3965

3743

1386

شناسايي و انتخاب و روش ساخت مواد

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1386

هشت، [94]، [II] ص.: مصور، جدول، نمودار

ص.ع. به: فارسي و انگليسي

عباس نجفي زاده

22/03/87

احمد جنابعلي جهرمي، محمد رضا طرقي نژاد

مهندسي مواد

ID3743

به فارسي و انگليسي: قابل رؤيت در نسخه ديجيتال

Abstract The aim of this study was evaluation of microstructure variations in AISI 316 stainlesssteel during hot rolling On condition that in the first wave of DRX new grains form along theinitial boundaries necklace mechanism will be predominant recrystallization mechanism Inorder to modeling the deformation behavior during hot rolling one hit compression tests wereperformed at temperatures of 950 1100 C with strain rates of 0 01 1 s 1 To study the dynamicrecrystallization phenomena the critical stress for initiation of dynamic recrystallization c should be determinded Accordingly it could be identified by the inflection point on the strainhardening rate d d versus flow stress curve Several methods have been proposed tocalculate this value on the basis of mathematical methods One of them was proposed byStewart Jonas and Montheillet in which this critical point appears as a distinct minimum inthe d d versus through differentiating from versus Another one was presented byNajafizadeh and Jonas which obtain by modifying the Poliak and Jonas method According tothis method the strain hardening rate was plotted against flow stress and the value of c wasobtained numerically from the coefficients of the third order equation that was the best fitfrom the experimental data The result shows that the method presented by Najafizadehand Jonas not only simpler than the previous one but also it has a good agreement withmicrostructures Furthermore the normalized critical stress for this steel was obtained uc 1 c p 0 92 The result shows that at the temperature of 1000 C with the strain rate of 0 1 s DRX developed by necklace mechanism it is far from completeness over the steady statestress By contrast the hardness increased by development of DRX The final microstructure isvery heterogeneous and comprises of very fine and coarse grains due to the occurrence ofpartial DRX The results also show that the necklace structure developed by increasing Zener Hollomon parameter Z Finally in order to evaluation the effect of primary grain size on therecrystallized microstructure and kinetics of recrystallization at specific temperature and strainrate samples have been annealed at T 1000 1100 and 1200 C and then deformed at 1100 C and with strain rate of 0 1 s 1 The results showed that with increasing in annealtemperature recrystallized fraction decreases from 100 to zero It can be interpreted thatincreasing the anneal temperature causes decrement in the fraction of boundry surface per unitvolume It means that the appropriate sites for dynamic nucleation have been decreased

عباس نجفي زاده

احمد جنابعلي جهرمي، محمد رضا طرقي نژاد