Steel is commonly classified based on its carbon content. While increased carbon content can make steel harder and stronger, it can also make the steel more brittle and harder to weld.
Typically there is less than 0.40% carbon in most steels, though it is possible to have as much as 2%. However, once the carbon content exceeds 0.65%, additional carbon does not change the hardness of steel, but it can enhance the steel’s hardenability and improve performance. All of the classifications of cast iron have a carbon content of at least 1.8%.
To ensure that steel meets the necessary element specifications for a particular alloy classification, it is important to use a testing method that can accurately measure the carbon content. The following are some of the more common metal identification methods, and whether they can measure carbon content in steel.
Visual Spark Analysis
One of the older techniques, visual spark analysis allows for steel testing in the field, reducing the amount of time required to get the results. The visual spark test requires a piece of steel to be abraded with a high-speed grinding wheel. As the spinning abrasive wheel is applied to the steel, the sparks that are emitted are compared to either a chart or other known sample. The appearance of the sparks indicates the classification of the steel. This test needs to be done in a darker setting to better observe the sparks. However, this method is not a quantitative analysis.
Arc sorting is one of the fastest methods of analyzing metal for content. Using a spectrometer, arc sorting analyzes the sample in air with an electrical discharge, and compares the light intensity of the sample to the intensity from a reference sample. Arc sorting of steel does not require argon during the process.
XRF Alloy Grade Identification
This type of analysis does not require the destruction of the sample to determine its alloy grade type.
Instead of an electrical discharge, the XRF uses X-ray diffraction analysis to complete a positive material identification, or PMI. The analysis typically takes only a few seconds to complete, and can be done with a handheld device. Since tests can be completed anywhere, it has become a very popular.
This technique can determine the steel grade based on an approximate analysis.
Spark OES Analysis
This type of analysis uses Argon as a shielding gas around the spark, allowing for Carbon analysis. This method, while being more accurate than XRF or Arc sorting, is also slower as the sample needs to be prepared with a sanding disc or belt, and the analysis can take several seconds. However, this is the only method that can provide an accurate, quantitative Carbon reading.
Measuring carbon content requires training in the proper use of the equipment. If the tests are not done properly, it can negatively affect the end results of a product or determination for how to proceed with available materials.
Understanding the pros and cons of each technique will help you make better decisions about how to test your steel, as well as ensuring that the steel you have meets the requirements for your intended application.
When working with steel, it is important to be able to accurately measure the carbon content so that each piece of material is correctly identified, and both traceability is maintained. Verichek offers a number of different testing methods of determining the percentage of carbon in steel, as well as several other types of metals and alloys.