Abstract
The formation of intermetallic phases alters the properties of duplex stainless steel and is therefore a crucial factor in its performance. For example, the formation of sigma phase in duplex steel increases its brittleness and decreases its corrosion resistance because this phase consumes chromium and molybdenum in solid solution, thus leading to the depletion of these elements in the matrix. This study investigated the corrosion resistance of as-cast SAF 2205 duplex stainless steel after solution annealing treatment at 1100 °C for 240 minutes, under varying cooling rates. The objective was to evaluate the correlation between cooling condition, microstructural changes and corrosion resistance based on cyclic potentiodynamic polarization and double loop electrochemical potentiokinetic reactivation (DL-EPR) measurements. The results revealed a significant reduction in the corrosion resistance of a slowly cooled sample, which presented an increase in the degree of Cr (Qr / Qa) depletion resulting from the formation of sigma phase.
Highlights
The addition of large amounts of alloying elements may cause the microstructure of duplex stainless steels to become unstable, and precipitation of intermetallic phases may occur during solidification, heat treatment, welding processes, or by thermal aging, if these processes are not carefully controlled[1,2,3,4]
The influence of the precipitation of intermetallic phases on the corrosion resistance of stainless steels can be evaluated based on double loop – electrochemical potentiokinetic reactivation (DL-EPR) tests, which provide information about chromium depletion[8,9]
This study investigated the effects of different cooling rates on microstructure and corrosion resistance of SAF 2205 duplex stainless steel (2205 DSS) solution annealing treated from the as-cast condition, through X-ray diffraction, optical microscopy and electrochemical tests
Summary
The addition of large amounts of alloying elements may cause the microstructure of duplex stainless steels to become unstable, and precipitation of intermetallic phases may occur during solidification, heat treatment, welding processes, or by thermal aging, if these processes are not carefully controlled[1,2,3,4]. The presence of these phases, such as M23C6 carbide, chromium nitride, chi, sigma and alpha prime, deteriorates the properties of steel due to the uneven distribution of alloying elements and their depletion in adjacent regions[1,2,5,6]. This study investigated the effects of different cooling rates on microstructure and corrosion resistance of SAF 2205 duplex stainless steel (2205 DSS) solution annealing treated from the as-cast condition, through X-ray diffraction, optical microscopy and electrochemical tests
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