Effects of Solid-Solute V on the Phosphatability of Hot-Rolled Steel Sheets

The phosphatability of hot-rolled steel sheets has become increasingly important with application of higher strength and thinner steel sheets to automotive parts. Although V is an alloying element which is often added to high strength hot-rolled steel sheets, the effect of V on phosphatability was s...

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Bibliographic Details
Published inTetsu-to-Hagane Vol. 105; no. 12; pp. 1135 - 1142
Main Authors Furuya, Shinichi, Yamazaki, Kazuhiko, Masuoka, Hiroyuki, Matsuzaki, Akira, Taira, Shoichiro
Format Journal Article
LanguageEnglish
Japanese
Published The Iron and Steel Institute of Japan 2019
Subjects
electrochemistry
high strength hot-rolled steel sheet
phosphatability
vanadium
vanadium-added steel
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Summary:The phosphatability of hot-rolled steel sheets has become increasingly important with application of higher strength and thinner steel sheets to automotive parts. Although V is an alloying element which is often added to high strength hot-rolled steel sheets, the effect of V on phosphatability was still unclear. This study investigated the phosphatability of V-added hot-rolled steel sheets by using V-free, 0.20% V and 0.47% V steel sheets as test specimens. After phosphate treatment, phosphate crystals covered the whole surface of the V-free and 0.20% V steel sheets, but there were no phosphate crystals on the surface of the 0.47% V steel sheets. In order to clarify the mechanism, potentiostatic electrolysis in the phosphate treatment solution was carried out. Phosphate crystals were found on the surface of the V-free steel sheet after both cathodic and anodic polarization. In contrast, no phosphate crystals were found on the surface of the 0.47% V steel sheet after anodic polarization, but similarly to the V-free steel sheet, phosphate crystals had formed after cathodic polarization. A surface analysis by XPS revealed that V oxides had precipitated on the surface of the 0.47% V steel sheet after anodic polarization. Evolution of hydrogen ions in the oxidation reaction of V inhibits the formation of phosphate crystals. Thus, oxidation of V on the steel surface in the phosphate treatment solution was identified as the factor responsible for deterioration of the phosphatability of V-added hot-rolled steel sheets.
ISSN:0021-1575
1883-2954
DOI:10.2355/tetsutohagane.TETSU-2019-029