Jfe Steel Corporation

Kawasaki Steel Corporation

Seiji Nakajima

Tatsuya Miyoshi

Hiroki Nakamaru

Takashi Kobayashi

Yoshimasa Funakawa

Katsutoshi Takashima

Satoru Ando

Hiroyuki Masuoka

Shinji Ootsuka

Hisatada Nakakoji

Minako Morimoto

Chiaki Kato

Nobuyuki Morito

Shuji Gomi

Akira Yasuda

Minoru Tanaka

Koichi Nakagawa

Rinsei Ikeda

Daisuke Mizuno

Yoichi Tobiyama

Yasuaki Okita

Kazuaki Kyono

Shuhei Ogawa

Tomokatsu Katagiri

Rinta Sato

Hajime Kumura

A hot-pressed member, a steel sheet for hot pressing, and methods for producing the hot-pressed member and the steel sheet for hot pressing. The hot-pressed member includes a steel sheet and a Zn-based alloy coated layer disposed on at least one surface of the steel sheet. The Zn-based alloy coated layer includes a solid solution phase including Zn with the balance being Fe and incidental impurities, an intermetallic compound phase including Fe with the balance being Zn and incidental impurities, and an oxide layer including Zn. The oxide layer serves as an uppermost layer of the Zn-based alloy coated layer and splits the intermetallic compound phase. The split density in at least one cross-section of the oxide layer per unit cross-section is 10 split positions/mm or more.

Hot-pressed member, steel sheet for hot pressing, and methods for producing the hot-pressed member and the steel sheet for hot pressing

Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing of 1780 MPa or more, excellent delayed fracture resistance, and high cross tensile strength after resistance spot welding by properly adjusting its chemical composition and its microstructure such that a prior austenite average grain size is 8 &#x3bc;m or less, a volume fraction of martensite is 90% or more, and at least 10 cementite grains having a grain size of 0.05 &#x3bc;m or more are present on average per 200 &#x3bc;mof a cross section parallel to a thickness direction of the member, and such that at least 10 Ti-based precipitates having a grain size of less than 0.10 &#x3bc;m are present on average per 100 &#x3bc;mof the cross section parallel to the thickness direction of the member in a range of 100 &#x3bc;m in the thickness direction from a surface of the member.

Hot-pressed member and method for manufacturing same, and cold-rolled steel sheet for hot pressing and method for manufacturing same

Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing, excellent delayed fracture resistance, and high tensile shear stress after resistance spot welding by properly adjusting its chemical composition and its microstructure such that at least 20 Nb-based precipitates having a grain size of less than 0.10 &#x3bc;m are present on average per 100 &#x3bc;mof a cross section parallel to a thickness direction of the member, a prior austenite average grain size is 8 &#x3bc;m or less, an average aspect ratio of prior austenite grains is 2.5 or less, and a volume fraction of martensite is 90% or more, and such that a standard deviation of Vickers hardness measured every 200 &#x3bc;m on a surface of the member is 40 or less.

Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing as high as TS: 1780 MPa or more, and excellent indentation peeling strength at projection welds by properly adjusting its chemical composition and its microstructure such that a prior austenite average grain size is 7 &#x3bc;m or less within a range of 50 &#x3bc;m or less in a thickness direction from a surface of the member, a volume fraction of martensite is 90% or more, and an average intergrain distance of Nb and Ti carbonitrides having a grain size of less than 0.10 &#x3bc;m within a depth range of 20 &#x3bc;m to 100 &#x3bc;m in the thickness direction from the surface of the member is 5 &#x3bc;m or less.

A hot-pressed member is formed using a tailored blank material obtained by butt joining respective ends of two or more coated steel sheets. The hot-pressed member has two or more sites formed by the respective coated steel sheets and at least one joining portion between the sites. Depending on a type of a coated layer of each of the coated steel sheets, t/tis appropriately controlled where tis a thickness of a thinnest portion in the joining portion and tis a thickness of a thinnest site of the sites. A tensile strength of each of the sites is 1180 MPa or more.

Hot-pressed member and manufacturing method therefor

Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing as high as TS: 1780 MPa or more, and excellent resistance to resistance welding cracking by properly adjusting its chemical composition and its microstructure such that a prior austenite average grain size is 7.5 &#x3bc;m or less, a volume fraction of martensite is 95% or more, and at least 10 Nb-based and Ti-based precipitates having a grain size of less than 0.10 &#x3bc;m are present on average per 100 &#x3bc;mof a cross section parallel to a thickness direction of the member within a range of 100 &#x3bc;m or less in the thickness direction from the surface of the member, and such that a B concentration in prior austenite grain boundaries is at least 3.0 times a B concentration at a position 5 nm away from the grain boundaries.

Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing as high as TS: 1780 MPa or more and excellent delayed fracture resistance after projection welding by properly adjusting its chemical composition and its microstructure such that at least 5 Ti-based precipitates having a grain size of 0.10 &#x3bc;m or less are present on average per 100 &#x3bc;mof a cross section parallel to a thickness direction of the member within a range of 100 &#x3bc;m in a thickness direction from a surface of the member, a volume fraction of martensite is 95% to 100% within a depth range of 20 &#x3bc;m to 100 &#x3bc;m in the thickness direction from the surface of the member, and at least 10 cementite grains having a grain size of less than 0.20 &#x3bc;m are present on average in a prior austenite grain.

Provided is a hot-pressed member excellent in terms of paint adhesiveness and a method of manufacturing the hot-pressed member. A hot-pressed member has a coating layer containing Zn and Ni on the surface of a steel sheet of which the member is formed, an oxide film containing Zn on the coating layer, and a void formation rate is 80% or less for voids formed between the coating layer and the oxide film.

Hot-pressed member and method of manufacturing the same

A method of manufacturing a hot-pressed member including heating a coated steel sheet to 850&#xb0; C. to 950&#xb0; C., the coated steel sheet including a substrate steel sheet and a coating layer formed on the substrate steel sheet and containing 10% to 25% by mass of Ni and the balance being Zn and incidental impurities, in which the coating weight of the coating layer is 10 to 90 g/mper a side; and starting hot press forming when the temperature of the coated steel sheet which has been heated is 650&#xb0; C. to 800&#xb0; C.

Method of manufacturing hot-pressed member

A method is provided for producing a hot-pressed member including heating a Ni-based coated steel sheet, which includes, on a surface thereof, a Zn&#x2014;Ni alloy coating layer containing 13% by mass or more of Ni, in a temperature region of an Ac3 transformation point to 1200&#xb0; C.; and then hot-pressing the steel sheet.

Method for producing hot-pressed member

The invention provides a steel sheet for hot press-forming that can reliably give hot press-formed parts having excellent paint adhesiveness, perforation corrosion resistance and joint corrosion resistance, and also provides a method for manufacturing the steel sheet for hot press-forming, and a method for producing hot press-formed parts using the steel sheet for hot press-forming. The steel sheet for hot press-forming includes a base steel sheet and a Zn-based coating layer with a mass of coating of 10 to 90 g/mon the base steel sheet, wherein the average ferrite grain diameter in the surface microstructure of the base steel sheet is not more than 20 &#x3bc;m.

Steel sheet for hot press-forming, method for manufacturing the same, and method for producing hot press-formed parts using the same

A steel sheet for hot pressing that is capable of suppressing formation of scales or ZnO in hot pressing and excellent in oxidation resistance, and a method for manufacturing a hot-pressed member using the steel sheet are provided. The steel sheet for hot pressing includes a base steel sheet and a plating layer that is formed on a surface of the base steel sheet at a coating weight of 10 to 90 g/mand contains 10 to 25% by mass of Ni and the balance Zn with inevitable impurities.

Steel sheet for hot pressing and method for manufacturing hot-pressed member using the same

A hot-pressing steel sheet has excellent oxidation resistance to be capable of suppressing the formation of scales and ZnO during hot pressing as well as is excellent in cold pressing properties. A process of manufacturing a hot pressed member uses the steel sheet. The hot-pressing steel sheet includes a coating layer containing 10 to 25 mass % of Ni and a balance of Zn and inevitable impurities and having a mass per unit area of 10 to 90 g/m, and a lubricating layer containing a solid lubricant, in the order named on the surface of a steel sheet.

Steel sheet for hot pressing and process for manufacturing hot pressed member using the steel sheet

A steel sheet for hot press-forming having a first coating layer on a surface of the steel sheet, containing 60% or more by mass Ni and a remainder composed of Zn and incidental impurities, a coating mass thereof being more than 5 g/mand 50 g/mor less per side, and a second coating layer on the first coating layer, containing 10% to 25% by mass Ni and a remainder composed of Zn and incidental impurities, a coating mass thereof being 10 to 90 g/mper side.

Steel sheet for hot press-forming

A steel sheet for hot press-forming includes a zinc coating layer and a Si-containing compound layer in this order on a base steel sheet, wherein the Si-containing compound layer contains a silicone resin having an organic functional group of a carbon number of 4 or more.

Growing community of inventors

Tokyo, Japan

Seiji Nakajima