The spindle of machine tool is the main shaft part in machine tool. Different types of machine tools, spindle working conditions are not the same. Depending on the size and type of load under which the spindle works, it can generally be divided into four categories: (1) Light spindle. The working load is small, the impact load is not big, the axle neck position is not serious, for example, the spindle of ordinary lathe. This type of shaft is generally made of 45 steel, by tempering or normalizing treatment, in the requirements of wear-resistant parts using high-frequency surface hardening. (2) spindle. Medium load, wear more serious, have a certain impact load, such as milling machine spindle. The general use of alloy quenched and tempered steel manufacturing, such as 40Cr steel, by quenching and tempering, require wear-resistant parts of surface hardening. (3) heavy-duty spindle. The work load is big, the abrasion and the impact are serious, for example, the combined machine tool spindle with large working load. Generally used 20CrMnTi steel manufacturing, through carburizing, quenching treatment. (4) High precision spindle. Some machine tool spindle work load is not big, but the precision request is very high, after heat treatment deformation should be very small. Wear should be very slight during the work, such as the spindle of the precision boring machine. The general use of 38CrMoAlA special nitriding steel Manufacturing, after the quality treatment, nitriding and dimensional stability of treatment. In the past, almost all of the spindle was made of steel, and the light load and the medium spindle were made of ductile iron.