The Study Of Duplex Stainless Steel Plastic Deformation And Heat Treatment

Duplex stainless steel is an important branch of the stainless steel, which the ferrite solution microstructure has the nearly same proportion to the austenite phase, and one of the phase could reach 30%. As the two-phase microstructure characteristics, it will both possess austenitic stainless steel which has excellent welding and the toughness and ferritic stainless steel which has high strength and resistance to chloride stress corrosion , it is superior performance to duplex stainless steel that can be developed rapidly as a welded structural material. The performance of duplex stainless steel depends on its composition and microstructure. When duplex stainless steel own a certain chemincal composition, it's an effective method of deformation and heat treatment to change its morphology and improve their overall performance. Therefore, the study of different deformation and heat treatment on SAF2205 which impact on its microstructure and properties has important theoretical and practical significance in engineering applications.The results show that: SAF2205 duplex stainless steel's thermal processing performance is not good, and the deformation temperature range is narrow. It produced a vertical crack that had two deformations when the deformation temperature was 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, and the holding time was 2h. As the deformation temperature improving, the cracks tend to decrease. The specimens were not cracks when the deformation temperature was 1200℃, 1250℃,which were via four deformations, but the less are cracks. When the deformation temperature was 1200℃,the room temperature tensile strength was lower than the deformation temperature was 1250℃, but plastic was better. When the deformation temperature was 1200℃, the microstructure of ferrite and austenite both grew smaller as the deformation ratio increases, and the proportion of ferrite also increased. When the deformation temperature was 1200℃and deformation ratio was 30%, the microstructure grain size of ferrite and austenite increased with the holding time increased, and deformation could not effectively reduce the grain size.When the heat treatment temperature was 800℃and 850℃, the specimen of austenite-ferrite and interface of austenite phase boundary produced large amounts of brittle phase, which gradually decreased with the heat treatment temperature increased. When the heat treatment temperature reached 1000℃, the brittle phase completely dissolved in the matrix. As the temperature increased, the specimen turned out the microstructure transformation ofγ→δ. The tensile strength reduced at 800℃~1000℃heat treatment, when it reached 1000℃, the tensile strength got to minimum. However, the temperature ranged 1000℃~1300℃, the tensile strength gradually increased, while the plasticity and toughness first increased and then decreased, but the heat treatment was 1300℃, plastic increased rather than 1250℃. Heat treatment was 1000℃, the ferrite grain interior appeared secondary austenite whose morphology was the island and length sheet, and with the holding time increased, the tip of a long sheet became smooth, and the ferrite grain where the other lattice defects precipitated long sheet of secondary austenite,which reduced the microstructure's strength and plasticity. When the heat treatment was at 1000℃,and held 30min, the austenite-ferrite phase boundary arised a small amount of brittle phase while air cooling, ,and the ferrite-austenite phase boundary interface precipitated a large number of black brittle phase when furnace cooling, the brittle phase could increase the strength of the microstructure and reduce the ductility.