The microstructure of the PH 15-5 steel in relation to the recrystallized portion and the former austenite grain size after hot forming tests is examined. The basis for the definition of the experiments are tests already carried out on the material PH 15-5 from another material batch, which are considered to be equivalent and which were provided by the same company the voestalpine BÖHLER Aerospace GmbH & Co KG. The experiments are carried out using a Gleeble testing machine. They consist of an austenitization followed by hot forming in a vacuum and subsequent quenching with water. For the used samples the temperature, strain rate and holding time after forming are varied. These samples are then examined with regard to their microstructure. They show that the microstructure in relation to the recrystallized fraction and the former austenite grain size result from the parameters mentioned and from the varying local degree of deformation over the sample cross-section. The differences to the experiments carried out in advance on the other sample batch are presented. They indicate that the recrystallization behaviour of the material is likely to depend significantly on the initial grain size in addition to the influencing parameters already mentioned. In order to classify recrystallization, the interrelated processes of recovery, recrystallization and grain coarsening are investigated. In particular, metadynamic and dynamic recrystallizations are discussed, the PH 15-5 steel is characterized and the results are presented, explained and discussed.