Jfe Steel Corporation

Kawasaki Steel Corporation

Thyssenkrupp Steel Ag

Thyssenkrupp Steel Europe Ag

Tokushu Kinzoku Excel Co., Ltd.

Kazuhiro Seto

Takashi Kobayashi

Takeshi Yokota

Hiroshi Matsuda

Yoshiyasu Kawasaki

Hidekazu Minami

Shinjiro Kaneko

Kei Sakata

Kaneharu Okuda

Akio Kobayashi

Chiaki Kato

Takako Yamashita

Hidetaka Kawabe

Yoshimasa Funakawa

Koichi Nakagawa

Yasushi Tanaka

Nobuyuki Nakamura

Katsumi Yamada

Osamu Furukimi

Yuji Tanaka

Yasunobu Nagataki

Takaaki Tanaka

Yuki Toji

Toshiyuki Kato

Noriaki Kohsaka

Kenji Kawamura

Yoshie Obata

Toru Hoshi

Reiko Sugihara

Takashi Obara

Yoshihiro Hosoya

Nobusuke Kariya

Satoshi Ueoka

Yuka Miyamoto

Tetsuya Mega

Kazunori Tahara

Makoto Isobe

Takashi Ono

Thomas Heller

Satoshi Kinoshiro

Shigeru Umino

Yukihiro Matsubara

Brigitte Hammer

Katsumi Nakajima

Masahide Watanabe

Keiji Ueda

Nobuo Nishiura

Fusae Shiimori

Masami Iwasaki

Masaaki Kohno

Kouichi Nakagawa

Rolf Bode

Günter Stich

Yoichi Tominaga

Tetsuo Yamamoto

Noriaki Kosaka

Tamako Ariga

Masahide Watabe

Nobuyuki Kageyama

Noriyuki Katayama

Tetsuo Mochida

Tomohisa Oonishi

Guenter Stich

Eiji Tsuchiya

Yuta Matsumura

Masanori Nishizawa

A high strength steel sheet having a high Young's modulus, the steel sheet having a chemical composition including, by mass %, C: 0.060% or more and 0.150% or less, Si: 0.50% or more and 2.20% or less, Mn: 1.00% or more and 3.00% or less, and one or both of Ti: 0.001% or more and 0.200% or less and Nb: 0.001% or more and 0.200% or less, in which the contents of C, N, S, Ti, and Nb satisfy the equation 500&#x2264;C*&#x2264;1300. The steel sheet has a microstructure including ferrite in an amount of 20% or more and martensite in an amount of 5% or more, in terms of area ratio, such that the average grain size of the ferrite is 20.0 &#x3bc;m or less and the inverse intensity ratio of &#x3b3;-fiber for &#x3b1;-fiber is 1.00 or more in the ferrite and the martensite.

High strength steel sheet having high Young's modulus and method for manufacturing the same

A steel sheet has a microstructure that contains ferrite in an area ratio of 20% or more, martensite in an area ratio of 5% or more, and tempered martensite in an area ratio of 5% or more. The ferrite has a mean grain size of 20.0 &#x3bc;m or less. An inverse intensity ratio of &#x3b3;-fiber to &#x3b1;-fiber in the ferrite is 1.00 or more and an inverse intensity ratio of &#x3b3;-fiber to &#x3b1;-fiber in the martensite and the tempered martensite is 1.00 or more.

High-strength steel sheet and production method therefor

Disclosed is a steel sheet having a predetermined chemical composition and a steel microstructure that contains, in area ratio, 35% or more and 80% or less of polygonal ferrite and 5% or more and 25% or less of martensite, and that contains, in volume fraction, 8% or more of retained austenite, in which the polygonal ferrite, the martensite, and the retained austenite have a mean grain size of 6 &#x3bc;m or less, 3 &#x3bc;m or less, and 3 &#x3bc;m or less, respectively, and each have a mean grain aspect ratio of 2.0 or less, and in which a value obtained by dividing an Mn content in the retained austenite in mass % by an Mn content in the polygonal ferrite in mass % equals 2.0 or more.

High-strength steel sheet and method for manufacturing same

Disclosed is a steel sheet having a predetermined chemical composition and a steel microstructure that contains, in area ratio, 15% or more and 55% or less of polygonal ferrite and 15% or more and 30% or less of martensite, and that contains, in volume fraction, 12% or more of retained austenite, in which the polygonal ferrite, the martensite, and the retained austenite have a mean grain size of 4 &#x3bc;m or less, 2 &#x3bc;m or less, and 2 &#x3bc;m or less, respectively, and each have a mean grain aspect ratio of 2.0 or less, and in which a value obtained by dividing an Mn content in the retained austenite in mass % by an Mn content in the polygonal ferrite in mass % equals 2.0 or more.

Disclosed is a high-strength steel sheet having a tensile strength (TS) of 780 MPa or more and excellent in ductility, fatigue properties, stretch flangeability, surface characteristics, and sheet passage ability that can be obtained by providing a predetermined chemical composition and a steel microstructure that contains, by area, 20-50% of ferrite, 5-25% of bainitic ferrite, 1-10% of martensite, and 5-15% of tempered martensite, and that contains, by volume, 10% or more of retained austenite, in which the retained austenite has a mean grain size of 2 &#x3bc;m or less, a mean Mn content in the retained austenite in mass % is at least 1.2 times the Mn content in the steel sheet in mass %, the retained austenite has a mean free path of 1.2 &#x3bc;m or less, and the tempered martensite has a mean free path of 1.2 &#x3bc;m or less.

High-strength steel sheet and production method for same, and production method for high-strength galvanized steel sheet

Disclosed is a high-strength steel sheet having a tensile strength (TS) of 780 MPa or more and excellent in ductility, fatigue properties, balance between high strength and ductility, surface characteristics, and sheet passage ability that can be obtained by providing a predetermined chemical composition and a steel microstructure that contains, by area, 20-50% of ferrite, 5-25% of bainitic ferrite, and 5-20% of martensite, and that contains, by volume, 10% or more of retained austenite, in which the retained austenite has a mean grain size of 2 &#x3bc;m or less, a mean Mn content in the retained austenite in mass % is at least 1.2 times the Mn content in the steel sheet in mass %, and the retained austenite has a mean free path of 1.2 &#x3bc;m or less.

A steel having a composition containing C: more than 0.20% and 0.45% or less, Si: 0.50% to 2.50%, Mn: 2.00% or more and less than 3.50%, and one or two selected from Ti: 0.005% to 0.100% and Nb: 0.005% to 0.100% is hot-rolled and cold-rolled. The steel sheet is heated to 800&#xb0; C. to 950&#xb0; C. and cooled to a cooling-end temperature of 350&#xb0; C. to 500&#xb0; C. at a cooling rate of 5&#xb0; C./s or more to form a steel sheet having a microstructure including martensite and bainite phases such that the total proportion of the martensite and bainite phases is 80% or more by volume. The steel sheet is heated to 700&#xb0; C. to 840&#xb0; C. and maintained at 700&#xb0; C. to 840&#xb0; C., cooled to a cooling-end temperature of 350&#xb0; C. to 500&#xb0; C. at a cooling rate of 5 to 50&#xb0; C./s, and maintained within the above temperature range for 10 to 1800 s.

Thin high-strength cold-rolled steel sheet and method of producing the same

Disclosed is a high-strength steel sheet having a predetermined chemical composition, satisfying the condition that Mn content divided by B content equals 2100 or less, and a steel microstructure that contains, by area, 25-80% of ferrite and bainitic ferrite in total, 3-20% of martensite, and that contains, by volume, 10% or more of retained austenite, in which the retained austenite has a mean grain size of 2 &#x3bc;m or less, a mean Mn content in the retained austenite in mass % is at least 1.2 times the Mn content in the steel sheet in mass %, and an aggregate of retained austenite formed by seven or more identically-oriented retained austenite grains accounts for 60% or more by area of the entire retained austenite.

A high-strength steel sheet with excellent formability and high yield ratio that has TS of 980 MPa or more and YR of 68% or more is obtained by providing a predetermined chemical composition and a steel microstructure that contains, in area ratio, 15 to 55% of polygonal ferrite, 8% or more of non-recrystallized ferrite, and 15 to 30% of martensite, and that contains, in volume fraction, 12% or more of retained austenite, in which the polygonal ferrite has a mean grain size of 4 &#x3bc;m or less, the martensite has a mean grain size of 2 &#x3bc;m or less, the retained austenite has a mean grain size of 2 &#x3bc;m or less, and a value obtained by dividing an Mn content in the retained austenite (in mass %) by an Mn content in the polygonal ferrite (in mass %) equals 2.0 or more.

High-strength steel sheet, high-strength hot-dip galvanized steel sheet, high-strength hot-dip aluminum-coated steel sheet, and high-strength electrogalvanized steel sheet, and methods for manufacturing same

A high-strength hot-pressed part having a specified chemical composition, a microstructure including, in terms of volume fraction, 80% or more of a martensite phase, in a range of 3.0% to 20.0% of a retained austenite phase, a tensile strength TS of 1500 MPa or more, and a uniform elongation uEl of 6.0% or more. A method for manufacturing the high-strength hot-pressed part, the method comprising performing a heating process and a hot press forming process on a raw material steel sheet in order to obtain a hot-pressed part having a specified shape.

High-strength hot-pressed part and method for manufacturing the same

A high strength steel sheet having a high Young's modulus, the steel sheet having a chemical composition including, by mass %, C: 0.060% or more and 0.150% or less, Si: 0.50% or more and 2.20% or less, Mn: 1.00% or more and 3.00% or less, Nb: 0.001% or more and 0.200% or less, and V: 0.001% or more and 0.200% or less, in which the contents of C, Nb, and V satisfy the equation 500&#x2264;C*&#x2264;1300. The steel sheet has a microstructure including ferrite in an amount of 20% or more and martensite in an amount of 5% or more, in terms of area ratio, such that the average grain size of the ferrite is 20.0 &#x3bc;m or less and the inverse intensity ratio of &#x3b3;-fiber for &#x3b1;-fiber is 1.00 or more in each of the ferrite and the martensite.

High strength steel sheet having high young's modulus and method for manufacturing the same

A slab has a steel composition including 0.020% to 0.065% of C, 0.1% or less of Si, 0.40% to less than 0.80% of Mn, 0.030% or less of P, 0.005% or less of S, 0.08% to 0.16% of Ti, 0.005% to 0.1% of Al, 0.005% or less of N, and the balance being Fe and incidental impurities, in which Ti*(=Ti&#x2212;(48/14)&#xd7;N) satisfies [Ti*&#x2267;0.08] and [0.300&#x2266;C/Ti*&#x2266;0.375], is subjected to hot rolling to obtain a hot-rolled steel sheet in which the steel microstructure includes, in terms of area fraction, 95% or more of a ferrite phase; the average ferrite grain size is 10 &#x3bc;m or less; the average grain size of Ti carbides precipitated in steel is 10 nm or less; and Ti in the amount of 80% or more of Ti* is precipitated as Ti carbides.

High strength hot-rolled steel sheet having excellent ductility, stretch flangeability and uniformity and method of manufacturing the same

Growing community of inventors

Tokyo, Japan

Kazuhiro Seto