Plain Carbon Steel strip has a very wide range of applications because it is particularly adaptable to low cost techniques of metal forming such as presswork. These materials combine ease of fabrication with adequate strength and excellent finishing characteristics. As a result, they provide a good surface finish on the final article.
The Knight Group range of Carbon Steels can be broadly split into two categories:
LOW CARBON MILD STEELS
HIGH CARBON SPRING STEELS
Spring Steels are available in the annealed condition for hardening after forming, or in the hardened and tempered condition.
The hardness or temper of cold rolled Mild Steel strip is determined by its analysis, the amount of cold rolling or by a final annealing process. Manufacturers select these Steel to achieve the optimum mechanical properties for the forming operation, whether it be deep drawing, forming or flat blanking.
“Skin passed” is a very light rolling reduction after the annealing process to prevent the formation of deformation bands called stretcher strains, which can ruin surface appearance of the formed article.
Mild steels cannot be hardened except by cold working because their carbon content is too low for significant heat treatment reaction to take place. However, they can be case hardened to give a harder surface.
Bright rolled Carbon Steels are often used in the annealed condition for forming of components. These can then be batch heat treated to increase their hardness and spring characteristics.
To maintain a good surface condition, heat treatment should be carried out in a controlled atmosphere furnace at the appropriate temperature for the grade (see table) and oil quenched to achieve maximum hardness.
Tempering must then be carried out to reduce the strength/hardness of the material but considerably improve its toughness and ductility. Temperatures in the range of 300 – 450°C should be used to achieve the required final hardness. Alternatively, austempering is frequently carried out by quenching into a molten salt bath @ 350 – 450°C.
Our Sales and Technical staff will give additional heat treatment advice for your particular application, upon request.
(b) Hardened & Tempered:
Hardened & Tempered Spring Steel has been heat treated in strip form at the mill, prior to being supplied to the customer. Many applications do not require severe bending and forming and it is often beneficial to use hardened and tempered strip in these cases.
The main benefits are:
- No risk of distortion.
- Uniformity of surface finish.
- Constant mechanical properties.
- These factors often mean reduced processing costs and a higher quality product
- Stress Relieving.
After severe deformation hardened & tempered spring steel requires a low temperature (250 – 300°C) stress relieving operation to “set” the components into shape. This will impart a coloured oxide finish ranging from bronze to blue which slightly improves corrosion resistance.