Shot Peening and Fatigue Strength of Steels

Author:  Lang, Schulze, Vohringer
Source:  Conf Proc: ICSP-8 Sept. 16-20, 2002 Garmisch-Partenkirchen, Germany
Doc ID:  2002037
Year of Publication:  2002
Authors Karl-Heinz Lang, Volker Schulze, Otmar Vohringer, Institut fur Werkstoffkunde I, Universitat Karlsruhe (TH), Karlsruhe, Germany Introduction Shot peening is a commonly used production process which changes the material state close to the surface. Depending on the material, the material state and the microstructure nearby the surface of the concerning workpiece, the topography, the residual stress state, the workhardening state and the microstructure may be altered. All these changes may influence the fatigue properties of a component more or less significantly. The lifetime may increase if shot peening is performed with optimized peening parameters. For this effect a smoothing of the surface, a workhardening of surface near areas of the material or the introduction of stable residual stresses can be responsible. The greatest lifetime increase may be reached if all three mechanisms act simultaneous. In [1] the characteristics of surface layers produced by shot peening are described in a systematical overview. In principle, the greatest potential for the lifetime increase is ascribed to residual stresses. Residual stresses may alter the cyclic deformation behavior, promote or retard crack initiation, accelerate or decelerate crack propagation, and may be beneficial or detrimental to finite fatigue life and the endurance limit. The consequences of residaul stresses at a concrete application depend strongly on the effects, which are connected with the production of residual stresses like the change of the surface and of the microstructure of surface near areas. Furthermore, the stability of the produced residual stresses under the operating conditions and the mechanical properties of the regarded material are relevant. In particular, the material strength is very important. Low strength materials (for example normalized steels or wrought alloys), medium strength materials (for example quenched and at a medium temperature tempered steels or y'-hardened Ni-base alloys) and high strength materials (for example quenched and at a low temperature tempered steel) have to be distinguished in this context. In the present paper a systematic overview of the knowledge about the influence of residual stresses - especially a shot peening induced residual stresses - on the different stages of fatigue process and on the endurance limit of different steels and steels in different states will be given using selected examples. A more detailed survey of this topic is given in [2].

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