8502

7883

كارشناسي ارشد

شناسايي ، انتخاب و روش ساخت مواد

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1392

سيزده،81ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

احمد كرمانپور، عباس نجفي زاده

14/11/92

محمود منير واقفي، احمد رضائيان

مهندسي مواد

ID7883

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

82 Evaluation of microstructure and mechanical properties of nano ultrafine grained low carbon steel produced by martensite process with warm deformation Mahdi Mohammadi hooyeh M mohammadihovieh@ma iut ac ir Date of Submission December 2 2013 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Ahmad Kermanpure Assoc Prof ahmad k@cc iut ac irAbass Najafizadeh Prof a najafi@cc iut ac irAbstract Grain refinement of the metallic alloy is one of the important strengthening mechanisms asis the only way to improve both strength and ductility Cold plastic deformation andsubsequent annealing of low carbon steels with martensitic structure known as themartensite process is one of the advanced thermomechanical methods to achieve ultrafinegrained steels Nevertheless the need to apply large thickness reduction during coldrolling relatively long annealing time and low uniform elongation have made somedifficulties in the production of such steels Since the warm deformation processes such aswarm rolling forging and extrusion have extensively used in industry attempts have beenmade in this study to apply the warm deformation in the martensite process to improve themechanical properties For this purpose two plain carbon and Nb steel 0 04 wt sampleswere cast The samples were austenitized at 1000 and 1200 followed by quench at 15 was performed Microstructural characterization was conducted by color etching andX ray diffraction XRD techniques Cold rolling up to 50 reduction in thickness wasdone at room temperature followed by warm rolling up to 50 reduction in thickness attemperature range of 450 to 700 with temperature increment of 50 was carried outon both steel The results showed a ferritic structure with the mean grain size of 120 nmand 198 nm for the plain carbon steel and the mean grain size of 236 nm and 3 8 m forthe Nb containing steel at the temperature of 600 and 650 The lower grain size in themicroalloyed steel was attributed to the influence of Nb carbide on grain growth Thehardness results of samples which were warm rolled at different temperatures confirmedthe dynamic precipitations of Nb The promising tensile properties of 846 MPa yieldstrength and 10 uniform elongation in Nb microalloyed steel and 521 MPa yield strengthand 16 uniform elongation in plain carbon steel were achieved Keywords Advance thermo mechanical processing Ultrafine grained structure Warm rolling Martensitetreatment Plain carbon steel Niobium

احمد كرمانپور، عباس نجفي زاده

محمود منير واقفي، احمد رضائيان