Title: Gas nitriding of En40B steel with highest growth rate of the case and reduced white layer formation

Authors: Shahjahan Mridha

Addresses: Department of Manufacturing and Materials Engineering, International Islamic University Malaysia, P.O. Box 10, 50728, Kuala Lumpur, Malaysia

Abstract: The Nitrided Layer (NL) thickness produced on En40B steel after treating in ammonia–hydrogen gas mixtures is found to increase parabolically with increasing the processing time, and its growth kinetics produces a linear relationship with nitriding potential up to a certain point where a white layer formed. At 470°C the growth rate is constant where presumably γ′-Fe4N only is present while at 520°C this constancy appears in the presence of ε-Fe₃N. At 570°C the growth rate continues to increase, but not linearly, even when γ′-Fe₄N is present and constancy appears well ahead of the presence of ε-Fe₃N phase. The findings suggest that the growth of NL is a maximum in an optimum gas mixture where the thickness of the white layer is a minimum.

Keywords: gas nitriding; diffusion layer; nitriding potential; growth rate; compound zone; microhardness; white layer; microstructure; material properties; heat treatment; ammonia–hydrogen gas; surface hardening; steel treating.

DOI: 10.1504/IJMMP.2007.012938

International Journal of Microstructure and Materials Properties, 2007 Vol.2 No.1, pp.54 - 63

Published online: 31 Mar 2007 *

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