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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 problems such as inability to ensure cooling rate.

Active Publication Date: 2011-06-29
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 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 characteris...

experiment example 3

[0129] Using 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 having 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 cent...

experiment example 4

[0138] Using 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 center...

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Abstract

Provided are thick, high tensile-strength hot-rolled steel sheets that have high strengths of TS: 521 MPa or higher and excellent low temperature toughness. Specifically, steel raw material is heated, and after hot-rolling that comprises roughing-down and finish rolling, cooling of 10 DEG C / s by mean cooling rate at the center of the sheet thickness is performed to below a specified end cooling temperature that is dependent on the amounts of alloy elements and the cooling rate. Then the steel is taken up at below a specified take-up temperature that is dependent on the amounts of alloy elements. It thereby becomes a thick hot-rolled steel sheet of excellent structural uniformity in the thickness direction that has a structure wherein the difference delta D in mean crystal particle diameters of the main ferrite phases between a position that is 1 mm in the thickness direction from the surface of the steel sheet and at the center of the steel sheet thickness is less than 2 [mu]m, and the difference delta V in proportion (volume%) of secondary phase structures is less than 2%. Thereby, low temperature toughness, particularly DWTT characteristics and CTOD characteristics, that are toughness tests over the entire thickness, are markedly improved.

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 A thick-walled high-strength hot rolled steel sheet used and a method for manufacturing the same, 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" mentioned 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, and a "thick-walled" steel sheet refers to Steel plates with a plate 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 diversification of energy sources (source of energy), t...

Claims

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Application Information

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IPC IPC(8): C22C38/00B21B3/00C21D8/02C21D9/46C22C38/14C22C38/58
CPCC21D2211/005C21D11/005C21D8/0226C21D2211/008C21D9/085C22C38/14C22C38/12C22C38/001C21D1/25C21D2211/002C22C38/58C21D6/001C21D6/002C21D6/004C21D6/005C21D6/008C21D8/02C21D8/0263C21D9/46C22C38/002C22C38/02C22C38/04C22C38/06C22C38/08C22C38/16C22C38/26C22C38/28C22C38/38C22C38/42C22C38/44C22C38/46C22C38/48C22C38/50
Inventor 上力中田博士中川欣哉
Owner JFE STEEL CORP
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