Phase Transformations of Iron Nitrides during Annealing in Nitrogen and Hydrogen Atmosphere

Abstract

The aim of the research discussed in the manuscript was to check the availability of control of nitrogen decomposition processes on nitrided AISI 52100 and AISI 1010 steels during annealing at 520 °C in N2 and at 600 °C in H2. The tests have shown that when annealing AISI 1010 steel at a temperature of 520 °C in N2 under a pressure of 200 Pa for 2 h, an ε → γ’ + N2↑ phase transformation occurs. Over the next 3 h, the ε phase disappears and the γ’ phase gradually transforms into Feα(N). When annealing AISI 52100 steel, the denitrification process is faster; after 2 h there is a complete transformation of ε → γ’ + N2↑, and in the next 3 h, there is a complete transformation of γ’-Feα(N). During annealing in H2 at a temperature of 600 °C, the denitrification processes are most intense; the complete transformation of γ’ → Feα(N) + N2 occurs after 45 min of the process. When annealing nitrided AISI 1010 steel in nitrogen at atmospheric pressure, phase transformation (ε → γ’ + N2↑) and weight loss of the sample are observed only in the first 20 min of the process, then the sample weight increases. This was the result of the formation of iron oxide, which also inhibited the denitrification process of the iron nitride layer.