This study aims to investigate the suitability of requirement for post-weld heat treatment(PWHT) temperature when different P-No. materials are welded, which is defined by ASME Sec. III Code. For SA-516 Gr. 60 and SA-106 Gr. B carbon steels that are typical P-No. 1 material, simulated heat treatment were conducted for 8 h at 610℃, 650℃, 690℃, and 730℃, last two temperature falls in the temperature of PWHT for P-No. 5A low-alloy steels. Tensile and Charpy impact tests were performed for the heat-treated specimens, and then microstructure was analyzed by optical microscopy and scanning electron microscopy with energy-dispersive spectrometry. The Charpy impact properties deteriorated significantly mainly due to a large amount of cementite precipitation when the temperature of simulated heat treatment was 730℃. Therefore, when dissimilar metal welding is carried out for P-No. 1 carbon steel and different P-No. low alloy steel, the PWHT temperature should be carefully selected to avoid significant deterioration of impact properties for P-No. 1 carbon steel.

Additive manufacturing (AM) is an interesting technology with the potential to replace general fabrication techniques such as machining, forming and casting. AM provides two main benefits: greater freedom of part design and lower material consumption. To improve quality, many researchers have investigated the mechanical characteristics of AM products and additive parameters. In the present study, tensile and fatigue tests were conducted on stainless steel (SS) 316L manufactured using powder bed fusion (PBF) technology. These tests were carried out using two different building directions, along the Z and X axis, to investigate the effect of additive direction. In addition, the effects of hot isostatic pressing (HIP) related to fatigue properties, which can influence the volume density and porosity of the specimen, was studied. Based on the test results, changes in the mechanical characteristic and fatigue strength due to the HIP treatment were investigated.