Review Chnzbtech ladle refining furnace advantages and refining method

Ladle refining furnace (Ladle refining furnace) refers to equipment that has both the heating and refining functions of a steelmaking furnace. It is an important metallurgical equipment used for refining molten steel melted in primary furnaces (electric arc furnace, open hearth, converter), and can adjust the temperature of molten steel, process buffering, and meet continuous casting and continuous rolling requirements.

Ladle heating furnace main functions

1. The function of heating the molten steel and keeping it warm. The molten steel obtains new thermal energy through arc heating, which can not only add alloys and adjust components during ladle refining, but also add slag, which is convenient for deep desulfurization and deoxidation of molten steel. In addition, the molten steel opening temperature required by continuous casting is guaranteed, which is beneficial to the improvement of the quality of the dry casting billet.

2. Argon stirring function. Argon gas is blown into the molten steel through the breathable brick installed at the bottom of the ladle, and the molten steel obtains a certain stirring function.

3. Vacuum degassing function. After the ladle is hoisted into the vacuum tank, the steam jet pump is used for vacuum degassing, and the molten steel is stirred by blowing argon at the bottom of the ladle, which can remove the hydrogen content and nitrogen content in the molten steel, and further reduce the oxygen content and sulfur content. Finally, a higher purity molten steel and a material with superior performance are obtained.

Lrf furnace composition and characteristics

1. Features of the equipment: The equipment has the functions of atmospheric pressure arc heating, vacuum degassing, argon blowing stirring, oxygen blowing feeding wire, atmospheric pressure or vacuum feeding, temperature measurement, sampling, TV camera, in-frequency observation and other functions.

2. Equipment composition: ladle and ladle car; heating device (electrode control mode: manual control or microcomputer automatic control. Energy-saving short net and conductive cross arm are used); vacuum and detection system; hydraulic and control valve system; argon, Oxygen, compressed air and cooling water system; electrical control system (using PLC control and CRT image simulation display); high voltage and strong current system; high current line.

Ladle heating furnace process flow

The refining process of the ladle refining furnace mainly includes three contents:

1. Heating and temperature control. The heating rate can reach 3～5℃/min, and the ladle refining furnace adopts the computer to dynamically control the end point temperature, which can ensure the control accuracy of the end point temperature (5℃). The use of submerged arc foam technology can reduce the radiant heat loss of the arc and improve the heating efficiency.

2. White residue refining process. The ladle refining furnace uses white slag to refine molten steel, realize desulfurization and deoxidation of molten steel, and produce ultra-low sulfur steel and low oxygen steel. Therefore, white slag refining is the core of the ladle refining furnace process operation, and it is also an important guarantee for improving the cleanliness of molten steel. The main points of the white slag refining process are:

(1) Tapping slag, control the amount of slag to be less than 5kg/t;

(2) The slag is upgraded, and the slag R is controlled to be 2.5, (TFe+MnO) 3.0%;

(3) White slag refining, generally use Al2O3-CaO-SiO2 slag, control the basicity of slag R 4, (TFe+MnO) 1%, to ensure the desulfurization and deoxidation effect;

(4) Control the atmosphere in the ladle refining furnace to be weakly oxidizing to avoid reoxidation of the slag;

(5) Proper stirring to avoid exposure of the molten steel surface and ensure a high mass transfer rate in the molten pool.

3. Alloy fine-tuning and narrow composition control. Alloy fine-tuning and narrow composition control technology is one of the key technologies to ensure the stability of steel composition performance, and it is also an important metallurgical function of the ladle refining furnace.

Ladle heating furnace refining methods

(1) CAS (CAB) method

An immersion sealing cover is added to the ladle slag liquid, the upper part of the cover has ventilation holes, and argon gas is blown into the bottom of the ladle. Blowing argon in an argon protective atmosphere, such as adding synthetic slag, this co-process can effectively reduce the oxygen content, and the lower the A1203 content in the lining, the better the deoxidation effect, and the sulfur content can also be reduced to below 20X10-4. The alloy yield increased significantly. This method is suitable for large tonnage of converter molten steel.

(2) CAS-OB method: On the basis of CAS, adding A1 to blow oxygen to heat the molten steel can increase the speed and depth of decarburization.

(3) U powder spraying metallurgy method: through the inert gas with a certain pressure, the metallurgical powder is passed through the molten steel inserted into the ladle.

The spray gun is blown into molten steel together for metallurgical reaction. The advantage is that the slag spray powder can strengthen desulfurization and dephosphorization. Blowing argon can clean non-metallic inclusions, blowing CaSi powder can control the shape of inclusions, and spraying mixed powder can improve the yield or fine-tune the composition. However, this device has a great influence on the temperature drop of molten steel, and was gradually replaced by the wire feeding process.

(4) WF wire feeding method: various vermicelli can be quickly fed directly into the molten steel of the ladle through the wire feeding device, which can achieve the same effect as the U method, but the equipment is simple, the yield is high, and the temperature drop of the molten steel is small. Different types of wire can also be fed into the bag with two or four streams.

(5) RH cycle degassing method: Insert the rising pipe and the descending pipe of the vacuum de-cylinder into the molten steel of the ladle at the same time, and blow argon gas into the lower end of the rising pipe, so that the ascending pipe and the descending pipe produce a pressure drop with each other, and the steel The liquid can be returned to the vacuum cylinder through the rising pipe for degassing, and then enter the ladle through the descending pipe. In the ladle, the molten steel near the descending pipe continuously flows to the rising pipe, and the flowing molten steel also continuously washes the bottom of the slag layer. Strong desulfurization effect. The kinetic energy of circulating degassing is also generated for molten steel to achieve the purpose of complete degassing. Recently, the powder spraying device was combined with RH to produce RH-U method; combined with top blowing oxygen to form RH-KTB method; combined with side-blown oxygen decarburization technology to form RH-OB method; and sprayed powder in the OB hole to form RH - PB method. The RH method is suitable for large-tonnage molten steel processing technology.

(6) Special purpose ladle refining furnace: There is a VOD furnace dedicated to the production of stainless steel. The type is basically similar to the VD furnace, and an additional top-blowing oxygen lance is added. Oxygen blowing and decarburization can be carried out under negative pressure to improve the purity of molten steel.