Microstructural Transformation in the Root Pass of Superduplex Stainless Steel Multipass Welding

Abstract

This work focuses on the identification of secondary phases in a superduplex stainless steel multipass welding performed by means of the GMAW process using two filler metals, one of the duplex type and the other of the superduplex type. To identify the secondary phases in the welding metal and the heat affected zone, the samples were analyzed by optical microscopy. The results showed a considerable formation of sigma phase in the welding metal in both samples, making evident the total consumption of ferrite. On the other hand, the heat affected zone corresponding to the superduplex-type filler metal, presents a remarkable sensitization, probably due to the occurrence of chromium nitrides in the center of the ferrite grains while the heat affected zone corresponding to the duplex-type filler metal depicts a more balanced microstructure of ferrite, austenite and secondary austenite.Keywords: thermal cycle, superduplex stainless steel, sigma phase, welding, GMAW, heat affected zone, welding metal. ResumenEste trabajo se centra en la identificación de las fases secundarias en una soldadura multipasos de acero inoxidable superdúplex realizada mediante el proceso GMAW, empleando dos metales de aporte, uno de tipo dúplex y el otro de tipo superdúplex. Para identificar las fases secundarias en el metal de soldadura y la zona afectada térmicamente, las muestras se analizaron por microscopía óptica. Los resultados mostraron una formación considerable de fase sigma en el metal de soldadura en ambas muestras, haciendo evidente el consumo total de la fase ferrita. Por otra parte, la zona afectada térmicamente correspondiente a la unión con metal de aporte del tipo superdúplex, presenta una sensibilización notable probablemente debido a la incurrencia de nitruros de cromo en el centro del grano ferrítico, mientras que la zona afectada térmicamente que corresponde a la unión con el metal de aporte del tipo dúplex, presenta una microestructura más equilibrada de ferrita, austenita y austenita secundaria.Descriptores: ciclo térmico, acero inoxidable superdúplex, fase sigma, soldadura, GMAW, zona afectada térmicamente, metal de soldadura.

Kinetics of Intermetallic Phase Precipitation in Manual Metal Arc Welded Duplex Stainless Steels

“…Various morphologies of austenite are observed: allotriomorphic austenite (γ A ), Widmanstätten austenite (γ W ), and idiomorphic austenite (γ I ). Their occurrence is consistent with literature reports for welds in grades 2209 [38,[45][46][47][48][49][50][51][52], 2101 [53,54], 2205 [55][56][57], 2507, and 2304 [55]. Observations regarding the occurrence of non-metallic inclusions are also consistent with literature reports [58][59][60] and result from the specificity of the manual metal arc welding process.…”

Microstructural Evolution Due to One Thermal Cycle in a Superduplex Stainless Steel ASTM A890/A890M - Grade 6A in the As-Weld and Post-Weld Heat Treatment Conditions

“…After welding, FZ presented a ferritic matrix with acicularized austenitic structure (Widsmanstätten type) 25 and precipitated in the contour and inside of the ferritic grain, see Figure 1f. This acicularized structure is typical in regions that melt during welding and which solidify rapidly.…”