What is the Difference Between Aluminium-Killed and Silicon-Killed Steel

The main difference between aluminium-killed steel and silicon-killed steel is that in aluminium-killed steel, the primary deoxidizing agent is, whereas in silicon-killed steel, the primary deoxidizing agent is silicon.

Aluminum-killed and silicon-killed steel are two variations of steel produced through different deoxidation processes. The choice between the two depends on specific manufacturing requirements and the desired steel characteristics.

Key Areas Covered

1. What is Aluminium-Killed Steel
     – Definition, Features, Applications
2. What is Silicon-Killed Steel
     – Definition, Features, Applications
3. Similarities Between Aluminium Killed and Silicon Killed Steel
     – Outline of Common Features
4. Difference Between Aluminium-Killed and Silicon-Killed Steel
     – Comparison of Key Differences
5. FAQ: Aluminium Killed and Silicon Killed Steel
     – Comparison of Key Differences

Key Terms

Aluminium Killed Steel, Silicon Killed Steel

What is Aluminium Killed Steel

Aluminum-killed steel derives its name from the specific deoxidation process used during its production. Deoxidation is a critical step in the steelmaking process, as it removes undesirable elements, such as oxygen and impurities, that can negatively affect the steel’s properties. In aluminum-killed steel, aluminum is the primary deoxidizing agent.

During the steelmaking process, aluminum in the form of aluminum shot or aluminum wire is added to the molten steel. The aluminum reacts with the dissolved oxygen in the steel, forming aluminum oxide (Al₂O₃). This reaction is as follows:

4Al + 3O_₂ → 2Al_₂O_₃

The aluminum oxide that forms during this reaction is a solid compound that has a lower density than the molten steel. As a result, it rises to the surface of the molten metal and forms a layer of slag.

The aluminum oxide slag is skimmed off the surface of the steel, leaving behind aluminum-killed steel with reduced oxygen content. Moreover, removing oxygen is critical because it prevents the formation of undesirable compounds and enhances the steel’s properties.

What are the Applications of Aluminium Killed Steel

The automotive sector extensively employs aluminum-killed steel for the manufacturing of body panels, chassis components, and structural parts. The steel’s superior formability and deep-drawing characteristics make it a preferred choice for stamping and forming processes. Aluminum-killed steel is also useful in the production of beverage cans, food containers, and aerosol cans. In the construction industry, aluminum-killed steel can be used for structural components, cladding, roofing, and a variety of architectural applications. Its fine grain structure and weldability are advantageous in construction projects. Household appliances, such as refrigerators, washing machines, and ovens, often incorporate aluminum-killed steel for the production of outer panels and interior components.

What is Silicon Killed Steel

In silicon-killed steel, silicon is the primary deoxidizing agent. During the steelmaking process, silicon in the form of ferrosilicon is added to the molten steel. The silicon reacts with the dissolved oxygen in the steel, forming silicon dioxide (SiO2). The chemical reaction is as follows:

2Si + O_₂ → 2SiO_₂

Silicon dioxide forms during the deoxidation reaction. Unlike aluminum-killed steel, where the oxide forms a layer of slag that is skimmed off, the silicon dioxide remains within the molten steel. Moreover, the addition of silicon significantly reduces the oxygen content in the steel. Moreover, the presence of silicon dioxide in the steel is not detrimental, as it is chemically stable and does not adversely affect the steel’s properties.

What are the Applications of Silicon Killed Steel

Silicon-killed steel is frequently used in the construction of power generation equipment, including boilers, pressure vessels, and heat exchangers. Its ability to withstand high temperatures and resist hot cracking is essential in power plant components. The petrochemical sector relies on silicon-killed steel for the fabrication of storage tanks, pipelines, and equipment exposed to high-temperature and corrosive environments.

Silicon-killed steel is useful in the automotive industry for components such as exhaust systems, catalytic converters, and other parts that must endure elevated temperatures and maintain structural integrity. Industrial machinery, particularly those operating in hot and demanding environments, may incorporate silicon-killed steel in their construction. In construction and architectural applications, silicon-killed steel can be used for structural components that require both high-temperature resistance and structural integrity. Moreover, in the aerospace industry, silicon-killed steel is employed in specific components and structures where elevated temperatures or resistance to hot cracking are essential.

Similarities Between Aluminium-Killed and Silicon-Killed Steel

• Both types of steel undergo deoxidation during their production to remove oxygen and impurities.
• Generally, both exhibit better weldability compared to non-killed steel, as deoxidization minimizes the potential for defects in welded joints.

Difference Between Aluminium-Killed Steel and Silicon-Killed Steel

Definition

Aluminium-killed steel is steel that has been deoxidized with aluminum during its production process to improve cleanliness, ductility, and weldability, whereas silicon-killed steel is steel that has been deoxidized with silicon during its manufacturing to enhance strength and high-temperature properties.

Deoxidizing Agent

In aluminium-killed steel, the main deoxidizing agent is aluminium, whereas, in silicon-killed steel, the primary deoxidizing agent is silicon.

High-Temperature Performance

Aluminum-killed steel is not primarily chosen for its high-temperature performance. Silicon-killed steel is specifically favored for its high-temperature performance.

Grain Structure and Characteristics         

Aluminum-killed steel typically has a fine-grained, uniform structure, offering improved ductility and toughness, while silicon-killed steel often exhibits a coarser grain structure and may not possess the same level of ductility and toughness.

FAQ: Aluminium Killed Steel and Silicon Killed Steel

What are the different types of killed steel?

Common killed steels include alloy steels, stainless steels, and heat-resisting steels.

What are the advantages of killed steel?

The advantages of killed steel include improved consistency, cleanliness, ductility, weldability, toughness, reduced porosity, and better surface finish.

What is the difference between Silumin material and aluminium?

Silumin is a type of aluminum alloy that contains silicon as one of its primary alloying elements, while pure aluminum (aluminium) is the chemical element with the symbol Al.  In fact, the main difference is that silumin is an alloy of aluminum with silicon and other elements, which can provide specific properties like improved strength and heat resistance, whereas aluminum is a pure metallic element.

Conclusion

The main difference between aluminium-killed steel and silicon-killed steel lies in the deoxidizing agents used during steelmaking. Aluminum-killed steel is deoxidized with aluminum, while silicon-killed steel is deoxidized with silicon. Furthermore, these distinct deoxidization methods result in variations in steel properties, cleanliness, and applications.

Reference:

1. “Killed Steel.” Science Direct. 
2. “Aluminum Killed Steel.” Science Direct. 

Image Courtesy:

1. “Металургыя” By Inna67895 – Own work(CC BY-SA 4.0) via Commons Wikimedia