In-plane constraint and relaxation type technology for the evaluation of solidification cracking susceptibility

Solidification cracking is a common welding defect, especially in high-sulfur steels, austenitic steels, and nickel-based superalloys. Various methods have been developed to evaluate solidification cracking by inducing tension during solidification, but none can locally assess susceptibility or yield precise high-temperature ductility curves without bending effects. In this study, a novel system was developed to evaluate solidification cracking susceptibility. The apparatus applies in-plane tension through compression and relaxation of die springs, referred to as in-plane constraint and relaxation, with a load capacity of 28 kN, extendable by higher-specification jacks and springs. 310S stainless steel, a fully austenitic alloy well known for its high susceptibility to solidification cracking, was selected as the test material. Bead-on-plate laser welding was performed on 1 mm-thick sheets under initial loads of 15.50–21.50 kN, with each experiment at a different level. Cracks occurred when the initial load exceeded 16.30 kN, making this load a global indicator of cracking response. Novel in-situ techniques were designed to assess cracking and measure temperature in the mushy zone, and their combined results yielded a precise high-temperature ductility curve. Fracture surface analysis and in-situ imaging confirmed that cracking occurred by interdendritic separation, promoted by liquid films persisting between grains. The ductility results showed that as the initial load increased from 16.30 kN to 21.34 kN, the critical strain rose slightly from 0.56% to 0.82%, while cracks initiated closer to the high-temperature region. Compared with traditional tests, the proposed system enables more localized and accurate measurement of the critical strain responsible for solidification cracking, thereby improving reliability and repeatability.