In the aerospace and motorsport industries, lightweight construction is very crucial. By increasing the strength of the used materials, it is possible to reduce the cross-section, thereby reducing the volume and saving weight. One such mechanism that increases strength is grain refinement. This can additionally lead to an increase in ductility. The aim of this work is to predict the microstructural changes of 300M quenched and tempered steel (designation according to EN 10027-2: 1.6928) after forming but also without forming. Flow curves at temperatures between 950 °C and 1200 °C were recorded by experiments on the Servotest test rig. The strain rate was varied between 1/s and 50/s. The evaluation of the flow curves shows the critical stress or critical strain, which indicate the starting point of dynamic recrystallization. By comparing the logged experimental data with the simulated data from the DEFORM® software, the good quality of the flow curves could be demonstrated. Further experiments on the Servotest test rig, so-called double cone specimens, were able to show the influence of the initial grain size, the temperature and the strain rate on the grain size after forming. The evaluated data made it possible to develop a model that can predict both the kinetics and the mean value of the dynamically recrystallized microstructure. To analyse the grain growth behaviour without forming from the 300M material, heat treatment experiments were performed in a Linn High Term laboratory furnace at temperatures ranging from 925 °C to 1250 °C and duration from 5 min to 135 min. By logarithmizing the grain size and time, linear relationships were found in the plotted data. Using the Curve Fitting App in the software Matlab the coefficients of the given equation were calculated. The result of this experiment is a model describing the grain size as a function of temperature and time for the 300M steel.