Gear materials and heat treatment technology in China

(1) Present situation

① The quality of gear materials is low, there are many defects in castings and forgings, and some materials with special requirements, such as high temperature and high hardness gear steel for helicopters, low temperature impact resistant gear steel for military vehicles in high and cold climate, low stress induction hardened gear steel, etc; ② Gear carburizing and quenching deformation is large, grinding cracks, burns and grinding steps are easy to appear during tooth grinding, and carburizing cycle is long, energy consumption is high, internal oxidation is easy to occur, which affects the bending fatigue strength of tooth root; The nitriding layer is thin, which is not suitable for gears with large modulus. If the layer depth is increased, the time is too long, and it is difficult to control the phase composition; Induction hardened gears are prone to root quenching cracking, and the weak transition layer between hardened layer and core often leads to early fatigue spalling, which seriously affects the bearing capacity and reliability of gears.

(2) Challenge

Low quality of gear materials, many defects and backward heat treatment technology are important reasons for low bearing capacity, low reliability and high scrap rate of gear products in China ‚ More research should be done to change this situation.

(3) Target

① Improve the metallurgical quality of gear steel and castings and forgings, reduce the gas content and non-metallic inclusions in the steel, and the gas content can reach [O] ≤ 10-5 and [H] ≤ 2 respectively × 10-6,[N]≤5 × 10-5; Control the hardenability bandwidth of gear steel, and the fluctuation of upper and lower limits is less than 3HRC; ② Develop high temperature high performance steel, low temperature impact steel, high pressure gas quenched micro deformation steel, rapid nitriding steel, precipitation hardening steel and other special performance gear steels; Develop non-metallic materials such as high-strength plastics for gears; ③ Overcome carburizing and nitriding technology, improve production efficiency, overcome deep nitriding technology, improve the bearing capacity of nitriding gear and expand the scope of application; ④ The mechanism and law of stress formation in gear induction quenching process are studied, the quenching process is optimized, the residual stress is controlled and the quenching cracking is overcome; The new technologies of multi frequency induction heating quenching and induction press quenching are studied; ⑤ Study the tooth surface strengthening technology of compound heat treatment, high-energy density hardening and shot peening to improve the bearing capacity and reliability of the gear; ⑥ Study the precision thermomechanical treatment technology of gears to improve gear strength and production efficiency.