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Vacuum Hardening High-Strength Steels

High Strength Steel Requirements

Due to the increasingly complex working environment of bearing steel, it must bear complex stress states such as tension, compression, bending, shearing, and alternating during the work process, and the stress situation is complex, which affects the high quality, reliability and Comprehensive performance puts forward higher requirements. It is very important to use heat treatment technology of Vacuum hardening to achieve high strength steel.

GCr15 bearing steel belongs to high carbon steel, and the ordinary quenching treatment surface is prone to oxidation and decarburization, which greatly affects the performance of GCr15 bearing steel, and its application range is greatly limited. According to the performance characteristics of GCr15 bearing steel, the vacuum oil quenching method is used to carry out vacuum heat treatment on GCr15 bearing steel.

Vacuum hardening process

Vacuum hardening was carried out in a vacuum oil quenching furnace, the quenching temperature was 860 °C, and the quenching heating time was 2 h. After vacuum oil quenching, two schemes were adopted for cooling: ①The quenching and cooling transmission mechanism was mechanical transmission, and the oil surface was not inflated and pressurized. The pressure on the quenching oil surface is 1-10 Pa, and the transfer time is 30 s; ②The vacuum oil quenching furnace adopts hydraulic transmission, and is equipped with a pressurization system. 13s. After the Vacuum hardening oil is cooled, cryogenic treatment is carried out quickly in the freezer. The cryogenic treatment temperature is -70 ° C, and the cryogenic treatment time is 1 h. The tempering time is 2 h.

The process flow of vacuum oil quenching is shown in Figure 1.

Fig.1 Vacuum oil quenching process curve of GCr15 steel

① Oil surface pressure 1.5x105Pa, transfer time 13s

② Oil surface pressure 1-10Pa, transfer time 30s

Key points of Vacuum hardening process

(1) The hardness of GCr15 steel after Vacuum hardening is closely related to the microstructure obtained after quenching and the distribution of carbides.

When the oil surface pressure of vacuum oil quenching is 1-10 Pa, and the quenching transfer time is 30 s, the structure of GCr15 steel quenched and tempered at low temperature is aphanitic martensite + pearlite + carbide, and the carbide is relatively coarse and distributed. uneven. When the Vacuum hardening oil surface pressure is 1.5×105Pa and the quenching transfer time is 13s, the structure of GCr15 steel after quenching and tempering at low temperature is aphanitic martensite + dispersed granular carbides, and the carbides are fine and uniformly distributed.

(2) The microstructure and properties of GCr15 steel in vacuum oil quenching depend on the cooling capacity of vacuum oil quenching, and the cooling capacity of vacuum oil quenching is affected by two aspects: the pressure of quenching oil surface and the transfer time.

When the oil surface pressure of vacuum oil quenching is 1-10 Pa, and the quenching transfer time is 30 s, the average hardness of GCr15 steel after quenching and tempering at low temperature is 51.2 HRC, and the hardness uniformity is poor. When the quenching oil surface pressure is 1.5×105Pa, and the quenching transfer time is 13s, the average hardness of the sample is 63.2 HRC, and the hardness uniformity is good. Increasing the pressure of the quenching oil surface and shortening the quenching transfer time can greatly increase the hardness of GCr15 steel and obtain uniform hardness.

Vacuum hardening Furnace Selection: SIMUWU manufactures vacuum hardening furnaces in a variety of sizes and configurations, depending on the specific needs of the application. They can be customized to include features such as rapid cooling systems, gas quenching, and temperature monitoring and control. Selection of appropriate heating and cooling parameters depends on the specific metal being heat treated and the desired properties of the final product. The VOGQ vacuum oil quenching furnaces have a two-chamber design to meet changing application needs. According to process requirements, users can choose to quench with oil or inert gas.