Jfe Steel Corporation

Tetsuya Mega

Takashi Kobayashi

Kei Sakata

Yoshimasa Funakawa

Nobuyuki Nakamura

Kazuhiro Seto

Katsumi Nakajima

Hiroshi Takahashi

Takeshi Yokota

Katsumi Yamada

Koichi Nakagawa

Yuji Tanaka

Shusaku Takagi

Nobusuke Kariya

Tetsuo Shimizu

Satoshi Kinoshiro

Noriaki Moriyasu

Tamako Ariga

Reiko Mizuno

A steel sheet for soft-nitriding has a composition containing: C: 0.05% or more to 0.10% or less; Si: 0.5% or less; Mn: 0.7% or more to 1.5% or less; P: 0.05% or less; S: 0.01% or less; Al: 0.01% or more to 0.06% or less; Cr: 0.5% or more to 1.5% or less; Nb: 0.005% or more to 0.025% or less; and N: 0.005% or less, on a mass percent basis, such that C and Nb satisfy 0.10&#x2264;Nb/C&#x2264;0.30 (where C and Nb are respective contents of the elements (by mass %)), wherein balance comprises Fe and incidental impurities, and a microstructure that is a complex-phase microstructure containing ferrite and pearlite, and the microstructure having a ratio of a microstructure other than the ferrite and the pearlite of 1% or less, and the microstructure having a ratio of polygonal ferrite in the ferrite of less than 50%.

Steel sheet for soft-nitriding and method for manufacturing the same

A high-strength steel sheet includes a composition containing, in mass percent, 0.08% to 0.20% of carbon, 0.2% to 1.0% of silicon, 0.5% to 2.5% of manganese, 0.04% or less of phosphorus, 0.005% or less of sulfur, 0.05% or less of aluminum, 0.07% to 0.20% of titanium, and 0.20% to 0.80% of vanadium, the balance being iron and incidental impurities.

High strength steel sheet and method for manufacturing the same

Hot-rolled steel has a chemical composition containing, by mass %, C: 0.18% or more and 0.29% or less, N: 0.0050% or less, Ti: 0.002% or more and 0.05% or less, B: 0.0005% or more and 0.0050% or less, and appropriately controlled amounts of Si, Mn, P, S, Al, and a tensile strength of 500 MPa or less with a variation in tensile strength of 60 MPa or less throughout a region including the edges in the width direction of the steel sheet, and having excellent cold formability and hardenability.

Hot-rolled steel sheet having excellent cold formability and hardenability and method for manufacturing the same

Described is a high tensile strength hot rolled steel sheet having high strength and formability, and a manufacturing method. It has tensile strength &#x2267;980 MPa and excellent formability, and specifically identified ranges by mass % of C, Si, Mn, P, S, N, Al, Ti, V, Solute V, and Solute Ti; (ii) microstructure with fine carbides dispersion precipitated therein, the fine carbides containing Ti and V and having the average particle diameter &#x3c;10 nm, as well as volume ratio with respect to the entire microstructure &#x2267;0.007; and matrix as ferrite phase having area ratio with respect to the entire microstructure &#x2267;97%. C, Ti, V, S and N satisfy (1) Ti&#x2267;0.08 +(N/14&#xd7;48+S/32&#xd7;48) and (2) 0.8&#x2266;(Ti/48+V/51)/(C/12)&#x2266;1.2, where 'C', 'Ti', &#x201c;V&#x201d;, &#x201c;S&#x201d; and &#x201c;N&#x201d; represent contents (mass %) of corresponding elements, respectively.

High tensile strength hot rolled steel sheet having excellent formability and method for manufacturing the same

The present invention relates to a high strength hot rolled steel sheet consisting of 0.04 to 0.15% C, 1.5% or less Si, 0.5 to 1.6% Mn, 0.04% or less P, 0.005% or less S, 0.04% or less Al, 0.03 to 0.15% Ti, 0.03 to 0.5% Mo, by mass, and balance of Fe and inevitable impurities, and having a microstructure consisting of ferrite containing precipitates, second phase of bainite and/or martensite, and other phase, wherein the percentage of the ferrite containing precipitates is 40 to 95%, and the percentage of the other phase is 5% or less. For example, the high strength hot rolled steel sheet having a thickness of 1.4 mm shows a tensile strength of 780 MPa or higher, an elongation of 22% or higher elongation, and a hole expansion ratio of 60% or higher, thus the steel sheet is suitable for reinforcing members automobile cabin and crash worthiness members of automobile.

High strength hot rolled steel sheet and method for manufacturing the same

This disclosure proposes a high-strength hot rolled steel sheet having excellent anti-die-galling property and anti-fatigue property, in which the steel sheet has a composition including C: not less than 0.02 mass % but not more than 0.2 mass %, Si: not less than 0.2 mass % but not more than 1.2 mass %, Mn: not less than 1.0 mass % but not more than 3.0 mass %, Mo: not less than 0.1 mass % but not more than 1.0 mass %, Al: not less than 0.01 mass % but not more than 0.1 mass %, P: not more than 0.03 mass % S: not more than 0.01 mass % and the remainder being substantially Fe and inevitable impurities, and has a steel microstructure containing not less than 55 vol % of ferrite and not less than 10 vol % but not more than 40 vol % of martensite provided that a total of both is not less than 95 vol %, and a ratio ds/dc of an average crystal grain size ds of the ferrite in a surface layer portion of the steel sheet to an average crystal grain size dc of the ferrite in a center portion of the steel sheet is 0.3&#x3c;ds/dc&#x2266;1.0 and a surface roughness is not more than 1.5 &#x3bc;m as an arithmetic mean roughness Ra, as well as a method of producing the same.

High tensile hot-rolled steel sheet excellent in resistance to scuff on mold and in fatigue characteristics

According to the invention, a high-strength hot rolled steel sheet having an excellent shape fixability as hot-rolled and an excellent fatigue durability after the forming, excellent weldability and phosphatability and a tensile strength of not less than 590 MPa level can be obtained by comprising C: not less than 0.02 mass % but not more than 0.2 mass %, Si: not less than 0.5 mass % but not more than 2.0 mass %, Mn: not less than 1.0 mass % but not more than 3.0 mass %, Al: not less than 0.01 mass % but not more than 0.1 mass %, N: not less than 0.002 mass % but not more than 0.006 mass %, P: not more than 0.03 mass %, S: not more than 0.01 mass % and solid-soluted (C+N): not less than 0.0010 mass % and the reminder being Fe and inevitable impurities, and having a steel structure that a primary phase is ferrite and a secondary phase is martensite phase of 5-30 % at a volume ratio and a total of both is not less than 95 % as a volume ratio, and further having an average crystal grain size of ferrite of not more than 8 &#x3bc;m.

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Tokyo, Japan

Tetsuya Mega