Insight into the microstructural stability and thermal fatigue behavior of nitrided layers on martensitic hot forging tools

The aim of this study is to evaluate some aspects related to the thermal-induced decomposition of the nitrided layers in dies used for hot forging made of tempered martensitic tool steel. Nitriding is used to improve the functional properties and durability of forging dies. The degradation of the tool surface without nitrided layers can be considered as an example of quenched and tempered steel. Thermal decomposition of nitrided layers on steel is an issue that is little known in the literature, especially when it concerns the decomposition under tribomechanical loading conditions. Changes occurring on the tool surface caused by service-life conditions have become the basis for considerations regarding the thermal stability of the nitrided layers. Material issues influencing the functional properties of dies have also been discussed. The conducted state-of-the-art literature reviews and metallographic analysis have shown that it is advisable to conduct further research on phase transformations related to the decomposition of nitrided layers. The strategy for further studies is also suggested.