Effect of Beam Oscillation on Metallurgical and Mechanical Properties of the Electron Beam Welded SS 316 Welded Joints

The effect of the circular beam oscillation on the quality of the electron beam welded joint of 18 mm thick SS 316 plates was assessed on tensile and impact performance. These tests were conducted in as-welded condition and after thermal aging treatments viz. 750°C for 24 h (T1) and 750°C for 300 h (T2). The results showed that the use of circular beam oscillation pattern enhanced the cooling rate through step solidification which restricts the transformation of ferrite (%) in the weld bead. The microstructure of the weld zone varied from the coarse lathy ferrite to colonies of fine lathy ferrite while traversing from top to bottom sections of the weld zone. The tensile and impact test results showed that the beam oscillation pattern reduced the UTS, ductility and impact toughness in all the sections. Further, it was observed that the thermal aging treatment for long hours improved the solidification pattern and reduced the effect of beam oscillation. The treatments T1and T2 enhanced the tensile properties as the carbides precipitation at the grain boundaries prevents the sliding of grain boundary against transverse load. Whereas, the impact toughness reduced drastically after the treatments T1 and T2 due to the embrittlement caused by precipitation of the Cr rich carbides.