Case hardening is a term used to describe several, more specific procedures which involve the addition of carbon or carbon and nitrogen to the surface of steel. This is done to give the material a hard, wear-resistant outer layer while preserving a softer, more ductile core that is better able to respond to stress without cracking. Case hardening allows manufacturers to work with softer materials and still meet basic requirements for hardness required by an application.
Raw, untreated steel is pliable and soft all the way through — which is not much use if you need a part to be hard at the surface but strong and ductile (or tough) in the middle. Though case hardening is not necessarily a strategy for adding material strength, it does effectively increase the hardness of the outer layer of the material, making it more wear resistant than it would otherwise be.
A steel cutting screw, for example, needs edges hard enough to cut through materials. The trouble is that hard steel is brittle and prone to breaking — so the case hardening provides this cutting edge on the screw while the tougher core holds everything together without breaking.
By diffusing either carbon or nitrogen and carbon case hardening is a suitable strategy for adopting relatively soft materials to applications where a hard exterior is paramount. These are a just a few of the common uses of case hardening:
- Bearings and gears
- Screw machine parts
- Cutting tools
- Engine parts
How does case hardening work?
Case hardening works by diffusing carbon or carbon and nitrogen through the surface of a metal by adding them to the atmosphere within a furnace. In case hardening, this is done at high temperatures. With other techniques, such as with ferritic nitrocarburizing, these higher temperatures are avoided to reduce the stress that can accompany phase changes.
Regardless of which specific case hardening technique is used, it’s ultimately a function of diffusion. That is, case depth behaves predictably over time and at given temperatures. In general, carbon and hardness in case hardened materials are high at the surface and gradually decrease with depth.
Paulo’s approach to case hardening
At Paulo, our furnaces are designed to handle a broad scope of case-hardening applications. We can harden parts up to 48 inches by 36 inches by 36 inches.
We can handle 3,000-pound loads and harden up to 3,800 pounds per hour. We can also meet key automotive requirements, including PPAP.
We have continuous belt furnaces and integral quench furnaces that can generate temperatures of 1750 degrees Fahrenheit in batch furnaces or 1650 degrees Fahrenheit for belt furnaces.
The kind of furnace we use depends on your application. Some parts may have to be heat-treated for hours or even days to accomplish the required case depth, which is why it’s important that your heat treating partner has the capacity to operate 24/7 when necessary.
Our decades of experience, high-tech processes and thorough understanding of metallurgy ensure your parts get cased hardened to your exact specifications.