12 - Ferrous (Fe-based) shape memory alloys (SMAs): properties, processing and applications

Abstract

Many ferrous (Fe)-based shape memory alloys (SMAs) have been discovered, such as Fe–Pt, Fe–Pd and Fe–Co–Ni–Ti. The Fe–Mn–Si system is one of the most distinctive SMAs in the sense that it is the only Fe–based SMA that has successfully been applied in the industrial field. The shape memory effect of the Fe–Mn–Si system was approved in 1982. The memory effect is associated with the strain field established by the formation of the hexagonal close packed (hcp) phase in the parent g phase. Various efforts have been made to develop these materials with an aim of producing high performance of the shape memory effect, high strength, high corrosion resistance, weldability and sufficient plasticity for industrial processing. It is currently possible to attain ~4% shape recovery or 180 MPa stress in the Fe–Mn–Si–Cr SMA by heating the ferrous material up to 350 °C after 5~8% deformation for martensite formation. The Fe–Mn–Si–Cr SMA has been applied in the industrial field as the material of a joint for pipes and rails. In this chapter, we will review the fundamental character of the Fe–Mn–Si–Cr SMA and report on the latest industrial applications of the steel pipe joints and the rail joint bar (fishplate) of heavy–duty crane rails.