Cementite Residual Stress Analysis in Gas-nitrided Low Alloy Steels

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Cementite Residual Stress Analysis in Gas-nitrided Low Alloy Steels

L. Barrallier, S. Goekjian, F. Guittonneau, S. Jégou

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Abstract. This paper deals with the measurement of residual stresses in cementite after gas-nitriding of a 33CrMoV12-9 steel. During nitriding, precipitation of nanometric alloying elements nitrides and cementite at grain boundaries occurs leading to an increase of superficial hardness and providing compressive residual stresses in the surface layer. The stress state in the ferritic matrix has generally been measured to characterize the mechanical behaviour of the nitrided case while the other phases are not taken into account. In order to better understand the mechanical behaviour (e.g. fatigue life and localization of cracks initiation) of heterogeneous material such as in case of nitrided surfaces, the nature (sign, level) of residual stresses (or pseudo-macro-stresses) of the present phases can be calculated from measurements using X-ray diffraction to select the considered phase. Due to a low volume fraction of cementite through a nitrided case, an approach based on X-ray and electron backscattered diffractions (XRD and EBSD respectively) is proposed to perform stress measurements in cementite. An optimization of the surface preparation (by mechanical and/or chemical polishing techniques) prior to EBSD analysis was performed in order to minimize deformation induced by surface preparation. Pseudo-macro-stresses were calculated in tempered martensite and cementite. Results are compared to local residual stress measurements carried out by a cross-correlation method using EBSD patterns.

Keywords
Nitriding, Residual Stress, X-ray Diffraction, EBSD

Published online 12/22/2016, 6 pages
Copyright © 2016 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA

Citation: L. Barrallier, S. Goekjian, F. Guittonneau, S. Jégou, ‘Cementite Residual Stress Analysis in Gas-nitrided Low Alloy Steels’, Materials Research Proceedings, Vol. 2, pp 139-144, 2017

DOI: http://dx.doi.org/10.21741/9781945291173-24

The article was published as article 24 of the book Residual Stresses 2016

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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