The invention provides a production method of an ultra low
carbon steel. The method comprises the steps of: employing a blowing process for desulfurization and
slag removal of molten iron, with control of
oxygen blowing time and
smelting cycle of a converter,
argon bottom-blowing in the whole course, and control of S content in
slag lime, [C] content at converter end point, and temperature and
oxygen activity at the endpoint, adding
lime in a tapping process, and modifying
ladle top
slag after tapping; employing natural
decarburization to control carbon content in an RH, wherein Als in
molten steel is less than 0.03% after deoxidation, carrying out vacuum-breaking, adding aluminum
powder and top slag modifier into the top slag, blowing
argon with stirring, vacuumizing again, and carrying out clean circulation for 2-10 min; and carrying out
continuous casting with protective
casting in the whole course, wherein a
nitrogen increase amount in the
molten steel is controlled at less than 2 ppm. The invention can effectively reduce
temperature drop in a transmission process, reduce
oxygen blowing heating rate in a subsequent RH refining treatment, save energy and shorten the time of refining. Besides, the method can effectively guarantee modification effect of the top slag, prevent
nozzle clogging and realize sequence
casting. Therefore, the method is particularly applicable to the production of high purity ultra low
carbon steel.