I'm interested in seeing what Hector has to say also. Si and Davy are pretty well known and they put out some pretty good info. That was just about the best video I've seen on the subject. The few springs I've cut and closed I've used oil too.
Might ask the 2 main spring manufacturers?
Heat TreatmentHeat treatment is a process designed to alter the properties of the metal to better suit its intended use. The main types of heat treatment are: Annealing Normalising Hardening TemperingAnnealingAnnealing is frequently used to soften metals including iron, steel, copper, brass and silver. The process involves heating the metal to a specific temperature then allowing it to cool slowly at a controlled rate. Annealing alters the physical and chemical properties of the metal to increase ductility and reduce hardness. This facilitates shaping, stamping or forming processes, and allows the metal to be cut more easily. Annealing also enhances electrical conductivity.NormalisingNormalising (commonly referred to as normalized) is applied to alloys to provide uniformity in grain size and composition. The metal is heated to a predefined temperature then cooled by air. The resulting metal is free of undesirable impurities and exhibits greater strength and hardness. Normalising is often used to produce a harder and stronger steel, albeit one that is less ductile than that produced by annealing. Typically, the normalising process is performed on materials that will be subjected to machining, because the process has improved this attribute.HardeningHardening is applied to steel and other alloys to improve their mechanical properties. During hardening, the metal is heated at a high temperature and this temperature is maintained until a proportion of carbon has been dissolved. Next the metal is quenched, which involves rapidly cooling it in oil or water. Hardening will produce an alloy which has high strength and wear resistance. However hardening will also increase brittleness and is not suitable for engineering applications. When there is a need to have the surface of the component hard enough to resist wear and erosion, while maintaining ductility and toughness to withstand impact and shock loading surface hardening would be used.TemperingTempering is applied to steel where ductility is desired. Untempered steel is very hard but too brittle for most practical applications. Tempering is a low temperature heat treatment process normally performed after hardening (neutral hardening, double hardening, atmospheric carburising, carbonitriding, or induction hardening) in order to reach a desired hardness/toughness ratio. The process involves heating steel to a lower temperature to reduce some of the excess hardness. The metal is then allowed to cool in still air which results in a tougher and less brittle steel.
As always Hector ....... Thank You .
Quoted from above"It also ignores the fact that modern steels are hardened, then tempered, and then made into springs (at least the airgun kind)."When that hardened wire is bent beyond it's yield point to make coils it's going to need stress relieved . Another heat treat process.