Criterion-driven control of grain morphology and its strengthening mechanisms in interrupted pulsed arc welding of AISI 430 ferritic stainless steel thin plates

This study systematically investigates the microstructure evolution and strengthening mechanisms of AISI 430 ferritic stainless steel (FSS) thin-plate butt joints welded by interrupted pulsed arc welding (IPAW). Microstructural characterizations using optical microscopy (OM) and electron backscatter diffraction (EBSD) , as well as mechanical testing for tensile strength and elongation, were performed to evaluate joint performance and grain evolution. Results indicated that when pulse current was ≤ 95 A, pulse time was ≤ 325 ms, interval time was ≥ 100 ms, and welding speed was ≥ 3 m/min, joints fractured in the base metal, exhibiting tensile strength and elongation similar to those of the base metal. A critical criterion for controlling grain morphology was established based on the ratio of spot distance (d) to radius (R): when 2R > d > R , independent snowflake grains with high strength were generated. In contrast d < R led to continuous columnar grains and a 10-20% reduction in strength. Epitaxial solidification was observed at the fusion line, where semi-molten base metal grains served as heterogeneous nucleation sites, facilitating grain growth along the <100> direction, indicative of BCC preferred orientation. Mechanisms for strengthening involved grain refinement through a snowflake structure and the suppression of coarsening of the heat-affected zone (HAZ). This work proposes a cost-effective and energy-efficient welding strategy for thin FSS components, with potential applications in automotive exhaust systems and precision electronics.