Journal of Phase Equilibria and Diffusion

, Volume 27, Issue 1, pp 102–112 | Cite as

Design criteria for high-temperature steels strengthened with vanadium nitride

  • V. A. Yardley
  • Y. de Carlan
Basic and Applied Research: Section I


Fe-8-12Cr ferritomartensitic steels are widely used in the power generation, petrochemical and nuclear industries where they are subject to high operating temperatures and stresses. Resistance to creep deformation is therefore a critical materials property. One method of providing creep resistance is to precipitate a fine homogeneous distribution of vanadium nitride (VN) particles in the matrix. Maximizing this precipitation hardening effect requires a high nitrogen content, but this could cause gas bubble formation during conventional fabrication processes. It is therefore necessary to determine how much N can be added without encountering such problems. Phase stability calculations, using Thermo-Calc, were carried out to find high-N compositions to optimize the fraction of VN and the fabrication route for obtaining fine particles. Several experimental compositions, including nine high-nitrogen alloys, were fabricated as ingots; out of these, two exhibited porosity Thermo-Calc predicts that, in all of the high-nitrogen alloys, nitrogen gas is a stable phase around the solidus temperature. It is evident that porosity cannot simply be predicted from the presence of the gas phase on the equilibrium diagram. However, detailed analysis of the equilibrium phases predicted in these alloys, including their variation with composition, allowed a porosity criterion to be obtained. This criterion links porosity formation to the nature of the liquid-to-solid transformation. Further calculations were carried out to predict the dependence of gas phase evolution on both composition and pressure. Thermodynamic calculations are a valuable tool for the design of these industrially important alloys. Input from experimental data has enabled the refinement of the initial design criteria such that it should now be possible to propose compositions with high VN hardening but without the risk of porosity.


nitrogen phase diagrams porosity steel thermody-namics vanadium 


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  1. 2002And: J-O Andersson, T. Helander, L. Hoglund, P. Shi, and B. Sundman, THERMO-CALC & DICTRA, Computational Tools For Materials Science, Calphad, 2002, 26 (2), p 273–312CrossRefGoogle Scholar
  2. 1991Bra: J-C. Brachel, Martensitic 9Cr-1Mo Alloys: Effects of Nitrogen, Niobium and Vanadium Additions on the Microstructure, Phase Transformations and Mechanical Properties, Ph.D. Thesis, Université de Paris-Sud, Paris, France, 1991, in FrenchGoogle Scholar
  3. 2004Car: Y. de Carlan, M. Murugananth, T. Sourmail, and H.K.D.H. Bhadeshia, Design of New Fe-9CrWV Reduced-Activation Martensitic Steels for Creep Properties at 650°C, J. Nucl. Mater., 2004, Vol 329–333, p 238–244CrossRefGoogle Scholar
  4. 2002Dav: R.H. Davies A.T. Dinsdale, J.A. Gisby, J.A.J. Robinson, and S.M. Martin. MTDATA—Thermodynamic and Phase Equilibrium Software from the National Physical Laboratory, Calphad 2002, 26 (2), p 229–271CrossRefGoogle Scholar
  5. 1993Eva: R.W. Evans and B. Wilshire, Introduction to Creep, Oakdale Publishing Company for The Institute of Materials, 1993Google Scholar
  6. 2004Har: M. Harzenmoser, Review: Welding of High Nitrogen Steels, Materials and Manufacturing Processes, 2004, 19 (1), p 75–86CrossRefGoogle Scholar
  7. 1995Hon: R.W.K. Honeycombe and H.K.D.H. Bhadeshia, Steels: Microstructure and Properties (2nd ed.), Edward Arnold, 1995, p 6Google Scholar
  8. 1992Por: D.A. Porter and K.E. Easterling, Phase Transformations in Metals and Alloys, 2nd ed., Chapman and Hall, 1992Google Scholar
  9. 2004Rab: V. Rabeau, Y. de Carlan, and V.A. Yardley, Commissariat à l'Energie Atomique, Centre d'Etudes de Saclay, SRMA, Bât 453, 91 191 Gif Sur Yvette Cedex, France, unpublished work, 2004Google Scholar
  10. 2004Shi: P. Shi, Ed.. Thermo-Calc Software Users' Guide, Version Q, 2004, Foundation of Computational Thermodynamics, Stockholm, Sweden, p 336–342Google Scholar
  11. 2001Toi: M. Du Toit, The Behaviour of Nitrogen during the Autogenous ARC Welding of Stainless Steel Ph.D. Thesis, University of Pretoria, South Africa, 2001, Scholar
  12. 2004Yar: V.A. Yardley, Commissariat à l'Energie Atomique, Centre d'Etudes de Saclay, SRMA, Bât 453, 91 191 Gif Sur Yvette Cedex, France, unpublished work, 2004Google Scholar

Copyright information

© ASM International 2006

Authors and Affiliations

  • V. A. Yardley
    • 1
  • Y. de Carlan
    • 1
  1. 1.Commissariat à l'Energie Atomique, Center d'Etudes de SaclaySRMAFrance

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