Optimization of heat treatments in gears: nitriding and localized induction hardening

Have you ever wondered how to achieve maximum wear resistance in a gear after heat treatment? A recent project of ours provides a real example, where we combined nitriding and localized induction hardening to solve a technical challenge.

When designing a mechanical component, such as a gear, subjected to high loads, the choice of heat treatment plays a crucial role in ensuring durability and optimal performance.

The problem: nitriding and post-treatment grinding

The analyzed case involved a gear subjected to nitriding over its entire surface. Nitriding is known for providing a high surface hardness and good wear resistance, making it a common choice for mechanical components in high-friction environments. However, a portion of the gear required subsequent grinding after the heat treatment to meet precise tolerances.

This grinding process, while necessary, significantly reduced the hardness in the affected area. In fact, the surface layer hardened by nitriding is very thin (between 0.2 and 0.6 mm), and even the removal of small amounts of material during grinding reduced the surface hardness, compromising the wear resistance of the gear.

The solution: double heat treatment

To address this issue, an ingenious solution was adopted: combining nitriding on the entire gear with localized induction hardening on the ground portion. This approach allowed the necessary surface hardness to be maintained and solved the problem of reduced wear resistance.

Here are the steps of this solution in detail:

• Nitriding on the entire gear: nitriding, performed at temperatures between 500-600°C, created a hard layer on the entire surface of the gear, ensuring wear resistance and dimensional stability without causing significant distortion.
• Localized induction hardening: induction hardening was applied exclusively to the area that required grinding. This process allowed the surface to be rapidly heated to over 800°C and then quickly cooled, achieving superior hardness and a deeper martensitic structure compared to nitriding.

Benefits of the double treatment

The adoption of a double heat treatment offered several benefits, including:

• Maintenance of hardness in the ground area: thanks to induction hardening, the area subjected to grinding maintained a high hardness, preventing the drastic reduction seen with nitriding alone.
• Uniform hardness: nitriding ensured uniform hardness across the entire component, improving the overall wear resistance of the gear.
• Greater fatigue resistance: the combination of the two treatments provided excellent fatigue resistance, thanks to the balance between surface hardness and core toughness.

This case highlights how choosing the right heat treatment is essential to maximize the performance of gears and other critical mechanical components. The combination of nitriding and induction hardening successfully addressed the problem of reduced hardness in the ground area, while also enhancing the gear’s durability and performance.

If your projects are also challenging and you face similar issues, contact GSI Ingranaggi to discover the solutions best suited to your needs.