On the effect of Qnet on compressive residual stresses and ductile toughness of dissimilar HAZ in robotic GMAW joints between A572-50 and A36 steels

Different heat input values applied in robotic dissimilar welded joints of A36 carbon and A572-50 alloyed steels were evaluated by X-ray residual stresses, Vickers hardness, impact energy, microstructural analysis, and fractography. A welding process using pulsed metal arc for ten combinations involving welding current, arc voltage, welding speed, and power was performed by welding robot. Residual stress measurements in thickness direction at the HAZ within both steels indicated that five weldings achieved compressive stresses, resulting in the highest value (171 MPa) in the HAZ of A572 steel for joint number 3. Greater absorbed energy levels were achieved for the HAZ of A572 steel, followed by weld bead ER70S6 and the HAZ of A36 steel, which was linked to formation of a major amount of fine needles of acicular ferrite, giving the largest energy (160 J) for the HAZ of A572 steel of trial 31. Moreover, three joints showed ductile type failure with microhollow morphology of different sizes, including welding 3 within both kinds of dissimilar HAZ in A36 and A572 steels. Trial 3 was the best showing superficial compressive residual stresses within both kinds of HAZ, intermediate microhardness, and larger Charpy energy associated with acicular ferrite and ductile failure as a consequence of higher heat (0.615 kJ/mm). Welding 27 was better with complete compressive residual stresses in the HAZ of A36 steel, major absorbed energy, and fragile fracture by mechanism of transgranular cleavage within both types of HAZs.