Shaft, Carburizing, Taguchi Method, Optimization

Carburizing is a widely-used thermochemical heat treatment process in shaft manufacturing. Insufficient case-depth, inadequate surface/core hardness, and distortion are the common reasons for scrapped products after carburizing. Thus, understanding, control and optimization of the process parameters in carburizing is crucial to avoid losses.In this study, carburizing parameters were investigated and optimized by Design of Experiments (DoE) using the Taguchi method. The target of the optimization is the minimization of the variability in the production due to the use of different furnaces for the process.Experiments were carried out on as-turned shafts (plain and stepped) made of two different grades of steel (16MnCr5 and 20NiCrMo2-2) using two different industrial gas carburizing furnaces. After the carburizing experiments, dimensional changes were measured using a Coordinate Measurement Machine (CMM), while carbon and hardness profiles were determined using Optical Emission Spectroscopy (OES) and Vickers indentation techniques.The results indicated that carbon potential of the carburizing gas is the most important parameter associated both with the variability and the mean effect for the case-depth and the diameter change.