EVALUATION OF MECHANICAL PROPERTIES OF DISSIMILAR WELDED SPECIMEN (TIG, EBW, FRICTION WELDING)

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. Fusion welding is far the most important process used in the fabrication of modern boilers.Componets are joined by the formation of a molten pool of metal between them. The production of high quality welds with a high degree of consistency is readily achievable. However; defects are more likely to occur in welds than in wrought material. Low alloy steel and Austenitic stainless steel possess a good combination of mechanical properties, formability and weldability.Owing to these attributes at moderately high temperatures,Cr-Mo steels are an extensively used family of engineering materials for applications such as steam generation/handling, petroleum processing/refining, thermal reforming/polymerization/cracking,.However,the strength of the weldment of Cr-Mo steels is generally inferior, and most of the in-service failures are reported to take place in weld region. The welding work was carried out at Defence Metallurgical Research Laboratory (DMRL-Hyderabad) on the AISI 4140 and AISI 304 by FRW, EBW and TIG welding processes by Research Scholar N. Arivazhagan, Department of Metallurgical and Materials Engineering, IIT-Roorkee. I received Samples from him for various Mechanical testing (Tensile, Impact, Microhardness, .Microstructure, etc). The dissimilar alloy weldments in as welded condition were characterized by Metallography, Micro hardness across the weldment, Tensile strength, Impact toughness. The peak hardness on the weld zone made by FRW is less as compared to TIG and EBW.This can be attributed to more formation of carbides and intermetallic compound in the weld zone when made by TIG and EBW. The yield strength of dissimilar weldment made by EBW is higher as compared to the once made by TIG and FRW.Tensile testing of FRW weldment shows that the failure took on 4140 side, where as in the case of weldment made by EBW and TIG, the dissimilar- metals it was observed that nature of fracture become more brittle with increase in the burn off length. Whereas the SEM fractography of impact tested dissimilar weldment made by EBW and TIG shows cleavage fracture. In case of friction welded specimens the increase of burn off length led to more brittle fracture, which may due to formation of more carbides and intermetallics.In case of EBW and TIG weldments the fractured surface indicates ductile nature.