Process-related fatigue strength

 

Quenching and tempering (Q&T) steels and precipitation-hardening ferritic-perlitic (AFP) steels represent the state of the art in the forging industry, in particular for the use in safety-relevant components of the automotive industry. Q&T steels are distinguished by a good combination of static strength and toughness. These properties are set by a multi-stage, costly heat treatment. In contrast, AFP steels are continuously cooled from the forging heat, thus shortening the process chain and avoiding expensive follow-up treatments due to distortion of components.

Process control has a significant influence on the mechanical properties of AFP steels. For example, deformation influences the transformation temperature, leading to diverse phase compositions and morphologies of the resulting microstructural constituents. In addition, the cooling rate influences the duration of the diffusion-controlled phase transformation, the refinement of the ferrite/pearlite microstructure and the ferrite/pearlite ratio.

In a joint research project, the influence of temperature and the forging parameters on the resulting behavior of AFP steel is to be quantified. For this purpose, the microstructures affected by the local temperature are investigated and both dynamic and cyclic tests are carried out. The aim is to develop a method that enables the resulting material behavior, especially the fatigue strength, to be estimated as a function of the process parameters.