A continuous-cast slab is provided where central porosity is reduced by surly crushing the slab. A method and apparatus of manufacturing the slab is also provided. The continuous-cast slab having horizontally symmetrical granular equiaxed crystals at least in the center in the thickness direction includes a first reduction dent and a second reduction dent that further dents from the bottom surface of the first reduction dent and is narrower than the first reduction dent at least on one long side surface. Such a configuration can makes it possible to achieve the continuous-cast slab of no more than 2.510.sup.4 cm.sup.3/g in a maximum porosity volume while segregation is reduced.

The billet rolling mill comprises two rolls for shaping a blank, each shaping roll being provided with at least one rolling tool and being rotated about an axis of rotation by a drive motor, and a manipulator subassembly for moving the blank with respect to the shaping rolls. The manipulator subassembly comprises a clamp gripping the blank and a carriage moving the clamp at least along a direction of rolling of the blank. The manipulator subassembly comprises a linear motor moving the carriage along the direction of rolling. The direction of rolling is perpendicular to the axis of rotation of the rolling tool. The linear motor is configured for accelerating the blank and selectively exerting on the blank, either a tensile force, to extract the blank from a gap defined between the rolling tools, or a braking force, to limit a speed of ejection of the blank.

The billet rolling mill comprises two rolls for shaping a blank, each shaping roll being provided with at least one rolling tool and being rotated about an axis of rotation by a drive motor, and a manipulator subassembly for moving the blank with respect to the shaping rolls. The manipulator subassembly comprises a clamp gripping the blank and a carriage moving the clamp at least along a direction of rolling of the blank. The manipulator subassembly comprises a linear motor moving the carriage along the direction of rolling. The direction of rolling is perpendicular to the axis of rotation of the rolling tool. The linear motor is configured for accelerating the blank and selectively exerting on the blank, either a tensile force, to extract the blank from a gap defined between the rolling tools, or a braking force, to limit a speed of ejection of the blank.

A device and a method for producing a continuous strip-shaped composite material. For this purpose, a base material, which is produced using at least one casting machine as a continuous strand, in particular made of steel, and providing at least one cladding material, which is unwound in the form of at least one metal strip by a coil unwinding unit are provided. Subsequently, a slab which has formed by solidification from the strand produced by the casting machine and the metal strip unwound by the coil unwinding unit, in the hot state are brought together, wherein the materials, which are moved in the direction toward one another, formed from the slab and the unwound metal strip are hot rolled, so that a single continuous strip-shaped composite material is thus produced by roll cladding. The base material is continuously cast in the vertical direction in the casting direction.

A steel pipe for line pipe has a composition of, in mass %: C: 0.02 to 0.11%; Si: 0.05 to 1.0%; Mn: 0.30 to 2.5%; P: up to 0.030%; S: up to 0.006%; Cr: 0.05 to 0.36%; Mo: 0.02 to 0.33%; V: 0.02 to 0.20%; Ti: 0.001 to 0.010%; Al: 0.001 to 0.100%; N: up to 0.008%; Ca: 0.0005 to 0.0040%; and other elements and satisfies Cr+Mo+V0.40, the chemical symbols in the equation substituted by the content of the corresponding element in mass %. The pipe contains tempered martensite and/or tempered bainite and further contains ferrite in at least one of a portion between a steel pipe outer surface and a depth of 1 mm from the outer surface, and a portion between a steel pipe inner surface and a depth of 1 mm from the inner surface.

When a zone surrounded by a grain boundary that is measured to be 5.0 or more by an EBSD analysis is assumed to be a grain, and when a K value is a value obtained by multiplying an average value of Image Qualities in a grain by 10.sup.3, a Y value is an average crystal misorientation () in the grain, a metallic phase 1 is a metallic phase the K value of which is less than 4.000, a metallic phase 2 is a metallic phase the K value of which is 4.000 or more and the Y value of which is 0.5 to 1.0, a metallic phase 3 is a metallic phase the K value of which is 4.000 or more and the Y value of which is less than 0.5, and a metallic phase 4 is a metallic phase that falls under none of metallic phases 1 to 3, there is provided a steel sheet that has a predetermined chemical composition and includes a microstructure including, in area percent, a metallic phase 1: 1.0% or more and less than 35.0%, a metallic phase 2: 30.0% or more and 80.0% or less, a metallic phase 3: 5.0% or more and 50.0% or less, and a metallic phase 4: 5.0% or less. The steel sheet has a strength as high as 590 MPa or more (further, 780 MPa or more) in terms of tensile strength and has an excellent hole-expansion property.

When a zone surrounded by a grain boundary that is measured to be 5.0 or more by an EBSD analysis is assumed to be a grain, and when a K value is a value obtained by multiplying an average value of Image Qualities in a grain by 10.sup.3, a Y value is an average crystal misorientation () in the grain, a metallic phase 1 is a metallic phase the K value of which is less than 4.000, a metallic phase 2 is a metallic phase the K value of which is 4.000 or more and the Y value of which is 0.5 to 1.0, a metallic phase 3 is a metallic phase the K value of which is 4.000 or more and the Y value of which is less than 0.5, and a metallic phase 4 is a metallic phase that falls under none of metallic phases 1 to 3, there is provided a steel sheet that has a predetermined chemical composition and includes a microstructure including, in area percent, a metallic phase 1: 1.0% or more and less than 35.0%, a metallic phase 2: 30.0% or more and 80.0% or less, a metallic phase 3: 5.0% or more and 50.0% or less, and a metallic phase 4: 5.0% or less. The steel sheet has a strength as high as 590 MPa or more (further, 780 MPa or more) in terms of tensile strength and has an excellent hole-expansion property.

Provided are an ultrathick steel material having excellent strength and low-temperature impact toughness for flanges and a method for manufacturing same. The steel material of the present disclosure comprises, by wt %, C: 0.05-0.2%, Si: 0.05-0.5%, Mn: 1.0-2.0%, Al: 0.005-0.1%, P: 0.01% or less, S: 0.015% or less, Nb: 0.001-0.07%, V: 0.001-0.3%, Ti: 0.001-0.03%, Cr: 0.01-0.3%, Mo: 0.01-0.12%, Cu: 0.01-0.6%, Ni: 0.05-1.0%, Ca: 0.0005-0.004%, and the balance of Fe and inevitable impurities, has Ceq satisfying the range of 0.35-0.55 as calculated by the following equation, has an average ferrite grain size of 25 m or less in the central portion thereof, and contains a microstructure including 5-30 area % of pearlite and the balance of ferrite.

The invention relates to a device (10) and to a method for producing a continuous strip-shaped composite material (11). A base material of metal, which is unwound in the form of a metal strip (13) by a first coil-unwinding apparatus (12), and at least one cladding material of metal, which is unwound in the form of a metal strip (15) by a second coil-unwinding apparatus (14), are provided. Then, the metal strips (13, 15) unwound by said coil-unwinding apparatuses (12, 14) are brought together in the hot state, wherein then the unwound metal strips (13, 15) brought toward each other are hot-rolled such that a single continuous strip-shaped composite material (11) is thus formed by roll cladding, said composite material consisting of the base material and the cladding material. Both the base material and the cladding material and the metal strips (13, 15) thereby unwound each consist of steel.

A method and a device for producing a continuous strip-shaped composite material. The device has at least one first casting machine, using which a continuous strand is produced, in particular from steel, at least one rolling stand, which is arranged in line with the first casting machine and downstream thereof. A fully solidified slab of the strand produced using the first casting machine can be hot rolled, and at least one second casting machine, using which a further continuous strand is produced from metal. Between the casting machines, on the one hand, and the rolling stand, on the other hand, a merging unit is arranged, by means of which the slabs can be moved in the direction toward each other in the hot state. The rolling stand is designed as a roll-cladding unit, by which a composite formed from the merged slabs can be hot rolled.