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Inclusions: Identification, Measurement and Influences

Freitag (23.09.2016)
09:35 - 09:55 Uhr Hörsaal A
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This talk gives an overview of the history of inclusion identification and measurement and the influence, positive or negative, on the mechanical properties and service performance of steels. Inclusions are broadly classified as being indigenous (occurring from natural processes) or exogenous (entrapped foreign material, such as refractory materials or slag). Exogenous inclusions are distributed irregularly and are mainly detected using ultrasonic inspection. Indigenous inclusions are a result of the limited solid solubility of oxygen and sulfur in solid steel. Their composition and quantity can be controlled. Inclusion composition has been determined by extraction techniques, but EDS and/or WDS techniques using the SEM or EMPA are far more commonly used and provide excellent results. Quantifying inclusions is primarily performed using standard charts, e.g., E 45. But, interlaboratory studies have demonstrated that chart ratings are not precise nor are they repeatable or reproducible. Image analysis, using stereological procedures works very well. However, those purchasing steels do not understand the method and do not know what measurement limits to request for acceptance or rejection. Aside from improving machinability, mechanical properties and service performance are degraded by inclusions, as will be discussed.