The small diameter seamless steel pipe has been hardened again heated to a certain temperature, then some method of cooling is called pipe tempering. Its purpose is to eliminate the internal stress generated by quenching, to reduce the hardness and brittleness, to obtain the desired mechanical properties. Tempering is divided into high temperature tempering, middle temperature tempering and low temperature tempering.

Seamless steel pipe tempering after quenching heated to below the critical temperature, holding time, and then cooled in air or oil. Immediately after quenching and tempering is carried out, is also the last step of heat treatment. 
① obtain the desired mechanical properties. In general, part of the strength and hardness after quenching is greatly improved, but there is significantly lower ductility and toughness, while the actual working conditions of the parts require good strength and toughness. Select the appropriate tempering temperature after tempering, the required mechanical properties can be obtained; 
② stable organization and stable size; 
③ eliminate stress. 

Tempering category 
(1) tempering the hardened steel is heated to 150-50oC, and at this temperature for a certain time, and then cooled in air, tempering used for cutting tools, measuring tools, molds, Rolling and carburizing parts, etc. Eliminate stress due to quenching of steel produced. 
(2) tempering the quenched steel is heated to 350 to 450%, after holding for some time to cool down, generally used for all kinds of hot springs and other parts die. The steel to obtain a higher elastic member, a certain toughness and hardness. 
(3) heating the steel to high-temperature tempering after quenching to 500 ~ 650oC, after the cooling after heat is mainly used for high strength, high toughness important structural parts, such as spindles, crankshaft, cams, gears and connecting rods. The steel pi