Investigation of Process Parameters of the Martensite Treatment on the Microstructure and Mechanical Properties of the Ultrafine/Nano Grained 201 Austenitic Stainless Steel Mohammad Moallemi m.moallemi@ma.iut.ac.ir Date of Submission: 2011/03/5 Department of Materials Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc. Language: Farsi Supervisor: Abbas Najafizadeh, a-najafi@cc.iut Ahmad Kermanpur, ahmad_k@cc.iut.ac.ir . Production of ultrafine/nanostructured steels with simultaneous high strength and good toughness has been the center of attention in recent years. Martensite process is one of the advanced thermo-mechanical processes for production of ultrafine grained austenitic stainless steel. This process is carried out by cold rolling of steel and formation of strain-induced martensite, followed by reversion of microstructure to the ultrafine grained austenite. The aim of the present project was to evaluate the process parameters of the martensite treatment for production of the ultrafine/nano grained 201 stainless steel. The 201 austenitic steel slabs were produced by casting in permanent mold followed by homogenization at 1200 °C for 15 h. The slabs were then hot forged in the temperature range of 1150-1200 °C. In order to reduce secondary phases, the forged specimens were annealed at 1150 °C for different time periods. Both one-step and two-step martensite processes were applied on the specimens. The annealed samples were cold rolled at -10, 0 and 25 °C followed by reversion at 750-900 °C for 15-1800 s. Microstructures were characterized by light and scanning electron microscopes. Phase characterizations were conducted by feritscope and XRD methods. A mathematical model was used to predict the behavior of austenite to martensite transformation behavior during the rolling process. Mechanical properties of the final products were examined by hardness and tensile tests. The results revealed that homogenization at 1200 °C caused an enormous grain growth with considerable reduction in the amount of delta ferrite.
