1. Carburizing Treatment

Process: The screws are heated in a carbon-containing atmosphere, allowing carbon atoms to penetrate the screw’s surface. After quenching and tempering, the surface becomes very hard while the core remains tough.

• Features:
  • High surface hardness and excellent wear resistance.
  • The core retains toughness, ensuring durability under stress.
• Applications:
  Ideal for screws requiring high surface hardness and wear resistance, such as screws used in automobiles and mechanical equipment.

Example: Automotive engine bolts that need to resist heavy wear while maintaining internal strength.

2. Nitriding Treatment

Process: Screws are heated in a nitrogen-rich atmosphere (like ammonia), allowing nitrogen atoms to penetrate the surface and form a hard nitride layer².

• Features:
  • Extremely high surface hardness.
  • Superior wear resistance and corrosion resistance.
• Applications:
  Commonly used in high-performance parts like engine components and high-strength screws that require resistance to extreme wear and corrosion.

Example: Screws in high-demand environments such as heavy machinery and precision equipment.

3. Quenching and Tempering

Process:

• Quenching: The screw is heated to a high temperature and then rapidly cooled to increase its hardness.

• Tempering: The quenched screw is reheated to a specific temperature and held to reduce brittleness³ and improve toughness.

• Features:

  • Enhances overall hardness and strength.
  • Reduces brittleness while increasing toughness for heavy-duty applications.

• Applications:
  Suitable for screws requiring high strength and toughness, such as construction screws and industrial machinery screws.

Example: Screws used in structural steelwork and heavy machinery assemblies.

4. Induction Heating

Process: An electromagnetic field generated by high-frequency currents heats the surface of the screw quickly. The screw is then rapidly cooled⁴, hardening only the surface layer.

• Features:
  • Fast heating speed for efficient processing.
  • Depth of the hardened layer can be precisely controlled.
  • Ideal for mass production due to its efficiency.
• Applications:
  Used for screws requiring localized hardening, such as those in automobiles and home appliances.

Example: Screws for car assemblies where specific hardening is needed on the surface to prevent wear.

5. Blackening Treatment

Process: The screw is heated in an alkaline solution, forming a black oxide film⁵ on its surface. This enhances surface hardness and improves resistance to rust.

• Features:
  • Increases surface hardness and corrosion resistance.
  • Enhances the appearance of screws with a uniform black finish.
• Applications:
  Widely used for screws in machinery, tools, and general industrial applications requiring both function and aesthetics.

Example: Tool screws or machinery fasteners where rust resistance and a clean, professional finish are essential.

Conclusion: Choosing the Right Hardening Process

The hardening process significantly improves the performance and lifespan of screws. By selecting the appropriate treatment—whether it’s carburizing, nitriding, quenching and tempering, induction heating, or blackening—you can ensure that screws meet the demands of their intended applications.

At FHT, we offer precision-engineered screws with advanced hardening treatments to deliver superior strength, wear resistance, and corrosion protection. No matter the application, our screws are crafted to perform reliably under the toughest conditions.

Need hardened screws tailored to your requirements?
Contact us today for expert advice and a customized solution!

Footnotes

1. Screw-hardening processes: Overview of methods used to enhance strength and durability.
2. Nitriding treatment: Explanation of the nitride layer and its advantages for wear resistance.
3. Quenching and tempering: How these heat treatments balance hardness and toughness.
4. Induction heating: Fast, precise hardening method for localized applications.
5. Black oxide coating: Details on blackening treatment for corrosion resistance and aesthetics.