Kobe Steel, Ltd.

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

Kabushiki Kaisha Kobe Seiko Sho

Shinshu Tlo Co., Ltd.

Voestalpine Stahl Gmbh

Shushi Ikeda

Hiroshi Akamizu

Junya Naitou

Keisuke Okita

Koichi Makii

Toshio Murakami

Yoichi Mukai

Shunichi Hashimoto

Koichi Sugimoto

Takahiro Kashima

Koh-ichi Sugimoto

Kenji Saito

Yosuke Shindo

Tatsuya Asai

Shinji Sato

Hideo Hata

Hitoshi Ishida

Andreas Pichler

Daisuke Matsuwaka

Fumio Yuse

Thomas Kurz

Masahiro Nomura

Yuzo Morikawa

Akihiko Nagasaka

Akinobu Kanda

Ryo Kikuchi

Tomokazu Masuda

Masaaki Miura

A casting method of an active metal includes, in an induction melting furnace using a water-cooled crucible, tapping a molten metal into a mold from a tapping hole provided at a bottom of the water-cooled copper crucible to cast an ingot of the active metal. In conducting the casting under a casting condition in which the ingot has a diameter (D) of 10 mm or more and a ratio (H/D) of an ingot height H to the ingot diameter D of 1.5 or more and a weight of the molten metal tapped in the casting is 200 kg or less, a temperature of the molten metal in the casting is set to be higher than the melting point of the active metal and a casting velocity V (mm/sec) is controlled to satisfy V&#x2264;0.1H in relation with the ingot height H by adjusting an opening diameter of the tapping hole.

Casting method for active metal

A steel sheet for hot pressing includes in a chemical composition, in percent by mass, C of 0.1% to 0.4%, Si of greater than 0% to 2.0%, Mn of 0.5% to 3.0%, P of greater than 0% to 0.015%, S of greater than 0% to 0.01%, B of 0.0003% to 0.01%, N of greater than 0% to 0.05%, Al in a content of 2&#xd7;[N]% to 0.3% at a Si content of greater than 0.5% to 2.0%; or Al in a content of (0.20+2&#xd7;[N]&#x2212;0.40&#xd7;[Si]N)% to 0.3% at a Si content of 0% to 0.5%, where [N] and [Si] are contents of N and Si, respectively, in mass percent, with the remainder being iron and inevitable impurities, where contents of Ti, Zr, Hf, and Ta, of the inevitable impurities, are each controlled to 0.005% or lower. The steel sheet includes nitride-based inclusions with an equivalent circle diameter of 1 &#x3bc;m or more in a number density of 0.10 per square millimeter.

Steel sheet for hot pressing and hot pressed article using the same

In the present invention, a press-formed product is manufactured by heating a steel sheet for hot pressing use to a temperature of 900&#xb0; C. or above and 1,100&#xb0; C. or below, the steel sheet for hot pressing use having a predetermined chemical component composition, some of Ti-containing precipitates contained in the steel sheet, each of which having an equivalent circle diameter of 30 nm or less, having an average equivalent circle diameter of 6 nm or less, and the precipitated Ti amount and the total Ti amount in the steel fulfilling the relationship represented by formula (1) shown below, thereafter starting press-forming, and holding at the bottom dead point and cooling to a temperature lower than the martensite transformation starting temperature Ms while securing the average cooling rate of 20&#xb0; C./s or more within a tool.Precipitated Ti amount(mass %)&#x2212;3.4[N]&#x3c;0.5&#xd7;[total Ti amount (mass %)&#x2212;3.4[N]]&#x2003;&#x2003;(1)(In the formula (1), [N] represents the content (mass %) of N in the steel.).

Method for manufacturing press-formed product and press-formed product

A hot-press formed product can be achieved which has regions corresponding to a shock resistant portion and an energy absorption portion within a single formed product without applying a welding method and achieves the balance of high strength and elongation with a high level according to each region by means of having a first forming region exhibiting a metal structure containing martensite: 80-97 area % and retained austenite: 3-20 area % respectively, the remaining structure being 5 area % or less, and a second forming region exhibiting a metal structure containing annealed martensite or annealed bainite: 30-97 area %, martensite as quenched: 0-67 area %, and retained austenite: 3-20 area %.

Hot-press formed product and method for manufacturing same

Provided is a hot-press molded article that can achieve a high level of balance between high strength and extension by region and has a region corresponding to an energy absorption site and a shock resistant site within a single molded article without applying a welding method by means of having first region having a metal structure containing both 80-97 area % of martensite and 3-20 area % of residual austenite, the remaining structure comprising no more than 5 area %, and a second region having a metal structure comprising 30-80 area % of ferrite, less than 30 area % (exclusive of 0 area %) of bainitic ferrite, no greater than 30 area % (exclusive of 0 area %) of martensite, and 3-20 area % of residual austenite.

There is provided a hot press-formed product, including a thin steel sheet formed by a hot press-forming method, and having a metallic structure that contains bainitic ferrite at 70% to 97% by area, martensite at 27% by area or lower, and retained austenite at 3% to 20% by area, the remainder structure of which is at 5% by area or lower, whereby balance between strength and elongation can be controlled in a proper range and high ductility can be achieved.

Hot press-formed product and process for producing same

There is provided a hot press-formed product, including a thin steel sheet formed by a hot press-forming method, and having a metallic structure that contains retained austenite at 3% to 20% by volume, whereby balance between strength and elongation can be controlled in a proper range and high ductility can be achieved.

Process for producing hot press-formed product

Provided is a press-forming product manufacturing method of manufacturing a forming product having satisfactory formability for a drawing process by press-forming a metal sheet using a press-forming tool with high productivity, including: heating the metal sheet to a transformation temperature Acor more; cooling the metal sheet to 600&#xb0; C. or lower; forming the metal sheet by a forming tool; ending the forming process at a martensite transformation start temperature Ms or more; taking out the metal sheet from the forming tool; and cooling the metal sheet.

Press-forming product manufacturing method and press-forming facility

There is provided a useful method for producing a press-formed product without making the structure of a press tool complicated, which product has favorable formability in a level so as to be able to be produced by deep drawing, and which product is produced by press-forming a thin steel sheet with a punch and a die, in which the thin steel sheet is heated to a temperature not lower than an Actransformation point thereof, and the press-forming is then started, wherein the forming is carried out so that a temperature difference in the thin steel sheet is adjusted to be not higher than 200&#xb0; C. at a stage when the thin steel sheet has reached one third of a forming height.

Method for producing press-formed product

There is provided a useful method for producing a press-formed product without causing disadvantages such as hardness variation, which product has favorable formability in a level so as to be able to be produced by deep drawing, and which method is carried out by heating a thin steel sheet to a temperature not lower than an Actransformation point thereof; and then cooling the thin steel sheet at a rate not lower than a critical cooling rate, during which the thin steel sheet is formed into the press-formed product, wherein the forming is started from a temperature higher than a martensitic transformation start temperature Ms thereof, the cooling rate is kept to be 10&#xb0; C./sec. or higher during the forming, and the forming is finished in a temperature range not higher than the martensitic transformation start temperature Ms.

Press-formed product and method for producing same

A dual phase steel sheet with good bake-hardening properties is provided. The steel sheet is characterized in containing (in terms of percent by mass) C: no less than 0.06% and less than 0.25%; Si+Al: 0.5 to 3%; Mn: 0.5 to 3%; P: no more than 0.15%; and S: no more than 0.02%; and also meeting the following condition (in terms of space factor) that retained austenite is at least 3%, bainite is at least 30%, and ferrite is no more than 50%, and further characterized in differing in stress larger than 50 MPa before and after application of 2% pre-strain and ensuing heat treatment for paint baking at 170&#xb0; C. for 20 minutes. The steel sheet has well-balanced strength and workability, exhibits good bake-hardening properties at the time of paint baking, and offers good resistance to natural aging.

Dual phase steel sheet with good bake-hardening properties

A high-strength cold-rolled steel sheet excellent in uniform elongation, including in percent by mass:

High-strength cold-rolled steel sheet excellent in uniform elongation and method for manufacturing same

A high-strength cold rolled steel sheet contains: 0.10 to 0.28% of C, 1.0 to 2.0% of Si, 1.0 to 3.0% of Mn, and 0.03 to 0.10% of Nb in terms of % by mass, Al is controlled to 0.5 or less, P is controlled to 0.15% or less, and S is controlled to 0.02% or less, and residual austenite accounts for 5 to 20%, bainitic ferrite accounts for 50% or more, and polygonal ferrite accounts for 30% or less (containing 0%), of the entire structure, and a mean number of residual austenite blocks is 20 or more as determined when the random area (15 &#x3bc;m&#xd7;15 &#x3bc;m) is observed by EBSP (electron back scatter diffraction pattern).

High-strength cold rolled steel sheet having excellent formability, and plated steel sheet

A high-strength forged part is disclosed which comprises a base phase structure, comprising 30% or more of ferrite in terms of a space factor, and a second phase structure, comprising bainite and/or martensite, and retained austenite having an average gain diameter of 5 &#x3bc;m or less and a content represented by 50X[C]&#x3c;[V]&#x3c;150x[C], wherein [V] represents a space factor of the retained austenite (&#x3b3;R) and [C] represents the mass % of C in the forged part. Furthermore, a high-strength forged part is disclosed which comprises a base phase structure, comprising 50% or more of tempered bainite or tempered martensite in terms of a space factor, and a second phase structure, comprising martensite and 3% to 30% retained austenite in terms of a space factor, wherein the portion of the retained austenite and martensite having an aspect ratio of 2 or less is 25% or less in terms of a space factor.

Method for producing high-strength forged parts having high reduction of area

To provide a high strength and low yield ratio cold rolled steel sheet having high elongation property and high flange drawing property, or a plated steel sheet made by plating the same. The high strength and low yield ratio cold rolled steel sheet or the plated steel sheet made by plating the same has such a constitution as 0.10 to 0.25% of C, 1.0 to 2.0% of Si and 1.5 to 3.0% of Mn, are contained in terms of weight percentage, while other elements are controlled such as Al within 0.2%, P within 0.15% and S within 0.02%, with residual austenite occupying at least 5%, bainitic ferrite occupying at least 60% (preferably 80% or more), and polygonal ferrite within 20% (containing 0%), so that a tensile strength is 980 MPa or higher, while an elongation (El in %), a flange drawing property (&#x3bb;in %), a tensile strength (TS in MPa) and a yield strength (YP in MPa) satisfy the following inequality (1): [(El &#xd7;&#x3bb;&#xd7;TS)/YP]&#x2267;645.

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Kobe, Japan

Shushi Ikeda