Case hardening is also known as surface hardening, which is a method that produces a tough layer on the surface of the metal by some other metal alloy which is mainly more durable. Often low carbon steel is being covered with a tough and a more durable metal alloy. This process of hardening the surface is normally done once a part is formed into its final shape. The hardening element content of bars can also be done which are further used in pattern welding or other similar processes. Generally the procedure is followed for parts which generally require a more wear resistant surface and which is internally tough to endure heavy loading.
In the case of high carbon steels when these are case-hardened, the hardness pierces into the core and cause fragility. This is the procedure in which the surface of the metal is chemically changed by commencing a high carbide or nitride content. The core of the material remains unaffected chemically. As and when its heat treated, the high carbon surface reacts to the hardening and the core becomes tough. Components which undergo this process of case hardening include: cardan joints, camshafts, link components, driving pinions, arbors and axles. In many of these cases, the surface which requires hardening is hardened selectively, while leaving the bulk of the part to its original state.
Applications of Case Hardened Components:
1. Energy Generation: The case hardened components are generally used for gear wheels and other components in large dimensions that have to bear both wear and stress such as in hydroelectric power stations, steam turbine gears in power stations or propeller drives of drilling rigs and wind turbine generators.
2. Transportation: Generally in all engine driven vehicles, these case hardened components are used including racing cars, trucks or even ocean vessels.
3. General Mechanical Engineering: Steel rolling equipments, heavy duty transmissions, forging presses, earth moving equipments and heavy construction cranes require case hardened materials. For these applications, the case hardened materials that are used features a combination of fatigue strength and resistance.
4. Another common application on which the process is done are screws, particularly the self-drilling ones. For drilling, the forming threads and the drill points must be harder than the material which is to be drilled, thus the process is done on screws. Cutting and tapping of the other materials like steel is also done.
Steel Case Hardening
Into the metal skin, carbon is penetrated in order to create mild steel which has an external covering with carbon than the nucleus. The mild steel is then heated to a particular temperature till the time its bright red. For the formation of the outer surface the mild steel is immersed into a carbon compound, however, it requires several dipping and re-heating. This procedure will produce on skin above the metal which is rich in carbon.
The principal forms of this process are: