Ti Influence on the Microstructure and the Mechanical Behaviour of an ODS Ferritic/Martensitic EUROFER97 Steel

A. Ramar (Sp), EPFL, Villigen PSI (Switzerland); T. Leguey, A. Munoz, Universidad Carlos III de Madrid, Leganes (Spain); N. Baluc, R. Schäublin, EPFL, Villigen PSI (Switzerland) 
Oxide dispersion strengthening (ODS) is a fruitful approach to improve strength of low activation ferritic/martensitic (F/M) steels at high temperature as well as their resistance to irradiation in view of their use in the future fusion reactor. The influence of 0.3 % wt. Ti additions on the microstructure and the mechanical properties of an ODS F/M steel has been investigated, as it may improve the oxide spatial distribution, refine particle size and decrease the O segregation that is detrimental to fracture properties. The base material is the F/M steel EUROFER97, whose chemical composition is 8.9 wt. % Cr, 1.1 W, 0.47 Mn, 0.2 V, 0.14 Ta, 0.11 C and Fe for the balance, and the base oxide used for strengthening consists in 0.3 wt % yttria. The ODS steel is produced by a powder metallurgical process, consisting of attrition milling for the mixing of the atomized EUROFER97 powder, the yttria particles and pure Ti powder. The milled powder is then prepressed uniaxially and finally by hot isostatic pressing (HIP) for the compaction of the blend. It was documented by TEM observations and chemical analyses. The resulting ODS steel microstructure and the nature, size and spatial distribution of the reinforcing material was investigated by TEM. It appears that the yttrium oxide and Ti tend to form Y-Ti-O complexes. Tensile tests were carried out from room temperature up to 700°C and Charpy impact tests were performed from room temperature to 500°C. Though relatively fragile, the yield strength is increased relatively to EUROFER97 and the ductility, reduced relatively to EUROFER97, is higher at high temperatures than the base ODS material. Results are presented here.

Download complete paperDownload complete paper
pdf 7.216 KB