Production method of rectangular flat steel with decarburized layer depth smaller than or equal to 0.3% thickness

The invention discloses a production method of rectangular flat steel with the depth of a decarburized layer smaller than or equal to 0.3% of the thickness, and belongs to the technical field of metallurgy. The method comprises the following steps: carrying out cold charging on an unpolished blank, closing an I section adding burner before the unpolished blank enters a furnace, and carrying out low-temperature heating by adopting a sectional heating process, wherein the temperature of a preheating section is less than or equal to 600 DEG C, the temperature of a heating section is 980-1030 DEG C, the temperature of a soaking section is 1010-1040 DEG C, the furnace pressure is micro-positive pressure, the heating mode is low-temperature rapid heating, the heating time is 150-350 minutes, and the residual oxygen of a heating furnace is less than or equal to 0.1%. After discharging, high-pressure water of 28 MPa or above is adopted for descaling, after rolling, through-water controlled cooling is adopted to reach