PURPOSE: To provide the screw joint excellent in seizure resistance under a condition of no lubricant applied in which any liquid lubricant such as grease and the like is not used at all, and no galling is caused even if the joint is repeatedly fastened and loosened, and furthermore, service performance such as sealing properties and the like are satisfied.
CONSTITUTION: In a pipe screw joint, a phosphoric acid system chemical conversion treatment coated layer 5 or a combination of a nitriding treated layer and the phosphoric acid system chemical conversion treatment coated layer is provided for the contact surface of a box or a pin, concurrently a resin coated layer 6 in which a molybdenum disulfide powder is dispersed so as to be mixed, is formed over the phosphoric acid system chemical conversion treatment coated layer 5, and the thickness of the resin coated layer is made thicker than that of the phosphoric acid system chemical conversion treatment coated layer 5. Or in addition to that, each surface roughness of surfaces faced to each other is made thinner than the thickness of the resin coated layer 6, so that the screw joint is thereby provided, which is excellent in seizure resistance under a condition of no lubricant applied where grease and liquid lubricant are not used when a pin or a box is threadedly engaged.
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OKA MASAHARU
NAGAYOSHI HARUYUKI
NAKAJIMA AKIRA
HIGUCHI YUKINOBU
INOUE RYUSUKE
NIHON PARKERIZING