高强汽车双相钢的连续退火与组织性能研究

Continuous Annealing and Microstructure and Properties of High Strength Automotive Dual Phase Steel

目的提升高强DP980双相钢的力学性能,优化连续退火工艺。方法对高强汽车双相钢进行了连续退火处理,研究了连续退火均热温度、均热时间、过时效温度对冷轧双相钢显微组织、物相组织和力学性能的影响。结果对于不同退火均热温度处理的双相钢,其组织均为铁素体(F)+马氏体(M),随着均热温度从715℃升高至865℃,残余奥氏体体积分数逐渐减小,抗拉强度、屈服强度先增后减,断后伸长率逐渐减小,在均热温度为815℃时,双相钢的抗拉强度和屈服强度达到最大值。随着均热时间从0.5min延长至5min,双相钢的晶粒尺寸逐渐增大,残余奥氏体体积分数先减后增,抗拉强度、屈服强度先增后减,断后伸长率先减后增,在均热时间为1.5min时,抗拉强度和屈服强度达到最大值。随着过时效温度从245℃上升至395℃,双相钢中的马氏体体积分数逐渐减小,当过时效温度为395℃时,出现了贝氏体,奥氏体体积分数先增后减,抗拉强度、屈服强度逐渐减小,断后伸长率逐渐增大。结论冷轧DP980双相钢适宜的连续退火工艺如下:均热温度为815℃、均热时间为3min、过时效温度为295℃。此时双相钢具有较好的强塑性。

The work aims to improve the mechanical properties of high strength DP980 dual phase steel and optimize the continuous annealing process.Continuous annealing treatment was conducted on high strength automotive dual phase steel,and the effects of soaking temperature,soaking time,and overaging temperature of continuous annealing on the microstructure,phase composition,and mechanical properties of cold rolled dual phase steel were studied.The microstructure of dual phase steel treated at different soaking temperature was divided into ferrite(F)and martensite(M).With the soaking temperature rising from 715℃to 865℃,the volume fraction of residual austenite gradually decreased,the tensile strength and yield strength firstly increased and then decreased,the elongation gradually decreased and the maximum tensile strength and yield strength of dual phase steel were obtained at the soaking temperature of 815℃.As the soaking time increased from 0.5 min to 5 min,the grain size of the dual phase steel gradually increased,the volume fraction of residual austenite firstly decreased and then in-creased,the tensile strength and yield strength firstly increased and then decreased,the elongation firstly decreased and then in-creased,and the maximum tensile strength and yield strength were obtained when the soaking time was 1.5 min.With the over-aging temperature rising from 245℃to 395℃,the volume fraction of martensite in dual phase steel gradually decreased,and bainite appeared when the overaging temperature was 395℃.Otherwise,the volume fraction of austenite firstly increased and then decreased,the tensile strength and yield strength gradually decreased,and the elongation gradually increased.The suitable continuous annealing process for cold-rolled DP980 dual phase steel is:soaking temperature of 815℃,soaking time of 3 min,and overaging temperature of 295℃,which can make the dual phase steel have good strength plasticity.