Materials Chemistry and Physics, Vol.163, 219-228, 2015
Laves-phase evolution during aging in 9Cr-1.8W-0.5Mo-VNb steel for USC power plants
Long term precipitation and coarsening of Laves-phase in tungsten strengthened 9% Cr steel under thermal aging at 923 K was investigated and reported in this paper. It experimentally measured the evolution of mean particle size, the number density, the volume fraction of Laves-phase precipitates, the partition coefficients of W and Mo in the matrix, as well as the change of hardness. Its main conclusions were: 1) Laves-phase nucleates and grows rapidly on grain boundaries and lath boundaries within the first 1500 h of aging time; 2) The two stages characteristics and kinetics of Laves-phase nucleation and growth which were determined experimentally; 3) The coarsening of Loves-phase is much faster than that of M23C6 carbides; 4) The precipitation of Laves-phase produces a pronounced matrix depletion of W and Mo atoms; and 5) The precipitated laves-phase gives rise to weaker precipitation strengthening in comparison with M23C6 carbides, and causes the loss of hardness due to the depletion of Mo and W from the solid solution. This paper contributes to the knowledge of kinetics of Laves-phase precipitation and coarsening, providing the essential information for comparative investigation of creep damage mechanisms. This paper also contributes to the understanding the creep damage broadly. (C) 2015 Elsevier B.V. All rights reserved.