The construction of mobile crane booms requires the usage of ultra‐high strength steels. Micro‐alloying elements promote grain refinement during hot rolling and result in increased toughness. The relevant strength is given through a martensitic microstructure, which is accomplished by elements retarding the γ to α transformation. Direct quenching (DQ) from the rolling heat and quenching after a preceding re‐austenitization (RQ) are two different production routes. They differ regarding their productivity, their achievable strength levels, and their resulting microstructures. In order to explore the influence of the production route in combination with prominent micro‐alloying elements, which come to application during hot‐rolling, six steels with varying content of V and Nb are investigated concerning their different properties after DQ and RQ as well as their behavior after tempering. It is found, that Nb strongly improves the strength after thermomechanical processing in the as‐rolled condition. Furthermore, Nb compensates the loss of strength during tempering. This effect is not thoroughly discussed in literature so far. Although Nb leads to grain refining during re‐austenitization, the effects on the strength of RQ steels are minimal. The effect after tempering is also weaker than after direct quenching. It is also shown, that V offers a high strength potential after tempering, however weakens the impact toughness significantly.

The standard application‐oriented test for abrasive wear of polymers on plastic mold steels is the platelet wear tester method in which two steel specimens form a thin wear slit. The glass fiber‐reinforced polymer melt is injected through the wear slit, and the surface of both specimens is abraded. In the injection molding process, similar conditions often occur in thin‐walled parts or film gates. Drastic loss of the hardness of a powder metallurgical steel (PM steel) is discovered after approx. 200 injection cycles while performing platelet wear tests. For experimentally analyzing the reason for the loss of steel hardness during injection molding, a new platelet wear testing apparatus is developed, which can be used to measure the increase in temperature inside the steel specimen while testing. The first results show and support the hypothesis that a temperature increase above the annealing temperature occurs inside the steel due to viscous dissipation at the steel surface. In cooperation with the company voestalpine BÖHLER Edelstahl & Co KG, tests on the PM steel in a dilatometer are performed to simulate the cycle‐by‐cycle heat pulses occurring in the injection molding process. With the results of those tests, it is possible to state a hypothesis for the reason of this hardness loss.

Grain boundary networks composed of equal microstructural elements were investigated in a recent paper. In this work a more complicated artificial grain topology consisting of one four-sided, two six-sided and one eight-sided grain is designed to further investigate the influence of grain boundary and triple junction mobilities on the kinetics of the system in more detail. Depending on the value of the equal mobility of all triple junctions, the initially square-shaped four-sided grain changes its shape to become more or less rectangular. This indicates that the grain morphology is influenced by the value of the mobility of the triple junctions. It is also demonstrated that a grain arrangement with low mobility triple junctions controlling the kinetics of grain growth enhances growth of the large eight-sided grains. In addition, grain growth is investigated for different values of mobilities of triple junctions and grain boundaries. A strong elongation of several grains is predicted by the modeling results for reduced mobilities of the microstructural grain boundary elements. The two-dimensional modeling results are compared to micrographs of a heat-treated titanium niobium microalloyed steel. This feature, namely the evolution of elongated grains, is observed in the micrograph due to the pinning effect of (Ti, Nb)C precipitates at elevated soaking temperatures of around 1100 °C. Furthermore, the experiments show that a broader distribution of the grain sizes occur at 1100 °C compared to soaking temperatures, where pinning due to precipitates plays a less prominent role. A widening of the distribution of the grain sizes for small triple junction mobilities is also predicted by the unit cell model.