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Metals 2019, 9(3), 296; https://doi.org/10.3390/met9030296

Effect of Thermomechanical Treatment on Acicular Ferrite Formation in Ti–Ca Deoxidized Low Carbon Steel

The State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China
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Received: 12 February 2019 / Revised: 28 February 2019 / Accepted: 2 March 2019 / Published: 6 March 2019
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Abstract

Transformation behaviors and mechanical properties under thermomechanical treatment conditions of Ti–Ca deoxidized low carbon steel were studied in comparison to Al–Ca treated steel. A thermomechanical simulation and a hot rolling experiment were carried out. Inclusions and microstructures were characterized, and the transformation mechanism was analyzed. The results indicated that typical inclusions in Ti–Ca deoxidized steel were TiOx-MnS-Al2O3-CaO, TiOx-MnO-Al2O3-CaO, and TiOx-MnS, which were effective for acicular ferrite (AF) nucleation. Acicular ferrite formation temperature decreased with an increase in cooling rate. A fine AF dominant microstructure was formed under a high driving force for the transformation from austenite to ferrite at lower temperatures. A high deformation of 43–65% discouraged the formation of acicular ferrite because of the increase in austenite grain boundaries serving as nucleation sites. The fraction of high-angled grain boundaries that acted as obstacles to cleavage cracks was the highest in the sample cooled at 5 °C/s because of full AF structure formation. The hardness increased significantly as the cooling rate increased from 2 to 15 °C/s, whereas it decreased under the condition of deformation because of the formation of (quasi-)polygonal ferrite. By applying accelerated water cooling, the mechanical properties, particularly impact toughness, were significantly improved as a result of fine AF microstructure formation. View Full-Text
Keywords: low carbon steel; Ti–Ca oxide; acicular ferrite; thermomechanical treatment; hot deformation; cooling rate low carbon steel; Ti–Ca oxide; acicular ferrite; thermomechanical treatment; hot deformation; cooling rate
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Wang, C.; Wang, X.; Kang, J.; Yuan, G.; Wang, G. Effect of Thermomechanical Treatment on Acicular Ferrite Formation in Ti–Ca Deoxidized Low Carbon Steel. Metals 2019, 9, 296.

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