Issue 48

J. Christopher et alii, Frattura ed Integrità Strutturale, 48 (2019) 554-562; DOI: 10.3221/IGF-ESIS.48.53 561 time data of E911 steel. From the microstructural aspects, it is evident that Feltham relation involving constancy in internal stress and activation volume is not applicable for describing the stress-relaxation behaviour of E911 steel. Contrary to this, Model-II can capable to capture the evolution of internal and effective stresses, activation volume and inter-barrier spacing with time for E911 steel during deformation under stress-relaxation. The predicted increase in inter- barrier spacing and activation volume with hold time confirms that continual substructural coarsening of E911 steel during stress-relaxation. R EFERENCES [1] Di Gianfrancesco, A., Cipolla, L., Cirilli, F., Cumino, G. and Caminada, S. (2005). Microstructural stability and creep data assessment of Tenaris Grades 91 and 911, In Proceedings of 1 th International Conference Super-High Strength Steels, pp. 2-4. [2] Manjoine, M. J. and Voorhees, H. R. (1982). Compilation of stress-relaxation data for engineering alloys, ASTM. DOI: 10.1520/MNL11954D. [3] Dotseneo, V.I. (1979). Stress relaxation in crystals, Phys. status solidi B, 93, pp. 11-43. DOI: 10.1002/pssb.2220930102. [4] Feltham, P. (1963). Stress relaxation in magnesium at low temperatures, Phys. status solidi B, 3, pp. 1340-1346. DOI: 10.1002/pssb.19630030805. [5] McCarthy, P.R., Robertson, D.G., Orr, J. and Strang, A. (2000). Recent development in stress relaxation methodologies within Europe, Key Eng. Mater., 171–174, pp. 9-16. DOI: 10.4028 /www.scientific.net/KEM.171-174.9. [6] Humphries, S.R., Snowden, K.U. and Yeung, W. (2010). The effect of repeated loadings on the stress relaxation properties of 2.25Cr-1Mo steel at 550 ºC and the influence on the Feltham ‘a’ and ‘b’ parameters, Mater. Sci. Eng., A, 527, pp. 3240-3244. DOI: 10.1016/j.msea.2010.02.011. [7] Trojanová, Z., Máthis, K., Lukác, P., Németh, G. and Chmelík, F. (2011). Internal stress and thermally activated dislocation motion in an AZ63 magnesium alloy, Mater. Chem. Phys., 130, pp. 1146-1150. DOI: 10.1016/j.matchemphys.2011.08.045. [8] Christopher, J. and Choudhary, B. K. (2018). Constitutive modelling of stress-relaxation behaviour of tempered martensitic P91 steel using sine hyperbolic rate law, Mater. Chem. Phys., 205, pp. 442-451. DOI: 10.1016/j.matchemphys.2017.11.053. [9] Christopher, J. and Choudhary, B. K. (2016). Constitutive description of primary and steady-state creep deformation behaviour of tempered martensitic 9Cr–1Mo steel, Philos. Mag. A, 96(21), pp. 2256-2279. DOI: 10.1080/14786435.2016.1197435. [10] Argon, A.S. and Takeuchi, S. (1981). Internal stresses in power-law creep, Acta Metall., 29, pp. 1877-1884. DOI: 10.1016/0001-6160(81)90113-9. [11] Nakajima, T., Spigarelli, S., Evangelista, E., & Endo, T. (2003). Strain enhanced growth of precipitates during creep of T91, Mater. Trans., 44(9), pp. 1802-1808. DOI: 10.2320/matertrans.44.1802. [12] Bose, S. C., Singh, K., Swaminathan, J. and Sarma, D. S. (2004). Prediction of creep life of X10CrMoVNbN-91 (P- 91) steel through short term stress relaxation test methodology, Mater. Sci. Technol., 20(10), pp. 1290-1296. DOI: 10.1179/026708304225022304. [13] Guguloth, K., Swaminathan, J., Roy, N. and Ghosh, R. N. (2017). Uniaxial creep and stress relaxation behavior of modified 9Cr-1Mo steel, Mater. Sci. Eng., A, 684, pp. 683-696. DOI: 10.1016/j.msea.2016.12.090. [14] Friedel, J. (1964). Dislocations. Pergamon Press, Oxford. [15] Northwood, D.O. and Smith, I.O. (1984). Steady - State Creep and Strain Transients for Stress - Dip Tests in Polycrystalline Magnesium at 300º C, Phys. status solidi A, 85, pp.149-158. DOI: 10.1002/pssa.2210850117. [16] Northwood, D. O., Moerner, L. and Smith, I. O. (1985). Effect of magnesium content on the stress exponent and effective stress in the steady state creep of Al-Mg alloys, J. Mater. Sci., 20(5), pp. 1683-1692. DOI: 10.1007/bf00555272. [17] Northwood, D.O. and Smith, I.O. (1986). Stress change tests during the steady .state creep of aluminum alloy 3004 at 300 º C, Mater. Sci. Eng., 79, pp.175-182. DOI: 10.1016/0025-5416(86)90402-7 [18] Northwood, D.O. and Smith, I.O. (1986). Internal and Effective Stresses in the Steady - State Creep of Polycrystalline Cadmium at 0.5 Tm, Phys. status solidi A, 98, pp.163-169. DOI: 10.1002/pssa.2210980117.