A seamless steel pipe of the present invention is a seamless steel pipe having a composition that includes, in mass %, C: 0.02 to 0.12%, Si: 0.010 to 1.00%, Mn: 0.10 to 2.00%, P: 0.050% or less, S: 0.004% or less, Al: 0.010 to 0.100%, Cu: 0.03 to 0.80%, Ni: 0.02 to 0.50%, Cr: 0.55 to 1.00%, Sb: 0.005 to 0.20%, and the balance Fe and incidental impurities, and satisfying the following formula (1),

1.7×Cu*+11×Cr*+3.8×Sb*≥13.5   (1), where Cu*, Cr*, and Sb* represent average concentrations of Cu, Cr, and Sb, respectively, in mass %, as measured in a region 0.5 to 2.0 mm away from an outer surface of the steel pipe, the seamless steel pipe having a yield strength of 230 MPa or more, and a tensile strength of 380 MPa or more.

An alloy material is provided that has a chemical composition consisting of, in mass %, C: 0.030% or less, Si: 0.01 to 1.0%, Mn: 0.01 to 2.0%, P: 0.030% or less, S: 0.0050% or less, Cr: 28.0 to 40.0%, Ni: 32.0 to 55.0%, sol. Al: 0.010 to 0.30%, N: more than 0.30% and not more than 0.000214×Ni.sup.2−0.03012×Ni+0.00215×Cr.sup.2−0.08567×Cr+1.927, O: 0.010% or less, Mo: 0 to 6.0%, W: 0 to 12.0%, Ca: 0 to 0.010%, Mg: 0 to 0.010%, V: 0 to 0.50%, Ti: 0 to 0.50%, Nb: 0 to 0.50%, Co: 0 to 2.0%, Cu: 0 to 2.0%, REM: 0 to 0.10%, and the balance: Fe and impurities, and in which Fn1=Mo+(½)W is 1.0 to 6.0, and a yield strength at a 0.2% proof stress is 1103 MPa or more.

An austenitic stainless steel material is provided that has high creep strength even when used at an average operation temperature of more than 600 to 750° C. after welding with higher heat input, and furthermore, has excellent stress relaxation cracking resistance even after use for a long time period at the average operation temperature after welding with higher heat input. The steel material has a chemical composition which consists of, in mass %, C: 0.030% or less, Si: 1.50% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.0300% or less, Cr: 15.00 to 25.00%, Ni: 8.00 to 20.00%, N: 0.050 to 0.250%, Nb: 0.10 to 1.00%, Mo: 0.05 to 5.00%, and B: 0.0005 to 0.0100%, with the balance being Fe and impurities, and a ratio of the dissolved N amount (mass %) with respect to the content of N (mass %) in the steel material is 0.40 to 0.90.

Provided is a forming device that forms a heated metal material, the forming device including: a die that performs quench forming by coming into contact with the metal material; a cooling unit that is provided inside the die to cool the die; and a temperature sensor that detects a temperature of the die, in which the cooling unit adjusts a cooling capacity on the basis of a detection result of the temperature sensor.

Provided is a steel used for chassis parts, etc. of an automobile and, more specifically, to a hot rolled steel plate for an electric resistance welded steel pipe, which shows an excellent weldability in electric resistance welding, and a manufacturing method thereof.

Provided are a hot-rolled steel sheet for an electric resistance welded steel pipe and a method for manufacturing the same, an electric resistance welded steel pipe and a method for manufacturing the same, a line pipe, and a building structure. The hot-rolled steel sheet has a chemical composition containing, by mass %, C: 0.030% or more and 0.20% or less, Si: 0.02% or more and 1.0% or less, Mn: 0.40% or more and 3.0% or less, P: 0.050% or less, S: 0.020% or less, N: 0.0070% or more and 0.10% or less, and Al: 0.005% or more and 0.080% or less, the balance being Fe and incidental impurities, in which N dissolved in steel is contained in an amount of 0.0010% or more and 0.090% or less, and letting a sheet thickness be t, a steel microstructure at a ½t position has an average grain size of 20.0 μm or less.

Special usage steels, particularly those intended to be in contact with combustion fumes, are described. Tubular components produced based on such steels are also described. The steel both is resistant to the coking phenomenon and has improved mechanical performances. The steel contains in percentage by weight from 0.08 to 0.15% carbon, from 0.4 to 0.8% manganese, from 1.5 to 2.5% silicon, from 0.5 to 2% copper, from 8 to 10% chrome, from 0.5 to 3% nickel, from 0.01 to 0.07% nitrogen, from 0.8 to 1.1% molybdenum, with the remainder being iron and impurities.

An electric resistance welded steel pipe, and a method for manufacturing the same are provided. An electric resistance welded steel pipe has a welded portion that includes a heat-affected zone having a steel microstructure principally including a bainitic ferrite phase and/or a bainite phase. The steel microstructure at half the wall thickness includes a bainitic ferrite phase and/or a bainite phase in a total area ratio of 90% or more. In the steel microstructure located 1 mm in the wall thickness direction, the bainitic ferrite phase and/or the bainite phase has an average grain size of 20 μm or less. The average grain size of the bainitic ferrite phase and/or the bainite phase located 1 mm in the wall thickness direction is 0.5 times or more and 2 times or less the average grain size of the bainitic ferrite phase and/or the bainite phase at half the wall thickness.

A method for manufacturing of steel tube from a long steel strip, including providing a length of steel strip material to the process, forming a tube of the steel strip material, welding the formed tube in longitudinal direction, giving the tube a heat treatment wherein the mentioned steps are performed in one continuous in-line manufacturing line and the heat treatment includes a heating regime such that in successive cross-sections of the tube a microstructure is achieved which holds at least 50 vol % austenite and a cooling trajectory to re-introduce ferrite, and/or bainite in desired volume fractions.

The invention relates to a method for producing a component from a medium manganese flat steel product having 4 to less than 10 wt. % Mn, 0.0005 to 0.9 wt. % C, 0.02 to 10 wt. % Al, the remainder iron, including unavoidable steel-accompanying elements, and having a TRIP effect at room temperature. In order to produce a component, which is distinguished by very high strengths and an increased residual strain and re-shaping capacity, the flat steel product, according to the invention, is re-shaped by at least one re-shaping step to form a component and, before and/or during and/or after the at least one re-shaping step, the flat steel product is cooled down to a temperature of the flat steel product of less than room temperature to −196° C. The invention further relates to a component produced by this method and to a use for said components.