he carburizing temperature from 930 ℃ to 1000 ℃ can increase the carburizing speed by more than twice. However, due to many problems, the future development is limited.

Vacuum chemical heat treatment is carried out in gas phase medium with negative pressure. Because the workpiece surface is purified under vacuum and higher temperature is adopted, the infiltration rate is greatly improved. For example, vacuum carburizing can increase the productivity by 1 ~ 2 times; At 133.3 × When Aluminizing and chromizing at (10-1 ~ 10-2) Pa, the infiltration rate can be increased by more than 10 times.

 

7. Ion chemical heat treatment

It is a chemical heat treatment process that uses glow discharge between workpiece (cathode) and anode to infiltrate elements at the same time in gas-phase medium containing elements to be infiltrated below one atmospheric pressure. For example, ion nitriding, ion carburizing and ion sulfurizing have the advantages of fast infiltration rate, good quality and energy saving.

 

8. Induction self tempering

Induction self tempering is used to replace tempering in the furnace. Because induction heating is used to transfer heat outside the quenching layer, quenching cooling does not take away all the residual heat to realize short-time tempering, it has high efficiency and energy saving, and can avoid quenching cracking in many cases (such as high carbon steel and high carbon high alloy steel), At the same time, once the process parameters are determined, it has the advantages of mass production and remarkable economic benefits.

 

9. Preheating and quenching after forging

Preheating and quenching after forging can not only reduce the energy consumption of heat treatment and simplify the production process, but also improve the product performance.

Using post forging residual heat quenching + high temperature tempering as pretreatment can eliminate the disadvantages of coarse grain and poor impact toughness when post forging residual heat quenching is used as final heat treatment. It has shorter time and higher productivity than spheroidizing annealing or general annealing. In addition, the temperature of high temperature tempering is lower than annealing and political activities, so it can greatly reduce energy consumption, simple equipment and easy operation.

Compared with general normalizing, residual heat normalizing after forging can not only improve the strength of steel, but also improve the plastic toughness and reduce the cold brittle transition temperature and notch sensitivity. For example, 20CrMnTi steel is cooled at 730 ~ 630 ℃ and 20 ℃ / h after forging, and good results are obtained.

 

10. Surface quenching instead of carburizing quenching

The systematic study on the properties (such as static strength, fatigue strength, multiple impact resistance and residual internal stress) of medium and high carbon steel with carbon content of 0.6% ~ 0.8% after high frequency quenching shows that it is completely possible to replace carburizing quenching with induction quenching. We used 40Cr steel for high-frequency quenching to manufacture gearbox gears instead of the original 20CrMnTi Steel Carburized and quenched gears, and achieved success.

 

11. Local heating instead of overall heating

For some parts with local technical requirements (such as wear-resistant tooth shaft diameter, roll diameter, etc.), local heating methods such as bath furnace heating, induction heating, pulse heating and flame heating can be used to replace the overall heating such as box furnace, so as to realize the appropriate coordination between the friction and bite parts of various parts and improve the service life of parts. Because it is local heating, Therefore, quenching deformation can be significantly reduced and energy consumption can be reduced.