Abstract
This study evaluated the as-cast microstructure of three alloys based on Fe-25%Cr-5%Ni weight (wt.) composition whose carbon content is 0.02 wt.%, 0.12 wt.%, and 0.37 wt.%, respectively. Thermocalc was applied to predict the possible phases that could be formed during the cooling of each alloy and then the cross-sections of the ingots were characterized. The first alloy, with 0.02 wt.%C, presented a microstructure composed of ferrite and austenite, which was formed through solid-state precipitation. The second alloy, with 0.12 wt.%C, showed a microstructure formed by ferrite, austenite from the peritectic reaction (L + δ → γ) and M23C6 (M=Fe, Cr) carbide. Finally, the third alloy, with 0.37 wt.%C, exhibited a microstructure formed by dendrites of ferrite and austenite, also formed according to the peritectic reaction (L + δ → γ), with an M23C6 (M = Fe, Cr) and M7C3 (M = Fe, Cr) carbide network in the interdendritic regions.
Highlights
Duplex stainless steels can be classified according to their carbon content into two groups: low carbon duplex stainless steels and high carbon duplex stainless steels
Among the high carbon duplex stainless steels, it is possible to mention some mass compositions of the German standard, such as those of material number 1.4464 (C = 0.3-0.5%; Cr = 26.0-28.0%; Ni = 4.0-6.0%; Mo = 2.0-2.5%)
It molten metal; γ2 to represent austenite resultant from precipitation in solid-state (δ → γ2), and γ3 to represent can be seen that the increase in carbon content promotes carbide formation and, as a result, in contrast to alloys 1 austenite formed from the eutectoid decomposition of ferrite
Summary
Duplex stainless steels can be classified according to their carbon content into two groups: low carbon duplex stainless steels and high carbon duplex stainless steels. The duplex stainless steels with low carbon content present a ferritic solidification mode and austenite is formed through solid-state precipitation.
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