Heat Treatment Process Gb 40cr Material Good Hardenability - China

Hardenability

GB 40Cr material has good hardenability.

Hardenability refers to the ability of steel to obtain martensitic structure during quenching.

Due to the addition of chromium, the critical cooling rate of GB 40Cr material is reduced, so that it can also obtain martensitic structure on a larger cross section.

For example, when quenching on a round bar with a diameter of 20-30mm, GB 40Cr material can obtain a complete martensitic structure, while ordinary carbon steel is difficult to achieve this hardening effect at the same size.

This makes 40Cr steel suitable for manufacturing parts with larger sizes and complex shapes, such as shaft parts.

Heat treatment process

Quenching

The quenching temperature of GB 40Cr material is generally around 830-870℃.

When quenching, oil quenching is usually used.

The cooling rate of oil quenching is slower than that of water quenching, which can avoid excessive quenching stress and deformation of the workpiece.

During the quenching process, the workpiece is heated to the austenitizing temperature and then quickly placed in oil for cooling, so that the austenite is transformed into martensite.

The hardness of 40Cr steel after quenching is very high, but there is a large internal stress, so tempering treatment is required.

Tempering

The choice of tempering temperature depends on the required hardness and performance.

For GB 40Cr material, high temperature tempering is generally used, and the temperature range is 500 - 650℃.

High temperature tempering can transform the quenched martensite into tempered troostite or tempered troostite.

After tempering, the hardness of GB 40Cr material is reduced, the toughness is improved, and the quenching stress is eliminated.

For example, when the tempering temperature is 550℃, the hardness of 40Cr steel can reach about 30 - 35HRC.

This hardness level is suitable for manufacturing some mechanical parts that require higher strength and toughness, such as gears, shafts, etc.

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