The continuous cooling transformation behavior, the effect of coiling temperature on microstructure and mechanical properties, and strengthening mechanisms of Ti microalloyed high strength hot strip steel were systematically investigated by thermal simulation testing machine, laboratory rolling mill, SEM and HR-TEM. The dynamic CCT curve was established. The results show that the austenite to ferrite and pearlite transformation takes place when the cooling rate is less than 1℃/s. The austenite to bainite transformation accompanied with austenite to ferrite and pearlite transformation takes place when the cooling rate is in the range of 5 ℃/s to 10 ℃/s. The bainitic transformation temperature is about 600℃. The amount of granular bainite decreases, while the amount of lath bainite increases with the increase of cooling rate in the range of 20℃/s to 50℃/s. Furthermore, the study on the effect of coiling temperature on the microstructure and mechanical properties of experimental steel has shown that the strength and plasticity of tested steel are improved with decreasing the coiling temperature. When the coiling temperature is 550℃，the experimental steel possesses optimal mechanical properties owing to the grain refinement and precipitation of nano-scale TiC particles. And the tensile strength, yield strength and elongation of tested steel were 742MPa, 683MPa and 225%, respectively.
Key words
Ti microalloyed /
high strength steel /
dynamic CCT curve /
mechanical properties /
strengthening mechanisms
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References
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Footnotes
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