Quantification of Mechanical Factors in the Control of Weld Hot Cracking

Hot cracking in fully austenitic stainless steel welds is mainly caused by plastic strain accumulated while the weld cools through the brittle temperature range (BTR). This study proposes a simple mechanical model to estimate the plastic strain increment in the BTR and to clarify the effects of heat input and plate size (thickness and width). In the model, the BTR plastic strain increment is expressed as the sum of three terms: thermal contraction strain, bending strain due to a non-uniform temperature field, and an additional term caused by external restraint. Hot cracking is judged by whether the BTR plastic strain increment exceeds the critical strain. The model is applied to a restrained plate hot cracking test and a side-bead cracking test. For the side-bead test, we formulate the crack-driving bending moment per unit weld length and derive a simple relation between crack-tip curvature and local plate width. Using this relation, the critical-strain criterion is converted into a critical curvature. The critical curvature provides a practical index to compare cracking sensitivity for different geometries and heat inputs in welded structures.