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Abstract
The effect of annealing temperature (1000–1150 °C) on the microstructure evolution, mechanical properties, and pitting corrosion behavior of a newly developed novel lean duplex stainless steel with 20.53Cr-3.45Mn-2.08Ni-0.17N-0.31Mo was studied by means of optical metallographic microscopy (OMM), scanning electron microscopy (SEM), magnetic force microscopy (MFM), scanning Kelvin probe force microscopy (SKPFM), energy dispersive X-ray spectroscopy (EDS), uniaxial tensile tests (UTT), and potentiostatic critical pitting temperature (CPT). The results showed that tensile and yield strength, as well as the pitting corrosion resistance, could be degraded with annealing temperature increasing from 1000 up to 1150 °C. Meanwhile, the elongation at break reached the maximum of 52.7% after annealing at 1050 °C due to the effect of martensite transformation induced plasticity (TRIP). The localized pitting attack preferentially occurred at ferrite phase, indicating that the ferrite phase had inferior pitting corrosion resistance as compared to the austenite phase. With increasing annealing temperature, the pitting resistance equivalent number (PREN) of ferrite phase dropped, while that of the austenite phase rose. Additionally, it was found that ferrite possessed a lower Volta potential than austenite phase. Moreover, the Volta potential difference between ferrite and austenite increased with the annealing temperature, which was well consistent with the difference of PREN.
Highlights
Duplex stainless steels (DSSs), strongly relying on a balanced two-phase microstructure of ferrite (α) and austenite (γ), have attractive mechanical and corrosion properties and are widely used in the chemical, petrochemical, nuclear, marine and paper industries [1,2,3,4]
In order to expand the application of this newly developed DSS used in this work, it is of great importance to obtain the suitable mechanical properties and good corrosion resistance
The effect of annealing temperature on the microstructure, mechanical properties and corrosion behavior of this novel lean duplex stainless steel has been characterized by microscope, mechanical test and electrochemical technique
Summary
Duplex stainless steels (DSSs), strongly relying on a balanced two-phase microstructure of ferrite (α) and austenite (γ), have attractive mechanical and corrosion properties and are widely used in the chemical, petrochemical, nuclear, marine and paper industries [1,2,3,4]. Great efforts have been made to improve the corrosion resistance of DSSs by increasing the content of chromium (Cr), molybdenum (Mo) and nitrogen (N), e.g., the DSS UNS S32750 with high mass fractions of 25%–27% Cr, 3%–4.5% Mo and 0.25%–0.28%. In order to conserve resources, “lean” route DSSs, e.g., UNS S32101 type with less nickel (Ni) but higher yield strength and better pitting resistance than standard austenitic grades, have been developed to meet the demand for grades with a lower cost [8,9,10,11,12]. Choi has reported the effects of nitrogen addition on the strain-induced martensitic transformation of Fe-20Cr-5Mn-0.2Ni duplex stainless steel and found that the elongation was up to 60% in some lean DSSs containing
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