Study on Effect of Gouge Depth on the Microstructure and Tensile Properties of 18%Ni Maraging Steel Welds Made Through Hot Wire GTA Welding

Abstract

Ultrahigh strength maraging steels are welded by gas tungsten arc welding (GTAW) over a wide range of thicknesses. However, the speed of conventional GTAW process is limited and hence the deposition rates are less. To enhance the productivity with reduced weld defects, hot wire GTAW (HW-GTAW) process is used to weld maraging steels. Apart from high speed, HW-GTAW provides the benefit of virtual elimination of porosity from the weld deposit resulting into cleaner and faster weld. Unacceptable defects, if any are repaired manually. During the repair, the original weld is gouged to remove the defect then re-filled by manual welding process using filler wire. These repairs affect the mechanical properties and microstructure of original weld. In the present work, effect of the depth of gouging in the original weld of 18%Ni maraging steel on the mechanical properties (tensile strength and hardness) is studied. Effects of burn through (full thickness reweld), from the reinforcement-side (face side) and root side, are also included for one-time repair (R1) and two times repair (R2) conditions. It reveals that strength of weldments decreases and ductility increases with increasing depth of weld repair resulting into wider heat affected zone (HAZ). 6–8% decrease in the strength with respect to virgin weld when the first repair (R1) is carried out by gouging and filling the virgin weld. Very minimal strength decrease is observed when welds are repaired from R1 to R2. Weld microstructure is found to be martensitic with dendrites. Microstructures analysis indicates that reverted austenite formation in HAZ is responsible for reduction in strength. Lowering of microhardness and correspondingly strength is attributed to presence of reverted austenite phase, which is found to increase with increase in gouge depth. Increased gouge depth requires higher heat input and provides scope for wider dark HAZ (HAZ2) with more amount of reverted austenite. Weakest zone is found to be HAZ 2(dark HAZ) where micro-hardness is lowest.