Procedure of Eliminating Porosity in Grey Cast Iron with Low Sulphur Content

Abstract

This study shows that the inoculation process of a molten alloy is crucial in disposing of porosity-type defects. A thermal analysis is used to assess the physico-chemical state of a molten alloy, which can be an indicator of the inoculation effect. A modern thermal analysis should be able to perform a quick data-analysis and provide information about any possible problems in a casting if it is poured with the analysed alloy. The time of the transmission of this information depends on whether we can make a decision and introduce changes to the metallurgical process. An important piece of information that can be obtained in this way is a message about the possibility of the appearance of porosity in a cast iron casting. In such a situation, an operator can react by applying an additional dose of inoculant. The porosity that is indicated by the thermal analysis systems can be either gaseous or shrinkage in nature. The research that is presented in this paper is based on two industrial castings that are made of cast iron with reduced sulphur content, in which shrinkage porosity occurred and was detected during the mechanical machining of the castings. As a result of laboratory tests in which iron powder was introduced along with an inoculant, a mixture was developed that, when applied under industrial conditions, eliminated the porosity defects by increasing the number of austenite dendrites. The ITACA thermal analysis system was used at each stage of the research, which allowed for the faster and more precise determination of the appropriate amount of the inoculant mixture that was used.