Evaluation of Bending Fatigue Strength and Static Properties in Wire Arc Additive Manufactured Carbon Steel Bead-on-Plate Laser Weld

This study comprehensively explores the characteristics, microstructure, mechanical properties, and fatigue behavior of laser welded wire arc additive manufactured (WAAM) carbon steel. The geometry analysis of the laser weld revealed successful material penetration, with a width of approximately 1.5 mm. The microstructure of the WAAM carbon steel base material showcased large grains with an equiaxed structure predominantly composed of ferrite grains. Following laser welding, rapid solidification induced a microstructure primarily comprised of martensite, exhibiting higher hardness levels than the base metal. The hardness increment in the weld metal and heat-affected zone (HAZ) adjacent to the fusion line was attributed to the prevalence of martensite, a consequence of rapid cooling rates during laser welding. Mechanical property analysis revealed an augmentation in yield strength from 381 MPa to 407 MPa after laser welding, indicating a strengthening effect. Tensile strength increased from 499 MPa to 536 MPa, showcasing improved resistance to axial forces. However, a trade-off was observed, as elongation decreased from 39% to 29%, signifying reduced ductility. The laser weld exhibited greater strength compared to the base material, evident in the fracture occurring within the base material during the tensile test. Bending fatigue tests revealed a notable reduction in the fatigue limit of laser-welded samples compared to the WAAM CS base material, with the laser weld exhibiting superior fatigue resistance in the low-cycle regime. The diminished fatigue strength in the high-cycle regime was attributed to the laser weld introducing a discontinuity on the sample's surface.