The optimum carburized and hardened case depth for each gear failure mode is different and must be defined at different locations on the gear tooth. Current gear rating standards do not fully explain the different failure modes and do not clearly define the different locations that must be considered.
Suppliers are working hard to make
sure their heat treating equipment is controllable, repeatable and efficient,
and manufacturers continue to incorporate technology that gives heat treaters and their customers more information about what's going on inside the magic box.
Effective case depth is an important factor and goal in gas carburizing, involving complicated procedures in the furnace and requiring precise control of many thermal parameters. Based upon diffusion theory and years of carburizing experience, this
paper calculates the effective case depth governed by carburizing temperature, time, carbon content of steel, and carbon potential of atmosphere. In light of this analysis,
carburizing factors at various temperatures and carbon potentials for steels with different
carbon content were calculated to determine the necessary carburizing cycle time.
This methodology provides simple (without computer simulation) and practical guidance
of optimized gas carburizing and has been applied to plant production. It shows that measured, effective case depth of gear parts covering most of the industrial application range (0.020 inch to over 0.250 inch) was in good agreement with the calculation.
This paper presents how low pressure carburizing and high pressure gas quenching processes are successfully applied on internal ring gears for a six-speed automatic transmission. The specific challenge in the heat treat process was to reduce distortion in such a way that subsequent machining operations are entirely eliminated.
This paper presents the results of a study performed to measure the change in residual stress that results from the finish grinding of carburized gears. Residual stresses were measured in five gears using the x-ray diffraction equipment in the Large Specimen Residual Stress Facility at Oak Ridge National Laboratory.