What is cold heading machine spheroidization
Source：http://www.rnbe.cn Author：冷鐓機 Time：2014/8/19 Click：
When the multi station cold heading machine is used to spheroidize (soften) annealed countersunk head screws and the internal hexagonal cylindrical head bolts are produced using cold heading technology, the original structure of the steel directly affects the forming ability during cold heading processing. During the cold heading process, the plastic deformation in local areas can reach 60% -80%, which requires the steel to have good plasticity. When the chemical composition of steel is constant, the metallographic structure is the key factor determining the quality of plasticity. The Leyte cold heading machine believes that coarse and large pearlite is usually not conducive to cold heading forming, while fine spherical pearlite can significantly improve the plastic deformation ability of steel. For medium carbon steel and medium carbon alloy steel with a large amount of high-strength fasteners, spheroidization (softening) annealing should be carried out before cold heading to obtain uniform and fine spheroidized pearlite, in order to better meet practical production needs. For the softening annealing of medium carbon steel wire rods, the heating temperature is often chosen to be kept above and below the critical point of the steel. The heating temperature should generally not be too high, otherwise three times of cementite will precipitate along the grain boundary, causing cold heading cracking. For medium carbon alloy steel wire rods, isothermal spheroidization annealing is used. After heating at AC1+(20-30%), the furnace is cooled to slightly lower than Ar1, and the temperature is isothermal at about 700 degrees Celsius for a period of time. Then, the furnace is cooled to around 500 degrees Celsius and discharged from the furnace for air cooling. The metallographic structure of steel changes from coarse to fine, from flaky to spherical, and the cold heading cracking rate will be greatly reduced. The general softening annealing temperature range for 35 \ 45 \ ML35 \ SWRCH35K steel is 715-735 degrees Celsius.
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