Effects of cooling rates on microstructures and mechanical properties of Nb-Ti microalloyed steel |
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Authors: | Su Zhao Yu-juan Wu Mei-feng He Li Zhang |
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Affiliation: | 1. School of Mechanical Engineering, Shanghai Dianji University, Shanghai, 200240, China 2. National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiaotong University, Shanghai, 200240, China 3. School of Material Science and Engineering, Shanghai Jiaotong University, Shanghai, 200240, China 4. Research Institute, Baoshan Iron & Steel Co., Ltd., Shanghai, 201900, China
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Abstract: | The mechanical properties and microstructure of as-cast Nb-Ti microalloyed steel at different temperatures and cooling rates are investigated in this paper. The III brittle zone (700?C900°C) is revealed. The reduction of the hot ductility is due to the film-like proeutectoid ferrite or the Nb(C, N) precipitates along the austenitic grain boundaries. In the temperature range of 850?C1 000°C, with the increase of the cooling rate, the hot ductility decreases. However, in the range of 650?C850°C, the appearance of large volume fractions of ferrite on austenite grain boundaries minimizes the effect of cooling rate on hot ductility. When the cooling rate is 10°C/s, austenite transforms more quickly to ferrite and at a lower temperature a larger amount of ferrite nucleates and precipitates in the grain, which leads to a sharper improvement in the hot ductility at 650°C. |
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Keywords: | Nb-Ti microalloyed steel cooling rate microstructure hot ductility |
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