Hitachi, Ltd.

Hitachi Kyowa Kogyo Co., Ltd.

Hiroshi Tsujimura

Yasumasa Tamai

Koichi Kurosawa

Hideyo Saito

Yutaka Watanabe

Kunio Enomoto

Masahiro Otaka

Keiichi Uraki

Masahiro Kobayashi

Masahito Mochizuki

Masayuki Kurihara

Seiichi Toyoda

By applying spot welding along a crack which has occurred in an austenitic stainless steel structure without use of welding material so that spot welds are connected, melting and solidifying of the crack can be achieved, thereby to provide a metal structure which is rich with delta ferrite of the austenitic stainless steel structure or prevent propagation of the crack by enclosing it into the interior of the austenitic stainless steel structure.

Metal member quality improving method by spot welding

A water jet peening method in which a pressurized water jet flow containing cavities is jetted through a nozzle having a velocity increasing orifice portion and a horn-like jetting hole formed continuously with the velocity increasing orifice portion to impinge against a surface of a metallic material immersed in water and to cause the cavities to collapse at the surface of the metallic member, and a tensile plastic deformation is caused in a surface layer of the metallic material by a local high pressure generated by the impingement and the collapse so that a residual tensile stress in the surface of the metallic member is reduced. In this method, the nozzle is vibrated so that vibration-induced cavities are formed in the vicinity of a nozzle wall surface, and the vibration-induced cavities are caused to impinge against the surface of the metallic member by the pressurized water jet flow containing cavities. It is thereby possible to promote the generation of cavities even in a case where pure water existing in a nuclear reactor and scant of nuclei from which cavities will be generated is used in peening of an internal structual member of the reactor.

Method of and apparatus for water-jet peening

A method for improving a property of a weld of an austenitic stainless steel which is a part of a structure being brought into contact with a corrosive fluid at a region having been affected by welding heat on both of opposed surfaces, comprising the steps of: cooling said thermally affected region on one of said opposed surfaces; and simultaneously with said cooling step, applying a melting treatment to the other surface, thereby changing the melting treatment portion into a micro structure that contains delta (.delta.) ferrite and is superior in corrosion resistance property. The latter surface is improved in high tensile stress generated by the welding work. Namely, its stress is reduced. The melting heat for said melting treatment is obtained by application of high density energy.

Method for improving property of weld of austenitic stainless steel

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Hitachi, Japan

Hiroshi Tsujimura