Heat Treatment Method of High Carbon Chromium Bearing Steel

---

Bearing steel is called the king of steel by people in the steelmaking industry. High-carbon chromium bearing steel is a large type of bearing steel, and it is the most commonly used steel for manufacturing bearings and bearing parts. The most commonly used high-carbon chromium bearing steels are GCr15 and GCr15SiMn, of which the former is the most used in my country’s bearing industry.

For high carbon chromium bearing steel, the heat treatment methods mainly include:

1. Martensite Quenching and Tempering

The martensite quenching process of high-carbon chromium bearing steel is as follows: the bearing parts are heated to 830-880°C for 0.5 to 1h, and then quenched in oil. It should be tempered immediately after quenching to eliminate internal stress, improve toughness, and stabilize structure and size. In order to eliminate the grinding stress generated during the grinding process, and to further stabilize the structure and size, an additional tempering is required after the grinding process. The structure of martensite after quenching is composed of martensite, retained austenite and undissolved carbides. The content of retained austenite is generally 6% to 15%. Retained austenite can improve toughness and crack propagation resistance, and its existence is beneficial to the performance of the material.

2. Bainite Austempering

The high-carbon chromium bearing steel is quenched at 230-250℃ for 2～4h after isothermal temperature. Its structure is composed of lower bainite, retained austenite and undissolved carbides. As the quenching temperature increases, the bainite bars become longer; the isothermal temperature increases, the bainite bars become wider, the carbide particles become larger, and the angle of intersection between the bainite bars becomes smaller, tending to be arranged equally, forming Similar to the structure of upper bainite; the amount of bainite after austempering increases with the extension of the isothermal time. Studies have shown that: the impact toughness of the bainite structure is about 3 times higher than that of the conventionally quenched and low-temperature tempered martensite structure; the impact toughness of the martensite structure is increased by 30%-50%, and the fracture toughness is increased by 20% than that of the martensite structure tempered at the same temperature; The wear resistance is lower than that of the martensite structure that is quenched and tempered at low temperature, and is close to or slightly higher than that of the martensite structure that is tempered at the same temperature.

3. Quenching of Composite Structure

In order to integrate the advantages of martensite and bainite, heat treatment scholars have studied the bainite-martensite composite structure quenching process, that is, the bearing parts are first heated to the temperature of Ac1～Accm for a period of time, and then transferred to cooling In a quenching medium (oil or salt bath) with sufficient capacity, part of the austenite in the workpiece is transformed into lower bainite, and finally continues to be cooled to a certain temperature below the martensite (Ms) point to make the remaining austenite in the workpiece Most of it is transformed into martensite. The bainite-martensite composite structure after quenching is composed of lower bainite, martensite, a small amount of retained austenite and a small amount of undissolved carbides. This is a new quenching technology with significant advantages and broad application prospects, which is still under development.

Learn more:

Vacuum Heat Treatment Furnace

Vacuum Tempering Furnace

Copyright: SIMUWU Vacuum Furnace