Effect of Peak Temperatures on Microstructure and Properties of Welding Coarse Grain Heat-Affected Zone of SA508 Gr.4N Steel

The effect of peak temperatures on the grain growth, microstructure transformation and Vickers hardness of the weld coarse grain heat-affected zone (CGHAZ) of SA508 Gr.4N steel for nuclear reactor pressure vessel was studied. The results show that different t8/5 time has no obvious effect on grain growth at the same peak temperature, but different peak temperatures have a great influence. The higher the peak temperature, the more obvious the effect on grain growth. The grain size distribution at different peak temperatures and t8/5 time conforms to the Gaussian normal distribution curve, and a grain growth model suitable for CGHAZ of SA508 Gr.4N steel has been established. The room temperature martensite structure can be obtained by treatment at different peak temperatures and t8/5 time. At the same peak temperature, there is no significant difference in martensite structure at different t8/5 time, and the size of martensite lath only increases with the increasing peak temperatures. At different peak temperatures and t8/5 time, grain size has less effect on the Vickers hardness, which is closely related to the room temperature microstructure of the material.