Thermodynamic Study Of The Phase Equilibria In The Fe-Cr-Ni-C-N Multi-component System

Austenitic, or300series stainless steels with high Ni content comprise over60%of total stainless steel production. Nickel accounts for a large proportion (70%) of the production costs. The serious lack of nickel resources becomes a bottleneck in the development of traditional Austenitic stainless steel. Enterprises must speed up the development and production of less nickel, nickel-free stainless steel:400series stainless steels,200series stainless steels and Duplex stainless steels. Fe, Cr, Ni, C, N are important basic alloying elements in nickel-free stainless steels. It is necessary to understand the information of thermodynamics and phase diagram for a better development of stainless steels. The aim of this study is to develop a reliable thermodynamic database for a multi-component system of Fe-Cr-Ni-C-N. Thermodynamic calculations (CALPHAD) were carried out on the phase equilibria of the Fe-Cr-Ni-C-N system, and the major work was as follows:(1) Experimental phase diagram data and thermodynamic properties are collected systematically.(2) The constituent binary phase diagrams, ternary phase diagrams, quaternary phase diagrams were evaluated by using the CALPHAD method based on the experimental data. Thermodynamic optimization will be done to the systems, like Fe-Cr-C and Fe-Cr-N, where the available thermodynamic parameters can not agree with the experiments.(3) By using the present thermodynamic database, the phase diagrams of the Fe-Cr-Ni. Fe-Cr-C, Fe-Ni-N, Fe-Ni-C systems, and the vertical sections of the Fe-13Cr-C, Fe-16Cr-C, Fe-18Cr-C,Fe-0.5C-N. Fe-Cr-2.5Ni-C and Fe-18Cr-Ni-0.02C were calculated.(4) Based on the thermodynamic calculations above, we can understand the effects of various alloying elements on the a and y phase regions, and in addition, the thermodynamic stabilities of different compounds with C and N can be well described, which are very important in alloy design and heat treatment for stainless steels.