Learn details of VOD smelting stainless steel denitrification method

VOD furnace smelting stainless steel requirements

The requirements for smelting raw materials and equipment for the method of smelting stainless steel in a vacuum oxygen decarburization refining furnace are as follows:

1. The nitrogen content of the stainless steel molten steel of the vacuum oxygen blowing decarburization refining furnace is not more than 500ppm, and the carbon content is more than or equal to 0.30%;

2. The temperature of molten steel before the treatment of the vacuum oxygen-blown decarburization refining furnace is not less than 1590℃, the slag thickness is not more than 40mm, and the distance from the slag liquid level of the ladle of the vacuum oxygen-blown decarburization refining furnace to the upper edge of the ladle wall is not less than 1250mm, according to the specific vacuum For oxygen-blown decarburization refining furnace equipment, adjust this distance requirement.

VD furnace smelting stainless steel method

1. Pour the stainless steel molten steel before treatment into the ladle of the vacuum oxygen-blown decarburization refining furnace, and vacuumize it. When the vacuum degree reaches 150-200torr, oxygen blows into the ladle.

2. Oxygen blowing amount m3=0.8×weight of molten steel (kg)×percentage of Si in molten steel+30 for desiliconization, stop blowing oxygen, turn on the bottom blowing argon to the maximum, generally require more than 1000NL/min, and improve the vacuum degree at the same time To not less than 5torr, boil for more than 8 minutes, carry out the first boiling denitrification, and decarbonize.

3. After boiling, the vacuum oxygen-blown decarburization refining furnace continues to blow oxygen and decarburize, and at the same time gradually increase the vacuum degree and reduce the pressure in the furnace. When the decarburization reaches the target, that is, when the national stainless steel standard or use requirements are met, the vacuum degree is 20-40torr .

4. Stop the oxygen blowing, pump the vacuum degree in the vacuum oxygen blowing decarburization refining furnace to below 5torr, blow argon from the bottom of the vacuum oxygen blowing decarburization refining furnace, and make the stainless steel water boil for more than 8 minutes. Carry out the second deoxygenation and decarburization.

5. After boiling, the vacuum degree should be controlled below 10torr, the bottom blowing argon should be exhausted, the equipment capacity of the decarburization refining furnace should be maximized, and lime and fluorite should be added. According to the chemical composition of molten steel at this time, chromium oxide is reduced according to silicon. The formula derived from the chemical reaction equation calculates the amount of ferrosilicon added, adding ferrosilicon or aluminum, and adding 80-150kg aluminum for some steel grades. Ferrosilicon or aluminum mainly reduces chromium oxide in slag. The reduction reaction principle and calculation formula are as follows: Calculated amount of ferrosilicon containing 75% of silicon = 1.67 × (total oxygen blown in m3-0.933 × initial carbon content of molten steel × initial molten steel Weight kg-0.8 × initial silicon content of molten steel × initial weight of molten steel kg) + weight of molten steel kg × silicon content of product molten steel required ÷ 0.75 Keep the vacuum time longer than 10 minutes.

6. After that, turn off the vacuum blowing oxygen decarburization refining furnace, blow argon gas at the bottom, blow nitrogen gas at the top to break the vacuum.

7. Open the vacuum cover, sample and test the composition of stainless steel water. When it meets the requirements, tap and pour. If the composition and temperature do not meet the requirements, you can go to other refining equipment in the ladle refining furnace to refine according to conventional smelting methods.

Vacuum oxygen decarburization smelting stainless steel advantages

Vacuum oxygen decarburization refining furnace smelting stainless steel denitrification method, the carbon content of stainless steel water before treatment in vacuum oxygen decarburization refining furnace is required to be controlled at more than 0.30%, after oxygen desiliconization, carbon, oxygen content in molten steel. Under the condition of high temperature, the activity coefficient of nitrogen is increased, oxygen blowing is stopped, and the first high vacuum boiling denitrification can be carried out, which can reduce the nitrogen content in molten steel to below 100ppm. At the same time, argon is used in the decarburization period. Small amount, simple process, short smelting time, light splash, little damage to the equipment of vacuum oxygen-blown decarburization refining furnace, prolonging the service life of splash-proof cover of vacuum oxygen-blown decarburization refining furnace.