APPLICATION OF NICKEL COATING ON LOW ALLOY STEEL SURFACE BEFORE FRICTION WELDING WITH 304 AUSTENITIC STAINLESS STEEL AND STUDY DIFFUSION OF CARBON

Abstract

Dissimilar metal joints are used widely in various industrial applications due to both technical and economical reasons. The adoption of dissimilar metal combinations provides possibilities for the flexible design of product by using each material efficiently, i.e. benefiting from the specific properties of each material in a functional way. There are welding processes available like friction welding, explosive bonding by which the welding of dissimilar metals can be done. But all of the processes available friction welding used in the present study of work are the most successful method for welding of dissimilar metals since there is no hindrance of same melting points for the base metals to be welded. The friction welding of dissimilar metals is a solid state welding process where the base metals to welded are rotated against each other by keeping one as stationary component. Here unlike other process the temperature is kept just below the melting point of the base metals to be welded. So, instead of melting the base metals gets diffused into one another to complete the welding of dissimilar metals. In the present work the problem of migration of carbon taking place across the interface of the weldment has been successfully removed by incorporating Nickel layer between the dissimilar metals. In present work the friction welding of 304 austenitic stainless steel and 4140 low alloy steel without and with Nickel interlayer has been successfully performed and study has been carried out to observe the diffusion of carbon. By microstructures obtained it clear that the inter-mixing of the dissimilar metals has been stopped at the interface region due to the presence of Nickel interlayer. XRD analysis has shown various intermetallics formed during the welding of dissimilar metals with and without Nickel interlayer. The colour mapping obtained from FESEM/EDAX at interface of with and without interlayer has shown the reduced carbon concentration at stainless steel side after application of the Nickel as interlayer. Also the line mapping of without and with Nickel interlayer comparison has shown a drastic fall in peaks of carbon element distribution across the weldment interface. Thus, from the above study done in present work the comparison between with and without Nickel interlayer between stainless steel and low alloy steel has shown that the diffusion of carbon across interface has been successfully prevented.