Abstract
The residual stresses (RS) induced in the substrate by case hardening treatment (HT) play a significant role in the behaviour of power train engineering components. In this paper, the results of RS investigation by neutron diffraction (ND) in 20NiCrMo2 steel car gear-shafts are presented. The RS were measured in correspondence of the critical region (notch) which is sensitive to fatigue-stress and/or crack, namely before/after a hardening treatment and after the successive finishing process. The achieved results can supply useful information on the effects of the various manufacturing processes on the RS status, better to evaluate the extent of distortion before and after the hardening treatment and to give a substantial support in the life assessment of the considered components. Furthermore, these results can yield parameters exploitable in monitoring of the hardening treatment characteristics, thereby confirming the relevance of thermal stresses induced by the same hardening treatment.

Key words
20NiCrMo2 steel, gear-shaft, case hardening, residual stress; neutron diffraction

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