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TECHNICAL PAPERS

Influence of Extra Coarse Grains on the Creep Properties of 9 Percent CrMoV (P91) Steel Weldment

[+] Author and Article Information
Rui Wu, Facredin Seitisleam

Swedish Institute for Metals Research, Drottning Kristinas väg 48, S-114 28 Stockholm, Sweden

Rolf Sandström

Materials Science and Engineering, KTH, Brinellvägen 23, S-100 44 Stockholm, SwedenSwedish Institute for Metals Research, Drottning Kristinas väg 48, S-114 28 Stockholm, Sweden

J. Eng. Mater. Technol 126(1), 87-94 (Jan 22, 2004) (8 pages) doi:10.1115/1.1631025 History: Received March 01, 2003; Revised June 03, 2003; Online January 22, 2004
Copyright © 2004 by ASME
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References

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Borggreen, K., 1995, “Some Effects of the Solution Heat Treatment Temperature on the Properties of Grade P91,” Proc. Int. Conf. on Plant Condition & Life Management, Eds Seijia Hietanen & Pertti Auerkari, VTT Manufacturing Technology, Baltica III, Vol. II, Helsinki-Stockholm, pp. 417–432.
Cerjak, H., Letofsky, E., and Schuster, F., 1996, “Heat-Affected Zone and Weld Metal Behavior of Modern-9–10% Chromium Steels,” Proc. 4th Int. Conf. on Trends in Welding Research, ASM International, Gatlingurg, Tennessee, USA, pp. 633–638.
Bergquist, E. L., Svensson, L. E., and Karlsson, L., 1998, “Creep Properties of Weldments in Modified 9Cr-1Mo Steel,” Proc. Int. Conf. on High Temperature Materials, Sigtuna, Sweden.
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Arav, F., Lentferink, H. J. M., Etienne, C. F., and Van Wortel, J. C., 1992, “Effect of Fabrication Processes on the Creep Behavior of 9–12% Chromium Steels,” Proc. 5th Int Conf. on Creep: Characterization, Damage and Life Assessments, Lake Buena Vista, Florida, pp. 117–125.
Okabayashi,  H., and Kume,  R., 1988, “Effects of Pre- and Post-Heating on Weld Cracking of 9Cr-1Mo-Nb-V Steel,” Trans. Jpn. Weld. Soc., 19(2), pp. 63–68.
Williams, K. R., Fidler, R. S., and Askins, M. C., 1981, “The Effect of Secondary Precipitation on the Creep Strength of 9Cr1Mo Steel,” Proc. Int. Conf. on Creep and Fracture of Engineering Materials and Structures, University College, Swansea, UK, pp. 475–487.
Prunier, V., Gampe, U., Nikbin, K., and Shibli, I. A., 1998, “HIDA Activity on P91 Steel,” Materials at High Temperatures, 15 (3/4), pp. 159–166.
Cerjak H., and Schuster F., 1994, “Basic Aspects of the Weldability of Advanced Creep Resistant Martensitic 9–10%Cr-Steels,” Proc. Int. Conf. on Welding, Joining, Coating and Surface Modification of Advanced Materials, Gansu University of Technoly, Dalian, China, pp. 132–137.
Maile, K., Schellenberg, G., Granacher, J. and Tramer, M., 1998, “Description of Creep and Creep Fatigue Crack Growth in 1% and 9% Cr Steels,” Materials at High Temperatures, 15 (2), pp. 131–137.
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Brühl, F., Cerjak, H., Müsch, H., Niederhoff, K., and Zschau, M., 1989, “Behavior of the 9% Chromium Steel P91 in Short and Long Term Tests, part II: Weldments,” VGB Kraftwerkstechnik, 69 (12), pp. 1074–1081.
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Scheller, H. J., Haigh, L., and Woitscheck, A., 1974, “Cracking in the Weld Region of Shaped Components in Hot Steam Lines,” Der Maschinenschaden, 47 , pp. 1–13.
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Figures

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LOM micrograph of a cross section of the welded pipe. Hardness profiles in the middle of the weld metal as well as across the weldment at 4.5 mm respectively 14.5 mm below the outer surface are schematically marked. Ruler scale showing 1 mm interval is given below the micrograph.
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LOM micrograph showing microstructures across the weldment of the welded pipe (a)–(d) and the simulated HAZ microstructures (e)–(f ). (a) the weld metal (to the left) and the coarse grained HAZ (to the right) adjacent to the fusion line (indicated by the arrows) near the outer surface, 25X. (b) the coarse grained HAZ, 400X. (c) the intercritical HAZ, 100X. (d) the intercritical HAZ (to the left) and the parent metal (to the right), 100X. (e) the simulated coarse grained HAZ at 1300°C, 100X. (f ) the simulated intercritical HAZ at 850°C, 100X.
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Hardness profiles in the welded pipe, (a) in the middle of weld metal through the thickness, and (b) across the weldment at 4.5 mm and 14.5 mm below the outer surface. FB refers to the fusion boundary, WM the weld metal, CGHAZ the coarse grained HAZ, ICHAZ the intercritical HAZ, and PM the parent metal.
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Hardness and grain size versus austenitizing temperature. Hardness and grain size from the as-received material and from the coarse grained HAZ (CGHAZ) of the welded pipe are included for comparison.
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Log stress σ as a function of log rupture time tR for the given series. Regressions by Eq. (1), shown by lines, are included.
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Log elongation at rupture εR as a function of log rupture time tR for the given series
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Minimum creep rate ε̇min as a function of log stress σ for the given series. Regressions by Eq. (2), shown by lines, are included.
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True creep strain rate as a function of true creep strain for the parent metal at stresses in the interval 110 to 180 MPa. Model values using Eqs. (4) to (6) are included in the figure.
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True creep strain rate as a function of true creep strain for the simulated intercritical HAZ at stresses in the interval 110 to 180 MPa. Model values using Eqs. (4) to (6) are included in the figure.
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LOM micrograph from the simulated coarse grained HAZ. Intergranular failure occurred after tR=7362 hours and εU=3.2 percent at 180 MPa. Perpendicular to the stress direction, microcracks developed intergranularly adjacent to fracture. Cavities formed at the grain boundary in front of the microcracks, indicated by arrows. 100X.
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LOM micrograph from the cross weld. Transgranular failure in the intercritical HAZ occurred after tR=5630 hours and εU=1.3 percent at 90 MPa. Microcrack and cavities, shown by arrows, in the unfailed intercritical HAZ. 50X.
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Comparison of cross weld creep strength at 600°C between the present and other published results

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