Weldability and microstructural aspects of shielded metal arc welded HSLA-100 steel plates

HSLA-100 steel with 14 mm thickness in quenched and tempered condition was shielded metal arc welded (SMAW) with 2 kJ/mm heat input using basic flux coated filler rods without any pre or post welding heat treatments, The steel was found to be welded satisfactorily in this condition without developing any defect. Optical microscopy studies revealed typical cast dendritic structure in the weld metal and coarse bainite in grain-coarsened area of the heat-affected zone (HAZ). Transmission electron microscopy (TEM) study confirmed incidence of mixed structure of martensite laths and bainite in weld metal, while, it was mainly of bainite laths in HAZ with evidence of martensite-austenite (M-A) constituent and massive ferrite. The yield strength (YS), ultimate tensile strength (UTS) and Charpy V-notch (CVN) impact energy of the weld metal (YS-695 MPa, UTS-842 MPa and CVN-105 J at -50degreesC) and HAZ (YS-790 MPa, UTS-891 MPa and CVN-130 J at -50degreesC) were found satisfactory although HAZ properties were inferior to the base metal properties. The hardening of HAZ was not very significant in this steel under the present welding condition.