Magnetic property changes during embrittlement of a duplex stainless steel

Changes in magnetic propel-ties were used to investigate the ferrite decomp osition that occurs in wrought duplex stainless steel(DSS) UNS S31803 at hi gh (800 degreesC) and low temperatures (475 degreesC). At 800 degreesC the saturation and residual induction, the coercive force and the differential permeability decrease with time, due to the increase in the austenite conte nt. Firstly, secondary austenite (gamma (2)) forms in the alpha/alpha grain boundaries causing embrittlement, but not hardening. Ferrite then decompos es into sigma and austenite phases (alpha-->sigma+gamma (2)), producing har dening and severe embrittlement. During embrittlement at 475 degreesC, only a small increase in the coercivity was observed, even on aging up to 500 h . On the other hand, the Curie temperature increased with aging time, as a consequence of spinodal decomposition (alpha-->alpha+alpha'). The results o btained show that the mechanical property changes of DSS UNS S31803 due to exposures at 475 and 800 degreesC map be monitored by magnetic measurements . (C) 2000 Elsevier Science B.V. All rights reserved.