Importance of Narrow Gap in Pulsed Current Gas Metal Arc Welding of Thick Wall Micro-alloyed Steel: Weld Appearance and Microstructure

Many diverse components are deployed for contemporary applications, ranging from the production of cars and other vehicles using sheet metal to heavy engineering using thick sections. These components are fabricated by welding high-strength micro-alloyed steels. The current study characterizes the microstructure of the controlled-rolled, 25 mm-thick micro-alloyed steel plate's tight gap weld joints. A controlled-rolled, micro-alloyed steel plate with dimensions of 250 x 100 mm is used for the welding process. By properly milling the plates, conventional gaps with width of 25 and 20 mm (CG-25 & CG-20) and narrow gaps with width of 13 mm (NG-13) are created as per the desired design. The root pass is created by gas tungsten arc welding (GTAW) process with autogenous technique, further filling passes are created by GTAW, and successive filling passes are made by pulsed current gas metal arc welding technique. It is found that increasing mean current (Im) from 160 to 230A reduces the dendrite fraction while increasing the reheat refined region in the matrix. However, at a particular Im, an increase in dimensionless factor (phi) and heat input (ohm) from 0.15 to 0.23 and 5.28-7.61 kJ/cm, respectively, has no effect on the matrix.