超強力マルエージ鋼の水素ガス中脆化におよぼすNi, CuおよびNi-P被覆の影響

Abstract

In order to improve the susceptibility of ultrahigh strength maraging steels to hydrogen gas environment embrittlement, the application of electroplated nickel or copper coatings and electroless nickel-phosphorus coatings, and the effect of heat treatment after coating on the susceptibility to hydrogen embrittlement have been studied.When the age-hardened steels were coated and then baked at 473 K, the notch tensile strength of nickel coated specimens in hydrogen gas was higher than that of uncoated specimens, and the thicker the coating, the higher the strength in the thickness range between 2.5 and 20 μm. The notch tensile strength of nickel-phosphorus coated specimens was equal to that of uncoated specimens.When the unaged steels were coated and then heated at 773 K to make them age-harden, the steel-coating bond was well established compared with the specimens baked at 473 K. In the nickel coated specimens, the notch tensile strength depended on the thickness of coating greatly, that is, the hydrogen embrittlement was improved by 10-20 μm nickel coatings, whereas it was enhanced by 2.5-5 μm nickel coatings. The notch tensile strength of nickel-phosphorus coated specimens was lower than that of uncoated specimens. In the copper coated specimens, the relief of hydrogen that had been absorbed during plating was insufficient by heating at 473 K or 773 K, and the hydrogen gas embrittlement was enhanced by the coating, particularly, in the 773 K specimens.