不同屈强比的冷轧DP780钢工艺调控技术分析

Analysis on process control technology of cold rolling DP780 steel with different yield ratios

采用不同的工艺调控技术,实现了一种成分体系可生产具有不同屈强比的经济型冷轧DP780钢,并通过分析力学性能测试结果、TEM和SEM组织形貌特征,得到热轧初始组织、冷轧压下量、连续退火工艺对屈强比的影响。结果表明,当热轧初始组织为F+P(铁素体+珠光体)时,随着平均晶粒尺寸细化至约7.5μm,屈服强度增加了50MPa,屈强比由0.48增至0.56;当热轧初始组织变为F+B(铁素体+贝氏体)、以贝氏体为主时,屈服强度达到532MPa,屈强比增至0.65,同时有利于保证DP780钢的扩孔性和塑性,扩孔率达到86%,特别适用于有扩孔翻边要求的汽车结构件和加强件。此外,适当增加冷轧压下量和降低退火保温温度,均有利于增强基体的强化效应,从而提高屈强比。

By utilizing different process control technologies,producing economical cold rolling DP780 with different yield ratios was realized.Through analyzing the testing results of mechanical properties,microstructural morphologies of TEM and SEM,it was obtained that the initial microstructure,cold rolling reduction and continuous annealing process had important effects on the yield ratio.The results indicated that when the initial microstructure of hot rolling was F+P,with the average grain size refined to about 7.5μm,the yield strength was increased by 50 MPa and the yield ratio was increased to 0.56 from 0.48.When the initial microstructure of hot rolling changed to F+B(mainly bainite),the yield strength reached 532 MPa and the yield ratio was increased to 0.65,it is beneficial to guarantee the hole expansion property and plasticity of DP780 steel.The hole expanding rate was reached to 86%,which is especially suitable for automobile structural and strengthen parts with the request of hole expansion and flanging.In addition,appropriately increasing the cold rolling reduction and decreasing the soaking temperature in annealing process properly were helpful to enhance the strengthening effect of the matrix structure,thus improving the yield strength.