Generation and propagation mechanism of cracks in welded joints of thin-walled capsules during hot isostatic pressing

The quality of the capsule has an important effect on the quality of hot isostatic pressing (HIP) products. The reliability of the capsule is a key factor in determining the success or failure of HIP. The capsule is mainly formed through a sheet welding process. In order to ensure the reliability of the weld in HIP, stainless steel with better high-temperature and high-pressure performance than Q235 steel needs to be used. In this case, the fusion line becomes a dissimilar-material interface, which is more prone to fusion-line failure. This paper focuses on examining and studying the formation mechanism of fusion line cracks in welded joints during HIP. The results show that, first, the increase of the HIP temperature weakens the strength near the fusion line significantly. Second, the higher the HIP temperature, the more severe the grain coarsening, and the grain size along the radial direction of the capsule exhibits a monotonic change. Third, since the HIP process changes the micro-zone grain orientation of mild steel, the distribution characteristics of ferrite and pearlite change as well. when the temperature and pressure are higher, the texture still exhibits a strong and complex distribution.