二次热循环对管线钢在役焊接粗晶区显微组织的影响

采用焊接热模拟技术、金相分析及透射电镜研究了X70管线钢在役焊接粗晶区及其经受不同峰值温度二次焊接热循环作用后热影响区各区的金相组织和精细结构. 结果表明,在役焊接粗晶区的金相组织主要是板条束贝氏体和粒状贝氏体,经历不同峰值温度的二次热循环后,组织类型没有发生变化,但各种组织的形态、大小、数量以及原奥氏体晶粒大小有些差异. 热影响区各区的主要形貌都是铁素体板条和分布在板条之间或板条基体上的M-A组元. 在役焊接粗晶区M-A组元形态以条状为主,经历二次热循环后,再热临界粗晶区的M-A组元有所细化. 再热临界粗晶区存在下贝氏体组织,且具有典型的"中脊"形貌.

Effect of second thermal cycle on the microstructure of the coarse grain heat-affected zone of in-service welded pipeline steel

Welding thermal simulation,metallographic analysis and transmission electron microscope(TEM) were used to study the metallurgical microstructure and fine structure of the coarse grain heat-affected zone(CGHAZ) of in-service welding and the zones that subject to second thermal cycle at different peak temperatures.The results show that the main metallurgical microstructures of the CGHAZ of in-service welding are granular bainite and lath bainite.After second thermal cycle,the types of microstructure have no change,but the shape and amount of each kind of microstructure and the grain size of original austenite are different when the peak temperature of second thermal cycle is different.Observing by TEM,the fine structures of each HAZ are ferrite laths and M-A constituents that distribute on or between ferrite laths.The M-A constituents in the CGHAZ of in-service welding are main strip-shaped.After second thermal cycle,the M-A constituents in the intercritically reheated CGHAZ are refined and lower bainite that has typical midrib morphology produces in the zone.