On the heterogeneous microstructure development in the welded joint of 12MnNiVR pressure vessel steel subjected to high heat input electrogas welding

Abstract Microstructure features of 12MnNiVR pressure vessel steel welded joint deposited by the high heat input electrogas welding have been systematically investigated. It is revealed that the weld joint is featured by a heterogeneous juxtaposition. The coarse grained heat-affected zone (CGHAZ) primarily consists of lath bainites and minor granular bainites. The fine grained heat-affected zone (FGHAZ) is dominated by polygonal ferrites, pearlites, and fine cementite particles. Moreover, electron backscatter diffraction results further demonstrate that the CGHAZ is populated by coarse prior austenite grains (PAGs) with high frequency (61.3%) of low angle grain boundaries (LAGBs). On the other hand, the FGHAZ is filled with fine PAGs with a lower frequency (19.6%) of LAGBs. Such microstructural differences may likely contribute to differed mechanical properties for samples tested at designed positions.