Experimental Study on the Influence of TiN/AlTiN PVD Layer on the Surface Characteristics of Hot Work Tool Steel

It is desirable to improve tool steel wear resistance to produce pieces with precise dimensions and increase the lifetime of tools. The aim of this work was to modify the surface of 1.2344 (X40CrMoV5-1) hot work tool steel to improve the wear properties. Surface modification was achieved in three steps: first, hardening was applied, followed by plasma nitridation and, finally, physical vapor deposition (PVD) was employed to produce a TiN/AlTiN multilayer coating. The microhardness and the wear coefficient of the surfaces were measured. PVD coating showed the highest hardness value, 2938 HV0,01, whereas plasma nitridation followed by PVD resulted in 2679 HV0,01. The surface modification resulted in an increase in surface roughness in all cases compared to the hardened sample. However, the wear coefficient showed a significant decrease for the surface treated samples. The lowest wear coefficient of K = 1.47 10–10 mm3/Nm, which is a magnitude lower than the reference hardened sample (K = 6.32 10–9 mm3/Nm), was achieved employing both plasma nitridation and PVD. The results confirm that the use of a combined surface modification of plasma nitridation and PVD significantly improve the wear resistance of the treated samples.

Effect of Heat Treatment on Microstructure Evolution of X38CrMoV5-1 Hot-Work Tool Steel Produced by L-PBF

The X38CrMoV5-1 hot-work tool steel produced by laser powder bed fusion was investigated to assess the effect of quenching and tempering and direct tempering on the as-built microstructure. After the printing process, the material microstructure appeared to be characterized by a fine cellular network consisting of γ-Fe cell boundaries and α′-Fe cores. Scheil–Gulliver curves, X-ray diffraction patterns, and transmission electron microscopy images suggested a transformation of the inner core zone from δ-Fe to α′-Fe through γ-Fe. Air quenching promoted the transition of the solidification structure into a fully martensitic microstructure. Both as-built and quenched samples revealed the presence of manganese oxides and vanadium carbonitrides forming core-shell structures. After tempering, starting from as-built and from quenched condition, a dispersion of nano-sized V and Cr-rich second phases was formed in the microstructure, achieving hardness values comparable to those obtained by the same alloy produced by conventional methods. The specimen tempered directly after the laser powder bed fusion process showed a hardness peak shifted towards higher temperatures compared to the conventionally tempered sample.