Deleterious phases precipitation on superduplex stainless steel UNS S32750: characterization by light optical and scanning electron microscopy

• Published in: Materials research (São Carlos, São Paulo, Brazil) Vol. 13; no. 3; pp. 401 - 407
• Main Authors: Pardal, Juan Manuel, Tavares, Sérgio Souto Maior, Fonseca, Maria da Penha Cindra, Souza, José Adailson de, Vieira, Lorena Menezes, Abreu, Hamilton Ferreira Gomes de
• Format: Journal Article
• Language: Portuguese
• Published: ABM, ABC, ABPol 01-09-2010
• Subjects: ENGINEERING, CHEMICAL; MATERIALS SCIENCE, MULTIDISCIPLINARY; METALLURGY & METALLURGICAL ENGINEERING; scanning electron microscopy; superduplex stainless steels; light optical microscopy; phase quantification
• ISSN: 1980-5373
• DOI: 10.1590/S1516-14392010000300020

Deleterious phases precipitation in superduplex stainless steels is the main concern in fabrication by welding and hot forming of this class of material. Sigma, chi and secondary austenite phases are considered deleterious phases because they produce negative effects on corrosion resistance. Besides, sigma and chi phases also promote strong decrease of toughness. In the present work, the precipitations of sigma, chi and secondary austenite under aging in the 800-950 °C interval were studied in two UNS S32750 steels with different grain sizes. The deleterious phases could be quantified by light optical microscopy, with no distinction between them. Scanning electron microscopy was used to distinguish the individual phases in various aging conditions. The results elucidate the influence of the aging temperature and grain size on the kinetics precipitation and morphology of deleterious phases. The kinetics of deleterious phases is higher in the fine grained material in the initial stage of aging, but the maximum amount of deleterious phases is higher in the coarse grained steel.