What is the hardness of 45# steel

45# steel belongs to high-quality carbon structural steel. The carbon content of No. 45 steel is between 0.4% - 0.5%, the hardness is not high, and it is easy to cut. It is generally formed by hot rolling or cold rolling. According to the requirements of 45# steel parts under different working conditions, if the quenching hardness is controlled between 48 and 52 after adjustment and high-frequency quenching, the surface hardness of the parts can be improved, while the wear resistance of the parts can be increased by carburizing. The hardness of 45# polished plate after processing is generally between HRC20 and 34. 45# steel is widely used for unimportant gears on machine tools or drilling machine transmissions with medium load, but it cannot be used to manufacture gears with high speed or high load.

The recommended heat treatment temperature of 45# steel specified in GB/T699 standard is 850℃ normalizing, 840℃ quenching, 600℃ tempering, and the property reached is yield strength ≥ 355MPa.

According to GB/T699, 45# steel has tensile strength ≥ 600MPa, yield strength ≥ 355MPa, elongation ≥ 16%, reduction of area ≥ 40%, and impact energy of 39J.

45# steel is qualified if its hardness is greater than HRC55 (up to HRC62) after quenching and before tempering. The highest hardness in practical application is HRC55 (high-frequency quenching HRC58).