Provided is a wire rod having enhanced strength and impact toughness comprising, by wt %, carbon (C): 0.05% to 0.15%, silicon (Si): 0.2% or less, manganese (Mn): 3.0% to 4.0%, phosphorus (P): 0.020% or less, sulfur (5):0.020% or less, boron (B): 0.0010% to 0.0030%, titanium (Ti): 0.010% to 0.030%, nitrogen (N): 0.0050% or less, aluminum (Al): 0.010% to 0.050%, iron (Fe) as a residual component thereof, and other unavoidable impurities. A microstructure includes bainitic ferrite in an area fraction of 90% or more, and a martensite/austenite (M/A) constituent as a residual component thereof.

A steel product bent by heating to 600° C. or more, specifically a heat treated steel product having high strength and excellent chemical conversion coating ability which has scale with FeO content of 90% or more, having a thickness of 1 μm or less on the surface.

A steel product bent by heating to 600° C. or more, specifically a heat treated steel product having high strength and excellent chemical conversion coating ability which has scale with FeO content of 90% or more, having a thickness of 1 μm or less on the surface.

Manufacturing a cold-rolled steel plate by smelting a steel slab having the 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, Ti from 0.04 to 0.3%, and Al at 0.05% or less, with a residue being formed of Fe and unavoidable impurities, the chemical composition satisfying 5*C%-Si %+Mn %−1.5 *Al %<1, and an average diameter of particles of a Ti-based carbide as a precipitate is from 20 to 100 nm; heating the slab to 1200° C. or more and hot rolling, forming a hot-rolled steel plate; winding the hot-rolled steel plate from 500 to 700° C. to form a hot-rolled coil; and cold rolling or annealing and cold rolling the coil obtaining cross-sectional hardness from 200 to 400 HV.

Manufacturing a cold-rolled steel plate by smelting a steel slab having the 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, Ti from 0.04 to 0.3%, and Al at 0.05% or less, with a residue being formed of Fe and unavoidable impurities, the chemical composition satisfying 5*C%-Si %+Mn %−1.5 *Al %<1, and an average diameter of particles of a Ti-based carbide as a precipitate is from 20 to 100 nm; heating the slab to 1200° C. or more and hot rolling, forming a hot-rolled steel plate; winding the hot-rolled steel plate from 500 to 700° C. to form a hot-rolled coil; and cold rolling or annealing and cold rolling the coil obtaining cross-sectional hardness from 200 to 400 HV.

Disclosed is a Grade 550 MPa high temperature-resistant pipeline steel, the chemical elements, in mass percentage, being: 0.061%≦C≦0.120%, 1.70%≦Mn≦2.20%, 0.15%≦Mo≦0.39%, 0.15%≦Cu≦0.30%, 0.15%≦Ni≦0.50%, 0.035%≦Nb≦0.080%, 0.005%≦V≦0.054%, 0.005%≦Ti≦0.030%, 0.015%≦Al≦0.040%, 0.005%≦Ca≦0.035%, and the balance being Fe and unavoidable impurities. Also disclosed is a manufacturing method of the Grade 550 MPa high temperature-resistant pipeline steel, comprising the steps of: smelting, casting, slab heating, rough rolling, finish rolling, controlled cooling, and air cooling to room temperature. The pipeline steel has an excellent mechanical property under a high temperature.

Disclosed is a Grade 550 MPa high temperature-resistant pipeline steel, the chemical elements, in mass percentage, being: 0.061%≦C≦0.120%, 1.70%≦Mn≦2.20%, 0.15%≦Mo≦0.39%, 0.15%≦Cu≦0.30%, 0.15%≦Ni≦0.50%, 0.035%≦Nb≦0.080%, 0.005%≦V≦0.054%, 0.005%≦Ti≦0.030%, 0.015%≦Al≦0.040%, 0.005%≦Ca≦0.035%, and the balance being Fe and unavoidable impurities. Also disclosed is a manufacturing method of the Grade 550 MPa high temperature-resistant pipeline steel, comprising the steps of: smelting, casting, slab heating, rough rolling, finish rolling, controlled cooling, and air cooling to room temperature. The pipeline steel has an excellent mechanical property under a high temperature.

Provided is a titanium cast product made of commercially pure titanium, the titanium cast product being produced by electron-beam remelting or plasma arc melting, comprising: a melted and resolidified layer in a range of 1 mm or more in depth at a surface serving as a surface to be rolled, the melted and resolidified layer being obtained by adding one or more kinds of β stabilizer elements to the surface and melting and resolidifying the surface. An average value of β stabilizer element(s) concentration in a range of within 1 mm in depth is higher than β stabilizer element(s) concentration in a base material by, in mass %, equal to or more than 0.08 mass % and equal to or less than 1.50 mass %. As the material containing the β stabilizer element, powder, a chip, wire, or foil is used. As means for melting a surface layer, electron-beam heating and plasma arc heating are used.

A hot-rolled steel sheet for nitriding or a cold-rolled steel sheet for nitriding, in which a dislocation density within 50 μm in the sheet thickness direction from the surface is not less than 2.0 times nor more than 10.0 times as compared to a dislocation density at the position of ¼ in the sheet thickness direction; and a method of manufacturing the same. The manufacturing method comprises, on a hot-rolled steel sheet or a cold-rolled steel sheet, performing pickling, and then performing skin pass rolling under the condition that a reduction ratio is 0.5 to 5.0% and FIT, defined as a ratio of a line load F (kg/mm) of a rolling mill load divided by a sheet width of the steel sheet and a load T (kg/mm.sup.2) per unit area to be applied in the longitudinal direction of the steel sheet, is 8000 or more.

A hot-rolled steel sheet for nitriding or a cold-rolled steel sheet for nitriding, in which a dislocation density within 50 μm in the sheet thickness direction from the surface is not less than 2.0 times nor more than 10.0 times as compared to a dislocation density at the position of ¼ in the sheet thickness direction; and a method of manufacturing the same. The manufacturing method comprises, on a hot-rolled steel sheet or a cold-rolled steel sheet, performing pickling, and then performing skin pass rolling under the condition that a reduction ratio is 0.5 to 5.0% and FIT, defined as a ratio of a line load F (kg/mm) of a rolling mill load divided by a sheet width of the steel sheet and a load T (kg/mm.sup.2) per unit area to be applied in the longitudinal direction of the steel sheet, is 8000 or more.