Cold drawn (rolled) spring steel includes steel wire and steel strip. This kind of steel surface quality and dimensional accuracy requirements are particularly strict. The production process of steel wire includes oil quenching and cold drawing.
Oil quenched steel wire is to cold draw the steel wire to the specified size, then heating, oil quenching and lead bath tempering. Therefore, the steel wire has the required mechanical properties when it leaves the factory. After the spring is made, it can be used as long as it is tempered and the stress is relieved. The advantages of the whole batch are uniform performance, stability and good straightness. It is suitable for mass production and can produce various important springs, especially valve springs. There are 65Mn, 50CrVA, 60Si2Mn, 55CrSi, etc.
Alloy spring steel wire can also be delivered in cold drawing state, or after annealing, normalizing and tempering treatment, and then quenched and tempered after being made into spring. Its properties are not as uniform and stable as oil quenched steel wire, with low production efficiency and high cost.
In addition, the process of high strength spring steel wire treated by high frequency induction heating has also been studied recently. After quenching and tempering in continuous induction heating device, the internal structure of cold drawn steel wire is uniform and fine. Its plasticity and toughness, elastic reduction resistance, fatigue limit and fracture toughness are obviously better than those of conventional treatment steel wire. This kind of steel wire has been produced in the United States and Japan. The suspension springs for automobiles and motorcycles, engine valve springs, emergency brake springs for trucks and trailers, and various kinds of high strength mechanical springs have been manufactured with satisfactory results. In addition, induction heating is also applied in the production of spring flat steel.
There is also a steel wire production process, namely lead bath isothermal quenching. After austenitizing, the steel is isothermal in lead bath to form fine pearlite structure, and then cold drawn to the specified size. The mechanical properties of the steel wire can be controlled by adjusting the carbon content and cold deformation of the steel wire. The spring can be used without heat treatment after spring making, as long as the processing stress is eliminated. All carbon steel wires produced by this process are carbon steel wires, but there are also a few alloy steel wires (such as 65Mn).
Generally, the cold-rolled spring steel strip is supplied after cold rolling or annealing, and then quenched and tempered after being made into spring, or only tempered to eliminate processing stress.