피스톤 크라운 용 단강의 용접부 특성에 미치는 인코넬 625 용접봉의 평가

Abstract

Abstract

Recently a fuel oil of the diesel engine of the marine ship is being changed with heavy oil of low quality as the oil price is higher more and more. Therefore the wear and corrosion in all parts of the engine such as cylinder liner, piston crown, spindle and seat ring of exhaust valves are predominantly increased with using of heavy oil of low quality. In particular the degree of wear and corrosion of piston crown is more seriously compared to the other parts of the engine due to operating in severe environment such as the high temperature of exhaust gas and repeating impact. Thus the repair weldment of the piston crown is a unique method to prolong the its life in a economical point of view.

By the way, their parts on the ships job site is often being actually welded with electrodes of mild steel. However, in the case welded with

the electrode of mild steel, the mechanical property and corrosion resistance of welding zone would be worse than other electrode.

In this study, the forged steel material for piston crown as a base metal was welded with Inconel 625 electrode. And each welding zone, that is, the mechanical and corrosion characteristics of base metal(BM), heat affected zone(HAZ) and weld metal(WM) zones were investigated using electrochemical methods such as measuring of Vickers hardness, corrosion potential, polarization curve, cyclic voltammogram and impedance in 35% H2SO4 solution. And the morphology of corroded surface was also observed by micro photograph. The weld metal and heat affected zones exhibited comparatively higher values of hardness compared to the base metal zone. The corrosion potential of the weld metal zone indicated a higher value than those of heat affected and base metal zones. As a result, the corrosion resistance of the weld metal zone was also better compared to heat affected and base metal zones. Consequently, it is considered that the weld metal zone exhibited the best corrosion resistance, indicating higher corrosion potential, higher hardness. Furthermore, in the case welded by Inconel 625 electrode to the forged steel material for piston crown, we can see that their mechanical properties and corrosion resistance in the welding zones were significantly superior to the case welded by the mild steel electrode.