The effect of purge gas condition on the amount of ferrite in tubular AISI 304 stainless steel during welding
The primary objective of the present work is to evaluate the influence of various commercial gases on the microstructure of tubular AISI 304 austenitic stainless during welding. This was carried out using CO2, Ar, N2, Ar + 25%CO2 and Ar + 2%O2 gases, which are common inert gases or mixture specified in numerous technical standards associated with welding. These five gases were evaluated using flow rate range of 6–18 L/min. Different welding speeds, wire feed speeds, shield gases (Ar + 2% O2), distance nozzle contact pieces, voltages and currents were employed to validate the present observations. The microstructures of the samples were evaluated along the cross section of the face of the weld using optical microscopy. The samples were further analyzed by means of magnetic testing, which could provide information related to the evolution of ferrite. The estimated phase fractions were then compared to the predictions provided by the Welding Research Council (WRC-92) diagram. The optical microscopy images showed small microstructural variations between the samples with different gas purge conditions, even when using the maximum gas flow rate. However, these observations were inconsistent with the magnetic response of the material, which provided significant differences in the phase fractions between the face and the root of the weld. The discrepancies between these two methods were analyzed to evaluate the phases and consistently track the phase fractions after welding.
KeywordsWelding Ferrite content Austenitic stainless steel Gas purge
The authors would like to thank the DINTER UFU/IFMA program, FEMEC/UFU, Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão—FAPEMA, CAPES, CNPq, IFMA—Campus Imperatriz/MA and the New Brunswick Innovation Fund for the support during the development of this research.
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