Kinetics of G-phase precipitation and spinodal decomposition in very long aged ferrite of a Mo-free duplex stainless steel

Cristelle Pareige (1) , J. Emo (1) , S. Saillet (2) , C. Domain (2) , Philippe Pareige (1)

1 GPM - Groupe de physique des matériaux
2 EDF R&D MMC - Matériaux et Mécanique des Composants

Evolution of spinodal decomposition and G-phase precipitation in ferrite of a thermally aged Mo-free duplex stainless steel was studied by Atom Probe Tomography (APT). Kinetics was compared to ki-netics observed in ferrite of some Mo-bearing steels aged in similar conditions. This paper shows that formation of the G-phase particles proceeds via at least a two-step mechanism: enrichment of a/a 0 inter-domains by G-former elements followed by formation of G-phase particles. As expected, G-phase precipitation is much less intense in the Mo-free steel than in Mo-bearing steels. The kinetic synergy observed in Mo-bearing steels between spinodal decomposition and G-phase precipitation is shown to also exist in Mo-free steel. Spinodal decomposition is less developed in the ferrite of the Mo-free steel investigated than in Mo-bearing steels: both the amplitude of the decomposition and the effective time exponent of the wavelength (0.06 versus 0.16) are much lower for the Mo-free steel. Neither the temperature of homogenisation nor quench effects or Ni and Mo contents could successfully explain the low time exponent of the spinodal decomposition observed in the Mo-free steel. The diffusion mechanisms could be at the origin of the different time exponents (diffusion along a/a 0 interfaces or diffusion of small clusters).

Domaines: Sciences de l'ingénieur [physics]; Matériaux

Cristelle Pareige, J. Emo, S. Saillet, C. Domain, Philippe Pareige. Kinetics of G-phase precipitation and spinodal decomposition in very long aged ferrite of a Mo-free duplex stainless steel. Journal of Nuclear Materials, 2015, 465, pp.383 - 389. ⟨10.1016/j.jnucmat.2015.06.017⟩. ⟨hal-01828030⟩