PREDICTION OF CONVECTIVE HEAT TRANSFER COEFFICIENTS AND THEIR EFFECTS ON DISTORTION AND MECHANICAL PROPERTIES OF CYLINDRICAL STEEL BODIES QUENCHED BY GAS COOLING

摘要

The primary objectives of this study are to model the nature of the complex high-turbulence quenching cooling-gas flow, and to examine its effects on the resulting distortions and mechanical properties of the quenched piece, here bearing steel tubes and solid cylinders. A k-ε turbulent flow and heat transfer model adopted was found to predict the convective heat transfer coefficient (h) distribution reasonably well for Reynolds number up to about (0.3)10{sup}6. At higher Reynolds number (to 10{sup}6) it still predicts the nature of the flow well, but overpredicts h by up to 100% in the transition zone. The distributions of h around the body surface were used as the boundary condition for computing the temperature distribution history, phase transformations, distortions and mechanical properties of the quenched bodies. Increasing variation in h was found to increase the probability of large out-of-roundness, and nonuniformity in the properties.