Low-carbon ultralow-sulfur pure iron smelting method

The invention relates to a low-carbon ultralow-sulfur pure iron smelting method. The process route comprises the steps of molten iron pretreatment, converter double-slag smelting, RH decarburization, LF dephosphorization, molten steel slagging-off, LF desulfurization and continuous casting. The method specifically comprises the following steps: 1) molten iron pretreatment desulfurization: the S content of molten iron before pretreatment is less than or equal to 0.040%; s is required to be less than or equal to 0.002% after molten iron pretreatment desulfurization; (2) converter double-slag smelting is carried out to control resulfurization, specifically, special pure iron waste steel is added into a converter, oxygen blowing is started, a slagging material is added after oxygen blowing is carried out for 40-50 s, oxygen blowing is carried out for 4-5 min, the oxygen accumulation amount of oxygen blowing is 3500-4500 standard cubic meters, and a gun is lifted to discharge slag; 3) LF desulfurization: after mol