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International audience; Heat treatment is widely used in automotive industry to improve mechanical properties of workpieces. It also generates side effects such as geometrical distortions. Scientific literature and experience show that the manufacturing process chain has an influence on heat treatment distortion. The purpose of the presented work is to experimentally determine the influence of each pre-heat treatment step on gear distortion. Residual stress is being neutralized and by comparison, connections between gear teeth geometry and manufacturing step are obtained. As a consequence, non-conformities roots can be determined more easily thanks to this diagnosis tool.

International audience; We present a mathematical method for identifying, separating and quantifying the 3D significant distortions. Measurement of a gas quenched C-ring type sample is performed by a Coordinate Measuring Machine (CMM). Quenching simulation is done with the commercial software Forge 2008 TTT. After comparisons, we notice that the distortions and their tendencies are the same but not exactly the amplitudes. We only focus on distortions which have a physical origin, like the pincers opening, often observed in the literature. As a first explanation, we underline the role of phase transformations and volume dilatation of the steel during quenching.