As a medium for the case hardening solid, liquid and gaseous substances may be used.
As carburizing medium the following substances are used:
The process is carried out in steel or cast iron boxes placed into a furnace at the temperature 1650°F - 1750°F (900°C - 950°C) resulting in formation of hard case of the thickness 0.02”-0.08” (0.5mm – 2mm) and containing 0.8-1% of carbon.
The process is carried out in a furnace (batch or continuous) at the temperature 1650°F - 1750°F (900°C - 950°C) for 3-4 hrs.
Thickness of the hard layer formed in the gaseous carburizing may reach 0.15” (4mm).
Nitriding is the process of diffusion enrichment of the surface layer of a part with Nitrogen.
Gas nitriding is carried out at 930°F - 1110°F (500°C - 600°C) for 40-100 hrs.in the atmosphere of Ammonia, which dissociates to Hydrogen and nitrogen. The latter diffuses into the steel forming nitrides of iron, aluminum, chromium and vanadium.
Ion nitriding (plasma nitriding) is a surface Hardening heat treatment, in which Nitrogen is delivered to the workpiece surface in form of ionized gas (plasma).
The case formed as a result of nitriding has a hardness of about 1100 HV which is higher than the hardness after carburizing.
No additional heat treatment is required after nitriding.
Carbonitriding is the process of diffusion enrichment of the surface layer of a part with carbon and nitrogen.
Gaseous carbonitriding is carried out in gaseous medium, consisting of carburizing gas (methane, propane) with addition of 3-8% of Ammonia.
There are two principal methods of the gaseous carbonitriding:
Cyaniding is the carbonitriding process, conducted in molten salt, containing 20-25% of sodium cyanide (extremely toxic substance).
The process is carried out at the temperatures 1500°F - 1580°F (820°C - 860°C) for 1 hour.
Carbonitrided parts possess better (than carburized parts) wear resistance.