The applicability of ferritic stainless steel is restricted due to its low weldability, and this can be attributed to the severe grain growth in the weld zone during the solidification of the weld pool and formation of fully ferritic structure. This study aims to investigate the weldability of 18 mm thick AISI 409 ferritic stainless steel plates using an electron beam welding process without the use of filler metal. The joints were investigated for metallography characterization (microstructure, macrostructure, and microhardness) and mechanical behavior (tensile strength and impact toughness) in as-welded condition and after post-weld heat treatment at 550 ºC for 75 minutes. The weld zone exhibited large columnar grains in the direction perpendicular to the weld centerline and got refined after post-weld heat treatment. The ultimate tensile strength, yield strength, and microhardness of the weld zone were found higher than the base metal. The impact toughness of weld zone was found to be reduced by 45%, but the post-weld heat treatment improved the toughness by 40%. Results revealed that the electron beam welding process could be successfully employed for welding of AISI 409 ferritic stainless steel, which will increase its application range that requires thicker section of welded plates. Post-weld heat treatment was found to be advantageous for improving the microstructure and mechanical properties.
In the present research, attempts have been made to weld 18 mm thick AISI 409 ferritic steel plate in a single pass with electron beam welding process. The welded joint was investigated for macrostructure, microstructural, microhardness, impact toughness, and tensile strength. The coarse ferritic grains of base metal were converted into fine equiaxed and columnar grains in the weld zone. The microhardness results revealed that for fusion zone and heat affected zone had 28% and 41% higher microhardness than the base metal. Further, post weld heat treatment at 550ºC/75 minutes resulted in 5% rise in ultimate tensile strength, 10% rise in yield strength, and 31% rise in impact toughness as compared to as welded specimens. The fractography of impact and tensile specimens revealed brittle mode of fracture and changed to ductile mode after post weld heat treatment.
The effect of the postweld heat treatment (550°C for 75 min) on the electron beam welded joints of AISI 409 thick plates was assessed in terms of tensile and impact performance. Through thickness, analysis was carried out by dividing the weld joint into three sections, i.e., top section, middle section, and bottom section. The results showed that the size of the grains got refined at the bottom. The heat treatment also led to reduction in the grain size. X-ray diffraction analysis showed the presence of martensite in the weld joint which reduced after heat treatment. The 532 MPa tensile strength was achieved after the heat treatment for the specimens extracted from the bottom of the welded plate. The impact toughness of the weld joint was 37% less than the base metal; however, impact toughness of 31J was achieved at the top section after postweld heat treatment.
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