Abstract: Abrasion resistant steel plates with excellent low-temperature toughness and hydrogen embrittlement resistance having a Brinell hardness of 401 or more, and methods for manufacturing such steel plates. The steel plates have a lath martensitic structure with an average grain size of not more than 20 ?m, and the steel plates include fine precipitates that are 50 nm or less in diameter and that have a density of 50 or more particles per 100 ?m2. Additionally, the steel plates include, by mass %, C: 0.20 to 0.30%, Si: 0.05 to 0.5%, Mn: 0.5 to 1.5%, Cr: 0.05 to 1.20%, Nb: 0.01 to 0.08%, B: 0.0005 to 0.003%, Al: 0.01 to 0.08%, N: 0.0005 to 0.008%, P: not more than 0.05%, S: not more than 0.005%, and O: not more than 0.008%, the balance being Fe and inevitable impurities.

Abstract: Provided is a steel structure for hydrogen gas such as a hydrogen storage tank or a hydrogen line pipe which achieves a lower fatigue crack propagation rate in a high-pressure hydrogen atmosphere than steels used in the related art and has high hydrogen embrittlement resistance. The steel structure for hydrogen gas, which has high hydrogen embrittlement resistance in high-pressure hydrogen gas, has a steel microstructure including any one of 10% to 95% of bainite on an area-ratio basis, 10% to 95% of martensite on an area-ratio basis, and 10% to 95% of pearlite on an area-ratio basis, with the balance being substantially ferrite.

Abstract: A steel material includes: a composition containing, by mass, C: 0.05% to 0.60%, Si: 0.01% to 2.0%, Mn: 0.3% to 3.0%, P: 0.001% to 0.040%, S: 0.0001% to 0.010%, N: 0.0001% to 0.0060%, Al: 0.01% to 1.5%, one or more elements selected from Ti: 0.01% to 0.20%, Nb: 0.01% to 0.20%, and V: 0.01% or more and less than 0.05%, and one or more elements selected from B: 0.0001% to 0.01%, Mo: 0.005% to 2.0%, and Cr: 0.005% to 3.0%, with the balance being Fe and inevitable impurities; and a steel microstructure that includes 95% or more of tempered martensite on a volume fraction basis, that includes a precipitate having a diameter of 100 nm or less and including one or more elements selected from Ti, Nb, and V and one or more elements selected from carbon and nitrogen at a density of 50 particles/?m2 or more, and that includes prior austenite having a grain diameter of 3 ?m or more.

Abstract: The invention provides a high tensile strength steel material having a tensile strength of 600 MPa, which is excellent in delayed fracture resistance property, and a method of manufacturing the steel material. As means for this, a steel material contains, in mass percent, C of 0.02 to 0.25%, Si of 0.01 to 0.8%, Mn of 0.5 to 2.0%, Al of 0.005 to 0.1%, N of 0.0005 to 0.008%, P of 0.03% or less, and S of 0.03% or less. In addition, the steel material contains at least one element selected from Mo, Nb, V, and Ti, and contains at least one of Cu, Ni, Cr, W, B, Ca, REM and Mg, as needed. The remainder includes Fe and inevitable impurities. In addition, in the steel material, precipitates having an average grain size of 20 nm or less, which contains at least one of Mo, Nb, V and Ti, are contained in steel in the number of at least 5 per 250000 nm2, and a microstructure includes residual austenite in a volume fraction of 0.5 to 5%. When Ca to be added is specified to be 0.0010% to 0.

Abstract: High tensile strength steels that have both favorable delayed fracture resistance and a tensile strength of 600 MPa or higher and are suitably used in construction machinery, tanks, penstocks, and pipelines, as well as methods for manufacturing such steels are provided. The safety index of delayed fracture resistance (%) is 100×(X1/X0), where X0: reduction of area of a specimen substantially free from diffusible hydrogen, and X1: reduction of area of a specimen containing diffusible hydrogen.

Abstract: High tensile strength steels that have both favorable delayed fracture resistance and a tensile strength of 600 MPa or higher and are suitably used in construction machinery, tanks, penstocks, and pipelines, as well as methods for manufacturing such steels are provided. The safety index of delayed fracture resistance (%) is 100×(X1/X0), where X0: reduction of area of a specimen substantially free from diffusible hydrogen, and X1: reduction of area of a specimen containing diffusible hydrogen.

Abstract: The present invention provides a method for manufacturing high tensile strength steel plate having 570 MPa (N/mm2) or larger tensile strength and having also extremely superior balance of strength and toughness both before PWHT and after PWHT to that of the conventional steel plates, by specifically specifying the temperature-rising rate at the plate thickness center portion of a quenched and tempered material during tempering, and to be concrete, the method has the steps of: casting a steel consisting essentially of 0.02 to 0.18% C, 0.05 to 0.5% Si, 0.5 to 2.0% Mn, 0.005 to 0.1% Al, 0.0005 to 0.008% N, 0.03% or less P, 0.

Abstract: The present invention provides a method for manufacturing high tensile strength steel plate having 570 MPa (N/mm2) or larger tensile strength and having also extremely superior balance of strength and toughness both before PWHT and after PWHT to that of the conventional steel plates, by specifically specifying the temperature-rising rate at the plate thickness center portion of a quenched and tempered material during tempering, and to be concrete, the method has the steps of: casting a steel consisting essentially of 0.02 to 0.18% C, 0.05 to 0.5% Si, 0.5 to 2.0% Mn, 0.005 to 0.1% Al, 0.0005 to 0.008% N, 0.03% or less P, 0.

Abstract: The invention provides a high tensile strength steel material having a tensile strength of 600 MPa, which is excellent in delayed fracture resistance property, and a method of manufacturing the steel material. As means for this, a steel material contains, in mass percent, C of 0.02 to 0.25%, Si of 0.01 to 0.8%, Mn of 0.5 to 2.0%, Al of 0.005 to 0.1%, N of 0.0005 to 0.008%, P of 0.03% or less, and S of 0.03% or less. In addition, the steel material contains at least one element selected from Mo, Nb, V, and Ti, and contains at least one of Cu, Ni, Cr, W, B, Ca, REM and Mg, as needed. The remainder includes Fe and inevitable impurities. In addition, in the steel material, precipitates having an average grain size of 20 nm or less, which contains at least one of Mo, Nb, V and Ti, are contained in steel in the number of at least 5 per 250000 nm2, and a microstructure includes residual austenite in a volume fraction of 0.5 to 5%. When Ca to be added is specified to be 0.0010% to 0.