卷取温度对QStE550TM钢组织及性能的影响

EFFECT OF COILING TEMPERATURE ON MICROSTRUCTURE AND MECHANICALPROPERTIES OF QStE550TM STEEL

采用拉伸试验机、光学金相显微镜及扫描电镜分析等试验方法,在其他热轧工艺参数不变的情况下,对不同卷取温度下生产的试验钢QStE550TM进行了分析。结果表明:卷取温度会影响QStE550TM组织结构、晶粒度和析出物数量及大小,进而影响其力学性能。当卷取温度为600℃时,试验钢基体组织以铁素体+珠光体为主。当卷取温度为560℃和580℃时,试验钢基体组织主要为铁素体+贝氏体,与计算的TTT曲线结果略有不同。另外,随卷取温度从560℃升高到600℃,基体组织晶粒度逐渐降级,细晶强化效果减弱。但析出相数量逐渐增多,析出强化效果增强,同时析出相尺寸逐渐长大也会弱化析出强化效果。相应地,试验钢的屈服强度与抗拉强度在析出强化和细晶强化的博弈下,在卷取温度为560℃时,细晶强化效果大于析出强化效果,综合强化效果差;卷取温度为600℃时,析出强化效果大于细晶强化效果,同样综合强化效果差。卷取温度为580℃时,两种强化效果达到平衡,此时试验钢QStE550TM的屈服强度和抗拉强度及伸长率满足目标要求。

With the same finishing parameters,QStE550TM steel was studied by using optical microscope(OM),scanning electron microscope(SEM),and tensile test machine at different coiling temperatures.The results showed that the change of the coiling temperature could change the grain size of microstructure,morphology,amount and size of precipitates in QStE550TM steel,and furtherly affect the mechanical properties of QStE550TM steel.When the coiling temperature is 600℃,the matrix structure of the test steel is mainly ferrite and pearlite.When the coiling temperature is 560℃and 580℃,the matrix structure of the test steel is mainly ferrite and bainite.The result is slightly different from the calculated TTT curve.In addition,as the coiling temperature increases from 560℃to 600℃,the grain size of the matrix decreases gradually,and the effect of fine grain strengthening decreases.However,as the number of precipitated phase increases gradually,the precipitation strengthening effect will be enhanced,and the size of precipitated phase will gradually grow,which will weaken the precipitation strengthening effect.Accordingly,under the game of precipitation strengthening and fine grain strengthening,the effect of fine grain strengthening is greater than that of precipitation strengthening at 560℃,and the comprehensive strengthening effect is poor.When the coiling temperature is 600℃,the effect of precipitation strengthening is greater than that of fine crystal strengthening,and the comprehensive strengthening effect is also poor.When the coiling temperature is 580℃,the two strengthening effects reach a balance,and the yield strength,tensile strength and elongation of the test steel QStE550TM meet the target requirements.