Characterization of a Cast Duplex Stainless Steel with 3.0%Cu and Modeling of Precipitation Hardening

Abstract

Duplex stainless steels (DSSs) are corrosion-resistant alloys extensively used in aggressive environments. Cast DSSs may be selected for pipes, valves and pumps in chemical, petrochemical and nuclear industries. The grade steel ASTM A890 1B is an example of cast DSS with 2.7-3.3%Cu addition. Copper increases the resistance to many types of corrosion, especially in non-oxidizing environments. When the copper content is higher than 2%, the steel can be precipitation-hardened. In this work, the precipitation hardening of a DSS ASTM A890 1B steel with 3.0%Cu was studied and modeled for aging temperatures in the 450-600°C range. Copper precipitates in the ferrite phase, but remains in solid solution in the austenite. The age hardening curves were modeled by DH = K(t) n model, where DH is the increase in hardness, t is the aging time, and K and n are constants to be determined. The microstructure and substructure were investigated by scanning electron and transmission electron microscopes.

Effect of Artificial Aging in the Microstructure and Corrosion Performance of Superduplex UNS S32750 Stainless Steel

“…The alloying elements such as Cr, Mo, and N besides the manufacturing process guarantee the material's properties since the phase balance and precipitated-free microstructure are ensured [4][5][6]. DSS and SDSS differ by their pitting resistance equivalent number (PREn) (PREn=%Cr +3.3%(Mo + 0.5%W + 16% N), which takes into account the contents of Cr, Mo, W, and N. The PREn of SDSS ranges from 40 to 42, which is more resistant to pitting than standard DSS alloys with a PREn ranging from 35 to 36 [7][8][9]. Components made of DSS are found in a broad range of different manufacturing processes including forging, rolling, welding, casting, and powder metallurgy.…”

“…Components made of DSS are found in a broad range of different manufacturing processes including forging, rolling, welding, casting, and powder metallurgy. After processing these materials, a solubilization treatment is often carried out to reach the balance of ferrite and austenite avoiding the presence of deleterious precipitated phases that can compromise mechanical resistance and corrosion performance [9][10][11]. SDSS is susceptible to the formation of intermetallic phases due to their higher number of alloying elements, which makes it also susceptible to the precipitation of secondary phases such as sigma (σ), chi (χ), and secondary austenite (γ2) [12,13].…”