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How to choose spring steel wire?

Steel is by far the most common spring material for the following reasons:

• High strength – exceeding 400 ksi (2.76 GPa) tensile strength.
• Low cost
• Magnetic
• Easy to form
• Excellent fatigue properties
• Resistance to creep
• Great surface finish

Music Wire

Music wire is a high carbon plain steel that boasts upwards of a 400 ksi (2.76 GPa) tensile strength. It is generally a material in the range of AISI 1070 to 1095. Due to its high carbon content, it is not weldable. (but why would you want to) These springs are readily available in a multitude of shapes and sizes as off the shelf parts.

The major down side is that music wire is only available in diameters up to 0.283” (7.2 mm). Generally speaking, as the diameter of a material increases the strength reduces. This is caused in the manufacturing process. If a wire is very small, you can filter out most of the impurities during the forming process. If that doesn’t happen, the wire will most likely break in the process or forming and a new wire is started. Either way, that material doesn’t have impurities in it. As you increase the diameter, it is harder to remove impurities and it is likely that you won’t break the material. This is the reason that filament fiberglass is super strong, but a plate of the same glass is much weaker.

If you need a strong spring in larger diameters, there are three main choices: chrome silicone wire, oil tempered carbon (MB) wire and hard drawn carbon (MB) wire. They are ordered in highest to lowest strength and as you can imagine, highest to lowest cost.

Chrome Silicon (Steel) Alloy Wire

This alloy wire leaves off where the music wire stops. The line of strength vs diameter doesn’t change much. This is however a much more expensive option costing roughly 1.7 times what music wire does.

Oil Tempered Carbon and Hard Drawn Carbon Wires

are more popular with larger springs. Of course, the reduction in carbon leads to decreased strength, but the cost will be lower as well. Since the strength is reduced, the size and weight of the spring will increase. Many times, these factors can justify the use of the chrome silicon wire instead. Be sure to contact your local spring distributor if this is your concern.