Nippon Steel Sumitomo Metal Corporation

Naoki Matsutani

Koichi Goto

Toshio Ogawa

Kunio Hayashi

Nobuhiro Fujita

Shinichiro Watanabe

Toshimasa Tomokiyo

Toshiki Nonaka

Yusuke Kondo

A cold-rolled steel sheet includes, by mass %: C: 0.020% or more and 0.080% or less; Si: 0.20% or more and 1.00% or less; Mn: 0.80% or more and 2.30% or less; and Al: 0.010% or more and 0.100% or less; and further includes: one or more of Nb and Ti which satisfy a requirement of 0.005%&#x2264;Nb+Ti&#x3c;0.030%, in which a structure consists of, ferrite, bainite, and other phases, an area ratio of the ferrite is 80% or more and less than 95%, an area ratio of a non-recrystallization ferrite in the ferrite is 1% or more and less than 10%, an area ratio of the bainite is 5% or more and 20% or less, a total amount of the other phases is less than 8%, an equivalent circle diameter of a carbonitride including one or both of Nb and Ti is 1 nm or more and 10 nm or less, and a tensile strength is 590 MPa or more.

Cold-rolled steel sheet, plated steel sheet, and method for manufacturing the same

The high-strength steel sheet includes, by mass %: C: 0.01% to 0.10%; Si: 0.15% or less; Mn: 0.80% to 1.80%; P: 0.10% or less; S: 0.015% or less; Al: 0.10% to 0.80%; Cr: 0.01% to 1.50%; N: 0.0100% or less; and a balance consisting of iron and inevitable impurities, in which a metallic structure is composed of ferrite and a hard second phase, the area fraction of the ferrite is 80% or more, the area fraction of the hard second phase is 1% to 20%, the fraction of unrecrystallized ferrite in the ferrite is less than 10%, the ferrite grain sizes are 5 &#x3bc;m to 20 &#x3bc;m, and the fraction of the ferrite crystal grains having an aspect ratio of 1.2 or less in the entire ferrite crystal grains is 60% or more.

High-strength steel sheet having excellent processability and paint bake hardenability, and method for producing of high-strength steel sheet

This high-strength steel sheet includes: in terms of percent by mass, 0.03 to 0.10% of C; 0.01 to 1.5% of Si; 1.0 to 2.5% of Mn; 0.1% or less of P; 0.02% or less of S; 0.01 to 1.2% of Al; 0.06 to 0.15% of Ti; and 0.01% or less of N; and contains as the balance, iron and inevitable impurities, wherein a tensile strength is in a range of 590 MPa or more, and a ratio between the tensile strength and a yield strength is in a range of 0.80 or more, a microstructure includes bainite at an area ratio of 40% or more and the balance being either one or both of ferrite and martensite, a density of Ti(C,N) precipitates having sizes of 10 nm or smaller is in a range of 10precipitates/mmor more, and a ratio (Hvs/Hvc) of a hardness (Hvs) at a depth of 20 &#x3bc;m from a surface to a hardness (Hvc) at a center of a sheet thickness is in a range of 0.85 or more.

High-strength steel sheet, hot-dipped steel sheet, and alloy hot-dipped steel sheet that have excellent fatigue, elongation, and collision characteristics, and manufacturing method for said steel sheets

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Tokyo, Japan

Naoki Matsutani