EFFECT OF FOLLOW-UP POST WELD HEAT TREATMENT ON MICROSTRUCTURE AND PWSCC OF ALLOY 52M WELD METAL IN DISSIMILAR METAL WELD JOINT

摘要

Ni-base Alloy 52M is used in pressurized waterreactors as weld filler metal to join the low alloy steel(LAS) and stainless steel. The transition region in 52Mbuttering weld metal near the fusion boundary (FB) ofLAS-nickel base alloy dissimilar metal weld joint (DMWJ)exhibits heterogeneous characteristics such as dendriticstructure and microchemistry, concentration gradient,residual strain and types of grain boundaries (GBs). Postweldheat treatment (PWHT) is used to lower the residualstress and temper the heat-affected zone of the welds. Twodilution zones in Alloy 52M weld near the FB in bothonce PWHT and followed up PWHT (FU-PWHT) DMWJare found. One hardness peak is observed in the AW-52Mwhile two hardness peaks in PWHT-52M. In the firstdilution zone, the precipitates at PWHT Alloy 52Mdendrite boundaries are fine and granular, while thoseare long wall-liked at FU-PWHT 52M dendriteboundaries. PWSCC is found in the first dilution zone inthe both PWHT and FU-PWHT Alloy 52M CT specimensbut not significant in the undiluted regions in Alloy 52M,showing higher PWSCC growth rate in the dilution zones.The length and density of cracks in FU-PWHT specimensare less than those in PWHT specimens. FU-PWHTdecreased the PWSCC growth rate.