On the Development of Parametrical Water Quenching Heat Transfer Model Using Cooling Curves by ASTM D6200 Quenchometer

摘要

For steels and aluminum alloys, liquid quenching is the most effective method to achieve fast cooling rates. In the example of water quenching an aluminum 319 cylinder head, the temperature drops rapidly within 30 seconds from solutionizing temperatures at 495 degrees C to water pool temperature below 100 degrees C. In this temperature range, the water boiling in the quenching process goes through three boiling regimes, film boiling, transition boiling and nucleate boiling, before reducing to convection heat transfer. Since each boiling regime has unique heat transfer characteristics that are governed by different physics, modeling the water quenching processes by computer simulation requires a heat transfer framework, instead of just a few equations, that can describe all the boiling regimes. Among several heat transfer frameworks found in the literature, we had successes in developing a CFD methodology to simulate the boiling process by adapting a heat transfer framework based on Leidenfrost point (LFP), minimum heat flux (MHF) and critical heat flux (CHF). This CFD methodology, when integrated with FEA structural analysis, is the key enabler for virtual process verification. This is achieved by first calculating temperature histories and profiles in CFD and then applying the temperature data as thermal load to FEA to predict thermal residual stress and distortion. Although the LFP, MHF and CHF framework have been proven useful to model the water quenching process, these parameters are not constants and they have to be calibrated through experiments for each quenching condition. The objective of this paper is to develop a consistent method to calibrate the boiling heat transfer framework using cooling curves obtained by the ASTM D6200 quenchometer. Also included in this paper is a preliminary discussion on broadening the standard in order to support: (1) generic cooling curve characteristics for any quenchant, (2) the analytical cooling curve for computation model calibration.