What Does 'Cold Working' Mean?
Stainless steel is naturally an especially hard and strong metal. If these qualities need to be further enhanced, the material can be cold worked. In this edition of the BS Stainless blog, we're going to be looking in more detail at what the cold working process entails.
Cold working is a process that plastically deforms stainless steel (or indeed any other alloy) below the temperature at which recrystallisation takes place. Recrystallisation occurs when the atoms that make up the alloy become more energised, causing new crystals to form. The temperature at which this occurs is different for each individual alloy; as a general guide, this temperature is about halfway to the alloy's melting point.
The primary reason for cold working stainless steel is to increase its hardness and strength (articularly its tensile strength). Cold working also makes the material smoother; in fact, stainless steel that has been cold rolled can be an impressive ten times smoother than stainless steel that has been subject to a hot rolling process. Hot working also requires soaking pits and furnaces; neither of these are needed for cold working and so this process is more cost-effective and has less environmental impact.
There are several different ways in which stainless steel can be cold worked. These include:
- Drawing. In the drawing process, stainless steel is pulled to extend its length without it cracking. Compressive force is used to force stainless steel from a rolled coil through a hole, causing the material's diameter to be reduced. The process can then be repeated with smaller and smaller holes until the required diameter is achieved.
- Shearing. Slitting is the most widely used shearing method for cold working. A slitting machine is fed with stainless steel from a master coil. The machine cuts the material into narrower strands, allowing for consistent and accurate measurements. The resulting strands can then be reworked to produce a complete coil.
- Bending. Stainless steel can be shaped by this form of cold working. The material is passed through a series of angles, tubes or rolls, producing the bend and cross-section profile specified.
- Squeezing. The most common cold working method is squeezing, which can be done in a multitude of ways including forging, rolling, coining and extruding. It is useful for a variety of products such as stainless steel strip, allowing smooth products to be created with the most precise mechanical properties. The squeezing method is also used to produce cold heading stainless steel wire, which can then be used to create all sorts of components from rivets and bolts to nails and screws.
Many of the stainless steel products in our extensive portfolio have been cold worked. For further information, please browse the BS Stainless website or get in touch with our expert technical team.