Development of Martensite Process to Produce Ultrafine/Nanostructured AISI 201 Stainless Steel Containing Niobium In recent years there is a great interest to production of third generation of high advanced strenght steels including austenitic stainless steels. Advanced thermomechanical processes an effective mechanism to produce nano/submicron grain structure in metastable austenitic alloys. In addition, some researches focused on the improvement of the ductility of nanostructured materials in order to create a good combination of strenght and ductility. The aim of this study was to produce ultrafine/nanostructure AISI 201 austenitic stainless steel containing niobium. heavy cold rolling and annealing. The ingots casted in metallic mould, homogenized as 1200 ?C for 15hr. In order to decrease the amount of delta ferrite and dissolution of niobium and choromium carbides, solution annealing treatment was carried out at 1200 ?C for 9hr after hot forging. The specimens quenched in water. The strips with the initial thickness of 10 mm were cold rolled to different reduction of 10 to 90%. Multipass cold rolling was performed at the room and zero temperatures with reduction in thickness of 0.1 mm per each pass. Dillatometry test was used to characterize the reversion temperatures. The reversion of martensite to austenite was carried out by an isothermal annealing treatment in the temperature range of 700 to 900 °C for different times from 15 to 1800s.The identification of phases was carried out using X-ray diffraction (XRD) and Feritscope. The specimen microstructures were observed by optical and scanning electron microscopy (SEM). The grain size was measured using image analyzer software. XRD results showed that the intensity of austenite peaks decrease and in return martensite peaks increase during cold rolling. Saturation strain of cold rolled specimen at room temperature was about 0.7. Rolling at 0 ?C and using of cross rolling decrease the saturation strain to 0.52 and 0.6 respectively. Reversion annealing results showed that complete austenite reversion at 700, 750 and 800 ?C needs to longer times.The reversion rate is much faster at higher annealing temperatures. Austenite reversion at 850 and 900 ?C completed for 300 and 60s respectively. These are longer than completed reversion annealing time in AISI 201 wihout niobium steel. The difference was due to pin effect of niobium. The grain size of specimen annealed at 900?C for 60s was 90±10nm . Increasing the annealing time resulted increasing grain size and precipitation of niobium carbide. Microstructure characterizations showed that the kinetics of carbides precipitation at 900 ?C in faster than 850 ?C. So, the rate of increasing grain size at 900 ?C
