Cyclic behaviour constitutive modelling of a tempered martensitic steel including ageing effect

Cyclic behaviour of a tempered martensitic tool steel is studied in relation with the tempering state and a cyclic fatigue-ageing constitutive model is proposed. Kinetics of tempering and hardness evolution in the form of Johnson–Mehl–Avrami relation is introduced in an anisothermal constitutive model developed in the framework of the thermodynamics of irreversible processes. Model parameter identification methodology based on two optimised cyclic tests is explained and applied in the temperature range from room temperature up to 600 °C on a 55NiCrMoV7 tool steel with four different initial hardness levels. Validation is performed comparing model prediction with experimental results obtained on one hand during cyclic tests performed above the tempering temperature inducing an important micro-structural evolution as well as for samples with different tempering conditions not used for the identification process.