Laser beam welding of a newly developed ferritic–martensitic stainless steel alloy: Microstructural evolution, mechanical performance and intergranular corrosion behaviour

This study investigates the laser weldability of a newly developed ferritic–martensitic stainless steel through microstructural, mechanical and intergranular corrosion assessments. Autogenous square-butt joint in a 3 mm thick sheet was produced using a 3 kW fibre laser at 80% digital-to-analog converter, 1000 Hz pulse-width modulation frequency and 80% duty cycle with a welding speed of 10 mm/s. Electron backscatter diffraction reconstruction indicated mean prior-austenite grain sizes of 23 ± 3 µm in the base material, 34 ± 14 µm in the weld zone, 64 ± 6 µm in the high-temperature heat-affected zone and 20 ± 6 µm in the low-temperature heat-affected zone. The weld zone showed a ferritic solidification morphology with interdendritic lath-like transformation products, while the heat-affected zone contained lath-like regions consistent with rapidly transformed martensitic constituents. Hardness increased from 205–216 HV0.2 in the base material to 320–329 HV0.2 in the weld zone and 350–358 HV0.2 in the heat-affected zone. The welded joints retained comparable yield strength, while ultimate tensile strength and elongation decreased slightly. Fracture occurred in the base material for all welded specimens. Guided bend and modified Strauss testing revealed no cracking or intergranular attack, demonstrating satisfactory weldability and corrosion resistance of the alloy.