The Effects Of Surface Coating And Texture On Heat Transfer And Solidification Process

The strip casting process is an advanced technology in metallurgy industry. It combines continuous casting with rolling and simplifies the production process from molten steel to hot-rolling. The productions of strip between 2 mm to 5 mm thick are cast directly from molten steel. This makes casting and rolling into one process. So the steel production process becomes more compact, more continuous, more efficient and more environment-friendly. The casting roller is the core component in the strip casting process. It plays a key role in achieving industrialization of strip casting process to make the casting roller have both excellent heat transfer performance and long service life. The surface coating and texture are general solutions. Therefore, it's necessary and important to study about the effects of surface coating and texture on interfacial heat transfer and solidification process. The research results will be helpful to control the strip casting process and improve the qualities of strip.The solidification process on the surface of casting rolls during strip casting is simulated by the interfacial heat transfer simulator system. During the melt immersion experiment, the K-type thermocouple will measure the temperature history of internal surface. There are a lot of optimizations and innovations been applied to improve the simulating and measuring accuracies in the experiment process. By solving the IPHC (Inverse Problem of Heat Conduction), the interfacial heat flux history on the surface between molten steel and substrate is gotten. MSA (Measurement System Analysis) is applied to ensure the stability and reliability of experimental data.The influences of the Ni and Co-Ni coatings on heat transfer and solidification structure are studied, and the effect of variations of coating's composition and thickness are also analyzed and discussed. The results show that with a surface coating, the maximum heat flux will decrease quickly and the impact on the average heat flux is not significant. At the same time, the solidification structures will be improved; the changes of coating compositions haven't obvious effects on heat transfer and solidification process; for the materials of low carbon steel and 304 stainless steel, with the increasing of coating's thickness, the decline of heat fluxes will be aggravated, but it may lead to surface defects on the solidification shells.The influences of various surface textures which are made by four surface treatment methods on heat transfer and solidification structure are studied. The results show that with the increasing of the surface roughness, the maximum heat flux will increase. But for a large surface roughness, it will reduce quickly and the solidification shell will appear the adhesion phenomena between it and substrate, which leads the quality to be worse. The effect of surface roughness on the average heat flux is not significant. Blasting process by corundum makes the residual particles embed in the substrate, but it can increase the maximum heat flux and improve the quality of solidification shell. So using corundum to blast is better than using steel shot. The dynamic cold spray process make a closed-pit texture on the surface of substrate. According to the results of calculation, there is a critical radius of pit and if the radius is bigger than it, the surface of solidification shell is easy to have dents. It will affect the quality of casting strip. Therefore, for avoiding defects, it will be useful to decrease the size of pit, make continuous texture, decrease the temperature of melted steel and increase the temperature of substrate. The ridge-type surface is able to guide the solidification process and improve the quality of shell. According to the results of calculation, the angle of texture has a greater effect on heat transfer and solidification process than the depth of texture.