PSI - Issue 33

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Saki Hayashi et al. / Procedia Structural Integrity 33 (2021) 1162–1172 Hayashi et al / Structural Integrity Procedia 00 (2019) 000 – 000

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iii) Determination of the maximum allowable amount of Sn by the model When the limiting amount of Δ T was set to plus 20 deg. C, the allowable upper limit of Sn was determined to be 0.03% as shown in Fig. 13.

Fig. 13. Maximum transition temperature change, ∆ estimated by the model.

4. Conclusion

In this study, fracture toughness tests by different amount of Sn and elevated tempering temperature conditions were conducted for clarification of the critical issues for electric furnace steels. As a result, it was found that a small amount of Sn (less than 0.01%) does not cause temper embrittlement, but a small amount of Sn (more than 0.1%) causes temper embrittlement. According to detailed fracture surface observation, temper embrittlement occurs in transgranular fracture manner instead of intergranular fracture, which is reported by many previous studies. We considered this difference is derived from grain size (large heat input HAZ) and microstructure and established the new thermo-dynamics calculation model by the proposed mechanism. By the model calculation, we concluded that Sn residual amount can be allowed up to 0.03 mass%. Our future plans are to verify the tentative results and to establish more accurate model for all possible microstructure. References Itaya, T., Orii, T., Nakanishi, E., Tomita, K., Takada, Y., Ishida, Y., Ishikawa, H., 2010. Iron recycling technology and CO2 reduction effect as an automobile body, in: Society of Automotive Engineers of Japan Symposium: New Development of CO2 Reduction in Body Structure Formation. Society of Automotive Engineers of Japan, Inc. The Japan Iron and Steel Federation. https://www.jisf.or.jp/data/seisan/month.html (accessed 6/7/2021) Ministry of Economy, Trade and Industry of Japan. https://www.meti.go.jp/committee/kenkyukai/sansei/kaseguchikara/pdf/010_s03_02_03_01.pdf (accessed 6/7/2021) Yamaguchi, M., 2015. Multiscale thermodynamic analysis on intergranular fracture of steel. Materia Japan 54, 3, 110-117. Mimura, H., 1974. Temper Brittleness in Steel. Tetsu-to-Hagane 57, 14, 2273-2284. McMahon, C. J. Jr., 1991. Mechanics of Intergranular Fracture in Alloy Steels. Materials Characterization 26, 269-287. Nagasaki, C. and Kihara, J., 1997. Effect of Copper and Tin on Hot Ductility of Ultra-low and 0.2% Carbon Steels. ISIJ International, 37, 5, 523 530. Peng, H., Chen, W., Chen, L. and Guo, D., 2014, Beneficial effect of B on hot ductility of 20CrMnTisteel with 0.05% Sn, Metall. Res. Technol.111, 221–227., DOI:10.1051/metal/2014027www.metallurgical-research.org.