165 results about "Delayed fracture" patented technology

The cold heading wire rod comprises the following components in percentage by mass: 0.20%-0.26% of C, less than or equal to 0.35% of Si, 1.2%-1.6% of Mn, less than or equal to 0.02% of P, less than or equal to 0.005% of S, 0.04%-0.14% of V, 0.02%-0.10% of Nb, less than or equal to 0.2% of Cr, less than or equal to 0.1% of Ni, 0.02%-0.06% of Al and the balance of Fe and inevitable impurities, the V + Nb is greater than or equal to 0.09%, the C / 4 + Si + Mn / 2 + Cr / 2 + 2Ni is greater than or equal to 1.1% and less than or equal to 1.3%, the F + P is greater than or equal to 95%, the F grain size is greater than or equal to grade 12, the longitudinal pearlite strip The steel plate prepared by the method does not crack at 1 / 5 of a hot rolling state, can meet the requirements of a user on strength and plasticity of cold heading forming after 5-50% of cold drawing deformation, and can meet the requirements of a 10.9-grade high-strength fastener on fatigue and delayed fracture resistance at the same time.

The invention discloses high-strength bolt steel and a preparation method thereof, and the high-strength bolt steel alloy comprises the following components in percentage by mass: 0.35%-0.45% of C, 0.03%-0.80% of O, 0.05%-1.20% of RE, 0.02%-0.70% of Si, 0.80%-1.20% of Cr, 0.05%-0.85% of Ti, 0.01%-0.05% of Nb, 0.02%-0.35% of V, 0.001%-0.1% of B, less than or equal to 0.005% of S, less than or equal to 0.015% of P and the balance of Fe. According to the high-strength bolt steel and the preparation method thereof, the obdurability and the hydrogen-induced delayed fracture resistance of the material are synchronously improved through dispersion strengthening of the high-number-density nanometer oxide, the high-strength bolt steel can be used for producing 15.8-grade high-strength bolts with the tensile strength being 1500 MPa or above, nanometer oxide particles serve as a dispersion strengthening phase and a hydrogen trap, and the high-strength bolt steel can be used for producing high-strength bolts with the tensile strength being 1500 MPa or above. While the strength and the toughness of the material are improved, the fatigue performance and the delayed fracture resistance of the material are greatly improved.

The invention relates to a delayed fracture resistant non-quenched and tempered 14.9-grade high-strength cold heading steel wire rod and a preparation method thereof. The wire rod comprises the following chemical components: 0.33%-0.55% of C, less than or equal to 0.10% of Si, 1.5%-2.3% of Mn, 0.4%-0.6% of Cr, 0-0.04% of Nb, 0-0.1% of V, 0-0.1% of Ti, 0.004%-0.008% of B, more than or equal to 0.020% of Als, less than or equal to 0.040% of Alt, less than or equal to 0.015% of P, less than or equal to 0.010% of S, less than or equal to 1ppm of H and the balance of Fe and impurity elements. Fine control is adopted in the steelmaking process, the H content is strictly controlled to be lower than 1 ppm, a hydrogen trap is manufactured by adding microalloy elements such as Nb, V and Ti, and the delayed fracture resistance is improved; the air cooling speed of the rolled hot-rolled wire rod is precisely controlled, so that the structure of the hot-rolled wire rod is lath bainite, and high strength is realized by utilizing a medium-carbon bainite structure; the finished wire rod has high strength, high plasticity, excellent low-temperature impact toughness and good delayed fracture resistance.

Provided is a steel sheet that simultaneously achieves a strength of TS: 1310 MPa or more and excellent delayed fracture resistance. The steel sheet has a defined chemical composition and a complex structure consisting mainly of martensite and bainite, where carbides in the grains of martensite and bainite are 5% or more and 25% or less, the average circle equivalent diameter of carbides is 10 nm or more and 80 nm or less, and the particle size distribution of carbides satisfies Expression (1).

The application belongs to the technical field of cold heading steel production, and particularly relates to a cold heading steel wire rod and a preparation method and application thereof. The mass percentage of each chemical component of the cold heading steel wire rod is shown in the specification. The cold heading steel wire rod provided by the application has good corrosion resistance, a weathering index I greater than or equal to 7, and good formability without cold heading cracking, and is suitable for the design and material selection of steel structures with strict requirements on the resistance to delayed fracture. The bolt prepared by the application has high strength, and the strength grade can be higher than or equal to 12.9.

The utility model relates to a device for testing hydrogen-induced delayed fracture of high-strength steel, which comprises an upper pressing cake, a lower pressing cake, an upper pressing block, a lower pressing block and a screw rod, a plurality of clamping grooves are uniformly distributed on the upper pressing block along the circumferential direction, the upper pressing block and the lower pressing block have the same structure, and the upper pressing cake and the lower pressing cake are connected on the screw rod in a penetrating manner; the upper pressing block and the lower pressing block are also connected to the threaded rod in a penetrating mode and are symmetrically arranged between the upper pressing cake and the lower pressing cake, a plurality of hydrogen-induced delayed fracture samples are arranged on corresponding clamping grooves of the upper pressing block and the lower pressing block respectively, the upper pressing cake and the upper pressing block can be locked and fixed to the threaded rod through nuts, and the lower pressing cake and the lower pressing block can be locked and fixed to the threaded rod through nuts. The hydrogen-induced delayed fracture experiment requirement of the high-strength steel with the pressure ranging from 1000 MPa to 2 GPa can be met, and reliable analysis data can be obtained when the hydrogen-induced delayed fracture experiment is carried out on the high-strength steel. Positioning and fixing holes are not required to be punched during sample preparation, a plurality of samples can be prepared by one clamp, and a bending test of a plurality of metal test pieces is allowed to be performed in one test.

The invention relates to a method for evaluating the hydrogen-induced delayed fracture risk of high-strength steel. The method comprises the following steps: stretching a notch sample to be measured at a strain rate in a range of 3.0 * 10 <-6 >-6.0 * 10 <-5 > s <-1 > until fracture so as to obtain a fracture stress sigma H, and stretching a reference notch sample at a strain rate in a range of 6.0 * 10 <-2 >-10.0 s <-1 > until fracture so as to obtain a reference fracture stress sigma 0; and evaluating the hydrogen-induced delayed fracture risk by using a hydrogen embrittlement risk index HERI = (sigma0-sigmaH) / sigma0 * 100%. According to the evaluation method, the influence of hydrogen in the high-strength steel on the performance can be accurately reflected, the test process is simplified, and rapid inspection on a production site is facilitated. The invention also relates to a method for determining the available dew point range of an austenitizing process for producing a hot-stamped product with an aluminum-silicon coating, which is resistant to hydrogen-induced delayed fracture.

Provided is a method for producing a high-strength hot-dip galvanized steel sheet which has excellent LME cracking resistance while ensuring the appearance quality of the steel sheet, and in which the deterioration of delayed fracture resistance characteristics due to hydrogen embrittlement is suppressed. This method for producing a hot-dip galvanized steel sheet is a method in which a steel sheet containing a prescribed amount of Si is subjected to oxidation treatment, then reduction annealing is performed, and then hot-dip galvanizing is performed. The oxidation treatment is carried out in an atmosphere containing N2 and 500 ppm by volume or more of O2 at a temperature of 500-800 DEG C (inclusive). The reduction annealing is performed by means of a first reduction annealing of a front stage, in which the reduction annealing is held at a predetermined temperature for a predetermined time in an atmosphere containing 5.0-25 vol% of hydrogen gas with a dew point of-45 DEG C or more and + 20 DEG C or less and a remainder of N2, and a second reduction annealing of a rear stage, in which the reduction annealing is held at a predetermined temperature for a predetermined time in an atmosphere containing 5.0-25 vol% of hydrogen gas with a dew point of-45 DEG C or more and + 20 DEG C or less and the remainder of N2. The steel sheet is held at a predetermined temperature for a predetermined time in an atmosphere having a dew point of-10 DEG C to + 20 DEG C inclusive and containing 2.0 vol% to 8.0 vol% inclusive of hydrogen and a remainder of N2. In addition, the hydrogen gas concentration is adjusted so that the hydrogen gas concentration in the first reduction annealing in the front stage is higher than the hydrogen gas concentration in the second reduction annealing in the rear stage.

Provided is a method for evaluating the delayed fracture characteristics of a metal material, the method being capable of accurately evaluating delayed fracture characteristics caused by hydrogen entering the inside of a metal material due to atmospheric corrosion in which a chloride is a dominant factor of corrosion.　This method for evaluating the delayed fracture characteristics of a metal material carries out, at least one time, a process involving: a chloride adhesion step (A) in which droplets of a chloride-containing aqueous solution are adhered to an evaluation surface of a metal material so as to achieve a predetermined adhesion amount of a chloride; and a corrosion step (B) in which a cycle having a predetermined drying step (b1), a wetting step (b2), a transition step (b3), and a transition step (b4) is regarded as one cycle, and the cycle is performed at least one time, wherein, regarding the distribution of the droplets on the evaluation surface of the metal material in at least the first chloride adhesion step (A), the average contact area of the droplets is at least 0.1 mm2 and less than 3.0 mm2, the area ratio of the total contact area of the droplets to the area of the evaluation surface is 40-80%, and the standard deviation of the contact area of the droplets is at most 3.0 mm2.

A method for manufacturing high-strength, hydrogen-embrittlement-resistant bolts based on microsphere shot peening, and the bolts themselves, are disclosed. The manufacturing method includes: S1, cold heading and thread rolling of alloy structural steel billets to obtain bolt forming parts; S2, surface cleaning of the bolt forming parts, followed by overall surface peening with microspheres driven by high-pressure air; after overall peening, targeted strengthening peening treatment is performed on stress concentration areas such as thread roots, undercut grooves, and flange transition corners to obtain reinforced bolt parts; S3, the reinforced bolt parts are cleaned, dried, and phosphated to obtain finished bolt parts. This design, through a "overall + targeted" composite microsphere shot peening strategy, introduces a uniform residual compressive stress field and a micron-level fine-grained plastic deformation layer on the bolt surface, forming a thicker strengthening layer in stress concentration areas, significantly improving the fatigue strength and delayed fracture resistance of high-strength bolts, while ensuring uniform surface roughness and stable assembly friction coefficient.

The present invention provides a steel sheet having a tensile strength of 1310 MPa or more and excellent press formability in a steel having a martensite structure as a main body and excellent delayed fracture resistance. The steel sheet is characterized by having a composition consisting of, in mass%, C: 0.12% to 0.40%, Si: 1.5% or less, Mn: 1.7% or less, P: 0.05% or less, S: 0.010% or less, sol. Al: 1.00% or less, N: 0.010% or less, Ti: 0.002% to 0.080%, and B: 0.0002% to 0.0050%, with the remainder being Fe and inevitable impurities, and a metal structure in which the area ratio of a martensite to the entire structure is 95% or more, the length L S of sub-block boundaries in the martensite is 0.5 to 2.0 μm, and the ratio L B / L S of the length L B of the sub-block boundaries to the length L of the block boundaries satisfies a prescribed formula (1), and the tensile strength is 1310 MPa or more.

The invention provides a hydrogen-induced delayed fracture resistant ultrahigh-strength steel plate and a preparation method thereof, and belongs to the technical field of metal materials. The hydrogen induced delayed fracture resistant type ultrahigh strength steel plate comprises the following components in percentage by mass: 0.18 to 0.25 percent of C, 2.0 to 2.8 percent of Mn, 0.3 to 1.0 percent of Si, 3.0 to 6.0 percent of Al, 0.001 to 0.015 percent of Ce, 0.05 to 0.25 percent of Mo, 0.02 to 0.10 percent of Ti, less than or equal to 0.01 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.004 percent of N and the balance of Fe and inevitable impurities. The steel plate with ultrahigh strength, high elongation and excellent hydrogen-induced delayed fracture resistance can be stably produced through rare earth microalloying and precise structure regulation and control in cooperation with a proper process.

Provided is a high-strength steel sheet having a tensile strength of 1180 MPa or more, excellent bendability and delayed fracture resistance, and a wide optimal gap range for bending and forming a sheared end surface. The high-strength steel sheet comprises, in mass%, 0.030 to 0.500% of C, 0.50 to 2.50% of Si, 1.50 to 5.00% of Mn, 0.100% or less of P, 0.0200% or less of S, 1.000% or less of Al, 0.0100% or less of N, 0.0100% or less of O, and 0.005 to 0.100% of Nb, with the remainder comprising Fe and unavoidable impurities, and has a martensite content of 70% or more, a retained austenite content of 3 to 20%, and a total of a ferrite content and a bainitic ferrite content of 10% or less, the instability index k of the retained austenite is less than 6.1, and the instability index d of the retained austenite at the initial stage of processing is less than 5.7.

The invention discloses a high-strength bolt, a steel material and a preparation method of the high-strength bolt, and relates to the technical field of alloy smelting, and the high-strength bolt is characterized by comprising the following components in percentage by mass: 0.18%-0.22% of C, 0.08%-0.12% of Nb, 0.02%-0.05% of Al, 0.004%-0.02% of Ti, 0.05%-0.08% of V, 0.0001%-0.002% of S, 0.00%-0.05% of Cu, 0.70%-0.90% of Mn, 0.20%-0.30% of Si, 0.90%-1.10% of Cr, 0.30%-0.50% of Ni, 0.15%-0.30% of Mo and the balance of Fe. The high-strength steel material has the advantages that the components of the high-strength steel material are optimized, an alloy structure composed of fine and uniform martensite, nanoscale precipitated phases and low internal stress is obtained, and the effects of improving the strength and the delayed fracture resistance are achieved.

The present invention provides a resistance spot welding method that can alleviate residual stress during resistance spot welding and can suppress occurrence of delayed fracture. In the resistance spot welding method, a pair of plate-shaped members having a hat-shaped cross section with a top plate portion and a pair of vertical wall portions extending from both ends of the top plate portion are overlapped, and resistance spot welding is performed on the pair of plate-shaped members. In the resistance spot welding method, there are included a step of detecting a contact load required for mutual contact of a portion where a gap between the pair of vertical wall portions becomes the largest due to a part tolerance of the plate-shaped members after the top plate portions of the pair of plate-shaped members are overlapped and resistance spot welding is performed on the top plate portions; and a step of setting a pressing force of a pair of electrodes that sandwich the pair of vertical wall portions during resistance spot welding on the overlapped pair of vertical wall portions in such a manner that the pressing force of the electrodes is greater than half of the contact load and smaller than the contact load, and performing resistance spot welding on the pair of vertical wall portions with the pressing force of the electrodes.

The invention relates to a 10.9-grade high-Si non-quenched and tempered steel wire rod for a fastener and a manufacturing method of the 10.9-grade high-Si non-quenched and tempered steel wire rod. The 10.9-grade high-Si non-quenched and tempered steel wire rod for the fastener comprises the following chemical components in percentage by weight: 0.08 to 0.12 percent of C, 1.45 to 1.90 percent of Si, 1.50 to 1.80 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.0005 to 0.0030 percent of B, 0.01 to 0.03 percent of Ti, 0.010 to 0.050 percent of Als, 0.02 to 0.04 percent of Nb and the balance of iron and trace impurities. The manufacturing process of the hot-rolled wire rod comprises the following steps: preparing raw materials according to chemical components, and sequentially carrying out converter / electric furnace-LF refining-vacuum degassing-casting-wire rod controlled rolling-wire rod controlled cooling. The steel wire rod produced by the method can obtain a uniform bainite structure at a relatively large range of cooling speed, and has the characteristics of uniform structure, good plasticity and excellent cleaning performance, and a fastener produced by drawing with relatively small area reduction rate, relatively small cold heading deformation and aging subsequently has the characteristics of stable mechanical property and excellent delayed fracture resistance; and the requirement of a 10.9-level fastener is met.

The application relates to the technical field of denture welding processing, in particular to a flexible support fastening component for denture root part in denture welding processing, which comprises a support table, an arc-shaped groove for loading a denture root part component is arranged on the inner side of the support table, a support assembly is arranged below the support table, and a flexible support fastener for fixing the denture root part component is arranged above the support table. The flexible support fastener comprises a support seat, a sliding seat is slidably arranged in the support seat, a positioning shaft with a conical top is detachably arranged on the top side of the sliding seat, and a return spring is fixed to one side of the sliding seat. The flexible support fastening component for the denture root part in the denture welding processing can pull the end part of the e-bar, effectively eliminates welding residual stress, prevents post-welding deformation and delayed fracture, the pulling force can effectively eliminate the internal stress of the e-bar welding position caused by high welding temperature, deformation and cracking of the e-bar caused by stress concentration are avoided, and the structural stability of the e-bar after welding is improved.

The present application relates to the technical field of metallurgical materials, and particularly relates to a rare earth micro-alloyed cold heading steel wire rod for 14.9-grade ultra-high strength fasteners and a preparation method thereof. Through reasonable alloy component design, synergistic micro-alloying of rare earth elements and precise control of process parameters, the plasticity and delayed fracture resistance of the fastener are significantly improved while meeting the ultra-high strength requirement of the 14.9-grade fastener, and the stability of rare earth addition and the industrial applicability of the process are realized. After the fastener prepared by the present application is subjected to a quenching and tempering heat treatment, the tensile strength is greater than or equal to 1400 MPa, the yield strength is greater than or equal to 1260 MPa, the elongation after fracture is greater than or equal to 9%, the reduction of area is greater than or equal to 48%, the core hardness is HRC 44-49, and the mechanical performance requirement of the 14.9-grade fastener is fully met.

Provided is a high-strength steel sheet having excellent member strength, stretch flangeability, bendability, and delayed fracture resistance under atmospheric corrosion and in a coated state. The steel sheet has a prescribed component composition, microstructure and the like, the average value [tau q] of the plastic deformation initiation stress [tau q] measured by nanoindentation at a position 1 / 4 of the sheet thickness of the steel sheet is 2.50-4.10 GPa, the standard deviation [sigma q] of the tau q is 0.30 GPa or less, and the average value [tau q] of the plastic deformation initiation stress [tau q] is 0.30 GPa or less. When [tau s] is the average value of the plastic deformation start stress [tau] s measured by the nanoindentation method at a position 10 [mu] m from the surface of the steel sheet, the ratio of measurement points less than 0.85 * [tau s] is 25.0% or less.

Provided are a steel sheet and a member, having high strength and high delayed fracture resistance, and methods for manufacturing the steel sheet and the member. The steel sheet has a specific chemical composition and a microstructure in which the area fraction of martensite is 95% to 100%, with the balance being one or more of bainite, ferrite, and retained austenite. In the steel sheet, prior-austenite grains have an average grain size of 18 μm or less, 90 mass % or more of the total content of Nb and Ti contained is present as a carbonitride having an equivalent circular diameter of 100 nm or more, and a Nb carbonitride and a Ti carbonitride, having an equivalent circular diameter of 1.0 μm or more, are present at a rate of 800 pieces / mm2 or less in total. The steel sheet has a tensile strength of 1310 MPa or more.

The invention provides a high-strength high-toughness hydrogen-induced delayed fracture-resistant oil casing material, and belongs to the field of oil exploitation equipment. The contents of Mn, Mo and V are optimized, and other components are matched, so that the material has good hydrogen-induced delayed fracture resistance while having high strength and high toughness. Experimental results show that the mechanical properties of the casing material provided by the invention are as follows: the tensile strength is not less than 1260Mpa, the yield strength is not less than 1200Mpa, the longitudinal impact energy at 0 DEG C is not less than 100J, and the transverse impact energy is not less than 70J; a notch constant-load delayed fracture test is carried out, the notch constant-load critical fracture stress ratio n is not smaller than 0.8, and fracture does not occur after more than 100 h.

The present invention contains 0.090-0.390% of C, 0.25-2.00% of Si, 2.00-3.70% of Mn, 0.100% or less of P, 0.0200% or less of S, 1.000% or less of Al, 0.0100% or less of N, and 0.0100% or less of O. At a position 1 / 4 through the sheet thickness, tempered martensite (M) is included at a proportion of 80% or more, fresh martensite (FM) is included at a proportion of less than 8%, ferrite (F) and bainite (B) are included at a total proportion of 15% or less, and retained austenite is included at a proportion of 15% or less. At a position located at the interface with respect to a zinc plating layer, tempered M and FM are included at a total proportion of 40% or less, F and B are included at a total proportion of 60% or more, and oxide particles (average aspect ratio of 1.2-6.0 and average long diameter of 0.10-0.70 µm) are included at a proportion of 2-18%. As a result, a high-strength zinc-coated steel sheet having excellent impact resistance, stretch flange properties, bendability, and shear disturbance stability for delayed fracture resistance can be obtained.

The present invention provides steel plates and components having a tensile strength (TS) of 980 MPa or more, and excellent formability, impact resistance, chemical conversion treatability, and delayed fracture resistance, as well as methods for manufacturing the same. It has a specific chemical composition, and the steel sheet surface coverage rate of Si-based oxides is 1% or less, At the 1 / 4 position of the plate thickness, the area fraction of ferrite is 3% or more and 30% or less, The area fraction of tempered martensite is 60% or more and 94% or less, The volume fraction of retained austenite is 3% or more and 15% or less, The steel sheet has a structure in which the area fraction of the remaining structure is 10% or less, and the ferrite has low-Mn ferrite in which the Mn concentration is less than 0.85 times the Mn content of the steel sheet, and high-Mn ferrite in which the Mn concentration is 0.85 times or more the Mn content of the steel sheet, and the proportion of the high-Mn ferrite in the ferrite is 20% or more and 90% or less in area fraction.

Provided is a high-strength hot-rolled steel sheet having excellent delayed fracture resistance and excellent flatness in addition to high stretch flangeability while maintaining a high strength with a tensile strength of 1310 MPa or above.　The high-strength hot-rolled steel sheet has: a predetermined component composition; a steel structure in which the area ratio of tempered martensite is 80% to 100%, the area ratio of bainite is 0% to 20%, the total area ratio of the remaining structure is 0% to 10.0%, and the number density of metastable carbides having a major-axis length of 10 nm or more is 5 × 1010 / mm3; a steepness of 2.0% or less; a tensile strength of 1310 MPa or more; and high stretch flangeability and excellent delayed fracture resistance.

The application provides an anti-hydrogen embrittlement stainless steel and a preparation method and application thereof, and relates to the technical field of special stainless steel.The anti-hydrogen embrittlement stainless steel provided by the application contains the following elements in percentage by mass: 0.05-0.08% of C, 7-9% of Mn, 13-16% of Cr, 8-10% of Ni, 0.8-1% of Cu, 2-3% of Co, 0.2-0.4% of N, 1-2% of RE, 0.01-0.05% of impurities and the balance of Fe; the RE contains at least one of La, Ce and Y. The multiple metal elements and non-metal elements are used to cooperate and jointly act, the Mn and N can stabilize the austenite structure, can improve the structural strength and toughness of the anti-hydrogen embrittlement stainless steel, and can make the stainless steel have the anti-hydrogen embrittlement capability, and the anti-delayed fracture performance is improved.

In the method for evaluating the delayed fracture characteristics of a metallic material, on the end face, a solution holding material containing a solution with a pH of 3.5 or more and containing a chloride is disposed on the end face of the metallic material, and the state of maintaining the deliquescence humidity of the chloride is continued to corrode the end face.

This invention provides a steel plate with a tensile strength of 1310 MPa or higher, which achieves excellent compressibility in a steel primarily composed of martensite with excellent resistance to delayed fracture. The steel plate is characterized by having the following composition and microstructure, wherein the composition, by mass%, contains C: 0.12%–0.40%, Si: less than 1.5%, Mn: greater than 1.7% and less than 3.5%, P: less than 0.05%, S: less than 0.010%, sol.Al: less than 1.00%, N: less than 0.010%, Ti: 0.002%–0.080%, and B: 0.0002%–0.0050%, with the remainder being Fe and unavoidable impurities. The martensite in the microstructure has an area fraction of 85% or more relative to the overall microstructure, and the length L of the subplate boundaries in this martensite is... S Length L of the lath boundary B The ratio of L S / L B It satisfies the specified formula (1) and has a tensile strength of 1310 MPa or more.

Provided are a galvanized steel sheet that is exceptional in terms of delayed fracture resistance characteristics of a stretch flange processed part, and a method for producing the galvanized steel sheet. This galvanized steel sheet has a base steel sheet and a zinc-based plating layer formed on the surface of the base steel sheet, wherein the galvanized steel sheet is characterized in that: the base steel sheet has a prescribed component composition; at a position amounting to one-fourth of the thickness of the base steel sheet a prescribed structure is present, the total coverage of residual austenite and fresh martensite at the old austenite grain boundaries is 20-45%, and the carbon concentration in the residual austenite that covers the old austenite grain boundaries is less than 0.60 mass%; and the tensile strength is 1470 MPa or greater.

The purpose of the present invention, configured in view of circumstances, is to provide a thick-walled seamless steel pipe that has a high martensite fraction and high strength, as well as has both excellent heat crack resistance and delayed fracture resistance, the seamless steel pipe being highly suitable for use as a member of pressure vessels etc. Another purpose of the present invention is to provide: a method for manufacturing the seamless steel pipe; a pressure vessel; a pressure vessel for hydrogen gas; and a method for manufacturing the pressure vessel or the pressure vessel for hydrogen gas.　The seamless steel pipe contains a specific composition that satisfies formula (1), where the manganese segregation ratio on the inner surface of the steel pipe is less than 1.50, the metal structure has a martensite area fraction of 85% or more, and the cross-sectional hardness is at least 250 HV but less than 480 HV.　Formula (1): [P] ≤ 0.042 − 0.002[C] − 0.024[Mn] − 0.001[Mo] − 0.001[Cr] − 0.002[Ni] (in formula (1), [element] represents the content (mass%) of the element indicated in the brackets).

A thin, high-strength steel sheet with a tensile strength of 1180 MPa or more is provided, exhibiting excellent malleability, excellent delayed fracture resistance from a base steel sheet, and excellent delayed fracture resistance from a projection weld, along with a method for its manufacture. The thin, high-strength steel sheet has a chemical composition containing C, Si, Mn, P, S, Al, and N, with the remainder consisting of Fe and unavoidable impurities, and a complex structure containing ferrite, quenched martensite, and bainite, wherein a volume fraction of the total quenched martensite and bainite contains five or more carbides with a particle size of 0.1 µm or more.0 µm or less in a grain with respect to the total quenched martensite and bainite is 85% or more, whereas the mass % of C and the mass % of Mn in a region of 20 µm or less in the thickness direction from a surface of the steel sheet is 20% or less with respect to the mass % of C and the mass % of Mn in a region of 100 µm or more and 200 µm or less from the surface of the steel sheet.