Nippon Steel Corporation

Takuya Takayama

Hiroshi Harada

Masashi Sakamoto

Yui Ito

Keita Ikeda

Yasuhiro Ito

Kenji Yamada

Mai Nagano

Satoshi Hironaka

Kanoko Yamamoto

An objective of the present invention is to provide a steel sheet having a high strength which can provide excellent appearance quality. The steel sheet has a chemical composition including, in mass %, C: more than 0.030% to 0.145%, Si: 0% to 0.500%, Mn: 0.50% to 2.50%, P: 0% to 0.100%, S: 0% to 0.020%, Al: 0% to 1.000% or less, N: 0% to 0.0100%, and the like, wherein a metal micro-structures consisting of 70 to 95% of ferrite in volume fraction and 5 to 30% of hard phases in volume fraction, and a value X1 obtained by dividing a standard deviation of average Mn concentrations in a rolling direction at ¼ sheet-thickness positions in a sheet thickness direction by an average Mn concentration at the ¼ sheet-thickness positions is 0.025 or less.

Steel sheet

Using an apparatus for manufacturing a thin steel sheet including the followings which are arranged in order: a continuous casting machine () for a thin slab having a slab thickness of 70 mm to 120 mm at a lower end of a mold; a holding furnace () that is configured to maintain a temperature of a cast slab () and/or heats the cast slab (); and a rolling stand () by which finish rolling is performed, the casting speed of the thin slab is set to 4 to 7 m/min, the slab () is reduced at a rolling reduction of 30% or more by the reduction roll () after solidification is completed and when a center temperature of the slab is 1300° C. or higher, and the slab () is held at a temperature of 1150° C. or higher and 1300° C. or lower for five minutes or longer in the holding furnace ().

Apparatus for manufacturing thin steel sheet and method for manufacturing thin steel sheet

A continuous casting facility used for thin slab casting has a mold for casting molten steel, an immersion nozzle that supplies the molten steel into the mold, and an electromagnetic stirring device capable of providing a swirl flow at a molten steel surface in the mold, and a thickness D(mm) of a copper plate of a long side wall, a thickness T (mm) of a steel piece, a frequency f (Hz) of the electromagnetic stirring device, electric conductivity &#x3c3; (S/m) of the molten steel, and electric conductivity &#x3c3;(S/m) of the copper plate of the long side wall are adjusted to satisfy the following formulae (1)-a and (1)-b:&#x3c;&#x221a;(2/&#x3c3;&#x3c9;&#x3bc;)&#x2003;&#x2003;(1)-a&#x221a;(1/2&#x3c3;&#x3c9;&#x3bc;)&#x3c;&#x2003;&#x2003;(1)-b,

Continuous casting facility and continuous casting method used for thin slab casting for steel

The device for controlling a flow in a mold in thin-slab casting of steel has a thickness on the short side of the meniscus portion of 150 mm or less and a casting width of 2 m or less and includes a DC magnetic field generation unit and an immersion nozzle having a slit formed at the bottom so that the slit leads to the bottom of the discharge hole and opens outside, the discharge hole and the slit are present in the DC magnetic field zone, and the magnetic flux density B (T) in the DC magnetic field zone and the distance L (m) from the lower end of the immersion nozzle to the lower end of the core satisfy Formulae (1) and (2) described below:0.35&#x2264;1.0&#x2003;&#x2003;Formula (1)&#x2265;0.06 m&#x2003;&#x2003;Formula (2)

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Tokyo, Japan

Takuya Takayama