Effects of water temparature and welding current of microstructure and mechanical performance of AH36 welded by SMAW and chemichal composition of seawater.

Abstract Underwater wet welding (UWW) is applied to repair offshore structures, underwater pipelines, water transport, docks and harbour equipment. In this study, the mechanical and microstructural properties of AH36 low carbon steel were investigated at different welding current strengths and different seawater temperatures using metal arc welding (SMAW), an underwater wet welding method. Changing seawater temperatures and welding current parameters were examined together, so that the change of seasonal variability in welding parameters and chemical structure of seawater was examined. For this purpose, in the first stage, the yield strength value of AH36 was statistically modelled using the central composite design with the response surface method with input parameters of seawater temperature (in the range of 9.7°C-25.3°C) and source current value (in the range of 49A-90A) and the best conditions were found as Optimum Yield stregth 270MPa, 17.5°C seawater temperature and 69.5 A source current value. In the second stage of the study, the data obtained from the optimisation studies were used in the multi-response optimisation model to obtain elemental exchange equations for Cr (R 2 = 87.3), Ni (R 2 = 64.45) and Mn (R 2 = 65.74) ionised in seawater. Accordingly, it was observed that the change in Cr content in seawater is affected by source current intensity, Ni content is affected by seawater temperature and Mn content is affected by current intensity and seawater temperature together. ICPMS was used for ion exchange in seawater, EDS point analysis for chemical composition in AH36 and SEM for microstructure analysis.