Laves-phase evolution during aging in 9Cr-1.8W-0.5Mo-VNb steel for USC power plants

Abstract

-Laves-phase precipitation and coarsening of tungsten strengthened 9% Cr steel under thermal aging at 923K up to 8000 h was reported in this paper, where the information of the evolution of mean particle size, the number density, the volume fraction of Laves-phase precipitates and the partition coefficients of W and Mo in the matrix over the aging time were determined. The change of hardness over time was also measured. The main results of this investigation were: 1) Laves-phase nucleates and grows rapidly on grain boundaries and lath boundaries within the first 1,500 h of aging time; 2) the coarsening of Laves-phase is much faster than that of M 23 C 6 carbides, meanwhile it demonstrates the two stages characteristics and kinetics of Laves-phase nucleation and growth which were determined experimentally; 3)The precipitation of Laves-phase produces a pronounced matrix depletion of W and Mo atoms; and 4) The precipitated Laves-phase gives rise to weaker precipitation strengthening in comparison with M 23 C 6 carbides, and causes the loss of hardenss and creep strength due to the Corresponding author. Tel.: +86 13554693820; fax: +86 02768772253. E-mail address: wxue2011@whu.edu.cn (Xue Wang) 2 depletion of Mo and W from the solid solution. This paper contributes to the knowledge of kinetics of Laves-phase precipitation and coarsening, as well as understanding the creep damage broadly.

The effect of inclusions on the high‐temperature low‐cycle fatigue performance of cast MarBN: Experimental characterisation and computational modelling

“…The tensile hold period allows deeper penetration of the oxide within the sample, and inclusions are again shown to influence crack initiation and propagation, as well as oxide pit formation. Backscatter electron SEM has been used to identify Laves phase in tungsten‐containing steels, because of the high atomic weight of tungsten resulting in a high contrast between the particles and matrix. It is conjectured that regions of Laves phase (Fe 2 W) have formed along grain boundaries in the post‐test MarBN samples as a result of high temperature loading.…”

“…These are observed close to the surface and near regions of cracking and oxidation; the high concentration of W in these particles, which commonly grow along grain boundaries, indicates that absorption into the oxide layer would result in reduced strengthening. The precipitation hardening effect of boron‐enriched M 23 C 6 carbides along boundaries is considered to be the primary strengthening mechanism in modified 9Cr steels, and is further enhanced through the addition of W; however, Laves phase particles (Fe 2 W) are prone to coarsening during prolonged high‐temperature exposure . In P92 steel, these particles have been identified as significant contributors to precipitate strengthening, as particles reach a similar saturated size to M 23 C 6 carbides in less than 10 000 hours .…”

Evolution of Microstructures and Mechanical Properties of Zr-Containing Y-CLAM During Thermal Aging

“…However, further nucleation was not possible because of the absence of a suitable nucleation location, which would result in a rapid decay in the nucleation rate. Furthermore, the segregation of W at the grain boundaries would accelerate Laves phase precipitation [24].…”

Cyclic behaviour of 12% Cr ferritic‐martensitic steel upon long‐term on‐site service in power plants

“…The decrease of hardness is due to the lower dislocation density and coarsening of carbides, 44,45 and it can be inferred that lower dislocation density and depletion of solid-solution elements solubility result in the softening behaviour during the cyclic loading. The decrease of hardness is due to the lower dislocation density and coarsening of carbides, 44,45 and it can be inferred that lower dislocation density and depletion of solid-solution elements solubility result in the softening behaviour during the cyclic loading.…”

“…(2) the solid-solution strengthening elements such as Cr and Mo; and (3) the precipitated strengthening carbides such as M 23 C 6 at grain/lath boundaries and MX in the grains. The decrease of hardness is due to the lower dislocation density and coarsening of carbides, 44,45 and it can be inferred that lower dislocation density and depletion of solid-solution elements solubility result in the softening behaviour during the cyclic loading. As for the as-received sample, the hardness at the grain boundary is higher than that in the matrix, which is mainly due to the precipitated carbides at boundaries.…”