The influence of PVD coating on the low cycle fatigue behaviour of Cr-Mo-V steel at elevated temperatures

Abstract

The paper reports on findings of an experimental investigation of the low cycle fatigue behaviour of high performance Cr-Mo-V hot working steel, which is used for the forging die inserts in hot forging operations. Fatigue tests of standardised uniform-gauge test specimens with duplex coating (plasma nitrided and hard PVD coating) were carried out in a low cycle regime at stress ratio R≈0.05 at elevated temperatures of 150°C and 500°C. These were determined for typical hot forging operations by means of computational simulations.The experimental results have shown that in a low cycle fatigue regime at stress ranges around yield strength the influence of PVD (Physical Vapour Deposition) surface coating on the fatigue behaviour is negligible. However, in a high cycle fatigue regime at stress ranges in elastic domain the PVD surface coating has a positive effect on the material fatigue behaviour, which results in a longer fatigue life in comparison to the uncoated specimens.The low cycle fatigue parameters for uncoated and duplex coated surface of treated Cr-Mo-V steel for operating temperatures of 150°C and 500°C have been derived from experimental results for the first time. The determined fatigue parameters can be used to predict the fatigue life of similar hot forging tools under low cycle fatigue conditions.