Evaluation of Effect of Welding Methods to Corrosion and Hardness Characteristics of Welded Zone

Recently a fuel oil of the diesel engine in the merchant ship has been changed with heavy oil of low quality as the oil price is getting higher and higher .Therefore, the wear and corrosion against all parts of the engine are significantly increased with using of heavy oil of low quality. In particular, the degree of wear and corrosion in between spindle and seat ring of exhaust valve are more serious compared to the other parts of the engine due to severe environment such as the high temperature of exhaust gas and repeating impact. Thus, repair welding is a unique method to prolong their lifetime in an economical point of view. In this study, an effect of welding methods to corrosion and mechanical properties of both weld and base metal zone was investigated with some electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram and AC impedance etc. in. The hardness of the weld metal zones exhibited comparatively higher values than that of the base metal zone. And their corrosion resistances were also increased compared to the base metal. The weld metal zone of P1F( plasma welding with 1 pass) showed a relatively good corrosion resistance as well as the hardness compared to the other welding methods. Consequently, it is considered that plasma welding method is a desirable method compared to other welding methods for both better corrosion and hardness properties.