Precipitates and Particles Coarsening of 9Cr–1.7W–0.4Mo–Co Ferritic Heat-Resistant Steel after Isothermal Aging

Abstract

The precipitates obtained by EPE technology from the 9Cr-1.7W-0.4Mo-Co ferritic heat-resistant steel subject to isothermal aging were investigated using SEM, TEM and XRD. The particle size distribution and the coarsening kinetics of M₂₃C₆ with duration of isothermal aging were also analyzed with or without consideration of Laves phase. The results show that the isolated dislocations were detected in delta ferrite interior, and the precipitates on delta ferrite and martensite boundaries are obviously larger than other locations. Fe₂W-Laves phase can only be found as duration of aging time to 2000 h, and is preferential to form adjacent to M₂₃C₆ particles. The small M₂₃C₆ particles firstly coarsen, but the large M₂₃C₆ are relatively stable during short aging. The total coarsening rate of M₂₃C₆ precipitates is 9.75 × 10^-28m³s^-1, and the coarsening of M₂₃C₆ depends on the formation of Laves phase.