Advertisement

Journal of Materials Engineering and Performance

, Volume 27, Issue 12, pp 6328–6338 | Cite as

Alternative PWHT to Improve High-Temperature Mechanical Properties of Advanced 9Cr Steel Welds

  • Ariel BurgosEmail author
  • Hernán Svoboda
  • Zhuyao Zhang
  • Estela Surian
Article
  • 34 Downloads

Abstract

Creep-resistant 9Cr steels are extremely important in thermal power generation industry due to their marked resistance to creep and corrosion. The weldability of these alloys is critical since they are used in welded construction equipment. The required mechanical properties are achieved after post-weld heat treatment. This study examined the effect of different post-weld heat treatments on microstructure and mechanical properties of creep strength-enhanced 9Cr steel welding deposits. It was obtained with an experimental flux-cored arc welding wire used under protective gas (Ar-20% CO2). The heat treatments used were: (1) tempering (760 °C × 2 h), (2) solubilizing (1050 °C × 1 h) + tempering (760 °C × 2 h) and (3) solubilizing (1150 °C × 1 h) + first tempering (660 °C × 3 h) + second tempering (660 °C × 3 h). All-weld metal chemical composition was analyzed, and hot tensile tests were carried out at different temperatures. Charpy-V impact tests and Vickers microhardness measurements were also performed. Microstructures were studied using x-ray diffraction and optical and scanning electron microscopy. In all cases, a martensitic matrix with intergranular and intra-granular precipitates was detected. In the as-welded condition, δ-ferrite was also found. Microhardness dropped, and the impact energy increased with post-weld heat treatments. The highest hot tensile strength result was achieved with samples submitted to austenization at 1150 °C and double tempering at 660 °C.

Keywords

creep strength-enhanced 9Cr steel FCAW mechanical properties microstructure PWHT 

Notes

Acknowledgments

The authors wish to express their gratitude to METRODE PRODUCTS LTD—UK for the design, fabrication and donation of the consumable used, to CONARCO-ESAB Argentina for performing the chemical analysis, to AIR LIQUIDE Argentina for donating gases for welding and to the SCANNING ELECTRON MICROSCOPY LABORATORY OF INTI-Mechanics, Argentina, for facilities for both SEM analysis and Charpy-V tests. They also recognize CONICET, ANPCyT and APUEMFI (National University of Lomas de Zamora), Argentina, for financial support.

References

  1. 1.
    R. Viswanathan, J.F. Henry, J. Tanzosh, G. Stanko, J. Shingledecker, B. Vitalis, and R. Purgert, U.S. Program on Materials Technology for Ultra-Supercritical Coal Power Plants, J. Mater. Eng. Perform., 2005, 14, p 281–292CrossRefGoogle Scholar
  2. 2.
    J. Oñoro, Weld Metal Microstructure Analysis of 9–12% Cr Steels, Int. J. Press. Vessels Pip., 2006, 83, p 540–545CrossRefGoogle Scholar
  3. 3.
    E. Oakey, L.W. Pinder, R. Vanstone, M. Henderson, and S. Osgerby, Review of Status of Advanced Materials for Power Generation Part 4, COAL R224 02/1509, DTI/Pub URN, 2003Google Scholar
  4. 4.
    G. Posch, S. Baumgartner, and M. Fiedler, GMA-Welding of Creep Resistant Steels with Flux Cored Wires (FCAW): Perspectives and Limitations, Weld. World, 2009, 53, p 619–624Google Scholar
  5. 5.
    W. Marshall, Z. Zhang, and G.B. Holloway, Welding Consumables for P92 and T23 Creep Resisting Steels A, in Fifth International EPRI RRAC Conference, June 27th, 2002, p. 1–17Google Scholar
  6. 6.
    Z. Zhang, J.C.M. Farrar, and A.M. Barnes, Weld Metals for P91—Tough Enough, Metrode Products Limited, U.K. TWI, Ltd., Chertsey, 2002Google Scholar
  7. 7.
    B. Arivazhagan, S. Sundaresan, and M. Kamaraj, A Study on Influence of Shielding Gas Composition on Toughness of Flux-Cored Arc Weld of Modified 9Cr-1Mo (P91) Steel, J. Mater. Process. Technol., 2009, 209(12–13), p 5245–5253CrossRefGoogle Scholar
  8. 8.
    C. Chovet, E. Galand, and B. Leduey, Effect of Various Factors on Toughness in P92 Saw Weld Metal, Weld. World, 2013, 52(7–8), p 18–26Google Scholar
  9. 9.
    Z. Zhang, G. Holloway, and A. Marshall, Properties of T/P92 Steel Weld Metals for Ultra Super Crtitical (USC) Power Plant, Weld. World, 2008, 6(1), p 1–13Google Scholar
  10. 10.
    H. Wang, H. Zhang, and J. Li, Microstructural Evolution of 9Cr-1Mo Deposited Metal Subjected to Weld Heating, J. Mater. Process. Technol., 2009, 209(6), p 2803–2811CrossRefGoogle Scholar
  11. 11.
    A.C. Chovet, E. Bauné, G. Ehrhart, E. Galand, and G. Liberati, Development of Filler Materials for New 9–12% Cr Martensitic Creep Resistant Steels, in New Developments on Metallurgy and Applications of High Strength Steels Brazil, 2008, p. 1–7Google Scholar
  12. 12.
    ISO, Welding Consumables—Covered Electrodes for Manual Metal Arc Welding of Creep-Resisting Steels—Classification, ISO 3580:2017, International Organization for Standardization, Geneva, 2017Google Scholar
  13. 13.
    K. Maruyama, K. Sawada, and J. Koike, Strengthening Mechanisms of Creep Resistant Tempered Martensitic Steel, ISIJ Int., 2001, 41(6), p 641–653CrossRefGoogle Scholar
  14. 14.
    P.J. Ennis, The Creep Rupture Behaviour and Steam Oxidation Resistance of P92 Weldments, Mater. High Temp., 2006, 23(3), p 187–193CrossRefGoogle Scholar
  15. 15.
    L.I. Yajiang, W. Juan, Z. Bing, and F. Tao, XRD and TEM Analysis of Microstructure in the Welding Zone of 9Cr-1Mo-V-Nb Heat-Resisting Steel, Bull. Mater. Sci., 2002, 25(3), p 213–217CrossRefGoogle Scholar
  16. 16.
    Y. Yin, R. Faulkner, P. Morris, and P. Clarke, Modelling and Experimental Studies of Alternative Heat Treatments in Steel 92 to Optimise Long Term Stress Rupture Properties, Energy Mater., 2008, 3(4), p 232–242CrossRefGoogle Scholar
  17. 17.
    L.O. Bueno and J.F.R. Sobrinho, Correlation between Creep and Hot Tensile Behaviour for 2.25Cr-1Mo Steel from 500 °C to 700 °C Part 1: An Assessment According to Usual Relations Involving Stress, Temperature, Strain Rate and Rupture Time, Rev. Mater., 2012, 17(3), p 1098–1108Google Scholar
  18. 18.
    J.A. Moreto, D.B.V. De Castro, L.D.O. Bueno, and H.D.A. Ponte, Correlação de Dados de Tração a Quente e Fluência Para a Liga Kanthal A1, Rev. Esc. Minas, 2011, 64(2), p 181–186CrossRefGoogle Scholar
  19. 19.
    P.R. Sreenivasan, Hot-Tensile Data and Creep p Properties Derived there-from for 316L (N) Stainless Steel with Various Nitrogen Contents, Procedia Eng., 2013, 55, p 82–87CrossRefGoogle Scholar
  20. 20.
    American Welding Society, Specification for Low-Alloy Steel Electrodes for Flux Cored Arc Welding, ANSI/AWS A5.29/A5.29M:2010, American Welding Society, Miami, 2010Google Scholar
  21. 21.
    ASTM International, Standard specification for seamless ferritic and austenitic alloy-steel boiler, superheater, and heat-exchanger tubes, ASTM A213/A213 M-17, ASTM International, West Conshohocken, 2017Google Scholar
  22. 22.
    ASTM International, Standard specification for seamless ferritic alloy-steel pipe for high-temperature service, ASTM A335/A335 M-15a, ASTM International, West Conshohocken, 2015Google Scholar
  23. 23.
    ASTM International, Standard test methods for notched bar impact testing of metallic materials, ASTM E23-16b, ASTM International, West Conshohocken, 2016Google Scholar
  24. 24.
    R.G. Faulkner, J.A. Williams, E.G. Sanchez, and A.W. Marshall, Influence of Co, Cu and W on Microstructure of 9%Cr Steel Weld Metals, Mater. Sci. Technol., 2003, 19(3), p 347–354CrossRefGoogle Scholar
  25. 25.
    V.T. Paul, S. Saroja, P. Hariharan, A. Rajadurai, and M. Vijayalakshmi, Identification of Microstructural Zones and Thermal Cycles in a Weldment of Modified 9Cr-1Mo Steel, J. Mater. Sci., 2007, 42(14), p 5700–5713CrossRefGoogle Scholar
  26. 26.
    P. Mayr, T.A. Palmer, J.W. Elmer, E.D. Specht, and S.M. Allen, Formation of Delta Ferrite in 9 wt Pct Cr Steel Investigated by In-Situ X-ray Diffraction Using Synchrotron Radiation, Metall. Mater. Trans. A Phys. Metall. Mater. Sci., 2010, 41(10), p 2462–2465CrossRefGoogle Scholar
  27. 27.
    F. Abe and M. Tabuchi, Microstructure and Creep Strength of Welds in Advanced Ferritic Power Plant Steels, Sci. Technol. Weld. Join., 2004, 9(1), p 22–30CrossRefGoogle Scholar
  28. 28.
    K. Kaneko, S. Matsumura, A. Sadakata, K. Fujita, W.J. Moon, S. Ozaki, N. Nishimura, and Y. Tomokiyo, Characterization of Carbides at Different Boundaries of 9Cr-Steel, Mater. Sci. Eng., A, 2004, 374(1–2), p 82–89CrossRefGoogle Scholar
  29. 29.
    M. Taneike, F. Abe, and K. Sawada, Creep-Strengthening of Steel at High Temperatures Using Nano-Sized Carbonitride Dispersions, Nature, 2003, 424(6946), p 294–296CrossRefGoogle Scholar
  30. 30.
    M.A. Yescas and P.F. Morris, Improved Creep Resistance of Steel 92 by the Use of Modified Heat Treatments, in ECCC Creep Conference, 2005Google Scholar
  31. 31.
    K. Tokumo, K. Hanada, R. Uemori, T. Takeda, and K. Itoh, A Complex Carbonitride of Niobium Ans Vanadium in 9% Cr Ferritic Steel, Scr. Mater., 1991, 25(4), p 871–876CrossRefGoogle Scholar
  32. 32.
    K. Hamada, K. Tokuno, Y. Tomita, H. Mabuchi, and K. Okamoto, Effects of Precipitate Shape on High Temperature Strength of Modified 9Cr-1 Mo Steels, ISIJ Int., 1995, 35(1), p 86–91CrossRefGoogle Scholar
  33. 33.
    M. Hättestrand and H.-O. Andrén, Boron Distribution in 9–12% Chromium Steels, Mater. Sci. Eng., A, 1999, 270(1), p 33–37CrossRefGoogle Scholar
  34. 34.
    T. Horiuchi, M. Igarashi, and F. Abe, Improved Utilization of Added B in 9Cr Heat-Resistant Steel Containing W, ISIJ Int., 2002, 42(Supplement), p S67–S71CrossRefGoogle Scholar
  35. 35.
    K. Coleman and W. Newell, P91 and Beyond, Weld. J. N. Y., 2007, 86, p 29–33Google Scholar
  36. 36.
    G. Sainath, B.K. Choudhary, J. Christopher, E. Isaac Samuel, and M.D. Mathew, Effects of Temperature and Strain Rate on Tensile Stress-Strain and Workhardening Behaviour of P92 Ferritic Steel, Mater. Sci. Technol., 2014, 30(8), p 911–920CrossRefGoogle Scholar
  37. 37.
    D.J. Michel, J. Moteff, and A.J. Lovell, Substructure of Type 316 Stainless Deformed in Slow Tension at Temperatures between 21° and 816 °C, Acta Metall., 1973, 21, p 1269–1277CrossRefGoogle Scholar
  38. 38.
    B.P. Kashyap, K. McTaggart, and K. Tangri, Study on the Substructure Evolution and Flow Behaviour in Type 316L Stainless Steel over the Temperature Range 21–900 °C, Philos. Mag. A, 1988, 57(1), p 97–114CrossRefGoogle Scholar
  39. 39.
    J.W. Edingtont and R.E. Smallman, The Relationship Between Flow Stress and Dislocation in Deformed Vanadium, Acta Metall., 1964, 12, p 1313–1328CrossRefGoogle Scholar
  40. 40.
    D.J. Dingley and D. McLean, Components of Iron, Acta Metall., 1967, 15, p 885–901CrossRefGoogle Scholar
  41. 41.
    A.M. Garde, A.T. Santhanam, and R.E. Reed-Hill, The Significance of Dynamic Strain Aging in Titanium, Acta Metall., 1972, 20(2), p 215–220CrossRefGoogle Scholar
  42. 42.
    J.G. Morris, Dynamic Strain Aging in Aluminum Alloys, Mater. Sci. Eng., 1974, 13(2), p 101–108CrossRefGoogle Scholar
  43. 43.
    S. Okamoto, D.K. Matlock, and G. Krauss, The Transition from Serrated to Non-Serrated Flow in Low-Carbon Martensite at 150 °C, Scr. Metall. Mater., 1991, 25(1), p 39–44CrossRefGoogle Scholar
  44. 44.
    G.B. Holloway, Z. Zhang, and A. Marshall, Properties of T/P92 CrMo Weld Metals for Ultra Super Critical (USC) Power Plant, Int. J. Microstruct. Mater. Prop., 2011, 6(1/2), p 20–39Google Scholar

Copyright information

© ASM International 2018

Authors and Affiliations

  1. 1.School of EngineeringNational University of Lomas de ZamoraLomas de ZamoraArgentina
  2. 2.Materials and Structures Laboratory, INTECIN, School of EngineeringUniversity of Buenos AiresBuenos AiresArgentina
  3. 3.National Council of Scientific and Technical ResearchBuenos AiresArgentina
  4. 4.Metrode Products Ltd.ChertseyUK
  5. 5.Argentine Siderurgy InstituteBuenos AiresArgentina

Personalised recommendations