Abstract
Niobium carbonitride (NbX) precipitates have been studied in a niobium stabilised austenitic stainless steel AISI type 347 with approximate nominal composition Fe–0.06C–17.5Cr–11.4Ni–0.8Nb. The steel was extruded to seamless tube, solution annealed at 1100°C for 3 min, water quenched, and subsequently isothermally aged at 700°C for times up to 70 000 h. Size distribution and volume fraction of the coarse distribution (1–10 µm) of NbX particles were measured using scanning electron microscopy (SEM). The fine distribution (∼30 nm) was investigated using energy filtered transmission electron microscopy (EFTEM). Size distribution and volume fraction were determined using jump ratio images. Coarse NbX (∼0.3% volume fraction) precipitates were formed during solidification and extrusion, and were little affected by solution annealing and isothermal aging. Fine NbX (∼0.5% volume fraction) precipitates formed during solution annealing and grew during the first 800 h of aging. Precipitate size determination using EFTEM appears to give accurate results, while volume fraction determination requires homogeneous material for good results.
Get full access to this article
View all access options for this article.