Experimental and thermodynamic study of tantalum-containing iron-based alloys reinforced by carbides: Part I — Case of (Fe, Cr)-based ferritic steels

Experiments and thermodynamic calculations were performed on three iron-based alloys containing 30 wt% of chromium and 3 to 6 wt% of tantalum. Solidus temperatures, natures, and surface fractions of all phases present after an exposure for 50 h at 1000, 1100, and 1200  ∘C, were determined for each alloy. These results were compared to values calculated using Thermo-Calc. Two alloys display solidus temperatures above 1400  ∘C, while all the liquidus temperatures are higher than 1500  ∘C. Tantalum carbides are present with high fractions, compared to similar Co-based and Ni-based alloys. Their observation and quantification using electron microscopy micrographs and image analysis may lead one to overestimate the surface fractions of TaC. Calculations of carbide fractions from the chemical composition of the matrix is to be preferred. A precipitation of coarse chromium carbides may occur for 1100 and 1200  ∘C.