Thermal treatment method for large-section axle-type forge pieces

Abstract

The invention discloses a thermal treatment method for large-section axle-type forge pieces. The thermal treatment method comprises the following steps that a forge piece is normalized with a temperature increasing rate of 4-7 DEG C / min; heat preservation is performed at 910-930 DEG C; the forge piece is air cooled to 500-600 DEG C with a temperature decreasing rate of 60-70 DEG C / min; the forge piece is air cooled to be below 150 DEG C with a temperature decreasing rate of 5-10 DEG C / min; quenching is performed with a temperature increasing rate of 4-7 DEG C / min; heat preservation is performed at 860-880 DEG C; then quenching is performed; the forge piece is rapidly cooled to be below 150 DEG C with a temperature decreasing rate of 100-150 DEG C / min; the forge piece is placed into an oil cooling system for cooling; tempering is performed with a temperature increasing rate of 4-7 DEG C / min; heat preservation is performed at 640-660 DEG C; and the forge piece is air cooled to an operable temperature with a temperature decreasing rate of 5-10 DEG C / min. By adopting the thermal treatment method, the large-section axle-type forge piece can get a good metallographic structure, and have high strength and toughness; and particularly, the core part structure of the large-section axle-type forge piece can be refined, so that the core part and the superficial structure of the large-section axle-type forge piece have the same metallographic structure and mechanical property.

Description

technical field [0001] The invention belongs to the technical field of heat treatment, in particular to a heat treatment method for a shaft forging with a large section. Background technique [0002] At present, the post-forging heat treatment of large cross-section shaft forgings such as rail vehicle axles in China basically adopts two times of normalizing and tempering or quenching and tempering. [0003] Among them, the air cooling process of the normalizing process mainly adopts the layout of the wind direction with large flow and low wind pressure and the wind direction flows along the axial direction of the workpiece. The disadvantage of this layout is that it cannot meet the process requirements of rapid cooling and uniform cooling. At the same time, the known air-cooled chamber cannot adjust the cooling speed, because the specific heat capacity of the air will change greatly with the change of temperature and humidity, so it cannot meet the axles of high-speed trains...

AI Technical Summary

Problems solved by technology

[0003] Among them, the air cooling process of the normalizing process mainly adopts the layout of the wind direction with large flow and low wind pressure and the wind direction flows along the axial direction of the workpiece. The disadvantage of this layout is that it cannot meet the process requirements of rapid cooling and uniform cooling.

At the same time, the known air-cooled chamber cannot adjust the cooling speed, because the specific heat capacity of the air will change greatly with the change of temperature and humidity, so it cannot meet the axles of high-speed trains, subways and heavy-duty trucks that are more refined and higher standards technical requirements

[0004] In the past, the quenching of large-section shaft forgings usually uses ordinary water as the medium, which is easy to cause vapor film due to the vaporization of water by the high-temperature workpiece, and finally fails to achieve the proper cooling rate, so it cannot be used on the forging 65- Dense martensite or lower bainite is formed in the core of 75mm

At the same time, due to the irregularity of the vapor film, the surface structure of the workpiece cannot be uniform

[0005] With the increase of the size of forgings and the improvement of performance requirements, the influence of the structure and mechanical properties of the core of the workpiece on the overall performance is increasing. The traditional heat treatment process has gradually been unable to meet the requirements for the structure and mechanical properties of the core of the workpiece. Moreover, the performance of the core of the product and the performance of the surface layer are often different.

Images