[en] In this study, samples of Eurofer 97 steel were subjected to processing by hydrostatic extrusion (HE) to a total true strain of about 4. HE processing resulted in a significant grain refinement. Microstructural changes caused by extrusion were observed using transmission and scanning electron microscopy. Thin foils for these observations were prepared using focus ion beam and electrochemical thinning. The microstructure of Eurofer 97 in the as-received state is characterized by ferrite grains, with some presence of martensite, and a significant density of carbides. The microstructures were quantitatively described in terms of the grain and particle size and their distributions. The average ferrite grain size in the as-received state was about 400 nm and the average size of carbides - 111 nm. After HE the grain size dropped to 86 nm and the average size of carbides to 75 nm HE also resulted in a more uniform grain size and spatial distribution of carbides. Various carbides were identified including TaC of the diameter of 20 nm. (au)

[en] 316L-type stainless steel is commonly used in fusion devices. Its mechanical properties at cryogenic temperatures, for rolled or forged products possessing a grain size of tens of micrometers have been widely reported. In this paper we present the properties of this steel after multi-pass hydrostatic extrusion (HE), which brought about significant grain refinement to the nanometer scale. Such grain refinement of 316L-type stainless steel would be expected to improve the yield and ultimate tensile strength and may also result in a better resistance to irradiation. The microstructure of the HE processed samples was determined by electron microscopy and the mechanical properties evaluated by its microhardness under a load of 200 g and by tensile tests at room temperature and after immersion in liquid nitrogen. The observed improvements of the mechanical properties are discussed in terms of the microstructural changes arising from the hydrostatic extrusion.