Flame vs. Induction Hardening

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Understanding the Heating Process of Steel

Whenever steel experiences heat, its crystalline structure transforms into a phase known as austenite. This configuration enhances its ability to absorb carbon due to its open cell structure. If it cools slowly, the austenite gradually releases carbon, allowing the metal to revert to its original characteristics.

Conversely, when steel is rapidly cooled in its austenitic state, the carbon remains entrapped within the crystal lattice, resulting in a needle-like structure called martensite. Martensite can be subjected to surface or through-hardening processes.

Carbon steel is inherently robust, but its adaptability to various applications is what renders it vital for modern industries. After carbon steel is cast or forged and has cooled, applications of either flame or induction hardening lead to a hardened surface.

Both techniques induce surface hardening while maintaining the ductility of the core metal, rendering it suitable for different operational demands. High carbon steel is particularly advantageous in settings that involve repetitive stress, where mild steel may wear out prematurely.

Differentiating Hardness in Steel Types

As detailed in our blog, the distinctions in steel formulations primarily pivot around their strength and hardness. Hardened steel is susceptible to cracking under pressure, whereas mild steel can flex, returning to its initial shape unless subjected to sufficient stress. Therefore, mild steel is preferred in construction applications, facilitating flexibility during seismic or high-wind events. On the other hand, hardened steel may fracture, jeopardizing structural integrity.

In manufacturing sprockets, hardened steel teeth withstand wear, extending the sprocket's life, while maintaining a ductile core that resists fracture under shock loads.

Explaining Flame Hardening

Flame hardening involves heating steel through a high-intensity flame delivered by a torch or specialized apparatus, which uniformly heats the surface to a specified temperature. Skilled steelworkers can gauge this temperature, often by visual assessment.

This method enables targeted heating of specific areas, such as the wear surface of a sprocket tooth, allowing for the hardening of only those sections while preserving the overall resilience of the steel. However, because flame heating is a slower process, sometimes taking up to thirty minutes for large surfaces, the underlying metal also receives some heat, limiting the depth to which flame hardening can penetrate. This process is ideal for applications that require a hardness depth of 1.5mm or greater.

The Pros and Cons of Flame Hardening

Advantages of Flame Hardening

1. Suitable for hardening steel in various shapes, including small and irregular items.
2. Allows for specific parts to be hardened while leaving other areas flexible.
3. Can achieve surface hardness or deeper hardness.
4. Cost-effective for small quantities compared to induction setups.
5. Scalable for larger items.

Disadvantages of Flame Hardening

1. Slower process in comparison to induction hardening.
2. Challenging to attain hardness below 1.5mm.
3. Demands skilled labor for accurate heat assessment.
4. Risk of overheating causing brittleness or other defects.
5. Not competitive with induction hardening for large scale operations.
6. Open flames may not be allowed in certain environments.

Understanding Induction Hardening

Induction hardening is a faster method than flame hardening, employing a water-cooled copper coil that generates an electromagnetic field when an electrical current passes through it. Eddy currents are produced in the steel part, resulting in rapid heating.

The Advantages of Induction Hardening

Induction hardening allows for swift heating of steel, typically achieving results in seconds rather than minutes, distributing heat evenly across the exposed surface of the steel within the coil's range. This setup can also be reused for items of similar shapes, making it highly suitable for batch processing.

The Disadvantages of Induction Hardening

The initial investment for induction hardening setups is higher than that of flame hardening, as specific copper coils need to be fabricated for different items to be treated.

Comparative Summary of Flame and Induction Hardening

Flame Hardening:

Utilizes a high-intensity flame and requires operator temperature control, with gradual heating.

Induction Hardening:

Employs induction coils with easily regulated temperature settings resulting in rapid heating.

Common Applications for Flame Hardening:

• Large engineered sprockets
• Drum sprockets
• Wear plates

Common Applications for Induction Hardening:

• Roller chain sprockets
• Cable sheaves and pulleys
• Gears

For further inquiries on material choices or hardness specifications, reach out to us for expert advice tailored to your application.

For more information, please visit Induction Hardening Machine.