异种钢熔合区马氏体相变过程及组织

Martensitic Transformation and Microstructure in Fusion Zone of Dissimilar Steel Welded Joint

高温金相显微镜观察发现，珠光体钢（ Ｚ Ｇ２０ Ｓｉ Ｍｎ） 与奥氏体焊材（ Ａ３０７ 、 Ａ４５７） 熔合区确实存在马氏体相变，且在约４００ ℃至室温均有相变产生。经透射电镜观察，熔合区马氏体为低碳板条马氏体，亚结构主要是位错，有少量孪晶亚结构。熔合区碳化物主要产生于焊后热处理过程中，其类型主要为 Ｍ２３ Ｃ６ ，也有部分 Ｍ７ Ｃ３ 。碳化物主要在马氏体上以及马氏体或铁素体和奥氏体界面析出。马氏体带、碳化物带宽度主要受 Ｎｉ 含量的控制，提高 Ｎｉ 含量使它们变窄，熔合区韧性提高。

The observation with elevated temperature microscope indicated that the martensite transformation really exists in the fusion zone of pearlitic base metal (ZG20SiMn) and austenitic welding consumables (A307、A457), and the transformation could occur from 400℃ to near room temperature. TEM analysis showed that martensite in the fusion zone is band type with low carbon, and its substructures are dislocation and a little twinning. The carbides in the fusion zone are mainly resulted from PWHT, typically M 23 C 6 and some M 7C 3 precipitated on the martensite and bandaries between austenite and martensite. The results showed that the martensite and carbides region is mainly controlled by the Ni content of welding consumables. The increasing of Ni content makes the region narrow and gets higher charpy toughness in fusion zone.