Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Simulated Weld Heat-Affected Zone of SA-516 Grade 70 Carbon Steel

The effect of post-weld heat treatment (PWHT) temperature on the mechanical properties of the heat-affected zone (HAZ) of P-No. 1 carbon steel was investigated by taking into account the change of the microstructure. SA-516 Gr. 70 plate was employed as the P-No. 1 carbon steel, and the specimens taken from the steel were thermally cycled using a Gleeble simulator to simulate coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), intercritical HAZ (ICHAZ), and subcritical HAZ (SCHAZ). The base metal and simulated HAZ specimens were heat treated in a furnace at 610, 650, 690, and 730° for 8 hours. The impact toughness of ICHAZ, FGHAZ, and CGHAZ improved significantly when the PWHT temperature was 690° or below. However, when the PWHT temperature was 730°, pearlite transformation occurred partially, and the mechanical properties deteriorated in all specimens with the exception of the simulated CGHAZ specimen. Therefore, the PWHT temperature should be below A1 of carbon steel to avoid the reduction of impact toughness of the carbon steel HAZ. Key words: Carbon steel, Heat-affected zone, Post-weld heat treatment, Impact toughness