WEB Characterization of forming-induced damage of hot flat rolled micro-alloyed steel by micromagnetic testing in correlation with fatigue behaviorThursday (24.09.2020) 14:45 - 15:00 S: Structural Materials 2 Part of:
During cold forming processes of metals, like forward rod extrusion, damage is caused in the microstructure, which can strongly influence the mechanical properties of components under operating conditions. So far, neither the influence of typical forming steps on the three-point bending fatigue behavior nor on the damage evolution while three-point bending fatigue testing were investigated. With the knowledge of the influence of the damage on the lifetime of a part, components can be specifically designed and will enable an optimization of lightweight construction.
In this study, the influence of the degree of deformation due to the forming process parameters and the associated microstructural damage on the three-point bending fatigue properties of 16MnCrS5 steel were investigated. The aim was to develop a method for damage characterization which allows conclusions about the expected lifetime of the parts. Micro-magnetic material characterization is suitable for the determination of the degree of damage non-destructively. Also, the degree of damage was validated by light and electron microscopy. In addition to that, a detailed characterization of the cyclic damage behavior under three-point bending loading was performed by measurements of stress-displacement-hysteresis, the change in deformation-induced temperature and electrical resistance based on direct current (DC). The investigations allow a description of the interaction between the ductile pre-damage and the fatigue damage behavior.
At first, flat steel-specimens in initial conditions and two different degrees of deformation are characterized by Barkhausen noise and harmonic analysis. The measurements were made at five positions in the bending zone with a measurement setup specially developed for this study. Furthermore, the evolution of damage in microstructure during intermittent three-point bending fatigue testing of these specimens were investigated. The micro-magnetic intermittent testing and the electrical resistance correlate well with the specimens’ fatigue behavior. Also, a significant influence of the deformation damage on the three-point bending fatigue behavior was shown.