MICROSTRUCTURE TRANSFORMATION IN THE WELDING HEAT AFFECTED ZONE OF 800MPa GRADE ULTRA FINE STRUCTURED STEEL
来源期刊：Acta Metallurgica Sinica2004年第3期
论文作者：J.B.Liu Z.Q.Liu Z.L.Tian K.Miao L.J.Hu Y.T.Wang
Key words：ultra fine structured steel; weld; heat affected zone; transformation rate; microstructure;
Abstract: The transformation behavior and microstructure development in the heat affected zone (HAZ) of 800MPa grade ultra fine structured steel was investigated. It was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates, with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the fast cooling regime. At relatively high cooling rates, which corresponded to low heat inputs, the hardness of the simulated HAZ was above that of the base metal. When the cooling rate was below 9℃/s, the welding HAZ would have an obvious softening. The analysis of transformation rates in continuous cooling processes was completed by numerical differential method. The result indicated that the microstructure transformation rate of the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time ts/5 is longer than 7s.
J.B.Liu1，Z.Q.Liu2，Z.L.Tian3，K.Miao2，L.J.Hu1，Y.T.Wang2
(1.Huazhong University of Science and Technology, Wuhan 430074, China;
2.Technology Center of Wuhan Iron and Steel (Group;
3.Central Iron and Steel Research Institute, Beijing 100080, China)
Abstract:The transformation behavior and microstructure development in the heat affected zone (HAZ) of 800MPa grade ultra fine structured steel was investigated. It was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates, with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the fast cooling regime. At relatively high cooling rates, which corresponded to low heat inputs, the hardness of the simulated HAZ was above that of the base metal. When the cooling rate was below 9℃/s, the welding HAZ would have an obvious softening. The analysis of transformation rates in continuous cooling processes was completed by numerical differential method. The result indicated that the microstructure transformation rate of the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time ts/5 is longer than 7s.
Key words:ultra fine structured steel; weld; heat affected zone; transformation rate; microstructure;
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