steel plate

Abstract

This invention provides a steel sheet that exhibits high tensile strength, excellent low-temperature toughness, corrosion resistance, and lamellar tear resistance, even without the need for reheating and quenching. [Solution] The steel sheet of this disclosure has the chemical composition described in the specification, with a Ceq defined by formula (1) described in the specification being 0.42 to 0.49, a SnEQ defined by formula (2) being 0.10 or more, an MV defined by formula (3) being 0.20 to 0.80, and an SC defined by formula (4) being 0.20 to 15.00, having a plate thickness of 75 to 105 mm, a tensile strength of 570 MPa or more, and the major axis D of the prior austenite grains in the center of the plate thickness of the L cross section. L 100 μm or less, aspect ratio AR L The ratio is greater than 2.0 and less than or equal to 3.0, and the major axis D of the prior austenite grains is at the center of the plate thickness of the C section. C 100 μm or less, aspect ratio AR C The Vickers hardness is greater than 2.0 and less than or equal to 2.5, the Vickers hardness in the segregation region at the center of the plate thickness of the C section is 250 HV or less, and the maximum length of porosity is 1.0 mm or less.

Claims

1. It is a steel plate, The chemical composition is expressed in mass percent. C: 0.06-0.15%, Si: 0.05-0.80%, Mn: 1.00-2.50%, P: 0.015% or less, S: 0.0024% or less, Ni: 0.1 to 1.0%, Mo: 0.01 to 0.60%, Nb: 0.005-0.050%, V: 0.001-0.200%, Ti: 0.005 to 0.050%, Al: 0.010-0.080%, Sn: 0.02-0.40%, N: 0.0010-0.0070%, O: 0.0005 to 0.0040%, and, It contains Ca: 0.0001 to 0.0080%, The remainder consists of Fe and impurities. The Ceq defined by equation (1) is between 0.42 and 0.

49. The SnEQ defined by equation (2) is 0.10 or greater, The MV defined by equation (3) is between 0.20 and 0.

80. The SC defined in equation (4) is between 0.20 and 15.00, Having a plate thickness of 75 to 105 mm, The tensile strength is 570 MPa or more. In the center of the thickness of the L-shaped cross-section of the steel plate, parallel to the rolling direction and the thickness direction, Major axis D of the old austenite grain Ｌ It is 100 μm or less, Aspect ratio AR of the aforementioned prior austenite grains Ｌ It is greater than 2.0 and less than or equal to 3.

0. In the central part of the thickness of the C cross-section of the steel plate perpendicular to the rolling direction, Major axis D of the old austenite grain Ｃ It is 100 μm or less, Aspect ratio AR of the aforementioned prior austenite grains Ｃ It is greater than 2.0 and less than or equal to 2.

5. The Vickers hardness in the segregation region at the center of the plate thickness of the C section is 250 HV or less. The maximum length of porosity in the aforementioned C section is 1.0 mm or less. steel plate. Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15 (1) SnEQ=Sn+W+Ni / 10+Mo / 4 (2) MV=Mo+4V (3) SC=S / Ca (4) Here, each element symbol in each formula is replaced with the mass percentage content of the corresponding element. If the corresponding element is not present, "0" is replaced with that element symbol.

2. It is a steel plate, The chemical composition is expressed in mass percent. C: 0.06-0.15%, Si: 0.05-0.80%, Mn: 1.00-2.50%, P: 0.015% or less, S: 0.0024% or less, Ni: 0.1 to 1.0%, Mo: 0.01 to 0.60%, Nb: 0.005-0.050%, V: 0.001-0.200%, Ti: 0.005 to 0.050%, Al: 0.010-0.080%, Sn: 0.02-0.40%, N: 0.0010-0.0070%, O: 0.0005 to 0.0040%, and, It contains Ca: 0.0001 to 0.0080%, Furthermore, it contains one or more selected from the groups consisting of Group 1 to Group 3, The remainder consists of Fe and impurities. The Ceq defined by equation (1) is between 0.42 and 0.

49. The SnEQ defined by equation (2) is 0.10 or greater, The MV defined by equation (3) is between 0.20 and 0.

80. The SC defined in equation (4) is between 0.20 and 15.00, Having a plate thickness of 75 to 105 mm, The tensile strength is 570 MPa or more. In the center of the thickness of the L-shaped cross-section of the steel plate, parallel to the rolling direction and the thickness direction, Major axis D of the old austenite grain Ｌ It is 100 μm or less, Aspect ratio AR of the aforementioned prior austenite grains Ｌ It is greater than 2.0 and less than or equal to 3.

0. In the central part of the thickness of the C cross-section of the steel plate perpendicular to the rolling direction, Major axis D of the old austenite grain Ｃ It is 100 μm or less, Aspect ratio AR of the aforementioned prior austenite grains Ｃ It is greater than 2.0 and less than or equal to 2.

5. The Vickers hardness in the segregation region at the center of the plate thickness of the C section is 250 HV or less. The maximum length of porosity in the aforementioned C section is 1.0 mm or less. steel plate. Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15 (1) SnEQ=Sn+W+Ni / 10+Mo / 4 (2) MV=Mo+4V (3) SC=S / Ca (4) Here, each element symbol in each formula is replaced with the mass percentage content of the corresponding element. If the corresponding element is not present, "0" is replaced with that element symbol. [Group 1] Cu: 0.80% or less, B: 0.0050% or less, Zr: 0.05% or less, Ta: One or more selected from the group consisting of 0.10% or less. [Group 2] Cr: 0.20% or less, W: 0.80% or less, Sb: 0.10% or less, As: 0.05% or less, Bi: 0.10% or less, Se: 0.05% or less, Te: 0.05% or less, Zn: 0.05% or less, Ga: 0.05% or less, Ge: 0.05% or less, Co: 0.10% or less, One or more selected from the group consisting of Hf: 0.05% or less. [Group 3] Mg: 0.010% or less, Sr: 0.020% or less, Ba: 0.010% or less, Rare earth elements: One or more selected from the group consisting of 0.020% or less.

3. The steel plate according to claim 2, The aforementioned chemical composition contains the first group, steel plate.

4. The steel plate according to claim 2, The aforementioned chemical composition contains the second group, steel plate.

5. The steel plate according to claim 2, The aforementioned chemical composition contains the third group, steel plate.

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