Effect of Phosphorus Content on Hydrogen Embrittlement for High Strength Steel Treated with Electroless Ni-P Plating

Hydrogen embrittlement of SK85 high-strength steel sheets was evaluated through a three-point bending test. The effects of electroless Ni-P plating and Ni electroplating on hydrogen embrittlement were examined with respect to the hydrogen permeability of the plated films. On the morrow of the plating, electroless Ni-P plating indicates a high degree of hydrogen embrittlement, irrespective of the phosphorus content in the film. However, hydrogen embrittlement of Ni electroplating is further suppressed than that of electroless Ni-P plating, which can be attributed to the excellent hydrogen diffusing ability of Ni electroplating. These results demonstrate that the hydrogen permeability of a plated film is an important factor for hydrogen embrittlement. Hydrogen present on the plated film surface was visualized by employing the hydrogen microprint technique, and the corresponding results reveal that the hydrogen permeability of the plated film is dependent on the film crystal structure. Furthermore, the pits in the film can become a route for hydrogen emission.