What are the correct materials to use in Flat Strip Products?

Just like wire, there are a wide range of materials available in the production and design of flat strip products.
 
Strip materials can be obtained in different grades of hardness, and some spring materials are able to be heat treated to increase their strength and hardness. We will look at carbon steels, stainless steels and copper alloys only in this blog as there are such a vast range of materials out there.
 
Carbon Steels
The different grades of carbon steel strip are classified according to the carbon content, the manufacturing method, and if heat treatment is used in the process.
 
When formability is need, annealed carbon steel strip is used. After forming, if a heat treatment is used this will increase the materials strength and hardness. If formability is not required there are heat treated grades of spring steel.
 
Clock springs and seat belt retaining springs utilise these materials in their hard condition. They provide a good surface finish, uniformity of mechanical properties and precision thickness tolerances. Carbon steel springs will corrode readily so they do require some form of protection if working in a harsh environment.
 
Stainless steels
Stainless steels are widely used for their corrosion resistance, their ability to withstand elevated temperatures and their resistance to relaxation.
 
They are generally obtained in the hard rolled condition, there is a need to take into account the effect of spring hardness when strip components are designed and manufactured from stainless steels.
 
Stainless steels are around 20% weaker than heat treated springs steels of the same size. During the cold rolling process the hardness of stainless steel is produced causing the stainless steel to be slightly magnetic.
 
Copper alloys
When it is necessary to have high electrical and thermal conductivity and/or non-magnetic properties it is essential to use copper based alloys.
 
Another benefit of copper alloys is their good atmospheric corrosion resistance, as the majority of copper-alloy strip components are used as electrical contacts, many copper parts are electro-plated. With its high tin content, phosphor bronze has the high tensile strength in comparison to other copper alloys resulting in it being the most commonly used.
 
Beryllium copper is a precipitation hardening material and can be purchased in a variety of harnesses, depending on the amount of heat treatment carried out. As one of the most expensive copper alloys, it can be precipitation hardened and used to greater working stresses than the other alternatives.
 
Next month our Director of Quality, Steve Blunt will look at ‘tooling materials’.

Jon Davies, Sales Manager

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