Influence of Mn/S ratio on inclusions and electrical conductivity of ultra-low carbon steel

YIN Haohui; LIU Man; GAN Xiaolong; XU Guang

doi:10.7513/j.issn.1004-7638.2026.02.021

Volume 47 Issue 2

Apr. 2026

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YIN Haohui, LIU Man, GAN Xiaolong, XU Guang. Influence of Mn/S ratio on inclusions and electrical conductivity of ultra-low carbon steel[J]. IRON STEEL VANADIUM TITANIUM, 2026, 47(2): 189-196. doi: 10.7513/j.issn.1004-7638.2026.02.021

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YIN Haohui, LIU Man, GAN Xiaolong, XU Guang. Influence of Mn/S ratio on inclusions and electrical conductivity of ultra-low carbon steel[J]. IRON STEEL VANADIUM TITANIUM, 2026, 47(2): 189-196. doi: 10.7513/j.issn.1004-7638.2026.02.021

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Influence of Mn/S ratio on inclusions and electrical conductivity of ultra-low carbon steel

doi: 10.7513/j.issn.1004-7638.2026.02.021

The Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China

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Received Date: 2025-09-08
Accepted Date: 2025-11-17
Rev Recd Date: 2025-10-23

Available Online: 2026-04-29

Publish Date: 2026-04-29

Abstract

Abstract

Ultra-low carbon steel is widely used in electrical engineering, automotive industry and other related fields, requiring excellent mechanical properties and electrical conductivity. In steel, FeS can induce the phenomenon of "hot brittleness," and the manganese-to-sulfur(Mn/S) ratio directly affects the FeS content in ultra-low carbon steel, thereby influencing its processability. Meanwhile, the regulation of the manganese-sulfur ratio also impacts the element content and inclusion characteristics in steel, which in turn affects the electrical conductivity of ultra-low carbon steel. To optimize the Mn/S ratio regulation of ultra-low carbon steel and enhance its comprehensive performances, ultra-low carbon steel samples with different Mn/S ratios were smelted using a vacuum induction furnace. The inclusion characteristics and conductivity evolution of ultra-low carbon steel with varying Mn/S ratios were investigated by means of optical microscopy, EBSD, EDS and conductivity testing. The results indicate that the inclusions formed in the steel are primarily near-spherical and long strip-shaped, with the near-spherical inclusions accounting for the vast majority and the long strip-shaped ones for a small proportion. For some inclusions, MnO-SiO₂ binary oxide inclusions serve as the core, around which FeS and MnS or (Mn, Fe)S inclusions are formed. Additionally, some inclusions directly form oxide-sulfide composite inclusions. With the increase of Mn/S ratio, the number of inclusions first increases and then decreases, while the size of inclusions first decreases and then increases. When the Mn/S ratio is 6.4 or higher, there are essentially no FeS inclusions present in the steel. Furthermore, as the Mn/S ratio increases, the electrical conductivity of the ultra-low carbon steel exhibits a monotonic increasing trend. At Mn/S =9.0, owing to the largest inclusion sizes and relatively high number of inclusions, the contents of Mn and S elements dissolved in the steel matrix are significantly reduced. Consequently, the electrical resistivity of the steel decreases, allowing it to achieve the highest electrical conductivity.
- ultra-low carbon steel,
- Mn/S ratio,
- MnS,
- FeS,
- electrical conductivity

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References(31)

References

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