The introduction of new light-weight high-strength materials, which are difficult to form, increases demands on tool properties, including load-carrying capacity and wear resistance. Tool properties can be improved by the deposition of hard coatings but proper combination and optimization of the substrate properties are required to prepare the tool for coating application. The aim of this paper is to elaborate on tool steel substrate properties correlations, including hardness, fracture toughness, strength and surface quality and how these substrate properties influence on the coating performance. Results show that hardness of the steel substrate is the most influential parameter for abrasive wear resistance and load-carrying capacity, which is true for different types of hard coatings. However, high hardness should also be accompanied by sufficient fracture toughness, especially when it comes to very hard and brittle coatings, thus providing a combination of high load-carrying capacity, good fatigue properties and superior resistance against impact wear. Duplex treatment and formation of a compound layer during nitriding can be used as an additional support interlayer, but its brittleness may result in accelerated coating cracking and spallation if not supported by sufficient core hardness. In terms of galling resistance, even for coated surfaces substrate roughness and topography have major influence when it comes to hard ceramic coatings, with reduced substrate roughness and coating post-polishing providing up to two times better galling resistance.

Creep is defined as the permanent deformation of materials under the effect of sustained stress and elevated temperature for long periods of time, which can essentially lead to fracture. Due to very time-consuming and expensive testing requirements, existing experimental creep data are often analyzed using derived engineering parameters and models to predict and find the correlations between creep life (time to rupture), temperature and stress. The objective of this study was to analyze and compare different numerical algorithms by using the Larson–Miller parameter ($LMP)$ extrapolation model. Calculations were performed using the classical $LMP$ equation where different values of parameter $C$ were selected, as well as using a modified $LMP$ equation in which parameter $C$ was stress dependent $C\left(\sigma \right)$. The impact of two different approaches of extrapolation and correlation functions (linear and polynomial) applied to fit the $LMP$ model was also investigated. A detailed analysis was performed to choose the best extrapolation fit function and error tolerance. The numerical algorithm implemented was validated through creep rupture testing performed on 10CrMo9–10 steel at 600 °C (873 K) and 80 MPa. Creep model behavior analysis proved that different values of $C$ can significantly change the estimated time to rupture. An excellent response of the $LMP$ model was obtained by considering polynomial dependency when parameter $C$ was assumed to be 18, especially for the temperature range from 773 to 873 K. Promising results were also achieved when parameter $C$ was taken as stress-dependent, but only for linear fitting, which requires further analysis. However, at validation stage it turned out that only the linear extrapolation function and $C$ taken as a constant value provided adequate time-to-rupture prediction. In the case of $C$ = 18, estimated time was slightly overestimated (~8%) and for $C$ = 20 it was underestimated by 27%. In all other cases error largely exceeded 50%.

The aim of this research was to investigate the influence of laser surface texturing sequence on the fatigue properties of cold-work tool steel. For this reason, polished hourglass-type test specimens made from cold-work tool steel (K890) were surface textured using laser texturing. Surface textures were introduced before and after hard coating deposition (TiAlN) with the aim to investigate the sequence of surface-texturing process. It was found that coating deposition prolongs the fatigue life. The fatigue life behaviour can be influenced also by the sequence of surface texturing. In the case when laser texturing is done after coating deposition, it suffers in fatigue life properties. From a lower magnification, a fractured surface looks like a quasi-ductile fracture, but a closer look reveals that there is very little plastic deformation and some small flat regions can be seen with clear evidence of a brittle fracture mechanism with cleavage. Due to low fracture toughness of investigated steel, no fatigue striations of crack growth steps were found on the fractured surfaces.