Effect of Zr Microalloying on Austenite Grain Size of Low-Carbon Steels
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The effect of microalloying addition of Zr on the characteristics of inclusions and prior austenite grain sizes following a quench heat treatment has been investigated for two custom-made steels. The average size of particles in the Zr-containing steel is found to be the same as the Zr-free steel (0.49 μm). However, the number of smaller particles in the Zr-containing steel is much higher than the Zr-free steel. The inclusions in the Zr-containing steel are composed of ZrO2-TiN-MnS, and inclusions in the Zr-free steel are consisted of TiOx-Ti(C,N). The average prior austenite grain size of the Zr-containing steel is consistently smaller than that of the Zr-free steel, due to a large number of fine oxide inclusions and Ti(C,N) precipitates, working to pin the austenite grain boundaries at temperatures up to 1673 K (1400 °C). The grain refinement mechanisms by inclusions through the addition of Zr are discussed via thermodynamic and kinetic calculations.
Minghao Shi gratefully acknowledges the financial support from China Scholarship Council.
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