AOD introduction to principle, composition and features

What is AOD?

AOD process is the abbreviation of argon-oxygen decarburization refining method. It is to blow oxygen and decarburize molten steel under normal pressure, while blowing argon (or nitrogen) to reduce the partial pressure of carbon monoxide during decarburization. At a reasonable temperature a refining method for smelting high-chromium stainless steel to achieve carbon removal and chromium retention.

In the process of AOD refining, the strong stirring caused by a large amount of argon (or nitrogen) oxygen mixed gas blowing greatly promotes the progress of various chemical reactions in the molten pool and the mixing of molten steel and slag.

An important technical progress of AOD furnace is to transplant the experience of oxygen blowing on the top of the converter, and develop the top-bottom composite blowing method. In the initial stage of smelting and decarburization in the AOD furnace, the top-bottom re-blowing method can accelerate the decarburization and heating of molten steel and shorten the smelting time.

AOD furnace working principle 

AOD furnace is an out-of-furnace refining technology for refining stainless steel by injecting mixed gas of argon and oxygen. The device was first developed in 1968 by Union Carbide Corporation and Josly Corporation in the United States.

The process is to pour the molten steel roughly refined by the electric furnace into the AOD, and blow a certain proportion of argon-oxygen mixed gas into the furnace from the lower side wall of the furnace body to decarburize the surface of the O2-Ar bubbles. Due to the dilution effect of argon on the generated CO, the partial pressure of CO in the O2-Ar bubbles is reduced, so it can promote decarburization and prevent the oxidation of chromium. high, so that stainless steel can be refined under false vacuum conditions.

Advantages of AOD Refining Process

1. The AOD method can quickly complete the decarburization task at a relatively reasonable temperature, and can use 100% stainless steel scrap or high-carbon ferrochromium and ordinary carbon steel scrap for ingredients, thereby reducing the cost of raw materials.

2. The AOD method has excellent decarburization ability, which can get rid of the limitations of high carbon ferrochromium alloys.

3. Compared with other stainless steel secondary refining technologies, the AOD method has simple equipment and less capital investment.

4. The AOD method replaces the traditional electric furnace refining process, which can achieve carbon removal and chromium retention at a relatively low temperature, reducing the excessive oxidation of metals and the consumption of furnace lining refractories.

5. The process control of the AOD method is relatively simple, the process reproducibility and predictability are good, and the automatic process control can be realized more stably.

6. AOD method can effectively remove hydrogen, sulfur, oxygen and oxide inclusions, and its refined products have better surface quality, tensile strength and yield strength, area shrinkage, impact toughness and cutting performance.

The AOD method has the following advantages when smelting stainless steel:

1. Compared with the VOD method for smelting stainless steel, the AOD method has less equipment investment, easy maintenance and simple operation.

2. The process is easy to master, and ultra-low carbon stainless steel can be smelted smoothly by using cheap raw materials such as scrap steel and high-carbon ferrochrome.

3. It can smelt ultra-low sulfur stainless steel, and the quality of the steel is comparable to that of molten steel treated by vacuum.

4. It can improve the total recovery rate of chromium, the recovery rate of chromium can reach 98%, and can be alloyed with nitrogen, and the production cost is low.

AOD refining furnace equipment composition

AOD equipment is mainly composed of furnace body, support ring, tilting mechanism, gas mixing modulation and blowing system, and temperature measurement and sampling system. The furnace body includes a furnace body and a furnace cap. The lower side wall of the furnace body forms an inclination angle of about 20° with the center line of the furnace body, which helps the blown gas to rise to the furnace mouth along the side wall, and reduces the serious erosion of the gas on the upper area of the air gun. The shape of the furnace cap includes three types: jaw type, asymmetric type and symmetrical type, but the symmetrical type is more commonly used at present. This not only improves the operator's observation of the furnace, but also simplifies the masonry process of the furnace roof, changing the previous castable masonry to brick masonry.

Specific components of AOD:

1. Furnace

2. Ring

3. Drive mechanism (floor or suspension)

4. Thin oil lubrication station

5. Torsion shaft

6. Top Gun

7. Ladle car

8. Slag truck

9. Continuous feeding system

10. Argon, oxygen, nitrogen gas regulating valve station

11. Furnace body replacement car

12. Equipment cooling water device

13. Argon blowing device for ladle car

14. Nitrogen sealing device

15. Servicing the tipping device

16. Dust removal system

17. Control system

Equipment control and software composition

The control system of the argon-oxygen blowing furnace includes the furnace body tilting frequency conversion control system, dust removal system, feeding system, gas control and adjustment system, etc.