Spray cooling is a key technology in the continuous casting process and has a marked influence on the product quality. In order to obtain the heat transfer characteristics, which are closer to the actual continuous casting to serve the design, prediction and simulation, we created an experimental laboratory setup to investigate heat transfer characteristics of air mist spray cooling during the continuous casting secondary cooling process. A 200-mm thick sample of carbon steel was heated above 1000 °C, and then cooled in a water flux range of 0.84 to 3.0 L/(m²∙s). Determination of the boundary conditions involved experimental work comprising an evaluation of the thermal history and the heat flux and heat transfer coefficient (HTC) at the casting surface using inverse heat conduction numerical schemes. The results show that the heat fluxes were characterized via boiling curves that were functions of the slab surface temperatures. The heat flux was determined to be 2.9 × 10⁵ W/m² in the range of 1100 to 800 °C with a water flux of 2.1 L/(m²∙s). The critical heat flux increased with the increase of water flux. The HTC was close to a linear function of water flux. We also obtained the relation between the HTC and the water flux in the transition boiling region for surface temperatures of 850 to 950 °C.