Will be high temperature tempering quenching workpiece (500 ~ 650 ℃) heat treatment operations, often referred to as conditioning treatment. Its mother is: softening alloy steel workpiece, easy cutting. So that the workpiece to obtain good comprehensive mechanical properties. As a preliminary heat treatment, it is also to prepare for the final heat treatment. It should be noted that the mechanical properties after quenching and tempering are closely related to the hardenability of the workpiece. Most of the quenched and tempered steels are medium carbon and low alloy steels. C=0.3 ~ 0.5%, and the total amount of alloying elements is less than 5%. Its service conditions are alternating bending, torsion, tension, impact and other complex stresses. M, Si, Cr, Ni and B are the main addition elements in quenched and tempered steel. The main purpose is to improve the hardenability of steel and strengthen the matrix (except for B). Auxiliary elements are W, Mo, V, Ti, etc., which can refine grain and improve tempering resistance.