A process for increasing the extent of afterburning of carbon monoxide formed during the decarburization of iron melts by the action of oxygen is presented. This process is accomplished by delivering a finely divided catalyst to the space above the iron bath. The catalyst may be comprised of any number of catalysts which promote carbon monoxide afterburning, and is preferably a metal oxide compound. The catalyst is preferably delivered via an oxygen blowing lance and effectively increases carbon monoxide afterburning even at very high temperatures.