Study on welding thermal cycle and residual stress of UNS S32304 duplex stainless steel selected as external shield for a transport packaging of Mo-99

Abstract

Thin plates of duplex stainless steel UNS S32304 were welded using the pulsed gas tungsten arc GTAW process (butt joint) without filler addition. The used shielding gas was pure argon and 98% argon plus 2% of nitrogen. The thermal cycles were acquired during welding, in regions near the melting pool. This alloy is candidate for the external clad of a cask for the transport of high activity radiopharmaceuticals substances. For the residual stress measurements in austenite phase an X-ray diffractometer was used in a Bragg-Brentano geometry with CuKα radiation (λ= 0.154 nm) and for ferrite phase was used a pseudo-parallel geometry with CrKα radiation (λ= 0.2291nm). The results of residual stress using sin2y methodology shown that the influence of the high welding temperature leads to compressive stresses for both phase of the duplex steels mainly in heat-affected zone. It was observed a high temperature peak and an increase of the mean residual stress after addition of nitrogen to the argon shielding gas.

Effect of Nitrogen Addition to Shielding Gas on Cooling Rates and in the Microstructure of Thin Sheets of Duplex Stainless Steel Welded by Pulsed Gas Tungsten Arc Welding Process

“…Thus, the DSS alloys have become a suitable alternative to austenitic stainless steels due to their special combination of good mechanical properties and corrosion resistance and lower costs 1,2,6 . The nuclear industry, especially requests alloys with high thermal stability in pipes for power generation systems and safe transportation equipment's for radioactive material [7][8][9] . DSS also presents satisfactory weldability, however it is possible to occur the formation of excessive ferrite, nitrides and intermetallic phases in the solidifying zone (SZ) and in the heat affected zone (HAZ) 1,2,10 .…”

“…However, 2% nitrogen is recommended in pure argon mixture for shielding gas and optimizing the phase balance, impact toughness and corrosion resistance of DSS 13 . Taking all aspects into account, Ar + 2%N 2 is the preferred shielding gas for welding duplex and super duplex with the GTAW process 6,9 .…”

“…Several authors have been mentioning the important role of N 2 in the microstructure evolution by being the strongest austenite forming alloying element 6,9,10,[13][14][15][16][17] . Moreover, N 2 is an economical and efficient substitute for nickel 10,17 .…”

Efeito De Tratamentos Térmicos Nas Propriedades Mecânicas De Chapas Soldadas Do Aço Inoxidável Duplex Uns S32304

“…Os aços inoxidáveis duplex (AID) são compostos por uma estrutura mista de ferrita e austenita, em proporções aproximadamente iguais, o que promove a combinação de excelentes propriedades mecânicas e elevada resistência à corrosão [1][2][3][4][5][6][7][8][9][10], e torna estes materiais bastante atrativos do ponto de vista econômico e tecnológico [1,4,[11][12][13]. O equilíbrio dessas fases é alcançado através de tratamento térmico de solubilização, seguido de um resfriamento Tecnol.…”