Transport critical current (I c ) was measured for Fe-sheathed MgB 2 round wires. A critical current density of 5.3 x 10 4 A/cm 2 was obtained at 32K. Strong magnetic shielding by the iron sheath was observed, resulting in a decrease in I c by only 15% in a field of 0.6T at 32K. In addition to shielding, interaction between the iron sheath and the superconductor resulted in a constant I c between 0.2 and 0.6T. This was well beyond the maximum field for effective shielding of 0.2T. This effect can be used to substantially improve the field performance of MgB 2 /Fe wires at fields at least 3 times higher than the range allowed by mere magnetic shielding by the iron sheath. The dependence of I c on the angle between field and current showed that the transport current does not flow straight across the wire, but meanders between the grains.

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