EFFECT OF SUBGRAIN BOUNDARIES ON THE STATE OF SUPERCOOLED AUSTENITE

The dislocation walls composing the low-angle boundaries (theta less t han or equal to 20 deg), acting as hydrodynamic funnels which are fill ed with carbon atoms due to the drift of these atoms in the attractive -force field are considered. The effects of misorientation angle on th e amount of carbon going to the dislocation wall from the adjacent zon e of the action of forces, on the time necessary for the saturation of subgrain boundary, and on the width of decarburized zone austenite ar e calculated. The time of the saturation of subgrain boundaries with c arbon is shown to be dependent on misorientation angle and temperature . Three stages of this process are revealed. The first stage accomplis hed for 2 . 10(-6) a at 620 degrees C for theta = 10 deg results in ma ximum nonuniformity and instability of austenite. The extent of nonuni formity decreases with increasing isothermal-treatment time.