Effects of Na2O, K2O and B2O3 on Deformability of SiO2-MnO-Al2O3 Inclusion in High-Carbon Steel

Abstract

Cord steel is used for making tire frames and wire saws for cutting silicon wafers. The diameter of mainstream cutting wire has been developed to be lower than 100 μm. The size and deformation ability of inclusions are very important to the wire breaking rate of cord steel during the drawing process. In order to improve the deformation ability of the inclusions in cord steel, alkali metal oxide was added into the molten steel to improve the inclusions in the steel so as to obtain good, plastic, low-melting-point inclusions. Mass fractions of 0.3%, 0.5% and 1.0% K2CO3, Na2CO3 and B2O3 were added into cord steel, which were melted in 10 furnaces (including 0% alkali metal oxides, mass fractions of 0.3%/0.5%/1.0% K2CO3, Na2CO3 and B2O3). The morphology and composition of inclusions were observed by SEM-EDS. Factsage phase diagram calculations and experimental results show that, with the increase in Na2CO3 content in cord steel, the aluminum content in the inclusions gradually decreased. When the mass fraction of Na2CO3 was 0.5% per ton, most of the inclusions in the steel fell in the low melting point region (less than 1300 °C). With the increase in K2CO3 content in cord steel, the silicon content in the inclusions decreased gradually. When the mass fraction of K2CO3 was 0.5% per ton, most of the inclusions in the steel fell in the low melting point region. The deformation ability of the inclusions added with 0.5% Na2CO3 in the steel during forging was better than that of the inclusions added with 0.5% K2CO3. After adding B2O3, the inclusions in the steel were SiO2-MnO-Al2O3 inclusions or inclusions with SiO2-MnO-Al2O3 as the core and BN wrapped around. Boron could not be dissolved into the inclusions for plastic modification.