Chemical composition

When a metallic material is produced as a raw material, its chemical composition is checked. When cast iron is converted to carbon steel in the oxygen process, all the relevant elements are weighed before being put into the converter. Before the steel is poured, the chemical composition is checked. When the steel is poured a sample is cast. The sample is analysed and its chemical properties are the properties of the melt. Certificates will show the name of the steelmaker and the melt, cast or heat number.

The chemical composition may show elements which are not required by the specification. Low carbon steels may show traces of nickel, chromium and molybdenum. The trace ele­ments are a welcome addition because they tend to enhance the physical properties of the material. Impurities such as sul­phur and phosphorous, will be shown very accurately. The chemical composition of specific components, when neces­sary, can be traced back to the original melt.

On rare occasions, a sample will be taken from a component and analysed. Modem techniques only require very small sam­ples. It is possible to analyse material without destroying it. Two devices are available which can analyse material without re­moval from the component. Neither method can detect carbon. However sufficient accuracy is present to differentiate between 304 and 316 stainless steel.

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