Introduction：
Cold heading steel rods are generally low and medium carbon high-quality carbon structural steel and high-quality alloy structural steel, which are used for cold heading forming to manufacture various mechanical standard parts and fasteners. Because the cold forging process requires the steel to have a high degree of cleanliness, the content of Si and Al in the steel is controlled, and the controlled rolling and cooling process is adopted to avoid the appearance of martensite, bainite and wetensite structure, so that the steel has fine crystal and carbide nodular structure, so as to improve the plasticity and cold forging performance of the steel. The development and production of cold heading steel at home and abroad, the influence of chemical composition on the properties of cold heading steel, and the special features of production process of cold heading steel are introduced.
The steel type of cold heading steel wire rod is generally low and medium carbon high-quality carbon structural steel and alloy structural steel. Cold heading steel products are mainly used in automobile, shipbuilding, equipment manufacturing, electronics, home appliances, bicycles, tools, light steel structure, construction and other industries.
Cold forging steel because of good cold forming performance, in the machining industry with cold drawing instead of hot rolled cold cutting machining, the advantages of this process is in saving a lot of hours at the same time, metal consumption can be reduced by 10% to 30%, and the product size accuracy is high, surface finish is good, high productivity, is the rise of the more advanced machining process in recent years.
use:
The steel used to manufacture fasteners and connectors (such as bolts, nuts, screws, rivets, etc.) by cold heading processing is called cold heading steel, commonly known as riveted screw steel. Usually used are tempered alloy steel, low temperature tempered alloy structural steel, low carbon and low alloy high strength steel, ferritic-martensitic two-phase steel and so on. Cold heading is formed by metal plasticity at room temperature. Using cold heading process to manufacture fasteners not only has high efficiency, good quality, but also saves material and low cost. However, the cold heading process requires higher quality of raw materials.Cold heading property is one of the important properties of cold heading steel. The main properties of cold heading steel are that it has good cold formability; For cold heading steel deformation should have as little resistance as possible and possibly high deformation capacity. For this reason, the strength ratio of cold heading steel is generally required to be 0.5~0.65, and the section shrinkage is greater than 50%. In addition, in order to avoid surface cracking during cold heading, the surface quality of the steel is required to be good, and the surface decarburization of the steel should be as small as possible. The standard stipulates that steel should be cold-topped. The ratio of the height of the sample before cold forging is required to be high. A quarter; More advanced; One third; Ordinary grade; 1/2. The general standard is 1/2.Cold forging steel because of good cold forming performance, in the machining industry with cold drawing instead of hot rolled cold cutting machining, the advantages of this process is in saving a lot of hours at the same time, metal consumption can be reduced by 10% to 30%, and the product size accuracy is high, surface finish is good, high productivity, is the rise of the more advanced machining process in recent years.
Types and characteristics:
Cold heading steels include high-quality carbon steels, alloy structural steels, duplex steels, bearing steels and stainless steels. Cold heading steel can be divided into non-heat treatment type, tempering type, non-tempering type and surface hardening type according to its production process route. Fasteners below 6.8 are mostly made of non-heat treatment medium carbon and low carbon cold heading steel, and finished fasteners do not need quenching and tempering treatment. High strength fastener steel is usually tempered medium carbon steel or medium carbon alloy steel, finished fasteners need to be quenched and tempered treatment, can also choose non-tempered steel, boron steel, F-M duplex steel or low carbon martensitic steel surface hardening steel for low carbon steel and low alloy steel (ML18A, M120Cr, etc.), mainly used for manufacturing self-taping screws and fastening screws, Finished screws need to be carburized, nitriding and other surface hardening treatment.
In the process of cold heading forming, the deformation of parts is large (60%~85%), and the forming speed is fast. In order to avoid cracks and other defects, the cold heading steel is required to have good plasticity and high surface quality. Cold heading performance is an important index of cold heading steel, which usually includes deformation ability and deformation resistance. Shrinkage greater than 500%. At the same time, in order to avoid cold heading cracking and other defects, the surface decarburization is small.
