ASSESSMENT OF THE DISTRIBUTION OF NON-METALLIC INCLUSIONS IN STEEL PRODUCTS USING THE STEREOLOGICAL RECONSTRUCTION METHOD

Abstract

The work shows that non-metallic inclusions formed in the steel production process significantly affect the properties of steel and metal products, and their removal in steel production processes plays a major role in obtaining high-quality products. It is proven that stereological analysis can be used to obtain quantitative information about the size and number of non-metallic inclusions. It is highlighted that “clean steel” includes controlling the content of all inclusions contained in steel, taking into account inclusions larger than the critical size, which affects the quality of the finished product. It is shown that non-metallic steels in the finished product are represented by oxides, while today the assessment of steel contamination is insufficient and in some cases is conditional. It is established that none of the current scales, namely ASTM E45, ISO 4967:1979, SKF and others, do not fully reflect the real degree of steel contamination [. At the same time, the data of chemical analysis of the studied samples indicate that the content of non-metallic inclusions exceeds by 20-30% the data obtained using standard metallographic methods. It is highlighted that at present, statistical methods for estimating the size and distribution of inclusions have become widespread among quantitative methods of analysis. It is shown that for a comprehensive assessment of the contamination of steel with non-metallic inclusions, it is necessary to conduct a complex analysis, which includes an assessment of their composition, morphology, size and distribution. It is shown that for the statistical assessment of the distribution of non-metallic inclusions by size, a method was developed in the work that allows detecting the distribution of large non-metallic inclusions in steel products. It was found that for the detection of large non-metallic inclusions, a logarithmically normal (lognormal) distribution of equivalent diameters of non-metallic inclusions can be used, which is based on the multiplicative process of forming random variables. It is shown that to obtain a distribution curve, the entire detected set of non-metallic inclusions (separately for sulfides and oxides) was divided by size intervals, while the analysis results largely depended on the number of intervals, i.e. size groups. It is shown that using the developed methodology, a quantitative assessment of the contamination of continuously cast billets with non-metallic inclusions was carried out. It is shown that as a result of the research, a method of stereological reconstruction of the distribution of nonmetallic inclusions was developed, which determines unaccounted non-metallic inclusions of a size exceeding the critical one. It was found that quantitative assessment of the contamination of continuously cast billets with non-metallic inclusions using the method of stereological reconstruction of the lognormal distribution of inclusions by size allows predicting the number of large non-metallic inclusions in metal products.