Author/Editor		Cvijović, Zorica; Ibrahim, Abdulwahab MA; Mihajlović, Draginja
Title		Secondary phases precipitation in duplex stainless steel with Widmanstatten austenite microstructure
Type		članek
Source		Image Anal Stereol
Vol. and No.		Letnik 20, št. Suppl 1
Publication year		2001
Volume		str. 151-6
Language		eng
Abstract		The extent and kinetics of secondary phases precipitation in Widmanstatten austenite (WA) microstructure of a cast 26.6Cr-7.6Ni-2.5Mo-2.9Cu-0.06C duplex stainless steel (DSS) heated in the 750°C to 1 100°C temperature range were quantified in order to detennine the thermal stability of this steel. It was established that the WA microstructure with the ratio of delta: gamma = 89-85:11-15 and 32.0-34.0 vol.% metastable delta-ferrite is very unstable and susceptible to secondary austenite (gamma2), M23C6 carbide and sigma-phase formation. The nucleation of gamma2 and carbide is more favorable and faster than the nucleation of sigma-phase. However, at all temperatures the delta-ferrite decomposition is primarily attributed to the sigma-phase formation. On the other hand, its amount varies significantly with the annealing temperature. The estimated value of Vvsigma first increases with increasing temperature, reaches a maximum in the intermediate part of the investigated temperature range and then decreases as temperature further increases. A similar acceleration in the rate of sigma-phase formation was found. At 800°C and 900°C the process kinetics are so fast that the precipitation is almost complete within 120 min. This indicates that delta ->sigma reaction displays the classical C curve behavior. From a drawn TTT diagram, the sigma-phase precipitation is fastest at about 950°C. During isothermal annealing 5 vol.% of sigma-phase is expected to fonn after about 6 min at this temperature, while almost 85 min is required to fonn 95 vol.%.
Descriptors		MATERIALS TESTING STAINLESS STEEL CORROSION CASTING IMAGE PROCESSING, COMPUTER-ASSISTED