Chemical composition of brass coating for steel cord

Abstract

The objective of the research was to identify transitional diffusion layers in the steel wire – brass coating system. Brass wire is used in the production of steel cord. Such wire made from steel 80 by dry drawing, two-stage deposition of brass coating (Cu + Zn) and subsequent diffusion annealing was used for this research. The chemical composition was studied using a TESCAN Vega3 SBH scanning electron microscope with an Oxford Instruments attachment for X-ray microanalysis (MRSA). To obtain maps of the elements distribution, the overlay of the received frames was used. The authors studied chemical composition of the brass coating of steel wire for steel cord by spectra; the copper concentration gradient was determined; iron content in the coating and copper content in the steel core were revealed. The presence of a transitional diffusion layer from a brass coating to a steel core on a wire for wet drawing with a diameter of 1.67 mm and 1.85 mm was determined in two parts with different thicknesses of a brass coating in opposite sections (maximum and minimum). A map of the elemental distribution of Fe, Cu and Zn is shown, as well as a general map of overlay of Fe, Cu and Zn content; graphs of the elements’ content for two studied cross-sections are presented. It was established that the transition diffusion layer has gradient transition in concentrations of Fe, Cu and Zn, which characterizes good connection of the brass coating with steel. Diffusion layer of a brass coating of a steel wire with a diameter of 0.30 mm, produced by wet drawing of a steel wire with a diameter of 1.67 mm, was studied. An image of the coating was obtained by overlaying frames. Thickness of the coating together with the diffusion layer was determined, the average value of which is 1.4 µm with an apparent coating thickness of 0.5 µm.