Quenching and Tempering Treatment of 40Cr Steel

Cr can increase the hardenability of steel, improve the strength and tempering stability of steel, and has excellent mechanical properties. 40Cr steel should be used for large or important quenched and tempered workpieces. But Cr steel has the second type of temper brittleness.

For the quenching and tempering of 40Cr steel, various parameters and process cards are stipulated, and the following points should be paid attention to in actual operation:

(1) Oil cooling should be used after 40Cr steel is quenched. 40Cr steel has better hardenability, can be hardened by cooling in oil, and the deformation and cracking tendency of the workpiece are small. However, in the case of tight oil supply in small enterprises, workpieces with uncomplicated shapes can be quenched in water, and no cracks have been found, but the operator must strictly control the temperature of entering and exiting water based on experience.
(2) The hardness of 40Cr steel is still high after quenching and tempering, and the second tempering temperature must be increased by 20~50°C, otherwise, it will be difficult to reduce the hardness.
(3) After the 40Cr steel is tempered at high temperature, the complex shape is cooled in oil, and the simple one is cooled in water, in order to avoid the influence of the second type of temper brittleness. After tempering and quick cooling, the workpiece should be treated with stress relief if necessary.