Hardened steels
What is Hardened Steel?
Hardened steel is a key material in metallurgy and industry, especially in machine shops and machining facilities. It undergoes a heat treatment process known as hardening. This process involves controlled heating and rapid cooling, which together give the steel a unique combination of properties, such as high strength, elasticity, and toughness.
The Heat Treatment Process for Hardened Steel
- Hardening: Hardening is a process in which steel is heated above its critical temperature and then rapidly cooled, usually in water or oil. This quick cooling leads to the formation of metastable martensite. Martensite is an extremely hard microstructure, but it is also brittle. The goal of hardening is to maximize the steel’s hardness and wear resistance.
- Tempering: Because the martensite produced by hardening is brittle, it is often followed by tempering. In tempering, the steel is reheated, but to a lower temperature, allowing the steel to achieve a balance between final hardness and toughness. The tempering process slightly reduces the steel’s hardness, but improves its overall durability by reducing the risk of brittleness.
Properties of Hardened Steel
- Strength and Durability: Hardened steel offers excellent strength and durability, making it an ideal material for tools and machine parts. Its high wear resistance ensures a long service life, even under demanding conditions.
- Elasticity and Toughness: Thanks to the tempering process, hardened steel features good elasticity and toughness, reducing the risk of breaking or cracking during use. This makes it a reliable material for critical applications where mechanical durability is essential.
Carbon Content in Steel Hardening
The carbon content in steel significantly affects its ability to be hardened. Medium-carbon and high-carbon steels are best suited for hardening because their carbon content allows modification of the steel’s microstructure. If the steel lacks sufficient carbon, its crystalline structure does not change enough to achieve the desired properties through hardening.
Applications of Hardened Steels in Machine Shops
- Tools and Machine Parts: Hardened steel is widely used in the production of tools and machine parts. These include, for example, the bodies and holders of cutting tools used in machining as well as other critical machining components. Thanks to hardening and tempering, these tools can withstand high forces and wear without breaking.
- Bearing Use: Hardened steels are also used in the production of bearings, particularly in applications demanding high strength and wear resistance. Compared to full ceramic bearings, hardened steel bearings offer better load capacity and are more economical in many applications.
Testing Methods for Confirming Hardened Steel
A quick and simple way to check if steel has undergone the hardening and tempering process is to use a hand file. If the file easily bites into the steel, the steel is not hardened. If the file slides over the steel surface without leaving a mark, the steel is likely hardened.
Summary
Hardened steel is a crucial material category, widely used in machine shops and machining facilities for its high strength, toughness, and wear resistance. Hardening and tempering processes, combined with the correct carbon content, produce steel suitable for demanding industrial applications where outstanding material performance is required.
