Effect of heating rate and phase transformation on the dimensional control of ferrous PIM compacts

Powder injection molded (PIM) parts usually show large amounts of shrinkage after sintering due to the low powder loading, resulting in poor dimensional stability. This problem is further aggravated when a high shrinkage rate occurs or when the furnace temperature is not uniform. To alleviate this dimensional control problem, the effects of the phase transformation, sintering temperature, and heating rate were investigated. The results show that when an abrupt volume change occurs, as happens during the α → γ phase transformation of iron, the dimensional stability deteriorates. This problem gets worse when the density of the part is low. By slowing down the heating rate in the region where the high shrinkage rate occurs, avoiding the phase changes, and adding alloying elements to broaden the temperature range of the phase transformation, the dimensional control of ferrous PIM compacts can be improved.