Influence of State of Stress on Dynamic Recrystallization in a Titanium-Modified Austenitic Stainless Steel
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namic recrystallization (DRX) is the most important restoration mechanism during the hot deformation of low-stacking fault energy, face-centered cubic alloys. The DRX process influences mainly the final microstructure and mechanical properties of the deformed material and, thus, the formability of materials.[1] Microstructure control through DRX requires a detailed knowledge of microstructural evolution as a function of processing parameters (i.e., strain, strain rate, and temperature). A special emphasis needs to be given in understanding the nucleation mechanisms during DRX. In our recent study, microstructural evolution and DRX behavior in a Ti-modified austenitic stainless steel (referred to as alloy D9) during hot working was investigated over a range of temperature (1173 K to 1373 K [900 C to 1100 C]) and strain (0.2 to 0.8) at a strain rate 10 seconds 1.[2] The nucleation of new DRX grains has been found to occur by bulging of the parent grain boundary. The processing parameters have been found to influence strongly the grain boundary character distribution and DRX in alloy D9. In addition to the processing parameters, the mode of deformation (i.e., state of stress) is expected also to influence the microstructure evolution and DRX behavior SUMANTRA MANDAL, Scientific Officer ‘E’, is with the Materials Technology Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India. Contact e-mail: sumantra@ igcar.gov.in A.K. BHADURI, Associate Director, is with the Materials Development and Technology Group, Indira Gandhi Centre for Atomic Research. V. SUBRAMANYA SARMA, Associate Professor, is with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India. Manuscript submitted August 5, 2011. Article published online December 10, 2011 410—VOLUME 43A, FEBRUARY 2012
of materials. Although most of the studies on DRX reported in the literature are based on uniaxial hotcompression tests,[1,3–7] a few studies are also based on plane-strain hot compression.[8,9] However, to the best of our knowledge, the influence of the state of stress (i.e., uniaxial vs plain-strain compression) on DRX kinetics and mechanisms has not been reported in the open literature. The objective of the current study is to investigate the role of state of stress on microstructural evolution and DRX behavior of alloy D9. The alloy D9 (in solution-annealed condition) used in this study is an austenitic stainless steel containing Fe-0.05C-1.51Mn-0.51Si-0.002S-0.01P-15.05Cr-15.07Ni2.25Mo-0.21Ti-0.01Co-0.006N (in wt pct). Uniaxial hot-compression tests were conducted on cylindrical specimen of 10 mm diameter and 15 mm height, whereas the plane-strain hot compression tests were conducted on a 20 9 15 9 10 mm3 solid bar using a specially designed anvil in a Gleeble thermomechanical simulator. The compression tests were performed in the temperature range of 1173 K to 1373 K [900 C to 1100 C] (in steps of 100 K) at a strain rate of 10 seconds 1. Various degrees of deformation (to true str
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