Cyaniding is a case-hardening process that is commonly used on low-carbon steels. It is a fast and efficient method of increasing the hardness and wear resistance of the steel surface. This process involves heating the part to a temperature between 871-954 °C and immersing it in a bath of sodium cyanide.
The sodium cyanide bath provides the necessary carbon and nitrogen for the case-hardening process. The high temperature causes the carbon and nitrogen atoms to diffuse into the surface of the steel, forming a hardened layer. This layer significantly improves the durability and strength of the steel, making it suitable for applications where wear resistance is crucial.
During the cyaniding process, a chemical reaction takes place between the sodium cyanide and oxygen present in the atmosphere. This reaction can be represented by the equation: 2NaCN + O2 → 2NaCNO. The formation of sodium cyanate (NaCNO) is an undesirable byproduct, as it can affect the quality of the hardened layer. Therefore, after the cyaniding process, the part is quenched and rinsed in water or oil to remove any residual cyanide and sodium cyanate.
Cyaniding is particularly effective on low-carbon steels because these steels have a lower carbon content, which makes it easier for the carbon atoms to diffuse into the surface. The process is commonly used in industries such as automotive, aerospace, and manufacturing, where components require high strength and wear resistance.
On the other hand, nitriding is another case-hardening process that is used to increase the surface hardness of steel. Unlike cyaniding, which involves the diffusion of carbon and nitrogen into the surface, nitriding focuses solely on nitrogen diffusion. Nitriding is commonly used on alloy steels, tool steels, and stainless steels.
In the nitriding process, the steel part is heated to a temperature typically between 482-621 °C in an atmosphere rich in nitrogen. This can be achieved in a furnace or by using specialized nitriding salts. The nitrogen atoms diffuse into the surface of the steel, forming a nitride layer. This layer significantly improves the hardness, wear resistance, and corrosion resistance of the steel.
Nitriding has several advantages over cyaniding. It does not require the use of toxic cyanide compounds, making it a safer and more environmentally friendly process. Nitriding also produces a more uniform and controlled case depth, allowing for precise control over the hardened layer thickness. Additionally, nitriding can be performed at lower temperatures, reducing the risk of distortion or dimensional changes in the steel part.
Cyaniding and nitriding are both case-hardening processes used to increase the surface hardness of steel. Cyaniding involves the diffusion of carbon and nitrogen into the surface, while nitriding focuses solely on nitrogen diffusion. Cyaniding is mainly used on low-carbon steels, while nitriding is commonly used on alloy steels, tool steels, and stainless steels. Each process has its advantages and is chosen based on the specific requirements of the application.