Effects of yttrium and zirconium additions on inclusions and mechanical properties of a reduced activation ferritic/martensitic steel

The effects of two alloying elements,i.e.,yttrium(Y)and zirconium(Zr),on the inclusion,microstructure,tensile property and impact toughness of reduced activation ferritic/martensitic(RAFM)steel are analyzed.The size and number of particles were determined by optical microscopy,and the particle types were examined by scanning electron microscopy.The size of?20% and?85% of the inclusions lied in the range of 0.5-1.0μm and 0.5-3.0μm,respectively.In Y-and Y-Zr-containing specimens,the density of the fine inclusions,with a size less than 0.5μm,was found to be 1.06×10^17 and 9.82×10^16 m^-3.respectively.All specimens were normalized at 1323 K for 30 min and tempered at 923 and 1023 K for 90 min,resulting in the formation of tempered martensite with M23C6 carbides and MX precipitates.Zr-containing RAFM steel tempered at 923 K formed M23C6 carbides and nano-sized carbides with Zr,conferring superior strength balance and impact toughness.The yield strength of alloy reached 695 MPa,and a low ductile-brittle transition temperature of 238 K was maintained.