  We have fabricated (Ba,K)Fe2As2 superconducting wires through ex-situ
powder-in-tube method. Silver was used as a chemical addition to improve the
performance of these superconducting wires. The transport critical current
densities (Jc) have reached 1.3\times104 A/cm and 1.0\times104 A/cm2 at 4.2 K
under self field in the wires with and without Ag addition. We used
magneto-optical (MO) imaging technique to investigate the properties of grain
boundaries in the (Ba,K)Fe2As2 superconducting wire with Ag addition. MO images
show the weak links in the Fe-based superconducting wires for the first time.
An intragranular Jc of 6.0\times104 A/cm2 at 20 K is obtained from MO image,
which is consistent with the estimation from M-H measurement.
