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 Date of Submission: 2010/11/20 Department of Materials Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: Ph.D. Language: Farsi Supervisors: Mahmood Meratian, meratian@cc.iut.ac.ir Abbas Najafizadeh, a-najafi@cc.iut.ac.ir In this work softening kinetics of 304 stainless steel during and after hot deformation was studied by hot compression test. Grain growth occurred during reheating stage was evaluated by four methods namely Jensen-Gunderson method, serial section analysis, 3-dimensional Monte Carlo simulation, and Abbruzzese-Lucke model. Results showed that the grain volume distribution during grain growth can be estimated from a random section area by Jensen-Gunderson method assuming lognormal distribution. Softening kinetics during hot deformation was considered for material with two initial grain sizes of 15 and 40 mm. It was shown that once dimensionless parameter Z/A 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 L 27 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 so, kinetics of static and metadynamic recrystallization were determined. The transition strain and its corresponded time were obtained as functions of Zener-Hollomon parameter regarding the normalized time of 50 % softening against normalized strain.
