Composite MgB 2 wires have been made by the powder-in-tube method using commercial MgB 2 powder (Alfa Aesar) in Fe and Fe-alloy (stainless steel (SS)) sheaths. Different deforming processes have been used. Two-axial rolling (TAR) produces the highest powder density leading to the best J c (0 T, 4.2 K) of 55000 A cm −2 in as-deformed wire. Therefore, four-core wire has also been made by TAR. The short samples were subjected to annealing at temperatures from 850 to 1100 °C for 30 min in argon, which leads to apparently improved J c values, 25000 A cm −2 at 4 T and around 10 6 A cm −2 in the self-field (at 4.2 K). An interdiffusion layer between MgB 2 and the Fe or SS sheath was observed and analysed. The SS sheath reacts more intensely than Fe due to the presence of Ni and Cr elements. Transport currents were measured at temperatures 4.2–25 K and an external magnetic field B = 0–8 T. The engineering current density level of 10 4 A cm −2 is used to estimate the magnetic field possibly generated by coils wound from MgB 2 composite wires.
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