In order to form direct bonding, the SiO 2 content of raw materials from magnesia brick manufacturers should be low, and the firing temperature must be raised. The content of SiO 2 in existing directly bonded magnesia-chrome bricks is generally less than 2%, and the firing temperature is between 1700 and 1800 C. The formation of direct bonding is a dissolution-precipitation process. Increasing the content of fine chromium concentrate powder is conducive to the formation of direct bonding. Therefore, we must pay attention to the proportion of chromium concentrate fine powder in the batching. In the presence of silicate, the bond between periclase and periclase will be strengthened by Cr2O3, but decreased by Al2O3 and Fe2O3. Adding Al2O3 or Fe2O3 to magnesia-chrome brick can reduce the melting point of silicate, and adding Cr2O3 can increase the melting point. Therefore, chromium ore with high Cr2O3 content has higher high temperature strength than chromium ore with low Cr2O3 content. Secondary spinel is the characteristic of direct bonding brick. The higher the content of Cr2O3, the more intragranular and intergranular spinel, the higher the strength of the product and the stronger the slag resistance.