Preparation and structural investigation of nanostructured oxide dispersed strengthened steels
Although capability of steels has been improved in the past by thermomechanical treatment, utilization of powder metallurgy provides more controlled microstructure, a homogeneous dispersion of nanosized oxide particles in the metal matrix and tailored properties in terms of strength and radiation resistance. This article is summarizing recent results on preparation, structural, and mechanical investigation of oxide dispersed strengthened steel (ODS). Two commercial steel powders, austenitic 17Cr12Ni2.5Mo2.3Si0.1C and martensitic Fe16Cr2Ni0.2C powders have been used as starting materials. Nanosized yttria dispersed martensitic and austenitic sintered steel samples have been realized by powder metallurgical methods. An efficient dispersion of nano-oxides in ODS steels was achieved by employing high efficient attrition milling. A combined wet and dry milling process of fine ceramic and steel particles is proposed. Spark Plasma Sintering (SPS) was applied to realize nanostructured steel compacts. Grains with 100 nm mean size have been observed by SEM in sintered austenitic ODS. In comparison, the sintered martensitic dry milled and martensitic dry and combined milled ODS microstructure consisted of grain size with 100–300 nm in each case. A brittle behavior is shown in all of the cases. The martensitic ODS is two times harder than the austenitic ODS. The bending strength high as 1806.7 MPa was found for the martensitic ODS, whereas 1210.8 MPa was determined for the austenitic ODS. The combined milling assured higher strength and hardness compared to dry milling.