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Quenched & Tempered Steel Strips

Hard Strips (India) is one of the biggest manufacturers of high quality quenched & tempered spring steel strips & quenched & tempered spring steel coils in India. The steel strips / coils that are produced during the quenching & tempering process can be quenched & tempered carbon steel strips / coils or quenched & tempered medium carbon steel strips / coils or quenched & tempered high carbon steel strips / coils.

Quenching is the process of rapid cooling. It can reduce crystallinity and thereby increase toughness of steel strips. It is most commonly used to harden steel strips by introducing martensite, thus the steel strips are rapidly cooled through its eutectoid point, the temperature at which austenite becomes unstable. In case when steel strips are alloyed with metals such as nickel, chromium and manganese, the eutectoid temperature becomes much lower, but the kinetic barriers to phase transformation remain the same. This allows quenching to start at a lower temperature, thus making the process much easier.

Quench hardening is a process in which spring steel strips are strengthened and hardened. This is done by heating the steel strips to a certain temperature and then rapidly cooling the material by applying oil. This produces harder steel strips by either surface hardening or through-hardening varying on the rate at which the steel strips are cooled. The steel strips are then often tempered to reduce the brittleness that may increase from the quench hardening process.

Tempering is a heat treatment technique for metals, alloys. For steel strips , tempering is done to toughen the steel strips by transforming brittle martensite or bainite into a combination of ferrite and cementite. Tempering is done by a controlled reheating of the work piece to a temperature below its lower critical temperature.

The brittle martensite becomes tough and ductile after it is tempered. The carbon atoms which were trapped in the austenite when it was rapidly cooled by oil quenching form the martensite. The martensite becomes strong after being tempered because when reheated, the microstructure rearrange and the carbon atoms diffuse out of the distorted body-centred-tetragonal structure. Thus the result is nearly pure ferrite with a body-centred structure. Tempering improves ductility and toughness, it reduces cracking, improves machinability, increases impact resistance, improves malleability, decreases hardness of the steel strips.

Steel strips are first heated to create a solid solution of iron and carbon in a process called austenizing (Austenitization is the process of heating the steel to a temperature at which it changes its crystal structure from ferrite to austenite.) Austenizing is followed by quenching. The steel strips are then tempered by heating between the ranges of 150–260 °C and 370–650 °C. Tempering in the range of 260–370 °C is avoided to reduce temper brittling. The steel strips are held at the particular temperature until the required specifications are achieved.