Atom Probe Study of the Aging Embrittlement of Cast Duplex Stainless Steel

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In this paper we discuss an analysis, with an atom probe, of nanometer-scale microstructural changes that occur during thermal aging of the ferritic phase of duplex stainless steel. The changes in electrochemical behavior and the magnetic hysteresis loop are examined and related to the microstructural changes. Cast duplex stainless steel containing 12.5% ferritic phase with a nominal composition of Fe-19%Cr-10%Ni-2%Mo was aged at 475℃ for 443 h. By analysis, it is found that aging promotes a significant phase separation of the ferrite into Cr-rich and Fe-rich regions with spatial durations of 10-20 nm. An electrochemical reactivation peak observed in the polarization curve of aged steel is thought to be related to the Fe-rich region with a Cr concentration below 14 at% (13% in weight). Nanometer-scale microstructural changes are shown to cause hardening and increase the loss in magnetic hysteresis.
1995-07-15