Influence of welding heat input on microstructure and structural integrity of FCAW EH36 marine structural steel

This study examines the influence of flux-cored arc welding heat input on microstructural evolution, EBSD characteristics, and mechanical performance of EH36 steel weldments. Heat input governs thermal gradients and resulting microstructural heterogeneity across the weld metal and heat-affected zone. Lower heat input suppresses grain coarsening and promotes microstructural refinement, particularly in the coarse-grained heat-affected zone, where lattice distortion and geometrically necessary dislocation density are reduced, while higher heat input increases heat-affected zone width and grain coarsening. Hardness values in all regions remain below 350 HV, and tensile properties satisfy American Bureau of Shipping requirements. Fractographic analysis reveals crack initiation at ferrite-pearlite interfaces in the base metal, whereas the weld metal exhibits mixed intergranular-transgranular fracture driven by inclusion-assisted crack propagation. Bending tests meet acceptance criteria; however, cracks are associated with slag inclusions and interfacial mismatch. Reduced heat input suppresses crack formation during bending, enhancing ductility without compromising strength.