Nippon Steel Sumitomo Metal Corporation

Kohsuke Kume

Daisuke Maeda

Kenichi Yamamoto

Yuji Ogawa

Hideaki Yamamura

Osamu Kawano

Yoshihiro Suwa

Junji Haji

Yuzo Takahashi

Katsuhiro Fuchigami

Masamitsu Wakoh

Akihiro Matsuzawa

The present invention provides a high-strength steel sheet including: C: 0.03 to 0.25 mass %, Si: 0.1 to 2.0 mass %, Mn: 0.5 to 3.0 mass %, P: not more than 0.05 mass %, T.O: not more than 0.0050 mass %, S: 0.0001 to 0.01 mass %, N: 0.0005 to 0.01 mass %, acid-soluble Al: more than 0.01 mass %, Ca: 0.0005 to 0.0050 mass %, and a total of at least one element of Ce, La, Nd, and Pr: 0.001 to 0.01 mass %, with a balance including iron and inevitable impurities, in which the steel sheet contains a chemical component on a basis of mass that satisfies 0.7&#x3c;100&#xd7;([Ce]+[La]+[Nd]+[Pr])/[acid-soluble Al]&#x2266;70 and 0.2&#x2266;([Ce]+[La]+[Nd]+[Pr])/[S]&#x2266;10, the steel sheet contains compound inclusion including a first inclusion phase containing at least one element of Ce, La, Nd, and Pr, containing Ca, and containing at least one element of O and S, and a second inclusion phase having a component different from that of the first inclusion phase and containing at least one element of Mn, Si, and Al, the compound inclusion forms a spherical compound inclusion having an equivalent circle diameter in the range of 0.5 &#x3bc;m to 5 &#x3bc;m, and a ratio of the number of the spherical compound inclusion relative to the number of all inclusions having the equivalent circle diameter in the range of 0.5 &#x3bc;m to 5 &#x3bc;m is 30% or more.

High-strength steel sheet exhibiting excellent stretch-flange formability and bending workability, and method of producing molten steel for the high-strength steel sheet

An environmentally friendly flux for molten steel desulfurization includes CaO and AlOso that [CaO]/[AlO] is within a range of 1.6 to 3.0, and includes one or more alkali metal oxides of NaO, KO, and LiO, and SiOso that [SiO]/[RO] is within a range of 0.1 to 3, [RO] is within a range of 0.5 mass % to 5 mass %, and [SiO] is within a range of 0.05 mass % to 15 mass % in a case in which the [CaO], the [AlO], the [SiO], and the [RO] represent the mass % of CaO, the mass % of AlO, the mass % of SiO, and the total amount of the mass % of NaO, the mass % of KO, and the mass % of LiO respectively.

Environmentally friendly flux for molten steel desulfurization

Growing community of inventors

Tokyo, Japan

Kohsuke Kume