High-strength threaded fasteners are generally divided […]
High-strength threaded fasteners are generally divided into four levels, 8.8, 9.8, 10.9 and 12.9, and are generally quenched and tempered medium carbon steel or medium carbon alloy steel. In order to eliminate the annealing and quenching and tempering process in the production process, high-strength fasteners can be produced from non-quenched and tempered steel. The non-quenched and tempered steel for fasteners is cold-work hardened non-quenched and tempered steel, which is mainly used to produce high-strength fasteners of 8.8 to 10.9. Use non-quenched and tempered steel to produce high-strength fasteners, use work hardening to strengthen the material, and at the same time eliminate the annealing and quenching and tempering process, shorten the production cycle, realize energy saving and consumption reduction, and can also avoid decarburization during heat treatment And so on, so it is valued by enterprises. Non-quenched and tempered steel is a kind of high-efficiency energy-saving steel developed with the shortage of international energy. According to the organization structure, it can be divided into ferrite-pearlite, bainite and martensitic. At present, the most widely used in industry is the first type. . The use of ferrite-pearlite non-quenched and tempered steel to make high-strength fasteners can reach the level of 8.8 and 9.8, while the production of high-strength fasteners of 10.9 requires further improvement of the steel For strength, use non-quenched and tempered steel of other organization types.
The high-strength non-adjusting bolt steel LF10Mn2VTiB developed by China in the 1990s has a granular bainite structure with a tensile strength of 838MPa, a reduction of area of 55% and an elongation of 19.4%. The steel can meet the mechanical performance requirements of 10.9 grade fasteners after 31% drawing reduction, but the development is in the laboratory stage and there is no industrial production. At present, the use of non-quenched and tempered steel to make grade 10.9 fasteners is only suitable for the manufacture of stud bolts and U-shaped bolts that do not require cold heading, and it is difficult to make triangle bolts that require cold heading. In order to develop non-quenched and tempered steel for grade 10.9 fasteners with high cold deformation ability, test rolling was carried out on a high-speed wire rod mill