Cold rolled steel is worked below its recrystallization temperature to reduce thickness and achieve tighter tolerances. Pickling removes impurities before the metal is passed through rollers. Cold rolling can produce a high-quality surface finish and prepare the metal for surface coating. The final stock can be manufactured in various shapes and sizes suitable for a wide range of applications. Cold rolled steel is highly resistant to dents, has useful magnetic properties, and accepts surface coatings easily.
Cold rolled steel is steel that has been worked below its recrystallization temperature by passing it between a pair of rolls. The recrystallization temperature is the temperature at which the grains in the metal lattice structure have been rearranged, leaving it free from stress and strain. In this way, cold rolling differs from hot rolling, which is used to work metal above its recrystallization temperature. Cold rolled steel material comes in a variety of sizes and shapes with characteristics that are useful in a wide range of applications.
The steel is pre-treated before it is cold rolled in a process known as pickling, which uses strong acids to remove scale and other impurities. The metal is then passed through rollers to reduce its thickness. Most cold rolling occurs in multiple passes and usually incorporates two stations to work the metal. One station is used for a larger initial reduction in size, while the other produces a smaller finish reduction to produce a quality surface. Due to the higher hardness created by cold rolling, this process is more limited than hot rolling in the size reduction achieved with each pass.
There are several reasons for cold rolling of steel. This process reduces the thickness of the metal being worked and achieves tighter thickness tolerances than those achievable with hot rolling. Cold rolling can also produce a high quality surface finish and prepare the metal to receive a surface coating.
A variety of types of cold rolled steel stock can be produced depending on the size reduction of the original stock. Skin Rolled Steel undergoes 0.5-1.0% shrinkage and is known for its smooth surface finish and good ductility. Other qualities include quarter hard, half hard and all hard, which can achieve up to 50% reduction in size compared to the original stock.
As cold-rolled steel shrinks in size further, its strength and hardness increase, but its ductility decreases. Quarter Hard steel retains enough ductility that it can be bent upon itself without breaking. Semi-hard steel can only be bent to 90 degrees, and fully hard steel can only be bent to 45 degrees without breaking. After cold rolling, heating the metal in a process known as annealing can restore some of its ductility. The final stock of cold rolled steel can be manufactured in the form of sheet, strip, rod or other shapes.
Cold rolled steel products exhibit a variety of attributes suitable for a wide range of applications. In addition to its high strength, cold rolled steel is highly resistant to dents and has useful magnetic properties. It also easily accepts surface coatings such as enamel and paint. Items fabricated from cold rolled steel range from commercial products such as appliances and bathtubs to automobiles to industrial products including motors, generators and transformers.
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