What is Case Hardening? Details, Variations and Advantages of the Process

Step-by-Step Guide: How Case Hardening Works

1. Carburizing: The First Step in Strengthening Steel

• Overview: Carburizing involves heating the steel in a carbon-rich environment at temperatures between 880°C and 950°C.
• Process Details: During this process, carbon diffuses into the surface layer of the steel, enriching it and increasing its hardness. The depth of this carburized layer can range from 0.1 mm to 4 mm, depending on the specific application and material requirements.

2. Hardening: Locking in Surface Strength

• Overview: After carburizing, the steel is rapidly cooled or quenched to lock in the carbon and achieve the desired surface hardness.
• Quenching Media: The steel can be quenched in various media, such as water, oil, or molten salt, depending on the required cooling rate and the material’s hardenability. The quenching process ensures that the surface remains hard while the core retains its ductility.

3. Tempering: Enhancing Toughness

• Overview: Tempering is the final step in the case hardening process, aimed at reducing brittleness and improving toughness.
• Process Details: The steel is heated to a lower temperature, typically between 160°C and 220°C, to relieve internal stresses without significantly reducing the surface hardness. This step enhances the ductility of the hardened surface, making the component more resistant to impact and fatigue.

Benefits of Case Hardening

Improved Wear Resistance

The increased surface hardness resulting from case hardening provides excellent protection against wear, making it ideal for components that are subject to constant friction.

Enhanced Load Capacity

By maintaining a tough core, case-hardened components can bear higher loads without deforming, making them suitable for heavy-duty applications.

Increased Fatigue Strength

The combination of a hard surface and a ductile core significantly improves the component’s resistance to fatigue, ensuring a longer service life.

Flexibility in Application

Case hardening allows for partial hardening of components, enabling precise control over which areas are hardened and which remain ductile. This flexibility is particularly useful in complex parts with varying functional requirements.

Variations of Case Hardening

Single Hardening

• Process: Single hardening involves carburizing the steel and then cooling it slowly before undergoing further heat treatment. This method is often used for steels prone to forming coarse grains.
• Applications: Single hardening is ideal for components that require a hard surface with a less aggressive core hardening.

Double Hardening

• Process: Double hardening involves two separate hardening processes: one at the core hardening temperature and another at the surface hardening temperature. This approach is more time-consuming and costly but provides superior grain refinement and strength.
• Applications: Double hardening is used for components where both surface hardness and core strength are critical, despite the higher costs and potential for workpiece distortion.

Which Metals Are Suitable for Case Hardening?

The primary goal of case hardening is to increase the carbon content at the surface of the metal. Therefore, only low-carbon steels, with a basic carbon content of less than 0.25% by mass, are generally considered suitable. These include mild steels and some alloy steels. The treated metals are typically unalloyed or low-alloyed, making them ideal candidates for this process.

Common Steel Grades Used in Case Hardening

1. 1.6587/18CrNiMo7-6
2. 1.0301/C10
3. 1.7131/16MnCr5
4. 1.7147/20MnCr5

These steel grades are frequently employed in case hardening due to their excellent response to the process. Typical applications include the manufacture of gear parts and gears, where high wear protection and good flexural fatigue strength are required.

Related Process: Carbonitriding

A process similar to case hardening is carbonitriding, where nitrogen is diffused into the surface layer in addition to carbon. This process provides additional benefits in terms of surface hardness and wear resistance.

Typical Applications of Case Hardening

Gear Manufacturing

Case hardening is widely used in the production of gears, which require high surface hardness to resist wear and good core toughness to withstand the forces of repeated stress.

Shafts and Bearings

These components benefit from case hardening as it enhances their ability to endure heavy loads and resist surface damage due to constant rotational movement.

Tools and Cutting Equipment

The process is also applied to cutting tools and other equipment where a hard, wear-resistant surface is necessary for maintaining sharpness and performance over time.

Bortec’s Advanced Hardening Solutions

BORINOX®: Hardening Stainless Steel at Low Temperatures

With BORINOX®, Bortec offers a unique process for hardening stainless steel and nickel-based alloys without compromising corrosion resistance. This low-temperature diffusion process not only increases surface hardness but also protects against cold welding and other forms of wear.

NICKELCOAT®: Corrosion and Wear Resistance

Bortec’s NICKELCOAT® process provides an additional layer of protection by applying a nickel-based coating that enhances both wear resistance and corrosion protection, particularly in acidic environments.

BOROCOAT®: Surface Hardening for High Durability

BOROCOAT® offers superior surface hardening by diffusing borides into the metal surface, creating an extremely hard, wear-resistant layer while maintaining core flexibility.

Get Expert Advice on Case Hardening

For more information on how Bortec’s case hardening processes can benefit your specific applications, contact our experts today. We’ll help you choose the best hardening solution tailored to your needs.