Abstract
To investigate the modification of type B inclusions in high-carbon hard-wire steel with Ca treatment, Si-Ca alloy was added to high-carbon hard-steel, and the composition, morphology, size, quantity, and distribution of inclusions were observed. The samples were investigated by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The experimental thermal results showed that the modification effect of inclusion was better in high-carbon hard-wire steel with Al of 0.0053% and Ca of 0.0029% than that in steel with Al of 0.011% and Ca of 0.0052%, in which the inclusions were mainly spherical semi-liquid and liquid CA2, CA, and C12A7. The inclusion size decreased from 3.2 μm to 2.1 μm. The degree of inclusions segregation was reduced in high-carbon hard-wire steels after calcium treatment. The results indicate that the modification of inclusions is conducive to obtaining dispersed inclusions with fine size. The ratio of length to width decreased and tended to be 1 with the increase in CaO content in the inclusion. When the content of CaO was higher than 30%, the aspect ratio was in the range of 1 to 1.2. The relationship between the activity of aluminum and calcium and the inclusions type at equilibrium in high-carbon hard-wire steel was estimated using classical thermodynamics. The calculated results were consistent with the experimental results. The thermodynamic software Factsage was used to analyze the effect of aluminum and calcium additions on the type and quality of inclusions in high-carbon hard-wire steels. The modification law and mechanism of type B inclusions in high-carbon hard-wire steels are discussed.
Highlights
The wire rod rolled by structural steel with carbon content not less than 0.6% is called high-carbon hard-wire steel, which is widely used in construction, transportation, and other industries [1,2,3]
Inclusions with a low deformation rate induce cracks in high-carbon hard-wire steel during drawing, mainly due to the different thermal expansion coefficients between inclusions and steel matrix where a radial tensile force is generated in the matrix around inclusions, which leads to a stress concentration around inclusions
It can be seen that all inclusions were alumina inclusions with irregular morphology
Summary
The wire rod rolled by structural steel with carbon content not less than 0.6% is called high-carbon hard-wire steel, which is widely used in construction, transportation, and other industries [1,2,3]. Compared with low-carbon steel, high-carbon steel has high hardness and low ductility and is more sensitive to nonmetallic inclusions [5,6]. The output and quality of high-carbon hard-wire steel produced in China have been greatly improved. The breaking rate of the wire is relatively high during the drawing and twisting processes [7]. Controlling the number, size, distribution, and morphology of brittle inclusions is very important in the smelting process of high-carbon hard-wire steel [1]
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