Preliminary investigation of grain refinement in a U-0.2 wt % V alloy casting by true isothermal transformation at 516(degree)C

摘要

Laboratory-scale isothermal transformation from beta phase to alpha phase at 516 C was accomplished using one U-0.2 wt % V alloy composition and with specimens up to 7.6 mm in thickness. Gravity was used to transfer individual specimens from a furnace at 720 C to one at 516 C. The lower-temperature, furnace contained two copper blocks between which the specimens were quenched by contact. The furnace also contained a partial atmosphere of helium. Results duplicate those of Reisse et al. at this temperature. Their work was done on smaller samples. Grain sizes obtained were consistently ASTM 7 to 8 (20 to 30 (mu)m), indicating that the cooling rates at the center of even the thicker samples were adequate to miss the nose of the (upper) TTT curve. The microstructure obtained, including the grain size, appears to be equivalent to that obtained by carefully controlled wrought processing, but we believe these castings lack the strong crystallographic textures that exist in wrought products.