Effects of Multiple Reductions on Grain Refinement During Hot Working of Alloy 718.

摘要

The simulation of microstructural evolution during primary breakdown of production sized alloy 718 ingots by radial forging was accomplished via multiple stroke axial compression testing of cylindrical specimens taken from a wrought and heat treated bar with a 254 mu m grain size. Four stroke compression heat sequences were performed at a constant true strain rate of 1.0 s (sup -1) and at temperatures of 950C, 1050C, and 1150C. The applied strain per stroke for each four stroke sequence was either 0.14 to 0.23. Static, rather than dynamic, recrystallization was found to be responsible for the observed grain size refinement and its repetitive occurrence during back to back dwell periods resulted in the maintenance of a fine grain microstructure during multiple pass deformation sequences. In order of importance, the critical hot working parameters for recrystallization are temperature, dwell time between passes, and strain per pass. Microstructure was found to vary with work piece position, simulated by the applied sequence of dwell periods. 9 refs., 17 figs., 7 tabs.