Speaker
Description
Both current and future planned „magnetic fusion reactors" demands very high mechanical properties at cryogenic conditions to ensure superconductivity of magnets and reactor structural integrity at the same time. This paper deals with the possibilities of increasing the mechanical properties of 316LN austenitic stainless steel by means of industrially-feasible thermomechanical processing. Based on available processing maps and numerical simulations a medium-sized upsetting experiment was proposed to enhance the mechanical properties of conventionally processed high-nitrogen 316LN austenitic steel. All processing parameters were chosen with the industrial manufacturability in mind. The experimental sample size was a cylinder with dimensions D40 x 80 mm on which an upsetting of 30% was conducted. Processing temperature T = 1376 K and upsetting velocity ~ 10 mm/s were chosen to achieve fine recrystallized and homogeneous grain. As numerically predicted the experiment geometry ensures a homogeneous deformation in the large volume of the specimen with true strain ~ 0.5 – 0.6. The microstructure was analyzed by means of light microscopy and electron microscopy (SEM + EBSD). Mechanical properties were determined based on tensile tests according to the standards at three different temperatures (300K, 77K, 4K). The reasoning of chosen processing parameters together with the discussion of archived results are presented in the paper.