Study on Surface Heat Transfer Coefficient of Mixture of Nitrogen-Spray Water Eject Quenching under Normal Pressure and High Velocity

Abstract

During mixture of Nitrogen and spray water ejecting quenching under normal pressure and high velocity, the liquid film that is formed on the surface of specimen to reduce the heat transfer between specimen and quenching media is removed on the one hand; on the other hand, the heat transfer performance of the mixture exceeds that of pure Nitrogen. Because the surface heat transfer coefficient is difficult to measure, according the cooling curve of surface and centre of specimen measured experimentally, the law of surface heat transfer coefficient and specimen temperature is calculated by nonlinear estimate methods and finite difference method based on inverse heat transfer method. The results show that the cooling performance of mixture of Nitrogen and spray water is as well as that of water or oil. During quenching, the surface heat transfer coefficient increases rapidly at begin, and at temperature of 170 °C, the surface heat transfer coefficient decreases. During martensite phase transformation, the latent heat is used to increase drive force of phase transformation and to overcome resistance of phase transformation, thus the martensite phase transformation can fulfill.

Analysis of the Significant Influence Factors of Spray Quenching Process

“…Based on 2 method, the two factors of water flow and nitrogen pressure are controllable, we analyzed the influences of the two factors of nitrogen pressure and water flow to the quenching cooling time. This paper induces and analyses the experiment results and numerical calculation results [1] . The conclusions are: water flow is the main factor of affecting the quenching rate, the interaction of the nitrogen pressure and water flow is significant: when the nitrogen pressure is low ,the water flow is high, the quenching cooling rate is guaranteed.…”