Iron-based superconductors (IBSs), discovered in 2008, formed the second high- T _c superconductor family after cuprate superconductors, and over the past decade have been the subject of extensive research into their physical nature and application potential. With their attractions of very high upper critical fields and small electromagnetic anisotropy, tremendous advances have been made in wire research and development (R&D) to explore the potential of IBSs for high-field applications. In recent years, rapid progress was made on the critical current density ( J _c ) of the 122-type IBS wires based on a powder-in-tube technique. Encouraging breakthroughs were made, including a high transport J _c exceeding the practical level of 10 ⁵ A cm ⁻² (at 4.2 K, 10 T) and the first 100 meter-class wire. This review covers the state-of-the-art techniques and their mechanism in realizing high transport J _c with respect to the grain connectivity, grain texture and flux pinning for IBS wires and tapes, as well as the temperature and field angle dependence of critical currents. The mechanical properties, AC losses and magneto-thermal stability of IBS wires are investigated, and further improvements in IBS conductors for large-scale applications are proposed. In addition to long wire fabrication, this review also highlights some remarkable advances relevant to practical applications, including scalable process optimization, copper sheaths, multifilamentary fabrication, and superconducting joints. Finally, a summary and outlook for R&D for IBS wires are presented.

Iron-based superconductors have become a promising candidate for high-field applications due to their high transition temperature, ultra-high upper critical field, and low anisotropy. For practical applications, it is important to improve the transport J _c and lower the cost of superconductors. In this paper, with groove rolling and hot isostatic pressing (HIP) process, the transport J _c of the Cu/Ag composite sheathed (Ba, K)Fe ₂ As ₂ powder-in-tube round wires was increased to 4.7 × 10 ⁴ A cm ⁻² at 10 T and 4.2 K. The utilization of HIP and groove rolling process improved the mass density of the wire. Moreover, a certain axial texture was introduced through groove rolling. It is suggested that the combination of groove rolling and HIP processes are of great help to improve the microstructure of the wires, thereby obtaining a higher transport J _c .