Investigation of precipitation and growth behavior of Ti inclusions in tire cord steel

School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, P.R. China
e-mail: xiaofengcai9056@163.com

Received: 12 May 2015
Accepted: 23 June 2015

Abstract

The precipitation and growth behavior of Ti inclusions in 82 grade tire cord steel was investigated by thermodynamic and kinetic calculation. Under the same condition without considering microsegregation, the priority of inclusions to precipitate is in the order of Ti₃O₅, Ti₂O₃, and TiO₂. The formation of TiN cannot precipitate in the liquid region, or in two-phase phase region. Considering microsegregation, the formation of TiN only took place in the two-phase region where the solid fraction is greater than 0.95, or in solid phase region. The segregation degree of oxygen is the strongest, followed by titanium and last by nitrogen. The higher the solute concentration, the earlier the inclusions precipitate. The greater the cooling rate during solidification, the shorter the time for Ti inclusion particles growth and the smaller the size of precipitated Ti inclusion particles. Under the current control condition, in the refining process, the main types of Ti inclusions are Ti₃O₅, which usually coexists with other oxides. In the billets, the main types of Ti inclusions are TiN in the tire cord steel. The calculated size of precipitated Ti oxide is in close agreement with the one measured by SEM.