Effects of Cooling Rates on Microstructures and Mechanical Properties of Nb-Ti Microalloyed Steel

doi:10.1007/s12204-012-1340-7

Abstract

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—900℃) 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—1 000℃, with the increase of the cooling rate, the hot ductility decreases. However, in the range of 650—850℃, 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℃/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℃.

Key words: Nb-Ti microalloyed steel| cooling rate| microstructure| hot ductility

摘要： 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—900℃) 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—1 000℃, with the increase of the cooling rate, the hot ductility decreases. However, in the range of 650—850℃, 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℃/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℃.

关键词: Nb-Ti microalloyed steel| cooling rate| microstructure| hot ductility

CLC Number:

TG 142.1

ZHAO Su1* (赵素), WU Yu-juan2* (吴玉娟), HE Mei-feng3 (何美凤), ZHANG Li4 (张立). Effects of Cooling Rates on Microstructures and Mechanical Properties of Nb-Ti Microalloyed Steel[J]. Journal of shanghai Jiaotong University (Science), 2012, 17(6): 653-657.

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