Investigation of gas nitriding in pure Fe, AISI 1070 steel and Fe-Cr alloys

Abstract

<p>Following a review of the gas nitriding process, of the Fe-N system and of the formation of the compound layer, this study investigates the interaction between the diffusing nitrogen and the material to be nitrided.</p> <p>The formation of the compound layer and diffusion case is discussed for pure iron. AISI 1070 low alloy steel is investigated using different microstructures and the resulting effect on the nitrided microstructure is presented. The interaction of a nitride forming element is studied with a Fe/Fe-5Cr diffusion couple specimen. The strengthening mechanisms resulting from the nitriding process for all these materials are discussed using standard models from the literature. The scale of the precipitates produced in pure iron as well as in the 1070 steel pearlitic and spheroidized microstructure is found to provide marginal hardening. The interaction between N and carbides obtained during the nitriding of the 1070 martensitic microstructure gives rise to a significant hardness increase up to 130HV. The most significant hardening effect (up to 900HV) is obtained with the formation of a high density of fine CrN precipitates in the Fe-Cr specimens.</p>