Design and simulation of supersonic profiling nozzle for U78CRV rail heat treatment

In order to address with the defects of poor cooling capacity and cooling uniformity of the rail air-quenching technology, the supersonic profiling (SP) nozzle was designed to improve the cooling capacity through supersonic jet and improve the cooling uniformity through the profiling structure of the rail head. Numerical simulation method combined with experimental were used to study the heat transfer characteristics of SP nozzle on rail. The results showed that air-cooled quenching at a pressure of 0.4 MPa increased the cooling capacity of the SP nozzle by 23.96%, 15.35%, and 31.69%, and the cooling uniformity by 36.82%, 46.98% and 22.19% over the existing circular normal nozzle, circular supersonic nozzle and normal profiling nozzle, respectively. A segmented cooling process curve of ?slow first and then fast? was designed, and the cooling time of the segmented cooling SP nozzle was shortened by 49 seconds compared with the CR nozzle. Compared to the SP nozzle cooled at a constant rate, the cooling time is shortened by 35 seconds. Regulate the inlet pressure of the SP nozzle to cool the rail at a cooling rate close to but not exceeding the critical cooling rate of pearlite transformation before the rail temperature is lower than the end temperature of pearlite transformation (about 500?C), and then increase the inlet pressure as much as possible, which is beneficial to improve the production efficiency on the premise of ensuring the performance of the heat-treated rail.