A method of improving the post-combustion heat recovery in a basic oxygen furnace by controllably forming a foamy slag. The foamy slag is generated by increasing the lance height and reducing the rate of lance height reduction during the oxygen blowing cycle. The foamy slag is controlled to prevent slopping by calculating the approximate starting point of the peak decarburization period for the charge and then adjusting the oxygen flow rate to be at a minimum at the commencement of the peak decarburization period.