Influence factors of thickness direction temperature of low carbon bainite steel Q690D during laminar cooling

Abstract

In this paper, the temperature-transformation finite element model of low carbon bainitic steel Q690D was established based on the characteristics of controlled cooling after rolling. In the process of controlled cooling after rolling, there are many factors that affect the temperature in the direction of the thickness of the steel plate, mainly from the thickness of the steel plate, cooling water flow, open cooling temperature and cooling water collection tube opening method analysis. The effect of different factors on the cooling rate is analysed by simulation to obtain the corresponding variation of temperature in the thickness direction. The results show that the greater the thickness, the less effective the energy transfer to the surface layer. This means that thinner steel plates are easier to control in terms of temperature. The temperature drop in the thickness direction is relatively large when using the mode with upper and Upper and lower spray volume ratio of (650/1000) for the DQ section and Upper and lower spray volume ratio of (500/1000) for the ACC section, and the reasonable range is easier to be obtained. On the premise of not being affected by the cooling rate of temperature drop, in the thickness direction, the latent heat value of phase change is different due to the different time periods of phase change, and the heat generated in each microstructure is different, so the temperature distribution shows that the starting cooling temperature of 860 °C is more gentle and uniform in the temperature slope than the starting cooling temperature of 750 °C. Among the four header opening modes, mode (1111111110000011111) makes the temperature of each layer of the steel plate more uniform and reasonable, superior to the continuous opening mode.