Dendrite-scale quantitative evaluation of solidification cracking in welding using in-situ synchrotron X-ray imaging: distribution characteristics of critical strain

Solidification cracking is a critical defect in welding, and its occurrence has conventionally been described using temperature-dependent critical-strain curves. However, whether the critical strain is uniquely determined by temperature remains unclear, particularly at the dendrite scale. In this study, solidification-cracking behavior in an Fe–15Mn–10Cr–8Ni–4Si alloy was investigated using in-situ synchrotron X-ray transmission imaging combined with local strain and temperature analyses. Crack-initiation events were identified from the time-resolved X-ray images, and the corresponding critical equivalent strains and critical temperatures were extracted at individual positions along the crack path. Solidification cracking occurred over approximately 1320–1000°C, corresponding to the effective solid–liquid coexistence region predicted by a Scheil–Gulliver calculation. The median critical strain was higher at lower temperatures and generally decreased toward higher temperatures. A broad critical-strain distribution remained within each 30°C temperature range. After subtraction of the temperature-bin median, the remaining variation was spatially nonuniform along the crack path. Comparison with a non-cracking case showed that most equivalent-strain values remained below the critical-strain distribution obtained in the cracking case, although the upper tail partially overlapped its lower part. These results provide experimental evidence that the critical strain at solidification-crack initiation is better represented as a temperature-dependent distribution than as a single-valued curve. The physical factors governing the distribution width and spatial variation remain to be identified.