Papers by Keyword: Static CCT Curve

Abstract: To achieve reasonable rolling technology of the novel Nb-V composite microalloyed steel, the continuous cooling transformation (CCT) curve was established by thermal simulation experiment. Microstructure and microhardness at different cooling rates were characterized using an optical microscope (OM) and microhardness tester. The results indicate that the critical quenching speed of Nb-V microalloyed steel is about 23 °C/s. The start and finishing temperatures of phase transformation decreased with the rise of cooling rate. Widmannstatten (W) structure appears at lower cooling rate interval. Microstructure transfers into martensite (M) and bainite (B) with obviously refined grains in higher cooling rate interval. Microhardness improves with the increase of cooling rates. Microhardness value is greatly improved to 298.6 HV at the cooling rate of 11 °C/s, which could be related to the formation of lower bainite during phase transformation process. When the cooling rate is above 29 °C/s, microhardness values remain unchanged basically. This illustrates that the microstructure of Nb-V microalloyed steel consists of martensite and lower bainite.

Abstract: Through the thermal mechanical simulation experiment，combined with the metallographic analysis and microhardness test on the Nb-Ti micro-alloyed steel for the austenitic continuous cooling process. The results shows that: with the increasing of the cooling rate, the phase transformation starting and ending temperature decrease and the ferrite content was decreased at room temperature. In less than 5°C/s low cooling speed region, with the increasing of the cooling rate, the grain size of tested steel obviously increases; In more than 17°C/s high cooling speed region, the grain size and vickers hardness of tested steel change and tends to be smoothly.