Yielding and Strain-Hardening of Reinforcement Materials

Part of the process for fabricating high field magnets using exceptionally strong reinforcement materials involves subjecting these materials to deformation at room temperature beyond the yield point. During the operation of the magnets, further plastic deformation may also occur at cryogenic temperatures. In most face-centered-cubic fcc) materials, strain-hardening occurs after plastic deformation, further increasing strength. This paper reviews some of our recent work concerning the effect of microstructure on both yielding and strain-hardening in 316LN, a modified stainless steel, and in Haynes 242, a Ni-Mo-Cr alloy. Although both materials have fcc matrix, Haynes 242 yielded at higher stresswith a lower strain hardening rate than 316LN at a low strain range. Because of high nitrogen content, 316LN showed pronounced yield point elongation. At cryogenic temperatures, both materials showed higher strain-hardening rates.