What are the metallographic structures of the metal surface after carbonitriding treatment of rolling mill bearings?

Dec 25, 2024

Carbonitriding is a chemical heat treatment process that simultaneously infiltrates carbon and nitrogen into the surface of steel parts. The metallographic structure of the metal surface(such as rolling bearings) after treatment varies depending on the treatment conditions (such as temperature, time, atmosphere, etc.) and the raw materials. The following are some typical metallographic structures of the metal surface after carbonitriding:

Surface area:

Mainly high carbon structure morphology, such as needle-shaped martensite and residual austenite.

In some cases, there may be a small amount of carbonitride particles on the surface.

Subsurface area:

Similar to the medium carbon structure area, such as tempered martensite or fine needle martensite.

The structure morphology of this area may be more blurred than that of the surface area.

Transition zone:

There may be a transition layer of martensite, troostite and other structures.

The structure morphology and distribution of this area will be affected by the depth of co-infiltration and quenching conditions.

Core structure:

Mainly ferrite and a small amount of low-carbon martensite.

The morphology and properties of the core structure are usually related to the initial structure state of the raw material.

In addition, the metallographic structure of the metal surface after carbonitriding treatment may also be affected by some undesirable factors, such as internal oxidation, decarburization or carburization. These factors may cause undesirable morphologies, such as black holes and black structures distributed along grain boundaries in the metallographic structure, thereby reducing the hardness and fatigue strength of the material.

In practical applications, in order to obtain the ideal carbonitriding layer structure and performance, it is necessary to strictly control the treatment conditions, raw material quality and subsequent heat treatment process. At the same time, it is also necessary to strictly test and analyze the treated metal surface to ensure that it meets the use requirements.

Please note that the above information only represents some typical metallographic structure characteristics of the metal surface after carbonitriding treatment. Due to the diversity of carbonitriding process parameters and the differences in raw materials, the actual metallographic structure may be different. Therefore, specific analysis is required according to the actual situation in specific applications.