توليد و ارزيابي فولاد زنگ نزن آستنيتي201L فوق ريز دانه/نانو ساختار با استفاده از فرايند ترموديناميكي پيشرفته

چكيده انگليسي :

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 Abstract 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 materials 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 Md30 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 It was found that the effect of decreasing the rolling temperature and strain path was more effective on the strain induced martensite than other parameters and reduced s from 0 5 to 0 28 Also the fragmentation of lath martensite during plastic deformation resulted in a remarkable increase of suitable nucleation sites during annealing The reversion of martensite to austenite in the cold rolled specimens was carried out by annealing in the temperature range of 750 900 C for different times from 15 to 1800 s The results showed that the nanocrystalline austenitic structure with an average grain size of 65 5 nm was obtained by annealing the 95 cold rolled specimen at 850 C for 30 s The yield strength total elongation and hardness of this specimen were measured as 1485 MPa 29 and 386 Vickers respectively Keywords Austenitic stainless steel Nanostructure Advanced thermo mechanical treatment Cold rolling Annealing

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توليد و ارزيابي فولاد زنگ نزن آستنيتي201L فوق ريز دانه/نانو ساختار با استفاده از فرايند ترموديناميكي پيشرفته

نورد سرد , آنيل