Abstract
Duplex and Super Duplex Stainless Steels are very prone to secondary phases formation related to ferrite decomposition at high temperatures. In the present paper the results on secondary phase precipitation in a 2510 Duplex Stainless Steel, heat-treated in the temperature range 850–1050 °C for 3–30 min are presented. The precipitation starts at grain boundaries with a consistent ferrite transformation for very short times. The noses of the Time–Temperature–Precipitation (TTP) curves are at 1000 °C for σ-phase and at 900 °C for χ-phase, respectively. The precipitation sequence involves a partial transformation of χ into σ, as previously evidenced in 2205 and 2507 grades. Furthermore, the experimental data were compared to the results of Thermo-Calc calculations. Understanding and ability to predict phase stability in 2510 duplex stainless steel is a key factor to design optimal welding processes that avoid any secondary phase precipitation in the weld bead as well as in the heat-affected zone.
Highlights
Duplex Stainless Steels (DSSs) and Super Duplex Stainless Steels (SDSSs) possess high mechanical and corrosion resistance properties, which can be ascribed to the presence of the characteristic biphasic structure, where austenite and ferrite are present in almost equal volume fractions [1,2]
The present paper reports the results obtained in a 2510 SDSS grade, which is usually employed as filler material in austenitic stainless steel welding
4 ofthe passing 1370 ◦ C, the solid-state formation of austenite (γ) from primary ferrite begins and at about 1060 ◦ C, ferrite gives rise to the simultaneous formation of simultaneous formation of austenite (γ) and sigma (σ-phase), throughBelow eutectoidic austenite (γ) and sigma (σ-phase), through eutectoidic transformation
Summary
Duplex Stainless Steels (DSSs) and Super Duplex Stainless Steels (SDSSs) possess high mechanical and corrosion resistance properties, which can be ascribed to the presence of the characteristic biphasic structure, where austenite and ferrite are present in almost equal volume fractions [1,2]. 600 ◦ C, which restricts the use of the DSS in a limited temperature range [3,4,5,6] Such solid-state phase transformations can occur during isothermal aging, welding or cooling after the solubilization treatment and are mainly concerned with ferrite decomposition, because alloying elements diffusivities. For a better understanding of the basic physical metallurgy of intermetallic phase precipitation, it seems reasonable to study such solid-state transformations in simpler and more well-controlled conditions, i.e., under isothermal annealing Those studies will be helpful in modeling continuous cooling transformations typical of welded joints in order to avoid any secondary harmful phases during welding processes
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