Role of Grain Boundary Character Distribution on Tensile Properties of 304L Stainless Steel
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This work describes the effect of thermomechanical processing (TMP) on grain boundary character distribution (GBCD) and the effect of GBCD on tensile properties of 304L austenitic stainless steel. The material was solution treated before the TMP. Electron backscattered diffraction and tensile properties evaluation were carried out. The tensile properties were found to vary with the processing conditions. The percent elongation and strain hardening exponent of the thermomechanically processed material was found to be larger than that of the starting material. The increase in the percent elongation was correlated with special coincidence boundaries. On the other hand, the strain hardening exponent was observed to be influenced by the type of texture developed from the TMP. DOI: 10.1007/s11661-007-9118-5 The Minerals, Metals & Materials Society and ASM International 2007
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INTRODUCTION
MOST of the engineering materials are used in the polycrystalline state and their performance is linked to microstructural features, such as the grain boundaries. The bulk properties, particularly mechanical properties of polycrystalline materials, are affected by microstructural heterogeneities or boundaries. During deformation, dislocations have to move from one grain to another. The transfer of dislocations across the grain through the grain boundary is an important step in controlling the deformation behavior of the material. Recently, the importance of the effects of the type, BANDARI RAVI KUMAR, S. GHOSH CHOWDHURY, N. NARASAIAH, B. MAHATO, and S.K. DAS, Scientists, are with the Materials Science and Technology Division, National Metallurgical Laboratory, Jamshedpur, India. Contact e-mail: [email protected] Manuscript submitted November 8, 2006. Article published online May 12, 2007. 1136—VOLUME 38A, MAY 2007
structure, and character distribution of grain boundaries on the bulk properties of materials has been well documented.[1–14] The introduction of a high fraction of strong low- R coincidence site lattice boundaries (CSLB) or conversely the reduction of the fraction of weak random boundaries is a key factor in controlling intergranular fracture through the control of the grain boundary character distribution (GBCD).[4] The GBCD can be manipulated through thermomechanical processing (TMP).[15,16] Strain hardening is an intrinsic aspect of plastic deformation. Strain hardening through plastic deformation is the most widely used technique for imparting strength to austenitic stainless steels (ASS), which are not hardenable by the conventional heat treatment process. Strain hardening is coupled with features such as the development of preferred lattice orientation, formation of localized shear bands, formation of subgrains, and residual stresses.[17] The reorientation of grains during plastic straining can further increase the resistance to deformation[18] and hence may influence strain hardening behavior. Austenitic steels have a higher strain hardening rate than ferritic steels. This is due to low stacking fault energy (SFE), wh
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