Abstract: A round bar tensile test specimen for a sulfide stress corrosion cracking test of a steel, the specimen including a parallel section, a shoulder section, and a grip section. A sectional shape of the shoulder section being formed by a curve having two or more radii of curvature. A radius of curvature R1 (mm) of a portion of the curve adjacent to the parallel section being 15 mm or more, and the radius of curvature R1 (mm) satisfying (0.22??119)?R1?100 in terms of load stress ? (MPa) of the sulfide stress corrosion cracking test. A length X1 (mm) of the portion of the curve having the radius of curvature R1 in a longitudinal direction of the test specimen satisfying X1??{(r/8)×(R1?r2/4)}. Additionally, other radii of curvature of the curve being smaller than the radius of curvature R1.

Abstract: A high-strength seamless stainless steel pipe for oil country tubular goods that is excellent in terms of hot workability, sulfide stress cracking resistance, and corrosion resistance, and a method for manufacturing the steel pipe. The steel pipe has a chemical composition containing Cr and Ni so that the relationship Cr/Ni?5.3 is satisfied. A microstructure of the steel pipe includes mainly a tempered martensite phase. Additionally, a surface layer microstructure of the steel pipe includes a phase which looks white when subjected to etching with a Vilella etching solution, the phase having a thickness in the wall thickness direction from the outer surface of the pipe of 10 ?m or more and 100 ?m or less and dispersing in the outer surface of the pipe in an amount of 50% or more in terms of area fraction.

Abstract: A method for manufacturing a heavy wall steel pipe includes a cooling step in which a steel pipe, with a wall thickness of ½ inch or more, that has been heated to the gamma range is dipped in water while supporting and rotating the steel pipe about the axis of pipe, an axial stream which is a water flow in the direction of axis of pipe is applied to the inside surface of the steel pipe under rotation in the water, and an impinging stream which is a water flow impinging on the outer surface of the pipe is applied to the outer surface of the steel pipe under rotation in the water.

Abstract: A method of manufacturing a high-strength stainless steel pipe includes forming a steel pipe having a predetermined size, the steel having a composition comprising by mass % 0.005 to 0.05% C, 0.05 to 1.0% Si, 0.2 to 1.8% Mn, 0.03% or less P, 0.005% or less S, 14 to 20% Cr, 1.5 to 10% Ni, 1 to 5% Mo, 0.5% or less V, 0.15% or less N, 0.01% or less O, 0.002 to 0.1% Al, and Fe and unavoidable impurities as a balance; applying a quenching treatment two times or more to the steel pipe where the steel pipe is quenched by reheating to a temperature of 750° C. or above and cooling to a temperature of 100° C. or below at a cooling rate equal to or higher than an air-cooling rate; and applying a tempering treatment where the steel pipe is tempered at a temperature of 700° C. or below.

Abstract: A seamless steel tube contains 0.15% to 0.50% C, 0.1% to 1.0% Si, 0.3% to 1.0% Mn, 0.015% or less P, 0.005% or less S, 0.01% to 0.1% Al, 0.01% or less N, 0.1% to 1.7% Cr, 0.4% to 1.1% Mo, 0.01% to 0.12% V, 0.01% to 0.08% Nb, and 0.0005% to 0.003% B or further contains 0.03% to 1.0% Cu on a mass basis and has a microstructure which has a composition containing 0.40% or more solute Mo and a tempered martensite phase that is a main phase and which contains prior-austenite grains with a grain size number of 8.5 or more and 0.06% by mass or more of a dispersed M2C-type precipitate with substantially a particulate shape.

Abstract: It is difficult in the related art to realize not only a decrease in material variability due to non-uniform microstructure distribution in the wall thickness direction of a pipe body but also the maintenance of satisfactory productivity of the whole heat treatment line at the same time. A method includes determining in advance whether or not the pipe body is made of a steel grade having an Ms point lower than 200° C.; leaving the pipe body of a steel grade having an Ms point lower than 200° C. additionally at room temperature (it is preferable to be transported to a holding bed 6 and left) until the temperature difference between the portion having the highest temperature and the portion having the lowest temperature in a cross section in a direction at a right angle to the pipe axis becomes less than 2.0° C.

Abstract: A steel pipe is formed by performing pipe making of a raw material having a composition containing C: 0.05% or less, Si: 0.50% or less, Mn: 0.20% to 1.80%, P: 0.030% or less, S: 0.005% or less, Cr: 14.0% to 18.0%, Ni: 5.0% to 8.0%, Mo: 1.5% to 3.5%, Cu: 0.5% to 3.5%, Al: 0.10% or less, Nb: more than 0.20% and 0.50% or less, V: 0.20% or less, N: 0.15% or less, and O: 0.010% or less, on a percent by mass basis, wherein Cr+0.65Ni+0.6Mo+0.55Cu?20C?18.5 and Cr+Mo+0.3Si?43.3C?0.4Mn?Ni?0.3Cu?9N?11 are satisfied and subjecting the resulting steel pipe to a quenching treatment to heat to a temperature higher than or equal to the Ac3 transformation temperature and, subsequently, cool to a temperature of 100° C. or lower at a cooling rate higher than or equal to the air cooling rate and a tempering treatment to temper at a temperature lower than or equal to the Ac1 transformation temperature.

Abstract: A method of manufacturing a high strength stainless steel tube or pipe includes using an online heat treatment equipment line for a seamless steel tube or pipe in which a heating furnace for quenching, equipment for quenching, and a tempering furnace are used in the lower process of a rolling line, arranging cooling facilities capable of cooling a heat treated steel tube or pipe to a temperature of 20° C. or lower between the equipment for quenching and the tempering furnace, and cooling the heat treated steel tube or pipe to a temperature of 20° C. or lower before a tempering treatment is performed.

Abstract: A high-strength stainless steel seamless tube or pipe has excellent corrosion resistance, where excellent carbon dioxide gas corrosion resistance in high-temperature environments containing CO2 and Cl? at high temperatures up to 200° C. and excellent sulfide stress cracking resistance and excellent sulfide stress corrosion cracking resistance at corrosive environments further containing H2S are ensured based on a composition of C: 0.05% or less, Si: 0.5% or less, Mn: 0.15% to 1.0%, P: 0.030% or less, S: 0.005% or less, Cr: 15.5% to 17.5%, Ni: 3.0% to 6.0%, Mo: 1.5% to 5.0%, Cu: 4.0% or less, W: 0.1% to 2.5%, and N: 0.15% or less such that ?5.9×(7.82+27C?0.91Si+0.21Mn?0.9Cr+Ni?1.1Mo+0.2Cu+11N)?13.0 is satisfied.

Abstract: A method for manufacturing a heavy wall steel pipe includes a cooling step in which a steel pipe, with a wall thickness of ½ inch or more, that has been heated to the gamma range is dipped in water while supporting and rotating the steel pipe about the axis of pipe, an axial stream which is a water flow in the direction of axis of pipe is applied to the inside surface of the steel pipe under rotation in the water, and an impinging stream which is a water flow impinging on the outer surface of the pipe is applied to the outer surface of the steel pipe under rotation in the water.

Abstract: A pipe having chemical composition contains, by mass %, C: 0.05% or less, Si: 0.5% or less, Mn: 0.15% or more and 1.0% or less, Cr: 13.5% or more and 15.4% or less, Ni: 3.5% or more and 6.0% or less, Mo: 1.5% or more and 5.0% or less, Cu: 3.5% or less, W: 2.5% or less, and N: 0.15% or less so that the relationship ?5.9×(7.82+27C?0.91 Si+0.21Mn?0.9Cr+Ni?1.1Mo?0.55W+0.2Cu+11N)?13.0 is satisfied.

Abstract: A steel material has a chemical composition containing, by mass %, C: 0.005% or more and 0.06% or less, Si: 0.05% or more and 0.5% or less, Mn: 0.2% or more and 1.8% or less, Cr: 15.5% or more and 18.0% or less, Ni: 1.5% or more and 5.0% or less, V: 0.02% or more and 0.2% or less, Al: 0.002% or more and 0.05% or less, N: 0.01% or more and 0.15% or less, O: 0.006% or less, and further contains one or more of Mo: 1.0% or more and 3.5% or less, W: 3.0% or less and Cu: 3.5% or less, in which Cr+0.65Ni+0.60Mo+0.30W+0.55Cu-20C?19.5 and Cr+Mo+0.50W+0.30Si-43.5C-0.4Mn—Ni-0.3Cu-9N?11.5 are satisfied, is made into a seamless steel tube by performing heating and hot rolling.

Abstract: A seamless steel pipe has a composition containing, by mass %, C: 0.15 to 0.50%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.0%, P: 0.015% or less, S: 0.005% or less, Al: 0.01 to 0.1%, N: 0.01% or less, Cr: 0.1 to 1.7%, Mo: 0.40 to 1.1%, V: 0.01 to 0.12%, Nb: 0.01 to 0.08%, Ti: 0.03% or less, and B: 0.0005 to 0.003%, a structure composed of a tempered martensite phase as a main phase with a prior austenite grain size of 8.5 or more, and a hardness distribution in which in four portions 90° apart from each other in the circumferential direction, hardness is 295 HV10 or less in any one of an inner surface-side region at 2.54 to 3.81 mm from the inner surface of the pipe, an outer surface side-region at the same distance from the outer surface of the pipe, and a center of the thickness.

Abstract: A heavy wall and high strength seamless steel pipe having high sour resistance is provided. In particular, a quenching and tempering treatment is conducted to adjust the yield strength to be higher than 450 MPa and adjust the Vickers hardness HV5 that can be measured at an outermost side or an innermost side of the pipe under a 5 kgf load (test load: 49 N) to be 250 HV5 or less.

Abstract: There is provided a high-strength steel tube having excellent chemical conversion treatability and excellent formability and a method for manufacturing the high-strength steel tube. More specifically, in processing a mother steel sheet containing, on the basis of mass percent, 0.05% or more C, more than 0.7% Si, and 0.8% or more Mn into a pipe shape, the sum total of absolute circumferential surface strains each applied in individual process steps of the processing is 5% or more as nominal strain. A welded steel tube thus manufactured using a steel sheet even containing more than 0.7% Si can have excellent chemical conversion treatability without mechanical grinding or chemical pickling treatment.

Abstract: A seamless steel tube contains 0.15% to 0.50% C, 0.1% to 1.0% Si, 0.3% to 1.0% Mn, 0.015% or less P, 0.005% or less S, 0.01% to 0.1% Al, 0.01% or less N, 0.1% to 1.7% Cr, 0.4% to 1.1% Mo, 0.01% to 0.12% V, 0.01% to 0.08% Nb, and 0.0005% to 0.003% B or further contains 0.03% to 1.0% Cu on a mass basis and has a microstructure which has a composition containing 0.40% or more solute Mo and a tempered martensite phase that is a main phase and which contains prior-austenite grains with a grain size number of 8.5 or more and 0.06% by mass or more of a dispersed M2C-type precipitate with substantially a particulate shape.

Abstract: In a method for processing a high-strength member having a high Si content of more than 0.7% by mass, a high-strength steel material containing, on the basis of mass percent, 0.05% or more C, more than 0.7% Si, and 0.8% or more Mn is subjected to processing controlled such that the sum total of absolute surface strains in a predetermined direction each applied in individual process steps of the processing is 5% or more as nominal strain to form a member having a predetermined shape. The member, even containing more than 0.7% Si, can have markedly improved chemical conversion treatability without mechanical grinding or chemical pickling treatment.

Abstract: A steel pipe blank having a composition containing 0.5% or less C and 85% or more Fe in terms of mass percent is heated, and stretch-reducing is then performed so that the diameter decrease ratio is 15% or more and the rolling finishing temperature is (the Ar3 transformation point?10)° C. or lower. Consequently, a structure in which the ratio of X-ray diffraction intensity obtained from the plane in which the <100> direction of crystal grains is preferentially oriented parallel to the circumference direction and the <011> direction of crystal grains is preferentially oriented parallel to the rolling direction of the steel pipe to that obtained for a three-dimensionally randomly oriented sample is 3.0 or more is formed, and the r-value is increased, thereby improving the magnetic properties of the steel pipe.

Abstract: A method of manufacturing a high strength steel sheet. The method including casting a slab consisting essentially of 0.05 to 0.15% C, 0.5% or less Si, 1.00 to 2.00% Mn, 0.09% or less P, 0.01% or less S, 0.005% or less N, 0.01 to 0.1% Sol.Al, and a balance of Fe and inevitable impurities; hot-rolling the slab at a temperature of the Ar3 point or more; beginning cooling the hot-rolled steel sheet within 2 seconds after completing the hot-rolling at a temperature of from 750° C. to 600° C. at a cooling rate of 150° C./s or more; holding the cooled steel sheet at a temperature between 750° C. and 600° C. for 2 to 15 seconds; cooling the steel sheet at a cooling rate of 20° C./s or more; and coiling the cooled steel sheet at a temperature of 400° C. or less.

Abstract: A steel pipe with good magnetic properties and a method of producing the same are proposed. Specific solutions are as follows. A steel pipe blank having a composition containing 0.5% or less C and 85% or more Fe in terms of mass percent is heated, and stretch-reducing is then performed so that the diameter decrease ratio is 15% or more and the rolling finishing temperature is (the Ar3 transformation point ?10)° C. or lower. Consequently, a structure in which the ratio of X-ray diffraction intensity obtained from the plane in which the <100> direction of crystal grains is preferentially oriented parallel to the circumference direction and the <011> direction of crystal grains is preferentially oriented parallel to the rolling direction of the steel pipe to that obtained for a three-dimensionally randomly oriented sample is 3.0 or more is formed, and the r-value is increased, thereby improving the magnetic properties of the steel pipe.