Finite Element Analysis of Welding and Heat Treatment of TC4 Titanium Alloy Pressure Vessels

Abstract Finite element analysis was carried out for the welding and heat treatment process of TC4 titanium alloy pressure vessel, aiming at revealing the distribution characteristics of welding residual stress and its changing law in the heat treatment process. By establishing a two-dimensional axisymmetric welding model, and considering the material properties, boundary conditions, heat source model and analysis methods, the temperature and stress fields in the welding process are successfully simulated.Based on the results of the post-welding stress field, the time-hardened creep model is quoted for the finite element calculations of the post-welding heat treatment process, and the effect of creep effect on the residual stresses of welded annulus is investigated, the results show that: the stress characteristics of the girth weld of the TC4 titanium alloy pressure vessel are obvious. The axial residual stress shows a tensile - compressive - tensile distribution along the thickness direction, while the hoop residual stress is a high tensile stress in the near-weld and heat affected zone, and the stress peak even exceeds the yield strength of the material; By comparing the heat treatment schemes considering and not considering the creep mechanism, it is found that the heat treatment introducing the creep mechanism significantly reduces the residual stress in the weld area. Among them, the hoop stress decreases by 80% and the axial stress decreases by 50%, and the stress distribution is more uniform, effectively alleviating the stress concentration phenomenon of the weld. In addition, the rebound amount of the residual stress in the cooling stage of the heat treatment scheme considering the creep mechanism is small. This study indicates that the creep mechanism plays a dominant role in eliminating residual stresses during heat treatment.