Kobe Steel, Ltd.

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

Kazuya Kimijima

Masanori Kobayashi

Mikako Takeda

Tetsuo Soshiroda

Yasuyuki Fujii

Keitaro Tamura

Shinobu Nakayama

Tohru Shiogama

Seiji Morishige

Ryo Sasaki

The present invention is a production method of a hot-dip galvanized steel sheet including annealing a belt-shaped steel sheet having a Si content of greater than or equal to 0.2% by mass, wherein the annealing is continuously carried out using an annealing furnace having an oxidation heating zone and a reduction heating zone in this order, while the steel sheet is fed using rollers. The annealing includes oxidizing a surface of the steel sheet in the oxidation heating zone at a temperature at which roll pickup does not occur and reducing an iron oxide layer, formed by the oxidizing, in the reduction heating zone before the iron oxide layer reaches an initial roller in the reduction heating zone.

Production method of hot-dip galvanized steel sheet

An aspect of the present invention is a production method of a rolled sheet for cold-rolling, the method being characterized by including: a hot-rolling step for forming a rolled sheet by hot-rolling a pure titanium material while coiling; and an annealing step for annealing the hot-rolled sheet after the hot-rolling step, the coiling temperature in the hot-rolling step being 500&#xb0; C. or less, and the annealing step being controlled so that the percentage area of recrystallized grains in the microstructure of the hot-rolled sheet after annealing is at least 90% and the mean grain size of the recrystallized grains is 5 &#x3bc;m to 10 &#x3bc;m.

Production method of rolled sheet for cold-rolling, and production method of pure titanium sheet

Disclosed is a hot rolled steel sheet which contains C, Si, Mn, Al, Ti, N, and S. The C, Ti, N, and sulfur contents satisfy the following condition (1), and the Si and Mn contents satisfy the following condition (2):[C]&#x2212;{[Ti]&#x2212;(48/14)&#xd7;[N]&#x2212;(48/32)&#xd7;[S]}/4&#x2266;0.01&#x2003;&#x2003;(1)0.20&#x2266;([Si]/[Mn])&#x2266;0.85&#x2003;&#x2003;(2)in which the symbol [X] represents the content (percent by mass) of the element X, and the steel sheet has a microstructure having an area percentage of bainitic ferrite of 90% or more, an area percentage of martensite of 5% or less, and an area percentage of bainite of 5% or less, based on the area of an observed field. This steel sheet excels in properties demanded in press working, such as shape freezing ability, hole-expandability, and bendability, even though it has a high tensile strength of 980 MPa or more.

High strength hot rolled steel sheet with excellent press workability and method of manufacturing the same

Disclosed is a hot rolled steel sheet in which it includes a steel having a chemical composition of 0.03 to 0.10% (the percent hereinafter representing % by mass) of C, 0.2 to 2.0% of Si, 0.5 to 2.5% of Mn, 0.02 to 0.10% of Al, 0.2 to 1.5% of Cr, 0.1 to 0.5% of Mo, and the residue of iron and inevitable contaminants, and in this steel sheet, at least 80% by area in longitudinal cross section has a martensitic structure. As a consequence, a high strength hot rolled steel sheet having a tensile strength of the level as high as 980 MPa or higher simultaneously with an excellent forming workability, and in particular, excellent stretch flangeability is provided at a relatively low cost.

High strength hot rolled steel sheet having excellent stretch flangeability and its production method

Growing community of inventors

Kakogawa, Japan

Kazuya Kimijima