Kawasaki Steel Corporation

Jfe Steel Corporation

Akio Tosaka

Hideo Kuguminato

Chikara Kami

Kaneharu Okuda

Osamu Furukimi

Toshiyuki Kato

Koichi Hashiguchi

Takuya Yamazaki

Chikako Fujinaga

Masatoshi Aratani

Kaku Sato

Shinjiro Kaneko

Kei Sakata

Kazunori Osawa

Makoto Aratani

Takashi Ishikawa

Toshio Irie

Masahiko Morita

Susumu Okada

Eiko Yasuhara

Shinobu Okano

Isao Takahashi

Yuji Miki

Toshio Ichida

Kazuaki Kyono

Fusao Togashi

Shigeru Umino

Keiji Nishimura

Yoichi Tominaga

Nobutaka Kurosawa

Tateo Higashino

Hiromasa Hayashi

Hiroshi Hashimoto

Takao Uchiyama

Sinjiro Kaneko

Nobuo Yamada

Noriyuki Katayama

Yukio Kobata

Yoshihiro Okawa

Naotoshi Ryu

A high tensile strength hot-rolled steel sheet having superior strain aging hardenability, which has high formability and stable quality characteristics, and in which satisfactory strength is obtained when the steel sheet is formed into automotive components, thus enabling the reduction in weight of automobile bodies is provided. Specifically, a method for producing a high tensile strength hot-rolled steel sheet having superior strain aging hardenability with a BH of 80 MPa or more, a &#x394;TS of 40 MPa or more, and a tensile strength of 440 MPa or more includes the steps of heating a steel slab to 1,000&#xb0; C. or more, the steel slab containing, in percent by mass 0.15% or less of C, 2.0% or less of Si, 3.0% or less of Mn, 0.08% or less of P, 0.02% or less of S, 0.02% or less of Al, 0.0050% to 0.0250% of N, and optionally 0.1% or less in total of at least one of more than 0.02% to 0.1% of Nb and more than 0.02% to 0.1% of V, the ratio N (mass %)/Al (mass %) being 0.3 or more, rough-rolling the steel slab to form a sheet bar; finish-rolling the sheet bar at a finishing temperature of 800&#xb0; C. or more; cooling at a cooling rate of 20&#xb0; C. to 40&#xb0; C./s or more within 0.5 second after the finish-rolling; and coiling at a temperature of 650&#xb0; C. to 450&#xb0; C. or less.

High tensile hot-rolled steel sheet having excellent strain aging hardening properties and method for producing the same

An object of the present invention is to provide a cold-rolled steel sheet and an alloyed hot-dip galvanized steel sheet in which tensile strength is effectively increased by press forming and heat treatment while maintaining excellent deep drawability in press forming. Specifically, a steel composition contains less than 0.01% of C, 0.005 to 1.0% of Si, 0.01 to 1.0% of Mn, 0.005 to 0.050% of Nb, 0.005 to 0.030% of Al, 0.005 to 0.040% of N, 0.0005 to 0.0015% of B, 0.05% or less of P, and 0.01% or less of S, the balance substantially composed of Fe, in which the following equations (1) and (2) are satisfied:N %&#x2267;0.0015+14/93&#xb7;Nb %+14/27&#xb7;Al %+14/11&#xb7;B %&#x2003;&#x2003;(1)C %&#x2266;(12/93)&#xb7;Nb %.&#x2003;&#x2003;(2)

Cold rolled steel sheet and galvanized steel sheet having strain age hardenability and method of producing the same

An object of the present invention is to provide a cold-rolled steel sheet and an alloyed hot-dip galvanized steel sheet in which tensile strength is effectively increased by press forming and heat treatment while maintaining excellent deep drawability in press forming. Specifically, a steel composition contains less than 0.01% of C, 0.005 to 1.0% of Si, 0.01 to 1.0% of Mn, 0.005 to 0.050% of Nb, 0.005 to 0.030% of Al, 0.005 to 0.040% of N, 0.0005 to 0.0015% of B, 0.05% or less of P, and 0.01% or less of S, the balance substantially composed of Fe, in which the following equations (1) and (2) are satisfied:N%&#x2267;0.0015+14/93.Nb%+14/27.Al%+14/11.B%&#x2003;&#x2003;(1)C%&#x2267;(12/93).Nb%&#x2003;&#x2003;(2)

The present invention presents a high tensile strength cold rolled steel sheet having excellent formability, impact resistance and strain age hardening characteristics, and the production thereof. As a specific means, a slab having a composition which contains, by mass %, 0.15% or less of C, 0.02% or less of Al, and 0.0050 to 0.0250% of N at N/Al of 0.3 or higher, and has N in a solid solution state at 0.0010% or more, is first hot rolled at the finish rolling delivery-side temperature of 800&#xb0; C. or above, and is subsequently coiled at the coiling temperature of 750&#xb0; C. or below to prepare a hot rolled plate. Then, after cold rolling, the hot rolled plate is continuously cooled at a temperature from the recrystallization temperature to 900&#xb0; C. at a holding time of 10 to 120 seconds, and is cooled by primary cooling in which the hot rolled plate is cooled to 500&#xb0; C. or below at a cooling rate of 10 to 300&#xb0; C./s, and furthermore if necessary, by secondary cooling in which a residence time is 300 seconds or less in a temperature range of the primary cooling stopping temperature or below and 350&#xb0; C. or higher. Provided is a steel sheet containing a ferritic phase having an average crystal grain size of 10 &#x3bc;m or less at an area ratio of 50% or more, and if necessary, a martensitic phase at an area ratio of 3% or more as a second phase.

High tensile strength cold rolled steel sheet having excellent strain age hardening characteristics and the production thereof

The present invention presents a high tensile strength cold rolled steel sheet having excellent formability, impact resistance and strain age hardening characteristics, and the production thereof. As a specific means, a slab having a composition which contains, by mass %, 0.15% or less of C, 0.02% or less of Al, and 0.0050 to 0.0250% of N at N/Al of 0.3 or higher, and has N in a solid solution state at 0.0010% or more, is first hot rolled at the finish rolling delivery-side temperature of 800&deg; C. or above, and is subsequently coiled at the coiling temperature of 750&deg; C. or below to prepare a hot rolled plate. Then, after cold rolling, the hot rolled plate is continuously cooled at a temperature from the recrystallization temperature to 900&deg; C. at a holding time of 10 to 120 seconds, and is cooled by primary cooling in which the hot rolled plate is cooled to 500&deg; C. or below at a cooling rate of 10 to 300&deg; C./s, and furthermore if necessary, by secondary cooling in which a residence time is 300 seconds or less in a temperature range of the primary cooling stopping temperature or below and 350&deg; C. or higher. Provided is a steel sheet containing a ferritic phase having an average crystal grain size of 10 &mgr;m or less at an area ratio of 50% or more, and if necessary, a martensitic phase at an area ratio of 3% or more as a second phase.

High tensile cold-rolled steel sheet having excellent strain aging hardening properties

The present invention provides a cold-rolled sheet exhibiting superior strain-aging hardenability which is suitable for use in automobile bodies, and a method for manufacturing the same. In particular, a slab including, by mass, not more than 0.15% carbon, not more than 0.02% Al, and 0.0050% to 0.0250% nitrogen in which Si&plus;Mn/5&plus;10P is adjusted to less than 0.44 and the ratio N/Al is adjusted to not less than 0.3 is hot-rolled at a finish-rolling delivery temperature FDT of not less than 800&deg; C., and then coiled at a temperature of not more than 650&deg; C. Next, after cold-rolling, continuous-annealing at a temperature between the recrystallization temperature and 950&deg; C., primary cooling for cooling to a temperature zone of not more than 500&deg; C., and overaging in the temperature zone of 350&deg; C. to 450&deg; C. for a retention time of not more than 30 seconds are performed to prepare a steel sheet containing not less than 0.0010% of solute nitrogen and having a structure in which the ferrite phase with the grain size of not more than 15 &mgr;m is included at a ratio of not less than 90%, the remainder of the structure being the pearlite phase. The resulting steel sheet has superior strain-aging hardenability in which the tensile strength is less than 440 MPa and the yield ratio is less than 70%.

Cold-rolled steel sheet having excellent strain aging hardening properties and method for producing the same

The present invention provides a high tensile cold-rolled steel sheet having superior ductility, strain age-hardening characteristics, and crash resistance properties, and also provides a manufacturing method therefor. As a particular means, a thin cold-rolled steel sheet containing 0.05% to 0.30% of C, 0.4% to 2.0% of Si, 0.7% to 3.0% of Mn, 0.08% or less of P, 0.02% or less of Al, and 0.0050% to 0.0250% of N on a mass % basis is manufactured in which N/Al is 0.3 or more. This thin cold-rolled steel sheet is heated to a temperature between (an Ac transformation point) and (an Ac transformation point&plus;50&deg; C.), is cooled at a cooling rate of 5 to 150&deg; C./second in the range of at least 600 to 500&deg; C., and is held in the temperature range of 350 to 500&deg; C. This steel sheet has superior ductility, strain age-hardening characteristics having a &Dgr;TS of 50 MPa or more, and crash resistance properties.

High tensile cold-rolled steel sheet excellent in ductility and in strain aging hardening properties, and method for producing the same

This invention can form a sufficiently internal oxide layer in a surface layer portion of an iron matrix of a steel sheet by hot rolling a base steel and subjecting to a heat treatment at a temperature range of 650-950&deg; C. in an atmosphere substantially not causing reduction while being adhered with a black skin scale irrespectively of a chemical steel composition or production history, or even when a radiation type heating of a radial tube or the like is used in a recrystallization annealing before a hot dipping treatment, and hence excellent hot-dipping property and conversion treating property can be given to a steel sheet for hot dipping.

Methods of producing steel plate, hot-dip steel plate and alloyed hot-dip steel plate

The invention provides a thin high-strength hot-rolled steel sheet with a thickness of not more than 3.5 mm which has excellent stretch flangeability and high uniformity in both shape and mechanical properties of the steel sheet, as well as a method of producing the hot-rolled steel sheet. A slab containing C: 0.05-0.30 wt %, Si: 0.03-1.0 wt %, Mn: 1.5-3.5 wt %, P: not more than 0.02 wt %, S: not more than 0.005 wt %, Al: not more than 0.150 wt %, N: not more than 0.0200 wt %, and one or two of Nb: 0.003-0.20 wt % and Ti: 0.005-0.20 wt % is heated at a temperature of not higher than 1200&deg; C. The slab is hot-rolled at a finish rolling end temperature of not lower than 800&deg; C., preferably at a finish rolling start temperature of 950-1050&deg; C. A hot-rolled sheet is started to be cooled within two seconds after the end of the rolling, and then continuously cooled down to a coiling temperature at a cooling rate of 20-150&deg; C./sec. The hot-rolled sheet is coiled at a temperature of 300-550&deg; C., preferably in excess of 400&deg; C. A fine bainite structure is obtained in which the mean grain size is not greater than 3.0 &mgr;m, the aspect ratio is not more than 1.5, and preferably the maximum size of the major axis is not greater than 10 &mgr;m.

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

A hot rolled steel sheet comprises ultrafine ferrite grains as a main phase and fine second phase particles. The ferrite grains have an average grain size of not less than 2 &mgr;m but less than 4 &mgr;m. The second phase has an average particle size of not more than 8 &mgr;m and in not less than 80% of the second phase, the spacing of the second phase particle with the closest second phase particle is not less than the second phase particle size. The steel sheet has an ultrafine grain structure, superior mechanical characteristics, reduced anisotropy in its mechanical characteristics and high formability. A process for producing the steel sheet is also disclosed.

Hot rolled steel sheet having an ultrafine grain structure and process for producing steel sheet

The invention provides a can steel sheet having satisfactory surface appearance and having workability, appearance property after working and high yield that can meet demands on complicated can forming, and a manufacturing process thereof. To be more specific, according to the invention, a slab having a composition containing, in weight %, C: more than 0.005% and equal to or less than 0.1%, Mn: 0.05-1.0% is subjected to hot-rolling at a finishing temperature of 800 to 1000&deg; C., to coiling at 500 to 750&deg; C., to cold-rolling, followed by continuous annealing at a recrystallization temperature or higher and 800&deg; C. or lower, and then to box annealing at a temperature higher than 500&deg; C. and equal to or lower than 600&deg; C. for 1 hr or longer. The steel sheet has preferably a structure containing ferrite as a principle phase and having a mean grain diameter of 10 &mgr;m or less and further containing 0.1-1% by weight of pearlite grains each having a grain diameter of 0.5-3 &mgr;m. To obtain satisfactory surface appearance, it is preferable that the steel contains: Ti: 0.015-0.10%, Al: 0.001-0.01%, and a total of 0.0005-0.01% of one or two members of Ca, REM, and S&minus;5&times;((32/40)Ca&plus;(32/140)REM) of 0.0014% or less.

Steel sheet for can and manufacturing method thereof

At least both ends of a sheet bar in the length direction, which is obtained by roughly rolling a steel slab including 0.1 wt % or less of C, 0.5 wt % or less of Si, 1.0 wt % or less of Mn, 0.1 wt % or less of P, 0.05 wt % or less of S, 0.20 wt % or less of Al, and 0.015 wt % or less of N, are heated so that the temperature at both ends of the sheet bar in the length direction is 15&deg; C. or more higher than the temperature of the remainder of the sheet bar. The rolling finish temperature is Ar,&plus;20&deg; C. to Ar,&plus;100&deg; C. in both end portions of the sheet bar in the length direction, and Ar,&plus;10&deg; C. to Ar,&plus;60&deg; C. in the remainder, and the rolling finish temperature in the both end portions in the length direction is 10&deg; C. or more higher than that of the remainder, so that a steel strip after cold rolling and annealing has r values within &plusmn;0.3 of the average r value, and &Dgr;r within &plusmn;0.2 of the average &Dgr;r in the region of 95% or more of each of the total length and total width of the steel strip.

Method of producing can steel strip

Steel sheet for double wound pipe and method of producing the pipe

A method of producing a steel sheet useful for making cans. The method steps include hot-rolling a slab consisting of about 0.0005 to 0.01 wt % C, about 0.001 to 0.04 wt % N (the total of C and N is at least about 0.008 wt %), about 0.05 to 2.0 wt % Mn, about 0.005 wt % or less Al, about 0.01 wt % or less O at a finish rolling temperature within a temperature range of about the Ar.sub.3 point to about 950.degree. C., coiling the rolled material at a temperature range of about 400 to 600.degree. C., cold rolling the material, continuously annealing the material at a temperature higher than the recrystallization temperature, and then temper-rolling the material. The steel sheet exhibits good workability during can making and which can be formed into a can having high strength.

Method of producing high-strength steel sheet used for can

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Chiba, Japan

Akio Tosaka