What is the difference between 40Cr steel and 45# steel

40Cr steel is the standard steel grade of GB in Chinese, and 40Cr steel is one of the most widely used steels in the machinery industry. After quenching and tempering treatment, it has good comprehensive mechanical properties, good low temperature impact toughness and low notch sensitivity. The steel has good hardenability. It can be hardened to Ф28-60mm when water quenching, and Ф15-40mm when oil quenching.

In addition to quenching and tempering, 40Cr steel is also suitable for cyaniding and high-frequency quenching. The machinability is good, when the hardness is 174-229HB, the relative machinability is 60%. The steel is suitable for making medium-sized plastic moulds.
45# steel is a high-quality carbon structural steel, corresponding to Japanese standard S45C, American standard 1045, and German standard C45. It is characterized by higher strength and deformation resistance than ordinary A3 steel.

What is the difference between 40Cr steel and 45 steel

1. Different carbon content

The carbon content of 40Cr steel is 0.37% to 0.44%, which is slightly lower than that of 45# steel (0.42% to 0.50%).

2. Different prices

Since the price of 40Cr steel is about half more expensive than that of 45# steel, 40Cr steel is not used if 45# steel can be used out of economical considerations.

3. Different hardenability

The difference is after heat treatment. The main function of Cr in heat treatment is to improve the hardenability of steel. Due to the improved hardenability, the strength, hardness, impact toughness and other mechanical properties of 40Cr steel after quenching (or quenching and tempering) treatment are also significantly higher than those of 45 steel.

4. Different cracking tendencies

But also due to strong hardenability, the internal stress of 40Cr steel is larger than that of 45# steel during quenching. Under the same conditions, the cracking tendency of 40Cr steel workpieces is larger than that of 45# steel materials.

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