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Materials (Basel). 2018 Nov 11;11(11). pii: E2241. doi: 10.3390/ma11112241.

Anisotropic Pinning-Effect of Inclusions in Mg-Based Low-Carbon Steel.

Author information

1
Department of Materials Science and Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan. cold19871025@gmail.com.
2
Department of Materials Science and Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan. lai57215308@gmail.com.
3
Steelmaking Process Development Section, China Steel Corporation, No. 1, Zhonggang Road, Kaohsiung 81233, Taiwan. 150151@mail.csc.com.tw.
4
Steelmaking Process Development Section, China Steel Corporation, No. 1, Zhonggang Road, Kaohsiung 81233, Taiwan. t120@mail.csc.com.tw.
5
Department of Materials Science and Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan. wshwang@mail.ncku.edu.tw.
6
Department of Materials Science and Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan. jckuo@mail.ncku.edu.tw.

Abstract

In this study, the effect of austenite grain size on acicular ferrite (AF) nucleation in low-carbon steel containing 13 ppm Mg is determined. The average austenite grain size was calculated using OM Leica software. Results show that the predicted and experimental values of austenite grain size are extremely close, with a deviation of less than 20 µm. AF formation is difficult to induce by either excessively small and large austenite grain sizes; that is, an optimal austenite grain size is required to promote AF nucleation probability. The austenite grain size of 164 µm revealed the highest capacity to induce AF formation. The effects of the maximum distance of carbon diffusion and austenite grain size on the microstructure of Mg-containing low carbon steel are also discussed. Next, the pinning ability of different inclusion types in low-carbon steel containing 22 Mg is determined. The in situ observation shows that not every inclusion could inhibit austenite grain migration; the inclusion type influences pinning ability. The grain mobility of each inclusion was calculated using in situ micrographs of confocal scanning laser microscopy (CSLM) for micro-analysis. Results show that the austenite grain boundary can strongly be pinned by Mg-based inclusions. MnS inclusions are the least effective in pinning austenite grain boundary migration.

KEYWORDS:

Mg-based inclusion; acicular ferrite; austenite grain size; low-carbon steel; pinning ability; predict grain size

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