Carburizing heat treatment

The carburizing heat treatment of steel is to heat the steel in the carburizing medium, to make the carbon atom infiltrate into the steel surface, to change the carbon concentration on the surface, so as to obtain the heat treatment process with certain carbon content and certain concentration gradient on the surface. The purpose of carburizing heat treatment is to obtain high surface hardness, wear resistance and fatigue strength of machine parts.

Carburizing heat treatment can be divided into solid carburizing, liquid carburizing and gas carburizing according to the different aggregation state of carburizing agent. Gas carburizing is a carburizing operation process that loads the workpiece into the sealed carburizing furnace, passes in the gas carburizing agent (methane, ethane, etc.) or the liquid carburizing agent (kerosene or benzene, alcohol, acetone, etc.), decomposes the activated carbon atom at high temperature and infiltrates the workpiece surface to obtain the high carbon surface layer. The solid carburizing heat treatment is one of the earliest carburizing methods to pack the workpiece together with the solid carburizing agent (composed of charcoal plus accelerator) in the sealed carburizing box, heat the box in the heating furnace to the carburizing temperature, and keep it for a certain period of time to make the surface of the activated carbon atom carburizing artificial part. Liquid carburizing heat treatment is to carburize with liquid medium. Common liquid carburizing medium include silicon carbide, "603" carburizing agent, etc.

Carburized workpiece material is generally low carbon steel or low carbon alloy steel (carbon content is less than 0.25%). After carburizing heat treatment, the chemical composition of steel surface can be close to high carbon steel. After carburizing the workpiece must be hardened to obtain high surface hardness, high wear resistance and fatigue strength, and keep the core of low carbon steel after quenching strong toughness, so that the workpiece can withstand impact load. Carburizing technology is widely used in aircraft, automobile and tractor machinery parts, such as gear, shaft, camshaft.