Effects of magnetic fields on martensite transformations and mechanical properties of steels at low temperatures

This paper reviews the combined effects of magnetic fields and mechanical loading on the martensite transformation of austenitic stainless steels used for the magnet structure in superconducting magnets. Both athermal and isothermal transformations are tested for the effects of magnetic fields. The four situations in which the presence of a magnetic field in addition to mechanical loading influence the mechanical properties of cryogenic structural alloys are listed, though none have been studied in detail. Two initial experiments with a pulsed magnetic field, testing the effect of magnetic fields on the toughness of overtempered 9Ni cryogenic steel, and 304 stainless steels are described. The straining fixture, and subsequent x-ray and optical metallographic analysis of the latter are shown. Finally, a new testing facility which has been established to measure cryogenic mechanical properties in steady 8T magnetic fields, the LBL Magneto-Mechanical Cryogenic Research (MMCR) facility, is described