One method is quenching, which simply increases the hardness, but the toughness is poor and easy to fracture; the second is annealing after quenching to increase the hardness without reducing the toughness; the third is carburizing or nitriding or carbonitriding to increase the surface hardness without the internal change .
No. 45 steel is qualified if the hardness is greater than HRC55 (up to HRC62) before being tempered after quenching. To
The highest hardness in practical application is HRC55 (high-frequency quenching HRC58).
The GB/T699-1999 standard stipulates that the tensile strength of 45 steel is 600MPa, the yield strength is 355MPa, the elongation is 16%, the reduction of area is 40%, and the impact energy is 39J.
Hardness: unheated ≤229HB; annealed steel ≤197HB, the surface hardness after quenching can reach 45～52HRC.
Link to this article：45 steel hardness
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