Establishment of Thermo-metallurgical-mechanical Coupling Constitutive Model for Armour Steel and Its Application in Welding Numerical Simulation

Solid-state phase transformation has significant effect on the evolution and magnitude of welding residual stress for armour steel during welding thermal cycle, while the current constitutive model can not take solid-state phase transformation into account. Based on heat transfer theory, solid-state phase transformation theory and continuum mechanics, a thermo-metallurgical-mechanical coupling constitutive model in which the effects of volumetric change, yield strength change and transformation induced plasticity(TRIP) on residual stresses due to solid-state phase transformation on welding residual stress are considered is established. The constitutive model is inserted into a general purpose implicit finite element program via user material subroutine UMAT. The change rules of temperature, microstructure and residual stresses are obtained for a butt welding of armour steel plates. The research results show that longitudinal residual stresses obtained from the coupling constitutive model are in good agreement with experimental results measured by X-ray diffraction perpendicular to weld centerline on the upper surface of the weldment. The correctness of developed computational method is confirmed, and TRIP has certain effects on the evolution of longitudinal residual stresses. For the magnitude of longitudinal residual stresses in the vicinity of weld zone, the fully-transformed region is less than partially-transformed region, and the partially-transformed region is less than untransformed region. © 2017, Editorial Board of Acta Armamentarii. All right reserved.