Effect of water depth and water flow on the physics and mechanic properties of the underwater wet welded low carbon steel with post weld heat treatment

Underwater welding is chiepest and easiest method in the maintenance and repairing offshore engineering equipment construction. It have disadvantage due to the water environment such as the high cooling rate and the hydrostatic pressure. Post weld heat treatment (PWHT) was proposed to improve underwater wet welded joint. Underwater wet welding processes were performed in the water depth (0 m, 2.5 m and 5.0 m) and water flow (0 m/s, 1 m/s and 2 m/s). PWHT were conduct in constant temperature of 560°C and holding time of 75 minutes. The result show that highest hardness was found in underwater wet welding with a depth of 5 m at water flow rate 2m/s with highest value in the weld metal area 180 VN, HAZ 171 VN and base metal 131 VN with tensile strength 199,64 Mpa. Whereas, weld joints which have the lowest hardness is 2.5 m with water flow rate 0m/s produced the weld metal hardness value 145 VN, HAZ 132 VN, BM 127.9 VN and tensile strength 173,1. Distribution hardness value increased in weld metal due to presence of ferrite second phase (FSP) which has a major contribution increasing hardness. In addition, due to the heat input in PWHT FSP structure that is brittle transforming into the acicular ferrite..