Microstructures and Creep Properties of Type 316LN Stainless Steel Weld Joints

In the present investigation, creep deformation and rupture behavior of type 316LN stainless steel weld joints fabricated from hotwire tungsten inert gas (HW-TIG), activated-TIG (A-TIG), and hybrid laser metal inert gas (HLM) welding processes were studied. The creep testing was carried out at 923 K under various stress levels. The weld joints have undergone a higher rate of deformation and exhibited lower creep rupture life as compared to that of the base metal. The welding process significantly influenced the delta ( δ )-ferrite content in the weld metal of stainless steel weld joints [A-TIG (1.7 ferrite number (FN)], HLM (1.3 FN), and HW-TIG (3.5 FN), its morphology and also the creep cavity density during creep deformation. The HW-TIG weld joint possessed significantly lower creep rupture life than that of the A-TIG and HLM weld joints. The HLM joint has exhibited a better creep rupture life than the A-TIG and HW-TIG weld joints. The microstructural constituents, i.e ., δ -ferrite content, columnar and equiaxed dendrites, and sigma ( σ )-phase formation during creep, have significantly influenced the creep deformation and rupture strength of the joints. The orientation of the columnar structure, which is parallel to stress direction and lower δ -ferrite content in the A-TIG and HLM joints, has resulted in lower creep cavitation and higher creep rupture strength as compared to that of the HW-TIG weld joint. As the 316LN stainless steel weld joint processed by the HLM welding process exhibited the best creep rupture life, the HLM welding process is recommended for the welding of 316LN stainless steel.