5475

5135

كارشناسي ارشد

شناسايي و انتخاب مواد فلزي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1389

ده،91ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

عباس نجفي زاده، احمد كرمانپور

24/7/89

فخرالدين اشرفي زاده، محمود منير واقفي

مهندسي مواد

ID5135

به فارسي و انگليسي:‌ قابل رويت در نسخه ديجيتالي

92 Comparison of microstructural evolution in a low carbon steel with ultrafine nano grained structure produced by plain strain compression cold rolling in martensite process Seyed Mehdi Hosseini sm hosseini@ma iut ac ir Date of Submission 2010 04 14 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Abbas Najafizadeh a najafi@cc iut ac ir Ahmad Kermanpur ahmad k@cc iut ac irAbstract Cold deformation and subsequent annealing of the martensite microstructure in low carbon steels knownas the martensite process is one of the most practical advanced thermomechanical processes to produceultrafine nano grained microstructures The aim of the present work was to compare the cold roll annealingand the plane strain compression annealing processes in a low carbon steel containing 13 wt C A fullymartensitic microstructure was first achieved by quenching and then was subjected to both cold rolling andplain strain compression up to 65 75 and 85 reduction in thickness The microstructures were subsequentlyannealed at temperature range of 400 to 550 C for 0 to 180 min The microstructures were characterized by optical and scanning electron microscopes Colormetallography was used to determine the martensite phase The texture formed in the cold deformedspecimens was studied The logarithmic curves of hardness were used to evaluate tempering mechanismduring annealing of the deformed specimens The results showed that fragmentation of lath martensite during plastic deformation in two methodsresulted in a remarkable increase of suitable nucleation sites during annealing Comparison of texture induced plastic deformation indicated that the texture including 110 plane was present in the most deformedspecimens by plane strain compression and in the all deformed specimens by cold rolling The deformedspecimens by the plane strain compression showed further drop in hardness after annealing at alltemperatures compared with the deformed specimens by cold rolling The most suitable temperature forachieving fully recrystallized microstructure in two methods was 500 C The final microstructure afterannealing included equiaxed ferrite grains nano sized precipitates of carbide and tempered martensite Microstructural and kinetic investigations indicated that increasing strain in the two methods resulted in adecrease on the recrystallization time and mean grain size The smallest grain size was 155 nm for cold roll annealing and 125 nm for plane strain compression annealing both obtained at 85 reduction in thickness The closest mean grain size for two deformation methods was obtained at 65 reduction with about 11 nmdeviation Increasing the reduction up to 85 resulted in an increase in the difference of the mean grain sizeof the two methods due to the difference in the strain path KeywordsThermomechanical treatment Martensite process Cold roll annealing Plane straincompression

عباس نجفي زاده، احمد كرمانپور

فخرالدين اشرفي زاده، محمود منير واقفي