Title: Diffusional model of expanded austenite layer growth on AISI 316L stainless steel during low-temperature hybrid thermochemical treatment

Authors: Esa Haruman; Annissa Fanya; Mohd Shahriman Adenan

Addresses: Faculty of Engineering and Computing Science, Bakrie University, Jakarta, 12920, Indonesia ' Faculty of Mechanical Engineering, Universiti Teknologi MARA, Selangor, 40450, Malaysia ' Faculty of Mechanical Engineering, Universiti Teknologi MARA, Selangor, 40450, Malaysia

Abstract: A simultaneous nitrogen and carbon diffusional model in AISI 316L stainless steel is presented in this numerical study to simulate expanded austenite layer growth developed during hybrid thermochemical treatment. This numerical model has not been previously discussed using a gaseous process. The present work considered the trapping-detrapping phenomenon, the concentration-dependent diffusion coefficient, and the composition-induced stress gradient as the boundary parameters. The study revealed that the stress gradient effect accelerated the diffusion rate of nitrogen and carbon species. The trapping-detrapping phenomenon caused the diffusional curvature to consist of convex and concave shapes, which differ from those derived from the Fick's 2nd law. The present model confirmed previous experimental evidence that the developed layer would be structured with nitrogen-enriched expanded austenite on the top of the layer and carbon-enriched expanded austenite underneath. This novel model can be considered in designing the hybrid thermochemical treatments using a gaseous process.

Keywords: austenitic stainless steel; hybrid thermochemical treatment; expanded austenite; nitrogen and carbon diffusions; numerical modelling; finite difference method.

DOI: 10.1504/IJCMSSE.2021.118516

International Journal of Computational Materials Science and Surface Engineering, 2021 Vol.10 No.2, pp.112 - 128

Received: 12 Feb 2021
Accepted: 07 May 2021

Published online: 27 Oct 2021 *

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