Surface Hardening in CNC Machining

Surface hardening treatment uses a specific method to obtain higher hardness on the surface of the part, while still maintaining relatively low hardness and good toughness inside. This combination can make the parts more resistant to external forces such as wear, friction and impact.

 

 

Carburizing is to place parts in a medium containing carbon and heat it to a certain temperature to allow carbon atoms to penetrate into the surface of the part to form a high carbon layer. After subsequent quenching and tempering treatments, the surface hardness can be significantly improved. Carburizing treatment is suitable for materials such as low carbon steel and low alloy steel, and is often used to manufacture parts such as gears and shafts that bear large loads.

In the carburizing process, the control of parameters such as temperature, time and carbon potential is crucial. If the parameters are improper, problems such as uneven carburizing layer, insufficient hardness or cracks may occur.

Nitriding is to place the parts in an atmosphere containing nitrogen at a certain temperature, so that nitrogen atoms penetrate into the surface of the parts to form a nitrided layer. Nitriding treatment can improve the surface hardness, wear resistance, corrosion resistance and fatigue strength of parts. Nitriding treatment is suitable for alloy steel, stainless steel and other materials, and is often used to manufacture high-precision parts such as molds and cutting tools.

The temperature of nitriding treatment is relatively low, the deformation is small, and a dense nitride layer can be formed on the surface of the part, which has good corrosion resistance. However, nitriding treatment takes longer and costs more.

 

Quenching is a process in which parts are heated above a critical temperature, kept warm for a period of time, and then cooled rapidly. Quenching can make parts obtain high hardness and strength, but it can also produce large internal stress inside the parts, which can easily lead to deformation and cracking of the parts.

In order to reduce the internal stress after quenching, tempering is usually performed. Tempering is a process in which the quenched parts are heated to a certain temperature, kept warm for a period of time, and then cooled slowly. Tempering can reduce the hardness and strength of parts and improve the toughness and plasticity of parts. It can also eliminate internal stress and prevent deformation and cracking of parts.

 

 

The high hardness of the parts surface can effectively resist wear and extend the service life of the parts. For example, in mechanical transmission, after the surface of the gear is hardened, the wear of the tooth surface can be reduced and the transmission efficiency can be improved.

 

Some surface hardening treatment methods, such as nitriding treatment, can form a dense nitride layer on the surface of the part with good corrosion resistance. This is especially important for parts operating in harsh environments.

 

Surface hardening treatment can produce residual compressive stress on the surface of the part. This compressive stress can offset the tensile stress suffered by the part during use, thereby improving the fatigue strength of the part. For example, on parts such as crankshafts of automobile engines, surface hardening treatment can significantly improve the fatigue life of the parts.