6. Precautions during the implementation of the heat treatment process:
Furnace loading method: When the plate is installed in the furnace, the plate is placed vertically, and should not be placed horizontally.
Austenitizing time: long-term time proof: the holding time can vary widely, the equivalent diameter of different plates, heating time can be calculated according to t=α×D+15min, α heating coefficient min/mm, D is effective size Mm.
The effective heating dimension D of the heat treatment of sheet metal should be calculated by the equivalent diameter, D=A×C, where A is the thickness of the sheet, and C is the shape factor of the sheet. The value range is shown in Table 1.
Figure 5 shows the shape of the plate
Table 1. Shape factor C of the board
project | Condition: H value > 2B value | ||||||
B/A= | 1 | 2 | 3 | 4 | 5 | 6 | >6 |
C= | 1 | 1.3 | 1.5 | 1.6 | 1.65 | 1.7 | ≈2 |
Project conditions: H value > 2B value
B/A=123456>6
C=11.31.51.61.651.7≈2
Preheating during heating and heating: In the listed specifications, the heating preheating section only needs one section. One section of preheating and two sections of preheating, the deformation of the same type of sheet after quenching, there is no significant difference. . However, the total heating rate cannot be greater than 200 ° C / h, and the number of preheating sections within this heating rate has no significant effect on the quenching deformation.
Intermittent quenching is to locally cool the surface of the workpiece to the vicinity of the MS point. The temperature of most other surface parts is still above the MS point, but at a temperature far below the tip of the pearlite transformation, the vacuum high pressure gas quenching is stopped in this area. The workpiece is taken out from the vacuum furnace and slowly cooled in still air, so that the plate gradually passes over the MS point from the periphery to the center, and the post-cooled portion tempers the martensite formed by the plate portion which first passes over the MS point. The quenching process is finally completed. Since the cooling capacity of high-pressure gas quenching is lower than that of oil quenching and quenching quenching, the quenching method of salt bath grading is maintained at a stage near the MS point, and the grading temperature fluctuates widely. The gas quenching grading isotherm. It is essentially a fluctuating and temperature-changing cooling method. It cannot fully achieve the traditional quenching effect. The high-pressure gas quenching is then turned to static air cooling near the MS point. It is also different from the two-liquid quenching, so we call it the interrupted temperature change. Quenching, which may be more reasonable, distinguishes it from traditional concepts.
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