Abstract
Relevance: This article examines an important scientific and practical problem of the surface structure in thin cold-drawn steel wire influenced by changing strain patterns during the actual drawing operation. Objectives: This research aims to look at how the microstructure is formed in the surface layers of thin wires and to identify the patterns, as well as to determine if this process can be controlled across the section of the wire to ensure the best combination of properties. Methods Applied: The material of the research was thin brass wire made from steel grade 80 of the following diameters (in mm): 1.75, 1.73, 1.574, 1.325, 1.113 and 0.933. The equipment of the research included a scanning electron microscope (SEM) by JEOL (with zoom rates of 2000, 5000 and 20000x) and the microhardness tester DUH - 211S by SHIMADZU. Findings: The authors of the study detected a near-surface zone with a turbulent structure caused by the shear stresses present in the zone, which, alongside the major shear strain, can induce an additional torsional deformation. The approximate depth and radius of the abnomal layer were determined. The authors show that a greater deformation leads to greater hardening of and more turbulence in the surface layer. This can be confirmed by the microhardness change dynamics versus the degree of deformation registered in a drawing operation. Thus, at small degrees of deformation the distribution of microhardness radially from the surface tends to be random. However, as the deformation becomes more intense, a clear trend is observed of the maximum microhardness being at the surface around the areas with abnormal turbulized structure. It can be explained by the fact that in thin wire drawing the rate of deformation tends to be higher at the surface than in the core. A higher degree of deformation is found to be accompanied with more intense hardening rates. The knowledge gained can be used to determine the ultimate drawability of wire rod and wire while identifying the structure and the quality of thin wires.
Keywords
Cold working, thin wire, shear strain, turbulized surface layer, strength, microhardness, SEM.
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