Abstract
Duplex stainless steels are a group of widely used stainless steels, because of their attractive combination of strength and corrosion resistance. However, these steels embrittle because of a phase separation phenomenon in the ferrite phase when exposed to temperatures within the miscibility gap. This manuscript investigates the phase separation in two commercial stainless steels, the duplex stainless steel (DSS) 22Cr-5Ni (2205 or UNS S32205), and the super-duplex stainless steel (SDSS) 25Cr-7Ni (2507 or UNS S32750), and its subsequent effect on mechanical property evolution. Long-term isothermal aging heat treatments were carried out at industrially relevant temperatures between 250 °C and 350 °C for up to 48,000 hours, and quantitative measurements of the amplitude and wavelength of the phase separated nanostructure were obtained using Small-Angle Neutron Scattering (SANS). These quantifications were used as input parameters in hardness models to predict the hardness evolution. It is concluded that the quantitative information from SANS combined with these hardness models enables the prediction of hardness evolution in DSS at low temperatures, which in turn correlates with the embrittlement of the DSS.
Highlights
DUPLEX stainless steels (DSS) usually contain both austenite and ferrite phases in roughly equal proportions
From the results presented here, and previous works from some of the present authors,[22] it is evident that even in the as-cooled samples of the 25Cr-7Ni super-duplex stainless steel (SDSS), there was already some amount of decomposition
A similar behavior would be expected to occur for room-temperature deformation in the long-term isothermally aged duplex alloys. This manuscript discusses the effect of long-term isothermal aging at in operando low temperatures on embrittlement phenomenon in a commercial grade duplex and a super-duplex stainless steel
Summary
DUPLEX stainless steels (DSS) usually contain both austenite (fcc) and ferrite (bcc) phases in roughly equal proportions. These steels give an attractive combination of high strength and excellent corrosion resistance and are a natural material choice in applications such as pressurized equipment in the nuclear, chemical, and pulp and paper industries.[1,2,3,4,5,6] DSS are susceptible to embrittlement at virtually all temperatures.[7,8,9] the service temperature of DSS is YADUNANDAN DAS is with the Department of Material Science and Engineering, KTH Royal Institute of Technology, 100 44.
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