Magnetic property changes during embrittlement of a duplex stainless steel

Abstract

Changes in magnetic properties were used to investigate the ferrite decomposition that occurs in wrought duplex stainless steel (DSS) UNS S31803 at high (800°C) and low temperatures (475°C). At 800°C the saturation and residual induction, the coercive force and the differential permeability decrease with time, due to the increase in the austenite content. Firstly, secondary austenite (γ 2) forms in the α/α grain boundaries causing embrittlement, but not hardening. Ferrite then decomposes into σ and austenite phases (α→σ+γ 2), producing hardening and severe embrittlement. During embrittlement at 475°C, 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 (α→α+α′). The results obtained show that the mechanical property changes of DSS UNS S31803 due to exposures at 475 and 800°C may be monitored by magnetic measurements.