Nippon Steel Sumitomo Metal Corporation

Nippon Steel Corporation

Sumitomo Metal Corporation

Kazuaki Nakano

Riki Okamoto

Nobuhiro Fujita

Kunio Hayashi

Kohichi Sano

Takeshi Yamamoto

Tatsuo Yokoi

Hiroshi Shuto

Toshio Ogawa

Yoshihiro Suwa

Hiroshi Yoshida

Yuri Toda

Hiroyuki Tanaka

Manabu Takahashi

Koichi Goto

Shinichiro Watanabe

Tetsuo Kishimoto

The present invention provides a bainite-containing-type high-strength hot-rolled steel sheet. The steel sheet, containing C: greater than 0.07 to 0.2%, Si: 0.001 to 2.5%, Mn: 0.01 to 4%, P: 0.15% or less, S: 0.03% or less, N: 0.01% or less, Al: 0.001 to 2% and a balance being composed of Fe and impurities, has an average value of pole densities of the {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e; orientation group at a sheet thickness center portion being a range of &#x215d; to &#x215c; in sheet thickness from the surface of the steel sheet is 4.0 or less, and a pole density of the {332}&#x3c;113&#x3e; crystal orientation is 4.8 or less, an average crystal grain diameter is 10 &#x3bc;m or less and vTrs is &#x2212;20&#xb0; C. or lower, and a microstructure is composed of 35% or less in a structural fraction of pro-eutectoid ferrite and a balance of a low-temperature transformation generating phase.

Bainite-containing-type high-strength hot-rolled steel sheet having excellent isotropic workability and manufacturing method thereof

A cold-rolled steel sheet satisfies that an average pole density of an orientation group of {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e; is 1.0 to 5.0, a pole density of a crystal orientation {332}&#x3c;113&#x3e; is 1.0 to 4.0, a Lankford-value rC in a direction perpendicular to a rolling direction is 0.70 to 1.50, and a Lankford-value r30 in a direction making an angle of 30&#xb0; with the rolling direction is 0.70 to 1.50. Moreover, the cold-rolled steel sheet includes, as a metallographic structure, by area %, a ferrite and a bainite of 30% to 99% in total and a martensite of 1% to 70%.

Method for producing a cold-rolled steel sheet

A hot-rolled steel sheet wherein an average pole density of orientation group of {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e; is 1.0 to 5.0 and pole density of crystal orientation {332}&#x3c;113&#x3e; is 1.0 to 4.0. The hot-rolled steel sheet includes, as a metallographic structure, by area %, 30% to 99% ferrite and bainite in total, and 1% to 70% martensite. The hot-rolled steel sheet satisfies Expression 1: dia&#x2264;13 &#x3bc;m, and also satisfies Expression 2: TS/fM&#xd7;dis/dia&#x2265;500, wherein an area fraction of the martensite is defined as fM in unit of area %, an average size of the martensite is defined as dia in unit of &#x3bc;m, an average distance between the martensite is defined as dis in unit of &#x3bc;m, and tensile strength of the steel sheet is defined as TS in unit of MPa.

Hot-rolled steel sheet and method for producing same

This high-strength cold-rolled steel sheet contains, in mass %, C: 0.02% to 0.20%; Si: 0.001% to 2.5%; Mn: 0.01% to 4.0%; P: 0.001% to 0.15%; S: 0.0005% to 0.03%; Al: 0.001% to 2.0%; N: 0.0005% to 0.01%; and O: 0.0005% to 0.01%; in which Si+Al is limited to less than 1.0%, and a balance being composed of iron and inevitable impurities, in which an area ratio of bainite in a metal structure is 95% or more, at a sheet thickness center portion being a range of &#x215d; to &#x215c; in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e; orientation group is 4.0 or less, and a pole density of the {332}&#x3c;113&#x3e; crystal orientation is 5.0 or less, and a mean volume diameter of crystal grains in the metal structure is 7 &#x3bc;m or less.

High-strength cold-rolled steel sheet having excellent local deformability

This high-strength hot-rolled steel sheet having excellent local deformability contains, in mass %, C: 0.07% to 0.20%; Si: 0.001% to 2.5%; Mn: 0.01% to 4.0%; P: 0.001% to 0.15%; S: 0.0005% to 0.03%; Al: 0.001% to 2.0%; N: 0.0005% to 0.01%; and O: 0.0005% to 0.01%; and a balance being composed of iron and inevitable impurities, in which an area ratio of bainite in a metal structure is 95% or more, at a sheet thickness center portion being a range of &#x215d; to &#x215c; in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e; orientation group is 4.0 or less, and a pole density of the {332}&#x3c;113&#x3e; crystal orientation is 5.0 or less, and a mean volume diameter of crystal grains in the metal structure is 10 &#x3bc;m or less.

High-strength hot-rolled steel sheet having excellent local deformability and manufacturing method thereof

In a hot-rolled steel sheet, an average pole density of an orientation group of {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e;, which is represented by an arithmetic average of pole density of each orientation of {100}&#x3c;011&#x3e;, {116}&#x3c;110&#x3e;, {114}&#x3c;110&#x3e;, {112}&#x3c;110&#x3e;, and {223}&#x3c;110&#x3e; in a center portion of a sheet thickness which is a range of the sheet thickness of &#x215d; to &#x215c; from a surface of the steel sheet, is 1.0 or more and 4.0 or less, the pole density of a crystal orientation of {332}&#x3c;113&#x3e; is 1.0 or more and 4.8 or less, an average grain size in a center in the sheet thickness is 10 &#x3bc;m or less, and a microstructure includes, by a structural fraction, pearlite more than 6% and ferrite in the balance.

Hot-rolled steel sheet for gas nitrocarburizing and manufacturing method thereof

In a hot-rolled steel sheet, an average pole density of an orientation group {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e;, which is represented by an arithmetic mean of pole densities of orientations {100}&#x3c;011&#x3e;, {116}&#x3c;110&#x3e;, {114}&#x3c;110&#x3e;, {112}&#x3c;110&#x3e;, and {223}&#x3c;110&#x3e; is 1.0 to 4.0 and a pole density of a crystal orientation {332}&#x3c;113&#x3e; is 1.0 to 4.8, in a thickness center portion which is a thickness range of &#x215d; to &#x215c; from the surface of the steel sheet; an average grain size in the thickness center portion is less than or equal to 10 &#x3bc;m and a grain size of cementite precipitating in a grain boundary of the steel sheet is less than or equal to 2 &#x3bc;m; and an average grain size of precipitates containing TiC in grains is less than or equal to 3 nm and a number density per unit volume is greater than or equal to 1&#xd7;10grains/cm.

Hot-rolled steel sheet and method of producing the same

A steel sheet includes, by mass %: C: 0.020% to 0.080%; Si: 0.01% to 0.10%; Mn: 0.80% to 1.80%; and Al: more than 0.10% and less than 0.40%; and further includes: Nb: 0.005% to 0.095%; and Ti: 0.005% to 0.095%, in which a total amount of Nb and Ti is 0.030% to 0.100%, and the steel sheet includes, as a metallographic structure, ferrite, bainite, and other phases, an area fraction of the ferrite is 80% to 95%, an area fraction of the bainite is 5% to 20%, a total fraction of the other phases is less than 3%, a tensile strength is 590 MPa or more, and a fatigue strength ratio as a fatigue strength to the tensile strength is 0.45 or more.

Steel sheet, plated steel sheet, and method for producing the same

A hot-rolled steel sheet satisfies that average pole density of orientation group of {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e; is 1.0 to 5.0 and pole density of crystal orientation {332}&#x3c;113&#x3e; is 1.0 to 4.0. Moreover, the hot-rolled steel sheet includes, as a metallographic structure, by area %, ferrite and bainite of 30% to 99% in total and martensite of 1% to 70%. Moreover, the hot-rolled steel sheet satisfies following Expressions 1 and 2 when area fraction of the martensite is defined as fM in unit of area %, average size of the martensite is defined as dia in unit of &#x3bc;m, average distance between the martensite is defined as dis in unit of &#x3bc;m, and tensile strength of the steel sheet is defined as TS in unit of MPa.dia&#x2266;13 &#x3bc;m&#x2003;&#x2003;(Expression 1)&#xd7;dis/dia&#x2267;500&#x2003;&#x2003;(Expression 2)

Cold-rolled steel sheet

A high-strength cold-rolled steel sheet having excellent stretch flangeability and precision punchability containing predetermined components and a balance being composed of iron and inevitable impurities, in which in a range of &#x215d; to &#x215c; in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e; orientation group represented by respective crystal orientations of {100}&#x3c;011&#x3e;, {116}&#x3c;110&#x3e;, {114}&#x3c;110&#x3e;, {113}&#x3c;110&#x3e;, {112}&#x3c;110&#x3e;, {335}&#x3c;110&#x3e;, and {223}&#x3c;110&#x3e; is 6.5 or less, and a pole density of the {332}&#x3c;113&#x3e; crystal orientation is 5.0 or less, and a metal structure contains, in terms of an area ratio, greater than 5% of pearlite, the sum of bainite and martensite limited to less than 5%, and a balance composed of ferrite.

High-strength cold-rolled steel sheet having excellent stretch flangeability and precision punchability and manufacturing method thereof

Manufacturing method of a high-strength cold-rolled steel sheet having excellent local deformability

In a hot-rolled sheet, an average value of pole densities of an orientation group {100}&#x3c;011&#x3e; to {223}&#x3c;110&#x3e;, which is represented by an arithmetic mean of pole densities of orientations {100}&#x3c;011&#x3e;, {116}&#x3c;110&#x3e;, {114}&#x3c;110&#x3e;, {112}&#x3c;110&#x3e;, and {223}&#x3c;110&#x3e; in a thickness center portion of a thickness range of &#x215d; to &#x215c; from a surface of the steel sheet, is 1.0 to 6.5 and a pole density of a crystal orientation {332}&#x3c;113&#x3e; is 1.0 to 5.0; and a Lankford value rC in a direction perpendicular to a rolling direction is 0.70 to 1.10 and a Lankford value r30 in a direction that forms 30&#xb0; with respect to the rolling direction is 0.70 to 1.10.

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Tokyo, Japan

Kazuaki Nakano