1.      Steel design
in the fastener manufacturing, the correct selection of fastener materials is an important part, because the performance of the fastener and the material has a close relationship. Improper or incorrect material selection may result in performance below standard, shorten the service life, or even an accident or processing difficulties, the manufacturing cost of the fastener material selection is a very important part.  Because it is the metal plastic forming molding at room temperature, deformation of each part, bear the deformation rate is also high, therefore, the very strict performance requirements for cold heading steel raw materials. On the basis of the long-term production practices and user research, 8.8, 9.8 bolts and screws, material requirements, for example, various chemical elements. C content is too high, cold forming properties will be reduced; too low, you can not meet the requirements of the parts of the mechanical properties, and therefore set at 0.25% -0.55%. Mn can improve the permeability of the steel, but add too much it will strengthen the matrix structure affected by the cold formability; parts quenched and tempered to promote the tendency to austenite grain growth, it is an appropriate increase in the international basis, will be 0.45% -0.80%. Si can strengthen the ferrite to promote cold-forming properties to reduce the material elongation decreased as Si is less than or equal to 0.30%. SP is the impurity elements, their presence along the grain boundary segregation, leading to grain boundary embitterment, damage to the mechanical properties of steel, should be as low as possible, at the P less than or equal to 0.030%, S is less than or equal to 0.035%. B. The maximum boron are 0.005% boron element has significantly improved the steel permeability, but at the same time will lead to an increase in steel brittle. B content is too high, bolts, screws and studs such need good mechanical properties of the work piece is very unfavorable.

2. Spheroidization (softened) annealing
countersunk head screws, hexagon socket head bolts using the cold heading process to produce the original organization of the steel will have a direct impact on the processing of cold heading forming ability. Local area in the cold heading process of plastic deformation up to 60% -80% of this steel must have a good plasticity. When the chemical composition of the steel when the microstructure is to decide the plastic pros and cons of the key factors generally considered coarse lamellar partite is not conducive to cold upsetting, small globular pearlier can significantly improve the ability of steel plastic deformation. More amount of high-strength fasteners in carbon steel and carbon steel, before the cold heading spheroid zed annealing (softening), in order to obtain a uniform and detailed ball partite, to better meet actual production needs. Softening annealing of medium carbon steel wire rod, the heating temperature is more than the critical point of the steel up and down the insulation, the heating temperature is generally not too high, otherwise it will produce three commentate along the grain boundaries, resulting in the cracking of the cold heading, and for isothermal spheroidization annealing of medium carbon alloy steel wire rod, AC1, + (20-30%) after heating, furnace cooling to slightly below the Ar1 temperature of about 700 degrees Celsius temperature for some time, and then furnace cooling to 500 degrees Celsius, cooled baked. Steel microstructure consists of course to fine, globular changed by the sheet, cold heading cracking rate will be greatly reduced. 35 \ 45 \ ML35 \ SWRCH35K steel to soften the general area of ??the annealing temperature of 715-735 degrees Celsius.