1000 However, HAZ of the joint changed into fine sorbite 口 Test I with coarsened M23 C6 carbides precipitated on the grain leading it the weak creep rupture test, such T91 welded joints could ensure sufficient heat strength under the operating conditions of most currently used nuclear reactors. And life was estimated to be over 10?h under 25 MPa and550°C. 10 The work was supported by both National Natural Science LMP=T(25+lgt)x10 Foundation of China ( Grant 50871076) and Shanghai Leading Academic Discipline Project(Project Number: B113). Meanwhile Fig. 7 Plot of stresses with LMP for the T91 welded joints part of the tests was cooperated by Shanghai Institute of Special Equipment Inspection Technical Research and Shanghai Boiler to and also supplemented the data(Ref 30)at other tempera- works Ltd. Finally, gratitude must also be given to Shanghai tures, but they were a bit inferior to the performance of the esearch Institute of Materials for providing various experimental T91 base material at the same temperature. Fu based on the two fitted lines, the threshold stresses 0623 C of the joints at 625C, after 10 h were approximately estimated: 47 and 40 MPa, already higher than the steam References pressures of USC condition. If considering the safety factor, these threshold stresses should also be divided by a safety 1. RL Klueh and A.T. Nelson. Ferritic/Martensitic Steels for Next- Generation Reactors, J. Nucl. Mater, 2007, 371, p 37-52 Defficient(Ref 44, 45)that ranges from 1. 2 to 1.6 to obtain 2. J. Van den Bosch and A. Almazouzi, Compatibility of Martensitic/ the permitted stresses in application. However, this is also Austenitic Steel Welds with Lead Bismuth Eutectic Environ- higher than the operating pressures of most nuclear reactors ment,J. Nucl. Mater, 2009, 385, P 504-50 presently used. 3. F Masuyama, History of Power Plants and Progress in Heat Resistant It is a common sense that Larson-Miller equation is always Steels, IS/ Int, 2001, 41, p 612-625 applied to predict service lives of components on basis of creep 4. R. Viswanathan and w. Bakker, Materials for Ultrasupercritical Coal Power Plants-Boiler Materials: Part 1, J. Mater. Eng. Perform, 2001 rupture data(Ref 46). As for T91 and its welded joints, the 10,p8l-95 Larson-Miller equation is defined 5. J. Hansen, M. Sato, R. Ruedy, K. Lo, D W. Lea, and M. Medina Elizade. Global Te re Change. Proc. Natl. Acad. Sci. USA LMP= T(25+Igt) 2006,103,p14288-1 6. Y. Gong and Z.G. Yang, Corrosion Evaluation of One Dry Desulfur- where LMP is the dimensionless Larson-Miller parameter, T 2011,32,p671-681 hour(Ref 47). Then, the creep rupture data can be plotted in 7. J. Cao. Y. Gong, K. Zhu, Z.G. Yang et al., Microstructure and form of lg o versus LMP, where LMP can be calculated by Mechanical Properties of Dissimilar Materials Joints Between Eq 2, seen in Fig. 7. After polynomial fitting, service lives of Martensitic and S304H Austenitic Steels. Mater: Des.. 2011 p2763-2770 the T91 welded joints can be easily predicted. For example, 8.K H. Lo, C H. Shek, and J K L. Lai, Recent Developments in Stainless under 30 MPa and 625C, the service life is nearly Steels, Mater. Sci. Eng. R, 2009, 60,000 h; under 25 MPa and 550C, the upper limit operat J. Cao, Y. Gong, Z.G. Yang et al., Creep Fracture Behavior of ing conditions of most current nuclear reactors(Ref 48-51) Dissimilar Weld Joint Between T92 Martensitic and HR3C Austenitic the service life could be over 10 h. Thus it can be con- Steels, Int J. Pres. Ves. Pip, 2011, 88, p 94-98 cluded that this kind of China-made T91 welded joints were 10. J.C. An, H.Y. Jing, G.C. Xiao, L. Zhao, and L.Y. Xu, Analysis of the Creep Behavior of P92 Steel Welded Joint, J. Mater: Eng. Perform. comprehensively qualified to be applied in nuclear power 010,doi:10.1007/s11665-010-9779- dustry 11. Y. Gong, J. Cao, L N. Ji, Z.G. Yang et al., Assessment of Cree 12. A. Roy, P. Kumar, and D. Maitra, The Effect of Silicon Content on 4. Conclusions pact Toughness of T91 Grade Steels, J. Mater. Eng. Perform, 2009 1. Mechanical properties of this China-made T91 welded 13. C. Keller. M.M es, Z. Hadjem-Hamouche, and L. Guillot Influence of the are on the tensile behaviour of a modified joints were qualified at both room and increasing temper 9Cr-IMo T91 Steel. Mater. Sci. Eng. 4, 2010, 527 atures according to relevant standards. What's more, aged p67586764 at 625C for 10,000 h, tensile properties of the joints did not exhibit obvious deterioration as well Oxidation of T91 Ferritic Steel Under Steam. Corros. Sci. 2004 p613-631 2. After welding, weld seam consisted of wider mar- 15. L Nieto Hierro, V. Rohr, P.J. Ennis, M Schutze, and w.J. Quadakkers, te laths than that of t91 base material and no coars- Effects on Creep Strength of Power ened carbides were observed on the grain boundaries. Station Materials. Mater. 1318--Volume 21(7) July 2012 Journal of Materials Engineering and Performanceto and also supplemented the data (Ref 30) at other tempera￾tures, but they were a bit inferior to the performance of the T91 base material at the same temperature. Furthermore, based on the two fitted lines, the threshold stresses r625 C 105 of the joints at 625 C, after 105 h were approximately estimated: 47 and 40 MPa, already higher than the steam pressures of USC condition. If considering the safety factor, these threshold stresses should also be divided by a safety coefficient (Ref 44, 45) that ranges from 1.2 to 1.6 to obtain the permitted stresses in application. However, this is also higher than the operating pressures of most nuclear reactors presently used. It is a common sense that Larson–Miller equation is always applied to predict service lives of components on basis of creep rupture data (Ref 46). As for T91 and its welded joints, the Larson–Miller equation is defined as: LMP ¼ Tð25 þ lg tÞ ðEq 2Þ where LMP is the dimensionless Larson–Miller parameter, T is the absolute temperature in K, and t is the rupture time in hour (Ref 47). Then, the creep rupture data can be plotted in form of lg r versus LMP, where LMP can be calculated by Eq 2, seen in Fig. 7. After polynomial fitting, service lives of the T91 welded joints can be easily predicted. For example, under 30 MPa and 625 C, the service life is nearly 60,000 h; under 25 MPa and 550 C, the upper limit operat￾ing conditions of most current nuclear reactors (Ref 48–51), the service life could be over 107 h. Thus, it can be con￾cluded that this kind of China-made T91 welded joints were comprehensively qualified to be applied in nuclear power industry. 4. Conclusions 1. Mechanical properties of this China-made T91 welded joints were qualified at both room and increasing temper￾atures according to relevant standards. Whats more, aged at 625 C for 10,000 h, tensile properties of the joints did not exhibit obvious deterioration as well. 2. After welding, weld seam consisted of wider mar￾tensite laths than that of T91 base material, and no coars￾ened carbides were observed on the grain boundaries. However, HAZ of the joint changed into fine sorbites with coarsened M23C6 carbides precipitated on the grain boundaries, leading it the weak region of the whole joints. 3. Based on the creep rupture test, such T91 welded joints could ensure sufficient heat strength under the operating conditions of most currently used nuclear reactors. And its service life was estimated to be over 107 h under 25 MPa and 550 C. Acknowledgments The work was supported by both National Natural Science Foundation of China (Grant 50871076) and Shanghai Leading Academic Discipline Project (Project Number: B113). Meanwhile, part of the tests was cooperated by Shanghai Institute of Special Equipment Inspection & Technical Research and Shanghai Boiler works Ltd. Finally, gratitude must also be given to Shanghai Research Institute of Materials for providing various experimental conditions. References 1. R.L. Klueh and A.T. Nelson, Ferritic/Martensitic Steels for Next￾Generation Reactors, J. Nucl. Mater., 2007, 371, p 37–52 2. J. Van den Bosch and A. Almazouzi, Compatibility of Martensitic/ Austenitic Steel Welds with Liquid Lead Bismuth Eutectic Environ￾ment, J. Nucl. Mater., 2009, 385, p 504–509 3. F. Masuyama, History of Power Plants and Progress in Heat Resistant Steels, ISIJ Int., 2001, 41, p 612–625 4. R. Viswanathan and W. Bakker, Materials for Ultrasupercritical Coal Power Plants–Boiler Materials: Part 1, J. Mater. Eng. Perform., 2001, 10, p 81–95 5. J. Hansen, M. Sato, R. Ruedy, K. Lo, D.W. Lea, and M. Medina￾Elizade, Global Temperature Change, Proc. Natl. Acad. Sci. USA, 2006, 103, p 14288–14293 6. Y. Gong and Z.G. Yang, Corrosion Evaluation of One Dry Desulfur￾ization Equipment—Circulating Fluidized Bed Boiler, Mater. Des., 2011, 32, p 671–681 7. J. Cao, Y. Gong, K. Zhu, Z.G. Yang et al., Microstructure and Mechanical Properties of Dissimilar Materials Joints Between T92 Martensitic and S304H Austenitic Steels, Mater. Des., 2011, 32, p 2763–2770 8. K.H. Lo, C.H. Shek, and J.K.L. Lai, Recent Developments in Stainless Steels, Mater. Sci. Eng. R, 2009, 65, p 39–104 9. J. Cao, Y. Gong, Z.G. Yang et al., Creep Fracture Behavior of Dissimilar Weld Joint Between T92 Martensitic and HR3C Austenitic Steels, Int. J. Pres. Ves. Pip., 2011, 88, p 94–98 10. J.C. An, H.Y. Jing, G.C. Xiao, L. Zhao, and L.Y. Xu, Analysis of the Creep Behavior of P92 Steel Welded Joint, J. Mater. Eng. Perform., 2010, doi:10.1007/s11665-010-9779-x 11. Y. Gong, J. Cao, L.N. Ji, Z.G. Yang et al., Assessment of Creep Rupture Properties for Dissimilar Steels Welded Joints Between T92 and HR3C, Fatigue Fract. Eng. M, 2011, 34, p 83–96 12. A. Roy, P. Kumar, and D. Maitra, The Effect of Silicon Content on Impact Toughness of T91 Grade Steels, J. Mater. Eng. Perform., 2009, 18, p 205–210 13. C. Keller, M.M. Margulies, Z. Hadjem-Hamouche, and I. Guillot, Influence of the Temperature on the Tensile Behaviour of a Modified 9Cr–1Mo T91 Martensitic Steel, Mater. Sci. Eng. A, 2010, 527, p 6758–6764 14. D. Laverde, T. Go´mez-Acebo, and F. Castro, Continuous and Cyclic Oxidation of T91 Ferritic Steel Under Steam, Corros. Sci., 2004, 46, p 613–631 15. L. Nieto Hierro, V. Rohr, P.J. Ennis, M. Schu¨tze, and W.J. Quadakkers, Steam Oxidation and Its Potential Effects on Creep Strength of Power Station Materials, Mater. Corros., 2005, 56, p 890–896 Fig. 7 Plot of stresses with LMP for the T91 welded joints 1318—Volume 21(7) July 2012 Journal of Materials Engineering and Performance