Inferences of Baking Time on Hydrogen Embrittlement for High Strength Steel Treated with Various Zinc Based Electroplating

Abstract

The hydrogen embrittlement of SK85 high-strength steel sheets was evaluated using a three-point bending test. The effect of electroplating the metal with zinc-based coatings on hydrogen embrittlement was examined by baking treatment of differently electroplated steel specimens. After electroplating, all the specimens underwent hydrogen embrittlement, promoted by hydrogen incorporation into the metal frame, owing to the reduction of hydrogen ions during electroplating. The hydrogen embrittlement of both zinc-and zinc-SiO2-electroplated SK85 steel continued after baking for 24 hours at 473 K, but that of zinc-nickel-and zinc-nickel-SiO2-electroplated SK85 steel ceased. Furthermore, TDA revealed that the trapped hydrogen could be released from steel at approximately 473 K. However, after baking, hydrogen embrittlement did not completely disappear, and we suggest that the formation of hydrogen vacancy clusters also accounts for this fracture phenomenon. The hydrogen incorporated into steel during electroplating led to the formation of hydrogen vacancy clusters, which allowed the formation of embrittlement. However, zinc and zinc-SiO2 films were not permeable enough to release these voids; while the peculiar zinc–nickel and zinc-nickel-SiO2 film structure enabled the hydrogen vacancy clusters to diffuse from the substrate.