There are three types of alloy spring steel wire in China: alloy spring steel wire, oil quenched and tempered silicon manganese spring steel wire, and oil quenched and tempered chromium silicon alloy spring steel wire for valve. According to the current use situation of alloy spring in developed countries, the proportion of oil quenched and tempered steel wire is increasing. According to Japanese industrial standard (JIS), all alloy spring steel wires are supplied in oil quenching and tempering state.
(1) GB / t5218-1999 alloy spring steel wire
The standard combines the original gb5218-85 “silicon manganese spring steel wire”, gb5219-85 “chromium vanadium spring steel wire” and gb5221-85 “chromium silicon spring steel wire” into one standard. The standard is applicable to the production of alloy spring steel wire for high and medium stress spring. The steel wire wound spring can only be used after quenching and tempering after forming.
The standard lists three grades of 60Si2MnA, 50CrVA and 55CrSiA, and stipulates that other grades of steel wire can be supplied according to the requirements of the demander.
The steel wire is generally delivered in cold drawn condition. The tensile strength σ B ≤ 1035mpa and Hb ≤ 302 are inspected for the finished steel wire with diameter ≤ 5.0mm, which is equivalent to the light drawing state. In the production of medium and large specifications (Ф > 8.0), the cold drawing reduction rate of finished products shall not exceed 25%, and the surface reduction rate of small steel wire (Ф ≤ 5.0) shall not exceed 30%.
The steel wire delivered in annealed state is too soft, so it is easy to produce dead bending. When winding the spring, the spring shape is not good and the pitch is uneven. When the reduction ratio of cold drawing is too large, the steel wire is too hard, and the rebound is large when the spring is wrapped, so the forming of the thick spring is difficult. Therefore, it is most suitable to supply the steel wire directly wrapped with spring in light drawing state. For the customers who need cold working (such as flattening, rolling into special cross-section, etc.) when the steel wire is purchased, the annealed steel wire shall be recommended for delivery.
In order to ensure the performance of the winding spring, the finished steel wire shall be wound for 6 turns on the mandrel with the diameter less than or equal to 5.0 mm, and shall not be broken or broken.
Decarburization and surface defects seriously reduce the fatigue life of spring, which must be strictly controlled. In particular, 60Si2MnA and 55CrSi have high silicon content and are easy to decarburize during annealing. Low temperature and long time annealing process is recommended for spheroidizing annealing and recrystallization annealing of semi-finished products. As mentioned above, for springs with high fatigue life requirements, polished steel wire must be selected, but it is necessary to distinguish between annealing polishing and cold drawing polishing. When 50CrV soft steel wire is polished, the grinding debris is easy to adhere to the steel wire surface and form irregular small white spots. Therefore, cold drawing polishing process should be adopted as far as possible to reduce the “white spots” on the surface.
Under the condition of surface quality assurance, the inclusion content becomes the most important factor affecting the fatigue life. Therefore, the standard stipulates that non-metallic inclusions and graphite carbon inspection can be added when the demander has requirements.
(2) Yb / t5104-93 oil quenched tempered silicon manganese alloy spring steel wire
After using oil quenched and tempered alloy spring steel wire, there is no need to carry out quenching and tempering treatment. As long as stress relief treatment is carried out like cold drawn carbon spring steel wire, it can be used. These two standards are more and more used for alloy spring with diameter less than 14.0 mm.
Yb / t5104-93 is supplied in three categories, class A is suitable for static spring with medium load, class B is suitable for dynamic spring with medium load and medium fatigue life, and class C is suitable for dynamic spring with high stress state, such as automobile suspension spring.
(3) Yb / t5105-93 oil quenched tempered chrome silicon alloy spring steel wire for valves.
Yb / t5105-93 is suitable for the valve spring of engine under severe dynamic load.