Estudo da influência da composição química do aço CA-50 em suas propriedades mecânicas

Abstract

The steel production process aims to transform iron ore or ferrous scrap into a strong and versatile material. The CA-50 specification, used in reinforced concrete, is a widely applied alloy in the construction industry, named according to its specified minimum yield strength of 50 kgf/mm². The objective of this study was to understand the relationships between the chemical composition and mechanical properties of CA-50 steel samples from two mills, one semi-integrated and the other integrated, of a renowned steel company known for its dedication to producing and supplying high-quality steel for various sectors. For this purpose, Optical Emission Spectrometry (OES) analysis, tensile testing, linear regression statistical analyses, Analysis of Variance (ANOVA), and correlations were conducted. It was identified that the components C, Mg, Mn, Si, P, S, Cr, Ni, Cu, Sn, Zn, O, and N have the greatest influence on the required product and that variations in their proportions can affect it. However, it was found that the differences in the levels of chemical elements converge to values very close to the equivalent carbon. This contributed to a better understanding of the relationship between the usual constitution of CA-50 steel and its Elongation (E), Tensile Strength (TS), Yield Strength (YS), and the ratio between these limits (YS/TS), which, in turn, assist in selection and quality control. In the semi-integrated mill, the average Yield Strength (YS) is 597.25 MPa, while in the integrated mill, it is slightly higher, with an average of 615.01 MPa. On the other hand, the average Tensile Strength (TS) in the semi-integrated mill is 692.28 MPa, compared to 721.55 MPa in the integrated mill. This quantitative difference directly reflects on the YS/TS ratio, which is 1.16 for the semi-integrated mill and 1.17 for the integrated mill. Although the variation is small, it suggests a slight difference in material ductility, with the integrated mill showing a slightly higher tendency for greater deformation before failure. It was noticed that despite being of different types, the mills supplying the alloy maintain values very close to those established by the ABNT 7480 standard for chemical composition and mechanical properties, with the integrated mill being more precise to the requirements, which can be explained by the origin of the raw material used. Thus, within the studied samples, it was observed that there is no considerable influence of chemical composition on mechanical properties, suggesting that other factors may play a more significant role.