Incidence of mechanical alloying contamination on oxides and carbides formation in ODS ferritic steels

Abstract

Ferritic ODS steels containing 14 or 18wt.% Cr are produced by mechanical alloying (MA), hot consolidation and cold working. This study focuses on the evolution of interstitials such as oxygen, nitrogen and carbon at each stage of the fabrication route by comparing two MA methods: attrition milling or ball milling. The milling time required to obtain a homogenous distribution of yttrium at the micron scale in the ground powders is relatively short by using an attritor. But, in this case the carbon and nitrogen contamination is more pronounced considering powders which have reached a similar metastable stationary state. The presence of oxygen in excess results in the formation of large micron-sized oxides after extrusion. Most of them are identified as titanium-based or silicon oxides by EDS analysis. For attrition milling, a high density of aligned Ti(C,N) compounds and some FeCrW carbides (M23C6 type) mainly distributed at the grain boundaries are identified, correlated with the higher carbon contamination.