Chiang Mai Journal of Science

This study of gas nitriding conditions in a vacuum furnace was the final part of a project in collaboration with an aluminium extrusion manufacturer. The project was aimed at furnace condition optimization to solve the problem of too-thin-nitrided layers experienced in a vertical top-loading vacuum gas nitriding furnace. Small samples cut from AISI H13 (JIS SKD61) tool steel dies were placed at 20 different positions to present the different nitriding conditions in the furnace. Four different stacking patterns in loading extrusion dies into the furnace were simulated using COSMOSFloWork^® to determine the most effective loading. Microstructural checks, depths of diffusion layer and case-hardness profiles were carried out. The results of the study enabled the determination of the optimum positions within the furnace for dies requiring different treatment conditions i.e. new dies receiving first nitriding, and used or repaired dies needing re-nitriding. Production management was then able to arrange furnace loading to meet these conditions so that for each batch full utilization could be made of the vacuum nitriding furnace leading to saving in energy consumption.