Optimization of Molybdenum Alloyed Carburizing Steels by Nb Microalloying for Large Gear Applications

摘要

Increasing demands with regard to performance of carburizing steels necessitate the further development of process technology as well as steel metallurgy. The present paper exemplifies recent developments based on alloy modifications with microalloying elements, which not only enhance the performance of existing carburizing steel types but also allow the application of new processing technologies. The focus is thereby on molybdenum alloyed carburizing grades that are typically applied e.g. in large gear for windmills. A dedicated addition of niobium enables better mechanical properties and higher carburizing temperatures. Simultaneously the carburizing time can be shortened and distortion by heat treatment is reduced, as the microstructure remains more homogeneous. Further development potential offered by microalloying in carburizing steels is seen in an improved toughness due to the finer sized grain structure allowing to produce higher strength and more economical steel. These measures when applied in new steel concepts enable significant cost savings along the entire manufacturing chain especially in the production of larger transmissions. Finally, additional cost savings can be expected by a reduction and optimization of processes and procedures at the end-user.