The development of a global model for oxygen steelmaking and its validation against industrial data has been reported in Part 1 of this paper. Part 2 of this paper explained the model development of decarburization reaction of emulsified droplets and discussed the effects of bloating behaviour of metal droplets on the overall kinetics of the process. Part 3 of this paper focussed on the development of one sub-model on the decarburization reaction in the impact zone and critically evaluates the important process variables affecting the decarburization kinetics. Decarburization rates in the impact zone were calculated using the semi-empirical relationships developed from experimental results. Based on previous experimental studies, both diffusion through the gas phase and surface control were considered in the rate calculations. The model was validated against experimental data from Belton and Sain, and against plant data from Cicutti et al. The model developed was consistent with the experimental and plant data, and provided a reasonable basis for predicting the decarburization of iron in the impact region of oxygen steelmaking. The model predicted that the decarburization rate is sensitive to the partial pressure of carbon dioxide and oxygen in the impact zone. As the partial pressure of oxygen decreased from 26.4 to 16.2 kPa, the model predicted that that the reaction rate of decarburization via oxygen decreased from 202 to 134 kg/min. The model predicted that approx. 40% of decarburization takes place in the impact zone during the main blow.