This invention relates to the fields of ultrapure stainless steel
smelting,
nitrogen removal from
molten steel, and
steelmaking heat balance. A method for
smelting ultrapure 409 series steel using AOD (Alkali
Oxide) includes the following steps: Step 1: After the
blast furnace hot iron undergoes three
decarburization treatments to achieve P≤0.025%, AOD is added for carbon removal; Step 2: In the initial stage of
decarburization,
inert gas is blown from the side of the AOD to remove
dissolved nitrogen from the
molten steel using CO generated from the carbon-
oxygen reaction; Step 3: When the carbon content in the
molten pool decreases to 0.3-0.4%, the
molten pool temperature is corrected by measuring the temperature of the
molten steel in the furnace using a secondary lance, and the total amount of
ferrosilicon to be added is calculated based on the measured temperature and the total
oxygen blowing volume; Step 4: During the
decarburization period, the
slag basicity is controlled at 1.8-2.0, and the amount of
lime added = total
metal content *
silicon content * 2.14 * 2.0 / 0.85. No more
lime is added after the temperature rises following the addition of
ferrosilicon; Step 5: After sampling to confirm the composition of the molten steel, the temperature and composition of the molten steel are adjusted. At the end of the
oxidation process, the temperature of the
molten pool is rapidly increased to 1700-1720℃ by adding
ferrosilicon, so as to achieve preferential oxidation of carbon and
chromium, thus achieving decarburization and
chromium preservation and improving
chromium yield.