously,and that the steel exhibited considerably increased residual austenite after annealing,and as the annealing temperature increased and holding time became longer,the retained austenite morphology transformed from lath into block,and the yield strength decreased,the tensile strength first increased then decreased,and the elongation increased.In addition,the steel annealed by holding at 680℃for 10 h then furnace cooling had the most stable retained austenite and the best mechanical properties,with tensile strength being 890 MPa,and elongation being as much as 20%.The increase in annealing temperature and the decrease in holding time gave rise to reduction in stability of retained austenite,therefore resulting in a weakening of TRIP effect,and decrease in mechanical properties of steel.