Effect of process temperature on the microstructures and properties of enamels coated on Ti-bearing substrate RT360

Abstract In this paper, we describe the experimental processing treatment of the enamel coating on Ti-bearing substrate RT360. The experiment simulates the process of manufacturing the enamel heat sink for use in a heat exchanger in nuclear power stations. The effect of processing temperature on the microstructures and properties of the enamel coating was investigated using a scanning electron microscope, X-ray diffraction, transmission electron microscope and other methodologies. Our research determined that the density of Ti (C, N) particles in RT360 substrate was maximized, due to the interaction between the precipitate and solid solution, when processing treatment was at 850 °C. At that temperature, the precipitate density optimized the hydrogen trapping sites, preventing the enamel coating from fish-scaling. Small Fe-rich islands were precipitated in the steel-enamel interface, forming anchor points due to Marangoni convection. Once the processing temperature exceeded 850 °C, sufficient anchor points were created, resulting in a good adherence interface. However, when processing treatment temperature reached 900 °C, excessive liquidity of the molten frit powders resulted in a nonuniform coating. We concluded that processing treatment of enamel-RT360 composite substrate at a temperature of 850 °C was optimum for improved coating of the heat sink.