Research Article 2017, 2(5), 304-309 Advanced Materials Proceedings Copyright © 2017 VBRI Press 25 Plasticity assessment based on Schmid factor in deformed 9Cr-1Mo steel Manmath Kumar Dash 1, 2 , T. Karthikeyan 1 , S. Saroja 1* 1 Physical Metallurgy Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India 2 Indira Gandhi Centre for Atomic Research, HBNI, Kalpakkam * Professor, Homi Bhabha National Institute, Department of Atomic Energy * Corresponding author: E-mail: saroja@igcar.gov.in; Tel: (+91) 44-27480204; Fax: (+91) 44-27480202 Received: 29 March 2016, Revised: 30 September 2016 and Accepted: 10 April 2017 DOI: 10.5185/amp.2017/505 www.vbripress.com/amp Abstract Chromium alloyed Ferritic/Martensitic steels are widely used as structural materials in power plants, and considered for core applications of fast and fusion reactors. Characterization and fundamental interpretation of deformed microstructure through crystal plasticity principles are useful for tailoring desired microstructure by optimal processing methods. This study reports the characterization of plastic strain distribution in cold rolled 9Cr-1Mo steel using Electron back scatter diffraction (EBSD) technique. Small orientation changes within the individual grains were studied to gauge the accumulation of ‘geometrically necessary’ dislocations in deformed material, and correlate with the load geometry. The correlated misorientation angle distribution showed a significant presence of low angle boundaries in the deformed microstructure as compared to the annealed specimen. Crystal orientation map of deformation bands indicated significant intra-grain rotation, and the extent of rotation was distinctly different for different grains. A heterogeneous accumulation of plastic strain distribution is inferred from the grain maps of local misorientation angle (0.5º-5º) and orientation spread parameters. Analysis by Schmid factor criteria (0.4-0.5) showed more than 50% of the grains to exhibit favorable orientation for {110} <111> slip activity, whereas higher stress would be required for plastic deformation of remaining grains. Copyright © 2017 VBRI Press. Keywords: Polygonal ferrite, EBSD, local misorientation, schmid factor, deformation. Introduction The 9Cr-1Mo ferritic steels find use in power plants, and are being considered for wrapper applications of nuclear reactors. They exhibit excellent void swelling resistance as compared to austenitic steels, which is an crucial property for achieving high burn up in fast reactors [1,2]. These steels are used in tempered martensite condition that imparts the necessary creep strength at the service temperatures [3]. Whereas, manufacturing steps by forming operations are carried out on ferritic polygonal microstructure possessing good ductility. In mechanical forming of components, the plastic strain accumulation is heterogeneously distributed among the individual grains, influenced by variations in shape/size and crystallographic orientations of grains [4, 5]. Dislocation motion assisted slip is the common deformation mechanism of metallic polycrystalline materials [6, 7]. The dislocation density is increased in the individual grains with increasing amounts of deformation. The ‘geometrically necessary’ dislocations result in a gradient of orientation within the grain, that can be detected as small shift/rotation of Kikuchi diffraction bands in electron backscatter diffraction (EBSD) experiment [8,10,11]. Also, dislocation defects lead to diffused diffraction patterns, but the band contrast quality parameter is not suited for quantitative analysis [12]. The parameters such as local misorientation [13] and kernel average misorientation (KAM) [9] are generally used to correlate the extent of deformation [14-16], and assess slip activity due to applied load [17]. In deformation, the nature of load geometry, temperature, strain and strain rate dictates the Table 1. Chemical composition (wt %) of the 9Cr-1Mo steel used in the study. C Si Mn S P Cu Ni Cr Mo N Fe 0.10 0.75 0.63 0.001 0.02 1.00 1.12 9.27 1.05 0.019 Bal.