Metal matrix composites (MMCs) can be manufactured by infiltrating a melting matrix alloy into hard powders — such as silicon carbide and tungsten carbide — loaded in a graphite mold and quenched to achieve a specific quenching temperature profile for proper solidification. Water quench is a widely used quenching technique within the aluminum and steel industry. It is more common to apply numerical simulation to optimize process parameters and help improve product quality, which depends upon reliable boundary conditions (e.g., heat flux or heat transfer coefficient); however, heat transfer coefficient changes with surface temperature and water flow rate. Moreover, the heat transfer coefficient in the discussed manufacturing process was never quantified. A combined experimental and simulation method to investigate heat transfer coefficient of the external surface of the graphite mold associated with water quenching is proposed. Firstly, the heat flux from the graphite mold is measured, which varies with water flow rate, mold surface temperature, nozzle arrangement, and water flow pattern. Without modifying the hardware design, this study focuses on the effects of water flow rate and mold surface temperature on surface heat flux. Secondly, the temperature distribution within the mold is used to inversely determine the heat transfer coefficient by solving an inversed optimization problem.