The ferritic-martensitic steel P92 is used for thick-walled components in thermal power plants. Besides continuous operation, the components are exposed to cyclic loadings so that creep-fatigue deformation is relevant for the assessment of the components in finite-element calculations. In this work, a non-unified viscoplasticity model is developed to describe the creep-fatigue deformation behavior of the P92 steel. For the determination of the relevant model parameters of the material model, results of service-like material tests are employed that mimic the material loading conditions in thick-walled components. A good description of the service-like material tests is achieved with the model.