Magneto-elastic Effect for 316LN-IG Stainless Steel at Low Temperature

Tensile tests of 316LN-IG austenitic stainless steel samples cut out from tubes along their axis are carried out in liquid and gaseous helium below 7 K. The tubes were intended for conductor conduits for the toroidal magnet system for ITER. Time dependences of temperature, strain and strain induced magnetization normal to the sample surface are examined with respect to stress. A complicated behavior of the local deformation near slip bands is detected that seems as unloading and shrinking regions adjacent to slip planes. The magneto-elastic effect indicating a negative longitudinal magneto-striction for the initial γ phase and the α phase induced by strain is found. The events without local heat release when jumping strain are explained as a result of the magneto-caloric effect in the regions unloaded in slipping.