Abstract: Residual stress, microstructure and mechanical properties of S11306 ferritic stainless steel thick plates were examined after welding and two heat treatment processes. The welding residual stress was determined both before and after heat treatment by using the blind hole method. The sequential coupling method and double ellipsoidal heat source were utilized to characterize the temperature and stress fields during welding. The microstructure evolution both before and after heat treatment was studied by using optical microscope. The results show that the error of the welding temperature field simulated by the heat source can be controlled within 10%. The difference between the stress results obtained through sequential coupling and the experimental values shall not exceed 23%. The heat treatment process can significantly reduce the peak residual stress in the weld zone. Compared to 770 ℃, the heat treatment temperature of 820 ℃ provides a greater residual stress-relieving impact on the 100 mm area surrounding the weld zone. The higher heat treatment temperature not only reduces the martensite content of the base metal, but also promotes the grain growth of the heat affected zone, concurrently the content of lower bainite and martensite composite phase (LB/M) in the weld zone is increased to 47.6%. The hardness values of the base metal and heat affected zone show a decreasing trend after heat treatment, while the hardness value of weld zone is increased by 33 HV0.05.

Key words: stainless steel thick plate, welding temperature field, welding residual stress, post weld heat treatment, microstructure, hardness