A microstructure-sensitive model that predicts the strain-rate sensitive flow behavior as well as creep-strain life of a refractory Ni-base superalloy, Low Solvus High Refractory (LSHR), is presented. The model is based on discrete dislocation simulations that are computationally expensive, but the design tool derived from the simulations is fast acting. The model employs experimental data on microstructure and mechanical behavior, as well as the thermodynamic model PANDAT™, to calibrate, validate and verify the use of the model as a design tool. The mechanical properties predicted include flow stress as a function of temperature and strain-rate, as well as time for 0.1-0.2% creep strain as a function of stress and temperature. The model extends prior work of a strain rate sensitive flow stress model developed for IN100 alloy, by calibrating the model to data on LSHR, and by including dislocation creep as well as grain size dependent diffusional creep behavior and predicting time to reach a design creep life in terms of creep strain. The resultant model was found to capture reported data on LSHR, in both subsolvus and supersolvus heat treated conditions. The calibrated model was validated using additional data on yield and creep of LSHR with two other microstructures. The validation makes the model a promising design tool in the engineering of complex heat treat disks, where location-specific properties are desired.