Carbon shrinkage is a term in metallurgy which refers to the decrease in volume of a material when it is heated. This process is the cause of the common phenomenon of metals cracking or warping when heated (thermal shock). A wide range of materials can undergo carbon shrinkage, including carbon steels, stainless steels and cast iron. The degree of carbon shrinkage can vary, depending on both the material and the heating rate.
Carbon shrinkage occurs due to the fact that most metals expand when heated, but carbon steel contracts. This is due to the structure of carbon steel, which is made from an alloy of iron, carbon and sometimes other elements. When this alloy is heated and the internal bonds rearrange, the result is a decrease in the overall volume of the material and hence carbon shrinkage.
There are a number of ways to minimize the risk of carbon shrinkage. One of the most effective methods is known as “strain-hardening” where the material is heated slowly and evenly to reduce the risk of internal stresses within the material. It is also important to control the composition of the material, as some elements such as sulfur can increase the risk of cracking.
The risk of carbon shrinkage can also be minimized by controlling the flow of heat. If the material is heated too quickly, it can cause the internal bonds to rearrange too quickly, leading to shrinkage and cracking. It is therefore important that adequate time is allowed between heating and cooling, and a temperature gradient is used to prevent hot spots in the material.
Another way to reduce the risk of carbon shrinkage is to temper the material after it has been heat treated. This is done by cooling the material at a controlled rate and then reheating it at a lower temperature. This process allows the internal bonds to rearrange slowly and evenly, reducing the risk of cracking.
Finally, an understanding of the materials carbon shrinkage rate can help when planning how the material needs to be processed. For example, a material with a low carbon shrinkage rate may require a longer heating cycle whereas a material with a higher carbon shrinkage rate may require a shorter heating cycle.
Carbon shrinkage is an important phenomenon in metallurgy which can lead to cracking and warping if not properly controlled. However, with a good understanding of the materials characteristics and the application of the right processes, it is possible to minimize the risk of carbon shrinkage.
