Microstructure and Deformation Behavior of a Hot Forged 9%Cr Creep Resistant Steel

Abstract:

The tempered microstructure and the creep behaviour were studied in an ultra low carbon 9%Cr martensitic creep resistant steel. The starting material was forged at 1050°C followed by air cooling and then tempered at a temperature of 750°C for 3 hours. This treatment resulted in the mean transverse lath size of about 240 nm; the dislocation density in lath interiors comprised 4 × 10¹⁴ m^-2. The tempered martensite lath structure (TMLS) is characterised by homogeneous precipitation of numerous MX-type carbonitrides and a small amount of relatively coarse M₂₃C₆–type carbides. Three kinds of MX carbonitrides were observed in the tempered lath martensite structure. Those were plate-shaped particles with longitudinal size of about 15 nm and thickness of 3 nm; round-shaped particles of about 10 nm in diameter; and relatively large almost equiaxed particles with mean size of about 90 nm. The large MX particles were resulted from incomplete dissolution of such carbonitrides at 1050°C, while the nanoscale particles homogeneously precipitated during the tempering. The creep tests conducted at 650°C showed that the studied steel demonstrated superior creep resistance. Namely, the rupture time was about an order as long as that for P92-type creep resistant steel.

• Periodical: Advanced Materials Research (Volume 409)
• Pages: 672-677
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.409.672
• Online since: November 2011
• Authors: Irina Fedorova, Zhanna Yanushkevich, Andrey Belyakov, Rustam Kaibyshev
• Keywords: Creep Resistance, Dispersion Strengthening, Second Phase Precipitates, Tempered Lath Martensite

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