Fracture Analysis of Drawn Composite Dual-Phase Steel Wire

摘要

The Fe/2 Si/0.1 dual-phase steel was studied with composition 0.08 C, 1.9 Si, 0.32 Mn, 0.004 P, 0.004 S (wt %) to develop the dual-phase structure with various morphologies. Thermal and control rolling thermomechanical processing were used. Treated samples were machined to 5.5 mm diameter and then drawn without coating in a hand operated drawing machine. The microstructures of longitudinal sections before and after deformation were assessed by light optical and scanning electron microscopy (SEM). Void density measurements were performed by SEM at 2000X. A linear relationship was found between true strain and void density after wire drawing low carbon duel-phase steels for all morphologies studied. Void formation was found to begin either by decohesion of the ferrite/martensite interface, or by shear microcracking of the martensite particles. The formation of voids during wire drawing can be correlated with differences in martensite morphology and martensite/ferrite interface coherency. A fibrous distribution of 20% lath martensite in fine-grained ferrite appears to be the most promising composite to obtain high strength ductile wire, e.g., for tire cord application and hence Fe/Si/C rather than Fe/Mn/C steels are preferred. 21 refs., 8 figs., 1 tab. (ERA citation 13:006005)