Changes in shape and dimension of automotive parts are influenced by many parameters, which can he allied with the pretreatment stage, the design of the parts, the loading and the heat treatment itself. Using a standardized pre-treatment stage the influence of the heat treatment on the distortion could he estimated and the influence of quenching parameters on changes in shape and dimension could be systematically investigated. Different types of quenching oils were tested and their influence on the distortion was examined. The oil circulation rate and the oil temperature were varied and the influence of a delayed circulation of the oil bath was studied. It was found that these parameters and the material properties (chemical composition, hardenability) had less influence on the distortion than the actual design of the parts. For comparison of oil and gas quenching a low pressure carburizing and pressurized gas quenching were applied. The changes in shape and dimension resulting from the different processes have been compared. It was shown that gas quenching caused a significant reduction in out-of-flatness and conicity, whereas the out-of-roundness was predominantly influenced by the design of the gear wheels.
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