5707

358 دكتري

دكتري

شكل دادن فلزات

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1389

نوزده،237ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

عباس نجفي زاده، محمود مرآتيان

15/1/89

جنابعلي جهرمي، عباس اكبر زاده، محمدرضا طرقي نژاد

مهندسي مواد

ID358 دكتري

به فارسي و انگليسي: "قابل رويت در نسخه ديجيتالي"

Study of the softening kinetics and microstructural evolution in AISI 304 stainless steel during and after hot deformation Javad Rasti J Rasti@ma iut ac ir January 30 2011 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Abbas Najafizadeh a najafi@cc iut ac ir 1st Supervisor 2nd Supervisor Mahmood Meratian Meratian@cc iut ac ir Department Graduate Coordinator Masoud Panjepour Abstract The kinetics of static dynamic and metadynamic recrystallization of AISI 304 stainless steel during and after hot deformation has been investigated at temperatures of 950 1100 qC and strain rates of 0 005 0 5 s 1 by hot compression test Softening kinetics was considered for material with two initial grain sizes of 15 and 40 Pm It was shown that once dimensionless parameter Z A Z Zener Hollomon parameter and A is a constant is greater than 1000 dynamic recrystallization develops by necklace mechanism Avrami equation was employed to quantify the softening kinetics The Avrami exponent and strain corresponding to 50 dynamic recrystallization were obtained by microstructural consideration and flow curve examination and results were compared The array L27 in Taguchi method was used to study softening kinetics during interpass time Prestrains varied in four groups within the range of 0 25 to 2 times the peak strain In each group Avrami equation was obtained via Avrami exponent and the time corresponding to 50 softening and therefore kinetics of static and metadynamic recrystallization were determined The transition strain and its corresponded time were obtained as functions of Zener Hollomon parameter To clarify the position of transition strain on the flow curve three methods namely hardness measuring X ray diffractometry and diffraction pattern of transition electron microscope were used for some samples quenched at different strains Cellular automata approach was also employed to simulate microstructure Results showed that the difference between average dislocation density in dynamically recrystallized and matrix grains reached to steady state condition beyond the transition strain Keywords AISI 304 stainless steel hot deformation softening kinetics transition strain Professor Department of Materials Engineering Isfahan University of Technology Isfahan Iran Associate Professor Department of Materials Engineering Isfahan University of Technology Isfahan Iran Assistant Professor Department of Materials Engineering Isfahan University of Technology Isfahan Iran 1

عباس نجفي زاده، محمود مرآتيان

جنابعلي جهرمي، عباس اكبر زاده، محمدرضا طرقي نژاد