VOD Furnace: What is the Purpose of Vacuum Degassing?

A VOD furnace is a refining equipment used for smelting high-purity stainless steel and special alloys. What is the purpose of its vacuum degassing? Let's explore and understand together.

A VOD/VD vacuum refining furnace is a commonly used refining process equipment, mainly used for deoxidation and impurity removal of molten steel to obtain high-purity steel with low impurity content. As a vacuum degassing device, its main function is to remove harmful gases such as hydrogen from the steel, reducing the hydrogen content in the molten steel to ≤2ppm, effectively reducing the generation of white spot scrap.

Simultaneously, the VD furnace can also perform partial deoxidation and desulfurization, composition fine-tuning, and inclusion modification, further improving the purity of the molten steel.

Main Applications of Vacuum Refining Furnaces

VD refining furnaces are widely used in the iron and steel metallurgy field, playing a particularly important role in the production of high-quality, special steels. They are suitable for producing high-speed steel, alloy structural steel, tool steel, heat-resistant steel, and corrosion-resistant steel.

Equipment Features

• High Purity: 

Utilizes vacuum refining technology to effectively remove harmful elements such as gases and impurities from molten steel, improving its purity and quality.

• High Efficiency & Energy Saving: 

Employs a closed-loop operation, reducing steel evaporation losses and achieving high heating efficiency and energy utilization.

• Flexible & Controllable: 

Can be adjusted according to different process requirements (such as vacuum degree, refining time, and alloying elements) to meet the needs of different steel production.

• Environmentally Friendly and Safe: 

Employs vacuum technology during operation, eliminating the generation of large amounts of dust, exhaust gases, and other pollutants, meeting environmental protection and safety production requirements.

Purpose of VOD Furnace Vacuum Degassing

The main purpose of VOD refining furnaces vacuum degassing is to remove gaseous impurities from molten steel, especially hydrogen, nitrogen, and oxygen. If these gases remain in the steel, they can cause defects such as porosity and inclusions, affecting the steel's quality and performance.

Through degassing in a vacuum environment, the content of these harmful gases in the molten steel can be effectively reduced, improving the steel's purity and mechanical properties, ensuring stable quality of the final product. In short, vacuum degassing makes steel cleaner, purer, and more reliable.

The main purposes of vacuum degassing include the following:

1. Deep Decarburization: 

Under vacuum conditions, oxygen is blown into the molten pool, causing carbon to react with oxygen to produce carbon monoxide (CO) gas. Because the vacuum environment lowers the partial pressure of CO, it promotes the decarburization reaction to proceed to the right (C + O → CO↑), thereby reducing the carbon content in the molten steel to extremely low levels (e.g., ≤ 0.02% or lower) without significantly oxidizing precious alloying elements such as chromium, meeting the composition requirements of ultra-low carbon stainless steels (e.g., 304L, 316L).

2. Degassing: 

Removal of hydrogen (H₂) & nitrogen (N₂): The vacuum environment effectively reduces the dissolved hydrogen and nitrogen content in the molten steel, preventing problems such as porosity, white spots, or age embrittlement in the billet, improving the purity and mechanical properties of the steel.

Promoting the flotation of inclusions: The CO bubbles generated during degassing can adsorb non-metallic inclusions in the steel, causing them to float to the surface and be discharged, further purifying the molten steel.

3. Controlling Alloy Composition and Yield

After decarburization, alloying elements (such as Cr, Ni, Mo, etc.) can be precisely added under vacuum or micro-positive pressure to reduce oxidation loss, improve alloy yield, and achieve precise composition control.

4. Improving Steel Cleanliness & Homogeneity

The vacuum stirring effect of the vacuum refining furnaces help to homogenize the temperature and composition of the molten steel, while reducing oxide inclusions and improving the surface and internal quality of the final product.

In summary, the core purpose of VOD furnace vacuum degassing is to achieve ultra-low carbon, low gas content, and high purity special steel smelting while protecting precious alloying elements (especially chromium) from excessive oxidation. This technology is widely used in stainless steel, bearing steel, tool steel, and high-temperature alloys.