Abstract: A high strength steel plate having excellent ammonia SCC resistance and low-temperature toughness for use in storage tanks used to contain liquefied gas in energy transport ships. The steel plate has a defined chemical composition, and has hardness properties such that, at a 0.5 mm depth position from the surface of the steel plate, average hardness is 230HV0.1 or less and hardness variation is 30HV0.1 or less, a maximum value of hardness in the thickness direction is at a position 1.0 mm or more and ¼ or less of the thickness of the steel plate from the surface of the steel plate, and hardness variation in the thickness direction is 70HV1 or less. Further, the steel plate has a metallic microstructure where, at a 0.5 mm depth position from the surface of the steel plate, a volume fraction of bainitic microstructure is 90% or more.

Abstract: A high strength steel plate having excellent ammonia SCC resistance and low-temperature toughness for use in storage tanks and the like used to contain liquefied gas in energy transport ships. The steel plate has a defined chemical composition, in particular including one or more of Cu: 0.01% to 0.5 %, Cr: 0.01% to 1.0%, Sb: 0.01% to 0.50%, or Sn: 0.01% to 0.50%, and the chemical composition satisfies a defined relationship of the Cu, Cr, Sb, and Sn content. Further, a hardness property at a 1.0 mm depth position from the surface of the steel plate is 300 HV or less, and the metallic structure at a ½ thickness position of the steel plate has a volume fraction of bainitic microstructure of 20% or more and a total volume fraction of ferritic microstructure and bainitic microstructure of 60% or more.

Abstract: A steel material of the disclosure has a chemical composition containing, in mass %: 0.03% to 0.3% C; 0.03% to 1.0% Si; 0.1% to 2.0% Mn; 0.003% to 0.03% P; 0.005% or less S; 0.005% to 0.1% Al; 0.005% to 0.5% Cu; 0.01% to 0.5% Sb; and 0.005% to 0.5% Ni, with a balance being Fe and incidental impurities. Thus, the steel material has excellent alcohol-induced pitting corrosion resistance and alcohol-induced SCC resistance, and can be used for large structures with no need for coating, inhibitor addition, or the like by improving the pitting corrosion resistance and SCC resistance of the steel material itself.

Abstract: A stress corrosion crack test method for evaluating the stress corrosion crack susceptibility of a steel material in alcohol. The method includes filling a cell containing a uniaxial tensile test piece of the steel material with an alcohol solution containing carboxylic acid: 0.1 mmol/L or more and less than 40 mmol/L, chloride ions: 0.05 mg/L or more and less than 300 mg/L, and water: 0.1 vol. % or more and less than 5 vol. %. Additionally, the method includes applying a fluctuating stress at a frequency of 2.0×10?5 Hz or more and 2.0×10?2 Hz or less to the uniaxial tensile test piece in the tensile direction. The maximum stress being equal to or more than the yield strength and less than the tensile strength at a test solution temperature, and the minimum stress being 0% or more and 90% or less of the yield strength.

Abstract: Steel for storage equipment and transportation equipment for ethanol, the steel having a chemical composition containing, by mass %. C: 0.02% to 0.3%, Si: 0.01% to 1.0%, Mn: 0.1% to 2.0%, P: 0.003% to 0.03%, S: 0.01% or less, Al: 0.005% to 0.100%, N: 0.0010% to 0.010%, at least one selected from W: 0.010% to 0.5% and Mo: 0.010% to 0.5%, at least one selected from Sb: 0.01% to 0.5% and Sn: 0.01% to 0.3%, and the balance being Fe and inevitable impurities, in which the ratio of the Al content to the N content satisfies the relationship 2.0?Al/N?70.0.

Abstract: A stress corrosion crack test method for evaluating the stress corrosion crack susceptibility of a steel material in alcohol. The method includes filling a cell containing a uniaxial tensile test piece of the steel material with an alcohol solution containing carboxylic acid: 0.1 mmol/L or more and less than 40 mmol/L, chloride ions: 0.05 mg/L or more and less than 300 mg/L, and water: 0.1 vol. % or more and less than 5 vol. %. Additionally, the method includes applying a fluctuating stress at a frequency of 2.0×10?5 Hz or more and 2.0×10?2 Hz or less to the uniaxial tensile test piece in the tensile direction. The maximum stress being equal to or more than the yield strength and less than the tensile strength at a test solution temperature, and the minimum stress being 0% or more and 90% or less of the yield strength.

Abstract: A steel material of the disclosure has a chemical composition containing, in mass %: 0.03% to 0.3% C; 0.03% to 1.0% Si; 0.1% to 2.0% Mn; 0.003% to 0.03% P; 0.005% or less S; 0.005% to 0.1% Al; 0.005% to 0.5% Cu; 0.01% to 0.5% Sb; and 0.005% to 0.5% Ni, with a balance being Fe and incidental impurities. Thus, the steel material has excellent alcohol-induced pitting corrosion resistance and alcohol-induced SCC resistance, and can be used for large structures with no need for coating, inhibitor addition, or the like by improving the pitting corrosion resistance and SCC resistance of the steel material itself.

Abstract: A steel material excellent in alcohol-induced pitting corrosion resistance and alcohol-induced SCC resistance enables application in large structures without the need of alloy treatment or addition of inhibitors, by improving the pitting corrosion resistance and the SCC resistance of the steel material itself, by having a chemical composition containing, by mass % C: 0.03% to 0.3%, Si: 0.01% to 1.0%, Mn: 0.1% to 2.0%, P: 0.03% or less, S: 0.01% or less and Al: 0.1% or less, and one or both of Mo: 0.03% to 1.0% and W: 0.03% to 1.0%, and at least two of Sb: 0.005% to 0.5%, Sn: 0.01% to 0.3% and Nb: 0.005% to 0.1%, and the balance including Fe and incidental impurities.

Abstract: A steel material excellent in weathering resistance by defining the chemical ingredients in the steel each to a predetermined range and setting an ingredient parameter formula in accordance with the working circumstance thereby reducing the flow rust and, particularly, forming stable rust with good protective property even in a salty circumstance such as in coast districts is provided. Further, also considering the amount of A type inclusions and B type inclusions according to JIS G 0555, a steel material of excellent earthquake proofness and weathering proofness also including weld heat affect zone is provided.

Abstract: A steel material excellent in weathering resistance by defining the chemical ingredients in the steel each to a predetermined range and setting an ingredient parameter formula in accordance with the working circumstance thereby reducing the flow rust and, particularly, forming stable rust with good protective property even in a salty circumstance such as in coast districts is provided.

Abstract: Steel is obtained which comprises by wt %, C: 0.001-0.025%, Si: not more than 0.60%, Mn: 0.10-3.00%, P: 0.005-0.030%, S: not more than 0.01%, Al: not more than 0.10%, Cu: 0.1-1.5%, Ni: 0.1-6.0%, B: 0.0001-0.0050%, and the balance being Fe and inevitable impurities; since the steel contains C and P in small contents, stable amorphous rusts are formed on the surface thereof at an early stage; and steel simultaneously realizes excellent weather resistance, material weldability and toughness particularly in an environment such as a seashore district and the like where salt is present in a large amount.

Abstract: The invention provides a steel product having superior weathering which is coated with a rust layer containing 50 or more weight % of non-crystalline rust, a method of producing the steel product, and a method of forming weathering protective rust on a material surface of the steel product. A material of a steel product is placed in an atmosphere in which the dew point is kept constant and the temperature of the steel product material is repeatedly varied between a temperature range of 5.degree. C. or more higher than the dew point and a temperature range of 5.degree. C. or more lower than the dew point. Weathering protective rust is thereby formed on the material surface of the steel product and a steel product having superior weathering is obtained. Preferably, the atmosphere contains 15 to 50 volume % of oxygen gas, and the temperature of the steel product is varied at a rising rate of 0.1 to 2.degree. C./minute and a lowering rate of 0.01 to 2.degree. C./minute.