Determination of carbon in steels by emission spectrometry with a high energy pre-discharge

Determination of carbon in plain carbon and low alloy steels by conventional emission spectrometry gives values somewhat higher than the standard values measured by chemical analysis, especially when specimens are annealed. This is attributed to the formation of carbide (cementite) during annealing. During spectrometric analysis preferential discharge occurs near the surface where the carbide is present, resulting in higher measured values. To eliminate the effect of preferential discharge, the authors have developed a new spectrometric method in which the specimen is treated with a high energy discharge prior to the measurement of the emission spectra with a low energy discharge. When the high energy discharge is applied, localized carbide is dissolved to form martensite. As a result, there is no preferential discharge and the data coincide with the standard values. The dissolution of the carbide for the short time of the high energy discharge is ascertained with microscopic observations. The deviation of values obtained by the present method from the standard values is about 0.0095 % for a variety of samples ranging from 0.03 to 1.03 % carbon.