Effects of titanium content on the large precipitates in 443 ultra-pure ferritic stainless steel

Abstract

ABSTRACT The effects of titanium contents on the precipitates of 443 ultra-pure ferritic stainless steel during solidification were determined experimentally and compared with a thermodynamic simulation software, that is, Thermo-Calc. Ultra-pure ferritic stainless steel was cast in a vacuum. The experimental results demonstrated that two types of precipitates during solidification exist in the as-cast ingot according to the compositional characteristics, that is, Al2O3–TiN–NbC and TiN–NbC. The number density of TiN–NbC is larger than the Al2O3–TiN–NbC with the Al2O3 core. The number density of the precipitates increases with the Ti content increasing. These precipitates are generated during solidification. The precipitating process could be well predicted through Thermo-Calc software. The Al2O3 forms first in the liquid steel before solidification, TiN appears later in the solidification process, NbC lastly below 1000°C. The titanium content variation from 0.10% to 0.29% has no apparent effect on the liquidus and precipitation temperatures of TiN, but it distinctly reduces the solidus temperature from 1422°C to 1378°C. The higher Ti content in 443 steel leads to TiN precipitates and Al2O3–TiN particles amount increase during solidification. The disregistry theory and thermodynamic calculation indicate that the Al2O3 could act as the nucleus of TiN and the TiN could act as the nucleus of NbC.