Understanding Killed Steel and Rimmed Steel: Key Differences and Characteristics

Steel, a ubiquitous material used in a myriad of applications from construction to manufacturing, comes in various types with unique properties and characteristics. Two specific types of steel, killed steel and rimmed steel, have distinct manufacturing processes and end-use applications. This article sheds light on the production methods, properties, and applications of both killed and rimmed steel.

Introduction to Killed Steel

Killed steel is a type of steel that has been completely deoxidized by the addition of an agent before casting, ensuring that there is very little evolution of gas during solidification. This process is crucial for producing high-quality steel with superior mechanical and metallurgical properties. The term "killed" refers to the complete elimination of gases such as oxygen, nitrogen, and hydrogen, which can cause porosity and other defects in the steel.

The Deoxidation Process

The deoxidation of molten steel is a vital step in its production. In the case of killed steel, a deoxidizer, often manganese, aluminum, or a combination of both, is added to the molten steel right before casting. The purpose of this addition is to react with the dissolved oxygen in the steel, thus reducing it to non-reactive forms. This results in a steel product that is essentially free of gas bubbles, leading to a more uniform and dense material.

Properties of Killed Steel

Killed steel exhibits several desirable properties that make it suitable for a wide range of applications:

Uniform Microstructure: The complete elimination of gas evolution during solidification results in a microstructure that is almost entirely free of inclusions or porosity. Improved Mechanical Strength: With a refined microstructure, killed steel has better strength and fatigue resistance compared to its non-killed counterparts. Elevated Tensile Strength: The steel has higher tensile strength, making it more durable and capable of withstanding greater loads. Excellent Weldability: Lower levels of impurities mean that killed steel welding can be more consistent and reliable, reducing the risk of porosity or cracking.

Applications of Killed Steel

Due to its high quality and performance, killed steel is used in applications where the integrity and reliability of the material are critical:

Structural Applications: Used in heavy machinery, bridge construction, and other large-scale projects. Machining and Forge Applications: Ideal for producing precision parts and tools that require high strength and wear resistance. Steel Plants and Steel Mills: Used in the construction of furnaces, boilers, and other high-temperature equipment.

Introduction to Rimmed Steel

Rimmed steel, on the other hand, is a low carbon steel with a carbon content of less than 0.1%. Unlike killed steel, rimmed steel is not completely deoxidized and typically does not undergo the addition of deoxidizers before casting. This less rigorous processing results in a different set of properties and applications.

Production Process of Rimmed Steel

The production of rimmed steel involves a “rimming” process, which occurs as the molten steel enters the mold. During this process, deoxidizers are added to the molten steel, but they are not fully incorporated until the steel solidifies. This allows for a higher level of gas to remain in the steel, leading to a less dense and more porous microstructure compared to killed steel.

Properties of Rimmed Steel

Rimed steel has distinct properties:

Lower Carbon Content: The low carbon content ( Much Porous Microstructure: The lingering gas in the steel results in a more porous microstructure, which can affect its durability and wear resistance. Lower Tensile Strength: Due to the higher presence of gases and inclusions, rimmed steel has lower tensile strength than killed steel.

Applications of Rimmed Steel

Given its properties, rimmed steel is employed in applications where flexibility and formability are more critical:

Battery and Container Manufacturing: Used in the production of battery shells, cans, and other containers that require deep drawing. Sheet Products: Suitable for the fabrication of sheets for packaging, household appliances, and automotive parts. Wire and Cable Production: Ideal for producing electrical wires and cables, where high ductility is necessary.

Conclusion

In summary, understood the key differences between killed steel and rimmed steel is essential. While both are important materials in the steel industry, they serve different purposes due to their distinct production processes and resulting properties. Killed steel is characterized by its high quality, uniform microstructure, and superior mechanical properties, making it ideal for structural and high-strength applications. Conversely, rimmed steel's low carbon content and more porous microstructure make it well-suited for applications requiring high formability and ductility.

References

- Killed Steel

Engineering ToolBox - Mechanical Properties of Steels