| Abstract |
| Effects of stabilizing elements such as titanium and niobium, and aluminium on toughness and corrosion of ferritic stainless steels were studied as a series of basic studies for optimizing the concentrations of minor alloying elements. Aluminum reduced the concentration of total oxygen and the size of oxides to improve toughness. Niobium, one of stabilizing elements used in this study improved toughness as well as corrosion resistance. It is due to the fact that niobium retards the formation of chromium-carbonnitride known as a site for crack initiation and as resulting in chromium depleted zone. Unexpectedly, titanium, the other of stabilizing elements did not improve toughness as effective as niobium. The cause in a angular shaped TiN formed at the temperature around the solidus line of the alloy. It was proved by inclusion analysis, measurements of DBTT, and the calculation on phase equilibrium. In addition, the reducement of pitting corrosion resistance by titamium seems to be contradictory to the previous known fact that titanium removes sulfur in steels and improves corrosion resistance. The discrepancy was solved by observation of the angular TiN on the surface causing micro cracks to provide a site for pitting. |
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| Key Words |
| Surface defects, TiN, Pitting corrosion, Crevice corrosion, Dual stabilization |
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