Effect of aging temperature on the microstructures and mechanical properties of ZG12Cr9Mo1Co1NiVNbNB ferritic heat-resistant steel

Abstract

The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9Mo1Co1NiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercritical power plant. The results show that the main precipitates during aging are Fe(Cr, Mo)₂₃C₆, V(Nb)C, and (Fe₂Mo) Laves in the steel. The amounts of the precipitated phases increase during aging, and correspondingly, the morphologies of phases are similar to be round. Fe(Cr, Mo)₂₃C₆ appears along boundaries and grows with increasing temperature. In addition, it is revealed that the martensitic laths are coarsened and eventually happen to be polygonization. The hardness and strength decrease gradually, whereas the plasticity of the steel increases. What’s more, the hardness of this steel after creep is similar to that of other 9%–12%Cr ferritic steels. Thus, ZG12Cr9Mo1Co1NiVNbNB can be used in the project.

Keywords

heat resistant steel / aging temperature / precipitates / microstructure / mechanical properties

References

[1] Hu P. Development of materials used for supercritical and ultra-supercritical boilers. Electr. Power Construct., 2005, 26(6): 26.

[2] Wu C.L. Suggestions for choice of material for high temperature pipes of 1000 MW class ultra supercritical sets. Power Equip., 2005, 2, 104.

[3] Gupta G., Ampornrat P., Ren X., Sridharan K., Alien T.R., Was G.S. Role of grain boundary engineering in the SCC behavior of ferritic-martensitic alloy HT-9. J. Nucl. Mater., 2007, 361(2-3): 160.

[4] Vaillant J.C., Vandenberghe B., Hahn B., Heuser H., Jochum C. T/P23, 24, 911 and 92: new grades for advanced coal-fired power plants — properties and experience. Int. J. Pressure Vessels Piping, 2008, 85(1-2): 38.

[5] Wang Y.F., Zheng K.Y., Wu Z.Y., Wang Q.J. Mechanical properties and microstructure stability of T92 steel tubes after long-term exposure to high temperature. Chin. J. Power Eng., 2010, 30(4): 245.

[6] Nie M., Zhang J., Huang F., Wu C., Ou-yang L.Z. Research progress of T/P92 heat-resistant steels. Heat Treat. Met., 2013, 38(11): 40.

[7] Bao H.S., Cheng S.C., Liu Z.D., Tan S.P. Aging precipitates and strengthening mechanism of T122 boiler steel. J. Iron Steel Res. Int., 2010, 17(2): 67.

[8] Abe F. Bainitic and martensitic creep-resistant steels. Curr. Opin. Solid State Mater. Sci., 2004, 8(3-4): 305.

[9] Lee J.S., Armaki H.G., Maruyama K., Muraki T., Asahi H. Causes of breakdown of creep strength in 9Cr–1.8W–0.5Mo–VNb steel. Mater. Sci. Eng. A, 2006, 428(1-2): 270.

[10] Kushima H., Kimura K., Abe F. Degradation of Mod.9Cr–1Mo Steel during long-term creep deformation. Tetsu-to-Hagane, 1999, 85(11): 841.

[11] Danielsen H.K., Hald J. Behaviour of Z phase in 9–12%Cr steels. Energy Mater., 2006, 1(1): 49.

[12] Ghassemi-Armaki H., Chen R.P., Maruyama K., Igarashi M. Contribution of recovery mechanisms of microstructure during long-term creep of Gr.91 steels. J. Nucl. Mater., 2013, 443(1-3): 23.

[13] Xu L.Q., Zhang D.T., Liu Y.C., Ning B.Q., Yan Z.X., Li H.J. Precipitation behavior and martensite lath coarsening during tempering of T/P92 ferritic heat-resistant steel. Int. J. Miner. Metall. Mater., 2014, 21(5): 438.

[14] Barraclough D.R., Gooch D.J. Effect of inadequate heat treatment on creep strength of 12Cr–Mo–V steel. Mater. Sci. Technol., 1985, 1(11): 961.

[15] Ha V.F., Jung W.S. Creep behavior and microstructure evolution at 750°C in a new precipitation-strengthened heat-resistant austenitic stainless steel. Mater. Sci. Eng. A, 2012, 558, 103.

[16] Kneževic V., Balun J., Sauthoff G., Inden C., Schneider A. Design of martensitic/ferritic heat-resistant steels for application at 650°C with supporting thermodynamic modelling. Mater. Sci. Eng. A, 2008, 477(1-2): 334.

[17] Panait C.G., Zielinska-Lipiec A., Koziel T., Czyrska- Filemonowicz A., Gourgues-Lorenzon A.F., Bendick W. Evolution of dislocation density, size of subgrains and MX-type precipitates in a P91 steel during creep and during thermal aging at 600°C for more than 100,000 h. Mater. Sci. Eng. A, 2010, 527(16-17): 4062.

[18] Abe F. Analysis of creep rates of tempered martensitic 9%Cr steel based on microstructure evolution. Mater. Sci. Eng. A, 2009, 510-511, 64.

[19] Li Q. Precipitation of Fe2W Laves phase and modeling of its direct influence on the strength of a 12Cr–2W steel. Metall. Mater. Trans. A, 2006, 37(1): 89.

[20] Maruyama K., Sawada K., Koike J. Strengthening mechanisms of creep resistant tempered martensitic steel. ISIJ Int., 2001, 41(6): 641.

[21] Muneki S., Okada H., Igarashi M., Abe F. Creep characteristics in carbon free new martensitic alloys. Mater. Sci. Eng. A, 2005, 406(1-2): 43.

[22] Dimmler G., Weinert P., Kozeschnik E., Cerjak H. Quantification of the Laves phase in advanced 9–12% Cr steels using a standard SEM. Mater. Charact., 2003, 51(5): 341.

[23] Ning B.Q., Yan Z.S., Fu J.C., Bie L.J., Liu Y.C. New strengthening methods of T91 ferritic heat resistant steel. Mater. Rev., 2009, 23(4): 72.

[24] Abe F., Horiuchi T., Taneike M., Sawada K. Stabilization of martensitic microstructure in advanced 9Cr steel during creep at high temperature. Mater. Sci. Eng. A, 2004, 378(1-2): 299.

[25] Yu J.Y. The Study on the Microstructure and Properties of 9–12%Cr Ferritic/Martensitic Heat Resistant Steels [Dissertation], 2008 10.