Effect of Fine Precipitation and Subsequent Coarsening of Fe_2W Laves Phase on the Creep Deformation Behavior of Tempered Martensitic 9Cr-W Steels

摘要

The effect of fine precipitation and subsequent coarsening of Fe_2W Laves phase on the creep deformation behavior was investigated for simple 9Cr-W steels containing 0, 1,2, and 4 wt pet W. After tempering, the specimens were subjected to creep tests at 823, 873, and 923 K for up to 15,000 hours. The precipitation of Fe_2W Laves phase takes place during creep at boundaries from the supersaturated solid solution of the high-W steels, the 9Cr-2W and 9Cr-4W steels, but not in the low-W steels, the 9Cr-OW and 9Cr-lW steels. The fine precipitation of Fe_2W Laves phase decreases the creep rate in the primary or transient creep region, while the subsequent large coarsening of Fe_2W Laves phase reduces the precipitation strengthening and promotes the acceleration of creep rate in the tertiary or acceleration creep region after reaching a minimum creep rate. The change in shape of creep rate curves with stress and temperature is explained by taking fine precipitation and subsequent coarsening of Fe_2W Laves phase into account.