A. M. Freborg, Z. Li, B. L. Ferguson, Deformation Control Technology, Inc., Cleveland, OH
Carburizing and quench hardening of steel gears is a complex metallurgical process involving mass diffusion, thermal gradient, phase transformations, and plastic strains. Hardness profile, phase distributions, residual stress, and distortion in heat treated gears are the combined results of this complex interaction. In engineering a gear for optimal performance, mechanical and metallurgical specifications are made during the design process based on well established standards and design experience. The advent of process modeling has provided an important tool for the gear designer. This paper demonstrates how process modeling can be successfully combined with metallurgical testing to obtain quantified descriptors of steel gear response to carburizing and quench hardening. Modeled heat treatment response of Pyrwoear® 53 gears was directly validated against metallography, residual stress measurement by x-ray diffraction, distortion and single tooth bending fatigue response. Predicted residual stress profiles were then used in modeling the effective stress response in the gears under dynamic load. By considering the predicted residual stresses, the relation between the gear fatigue life and actual loading can be more directly quantified than using the AGMA standard.
Summary: Carburizing and quench hardening of steel gears is a complex metallurgical process involving mass diffusion, thermal gradient, phase transformations, and plastic strains. Hardness profile, phase distributions, residual stress, and distortion in heat treated gears are the combined results of this complex interaction. In engineering a gear for optimal performance, mechanical and metallurgical specifications are made during the design process based on well established standards and design experience. The advent of process modeling has provided an important tool for the gear designer. This paper demonstrates how process modeling can be successfully combined with metallurgical testing to obtain quantified descriptors of steel gear response to carburizing and quench hardening. Modeled heat treatment response of Pyrwoear® 53 gears was directly validated against metallography, residual stress measurement by x-ray diffraction, distortion and single tooth bending fatigue response. Predicted residual stress profiles were then used in modeling the effective stress response in the gears under dynamic load. By considering the predicted residual stresses, the relation between the gear fatigue life and actual loading can be more directly quantified than using the AGMA standard.
