Abstract
Effects of the evolution of inclusions on the pitting corrosion resistance of 304 stainless steel with different contents of the rare-earth element yttrium (Y) were studied using thermodynamic calculations, accelerated immersion tests, and electrochemical measurements. The experimental results showed that regular Y2O3 inclusions demonstrated the best pitting resistance, followed in sequence by (Al,Mn)O inclusions, the composite inclusions, and irregular Y2O3 inclusions. The pitting resistance first decreased, then increased, and then decreased again with increasing Y content, because sulfide inclusions were easily generated when the Y content was low and YN inclusions were easily generated at higher Y contents. The best pitting corrosion resistance was obtained for 304 stainless steel with addition of 0.019% Y.
Highlights
As very important strategic resources, rare-earth elements are widely used in the petroleum, chemical, metallurgical, textile, ceramics, and glass industries, and as permanent magnetic materials
A large number of YN inclusions were severely etched after 5 s in 304 stainless steel containing 0.049% Y, but its pitting corrosion resistance was greater than the steel containing 0.007% Y because of the generation of regular Y2O3 inclusions (Fig. 10)
The best pitting corrosion resistance was exhibited by 304 stainless steel containing 0.019% Y, which contained the largest proportion of regular Y2O3 inclusions (Figs 5, 9)
Summary
As very important strategic resources, rare-earth elements are widely used in the petroleum, chemical, metallurgical, textile, ceramics, and glass industries, and as permanent magnetic materials. Addition of rare-earth elements at an appropriate content is beneficial to enhancing the mechanical properties of metallic materials by refining the grains, improving wear and corrosion resistance, and improving plasticity, strength, grain boundary strength, and dislocation movement[1,2]. Rare earths enhance overall corrosion resistance by changing the inner structure and the chemical composition and structure of the material surface, and promote and stabilize the formation of uniform and compact surface films[8,9,10,11]. Kim et al illustrated that the addition of rare-earth metals to a base alloy led to the formation of (Mn,Cr,Si,Al,Ce) and (Mn,Cr,Si,Ce) oxides, which improved resistance to pitting corrosion[4]. There are, few studies focusing on modifying oxide inclusions by adding rare-earth Y to improve the pitting corrosion resistance of clean 304 stainless steel
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