Deformation Behavior and Evolution of Microstructure and Texture During Hot Compression of AISI 304LN Stainless Steel
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HIGH-NITROGEN AISI 304LN austenitic stainless steel (ASS) is widely used, for example, in primary heat transport piping (PHT) system of nuclear power plant.[1] This is due to its superior elevated-temperature mechanical properties and excellent corrosion/oxidation resistance.[2,3] 304LN ASS is processed thermomechanically before application. Therefore, it is very important to study the mechanisms of microstructural evolution during thermomechanical processing in order to achieve the desirable properties. The 304L ASS have face-centered cubic (FCC) structure with low stacking fault
MATRUPRASAD ROUT and SURJYA KANTA PAL are with the Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India. SOMJEET BISWAS, RAVI RANJAN, and SHIV BRAT SINGH are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur. Contact e-mail: [email protected] Manuscript submitted March 5, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
energy (SFE).[4] In these alloys, cross-slip of screw dislocations and climb of edge dislocations are restricted due to large distance between the partials.[5] Dynamic recrystallization (DRX) occurs readily, and this leads to microstructural refinement.[6] This helps in softening of the material during hot deformation and therefore reduces the stress required for further hot working.[7] The 304LN ASS has nitrogen (N) that enhances mechanical properties and corrosion resistance of ASS. Addition of N increases SFE, this enhances cross-slip resulting in delayed initiation of DRX,[8,9] thereby increasing the work hardening rate.[10] The effect of carbon content of ASS has been studied in detail by Wahabi et al.[9] It was shown that the work hardening behavior and dynamic recovery depend on carbon content, but DRX remains unaffected. There are many extensive researches on deformation behavior and DRX in ASS where it is shown that these phenomena depends on SFE which in turn depends on composition and temperature.[11,12] During hot working, metallic materials undergo shape change. At the same time, changes in microstructure,
texture, and grain boundary character occur. These changes depend on the processing history of the material. Venugopal et al.[13] generated processing maps of 304L ASS from flow curves under compression at different temperatures and strain rates. His research team showed the occurrence of DRX in 304L ASS with a peak efficiency of power dissipation of about 35 pct at 1523 K (1250 C) and 0.1 s1. Considering different mathematical models to characterize different segments of the flow curves, McQueen et al.[14] found that energy dissipative efficiency (EDE) is dependent on the shape of the flow curve, and it is the highest during the initial stages of flow softening. They observed that the nucleation of DRX grains also occurred on the parent grain boundaries in 304 ASS. This is due to fluctuation of grain boundaries followed by serration and bulging.[15,16] The bulging mechanism includes continuous
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