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-base 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 hours at 1000°C, 1100°C 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-base and Ni-base alloys. Their observation and quantification using electron microscopy micrographs and image analysis may lead to overestimate the surface fractions of TaC. Calculations of carbide fractions from the chemical composition of matrix is to be preferred. A precipitation of coarse chromium carbides may occur for 1100°C and 1200°C.