Fabrication and Evaluation of Ultrafine/Nano Grained 201L Stainless Steel by Advanced Thermo-Mechanical Process Ahad Rezaee a.rezaee@ma.iut.ac.ir Date of Submission: February 28, 2011 Department of Materials Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc. Language: Farsi Supervisors: A. Najafizadeh, Prof. and A. Kermanpur, Assoc. Prof. In recent years, there is a growing interest in developing the third generation of advanced high strength steels, including stainless steels, for light weight constructions. Austenitic stainless steels are promising engineering materi als demonstrating suitable corrosion resistance and formability, but they posses relatively low yield strength, which limits their applications. Among the different strengthening mechanisms, grain refinement is the only method to improve both strength and toughness. Metastable austenitic stainless steels can be transformed to martensite by deformation below the Md 30 temperature. In this study, effects of process parameters including strain, strain rate, strain path, rolling temperature, initial grain size and chemical composition on the volume fraction of strain induced martensite in AISI 201L stainless steel are investigated. The as-cast specimens were first homogenized and then hot forged in order to prepare a suitable microstructure for the subsequent treatment involving conventional cold rolling and annealing to produce nano/ultrafine grained AISI 201L stainless steel. Cold rolling was carried out at -40 ?C, -10 ?C, and 25 ?C with a strain rates of 0.1-1.2 s -1 and reductions of 0-95%. The identification of different 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. The results showed that saturation strain (? s ) of martensite formation during the cold rolling at room temperature with a strain rate of 0.5 s -1 in 201L stainless steel was about 0.5. Increasing the strain, strain rate, initial austenite grain size, decreasing the rolling temperature, and the use of cross rolling resulted in an increased volume fraction of the strain induced martensite during cold rolling and a reduced martensite saturating strain.
