Vol. 7, Issue 1, Part A (2025)

High-temperature applications require stainless steel as an essential material because its chromium and nickel content makes it show exceptional oxidation resistance. API 5L steels function as high-strength low-alloy steels that constitute critical components within oil and gas pipelines because of their strong mechanical features. The research focuses on examining the TIG welded interface between API 5L Gr-B steel and ASTM 312 stainless steel when using ER 309L and ER NiCrMo-3 filler metals as the welding technique. Displacements in the welded joints received comprehensive evaluation through optical microscopy combined with tensile testing and hardness testing and bending analysis. The microstructural analysis of weld metal made with ER 309L filler metal showed ferrite as the matrix with embedded acicular ferrite and delta ferrite islands in austenite austenitic structure. The weld metal that used ER NiCrMo-3 filler metal contained large nickel grains alongside insoluble precipitates within its nickel-based solid solution. The measurements revealed that the weld zone area became harder in comparison to the base metal material in both testing conditions. The weld metal made with ER 309L exhibited a hardness level of 263 Vickers yet the weld metal made with ER NiCrMo-3 reached 206 Vickers. The Bending tests on welded samples with ER NiCrMo-3 metal filler material showed cracks in the weld area which implied reduced ductility. The ER NiCrMo-3 stainless steel filled metal caused fractures to appear in the stainless steel section but ER 309L stainless steel filled metal caused fractures in the carbon steel section during tensile testing. The tests showed that welded joint ultimate tensile strength reached 550 MPa in ER NiCrMo-3 specimens while reaching 453 MPa in ER 309L specimens.