Physical Simulation of Thermo Mechanical Phenomena to Obtain an Optimal Micro Structure for a Soft Magnetic Fe-Co-Alloy

Abstract

For the application of Fe-Co-alloys in fuel-injection systems several physical properties as saturation magnetization, permeability, remanence and the electric resistivity are the predominant parameters to achieve an optimal functionality of coil formers. These properties are achievable by a process technology which starts at the vacuum melting and a vacuum arc remelting process and is continued at the blooming and the multi line rod rolling mill and ends finally at the finishing line. The above listed properties are associated with the low carbon ferrite structure, which can be achieved by the y/a- transformation and a subsequent ferritic recrystallization. Further the homogeneity and purity of the material take a dominant role in the thermo-mechanical controlled rolling process. To stabilize the deformed ferrite structure, the alloy has small additions of Vanadium, which is precipitated strain induced as vanadium-carbo-nitride in the deformed ferrite at 750 °C. Impurities as oxides or sulphides, which act as nucleation sites for this V(C,N)-precipitation reaction, consume therefore a part of the required nucleation potential. The second purpose of the small vanadium addition, associated with the precipitation, is to reduce the solute carbon content of the ferrite structure to achieve a low magnetic remanence. To investigate these interactions, several process steps were physically simulated on a Gleeble 3800TM system which has been extended by a maxstrain unit to simulate multistep deformation sequences below the γ/α- transformation temperature. Subsequently the achieved structures were investigated by transmission electron microscopy and electron back scatter diffraction analysis. The results have been successfully transmitted to the process and confirmed by the operational results.