PSI - Issue 60

K. Mariappan et al. / Procedia Structural Integrity 60 (2024) 444–455 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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strain during the course of deformation. Similar universal scaling of work hardening parameters has been reported in Type 316L(N) steel [Isaac Samuel and Choudhary (2010)]. The inter-relation between the strength parameters and the strain parameters of the constitutive relations are manifestations of the constrained variation of the stress and strain during deformation. The applied strain rate may be partitioned in terms of plastic strain rate and elastic strain rate as below: ̇ = ̇ + ̇ (6) The above equation may be re-arranged in terms of work hardening rate and plastic strain rate as = ̇ − , where = . ̇ (7) The above relation brings out the inverse linear relation between the work hardening rate and plastic strain rate. Figure 11b shows the plot of work hardening rate as a function of the plastic strain rate for 316 L(N) SS with the extent of prior fatigue deformations at 300, 823 and 873 K. Figure 11b also brings out the universal relation between the work hardening rate with plastic strain rate and rationalises the linear relation observed between the stress parameters and strain parameters across the temperature and deformation conditions. 4. Conclusions Tensile work hardening behaviour of Type 316LN stainless steel with prior fatigue damage in terms of prior fatigue cycles of 0 N f , 0.05 N f , 0.1 N f , 0.3 N f and 0.5 N f , were studied at 300, 823 and 873 K. Significant increase in flow stress with increase in prior fatigue damage was observed at higher temperatures of 823 and 873 K due to dynamic strain aging. Tensile flow behaviour of 316L(N) SS at 300 K for all material prior conditions were well described by Ludwigson relation. At 823 and 873 K, both the Ludwigson and Voce equations were found to describe well the flow behaviour of the specimens at all conditions, i.e. 0 N f , 0.05 N f , 0.1 N f , 0.3 N f and 0.5 N f . At 300 K, the specimens under all prior tested conditions exhibited three stage work hardening behaviour. The stage II hardening was absent in the specimens subjected to prior fatigue damage at 823 and 873 K. The inter relation between Ludwigson strength parameter and the strain hardening coefficient was rationalised in terms of the universal linear relation between the work hardening rate and reciprocal of plastic strain rate. References Baldev Raj, Mannan S. L., Vasudeva Rao P. R. and Mathew M. D. 2002, Development of fuels and structural materials for fast breeder reactors, Sadhana, 27, 527–558. Choudhary, B. K., Isaac Samuel, E., Bhanu Sankara Rao K. and Mannan, S. L, 2001, Tensile stress–strain and work hardening behaviour of 316LN austenitic stainless steel. Mater. Sci. Technol., 17, 223-231. Feaugas, X., 1999, On the origin of the tensile flow stress in the stainless steel AISI 316L at 300 K: back stress and effective stress. Acta. Mater., 47, 3617-3632. Girish Shastry, C., Mathew, M. D., Bhanu Sankara Rao, K. and Pathak, S. D., 2007, Tensile deformation behaviour of AISI 316L(N) SS. Mater. Sci. and Tech., 23, 1215-1222. Gottstein, G. G. and Argon, A. S., 1987, Dislocation theory of steady state deformation and its approach in creep and dynamic tests. Acta. Metall., 35, 1261-1271. Hollomon, J. H., 1945, Tensile Deformation. Trans. of the Metallurgical Society of AIME, 162, 268-290. Isaac Samuel E., Choudhary B.K., Bhanu Sankara Rao K., 2002, Influence of temperature and strain rate on tensile work hardening behaviour of type 316 LN austenitic stainless steel, Scripta Mater. 46, 507–512 Isaac Samuel E. and Choudhary B.K., 2010, Universal scaling of work hardening parameters in type 316L(N) stainless steel, Mater. Sci. and Engg. A, 527, 7457–7460 Ludwigson, D. C., 1971, Modified stress-strain relation for FCC metals and alloys. Metallurgical Transactions, 2, 2825–2828. Mughrabi, H. and Christ, H.J., 1997, Cyclic Deformation and Fatigue of Selected Ferritic and Austenitic Steels: Specific Aspects. ISIJ Int., 37, 1154–69. Pesicka, J., Kuzel, R, Dronhofer, A.and Eggeler, G., 2003, The evolution of dislocation density during heat treatment and creep of tempered martensite ferritic steels. Acta Mater., 15, 4847–62