The effect of heat treatment on the mechanical, tribological and load-carrying properties of PACVD-coated tool steel

The limited load-carrying capacity of tool steels greatly restricts the use of hard coatings in forming applications. This can, however, be improved by increasing the substrate's hardness, but especially for hot forging, the fracture toughness and resistance to cracking are equally important. The present work was focused on the possibilities of combining a vacuum heat treatment, a deep-cryogenic treatment and plasma nitriding in order to improve the properties of PACVD-coated tool steel. The investigation included TiCN-coated P/M high-speed steel, with 12 different combinations of the vacuum heat treatment, the deep-cryogenic treatment and plasma nitriding, which were investigated as a way of simultaneously improving the mechanical, tribological and load-carrying properties of tool steel. The results show that for the most demanding forming operations the substrate toughness is far more important than the hardness, especially at elevated temperatures, with just a vacuum-heat-treated steel substrate giving the best support for the top coating. •Heat treatments combinations allow optimization of tool steel substrate properties.•Load carrying and friction of coated tool steel depends on substrate preparation.•Highest substrate hardness is provided by cryogenic treatment and post nitriding.•Best load carrying capacity is provided by only vacuum heat treatment.•In heavily-loaded contacts toughness of substrate is more important than hardness.