Computer simulation study of high-pressure gas quenching of a steel element within vacuum furnace batch for different working conditions

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.

The paper presents analysis of the high-pressure gas quenching of metal elements, after their vacuum carbonisation process, based on the computer simulation. The ANSYS-CFX code has been used for this purpose. This transient quenching process includes challenging problems, which requires deep knowledge and application of heat transfer, fluid mechanics and thermodynamics. The numerical simulation analysis method focuses on a single element contained in an elementary, repeatable section (usually a cuboid) of the whole batch. In this study quenching of a steel cylinder of diameter d = 20mm and length L = 150 mm is analysed. This approach allows defining precisely: (i) the geometries of the metal element and of the elementary cubical section associated with it and, also, (ii) flow and thermal boundary conditions on the walls of this elementary section. Above definition of the elementary section (a computing domain) allows using the whole available computing power for the quenching process simulation in it. The ratio of volumes mentioned in (i) defines a “porosity of batch” and the analysis covers the range from 7 to 70%. The number of grid points used for the elementary section varies from 55000 to 240000. The influence of the pressure gradient value (a flow “driving force” through the elementary section) and its direction – on temperature and quenching rate time distributions in a steel element – is analysed and presented. The use of periodicity and symmetry conditions, for the velocity field, on the elementary section walls, allows simulating different single element quenching conditions – reflecting its position in the batch. The transient quenching has been usually analysed for a fixed velocity field. However, the steel element body thermal properties in this transient process varied – appropriately to its time dependent temperature distribution. The initial element temperature is assumed to be equal 1300 K. The influence of different gases, i.e. argon, helium, nitrogen and hydrogen, and their static pressures (up to 30 bar), on the steel element quenching process, is analysed and presented.