Thernal Relaxation of Shot Peening Induced Residual Stresses in a Quenched and Tempered Steel 42 CR MO 4

Author:  V. Schulze, O. Voehringer, E. Macherauch
Source:  Conf Proc: ICSP-5, (p.264-273)
Doc ID:  1993078
Year of Publication:  1993
Abstract:  
If machine parts bearing shto peening induced macro residual stresses are exposed to elevated temperatures during application, thermal stress relaxation occurs. In order to obtain quantitative knowledge of the stress relaxation behaviour a quenched and tempered 42 CrMo 4 steel was investigated using X-rays. The thermal relaxation behaviour was described by the Avrami-approach whose parameters were determined applying a new, iterative method which allows to evaluate and compare the relaxation behaviour of macro and micro residual stresses. It was found out that the rate controlling process of thermal relaxation of shot peening induced macro and micro residual stresses is due to volume diffusion controlled dislocation creep. As at the beginning of annealing a very stron relaxation was observed, the transient relaxation of macro residual stresses during heating up to the temperature required is investigated. For the first time it is possible to model this material behaviour, extending the above-mentioned new iterative Avrami-approach to non-isothermal stress relaxation. A very good agreement with the data measured during the first stage of transient annealing is achieved by this method. It was found out that the further stress relaxation behaviour is not determined by the heating time already elapsed but rather by the relaxed residual stress value already achieved during heating up.