Jfe Steel Corporation

Kana Sasaki

Hiroshi Hasegawa

Tatsuya Nakagaito

Shoji Tanaka

Hidekazu Minami

Taro Kizu

Noriaki Moriyasu

Kazunori Tahara

Shigeyuki Nabeshima

A high-strength galvanized steel sheet includes a base steel sheet and a galvanized layer on a surface thereof. The base steel sheet has a predetermined chemical composition and a microstructure in which an area fraction of martensite is 30% or less, an area fraction of pearlite is 1% or less, a total area fraction of tempered martensite and carbide-containing bainite is 30% or more and 99% or less, an area fraction of retained austenite is 1% to 20%, and a total area fraction of ferrite and non-carbide-containing bainite is 45% or less in the steel sheet microstructure in a predetermined region and in which an area fraction of retained austenite grains having two or more crystal orientations is 40% or less in all the retained austenite grains in a predetermined region.

High-strength galvanized steel sheet and method for manufacturing the same

A high-strength steel sheet has a specific composition and a microstructure. In the microstructure, the area fraction of elongated ferrite phase grains having an aspect ratio of 3 or more is 1% or less, the average crystal grain size of martensite included in a region extending 50 &#x3bc;m from a surface of the steel sheet is 20 &#x3bc;m or less, the content of oxide particles having a minor axis length of 0.8 &#x3bc;m or less in the region extending 50 &#x3bc;m from the surface of the steel sheet is 1.0&#xd7;10particles/mor more, and the content of coarse oxide particles having a minor axis length of more than 1 &#x3bc;m in the region extending 50 &#x3bc;m from the surface of the steel sheet is 1.0&#xd7;10particles/mor less. The content of hydrogen trapped in the steel sheet is 0.05 ppm by mass or more.

High-strength steel sheet and method for producing the same

There is provided a galvanized steel sheet more highly excellent in terms of punchability. The steel sheet has a specified chemical composition and a microstructure including a ferrite phase and a tempered bainite phase in a total amount of 95% or more in terms of area ratio, in which the average grain diameter of the microstructure is 5.0 &#x3bc;m or less, the amount of Fe precipitated is 0.10 mass % or more, the amount of Ti, Nb, and V precipitated in the form of precipitates having a grain diameter of less than 20 nm is 0.025 mass % or more in terms of precipitate C equivalent, and half or more of precipitates having a grain diameter of less than 20 nm are formed at random.

Galvanized steel sheet and method for manufacturing the same

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Tokyo, Japan

Kana Sasaki