Carburizing has a long history and has been used as a steel-making technology since the days of sword forging. With the aim of high strength and wear resistance, we provide high-quality services in production bases in Japan and abroad for various material needs.

Carburizing treatment refers to a chemical heat treatment process in which the steel is heated in a carburizing medium and kept warm so that carbon atoms penetrate into the surface in order to increase the carbon content of the steel surface and form a certain carbon concentration gradient.

Method of heat treatment carburizing

Carburizing can only change the chemical composition of the surface of the part. In order to obtain the properties of outer hard inner toughness, quenching and low temperature tempering need to be carried out after carburizing heat treatment to increase the strength and toughness of the steel and stabilize the size of the parts. According to the composition, shape and mechanical properties of the workpiece, the method of heat treatment carburizing.

1) Direct quenching + low temperature tempering

Parts are removed from the heat treatment furnace, directly quenched, and then tempered to achieve the desired surface hardness. There are two conditions for direct quenching: after the carburizing heat treatment, the austenite grain size is above grade 5 to 6; there are no network carbides and block carbides in the carburized layer. 20CrMnTi steel is mostly quenched directly after carburizing.

2) Pre-cooling direct quenching + low temperature tempering

The purpose of pre-cooling is to reduce the deformation of the part and reduce the retained austenite of carbide precipitation on the surface. The results show that the pre-cooled direct quenched surface hardness slightly increases, but the grain size does not change. The pre-cooling temperature should be higher than Ar3 to prevent the precipitation of core ferrite. Excessive temperature affects the precipitation of carbides during the pre-cooling process, the volume of retained austenite increases, and the quenching deformation increases.

3) One heating quenching + low temperature tempering

Heat treatment carburizing is suitable for parts with high central strength and good toughness after quenching.

4) High temperature tempering + quenching + low temperature tempering

After high temperature tempering, the retained austenite is decomposed, and the carbon and alloy elements in the carburized layer are precipitated in the form of carbides, which is easy to process and the retained austenite is reduced. Mainly used for chromium-nickel alloy steel parts.

5) Secondary quenching + low temperature tempering

After the workpiece is cooled to room temperature, it is quenched and tempered twice. This surface heat treatment method is a way to maintain heat treatment properties. Secondary quenching is beneficial to reduce the amount of retained austenite on the surface.

6) Secondary quenching + cold treatment + low temperature tempering

Also called high alloy steel heat treatment to reduce the volume of retained austenite on the surface, mainly used for gear and shaft parts.