Powder Particle Size Effects on Microstructure and Mechanical Properties of Mechanically Alloyed ODS Ferritic Steels

Moisés Oñoro,Julio Macías-Delgado,María A Auger,Jan Hoffmann,Vanessa De Castro,Teresa Leguey

doi:10.3390/met12010069

Moisés Oñoro, Julio Macías-Delgado + Show 4 more

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https://doi.org/10.3390/met12010069

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Abstract

Reduced activation ferritic (RAF) steels are expected to be widely used in challenging nuclear industrial applications under severe thermo-mechanical regimes and intense neutron loads. Therefore, actual research panorama is facing the strengthening strategies necessary to maximize both performance and endurance under these conditions. Oxide dispersion strengthened (ODS) RAF steels are leader candidates as structural materials in fusion energy reactors thanks to the reinforcement obtained with a fine dispersion of nanosized oxides in their matrix. In this study, the influence of the initial powder particle size and the selected processing route on the final material has been investigated. Two RAF ODS steels coming from atomized pre-alloyed powders with nominal particle powder sizes of 70 and 30 µm and composition Fe-14Cr-2W-0.4Ti-0.3Y2O3 (wt. %) were manufactured by mechanical alloying. Alloyed powders were compacted by hot isostatic pressing, hot crossed rolled, and annealed at 1273 K. Initial powder particle size differences minimize after milling. Both steels present an almost completely recrystallized material and similar grain sizes. The same type and distributions of secondary phases, Cr-W-rich, Ti-rich, and Y-Ti oxide nanoparticles, have been also characterized by transmission electron microscopy (TEM) in both alloy samples. The strengthening effect has been confirmed by tensile and Charpy impact tests. The two alloys present similar strength values with slightly better ductile brittle transition temperature (DBTT) and ductility for the steel produced with the smaller powder size.

Highlights

Development of strengthening techniques on reduced activation ferritic and ferritic/martensitic (RAF and RAFM) steels for high-temperature applications represent one of the main objectives in research activities on new materials for nuclear energy applications [1,2,3]
Oxide dispersion strengthened (ODS) Reduced activation ferritic (RAF) steels are leader candidates as structural materials in fusion energy reactors thanks to the reinforcement obtained with a fine dispersion of nanosized oxides in their matrix
Two RAF ODS steels coming from atomized pre-alloyed powders with nominal particle powder sizes of 70 and 30 μm and composition Fe-14Cr-2W-0.4Ti-0.3Y2O3 were manufactured by mechanical alloying

Summary

Introduction

Development of strengthening techniques on reduced activation ferritic and ferritic/martensitic (RAF and RAFM) steels for high-temperature applications represent one of the main objectives in research activities on new materials for nuclear energy applications [1,2,3]. Innovative concept designs, such as DEMO and first-generation prototypes, aim to improve reactor specifications by developing new technologies and materials that could withstand extreme operation conditions [4]. The nanodispersoids could be stable under irradiation up to 1000 K, trapping He in fine-scale bubbles, inhibiting void swelling and fast fracture embrittlement at lower temperatures as well as creep rupture embrittlement at high temperatures [6,10]

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