Prediction of the Temperature Distribution and Microstructure in the HAZ of SA508Gr4 Reactor Pressure Vessel Steel

SA508Gr4 is a newly developed steel for reactor pressure vessel and its behavior data is rare, especially its welding characters attract researchers and industries attention. In this paper, a finite element method (FEM) is employed to investigate the thermal process and phase transformation process of arc welding of SA508Gr4 steel, where a body heat source model and element birth and death technique were used in this simulation process. This study focuses on the effect of peak temperature (t(m)) and cooling rate (t(8/5)) on microstructural transformation in HAZ, which is to be overcome by combining SH-CCT diagram with numerical thermal cycle curves. Through conversion of thermal cycle data into microstructural information, it is found that the quenched zone is developed rapidly whose width is 1 560 mu m, while the inter-critical HAZ region is three times smaller than the quenched zone dimension, which is 450 mu m. Post weld heat treatment was suggested to be adopted for improving the property of HAZ. In addition, the metallographic analysis confirms the expected microstructural evolutions. The microstructure is martensite (M) + some bainite (B) and the microhardness is between 429 HV and 432 HV.