In situ observation of solidification crack propagation for type 310S and 316L stainless steels during TIG welding using synchrotron X-ray imaging

In situ observation of solidification cracking at the weld bead during tungsten inert gas (TIG) welding for type 310S and 316L austenitic stainless steels without the application of an external force was carried out using synchrotron X-ray radiography. The temperature distribution at the weld bead was simultaneously measured using a high-speed camera to directly determine the temperature, in which the propagation of solidification cracking occurred. The solidification cracking was clearly identified and it continuously propagated in the welding direction. The interface of the solidification cracking showed an irregular and zigzag morphology. It was found that the tip velocity of the solidification cracking periodically changed by translating between the high solid fraction (~ 90%) and the relatively lower solid fraction (~ 70%) regions at the centerline of the weld bead for both the type 310S and 316L stainless steels. The solidification cracking propagated at the lower temperature than the solidus temperature due to the segregation of low melting-point components. The tensile strain and strain rate were highly localized in the propagated area every 0.1 s which was the almost same as the time period, in which the tip velocity of the solidification cracking remarkably increased. The periodicity of the solidification cracking velocity at the weld bead can be explained by the dendrite morphology at each solid fraction and strain rate.