| 2205 duplex stainless steel is the most widely used in the world at present with c apacity of 80%. With development of the world the research of low-cost duplex stainl ess steel has become the main trend of duplex stainless steel industry. The most funda mental way of reducing the cost of the duplex stainless steel is to reduce the amount o f duplex stainless steel, and the most direct way of reducing the amount of duplex stai nless steel is to improve the comprehensive properties of the duplex stainless steel. Th erefore this paper mainly introducted that 2205 duplex stainless steel with nanocrystal line dual-phase were prepared by an aluminothermic reaction, the microstructure form ation mechanism of nano/micro-crystalline dual-phase bulk duplex stainless steel wer e investigated. In order to control the volume fraction and the grain size of the nanocr ystalline, the casted alloys have been isothermal treatment at different time under 1000℃. The effect of isothermal treatment on microstructural of nano/micro-crystalline d ual-phase duplex stainless steel were researched, and propose microstructural evolutio n mechanisms. We have found that 2205 duplex stainless steel prepared by aluminoth ermic reaction contains a large amount of unreacted Al element,which caused microst ructure of material to contain only ferrite phase. We have prepared 2205 duplex stainl ess steel with different ratio of ferrite and austenite phase by adding different amount s of Fe2O3 to original raw material alloy powder to ensure futher aluminothermic react ion. When we added 2.5% Fe2O3 to the original raw material alloy powder the volum e fraction of ferrite and austenite phase were 66.82% and 33.18%; When we adde d 5% Fe2O3 to the original raw material alloy powder the volume fraction of ferrite an d austenite phase were 40.44% and 59.56%; When we added 7.5% Fe2O3 to the origi nal raw material alloy powder the volume fraction of ferrite and austenite phase wer e 51.93% and 48.07%; When we added 10% Fe2O3 to the original raw material allo y powder the volume fraction of ferrite and austenite phase were 62.70% and 37.30%; When we added 12.5% Fe2O3 to the original raw material alloy powder microstr ucture of material almost contained ferrite phase. And the study found that with the Fe2O3 content gradually increased the hardness of alloy first reduce and then upward. Th e 2205 duplex stainless steel prepared by adding 5% Fe2O3 to original raw material all oy powder had the lowest hardness, which was 264.67 HV. 2205 duplex stainless ste el prepared by adding 5% Fe2O3 to original raw material alloy powder have been isoth ermal treatment at different time under 1000℃.The results showed that materials wer e consisting of ferrite and austenite phase before and after isothermal treatment. The v olume fraction of alloy’s ferrite and autenite phase were 46.79% and 47.45% after isothermal treatment at 0.5h under 1000℃; The volume fraction of alloy’s ferrite and aut enite phase were 59.98% and 35.98% after isothermal treatment at 1h under 1000℃; The volume fraction of alloy’s ferrite and autenite phase were 37.40% and 56.43% after isothermal treatment at 1.5h under 1000℃; The volume fraction of alloy’s fe rrite and autenite phase were 35.16% and 58.18% after isothermal treatment at 2h und er 1000℃. Before and after annealing at 0.5h 、1h、1.5h、2h under 1000℃, the grai n size nanocrystalline of in steel was 20.90nm、22.05nm、23.44nm、31.37nm、40.64 nm, and the volume fraction nanocrystalline in steel was 74.2%、69.8%、65.1%、54.3%、40.11%. With the increase of annealing time at 1000℃, the hardness of 2205 d uplex stainless steel increased first and then decreased. The steel after annealing 1h un der 1000℃ had the highest hardness, which was 324.33 HV. |
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