High-strength pearlitic steel–copper composite wires for conductors in pulsed high-field magnets

Pearlitic steel/copper macrocomposite wires were fabricated by the ‘rod-in-tube’ technology. As a starting material, tubes 25 mm in diameter of patented steel with 0.6 wt.% C were used. A composite with 56 vol.% Cu yields an ultimate tensile strength of 1.53 GPa after a final patenting at 14.7 mm diameter and a logarithmic drawing strain of η=4. This high strength level is connected with a low elongation to fracture of the order of 1.3–1.5%. Intermediate annealing leads to a solely temporary increase of elongation to fracture. Therefore, annealing cannot contribute to improving the formability at high strength level. The evolution of strength as a function of drawing strain was discussed including the model of Embury and Fisher. Assuming homogeneous strain the postulated proportional decrease of the interlamellar spacings of the pearlitic cells with the wire diameter takes place only after high drawing strains. A distribution of interlamellar spacings can be expected after heavy deformation depending on the initial orientation distribution of the pearlitic cells.