A computer study of the thermomechanical deformation behavior of a duplex steel

Specimens of ferritic-austenitic duplex steels with an anisotropic microstructure undergo irreversible length changes even under pure thermal cycling conditions. This unexpected behavior is due to the different coefficients of thermal expansion of ferrite and austenite which, upon thermal cycling, can generate stresses in the phases exceeding their yield strength. In this report, results of an extended elasto-plastic analysis of the thermomechanical deformation behavior of the duplex steel are presented. In addition to thermal loading, external tensile stresser smaller than the yield strength of the two phases are exerted on the microstructure. A full thermal cycle 900°C-20°C-900°C is analysed. The instantaneous coefficient of thermal expansion of the duplex steel depends on the applied load. It is shown that the combination of thermal and mechanical loads causes irreversible deformations. The amount of these deformations depends on the applied load. The deformations are identified as plastic deformations since the volume of the considered body is the same at the beginning and the end of the thermal cycle.