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Vacuum heat treatment process of steel
In general, the heat treatment process has intermediate components within the standard range, and there is an adjustment range for the heat treatment temperature. If there is a deviation in the composition within the range, the quenching temperature and tempering temperature can be adjusted accordingly.
The critical temperature refers to the austenite transformation temperature of the steel. Different content of steel has different critical points, but the critical point fluctuates within a range, so the lower critical point temperature refers to the lowest temperature of austenite transformation.
The critical point of commonly used carbon steel:
Steel grade critical point (℃)
20 steel 735-855 (℃)
45 steel 724-780 (℃)
T8 steel 730 -770(℃)
T12 steel 730-820 (℃)
20Cr, 40Cr, 35CrMo, 40CrMo, 42CrMo: the normalizing temperature is 850-900 ℃, and the normalizing temperature of No. 45 steel is about 850 ℃. No. 50 steel and No. 45 steel are distinguished according to their carbon content, generally taking the middle value of carbon content. For example, No. 45 steel represents high-quality carbon structural steel with a carbon content of 0.42~0.50%, and 45 is an intermediate value, which is good for distinguishing carbon content. 45-gauge steel is often used to make shafts or bearings. No. 50 steel contains carbon C 0.47~0.55. No. 50 steel is often used in the manufacture of mechanical parts with low dynamic load, low impact load and good wear resistance, such as forged gears, shaft friction discs, machine tool spindles, engine spindles, rolls, tie rods , spring washers, etc. No. 75 steel, carbon (C) 0.72~0.80, No. 75 steel is used to manufacture coil springs, leaf springs, and worn mechanical parts with low strength and slightly smaller cross-sectional dimensions. No. 80 steel, carbon (C) 0.77 ~ 0.85, the performance of No. 80 steel is similar to that of No. 65 steel, its elasticity is slightly worse than that of No. 65 steel, its strength is higher, and its hardenability is low. Generally, it is in the state of quenching and tempering. use. It is used to manufacture coil springs, leaf springs, and worn mechanical parts with low strength and slightly smaller cross-sectional dimensions.
Cr12MoV vacuum heat treatment knowledge
Cr12MoV steel is a high-carbon and high-chromium ledeburite steel, which is often used in cold work molds, and its carbon content is lower than that of Cr12 steel. The steel has high hardenability, the section below 300mm can be completely hardened, and the volume change during quenching is also smaller than that of Cr12 steel.
The vacuum heat treatment system is: 960 ℃ air cooling for steel bars and forgings + 700~720 ℃ tempering, air cooling.
Final heat treatment process:
1.Vacuum quenching:
The first preheating: 300~500℃,
The second preheating is 840~860℃;
Vacuum quenching temperature: 1020~1050℃;
Cooling medium: oil, medium temperature: 20~60℃,
Cool to oil temperature; then, air cooling, HRC=60~63.
2.Vacuum tempering:
After the following vacuum quenching process, the effect of reducing hardness can be achieved. The specific vacuum tempering process is as follows:
The heating temperature is 400~425℃, and HRC=57~59 is obtained.
The vacuum tempering between 480-520 degrees is just the brittle tempering area of this steel, and tempering in this area is easy to cause the mold to collapse. The most ideal tempering range is 380–400 ℃. This range of tempering has the best toughness and good wear resistance. If after vacuum quenching, cryogenic treatment (ideal temperature is minus 120) is combined with medium temperature vacuum tempering, good use effect and long life will be obtained. The tempering brittleness temperature range of Cr12MoV is 325~375℃. The hardness of CR12MoV380-400 after vacuum tempering is 56-58HRC as a cold die punching material with good toughness, which is not easy to crack, especially when the quality of raw materials is not very good, this method is economical.
Selection of vacuum tempering furnace equipment: The RVT series vacuum tempering furnace produced by SIMUWU is a high-quality product for the vacuum tempering process of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum tempering process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.
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