A primary object of this invention is to provide a continuous casting method by which a slab of excellent internal quality can be obtained even if the casting speed is changed. In this invention, upon continuous casting with two pairs of the reduction rolls arranged along a casting direction and support rolls arranged between the reduction rolls, when a casting speed is reduced compared to a state where combination of reduction with reduction rolls at a first stage on an unsolidified portion of the slab and reduction with reduction rolls at a second stage on a solidified portion thereof is employed, the combination is switched to combination of reduction with the reduction rolls at the first stage on a portion of the slab at an end of solidification and the reduction with the reduction rolls at the second stage on the solidified portion thereof.

In a steel sheet pile according to the present invention, a carbon equivalent CE.sub.N is 0.260 to 0.500, a structure includes a ferrite, a pearlite, a Widmansttten ferrite, and a precipitate, the precipitate is one or both of Nb carbonitride and V carbonitride, a total number density of the precipitate is 0.10 to 0.30 pieces/m.sup.2, a total area ratio of the ferrite and the pearlite is 70% or more, an area ratio of the Widmansttten ferrite is 1% or more, an average grain size of the ferrite and the pearlite is 10 to 80 m, and a yield strength is 460 MPa or more.

A cold-rolled steel plate having favorable heat spot resistance and favorable antiwear performance is provided. The cold-rolled steel plate has a chemical composition containing, on the basis of percent by mass, C from 0.03 to 0.12%, Si from 0 to 1.0%, Mn from 0.2 to 0.8%, P at 0.03% or less, S at 0.03% or less, and Al at 0.05% or less. The chemical composition further contains any one of Nb from 0.03 to 0.4% and V from 0.03 to 0.3%. These elements satisfy 5*C %Si %+Mn %1.5*Al %<1 within the aforementioned range of the corresponding content. A residue is formed of Fe and unavoidable impurities. An average diameter of particles of carbides containing any one of Nb, V and Ti as precipitates is from 20 to 100 nm. In this way, the chemical composition is regulated and the precipitates are dispersed finely and uniformly, thereby enhancing heat spot resistance and antiwear performance.

A titanium material for hot rolling 1 includes a titanium cast piece 3, and titanium sheets 4 that are welded to faces corresponding to rolling surfaces 3a of the titanium cast piece 3. The titanium cast piece 3 and the titanium sheets 4 have the same kind of chemical composition. The titanium material for hot rolling 1 can maintain good surface properties after hot rolling even if a slabbing process or a finishing process is omitted.

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.

A process may be used to produce a composite material in a rolling plant. The process may involve providing a first workpiece and a second workpiece, which workpieces are configured in the form of a temporary composite. The process may further involve producing a planar connection between the first and second workpieces in the temporary composite by prerolling. Still further, the process may involve rolling, in particular hot rolling, the temporary composite to form the composite material after the planar connection has been produced by prerolling. The process may also involve heating the temporary composite before and/or after the prerolling.

A steel sheet for heat treatment having a chemical composition including, by mass %: C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn; 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; Cr: 0 to 1.0%; Ni: 0 to 2.0%; Cu: 0 to 1.0%; Mo: 0 to 1.0%; V: 0 to 1.0%; Ca: 0 to 0.01%; Al: 0 to 1.0%; Nb: 0 to 1.0%; REM: 0 to 0.1%; and the balance: Fe and impurities, wherein a maximum height roughness Rz on a surface of the steel sheet is 3.0 to 10.0 ?m, and a number density of carbide being present in the steel sheet and having circle-equivalent diameters of 0.1 ?m or larger is 8.0?10.sup.3/mm.sup.2 or lower.

A method for preparing a high-performance tantalum target, a high-performance target prepared by the method, and a use of the high-performance target. The method for preparing the high-performance tantalum target comprises: firstly, preparing a tantalum ingot into a forging blank by a method of cold forging in conjunction with hot forging; then, rolling the forging blank by a hot rolling method; and finally, performing leveling, and performing discharging, milling and surface treatment according to a size of a finished product, so as to obtain the tantalum target. The tantalum target prepared by the method has uniform crystallization, with a grain size between 50 m and 120 m. A texture component where a texture (110) dominants in the thickness direction of the target is obtained. A total proportion of three textures (111), (110) and (100) is between 40% and 50%, ensuring a consistent sputtering rate of the tantalum target during use.

Electric resistance welded steel pipe securing the high strength and high toughness demanded from oil well pipe in recent years. The metal structure in a region having a width of 0.5 mm in both the thickness directions from a reference point, when using a point defined as a point of the thickness in the thickness direction from the surface in the base material part of the steel pipe as the reference point, consists of polygonal ferrite: 10 area % or less and a balance: bainitic ferrite. The thickness is 15 mm or more.

The pickling loss when a hot-rolled steel sheet having a predetermined chemical composition is annealed at 1000 C. for 30 seconds in a nitrogen atmosphere and then immersed in a solution of 7% HCl at 80 C. for 60 seconds is in a range of 40 g/m.sup.2 or more and 100 g/m.sup.2 or less. A hot-rolled steel sheet for production of a non-oriented electrical steel sheet with not only excellent magnetic properties such as iron loss and magnetic flux density but also excellent recyclability and steel sheet surface appearance can thus be obtained.