Effect of Ti Addition on Yield Strength of Low-Mo Fire-Resistant Steel at Elevated Temperatures |
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Authors: | Dong-Jun Choi Tae-Yeong Kim Hyun-Uk Hong Joonoh Moon Chang-Hoon Lee Dong-Ik Kim Jae-Hyeok Shim Heung Nam Han Young-Su Lee |
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Affiliation: | 1. Energy Materials Research Center, Korea Institute of Science and Technology, Seoul, 02792 Republic of Korea;2. Department of Materials Convergence and System Engineering, Changwon National University, Changwon, 51140 Republic of Korea;3. Steel Department, Advanced Metallic Materials Division, Korea Institute of Materials Science, Changwon, 51508 Republic of Korea;4. Department of Materials Science and Engineering, Seoul National University, Seoul, 08826 Republic of Korea |
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Abstract: | Herein, a series of low-Mo (0.2 wt%) fire-resistant steels with varying amounts of Ti (0.008–0.13 wt%) are investigated to study the effects of Ti on yield strength at elevated temperatures. At room temperature (RT), precipitation strengthening by nanoscale TiC precipitates is found to be the major factor for the enhanced strength. The amount of TiC precipitates and both the yield and tensile strengths increase monotonically with the Ti content. However, the yield strength ratio (YS at 600 °C divided by YS at RT) of the steel with the highest Ti content (0.13 wt%) is significantly reduced to 0.6. In contrast, the YS ratio of the steels with Ti content in the range of 0.008–0.087 wt% remains above 0.7 and increases with Ti content. The difference between the steels lies in the B content and the resultant bainite volume fraction. The steel with 0.13 wt% Ti does not contain B and has only 4% bainite, whereas the other steels contain 20 ppm B and approximately 60% bainite. Hence, a microstructure with a sufficient fraction of bainite is required to ensure strength at elevated temperatures. The properties can be further improved by Ti precipitation strengthening. |
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Keywords: | fire-resistant steel precipitation strengthening yield strength |
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