Evaluation of sigma and laves phases in a niobium modified austenitic-ferritic stainless steel using FactSage software
Year: 2025
Type: article
Abstract: ABSTRACT In austenitic-ferritic or duplex stainless steels, the microstructure is basically determined by the chromium and nickel contents, which are ferritic or austenitic phases stabilizers. Currently, duplex stainless steels are used to replace austenitic stainless steels in industrial applications, where requirements for corrosion resistance and mechanical strength are greater. In these steels, solidification starts at about 1450 oC with the formation of ferrite (α), which gives origin to austenite (γ) near 1300 oC. The σ phase nucleates preferentially in austenite/ferrite interface incoherent with the matrix in the range of 600 to 950 oC and compromises the cast steels toughness. Laves phase (Fe2Nb) is favored in stainless steels containing niobium. In this context, the objective of this research was to evaluate the effect of niobium on the formation of sigma and Laves phase in conventional austenitic-ferritic stainless steel and modified with 0.2, 0.5 and 1.5% niobium. The steels were heated at 1050 ºC for one hour and subsequently at 650 °C too, with cooling in water. The chemical compositions of sigma and Laves were determined semi-quantitative by energy dispersive X-rays (EDS). The amounts of Laves and sigma were obtained by computational thermodynamic simulation with the FactSage software. The results show that the thermodynamic simulation predicts Laves in the four steels, although in conventional stainless steel the microstructure is free from this phase. Regarding microstructural analyses by SEM, it is possible to observe the sigma phase in all steels, only after aging, while Laves appears in those modified with niobium in both heat treatment conditions. Whit regard to niobium, it favors the formation of sigma and Laves phase, however, the thermodynamic simulation results are different from the experimental ones.
Source: Matéria (Rio de Janeiro)
Language: English
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W4416865267