توسعه فرايند مارتنزيت جهت توليد فولاد فوق ريز دانه/نانو ساختار AISI 201 حاوي نيوبيوم

چكيده انگليسي :

Development of Martensite Process to Produce Ultrafine Nanostructured AISI 201 Stainless Steel Containing Niobium Hojat Samaei Baghbadorani h samaeibaghbadorani@ma iut ac ir April 25 2011 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Ahmad Kermanpur ahmad k@cc iut ac ir Abbas Najafizadeh a najafi@cc iut ac irAbstractIn recent years there is a great interest to production of third generation of high advanced strenght steelsincluding austenitic stainless steels Advanced thermomechanical processes an effective mechanism toproduce nano submicron grain structure in metastable austenitic alloys In addition some researches focusedon the improvement of the ductility of nanostructured materials in order to create a good combination ofstrenght and ductility The aim of this study was to produce ultrafine nanostructure AISI 201 austeniticstainless 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 niobiumand 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 differentreduction of 10 to 90 Multipass cold rolling was performed at the room and zero temperatures withreduction in thickness of 0 1 mm per each pass Dillatometry test was used to characterize the reversiontemperatures The reversion of martensite to austenite was carried out by an isothermal annealing treatmentin the temperature range of 700 to 900 C for different times from 15 to 1800s The identification of phaseswas carried out using X ray diffraction XRD and Feritscope The specimen microstructures were observedby optical and scanning electron microscopy SEM The grain size was measured using image analyzersoftware XRD results showed that the intensity of austenite peaks decrease and in return martensite peaksincrease 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 longertimes The reversion rate is much faster at higher annealing temperatures Austenite reversion at 850 and900 C completed for 300 and 60s respectively These are longer than completed reversion annealing time inAISI 201 wihout niobium steel The difference was due to pin effect of niobium The grain size of specimenannealed at 900 C for 60s was 90 10nm Increasing the annealing time resulted increasing grain size andprecipitation of niobium carbide Microstructure characterizations showed that the kinetics of carbidesprecipitation at 900 C in faster than 850 C So the rate of increasing grain size at 900 C was slower than850 C to some extent due to interaction between carbides and grain boundaries The ultimate tensilestrenght yield srenght hardness and elongation of specimen annealed at 900 C for 60s were 1407 MPa 1170 MPa 405 HV and 37 The higher elongation compared to nanostructured AISI 201 without niobiumsteel was related to promotion of deformation mechanisms such as strain induced martensite due to carbideprecipitation in ultrafine nanostructured samples Keywords Martensite process AISI 201 stainless steel containing niobium Elongation

سماعي باغبادراني، حجت

توسعه فرايند مارتنزيت جهت توليد فولاد فوق ريز دانه/نانو ساختار AISI 201 حاوي نيوبيوم

درصد ازدياد طول , فولاد زنگ نزن آستنيتي 201 حاوي نيوبيوم