ASCOMETAL produces alloy steels used for spring (leaf or coil), where the weak fatigue points are on the surface which is reinforced by shot-peening. So, the fatigue optimization with the steel grade needs a perfect knowledge of the material answer after shot-peening. For that reason, an analytical model has been developed where low cycle fatigue behaviour and all the usual process parameters are integrated (especially the impact position, and the covering-rate). Moreover, through a Monte-Carlos approach, the model permits to analyse the effect of scattering elements like impact speeds, ball sizes, or material fatigue behaviour. With this model several key process parameters have been analysed and validated with residual stress profiles evaluated by X-ray diffraction. So, for spring leaf, the effect of an applied load during shot-peening or shakedown during bending fatigue is described.