钛微合金化SQ700MCD高强钢粗晶热影响区软化的原因

利用热模拟试验研究了钛微合金化SQ700MCD高强钢母材及热模拟粗晶热影响区(CGHAZ)的组织与第二相粒子的溶解及析出行为,对CGHAZ软化的原因进行了分析。结果表明:随着冷却时间(t8/5)的增加,CGHAZ的显微组织由板条状马氏体逐渐向粒状贝氏体转变,这是软化的原因之一;母材中的第二相粒子为碳氮化物,平均尺寸在10nm以下且弥散分布,而CGHAZ中绝大部分碳氮化合物粒子发生了回溶现象,弥散析出强化效果消失是软化的另一原因;未完全回溶粒子的尺寸随着t8/5的延长而增大,软化程度也逐渐增大。

Softening Reasons for Coarse Grain Heat Affected Zone of Ti Microalloyed SQ700MCD High Strength Steel

The microstructure and the behavior of dissolution and precipitation of the second phase particles in base metal and thermal simulating coarse grain heat affected zone(CGHAZ) of Ti microalloyed SQ700MCD high strength steel were studied by thermal simulation test,and the reasons of CGHAZ softening were analyzed.The results show that one of reasons for softening was the microstructure change of CGHAZ from lath martensite to granular bainite with the increase of cooling time(t8/5).The second phase particle in base metal was carbonitride,and it had the average size of less than 10 nm and distributed diffusely,but a phenomenon of re-dissolution of most carbonitride particles in CGHAZ was found,the disappearance of dispersive precipitation strengthening was the another reason.The size of particles without complete re-dissolution increased with the increase of t8/5,and the degree of softening also increased gradually.