Vacuum Heat Treatment of Cr12MoV Steel

---

The vacuum heat treatment process of the Cr12MoV steel mold in our factory is generally heated and kept at a medium temperature (1020°C), cooled in vacuum quenching oil, and finally tempered at a low temperature (200°C). Practice has proved that this process is not a big problem for workpieces with simple shapes and small sizes, but it is more complicated for workpieces with larger thickness (>50mm) and workpieces with complex shapes and larger sizes (250×400). It can be summed up as follows:

1) The hardness of the workpiece with larger thickness is low after quenching in oil (HRC 56~58), which cannot meet the design requirements;

2) Even if the thickness of the workpiece is not large, although the hardness after quenching is very high (HRC63), after three times of sufficient tempering at 180~200℃, the hardness will be reduced to HRC58~59.

3) When workpieces with complex shapes and sharp notches are quenched, cracking is prone to occur, so that some workpieces have to be quenched and processed by electrical machining.

4) The period of low temperature tempering is long. Cr12MoV steel is a high-alloy steel with high austenite stability and can be hardened in air, so it is called air-cooled steel. When air-cooled steel is quenched, there is no problem of cracking. Because the cooling in air is slow, the stress generated is only 10% of the stress generated by rapid quenching in liquid. In addition, sub-zero cooling can make the quenched steel get higher hardness. According to the above theory, our factory adopts the method of air-cooling quenching followed by ice-cooling treatment.

1. Method

1). Material and sample size

Standard spheroidizing annealing of Cr1 2MoV steel.

Specimen Size: 1* Specimen- -180X180x 50、2*Sample–190X190x 25(with sharp notches)、3*Sample – -120X120x 35

2). Test conditions: RVGQ vacuum furnace.

3). Heat treatment process: 1* and 2* sample treatment process – -1020℃ x 30min + air cooling (nitrogen pressure is 460 Torr) + – 60°C ice cooling treatment x 2h + return at 260°C and 280°C respectively Fire; 3# sample treatment process – -1020 ° C X30min + oil cooling + 200 ° C tempering x 3h (three times).

4). Measure the hardness and observe the cracking of the workpiece.

2. The hardness measurement results are shown in Table 1.

1) Hardness value (HRC) of sample in Table 1.

Sample number	Hardness value (HRC)
	Quenching	Cold treatment 一60°C	Tempering temperature (°C)
			200	260	280
1*	58~59（gas quenching）	63~64		62~63
2*	60~61（gas quenching）	64~65			60~61
3*	63~64（gas quenching）		58~59

2) After gas quenching and cold treatment, the samples with sharp notches were observed in detail, and no cracking was found.

3. From the above test results, the following conclusions can be drawn:

1). Ice cold treatment can make Cr12MoV steel get higher hardness at the same tempering temperature~, in other words, under the condition of obtaining the same hardness, the tempering temperature can be increased by about 100C, which provides a better solution for eliminating heat treatment stress. sufficient conditions. This is of great significance for complex workpieces that are prone to cracking during wire cutting.

2). It can reduce the deformation of the workpiece and avoid quenching cracking.

3). The number of tempering can be reduced, and it is not necessary to carry out three temperings, only one tempering.

Shanghai Geheng Vacuum Technology Co., Ltd. is a vacuum heat treatment furnace manufacturer with many years of experience in design, manufacturing and production. Mainly produce vacuum heat treatment furnace, vacuum sintering furnace, vacuum brazing furnace, New Energy And Environmental Protection Equipment and Vacuum Carbonization Furnace .Provide customized services, equipment work area can be based on customer output.