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Influence of Vacuum Quenching and Tempering Process on Steel

42CrMo steel has high strength, high toughness, good penetration resistance, no obvious temper brittleness, high fatigue limit and impact resistance after quenching and tempering treatment, and good low-temperature impact performance, so it has become the main component of key parts in the manufacturing industry. Choose material.

The vacuum heat treatment process is the key to realize the excellent properties of 42CrMo steel, and it is also the focus of research. Different application fields put forward different requirements for the performance of 42CrMo steel. With the increase of material use extreme and durability, higher requirements are put forward for its performance. In order to systematically and comprehensively study the vacuum heat treatment process on 42CrMo steel Influence of microstructure, this paper studies the effect of vacuum quenching and vacuum tempering process parameters on the microstructure of 42CrMo steel.

1 Effect of vacuum quenching temperature on microstructure

Microstructure of 42CrMo steel at different vacuum quenching temperatures. The microstructure of the original rolled 42CrMo steel is mainly ferrite (F) + pearlite (P). When 42CrMo steel is vacuum quenched at 860°C, the microstructure is mainly lath martensite + sheet carbide and retained austenite; when it is vacuum quenched at 880°C, the microstructure is still lath martensite. , and there are many dispersed granular carbides, and retained austenite is also mixed between the martensite laths. As the vacuum quenching temperature continues to increase, the lath martensite becomes denser, the number of granular carbides decreases, and a small amount of retained austenite still exists. This is mainly due to the fact that with the increase of vacuum quenching temperature, the diffusion of carbon becomes more uniform, which makes the microstructure transform into lath martensite more uniformly.

2 Effect of vacuum quenching holding time on microstructure

Microstructure of 42CrMo steel after quenching at 860℃ for different time. The longer the holding time, the more complete the transformation of pearlite to austenite; when the holding time is 30 min, the microstructure of 42CrMo steel is basically composed of lath martensite, but there is still a small amount of undissolved cementite , indicating that the austenitization is basically complete at this time. When the holding time is extended to 60min, the lath martensite still maintains a relatively fine shape, and the cementite is almost completely dissolved. When the holding time was extended to 120 min, the lath martensite structure became obviously elongated and gradually became coarse.

3 Effect of vacuum tempering process on microstructure

Microstructure of 42CrMo steel after quenching at 88O℃ and tempering at different temperatures. After vacuum quenching at 880°C and vacuum tempering at 200°C, the structure of 42CrMo steel changes from lath martensite to tempered martensite. The form of precipitation, so there are still strips of carbides. When the vacuum tempering temperature rises to 400 °C, the main microstructure of 42CrMo steel is tempered martensite + tempered sorbite, but the retained austenite has been basically dissolved, and the carbides precipitated from the supersaturated solid solution transformed into granular cementite. When the tempering temperature reaches 600℃, the structure has transformed into tempered sorbite.

4 Conclusion

1) With the increase of vacuum quenching temperature, the lath martensite in the microstructure of 42CrMo steel is more dense, and the flaky carbides gradually transform into granular carbides and the number decreases. With the extension of the holding time, the degree of austenitization becomes more complete and the martensite is finer, but when the holding time is extended to 120 min, the lath martensite gradually becomes coarser.

2) With the increase of vacuum tempering temperature, the microstructure of 42CrMo steel transforms into tempered martensite, tempered troostite and tempered sorbite. When the tempering temperature reaches 600℃, the microstructure has transformed into tempered sorbite, and the fine-grained cementite is evenly distributed on the matrix.

3) With the increase of quenching temperature, the austenite grain size increases gradually.