Evolution of Ti-Based Nonmetallic Inclusions During Solution Treatment of Maraging 250 Steel: Thermodynamic Calculations and Experimental Verification

摘要

The evolution of Ti-based nonmetallic inclusions in Maraging 250 steel, namely Ti(C_xN_1–x) and Ti₄C₂S₂, was investigated experimentally. Their stability in austenite also was analyzed by a thermodynamic analysis of the Fe-Ni-Ti-C-N-S system. It was established that the total concentration of the inclusions decreases from 0.024 pct to 0.008 pct after treatment at 1453 K (1180 °C) for 3 hours. The Ti₄C₂S₂ inclusions completely dissolve in austenite at 1523 K (1250 °C) during 1 hour of treatment. The composition of the carbonitride inclusions is shifted toward higher TiN contents when they dissolve in austenite. Nitrogen-enriched titanium carbonitride inclusions are stable in austenite and their fraction may be reduced only by controlling nitrogen content in the steel. The experimental observations are in good agreement with the results of the thermodynamic analysis.