DOI QR코드

DOI QR Code

The Effects of δ-ferrite on Weldment of 9-12% Cr Steels

9-12% Cr강의 용접부에 미치는 δ-ferrite의 영향

  • Received : 2013.12.19
  • Accepted : 2013.12.20
  • Published : 2013.12.31

Abstract

As the energy consumption increases rapidly, power generation needs the high energy efficiency continuously. To achieve the high efficiency of power generation, the materials used have to endure the higher temperature and pressure. The 9-12%Cr steels possess good mechanical properties, corrosion resistance, and creep strength in high temperature due to high Cr contents. Therefore, the 9-12%Cr steels are widely used for the high-temperature components in power plants. Even though the steels usually have a fully martensitic microstructure, they are susceptible to the formation of ${\delta}$-ferrite specifically during the welding process. The formation of ${\delta}$-ferrite has several detrimental effects on creep, ductility and toughness. Therefore, it is necessary to avoid its formation. As the volume fraction of ${\delta}$-ferrite is less than 2% in microstructure, it has the isolated island morphology and causes no significant degradation on mechanical properties. For ${\delta}$-ferrite above 2%, it has a polygonal shape affecting the detrimental influence on the mechanical properties. The formation of ${\delta}$-ferrite is affected by two factors: a chemical composition and a welding heat input. The most effective ways to get a fully martensite microstructure are to reduce the chromium equivalent less than 13.5, to keep the difference between the chromium and nickel equivalent less than 8, and to reduce the welding heat input.

Keywords

9-12%Cr steel;Delta ferrite;Austenite;Carbide;Heat input;Cooling rate

References

  1. F. Abe, M. Igarashi, N. Fujitsuna, K. Kimura, S. Muneki : Alloy design of advanced ferritic steels for 659 C USC Boilers, Conference proceeding advanced heat resistant steel for power generation (1998), 84-87
  2. T. Masse, Y. Lejeail : Creep mechanical behavior of modified 9Cr1Mo steel weldments: Experimental analysis and modeling, Nuclear Engineering and Design 254 (2013), 97-110 https://doi.org/10.1016/j.nucengdes.2012.09.007
  3. Y.H Lee, K.C. Lee, E.P. Yoon, K.C. Kim : Study on Softening Characteristics of 9Cr-1Mo Steel Weldments for High Temperature and Pressure Vessels Application, Journal of KWS, 10-3 (1992), 40-53 (in Korean)
  4. M. Sireesha, S. K. Albert, S. Sundaresan : Microstructure and mechanical properties of weld fusion zones in modified 9Cr-1Mo steel, Journal of Materials Engineering Performance, 10 (2001), 320-330 https://doi.org/10.1361/105994901770345033
  5. B. Arivazhagan, G. Srinivasan, S.K. Albert, A.K. Bhaduri : A study on influence of heat input variation on microstructure of reduced activation ferritic martensitic steel weld metal produced by GTAW process, Fusion Engineering and Design, 86 (2011), 192-197 https://doi.org/10.1016/j.fusengdes.2010.12.035
  6. RJ. Castro, JJ. Cadenet : Welding metallurgy of stainless and heat-resisting steels, Cambridge University Press (1968)
  7. K. Anderko, L. Schafer, E. Materna-Morris : Effect of the ${\delta}$-ferrite phase on the impact properties of martensitic chromium steels, Journal of Nuclear Materials, 179-181 (1991), 492-495 https://doi.org/10.1016/0022-3115(91)90132-Q
  8. B. Arivazhagan, M. Kamaraj : Metal-cored arc welding process for joining of modified 9Cr-1Mo(P91) steel, Journal of Manufacturing Processes, 15-4 (2013), 542-548 https://doi.org/10.1016/j.jmapro.2013.07.001
  9. E. Ayala, M.A. Roman, J. Vega, X. Gomez, T. Gomez- Acebo, J. Echeberria : Delta ferrite formation in 9-12% chromium steel weldments, Advanced heat resistant steels for power generation, (1998) 633-643
  10. J. Hald : Metallurgy and creep properties of new 9-12%Cr steels, Steels Research, 67-9 (1996) 369-374 https://doi.org/10.1002/srin.199605503
  11. K. Prasad Rao : Effect of weld cooling rate on deltaferrite content of austenitic weld metals, Journal of Material Science Letters, 9 (1990) 675-677 https://doi.org/10.1007/BF00721800
  12. K.S. Chandravathi, K. Laha, B.S. Rao, S.L. Mannan : Microstructure and tensile properties of modified 9Cr-1Mo steel(grade 91), Materials Science and Technology, 17 (2001) 559-565 https://doi.org/10.1179/026708301101510212
  13. A. Kumar, K. Laha, T. Jayakumar, K. Bhanu Sakara Rao, B. Raj : Comprehensive microstructure characterization in modified 9Cr-1Mo ferritic steel by ultrasonic measurements, Metallurgical and Materials Transactions A, 33A (2002) 1617-1626
  14. R. G. Faulkner, J. A. Williams, S. Gonzales, A. W. Marshall : Influence of Co, Cu and W on the microstructure of 9%Cr steel weld metals, Materials Science and Technology, 19 (2003) 347-354 https://doi.org/10.1179/026708303225009652
  15. K. Laha, K.S. Chandravathi, K.B.S. Rao, S.L. Mannan : Hot tensile properties of simulated heataffected zone microstructures of 9Cr-1Mo weldment, International Journal of Pressure Vessels and Piping, 62 (1995) 303-311 https://doi.org/10.1016/0308-0161(94)00023-C
  16. D. Carrouge, H.K.D.H. Bhadeshia, P. Woolin : Effect of delta ferrite on the impact properties of supermartensitic stainless steel heat affected zone, Science and Technology of Welding and Joining, 9-5 (2004) 377-389 https://doi.org/10.1179/136217104225021823
  17. J. Vekeman, A. Dhooge, S. Huysmans, B. Vandenberghe, C. Jochum : Weldability and high temperature behavior of 12% Cr-steel for tubes and pipes in power plants with steam temperatures up to $650^{\circ}C$, IIW Report XI-863-06 (2006)
  18. P. J. Grobner, W. C. Hagel : The effect of molybdenum on high-temperature properties of 9%Cr steels, Metallurgical Transactions A, 11A (1980) 633-642
  19. A. Iseda, M. Kubota, Y. Hayase, S. Yamamoto, K. Yoshikawa : Sumitomo Res., 36 (1998) 17-30
  20. L. Schafer : Influence of delta ferrite and dendritic carbides on the impact and tensile properties of a martensitic chromium steel, Journal of Nuclear Materials, 258-263 (1998) 1336-1339 https://doi.org/10.1016/S0022-3115(98)00200-1
  21. V. Foldyna, J. Purmenesky, Z. Kubon : Development of Advanced Chromium Steels with Respect to Microstructure and Structural Stability, ISIJ International, 41 (2001), S81-S85 https://doi.org/10.2355/isijinternational.41.Suppl_S81
  22. T. Sourmail : Precipitation in Creep Resistant Austenitic Stainless Steels, Materials Science and Technology, 17 (2001) 1-14 https://doi.org/10.1179/026708301101508972
  23. D. Jandova, J. Kasl : Influence of Precipitation on Dislocation substructure and Creep Properties of P91 Steel Weld Joints, Materials at High Temperature, 27-2 (2010), 135-140 https://doi.org/10.1179/096034010X12710730545552
  24. J. Besson : Analysis of Creep Lifetime of a ASME Grade 91 Welded Pipe, Engineering Fracture Mechanics, 76-10 (2009), 1460-1473 https://doi.org/10.1016/j.engfracmech.2008.12.007
  25. FB Pickering: Physical metallurgy and the design of steels, Applied Science Publishers (1978), 165-166
  26. S.W. Kim, S.H. Yang, J.K. Kim, Y.H. Lee : Evaluation of Underclad Crack Susceptibility of the SA508 Class 3 Steel for Pressure Vessels, Journal of KWS, 13-2 (1995) 139-149 (in Korean)
  27. J. Onoro : Martensite microstructure of 9-12% Crsteels weld metals, Journal of Materials Processing Technology, 180 (2006), 137-142 https://doi.org/10.1016/j.jmatprotec.2006.05.014
  28. J. Onoro : Weld metal microstructure analysis of 9-12% Cr steels, International Journal of Pressure Vessels and Piping, 83 (2006), 540-545 https://doi.org/10.1016/j.ijpvp.2006.03.005
  29. 1E-L. Bergquist : Consumable and welding modified 9Cr-1Mo steel, Svetsaran, 25-1/2 : 22-5, (1999)
  30. S. Kobayashi, K. Sawada, T. Hara, H. Kushima, K. Kimura : The formation and dissolution of residual ${\delta}$ ferrite in ASME Grade 91 steel plates, Materials Science & Engineering, 592 (2013) 241- 248
  31. H. Tanigawa : Technical issues of reduced activation ferritic/martensitic steels for fabrication of ITER test blanket modules, Fusion Engineering and design, 83 (2008), 1471-1476 https://doi.org/10.1016/j.fusengdes.2008.07.024

Acknowledgement

Supported by : 한국연구재단