PRECIPITATION PHENOMENA IN HIGH-NITROGEN AUSTENITIC STEEL (19-PERCENTCHROMIUM AND 19-PERCENT MANGANESE)

This paper describes the precipitation evolution that occurs in a not prestrained 1%N Mn-Cr austenitic steel aged in the [400-degrees-C-900- degrees-C] temperature range, and for various times up to 150 hours. T hermal treatments carried out between 700-degrees-C and 900-degrees-C lead to a discontinuous precipitation of plates of Cr2N at grain bound aries. The nucleation stage of this precipitation reaction arises from the migration of the grain boundary along the high-energy interface, in order to reduce the interfacial energy of the primary surface betwe en the plate and the grain boundary. On the contrary, the cell growth is characterized by numerous properties that differ from the hypothese s of usual theories. These non-steady state growth features arise from the continuous modifications of the diffusion-controlled mechanisms d uring isothermal aging. Beside this cellular precipitation, the sigma phase forms with significant volume fractions in the cells.