Characteristics of Al₂O₃, MnS, and TiN inclusions in the remelting process of bearing steel

Abstract

The Al₂O₃, MnS, and TiN inclusions in bearing steel will deteriorate the steel’s mechanical properties. Therefore, elucidating detailed characteristics of these inclusions in consumable electrode during the electroslag remelting process is important for achieving a subsequently clean ingot. In this study, a confocal scanning violet laser microscope was used to simulate the remelting process and observe, in real time, the behaviors of inclusions. The obtained images show that, after the temperature exceeded the steel solidus temperature, MnS and TiN inclusions in the specimen began to dissolve. Higher temperatures led to faster dissolution, and the inclusions disappeared before the steel was fully liquid. In the case of an observed Al₂O₃ inclusion, its shape changed from angular to a smooth ellipsoid in the region where the solid and liquid coexisted and it began to dissolve as the temperature continued to increase. This dissolution was driven by the difference in oxygen potential between the inclusion and the liquid steel.

Keywords

characteristics / inclusions / remelting / bearing steel / confocal microscope

References

[1] Mitchell A. Oxide inclusion behaviour during consumable electrode remelting. Ironmaking Steelmaking, 1974, 1(3): 172.

[2] Carmona F.R. Non-metallic Inclusions in Electroslag Refined Ingots, 1983, Vancouver, The University of British Columbia 148.

[3] Li Z.B., Zhou W.H., Li Y.D. Mechanism of removal of non-metallic inclusions in the ESR process. Iron Steel, 1980, 15(1): 20.

[4] Fu J. An investigation of mechanism on the removal of oxide inclusions during ESR process. Acta Metall. Sinica, 1979, 15(4): 526.

[5] Fraser M.E., Mitchell A. Mass transfer in the electroslag process: Part 1. Mass-transfer model. Ironmaking Steelmaking, 1976, 3(5): 279.

[6] Li Z.B., Zhang J.W., Che X.Q. Control of content and composition of nonmetallic inclusion in ESR steel. J. Iron Steel Res., 1997, 9(2): 7.

[7] Janis J., Karasev A., Nakajima K., Jönsson P.G. Effect of secondary nitride particles on grain growth in a Fe–20 mass% Cr alloy deoxidised with Ti and Zr. ISIJ Int., 2013, 53(3): 476.

[8] Fu J., Zhu J., Di L., Tong F.S., Liu D.L., Wang Y.L. Study on the precipitation behavior of TiN in the microalloyed steels. Acta Metall. Sinica, 2000, 36(8): 801.

[9] Chen J.X. Manual of Chart and Data in Common Use of Steel Making, 2010, Beijing, Metallurgical Industry Press 510.

[10] Qü Y. Physical Chemical Calculation in Steelmaking, 1993, Beijing, Metallurgical Industry Press 121.

[11] Goto H., Miyazawa K.I., Yamaguchi K.I., Ogibayashi S., Tanaka K. Effect of cooling rate on oxide precipitation during solidification of low carbon steels. ISIJ Int., 1994, 34(5): 414.

[12] Wei J.H., Mitchell A. Changes in composition during A.C. ESR—I. Theoretical development. Acta Metall. Sinica, 1984, 20(5): B261.

[13] Yang L., Cheng G.G., Li S.J., Zhao M., Feng G.P. Generation mechanism of TiN inclusion for GCr15SiMn during electroslag remelting process. ISIJ Int., 2015, 55(9): 1901.

[14] Takashi M., Masafumi Z. Effect of silicon content in steel on the formation of titanium nitride and solidification structure. Tetsu-to-Hagané, 2013, 99(3): 191.

[15] Ohta M., Morita K. Interaction between silicon and titanium in molten steel. ISIJ Int., 2003, 43(2): 256.

[16] Shin D.J., Min D.J. Investigation on the decomposition of Al₂O₃ using an electrochemical method. ISIJ Int., 2013, 53(3): 434.