The effects of tungsten addition on the microstructural stability of 9Cr–Mo Steels

• Published in: Journal of nuclear materials 2001-02, Vol.288 (2), p.202-207
• Main Authors: Hong, S.G., Lee, W.B., Park, C.G.
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Installations for energy generation and conversion: thermal and electrical energy
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/S0022-3115(00)00558-4

The effects of tungsten addition on the microstructure and high-temperature tensile strength of 9Cr–Mo steels have been investigated by using three different steels: M10 (9Cr–1Mo), W18 (9Cr–0.5Mo–1.8W), and W27 (9Cr–0.1Mo–2.7W) steels. The tungsten-added 9Cr steels have revealed better high-temperature tensile strength. Microchemical analysis for (Cr,Fe) 2 (C,N) revealed that the tungsten addition increased the Cr/Fe ratio, which resulted in the lattice expansion of (Cr,Fe) 2 (C,N), and then the enhanced pinning effect on the glide of dislocation. In addition, in M10 steel, the M 23C 6 carbides quickly grew and agglomerated, while the tungsten-added 9Cr steels revealed a fine and uniform distribution of M 23C 6 carbides. Dislocation recovery during tempering treatments was delayed in tungsten-added 9Cr steels, which was correlated with the stabilized precipitates and the decreased self-diffusivity of iron. It is, thus, believed that the excellent high-temperature tensile strength of tungsten-added 9Cr steels is attributed to the stabilized M 2X carbo-nitrides and M 23C 6 carbides and the decreased self-diffusivity of iron.