In practice, the upper and lower limits of the temperature generally correspond to the highest and minimum secondary hardening levels available, respectively. Of course, the temperature setting value of the meter should be selected according to the type and size of the workpiece and the temperature control accuracy of the equipment used.
From the point of view of the tool type, the shape of the turning tool, the end mill, the drill bit, etc. is relatively simple, especially the single-edged tool, the rigidity and toughness requirements are not high, and the high quenching heating temperature can be adopted to fully exert the red hard potential of the steel; For complex shapes, slender or thin sections, especially multi-blade tools such as hobs, moderate or lower quenching heating temperatures are used. The same tool and different sizes are suitable for two situations:
First, the larger the size, the higher the temperature can be used. Such as turning tools, drills, regardless of the size of the raw material tissue is not very different, the characteristics of adapting to quenching are similar; large-sized workpieces are more suitable for high quenching heating temperature.
Second, the larger the size, the lower the selection temperature, such as a gear cutter. This is because the carbide unevenness of the gear cutter material is related to the size. In the large size, due to the uneven carbide, it is easy to overheat the microstructure in the grain unevenness or carbide accumulation. The quenching heating temperature and the holding time must be appropriately reduced. . At the same time, the price of large gears is expensive, and in order to ensure the safety of the quenching-tempering-grinding process, it is required to slightly lower the quenching heating temperature.
The choice of quenching heating temperature is also related to the furnace type and furnace condition. When a vacuum furnace is used, since the heating rate is slow and the soaking (heating) time is long, it is necessary to select a heating temperature slightly lower than the quenching of the salt bath furnace, otherwise grain growth is likely to occur.