1.Spheroidizing (softening.annealed countersunk screws. When the hexagonal cylinder head bolts are produced by the cold heading process, the original structure of the steel directly affects the forming ability during cold heading.
2.The plastic deformation of the local area during the cold rolling process can reach 60%-80%. Therefore, the steel must have good plasticity. When the chemical composition of the steel is constant, the metallographic structure is the key factor determining the quality of the plastic. It is generally considered that the coarse flaky pearlite is not conducive to cold heading, and the small spherical pearlite can significantly improve the plastic deformation of the steel.
3.For medium carbon steel and medium carbon alloy steel with high strength fasteners, spheroidize (soften.annealing before cold heading to obtain uniform and fine spheroidized pearlite to better meet actual production. need.
4.For the softening annealing of medium carbon steel wire rod, the heating temperature is selected to be kept above and below the critical point of the steel, and the heating temperature is generally not too high, otherwise three cementites will be precipitated along the grain boundary, causing cold cracking.
5.The wire rod of medium carbon alloy steel adopts isothermal spheroidizing annealing. After AC1+ (20-30%.heating, the furnace is cooled to slightly lower than Ar1, the temperature is about 700 degrees Celsius for a certain period of time, and then the furnace is cooled to about 500 degrees Celsius. Air-cooled. The metallographic structure of the steel is coarse and thin, and the shape of the steel is changed from spherical to spherical. The cracking rate of cold heading is greatly reduced. 35\45\ML35\SWRCH35K steel softening annealing temperature is generally 715-735 degrees Celsius.
