Microstructure based flow stress modeling for quenched and tempered low alloy steel

Quenching and tempering (Q&T) process is commonly applied in part making industries for improving mechanical properties of carbon low alloy steels. After Q&T, microstructure of the steel consists of temper martensite and carbide precipitations. In this work, material modeling for describing flow stress behavior of the SNCM439 alloy steel under different tempering conditions was introduced. Microstructure based models were developed on both macro- and micro-scale. The models were afterwards applied in FE simulations for predicting stress–strain responses of the tempered steels. For the macroscopic model, the Ludwik equation was used, in which precipitation strengthening depending on particle size was incorporated by the Ashby–Orowan relationship. For the microscopic model, representative volume elements (RVEs) were generated considering microstructure characteristics of the examined steels. Flow curves of the individual constituents were described based on dislocation theory and chemical compositions. The FE simulations of tensile tests and RVE simulations under uniaxial tension were performed using the introduced models. The influences of the carbide precipitations on mechanical behavior of the tempered steels were investigated. The resulted effective stress–strain curves were determined and compared with the experimental ones. Both macroscopic and microscopic approaches accurately predicted mechanical properties and strain hardening behaviors of the tempered steels.