STUDY OF HOT CORROSION & AQUEOUS CORROSION OF EBW DISSIMILAR WELDS

Abstract

Dissimilar-metal joints are used widely in various industrial applications due to both technical and economic reasons. The adoption of dissimilar-metal combinations provides possibilities for the flexible design of the product by using each material efficiently, i.e., benefiting from the specific properties of each material in a functional way. The special features of Electron Beam Welding has proven to be an efficient way of joining dissimilar metals. There are many industries where austenitic stainless steel needs to be welded to low alloy steel, especially in the power generation industry, has been subject of interest. In the present work Hot and Aqueous Corrosion Experimental Studies are carried on the Electron Beam Welded austenitic stainless steel(AISI-304) and low alloy steel(AISI-4140) weldment. It has been found that there are differences in corrosion rates on the base metals and the weld zone of the dissimilar weldment in hot and aqueous corrosion respectively. In hot and aqueous corrosion, the corrosion rate is of the order AISI 4140 > Weld Zone > AISI 304 in dissimilar weldment, hot corrosion follows parabolic law and higher content of Fe203 and Cr203 on scale over weld zone may be due to enrichment of this zone with Fe and Cr as indicated by EDAX analysis on the dissimilar weldment and the reason is chromium diffuse towards AISI 4140 from the AISI 304 and diffusion of iron from AISI 4140 side towards AISI 304 . The dissimilar weldment has more corrosion than the individual base metals in aqueous corrosion. Dissimilar weldment suffered accelerated hot corrosion in the chloride+sulfate mixed molten salt environment in the form of intense spalling and sputtering of its scale. The cracking of oxide scale on the weldment as observed in the hot corrosion study in molten salt environment might be attributed to different composition of base metals, weld metal and oxide formed.