Precipitation thermodynamics analysis and control of titanium nitride inclusions in extra-low oxygen wheel steel

The liquidus and solidus temperatures and the Ti and N activities of high speed wheel steel at 1 873 K were obtained by thermomechanically analyzing the precipitation of TiN inclusions.The formation reaction of TiN and the solubility product of Ti and N in the steel were calculated,and the results show that TiN inclusions only form in solid phase,but under the chemical composition of this wheel steel,TiN inclusions can not be produced in solid phase.Only in a solidification front,the formation reaction of TiN can take place owing to the enrichment of Ti and N in the two-phase region.During an engineering process,properly increasing the cooling rate of the secondary cooling zone in a continuous caster to make the rapid solidification of molten steel and shorten the enrichment time of Ti and N in a solidification front can decrease the precipitation of pure TiN inclusions.The calculations and analysis on detection results of TiN inclusions in the experimental wheel steel show that the best way of removing the precipitation of pure TiN inclusions in theory and improving the fatigue properties and service life of the wheel steel is controlling the content of Ti below 3.5×10^-5 and the content of N below 3.1×10^-5 in the steel under the condition of normal cooling rate.