Yttrium Oxide Concentration Effect on Helium Porosity Formation in Oxide-Dispersion-Hardened Ferrite-Martensite Steel

Studies are presented of helium porosity in EP-450 oxide-dispersion-hardened yttrium steel, obtained by electopulse sintering, as a function of the Y₂O₃ content in comparison with EP-450 matrix steel and dispersion-hardened steel fabricated by hot extrusion. It is found that multiple zones with different types of helium porosity and different zone distribution develop in steel with 1 wt.% Y₂O₃; in steel with 0.3 wt.% Y₂O₃, there are fewer such zones than in matrix steel and steel obtained by hot extrusion. It is proposed that the extremely nonuniform distribution of porosity over volume and size in steel fabricated by electropulse sintering is associated with the initially strongly defective structure, including residual porosity, as well as with the chromium redistribution between ferrite grains and tempered-martensite grains during the sample preparation process.