Abstract
Despite of their excellent combination of high mechanical strength, toughness and corrosion resistance, duplex stainless steels (DSS) are susceptible to sigma phase formation, negatively affecting their superior properties. Sigma formation continuous cooling transformation (CCT) diagrams can be a useful tool to avoid sigma formation during cooling from solution treatment temperatures; however, non-isothermal information about sigma formation in DSS are scarce in literature. This work presents a methodology to simulate CCT diagrams in DICTRA® software, showing excellent adherence to literature data. The methodology here presented was also able to describe sigma phase formation behaviour for different DSS compositions.
Highlights
Duplex stainless steels (DSS) are largely used in industrial equipment that need the combination of high mechanical strength, toughness, and corrosion resistance, such as the ones found in chemical and petrochemical plants, pulp and paper industries, offshore structures and machinery, and desalinization plants
The 2-step methodology here proposed using DICTRA® software is capable of reproducing sigma phase formation curves during continuous cooling, and microstructures such as those in the literature
By adding the parameters of chemical composition, solution-treatment temperature, and computational cell size, it is possible to study the formation of the sigma phase during cooling for different DSS. 2
Summary
Duplex stainless steels (DSS) are largely used in industrial equipment that need the combination of high mechanical strength, toughness, and corrosion resistance, such as the ones found in chemical and petrochemical plants, pulp and paper industries, offshore structures and machinery, and desalinization plants. The most deleterious phase formed in this temperature range is sigma, due to the large amounts of Cr and Mo in its composition, causing impoverishment of those elements, which are essential to a proper passive film formation[7,8]. Development of higher Cr and Mo DSS, creating the so-called superduplex or hyperduplex stainless steels for even higher corrosion resistance in the solution-treated condition, worsens the problems involving sigma formation, since higher amounts of Cr and Mo facilitate nucleation and growth of sigma[11,12]
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