In-situ observation of solidification behaviors of Fe-Mn-Cr-Ni-Si alloy during TIG melt-run welding using synchrotron radiation X-ray

The solidification behaviors, including the solidification cracking and solidification mode of the Fe-Mn-Cr-Ni-Si alloys at the weld bead during tungsten inert gas (TIG) melt-run welding, were examined by time-resolved in-situ observations using synchrotron radiation X-ray imaging and X-ray diffraction. The dynamics of initiation and propagation of solidification cracking at the weld bead could be observed at the dendrite scale. For the specimen solidified in the austenite mode at a welding speed of 10 mm/s, solidification cracking with a zigzag interface developed via the coalescence of many small pores at the centerline, where the columnar dendrite tips impinged. Quantitative image analysis indicated that the local tensile strain was highly localized at the centerline, and the critical local tensile strain for the initiation of solidification cracking was approximately 0.04. For the specimen solidifying in the ferrite-austenite mode at the welding speed of 10 mm/s, the centerline solidification cracking was suppressed by the formation of many equiaxed gamma-Fe dendrites ahead of the growing columnar delta-Fe dendrites. Grain refinement at the centerline can be achieved at a welding speed of more than 7 mm/s without requiring inoculants.