Etude des phénomènes de précipitation dans un acier austénitique à 19% de chrome et 19% de manganèse, et à très forte teneur en azote

Abstract
This paper describes the precipitation evolution that occurs in a not prestmined 1%N Mn-Cr austenitic steel aged in the [40O°C-900°C] temperature range, and for various times up to 150 hours. Thermal treatments carried out between 700°C and 900°C lead to a discontinuous precipitation of plates of Cr₂N at grain boundaries. The nucleation stage of this precipitation reaction arises fiom the migration of the grain boundary along the high-energy interface, in order to reduce the interfacial energy of the primary surface between the plate and the grain boundary. On the contrary, the cell growth is characterized by numerous properties that differ from the hypotheses of usual theories. These non-steady state growth features arise from the continuous modifications of the diffusion-controlled mechanisms during isothermal aging. Beside this cellular precipitation, the sigma phase forms with significant volume fractions in the cells.