Study on metallurgical and mechanical aspects of GMA welded nitronic steel under the influence of weld quenching

Abstract

Nitronic steel (21-4-N) was solution annealed in as received (AR) condition at 950 °C and 1150 °C, followed by water quenching. Solution annealing at 1150 °C dissolves maximum carbides and minimum re-precipitation. The welding was performed with gas metal arc welding process using ER2209 filler wire. Microstructural and mechanical properties for different base and weld metal conditions were characterized using an optical microscope, FE-SEM, XRD. Dissolution of carbides after base metal solution annealing has resulted in enhanced tensile strength (998 MPa), ductility (12.73) and impact toughness (32 J). The properties of heat affected zone were dependent on the residual carbides. The ferrite content of weldmetal was found to be maximum at the weld center and decreased towards weld-HAZ interface. The precipitation of phases like Cr23 C6 and Cr7 C3 formed in base metal and weld-HAZ region caused the crack initiation, which leads to failure of specimens. The weld joint made with SA-2 was observed to possesses the best combination of mechanical properties with ultimate tensile strength (UTS) 960 MPa, ductility (%EL) 17.91 and impact strength (J) 91 with minimum residual carbides at weld-HAZ interface.