Abstract: It has been studied that: (1) The law of precipitating titanium inclusions during the solidification of tire cord steel and titanium inclusions’ characteristics; (2) The effect of the composition (C、N、Ti) in tire cord steel and cooling rate of solidification on the titanium inclusions’ composition and its size; (3) The thermodynamic conditions and the factors influencing the decomposition, solid solution and reprecipitation of titanium inclusions during heating of billets at high temperature, by means of thermodynamics, dynamics and experimental detection. The results show that: (1) The inclusions of Ti（C_xN_1-x） start to precipitate in earlier stage of the solidification of molten tire cord steel, while the inclusion of TiN precipitates at the end period of the solidification. (2) The higher the carbon content of tire cord steel is, the lower the temperature of precipitating the titanium inclusions, the greater the supersaturation of solute elements, the earlier the precipitation of titanium inclusions at solidification front, the larger the value of x in Ti（C_xN_1-x）inclusions is. (3) The cooling rate has a remarkable influence on the size of titanium inclusion precipitated during molten steel solidification. The lower the initial nitrogen content of molten steel, the smaller the size of titanium inclusion. But the initial titanium content of molten steel has little influence on the size of titanium inclusion. (4) The titanium inclusions in billets can be decomposition and then solid solution during heating at high temperature before hot working. The carbon content in tire cord steel has a little influence on  the temperature of thermal decomposition of titanium inclusion, but the contents of nitrogen and titanium have great influence on  the temperature of thermal decomposition of titanium inclusion. The solute atoms originated from decomposition of titanium inclusion are dissolved in austenite by diffusion, which make the small inclusion dissolve and disappear, the larger inclusion become smaller and smaller gradually. (5) If the billets are slow cooling after heating at high temperature, the solute atoms in a supersaturation could reprecipitate to make the titanium inclusion grow up. During the quick cooling after hot rolling, the supersaturated solute atoms can reprecipitate to form titanium inclusion,but have no opportunity to grow up.

Key words: tire cord steel, titanium inclusions, titanium carbonitride inclusions, precipitation during solidification, solid solution