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 real example is a recent project of ours that combined nitriding and localized induction hardening to solve a technical challenge.

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

The problem: nitriding and post-treatment grinding

The case study involves a gear that has been nitrided over its entire surface. Nitriding is known to provide high surface hardness and good wear resistance, making it a popular choice for mechanical components intended for high friction conditions. However, a portion of the gear required a subsequent post-treatment grinding operation to ensure precise tolerances.

This grinding, while necessary, caused a significant drop in 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 problem, an ingenious solution was adopted: combining nitriding on the entire gear with localized induction hardening on the ground part. This approach made it possible to maintain the necessary surface hardness and solve the problem of loss of wear resistance.

Let's look at the steps of this solution in detail:

Nitriding on the entire piece: nitriding, carried out at temperatures of 500-600°C, created a hard layer on the entire surface of the gear, ensuring wear resistance and dimensional stability, without causing significant distortions.

Localized induction hardening: induction hardening was applied exclusively to the area that would undergo grinding. This process allowed the surface to be rapidly heated to over 800°C and cooled rapidly, resulting in higher hardness and a deeper martensitic structure than nitriding.

Benefits of double treatment

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

Maintained hardness in the ground zone: Thanks to induction hardening, the ground zone maintained a high hardness, preventing the drastic drop that occurs with nitriding alone.

Uniform hardness: Nitriding ensured uniform hardness across the entire component, improving the gear's overall wear resistance.

Increased fatigue resistance: The combination of the two treatments ensured excellent resistance to mechanical fatigue, thanks to the balance between surface hardness and core toughness.

This case highlights how choosing the optimal heat treatment is essential to maximise the performance of gears and other critical mechanical components. The combination of nitriding and induction hardening has successfully solved the problem of loss of hardness in the ground area, while improving the durability and performance of the gear.

If your projects are also challenging and you come across this type of problem, contact GSI Ingranaggi at [email protected] to discover the solutions best suited to your needs.