The Quality Effect of Vacuum Quenching

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(1) The effect of vacuum quenching on the surface quality of the workpiece

①Reduction of heating oxides under vacuum.

②The influence of the elements.

③The influence of steel type.

④The influence of cooling method.

⑤The effect of tempering.

⑥The influence of oil return from vacuum pump, oil booster pump and oil diffusion pump.

⑦Vacuum quenching oil degassing.

⑧ Furnace leakage rate.

⑨ Influence of heating speed.

⑩ The air leakage problem of the inflation pipe.

(2) Specific measures to reduce vacuum quenching deformation

①Reducing deformation in heating technology

a. Warm up multiple times.

b. Convection heating below 800°C.

c. Improve the uniformity of furnace temperature and arrange rationally.

d. Reasonably control the pressure in the furnace, and 13. 3Pa is appropriate for backfilling N2.

② Reduce the deformation of the workpiece in terms of cooling technology

a. Try to use high pressure gas quenching instead of oil quenching.

b. In order to reduce the pressure of the organization, the oil is quenched above the M point and the furnace is air-cooled.

c. Gas grading quenching.

d. Control the start time of oil mixing.

e. Reduce the vibration of the workpiece in the hot state.

f. The deformation of the material tray and tools will affect the deformation of the workpiece.

g. The thickness is uneven, and the acute corners are wrapped with alumina wool.

h. Install the furnace reasonably.

i. The spray mode of cooling gas during high-pressure gas quenching.

(3) Mechanical properties of steel after vacuum quenching. When vacuum quenching is heated, the workpiece has degassed, non-oxidized, and non-decarburized, so it has higher mechanical properties. Table 1 shows Cr 12MoV steel after vacuum quenching and salt bath quenching. Performance comparison, for reference.

Quenching temperature /°C	Tempering temperature /°C	Rm/(N/mm2 )		F/mm		ak/(N.m/cm2 )		(Hardness HRC) vacuum quenching		(Hardness HRC) Salt bath
		Vacuum	Salt bath	Vacuum	Salt bath	Vacuum	Salt bath	Quenched	Quenched and tempered	Quenched	Quenched and tempered
950	180	4239	3150	4.3	2.87	12.7	18.4	60.8	61	61.3	60.5
950	180	3756	2814	4	2.4	21.6	14.7	64.7	61.9	65.8	63
1020	240	3851	3048	4.4	2.36	21.6	21.6	65.8	60.8	66.2	60.8
1080	240	3584	2139	4.1	1.76	25.1	14.7	61.9	58.6	65.5	59.7
1120	520(cold)	2501	2755	5.1	3.5	27.5	26.5	55.3	55.6	59.3	60.7

Table 1 Comparison of mechanical properties of Cr 12MoV steel after vacuum quenching and tempering and salt bath quenching and tempering

Note: Vacuum quenching: preheating at 800°C for 25min. Quenching temperature for 20min.

Salt bath quenching: when the quenching temperature is 950~1020°C, preheating at 400°C for 1h, quenching holding time for 9min;When the quenching temperature is 1080~1120°C, preheating at 850°C for 6min, quenching holding time for 3min, 600~650°C grading for 2~3min and then air cooling.

(4) The service life of vacuum quenched products. Because vacuum quenched workpieces are heated under vacuum, their surface has no oxidation and decarburization, small deformation, small machining allowance, and can realize the characteristics of non-processing after heat treatment, and its service life It is several times or even tens of times higher than salt bath quenching. It is the most promising heat treatment technology. With the improvement of heat treatment technology for parts, vacuum heat treatment will replace salt bath heat treatment and non-protective heating furnaces.

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 other vacuum equipments.Provide customized services, equipment work area can be based on customer output.

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