Activation of surfaces prior to gaseous nitriding of a 3wt.% Cr carbon iron-based alloy
TypeCommunications avec actes
Gaseous nitriding is a well-established thermochemical treatment of carbon iron-based alloys that considerably enhances corrosion, wear and fatigue resistances of critical mechanical parts such as crank shafts and bearings. It is based on the diffusion of nitrogen atoms from the catalytic decomposition of ammonia at the outer surface. The process has generally been relying on the fast development of a compound layer that mainly serves as a nitrogen reserve during the treatment. The growth of the compound layer directly depends on the adsorption of nitrogen atoms at the surface of treated parts. Any barriers to the nitrogen adsorption may induce detrimental kinetics of nitriding, and so a lack of mechanical properties. So-called surface preparations prior to nitriding thus fundamentally assist with (i) nitriding of superior quality (i.e. with the required properties such as the effective depth and mechanical properties), (ii) uniform nitriding of the whole treated part (i.e. no mechanical heterogeneities induced by the process) and (iii) repeatable nitriding from batch to batch. The present work deals with three in-situ surface activation solutions prior to nitriding that are oxidation, urea and ammonium chloride. Pre-treatments are compared based on their efficiency on uncleaned samples, defined by different degrees of residues of water dissolved machining oil, to be nitrided. The first few hours of nitriding are reported on a 3wt.%Cr carbon iron-base alloy.
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GUILLOT, Benjamin; JEGOU, Sébastien; BARRALLIER, Laurent (ASM International, 2016)Machining is known to introduce plastic straining and residual stress gradients in surface of mechanical parts. If not controlled, the mechanical state of a surface can influence adsorption and diffusion of atoms during ...
Degradation of gaseous nitriding of steel by lubricant contamination — Effect of in-situ pre-treatments GUILLOT, B.; JEGOU, Sébastien; BARRALLIER, Laurent (Elsevier, 2017)The present work focuses on the industrial inhibition of gaseous nitrided parts and on the industrial in-situ pre-treatment that can be used to avoid these inhibitions. The first objective is to obtain a repeatable defective ...
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 ...