Research On Welding/Repair Welding Mechanical Behaviors Of HSLA Steel Considering Solid-state Phase Transformation Effects

High-strength steel has been widely used in ship construction, the welding residual stresses have significant influence on its structure safety and reliability. As an efficient method in welding mechanical behaviors analysis, finite element method, FEM, could display residual stress field in all dimensions. But it might cause a great error in welding mechanical simulation if the solid-state phase transformation effects were neglected for some high-strength steels for Marine. This paper is conducted to research on welding and repair welding mechanical behaviors of 10Ni5 Cr Mo V steel considering solid-state phase transformation effects.Firstly, several factors such as the material parameters, annealing effects and phase transformation strain are discussed using single factor analysis method in order to investigate their influence on welding mechanical simulation results, which is the foundation of follow-up works. The simulation results turn out that the material parameters have a great effect on welding residual stresses and deformation. And then an annealing model is established because work hardening behaviors are eliminated or reduced by several physical phenomena like recovery, recrystallization and melting in varying degrees during welding process. It indicates that the magnitude of welding residual stress become lower slightly if annealing effect is considered. Welding simulations with different phase transformation strain parameters are conducted, it figures out that transformation strain parameters affect welding residual stress and deformation greatly, so that carrying out accurate welding mechanical simulation requires precise phase transformation models.Welding thermal simulation of 10Ni5 Cr Mo V steel is conducted, and results indicates that there are austenite transformation during heating and martensite transformation during cooling for a wide range of welding thermal cycles. The effects of solid-state phase transformation during welding process includes volume change and yields strength change, so the phase transformation model and yield strength model are constructed respectively. The former is based on thermal simulation results, and the latter is based on high-temperature tensile testing. On the basis of these two models, a series of ABAQUS subroutines are developed to conduct welding mechanical behaviors simulation with solid-state phase transformation effects. Results indicate that yield strength model don’t change the distribution trend of residual stress, but change its magnitude; and phase transformation strain change both its distribution and magnitude.Welding experiment is carried out. It is proved that the heat transfer and mechanical simulation with solid-state phase transformation effects are reasonable by comparing the thermal cycles and stresses of certain locations between experiment and simulation.Finally, repair welding mechanical simulation considering solid-state phase transformation effects is carried out. It indicates that the magnitude of longitudinal welding residual stress changes slightly and the transverse one increases a lot after repair welding. And several repair welding schemes including 2 typical repair locations and 3 different repair length are simulated. Results show that there are little difference of stress magnitude between 2 repair locations, but a great difference among 3 repair length, and the magnitude of transverse stress reduces to the value before repair welding gradually as the repair length increases.