Other

Hiroshi Onoe

Tetsuo Shiraga

Katsuhiko Kikuchi

To provide a high-strength steel having a desired strength (800 N/mm or higher) for screws and bolts of a large diameter (M8 or larger) that also have a tapping ability, and a high-strength screw made from such a steel. The steel comprises (by % mass) C: 0.05 to 0.20, Si: 0.20 or less (not including 0), Mn: 0.5 to 2.0, P: 0.015 or less, S: 0.015 or less, sol. Al: 0.020 to 0.080, N: 0.0060 or less, Cr: more than 0.80 to 2.0 and the balance being iron and unavoidable impurities.

High strength screw

An object is to provide a high strength screw in which a high strength steel material not used in the prior art is employed as the tapping screw or gib-head screw or bolt or the like, and moreover, which, by the administering of a carburization hardening process on the surface thereof, has high tensile stress and shear stress, and has high surface hardness, and which has, particularly in tapping screws, good male thread formability with respect to the foundation hole of the opposing member, and very good tightening and joining properties and durability. Another object of the present invention is to provide compatibility with a machine screw in such a way that, once the tapping screw has been removed from the opposing member, a machine screw can be screwed into the male thread formed by the tapping screw. A screw is formed from a screw material which comprises a high tensile steel, and a surface hardening process, in particular a continuous quenching gas carburization process, is performed on, at the least, the thread part to form a surface hardened layer of a depth in the range of 0.05 to 0.3 mm.

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Higashinari-ku, Osaka-shi, Osaka 537-0013, Japan

Hiroshi Onoe