In order to increase the hardness of the raw material, the raw material is heated to a high temperature (about 800 °C) and then cooled quickly. It can be divided into different cooling methods basing on different cooling medium, such as oil cooling/water cooling/jet cooling and the so on. The material will become hardenability easily and it will lead to the material easy broken. In order to increase the toughness of the steel, it needs to be tempered again. Pure iron will not become harden even though it has been quenching. If the carbon content of the raw material is more than 0.35%, it may cause quench hardening.