Ni被覆した超強カマルエージ鋼の水素ガス中遅れ破壊

抄録

The delayed fracture of a nickel coated ultrahigh strength maraging steel was studied in hydrogen gas pressure of 6.67 kPa and 66.7 kPa using notched tensile specimens. The delayed fracture strength for 180 ks increased with the increase in the thickness of a nickel coating and was lowered with increasing hydrogen gas pressure. The effect of coating on the hydrogen gas embrittlement of maraging steel varied drastically from reduction of embrittlement to its enhancement with the change in the thickness of coating from 10-20 μm to 2.5 μm. Hydrogen absorption into the specimens was active at the fresh surface of the coating that was produced by plastic deformation during loading the specimens, but it was extremely suppressed after the fresh surface had once been exposed to the air. A delayed fracture model in which the degree of hydrogen absorption at the surface was varied was discussed, and the delayed fracture behaviors were successfully explained by the consideration that the nickel coating layer had an effect of storing hydrogen because the distribution of hydrogen was much richer in nickel than in steel.