Evaluation of mechanical and fatigue properties of weld deposit and its comparison with that of die steel

In hot forging process, a billet is heated to a high temperature and then pressed between a set of dies in order to achieve the required shape. During production, dies are continuously under thermal and mechanical cyclic loading. The combination of these two phenomena may lead to die failure due to Low Cycle Fatigue (LCF) cracking. A cracked die cannot be replaced completely due to high costs and long turnaround time associated with procurement of the die steels. Hence, the cracked dies are repaired using the process of gouging – welding – machining. The weld deposited material becomes an integral part of forging dies and the strength of the repaired die depends on the quality and strength of the welding. Present work evaluates the mechanical, metallurgical and LCF properties of the weld deposit and compare it with that of die steel, AISI L6. Generally, Mailam 535 is employed for welding AISI L-6. Tensile properties i.e. Yield Strength and Ultimate Tensile Strength of weld deposit were found to be 19% less and 7% higher than that of die steel, respectively. Charpy impact properties of weld deposit were observed to be 61% and 74% less than that of die steel in longitudinal and transverse direction, respectively. LCF strength of weld deposit weld material was found to be 50% less than that of die steel. Fractography and optical microstructure were studied for failed specimen in mechanical testing to study failure mode of welding material. The difference in properties can be attributed to the different microstructure observed in weld deposit and the die steel.