Analysis of the Distribution of Non-Metallic Inclusions and Its Impact on the Fatigue Strength Parameters of Carbon Steel Melted in an Electric Furnace

Steels are currently the most commonly used industrial construction materials. The use of steels depends on their properties, including their fatigue strength. Despite the fact that many works have been devoted to fatigue strength studies, there is still a lack of research discussing the fatigue strength of low-carbon steels. This deficiency is also visible when analyzing the influence of impurities on the fatigue properties of these steels. In most cases, the literature of material fatigue tests includes results obtained for materials produced on the laboratory scale, and it is difficult to directly translate these results to the industrial scale, on which steels for industrial applications are produced. This paper presents studies on the influence of non-metallic inclusions on the fatigue strength coefficient. The analyzed steel contained an average of 0.23% C, 1.23% Mn, and 0.0025 B. It was melted in 140-ton production furnaces, and after being tapped into a ladle, it was desulphurized and refined with argon. A classic plastic working process was used to produce steel samples. Based on the analysis of the test results, it was mainly found that the fatigue resistance coefficient k decreased with the increase in impurities spacing, and with a large share of smaller non-metallic inclusions, a higher fatigue resistance coefficient was noted, which may indicate that small non-metallic inclusions with an oval shape do not reduce the fatigue life of steel, regardless of its microstructure.