The experimental material was a drawn and patented 3.4 mm diameter wire from C78DP steel. The wire was drawn from the diameter of 3.4 mm to 1.5 mm using a straight-through single-block KOCH KGT 25 – E wire drawing machine. Two pass schedules were used with different one-pass reduction. Metallographic analysis was conducted on scanning electron micrographs (SEM) of the wire axis area. True interlamellar spacing (IS) was determined for all individual passes by statistical analysis of the measured apparent IS. Histograms constructed using true measured data were compared with each other passes for both pass schedules. Both a tensile test and a torsion test were conducted. The evolution of the measured mechanical properties (ultimate tensile strength, elongation to fracture and shear strain to fracture) was compared with the evolution of the true IS. We confirmed that there is a strong correlation between true IS and tensile strength or elongation to fracture. We also discovered that low cycle toughness represented by shear strain to fracture reached the maximum value before the deformation of cementite lamellae starts. From this viewpoint, we also mutually compared both pass schedules.Keywords: Wire drawing, interlamellar spacing, mechanical properties, steel
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