Precipitation of Fe2W laves phase and modeling of its direct influence on the strength of a 12Cr-2W steel

Abstract

Precipitation of Fe 2 W Laves phase in a 12Cr-2W power plant steel is investigated by using transmission electron microscopy (TEM). Fe 2 W Laves phase is found to be coherent with the matrix and has a stacking fault structure. The influence of formation of Fe 2 W Laves phase on the yield strength of the steel is quantitatively evaluated. The modeling result indicates that the strengthening effect from the formation of Laves phase particles is diminished by the loss of solid solution strengthening of alloying elements, and, as a result, the strength of the steel remains similar. The effect of clustering and coarsening of Laves precipitates on the strength of the steel is also studied. It is showed that clustering and coarsening decreases the strengthening effect of Laves phase. The limitation of the modeling approach currently adopted is also discussed.

Relationship between Laves phase and the impact brittleness of P92 steel reevaluated

“…After aging at 600 °C for 500 h, a good amount of Laves phase in the P92 steel was in rod like shape. According to the previous study [13] , this rod like shape illustrated that Laves phase was still coherent to the matrix. With the increase of the aging time, both the amount and the size of Laves phase were obviously…”

“…Kunimitsu et al reported this phenomenon in 9Cr-2W, 9Cr-2Mo and 9Cr-4W steels [12] . Li has well reviewed this subject in his article [13] . In general, a conclusion can be drawn from all the above reports that impact brittleness happens when Laves phase forms during aging.…”

Effect of Tungsten on Creep Behavior of 9%Cr–3%Co Martensitic Steels

“…These carbides were replaced by more stable Laves phase under short-term creep as in other high-chromium martensitic steels [22].…”

“…These elements provide an effective solid solution strengthening [1]. It was shown [21] that addition of 1% W gives +35 MPa increase in the creep rupture strength at 600 • C for 1000 h. However, in contrast with cobalt, the tungsten and molybdenum have limited solubility within ferrite, and their excessive content leads to precipitation of such W-and Mo-rich particles as Laves phase Fe 2 (W,Mo) or M 6 C carbides [1,7,[9][10][11][12]22,23]. This depletion does not occur in the 9%Cr steel containing no or low amount of W [7].…”

Effect of Long-Term Creep on Microstructure of a 9% Cr Heat Resistant Steel

“…However, during long-term aging and creep the M 23 C 6 carbides and Laves phase most likely lose their coherency with ferritic matrix previously and these grain boundary particles coarsen up to nearly the same sizes in the both portions of specimen. The contribution of plastic deformation to coarsening of Laves phase is in acceleration of coherency loss of Fe 2 W particles, precipitated on the boundaries of packets and laths of martensite [4,8]. This process occurs quickly and difference between average sizes of Laves phase in grip and gauge portions is significant when the rupture time is less than 2 000 hours and volume fraction of Laves phase precipitated on high-angle boundaries is similar to that on low-angle boundaries [4].…”