Cold heading steel wire of the technical requirements
Technical requirements of cold heading wire is more strict, standard parts dimension accuracy requirement for raw materials is strict, hot rolled steel specification is limited, dimension precision is difficult to meet the requirements, so almost all adopt the cold drawn steel wire as raw materials, standard parts in general, we qualified cold heading steel wire must meet the following requirements:
1, the cold heading property. Good cold heading is refers to the deformation resistance of steel wire has lower, can withstand a greater degree of deformation and crack. It is generally believed to reduction of area and QuJiang ratio as a measure of cold upsetting performance more reliable. Alloy steel reduction of area shall not be less than 50%. Cold heading steel wire QuJiang than small, cold heading performance is relatively better, alloy steel showed should be no greater than 0.70. Think in terms of performance of cold heading, wire cold enhancement coefficient is lower, the better, that is not easy the creation work hardening.
2, the surface quality. Standard parts factory statistics show that the cracking in cold heading machine 80% is caused by steel wire surface defects, such as folding, scratch, dense hair lines, local micro cracks, scarring. So the wire surface quality requirement is very strict, dimensional tolerance + / - 0.20 mm, out of roundness < 0.30 mm, surface crack, scratch the deepest < 0.07 mm.
3, decarburization. Decarburization on the surface of the surface strength of the bolts is reduced, the fatigue life declined dramatically. The average depth of decarburization layer requirements. 4, metallographic organization. Cold heading steel microstructure of ferrite + granular pearlite, the grain size and distribution of pearlite and the influence factors of cold heading, the ideal organization is similar pearlite grain size and evenly distributed on the ferrite matrix. Different pearlite microstructure performance from good to bad cold heading for granular pearlite, the order of sorbite, fine lamellar pearlite lamellar pearlite.
5, chemical composition requirement. O, P, S and other elements on the morphology of inclusions in steel and the size of the quantity, have a decisive influence, so the requirements to control its content; For alloy steel, silicon, aluminum, manganese and other control elements in the lower limit advisable, avoid to cause cold upset forging crack.
6, the grain size. Cold heading steel wire internal organization differs from that of other steel wire, grain size is not as thin as possible. Grain size is too fine, the tensile strength, yield strength increases, the deformation resistance increases, the cold heading forming is very bad. In addition to the above magnitude 10.9 bolt grain fine, ensure product strength, the grain size of cold heading steel wire should be controlled in 5 to 7.
7, macrostructure. Macrostructure of cold heading steel wire for steel demand is strict, the low power inspection should not have shrinkage, layered, white spots, defects such as crack, air hole, the center loose, square segregation, carburization, level of different steel grade have clear rules.
8, non-metallic inclusions. Non-metallic inclusion content in steel is high, the size is an important cause of the standard cold heading cracking, especially the nonmetallic inclusions in the class B and class D brittle inclusion, away from the surface of steel wire for the greater, so the requirements class B inclusions from the surface should be no greater than 15 microns within 2 mm.
Quality requirements for raw materials of high grade standard: wire rod has high plasticity index, reduction of area and elongation; In the cold plastic deformation, material deformation resistance small, work hardening rate is low, material QuJiang than small, wire rod hardness is moderate, not too high; Wire rod has good surface quality, surface roughness, surface defects such as folding, crack is not permitted; Compact steel group, free from internal defects.
  BAOSTEEL GROUP BAORI WIRE All Right Reserved 2004