Our company's foundry workshop is mainly responsible for the production of major steel castings. The precision of castings is high and the equipment is relatively advanced. Especially in recent years, the company has developed a variety of ultra-low carbon stainless steel (ZG00Cr13Ni5MoRE) and low-phosphorus, low-sulfur cast steel, which is difficult to smelt. Therefore, how to achieve this in a short period of time with less consumption The goal becomes a big issue, and the carbon oxide gun is an effective means to achieve this goal. The following describes the working principle and process of the carbon oxide gun.
Principle of slagging
The foamed slag smelted in the electric furnace is generally formed in the late stage of melting and oxidation. The CO formed by the reaction of [C] and [O] in the steel or a certain amount of coke powder is sprayed into the slag, and the slag is reacted by oxygen. In the CO dispersion slag, the slag is foamed to achieve foaming of the slag.
Under the conditions of electric furnace smelting, the main sources of slag foaming gas are as follows:
The blown oxygen reacts with [C] to produce a carbon-oxygen reaction:
O 2 (g)=2[O]
[C]+[O]=CO(g)
The unstable oxide in the slag reacts with the carbon in the steel:
FeO + [C] = [Fe] + CO (g)
The unstable oxide in the slag reacts with the carbon in the slag:
FeO+C(s)=[Fe]+CO(g)
2. The role of foam slag
(1) The molten steel and steel slag splash in the arc zone is reduced during the submerged arc operation of the foamed slag.
(2) The foam slag submerged arc operation envelops the arc, reduces the noise generated by the arc, and reduces dust and arc light flicker.
(3) The use of foam slag operation can improve arc stability.
(4) Long arc foam slag operation can reduce power consumption and electrode consumption.
(5) The foaming slag requires higher decarburization and decarburization speeds during operation, and thus has a higher degassing effect and lowers the content of hydrogen and nitrogen in the molten steel.
(6) Increasing the input power and thermal efficiency, greatly reducing the heat radiated to the lining, and facilitating the homogenization of the heat of the furnace wall. When the foaming slag is not used, the thermal efficiency of the arc is about 40%; and the thermal efficiency of the arc after the carbonization of the foamed slag is increased to 70%, thereby accelerating the temperature rise of the molten steel, and the heating rate is doubled compared with the operation without the foaming slag. In the above, the smelting time is shortened, the life of the lining is increased, and the power consumption is reduced.
(7) Foam slag has a high reaction capacity, which expands the area of ​​slag steel, which is particularly beneficial for dephosphorization and desulfurization. At the same time, the electric furnace operation can slag while blowing oxygen, and the slag with high phosphorus content is removed to the outside of the furnace in time, which is also beneficial for dephosphorization. Due to the early addition of the bottoming lime and the high degree of foaming of the slag, the fluidity is good, and the oxygen and stirring of the steel liquid and the slag are continuously blown, the contact area of ​​the steel slag is greatly increased, which is favorable for the decarburization reaction of the oxidized slag. Due to the early addition of lime, the molten steel provides good conditions for dephosphorization at lower temperatures (the best dephosphorization effect of molten steel at 1500 ~ 1550 °C).
(8) Using foaming foaming slag operation, it can also be charged with oxygen, reduce power consumption, reduce the amount of pig iron used for carbon blending, allow a large increase in oxygen consumption without increasing the consumption of alloys, and have an alloy and steel yield. improve. After carbon injection, the FeO in the carbon reduction slag can well control the oxidization of the slag and the molten steel, and is favorable for oxidative tapping and refining outside the furnace. In addition, the combination of coke and oxygen-enriched operation, and carbonization by coke, can make the operation of molten oxygen mode, simplifying the control of carbon during oxidation period.
3. Slag control
The foamed slag is a slag of a fixed alkalinity range, which allows a submerged arc operation, and sufficient CO escapes from the molten metal pool to foam the slag, and the alkalinity of the slag is between 1.8 and 2.3 to form a foamed slag. The foam slag can surround the arc, improve the utilization of electric energy, prevent the arc from radiating to the lining, improve the service life of the lining, and prevent the molten steel from absorbing nitrogen. The slag formation in advance has a very important significance in the steelmaking production, and the phosphorus in the molten steel can be oxidized by more than 50% in advance. Phosphorus oxidation is a strong exothermic reaction. According to its reaction thermodynamics theory, it can inhibit dephosphorization under high temperature conditions. Therefore, it should take advantage of the low melting temperature (1500~1550 °C) to quickly form slag and increase slag. Quantity, dephosphorization as soon as possible.
The foamed slag greatly increases the contact interface of the slag-steel, accelerates the transfer of oxygen and the physicochemical reaction between the slag and the steel, and greatly shortens the smelting time of the steel. In the electric furnace, the thickness of the foam slag is required to be more than 2.5 times the length of the arc column, which requires high-quality foam slag to be produced as soon as possible in the electric furnace smelting process.
4. Process operation for making foamed slag
The key to making foamed slag is to control the composition of the slag and the temperature of the molten pool, and provide enough gas. The main points of operation are as follows:
(1) Appropriately increase the carbon content of the charge, generally 0.08% to 0.12% (mass fraction) higher than the traditional smelting process.
(2) Before charging, the bottom of the furnace or the first basket is added with 2% to 4% of lime and 5 to 7kg/t of iron oxide, to ensure alkalinity of about 2.0 after melting and 20% of FeO. Left and right; at the same time add 6 ~ 8kg / t of broken coke block to ensure the carbon content.
(3) After the bottom of the furnace forms a molten pool, oxygen can be blown and the oxygen pressure is 0.5-0.7 MPa.
(4) In the middle of molten oxygen, the oxygen pressure is increased to 0.7 to 1.0 MPa, and oxygen is occasionally blown to the steel slag interface to make the slag foam normally.
(5) After automatic slag, add 50% to 85% lime and 15% to 50% coke powder to form a foam slag slag to maintain the alkalinity and foaming capacity of the slag.
(6) At the end of the molten oxygen phase, 4 to 6 kg/t of coke powder is sprayed into the steel slag, and high-voltage, high-power supply is used, and the submerged arc is heated.
5 Conclusion
The working principle of the carbon oxide gun is to realize its action and advantages through its foaming slag. It performs dephosphorization and desulfurization early in the process of slag formation, reduces the smelting time, reduces the consumption of refractory materials, and at the same time casts Steel production provides high quality steel and pre-order protection.
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