Experimental study on the microstructure, mechanical properties, and corrosion behaviour of ASTM A106 Grade B steel pipes welded using fibre laser welding

This study investigates the mechanical properties, microstructural characteristics, and corrosion behaviour of circumferential ASTM A106 Grade B steel pipe joints produced by handheld fiber laser welding. Continuous-wave welding was performed using 1.6 mm ER70S-6 filler wire and high-purity argon shielding. Four process parameters—laser power (1.8–2.6 kW), welding speed (18–30 mm/s), focal position (−1 to +1 mm), and shielding gas flow rate (10–20 L/min)—were optimized using a Taguchi L9 orthogonal array. Joint quality was evaluated through tensile, Charpy impact, 180° bend, notched-tensile, and Vickers microhardness tests, while optical microscopy, SEM-EDS, XRD, and potentiodynamic polarization in 3.5 wt.% NaCl were employed for microstructural and corrosion characterization. ANOVA identified welding speed as the dominant factor for ultimate tensile strength (55.6%), followed by gas flow rate (31.1%), focal position (6.9%), and laser power (6.4%). Under optimized conditions (2.6 kW, 24 mm/s, −1 mm, 20 L/min), the joint achieved 351.8 MPa yield strength, 470.1 MPa ultimate tensile strength, 118 J impact strength, a notch tensile strength ratio of 1.09, and peak weld hardness of ∼200 HV versus 140–145 HV for the base metal. The weld zone showed refined ferrite-pearlite microstructure and ductile fracture. Corrosion rates were 0.082 and 0.074 mm/year for the weld and base metal, respectively, indicating largely retained corrosion resistance.