Selection of the optimal hard-facing technology for reparation of the machine parts made of hot work tool steel

Abstract

The selection procedure for welding/hard-facing of thermo-resistant steels, with emphasis on the reparatory hard-facing of the forging dies, is presented in the paper. The forging dies for hot forging are being exploited in the extreme conditions of the compressive-impact loading and high temperatures, which locally can reach even 600 ºC. This is the reason why, after certain number of cycles, damages of the forging dies can arise, regardless of the cause that can be either wear, thermal fatigue or appearance of surface cracks. Reparatory hard-facing of these steels is a very complex procedure, which consists of careful selection of the welding process type, the filler metal, welding parameters, as well as adequately prescribed heat treatment regime. Besides that, in the paper are presented results of hardness measurements in various zones of the hard-faced samples, as well as the metallographic investigations performed on the optical and scanning microscopes. For the prescribed technology one can say that it is adequate if the brittle phases or the zones of high hardness do not appear in the material after the welding, since they could cause stress concentration and places of eventual fracture.