Kobe Steel, Ltd.

Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.)

Kabushiki Kaisha Kobe Seiko Sho

Masahiro Nomura

Shunichi Hashimoto

Koichi Makii

Shinji Kozuma

Shushi Ikeda

Hiroshi Yaguchi

Takuya Kochi

Yoichi Mukai

Mamoru Nagao

Hiroshi Akamizu

Takaaki Minamida

Yosuke Shindo

Takahiro Kashima

Hiroyuki Takeda

Kouki Ikeda

Masafumi Shimizu

Noriaki Hiraga

Takayuki Yamamoto

Ikurou Hashimoto

Kenji Saitou

Ikuro Hashimoto

The invention provides a high strength cold rolled steel sheet having excellent chemical conversion treatment property stably even Mo is added aiming high strengthening. The surface property of the cold rolled steel sheet satisfies that the characteristic of 10 &#x3bc;m or more of the maximum depth (Ry) of the unevenness and 30 &#x3bc;m or less of the average spacing (Sm) of the unevenness, and that either one or more preferably both of, the characteristic of the load length ratio (tp40) of the unevenness of the surface is 20% or less, and the characteristic of the difference of the load length ratios (tp60) and (tp40) is 60% or more, is satisfied, and the crack of 3 &#x3bc;m or less width and 5 &#x3bc;m or more depth does not exist on the surface.

High-strength cold rolled steel sheet excelling in chemical treatability

There is provided a high-strength hot rolled steel sheet excellent in phosphatability, wherein a maximum depth (Ry) of pits and bumps, existing on a surface thereof, is not less than 10 &#x3bc;m, and an average interval (Sm) of the pits and the bumps is not more than 30 &#x3bc;m, meeting either a requirement for a load length ratio (tp40) of the pits and the bumps on the surface at not more than 20%, or a requirement for a difference between a load length ratio (tp60) and the load length ratio (tp40), at not less than 60%, or both thereof. The high-strength hot rolled steel sheet is capable of exhibiting stable and excellent phosphatability even if Mo highly effective for reinforcement in strength is added thereto in expectation of a higher strength.

High-strength hot-rolled steel sheet excellent in chemical treatability

The present invention provides a steel wire rod excellent in scale peelability for mechanical descaling, and a manufacturing method thereof. The steel wire rod in accordance with the present invention has: a base metal portion formed of a steel containing C in an amount of not more than 1.1% and Si in an amount of 0.05 to 0.80% on a mass % basis as components; and a scale layer deposited on the surface of the base metal portion, wherein the Si average concentration in the interface portion of the scale with the base metal portion is not less than 2.0 times the Si content of the base metal portion.

Steel wire excellent in descalability in mechanical descaling and method for production thereof

A hot-dip galvanized steel sheet composed of a basis steel sheet containing Si in an amount of 0.05-2.5 mass % and Mn in an amount of 0.2-3 mass % and a hot-dip galvanized zinc layer formed on the surface thereof, wherein said hot-dip galvanized zinc layer is formed in such a way that there is an Si&mdash;Mn enriched phase which is found, by observation under a scanning electron microscope or a transmission electron microscope, in the vicinity of the interface in a region no shorter than 50 &mgr;m in the cross section perpendicular to the interface between the basis steel sheet and the hot-dip galvanized zinc layer, said Si&mdash;Mn enriched phase containing more than twice as much Si and/or Mn as the basis steel sheet and extending over a length no more than 80% of the length of the interface observed. This hot-dip galvanized steel sheet is free of bare spots even in the case where the basis steel sheet contains Si and Mn in a comparatively large amount and hence is liable to suffering bare spots.

Hot-dip galvanized steel sheet

A hot-dip galvanized steel sheet which is produced from a cold-rolled steel sheet, as a base steel sheet, consisting essentially of C: 0.010-0.06 wt %, Si: no more than 0.5 wt %, Mn: no less than 0.5 wt % and less than 2.0 wt %, P: no more than 0.20 wt %, S: no more than 0.01 wt %, Al: 0.005-0.10 wt %, N: no more than 0.005 wt %, Cr: no more than 1.0 wt %, Mn&plus;1.3Cr: 1.9-2.3 wt %, Fe: remainder, and having a structure composed of ferrite and a second phase containing martensite, said second phase in the structure accounting for no more than 20% in terms of area and martensite in the second phase accounting for no less than 50%, and which has a zinc-plated layer formed on the surface thereof by hot-dip galvanizing or hot-dip galvannealing. A process for production of said hot-dip galvanized steel sheet. This steel sheet has a composite structure containing martensite and yet it has a low strength (no higher than 500 MPa) and also has good strength-ductility balance.

Hot-dip galvanized steel sheet and process for production thereof

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Kobe, Japan

Masahiro Nomura