Formation of TiN Inclusions During Solidification of Titanium Micro-Alloyed Steel: Modeling With ChemAppPy

ChemAppPy integrates ChemApp into the Python programming language, which makes it possible to calculate complex equilibria and thermochemical properties in a convenient Python environment. Based on ChemAppPy, a modified coupled model, which considers microsegregation, growth of TiN inclusions, and variable solute partition coefficients, was established to investigate precipitation and growth of TiN inclusions in Ti micro-alloyed steel. Results showed that it is more reasonable to calculate inclusion formation with a variable ki than a fixed one. With decreasing temperature, both kN and kTi decreased in the liquid and δ phases, subsequently in the L + δ + γ phases kTi decreased quickly while kN increased rapidly. In a 0.06 wt pct Ti micro-alloyed steel, TiN inclusion starts to precipitate at fS = 0.77, while for a higher Ti content (0.18 wt pct), it starts to precipitate earlier at fS = 0.49. Compared to the initial Ti and N content, the cooling rate significantly affects the size of TiN inclusions. The predicted size of TiN inclusions in the slab of 0.12 pct Ti micro-alloyed steel (58 ppm) increased from 0.83 to 13.38 μm when the local cooling rates decreased from 10 to 0.05 K/s. The TiN inclusion size distribution modeled with ChemAppPy is in good agreement with the analyzed results of industrial samples.