Cementite Residual Stress Analysis in Gas-nitrided Low Alloy Steels
TypeArticles dans des revues avec comité de lecture
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.
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Determination of residual stress in nitrided steels with transmission angle-dispersive diffraction JEGOU, Sébastien; BARRALLIER, Laurent (2014)Residual stress analysis with transmission angle-dispersive diffraction is carried out on nitrided steels. It aims evaluating residual stresses within the ferritic matrix but also within secondary phases such as nano-scale ...
JEGOU, Sébastien; BARRALLIER, Laurent; KUBLER, Régis; SOMERS, Marcel (Hanser, 2011)Development and evolution of compressive residual stress during nitriding treatment are studied. A model carbon iron-based alloy Fe-3wt.%Cr-0.35wt.%C was nitrided in gas at 550 °C for different times. Microstructural ...
JEGOU, Sébastien; KUBLER, Régis; BARRALLIER, Laurent; ROCH, François (2009)Nitriding of steels is an important treatment in duplex hardening methods. This treatment is known in the art but some advances still need to be done in terms of residual stress understanding. Although residual stresses ...
JEGOU, Sébastien; KUBLER, Régis; BARRALLIER, Laurent (Trans Tech Publications, 2010)This work deals with the development of residual stresses during nitriding of steels. The main features of a chemico-thermo-mechanical model of nitriding are presented. A micro-macro approach is applied based on volume ...
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