VOD Refining Furnace: Which Steel Products Are Suitable For?

In steel production, not all steel grades require VOD refining furnace.

For ordinary carbon steel and general steel products, conventional steelmaking and refining processes can usually meet basic quality requirements. However, for stainless steel, low-carbon steel, ultra-low-carbon steel, high-alloy steel, and some special steels, the carbon content, gas content, chemical composition, and cleanliness of the molten steel often have higher requirements. This is also an important application area for Vacuum Refining Furnaces

VOD furnaces further refine molten steel through vacuum treatment and oxygen blowing decarburization processes, enabling steel mills to more stably control the composition and quality of the molten steel, meeting the prodction requirements of high-quality steel.

I. Characteristics of VOD Refining Furnace

VOD furnaces are mainly used in the production of high-quality and special steels.

Compared to ordinary steel products, these products have higher requirements for the quality of the molten steel. For example, in the production of low-carbon stainless steel, it is necessary not only to reduce the carbon content in the molten steel but also to minimize the oxidation loss of alloying elements such as chromium; in the production of some special steels, more stringent control of gases and impurities in the molten steel is also required.

Therefore, the core value of a vacuum oxygen blowing decarburization refining furnace is not simply "refining molten steel again," but rather helping steel mills obtain molten steel that better meets their target requirements through decarburization and refining processes in a vacuum environment.

VOD also has distinct industry characteristics: it is typically used on steel production lines with high steel quality requirements and high added value. For steel mills that only produce ordinary steel, investing in a VOD refining furnaces may not be necessary; however, for steel mills producing high-quality stainless steel, special steel, and low-carbon steel, it can become an important refining device.

Simply put: the higher the steel grade requirements, the lower the carbon content requirements, the more alloying elements, and the stricter the requirements for molten steel cleanliness, the more obvious the application value of VOD is usually.

II: Which Steel Grades/Products Require a VOD Refining Furnace?

The most typical application area for vacuum oxygen blowing decarburization furnace is the production of stainless steel and special steel, but whether VOD is specifically needed depends on the steel grade, product quality requirements, and production process.

1. Stainless Steel

Stainless steel is one of the most important application areas for vacuum refining furnaces. Especially in the production of low-carbon and ultra-low-carbon stainless steel, steel mills need to reduce the carbon content while maintaining the content of alloying elements such as chromium and nickel as much as possible. VOD (Vacuum-Oxygen Decarburization) in a vacuum environment helps steel mills achieve a deeper degree of decarburization and reduce unnecessary oxidation of alloying elements.

Common VOD stainless steel production includes:

• Austenitic stainless steel

• Ferritic stainless steel

• Martensitic stainless steel

• Low-carbon stainless steel

• Ultra-low-carbon stainless steel

For example, low-carbon stainless steels such as 304L and 316L may utilize VOD furnaces or other suitable refining processes under specific production conditions.

2. Low-carbon Steel and Ultra Low-carbon Steel

For some high-quality steels, the carbon content requirements are very strict. When ordinary smelting processes cannot consistently achieve the target carbon content, VOD furnaces can utilize vacuum conditions to promote the decarburization reaction, thereby further reducing the carbon content in the molten steel. Therefore, it is also suitable for some:

• Low-carbon steel

• Ultra-low-carbon steel

• High-quality sheet metal

• Automotive steel

• Special steels with strict carbon content requirements

3. Special Steels

Special steels typically have more stringent chemical composition and quality requirements.

Some tool steels, die steels, heat-resistant steels, high-strength special steels, and other high-quality steels require more precise composition control and purification treatment of the molten steel during production. For these products, VOD refining furnaces can be used as part of a secondary refining process to help steel mills improve the quality of molten steel and enhance production stability.

4. High-Alloy Steels

For steels containing a high proportion of alloying elements such as chromium, nickel, and molybdenum, the production process needs to consider both reducing carbon content and protecting alloying elements.

Using overly strong oxidation methods for decarburization may result in the oxidation and loss of some alloying elements. VOD refining furnaces utilize a vacuum environment for decarburization, making them particularly suitable for the production of some high-alloy steels and high-alloy stainless steels.

5. Products With High Requirements for Molten Steel Cleanliness

In addition to reducing carbon content, the vacuum treatment of VOD can also help reduce some dissolved gases in the molten steel. For some high-quality steels, hydrogen, nitrogen, oxygen, and non-metallic inclusions can all affect the internal quality and performance of the final product.

Therefore, vacuum oxygen blowing decarburization furnace of significant application value for products requiring high steel cleanliness.

III: Main Functions of VOD Refining Furnaces

The functions of a VOD furnace can be summarized as: deep decarburization, vacuum treatment, composition control, and steel purification. One of the core functions is vacuum decarburization.

In a vacuum environment, carbon in the molten steel reacts with oxygen to produce carbon monoxide. Because a vacuum reduces the partial pressure of CO, the generated CO is more easily expelled from the molten steel, thus promoting the continuous decarburization reaction. This makes VOD particularly suitable for producing steel grades with strict carbon content requirements.

1. Reducing the Carbon Content in Molten Steel

This is the most important function of the refining furnace. For low-carbon, ultra-low-carbon stainless steel, and some special steels, vacuum oxygen blowing decarburization refining furnaces can help steel mills further reduce the carbon content in the molten steel and improve the stability of low-carbon production.

2. Reduce Oxidation Loss of Alloying Elements

For steels containing alloying elements such as chromium and nickel, minimizing alloying element loss during decarburization is crucial. The vacuum decarburization process in a VOD furnace can reduce unnecessary oxidation of alloying elements to a certain extent, thus facilitating control of the final molten steel composition and reducing alloy material consumption.

3. Remove Some Gases from Molten Steel

Vacuum treatment promotes the removal of some dissolved gases from molten steel. For high-quality steel, reducing the content of gases such as hydrogen and nitrogen in the molten steel helps improve steel quality and the stability of the final product.

4. Improve Molten Steel Cleanliness

During VOD refining, inclusions and gases in the molten steel can be further controlled. This is especially important for special steel products with high requirements for internal quality and cleanliness.

5. Precisely Adjust Molten Steel Composition

After completing the main decarburization and vacuum treatment, the alloy composition of the molten steel can be adjusted according to the requirements of the target steel grade, making the final chemical composition closer to product standards.

Therefore, the vacuum oxygen blowing decarburization furnace is not only a "decarburization device" but also an important refining step in the production of high-quality steel.

Ⅳ: How to Determine if a Steel Mill Needs a VOD Furnaces?

For steel mills preparing to build new steelmaking production lines or upgrade existing ones, the decision to install a VOD furnace should first be based on product and production requirements, rather than simply looking at the equipment itself. Consider the following key questions:

1. What are your main products?

If you mainly produce ordinary carbon steel with low requirements for carbon content and molten steel cleanliness, then a VOD furnaces may not be necessary.

If you mainly produce stainless steel, low-carbon steel, ultra-low-carbon steel, high-alloy steel, and special steel, further evaluation is warranted.

2. What is your target carbon content?

If your product requires very low carbon content and needs to consistently maintain that low carbon content, the value of a vacuum oxygen blowing decarburization furnace will be more apparent.

3. Does your product have high requirements for molten steel cleanliness?

If your product is high-quality steel requiring strict control of gases and non-metallic inclusions, then the importance of vacuum refining will further increase.

4. What is your production scale and existing processes? 

The selection of a vacuum refining furnaces require comprehensive consideration of factors such as ladle capacity, annual output, target steel grade, existing steelmaking equipment, and subsequent continuous casting processes.

Therefore, it's not a matter of "the larger the tonnage, the better," but rather choosing a VOD vacuum refining furnaces that matches the steel mill's actual production needs.

A VOD refining furnace is not a necessity for all steel mills; it is more suitable for high-quality stainless steel, low-carbon/ultra-low-carbon steel, high-alloy steel, and special steels—products requiring high-quality molten steel.

For steel mills planning to invest in a VOD furnaces, the most important step is not simply selecting a particular equipment specification, but rather first determining: what steel grade to produce, the target carbon content, the annual output, and the existing steelmaking process.

Only after these conditions are determined can the appropriate vacuum oxygen blowing decarburization furnace capacity, vacuum system, oxygen blowing system, and automation configuration be selected, thus forming a VOD refining solution truly suited to production needs.