1, 40cr, medium carbon quenched and tempered steel, the most widely used steel in machinery manufacturing, the hardness after quenching and tempering can reach HRC43-55;

2, 35# steel, similar to 45# steel, but its strength is slightly lower, up to HRC38-45;

3, 45# steel, the most commonly used medium carbon steel in the production of smooth rod, its hardness is about HRC20, after high frequency quenching up to HRC55;

4, bearing steel, high carbon chrome steel, its hardness is very high, can reach about HRC62, wear-resistant, long life, but not easy to process, so it is not commonly used;