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Vacuum Heat Treatment of 65Mn Steel Sheet Spring Support

Material: 65Mn steel

Technical requirements: the suture gland on the plane of the frame and the edge of the bracket should not exceed 0.2mm

The 0.3mm thick 65Mn spring sheet is the button bracket used to select the channel on the TV [see Figure 1(a)]. The elastic parts require uniform structure during heat treatment. The biggest problem of heat treatment is quenching deformation. The spring sheet is made of steel. The supply state is cold-rolled and annealed, and the structure is fine pearlite + ferrite. It is required that the heat treatment bracket plane and the edge of the bracket are not more than 0.2mm apart on the flat plate, and it is also required to bend 180° in the length direction, and then loosen it completely. Return to its original shape without allowing any plastic deformation. The use of box-type electric furnaces, salt bath furnaces, etc. can not meet the technical requirements such as deformation.

The vacuum heat treatment process is adopted, as shown in Fig. 1(b). Preheating at 680°C (near the phase transition point) has a slow heating rate, and the heating uniform stress is small. After preheating, quenching and heat preservation, it is moved to the cooling chamber for oil cooling. The furnace is installed in a cold state, and the temperature rises with the furnace. The vacuum degree in the cold state is 1.33Pa. After preheating, quenching and heat preservation, the spring pieces are transferred to the cooling room for oil cooling. Nitrogen. Compared with ordinary quenching oil, vacuum quenching oil has a lower cooling rate in the low temperature region. Under the structural stress of the quenching spring sheet, in order to reduce the deformation, the quenching oil does not open the stirring system and prolongs the steam film stage.

Fig.1 0. 3mm thick thin 65Mn spring sheet and its vacuum heat treatment process curve

It should be noted that for this thin and slender spring sheet, the prestress before vacuum heat treatment, that is, the clamping state, has a great influence on the deformation after heat treatment. During the heating and cooling process, its own weight and mutual extrusion force , unevenness and even vibration also lead to deformation, so special fixtures should be designed (Figure 2). In the figure, the upper and lower inclined irons are fixed with the bottom plate 4 with screws. Tighten the fixing bolt 1, in which the lower inclined iron 5 and the fixing screw of the bottom plate 4 are movable, and the bottom plate 4 is a plate with 5 U-shaped grooves, which can ensure the tight fit between the spring sheets and between the spring sheets and the fixture. ,Even by force. In order to ensure the close contact between the spring sheets and between the spring sheets and the fixture, the force is uniform, and the heat treatment deformation is effectively controlled.