ABNORMAL GRAIN-GROWTH IN A MEDIUM-CARBON MICROALLOYED STEEL

An experimental study on the grain growth of a medium-carbon V-Ti micr oalloyed steel with two levels of AIN has been carried out. A system t o study grain-size distributions in order to detect the abnormal grain growth has been proposed. Log-normal distributions were verified and then properties of normal distributions were applied to distinguish no rmal and abnormal grains. The benefits of working with the relative di fference (RD) of grain size in order to compare the grain-growth behav iour have been discussed. It was experimentally concluded that abnorma l growth appears when RD is larger than 2.5. From the results a map of abnormal grain growth against time and temperature could be plotted. It was concluded that abnormal grain growth is due to the AlN dissolut ion when the above maps are correlated with the theoretical volume fra ction of precipitates. The importance and effect of heating rate have also been shown: high heating rates can produce abnormal growth at hig her temperatures than those of the equilibrium dissolution.