Microstructure and Durability Analysis of Multi-layer Repaired Forging Dies

Abstract

Multilayer Flood-welding repair of hot forging dies is a very useful technique which can remarkably enhance the working life of the die. Conventional quenched and tempered dies do not exhibit good resistance to wear. Therefore, these dies are nitrided to improve wear resistance but after the production of few numbers of forgings cracks are produced. That’s why here multilayer flood-welding technique has been adapted to improve the die life and to establish the optimum parameters for this technique. In the current work, the modified H12 hot-work tool steel was weld deposited in the cavity of hot-forging dies and their performance was monitored visually for the die condition and with the macroscopic and microscopic examination. It was analyzed that the thicknesses of the both hard upper ‘capping layer’ and intermediate ‘buffer layer’ have a prominent influence on the performance and the life hot forging die. For a particular dimensions and contour of the die impression, there came out an optimal thickness of the capping layer that provided the best performance. Further increase in capping layers thickness exhibited brittle cracking, whereas thinner capping layers produced early wear and plastic deformation. For intermediate buffer layer, in order to provide adequate backup support to capping layer, a certain minimum thickness level is required. This process minimized the die steel consumption because the thickness of the forging die is not reduced in the process of reworking and ultimately the process is cost effective. Moreover, the Multilayered flood-welded dies were gas nitrided to further enhance the life of the forging die. The results have shown that double stage nitriding process is good for these dies which produced minimum compound layer on the nitrided surface. The die life as a result of nitriding was amazingly increased compared to normal Multilayered flood- welded dies. The dies showed very slow wear and thermal fatigue cracking after the production of large number of forgings. By employing these dies excellent overall surface finish of the forged parts was achieved.