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Abstract

A powder metallurgical 10%Cr steel containing molybdenum, tungsten, vanadium, niobium, and boron was studied. Results from tensile, impact, and creep rupture tests are reported. The alloy studied had a considerably higher creep resistance than the standard steel X 21 CrMoV12 1. After tempering, the microstructure consisted of tempered martensite with M₂₃ C₆ and M₂N precipitates at grain and lath boundaries and inhomogeneously distributed disc shaped fine MX precipitates a few nanometers thick and 5–20 nm in diameter. Boron was found inside the M₂₃ C₆ precipitates after tempering and after creep testing at 600°C. Laves phase (Fe,Cr)₂(Mo,W) precipitated at grain and lath boundaries during creep. Atom probe analyses of the matrix in the tempered and creep tested material indicated the presence of very small precipitates rich in chromium, vanadium, iron, and nitrogen. A latent creep resistance of the material, giving rise to a dynamic nucleation of small precipitates at dislocations, is suggested.

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Microstructure and mechanical properties of a 10% chromium steel with improved creep resistance at 600°C

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