Effects of rapid heating and uniaxial loading on the phase transformation and mechanical properties of direct partial remelted butt joint of AISI D2 tool steel

Abstract

Tool steels are widely used in various industries, such as automotive, shipbuilding, manufacturing, and marine, for rolling mills, blanking metals, and punching dies, given their distinctive hardness, resistance to abrasion, and deformation. However, joining tool steels using the conventional fusion welding process is difficult because of the formation of dendritic structures and hot cracking, which affect the strength of joining. Therefore, this study proposed the direct partial remelting process (DPRMP) for the butt joining of AISI D2 tool steel. Moreover, different uniaxial loads of 0, 0.5, 2.5, and 5 N were applied during the joining process to investigate the microstructural evolution and mechanical properties of DPRMP samples. Results showed that the ferrite phase in the base material was changed to the austenite phase with globular shape in the joined samples through DPRMP. In addition, increasing the uniaxial load from 0 N to 5 N reduced the average grain size, increased the shape factor, and caused joining defects, such as voids, to disappear. Furthermore, the tensile strength of the DPRMP samples improved by increasing uniaxial loading from 0 N to 5 N due to the effect of grain boundary diffusion and the decrease in eutectic carbide at the joint interface. The highest tensile strength was achieved in DPRMP-5, with a value of 652 MPa and a welding efficiency of 103%. Moreover, the average hardness value of the fusion zone improved in the DPRMP samples and increased to 400 HV wherein the as-received material presented a value of 226 HV.