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Thick, high tensile-strength hot-rolled steel sheets with excellent low temperature toughness and manufacturing method therefor

A technology of hot-rolled steel sheet and manufacturing method, which is applied in the direction of manufacturing tools, metal rolling, heat treatment process control, etc., and can solve the problems such as the inability to ensure the cooling rate.

Active Publication Date: 2013-11-06
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, in the technology described in Patent Document 5, the required cooling rate cannot be ensured for a thick steel plate, and there is a problem that the cooling capacity needs to be further increased in order to ensure the required properties.

Method used

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  • Thick, high tensile-strength hot-rolled steel sheets with excellent low temperature toughness and manufacturing method therefor
  • Thick, high tensile-strength hot-rolled steel sheets with excellent low temperature toughness and manufacturing method therefor
  • Thick, high tensile-strength hot-rolled steel sheets with excellent low temperature toughness and manufacturing method therefor

Examples

Experimental program
Comparison scheme
Effect test

experiment example 1

[0106] A slab consisting of 0.037%C-0.20%Si-1.59%Mn-0.016%P-0.0023%S-0.041%Al-0.061%Nb-0.013%Ti-the balance being Fe in mass % was used as a steel raw material. In addition, (Ti+Nb / 2) / C was 1.18.

[0107] Heating the raw material of steel with the above composition to 1230°C, performing hot rolling at a finish rolling start temperature of 980°C and a finish rolling finish temperature of 800°C to produce a hot-rolled sheet with a plate thickness of 14.5mm, after the hot rolling is completed, implement Cool at a cooling rate of 18°C / sec in the temperature range where the temperature at the central position of the plate thickness is higher than 750°C until reaching various cooling stop temperatures for accelerated cooling, and then, at various coiling temperatures (central position of the plate thickness) temperature) to make a hot-rolled steel sheet (steel strip).

[0108] Test pieces were cut out from the obtained hot-rolled steel sheets, and the microstructure and DWTT charac...

experiment example 3

[0129] Use in mass % 0.04~0.06%C-0.2~0.7%Si-0.93~1.84%Mn-0.030~0.048%Al-0.045~0.15%Nb-0.009~0.03%Ti-0~0.25%Ni-0~0.25 %Cu-0-0.059%V-The balance is composed of Fe and unavoidable impurities, and a steel slab with a carbon equivalent Ceq of 0.234-0.496 is used as a steel raw material. In addition, the carbon equivalent Ceq was calculated using the following formula.

[0130] Ceq(%)=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15...(4)

[0131] (Here, C, Mn, Cr, Mo, V, Cu, and Ni are the content (mass %) of each element)

[0132] Heating the raw material of steel with the above composition to 1200°C, performing hot rolling at a finish rolling start temperature of 1010°C and a finish rolling finish temperature of 810°C to produce a hot-rolled sheet with a plate thickness of 25.4mm, after the hot rolling is completed, implement Perform various cooling under the following conditions until the accelerated cooling reaches the cooling stop temperature of 470°C to 490°C with the thermometer at the cente...

experiment example 4

[0138] Use in mass % 0.04~0.06%C-0.20~0.70%Si-0.93~1.84%Mn-0.030~0.048%Al-0.045~0.15%Nb-0.009~0.03%Ti-0~0.25%Ni-0~0.25 %Cu-0-0.06%V-The balance is composed of Fe and unavoidable impurities, and a steel slab with a carbon equivalent Ceq of 0.234-0.496 is used as a steel raw material. In addition, the carbon equivalent Ceq was calculated using the following formula.

[0139] Ceq(%)=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15...(4)

[0140] (Here, C, Mn, Cr, Mo, V, Cu, and Ni are the content (mass %) of each element)

[0141] Heating the raw material of the above-mentioned composition to 1210°C, performing hot rolling at a finish rolling start temperature of 1000°C and a finish rolling finish temperature of 800°C to produce a hot-rolled sheet with a plate thickness of 25.4mm, after the hot rolling is completed, implement Cooling is carried out under the following conditions until the cooling stop temperature reaches a cooling stop temperature of 200°C to 500°C with a thermometer at the cente...

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Abstract

There is provided a thick-walled high-strength hot rolled steel sheet having a high tensile strength TS of 521 MPa or more and excellent low-temperature toughness. Specifically, a steel material containing 0.02%-0.08% C, 0.01%-0.10% Nb, and 0.001%-0.05% Ti is heated, C, Ti, and Nb satisfying (Ti + (Nb / 2)) / C < 4. After hot rolling including rough rolling and finish rolling is performed, cooling is performed at an average cooling rate of 10 °C / s or more at a middle position of the steel sheet in the thickness direction to a specific cooling stop temperature or lower, the cooling stop temperature being dependent on the amounts of alloy elements and the cooling rate. Then coiling is performed at a specific coiling temperature or lower, the coiling temperature being dependent on the amounts of alloy elements, thereby producing the thick-walled hot rolled steel sheet having excellent uniformity of a microstructure in the thickness direction and having the microstructure in which the difference ”D between the average grain size of a ferrite phase serving as a main phase at a position 1 mm from a surface of the steel sheet in the thickness direction and the average grain size of the ferrite phase at a middle position of the steel sheet in the thickness direction is 2 µm or less and in which the difference AV between the fraction (percent by volume) of a second phase at the position 1 mm from the surface of the steel sheet in the thickness direction and the fraction (percent by volume) of the second phase at the middle position of the steel sheet in the thickness direction is 2% or less. This results in significant improvement in low-temperature toughness. In particular, DWTT characteristics and CTOD characteristics are significantly improved, in which DWTT and CTOD are tests using full-thickness test specimens.

Description

technical field [0001] The present invention relates to a line pipe suitable for transporting crude oil, natural gas, etc., and suitable as a raw material for a high strength electric resistance welded steel pipe or a high strength spiral steel pipe requiring high toughness Thick-walled high-strength hot-rolled steel sheet (thick-walled high-strength hot-rolled steel sheet) and its manufacturing method, particularly relating to improvement of low-temperature toughness. In addition, a "steel sheet" includes a steel plate and a steel strip. In addition, the "high-strength hot-rolled steel sheet" referred to here refers to a high-strength hot-rolled steel sheet (hot rolled steel sheet) having a tensile strength (tensile strength) TS of 510 MPa or more. In addition, a "thick-walled" steel sheet is Refers to steel plates with a thickness of 11 mm or more. Background technique [0002] In recent years, due to the high price of crude oil since the oil crisis and the diversificati...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22C38/00B21B3/00C21D8/02C21D9/46C22C38/14C22C38/58
CPCC21D9/085C21D2211/008C21D1/25C21D8/0226C22C38/14C22C38/12C21D2211/005C21D11/005C22C38/001C21D2211/002C22C38/58C21D6/001C21D6/002C21D6/004C21D6/005C21D6/008C21D8/02C21D8/0263C21D9/46C22C38/002C22C38/02C22C38/04C22C38/06C22C38/08C22C38/16C22C38/26C22C38/28C22C38/38C22C38/42C22C38/44C22C38/46C22C38/48C22C38/50
Inventor 上力中田博士中川欣哉
Owner JFE STEEL CORP
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