JP2008214653A - High strength thick steel plate for structural purpose having excellent brittle crack arrest property, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high strength thick steel plate for structural purpose with a plate thickness of ≥50 mm having excellent brittle crack arrest properties, and used for large structure such as vessels, marine structures, low temperature storage tanks, building-civil engineering structures, and to provide a method for producing the high strength thick steel plate. <P>SOLUTION: The thick steel plate has a texture where the X-ray intensity ratio in the (100) plane at the rolling face in the central part of the plate thickness is ≥1.5, and also, the X-ray intensity ratio in the (100) plane at the rolling face in the 1/4 part of the plate thickness is ≥1.5, and Charpy fracture transition temperature in the 1/4 part of the plate thickness is ≤-40°C. The steel plate has a steel composition comprising, by mass, 0.03 to 0.20% C, 0.03 to 0.5% Si, 0.5 to 2.0% Mn, 0.005 to 0.08% Al, ≤0.03% P, ≤0.01% S and ≤0.0050% N. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a structural high-strength steel plate having a thickness of 50 mm or more and excellent in brittle crack propagation stopping characteristics used for large structures such as ships, offshore structures, low-temperature storage tanks, and construction / civil engineering structures. It relates to a manufacturing method.

  In large structures such as ships, offshore structures, low-temperature storage tanks, and construction / civil engineering structures, accidents associated with brittle fractures have a large impact on the economy and the environment, and therefore safety is always required to be improved.

  Therefore, steel materials used in such structures are often required to have low temperature toughness, and recently, even if a crack occurs in the structure due to an accident, etc. From the viewpoint of prevention, brittle crack propagation stop characteristics at low temperatures are required.

  As a means of improving the brittle crack propagation stopping characteristics of steel materials, a method of increasing the Ni content has been conventionally known. In a LNG storage tank, 9% Ni steel is used on a commercial scale. ing. However, an increase in the amount of Ni necessitates a significant increase in cost, so it is difficult to apply to applications other than the LNG storage tank.

  On the other hand, for thin steel materials with a plate thickness of less than 50 mm, such as LNG, which does not reach extremely low temperatures and are used for ships and line pipes, fine graining is performed by the TMCP method to achieve low temperature toughness. It can be improved to give excellent brittle crack propagation stopping properties.

  In recent years, a technique for making the structure of the surface layer portion of a steel material ultrafine without increasing the alloy cost has been proposed as a means for improving the brittle crack propagation stop characteristic. For example, in Patent Document 1, when a brittle crack propagates, the shear lip (plastic deformation region) generated in the steel surface layer portion is effective in improving the brittle crack propagation stop characteristic, and the crystal grains of the shear lip portion are changed. A method is disclosed in which the propagation energy possessed by the brittle cracks that are propagated by miniaturization is absorbed.

The process of cooling the surface layer portion below the Ar ₃ transformation point by controlled cooling after hot rolling, and then stopping the controlled cooling to reheat the surface layer portion above the transformation point is repeated one or more times. An ultrafine ferrite structure or a bainite structure is generated in the surface layer portion by applying transformation and repeatedly transforming or processing recrystallization.

  Further, in Patent Document 2, in order to improve the brittle crack propagation stop property in a steel material mainly composed of ferrite-pearlite, both surface portions have ferrite grains having a circle-equivalent grain size of 5 μm or less and an aspect ratio of 2 or more. It is disclosed that it is important to configure a layer having a ferrite structure having 50% or more to suppress variation in ferrite grain size.

  As a method for suppressing variation, the local recrystallization phenomenon is suppressed by setting the maximum rolling reduction per pass during finish rolling to 12% or less.

  However, the above-mentioned invention obtains a structure with improved brittle crack propagation stop characteristics by cooling only the steel surface layer part and then recovering it, and adding processing during the recovery process. Therefore, it is not easy to expand to the actual production scale, and since there is no description with a thick material having a plate thickness of 50 mm or more, the applicability to a thick material is unknown.

  Patent Document 3 has developed a TMCP method for forming subgrains in ferrite crystal grains as well as miniaturization of ferrite grains in order to improve brittle crack propagation characteristics after being subjected to plastic deformation as it is not rolled. Technology is provided.

  Specifically, in a plate thickness of 30 to 40 mm, without requiring complicated temperature control such as cooling and recuperation of the steel sheet surface layer, (a) rolling conditions for securing fine ferrite crystal grains, (b) steel plate Rolling conditions for generating a fine ferrite structure in a portion of 5% or more of the thickness, (c) A texture is developed in the fine ferrite, and dislocations introduced by processing (rolling) are rearranged by thermal energy to form subgrains. Providing a method for improving brittle crack propagation stop characteristics after undergoing plastic deformation by rolling conditions and (d) cooling conditions that suppress coarsening of the formed fine ferrite crystal grains and fine subgrain grains Yes.

  However, the maximum plate thickness is 40 mm, and it is unclear whether a desired brittle crack propagation stop characteristic can be obtained in a thick material exceeding 50 mm.

  On the other hand, in controlled rolling, there is also known a method of improving brittle crack propagation stop characteristics by developing a texture by reducing the transformed ferrite. Separation occurs on the fracture surface of the steel material in a direction parallel to the plate thickness direction to relieve stress at the tip of the brittle crack, thereby increasing resistance to brittle fracture.

  For example, in Patent Document 4, the brittle fracture resistance is improved by controlling the rolling to have a (110) plane X-ray intensity ratio of 2 or more and coarse grains having an equivalent circle diameter of 20 μm or more to 10% or less. .

  Moreover, in patent document 5, as a steel for welded structures excellent in the brittle crack propagation stop performance of a joint part, the X-ray surface strength ratio of the (100) plane at the rolled surface in the plate thickness has 1.5 or more. A steel sheet featuring the above is disclosed. It utilizes the fact that a shift occurs between the stress loading direction and the crack propagation direction due to the development of the texture.

However, also in this technique, the maximum thickness of the object to be applied is 50 mm, and there is no description of the thickness exceeding 50 mm, and applicability to thicker materials and the obtained characteristics are unknown.
JP-A-4-141517 JP 2002-256375 A Japanese Patent No. 3467767 Japanese Patent No. 3548349 JP-A-6-207241

  By the way, the brittle crack propagation stop characteristic of a steel plate tends to deteriorate as the strength or thickness of the steel plate increases.

  For example, in a recent large container ship exceeding 6,000 TEU, the plate thickness of the steel plate is 50 mm or more. However, when the brittle crack propagation stopping performance of the steel plate for shipbuilding having a plate thickness of 65 mm is evaluated by a large brittle crack propagation stop test, it is brittle. The result that the crack does not stop has been obtained (Inoue et al., “Long Brittle Crack Propagation Behavior in Thick Shipbuilding Steel”, Japanese Society of Marine Science and Technology, No. 3 2006pp 359-362).

In addition, in the ESSO test of the test material, the Kca at a use temperature of −10 ° C. was less than 3000 N / mm ^3/2 . These results show that the plate thickness of the hull such as a container ship or a bulk carrier is 50 mm. It has been discussed as influencing the safety evaluation of hull structures using high strength steel plates that exceed.

  Therefore, the present invention has an object to provide a structural high-strength thick steel plate excellent in brittle crack propagation stopping characteristics and a method for producing the same, with a plate thickness suitable as a hull outer plate of a container ship or a bulk carrier exceeding 50 mm. To do.

  In order to achieve the above-mentioned problems, the present inventors have earnestly studied the relationship between the texture and the brittle crack propagation stop property for thick-walled materials, and obtained the following knowledge.

  (1) When a method of improving the brittle crack propagation stop characteristic by applying a method of reducing the transformed ferrite in two-phase rolling to develop a texture and improving the brittle crack propagation stop characteristic is effective for improving the brittle crack propagation characteristic (100 ) The surface is accumulated only near the center of the plate thickness.

  That is, when the texture is distributed in the plate thickness direction, if the plate thickness is thin, the (100) plane develops over almost the entire area inside the plate thickness, but as the plate thickness increases, the (100) plane becomes Accumulation occurs only in the central part of the plate thickness, and the brittle crack propagation stop characteristic deteriorates as compared with the case where the plate thickness is thin.

  FIG. 1 shows the results of investigating the influence of sheet thickness on the distribution of texture in the sheet thickness direction for a two-phase zone rolled material, and the (100) plane develops regardless of the sheet thickness at 1/2 sheet thickness. However, it is recognized that as the plate thickness increases, the degree of integration of the (100) plane at the 1/4 thickness portion decreases.

  (2) This phenomenon is because the shear strain inside the plate thickness increases as the plate thickness increases, and the brittleness of the thick-walled material whose plate thickness exceeds 50 mm in the controlled rolling simply by extension of the prior art. It is difficult to improve the crack propagation stop characteristics.

  (3) In the case of a thick steel plate having a thickness of 50 mm or more, excellent brittle crack propagation is stopped when the (100) plane X-ray intensity ratio at the rolling surface in the central portion of the plate thickness and the 1/4 thickness portion is a certain value or more. It has been found that the characteristics are obtained and that the steel sheet having the structure is obtained by applying a specific cumulative rolling reduction in a specific temperature range to the central part of the plate thickness.

The present invention has been made based on these findings and further studies, that is, the present invention,
1. Aggregation in which the (100) plane X-ray intensity ratio at the rolled surface in the central portion of the plate thickness is 1.5 or more and the (100) plane X-ray intensity ratio in the rolled surface at the 1/4 thickness portion is 1.5 or more A structural high-strength thick steel plate having a structure having a brittle crack propagation stopping characteristic and having a brittle crack propagation stopping property and having a Charpy fracture surface transition temperature at ¼ part of a thickness of −40 ° C. or less and exceeding 50 mm.
2. Steel composition is mass%, C: 0.03-0.20%, Si: 0.03-0.5%, Mn: 0.5-2.0%, Al: 0.005-0.08 %, P: 0.03% or less, S: 0.01% or less, N: 0.0050% or less, with the balance consisting of Fe and unavoidable impurities. An excellent structural high-strength thick steel plate having a thickness of more than 50 mm and having a Charpy fracture surface transition temperature of -40 ° C. or lower at a thickness of 1/4 part.
3. Steel composition is further mass%, Ti: 0.005-0.03%, Nb: 0.005-0.05%, Cu: 0.01-0.5%, Ni: 0.01-1 0.0%, Cr: 0.01-0.5%, Mo: 0.01-0.5%, V: 0.001-0.1%, B: 0.003% or less, Ca: 0.005 % Or less, REM: 0.01% or less of any one kind, or two kinds or more A structural high-strength thick steel plate having a surface transition temperature of −40 ° C. or lower and a plate thickness exceeding 50 mm.
The steel material having the composition described in 4.2 or 3 is heated to a temperature of 900 to 1200 ° C., and the temperature at the center of the plate thickness in hot rolling is ₃ points or more at an Ar ₃ point or more, and the cumulative reduction rate is 30% or more. After rolling at a central thickness of _{3 to} −10 ° C. or lower and an Ar _{3 to} −50 ° C. or higher temperature at a cumulative reduction rate of 30% or more and an average pass reduction rate of 8% or more, 2 ° C. / The Charpy fracture surface transition temperature at ¼ part of the plate thickness excellent in brittle crack propagation stopping characteristics characterized by cooling to 600 ° C. or less at a cooling rate of s or more is a plate thickness exceeding 50 mm, which is −40 ° C. or less. A manufacturing method for structural high-strength thick steel plates.

  According to the present invention, a thick plate having a thickness of 50 mm or more is excellent in brittle crack propagation stopping characteristics in the thickness direction. For example, in a shipbuilding field, a deck joined to hatch side combing in a strong deck structure of a container ship or a bulk carrier. By applying this steel plate to the member, it contributes to the improvement of ship safety and is extremely useful in industry.

In the present invention, 1. Texture inside the plate thickness; 2. steel composition; Define manufacturing conditions.
1. In order to improve the crack propagation stop characteristics for cracks that propagate in the horizontal direction, such as the rolling direction or the direction perpendicular to the rolling direction, in the center of the plate thickness and the 1/4 of the plate thickness, The (100) plane is developed in parallel with the rolled surface, and the (100) plane X-ray intensity ratio at the rolled surface at those positions is set to a texture of 1.5 or more.

  This is because when the (100) plane is developed within the plate thickness, a microscopic crack is generated prior to the crack progress, and resistance to the crack progress.

  When a crack occurs at the tip of a brittle crack, the crack becomes a resistance to destruction. In the process in which the brittle crack merges with the crack, the fracture driving force (energy release rate) of the brittle crack increases, but the brittle crack stops because it significantly decreases after coalescence.

  Here, the (100) plane X-ray intensity ratio is a numerical value indicating the degree of integration of the (100) crystal plane of the target material, and is a random standard having no (200) reflection X-ray diffraction intensity and texture of the target material. It refers to the ratio of the X-ray diffraction intensity of (200) reflection from the sample.

  Since the base metal toughness has good characteristics is a precondition for suppressing the progress of cracks, in the steel sheet according to the present invention, the Charpy fracture surface transition temperature at ¼ part of the sheet thickness is defined as −40 ° C. or less. To do.

  The reduction of the Charpy fracture surface transition temperature is achieved by making the fracture surface unit finer, but it is possible to obtain the characteristics by adjusting the components, rolling conditions and the like described later.

  The above-described texture can be obtained when the chemical components and production conditions of steel are appropriately selected. Hereinafter, preferable chemical components and production conditions of steel in the present invention will be described.

2. In the description of chemical components,% is mass%.

C: 0.03-0.20%
C is an element that improves the strength of steel. In the present invention, it is necessary to contain 0.03% or more in order to ensure a desired strength, but if it exceeds 0.20%, the weldability deteriorates. As well as adversely affecting toughness. For this reason, C was specified in the range of 0.03 to 0.20%. In addition, Preferably it is 0.05 to 0.15%.

Si: 0.03-0.5%
Si is effective as a deoxidizing element and as a strengthening element for steel, but if its content is less than 0.03%, it has no effect. On the other hand, if it exceeds 0.5%, not only the surface properties of the steel are impaired, but also the toughness is extremely deteriorated. Therefore, the addition amount is set to 0.03% or more and 0.5% or less.

Mn: 0.5 to 2.0%
Mn is added as a strengthening element. If the content is less than 0.5%, the effect is not sufficient. If the content exceeds 2.0%, the weldability deteriorates and the steel material cost increases, so the content is made 0.5% or more and 2.0% or less.

Al: 0.005 to 0.08%
Al acts as a deoxidizer, and for this purpose, it needs to contain 0.005% or more. However, if it contains more than 0.08%, it reduces the toughness and, when welded, weld metal Reduce the toughness of the part. For this reason, Al was specified in the range of 0.005 to 0.08%. In addition, Preferably, it is 0.02 to 0.04%.

N: 0.0050% or less N combines with Al in the steel, adjusts the crystal grain size at the time of rolling, and strengthens the steel. However, if it exceeds 0.0050%, the toughness deteriorates. 0050% or less.

P, S
P and S are unavoidable impurities in the steel, but P exceeds 0.03%, and if S exceeds 0.01%, the toughness deteriorates. Therefore, 0.03% or less and 0.02%, respectively. The following is desirable.

  The above is the basic component composition of the present invention. In order to further improve the characteristics, it is possible to contain one or more of Nb, Ti, Cu, Ni, Cr, Mo, V, B, Ca, and REM. It is.

Nb: 0.005 to 0.05%
Nb precipitates as NbC at the time of ferrite transformation or reheating, and contributes to the increase in strength. In addition, it has the effect of expanding the non-recrystallized region in rolling in the austenite region, and contributes to the refinement of ferrite, so it is also effective in improving toughness. In order to obtain the effect, 0.005% or more of addition is necessary, but if added over 0.05%, coarse NbC precipitates and conversely causes a decrease in toughness, so the upper limit is 0.05. % Is preferable.

Ti: 0.005 to 0.03%,
Ti has the effect of forming nitrides, carbides, or carbonitrides by adding a small amount, and refining crystal grains to improve the base material toughness. The effect is obtained by addition of 0.005% or more, but the content exceeding 0.03% lowers the toughness of the base metal and the weld heat affected zone, so Ti is 0.005 to 0.03%. The range is preferable.

Cu, Ni, Cr, Mo
Cu, Ni, Cr, and Mo are all elements that enhance the hardenability of steel. It contributes directly to strength improvement after rolling, and is added to improve functions such as toughness, high-temperature strength, or weather resistance, but excessive addition degrades toughness and weldability, so the upper limit is 0.5% respectively. 1.0%, 0.5%, 0.5%. On the contrary, if the addition amount is less than 0.01%, the effect does not appear, so 0.01% or more is added.

V: 0.001 to 0.1%
V is an element that improves the strength of the steel by precipitation strengthening as V (CN), and may be contained in an amount of 0.001% or more, but if it exceeds 0.10%, the toughness is lowered. For this reason, V is added in the range of 0.001 to 0.10%.

B: 0.003% or less B may be added as an element that enhances the hardenability of steel in a small amount. However, if contained over 0.003%, the toughness of the welded portion is lowered, so B is added at 0.003% or less.

Ca: 0.005% or less, REM: 0.01% or less Ca, REM is necessary because the structure of the weld heat-affected zone is refined to improve toughness, and even if added, the effect of the present invention is not impaired. It may be added accordingly. However, if added excessively, coarse inclusions are formed and the toughness of the base material is deteriorated. Therefore, it is preferable to set the upper limit of the addition amount to 0.005% and 0.01%, respectively.

3. Manufacturing Conditions The steel plate having the above chemical components and texture has excellent brittle crack propagation stopping properties, and the following manufacturing process is appropriate.

First, molten steel having the above composition is melted in a converter or the like, and is made into a steel material (slab) by continuous casting or the like.
Next, hot rolling is performed after the steel material is heated to a temperature of 900 to 1200 ° C.

  When the heating temperature is 900 ° C. or lower, the rolling efficiency is lowered, and when the heating temperature is 1200 ° C. or higher, the austenite grains are coarsened and the toughness is lowered, and the oxidation loss becomes remarkable and the yield is lowered. Therefore, heating temperature shall be 900-1200 degreeC.

  The range of preferable heating temperature from a viewpoint of toughness is 1000-1150 degreeC, More preferably, it is 1000-1050 degreeC.

In the hot rolling, first, rolling is performed such that the temperature at the central portion of the plate thickness is Ar ₃ point or higher and the cumulative rolling reduction is 30% or higher. If the cumulative rolling reduction is less than 30%, the austenite is not sufficiently refined and the toughness is not improved.

Next, rolling is performed with a cumulative reduction rate of 30% or more and an average pass reduction rate of 8% or more in a temperature range where the temperature at the center of the plate thickness is Ar ₃ points −10 ° C. or lower and Ar ₃ points −50 ° C. or higher.

  By this rolling, a (100) plane develops parallel to the rolling surface at a position that is ¼ of the central portion of the plate thickness and the plate thickness, and the (100) plane X-ray intensity ratio at the rolling surface at those positions is 1. More than 5 textures can be obtained.

  That is, a (100) plane X-ray intensity ratio of 1.5 at the center of the plate thickness is obtained when the cumulative rolling reduction in the temperature range is 30% or more.

  The rolling pass reduction ratio is an important factor in the present invention. In the present invention, it is preferable that the rolling pass reduction ratio is higher in the temperature range, and the average pass reduction ratio is defined as 8% or more. If it is less than 8%, the (100) plane X-ray intensity ratio of 1/4 part of the plate thickness cannot be 1.5 or more.

  In finish rolling of thick materials, shear strain is usually introduced into the thickness of the plate by multi-pass rolling under a small reduction, and the development of the (100) plane integration degree at the 1/4 thickness portion is hindered.

  Note that the present invention does not limit rolling outside the specified temperature range. If the specified cumulative reduction is performed in the specified temperature range, the structure specified in the present invention can be obtained.

  The rolled steel sheet is cooled to 600 ° C. or lower at a cooling rate of 2 ° C./s or higher. This is to prevent reworking of the work texture introduced by the two-phase rolling, and it is necessary to cool the steel sheet to a low temperature after rolling.

  If the cooling rate is less than 2 ° C./s, not only the desired texture is not obtained, but also the strength of the steel sheet is lowered, so the cooling rate is 2 ° C./s or more. If the cooling stop temperature is higher than 600 ° C., recrystallization proceeds even after the cooling stop and a desired texture cannot be obtained. Therefore, the cooling stop temperature is preferably 600 ° C. or lower.

  Molten steel of each composition shown in Table 1 was melted in a converter and used as a steel material (slab) by a continuous casting method (steel symbols A to T). Using these slabs (steel material: 280 mm thick), after hot rolling, cooling is performed and Sample steels 1 to 31 were obtained. Table 2 shows rolling conditions and cooling conditions.

  A JIS14A test piece of Φ14 was taken from 1/4 part of the plate thickness of the obtained thick steel plate, subjected to a tensile test, and a yield point (YS) and a tensile strength (TS) were measured. Further, a JIS No. 4 impact test piece was collected from 1/4 part of the plate thickness, and a Charpy test was performed to determine the fracture surface transition temperature (vTrs). The Charpy fracture surface transition temperature at ¼ part of the plate thickness was within the range of the present invention within the range of −40 ° C. or less.

  Further, in order to evaluate the texture of the steel sheet, the (100) plane X-ray intensity ratio at the rolling surface at the center part of the sheet thickness and the (100) plane X-ray intensity ratio at the rolling surface at the ¼ part sheet thickness are It was measured.

Next, in order to evaluate the brittle crack propagation stop characteristics of these thick steel plates, a temperature gradient type ESSO test was performed to obtain K _{ca-50 ° C.}

Table 3 shows the tensile test results, the texture evaluation results, and the ESSO test results. In the case of a test steel plate in which the texture at the center of the plate thickness, the texture at the 1/4 thickness, and the Charpy fracture surface transition temperature at the 1/4 thickness of the plate satisfy the provisions of the present invention (example of the present invention: steel plates No. 1 to No. 1) 16), K _{ca-50 ° C.} was 5000 to 7000 N / mm 3/2 and showed excellent brittle crack propagation stopping performance.

The texture in the central part of the plate thickness and 1/4 part of the plate thickness satisfies the provisions of the present invention, but the Charpy fracture surface transition temperature in the plate thickness of 1/4 part exceeds -40 ° C (Comparative Example: Steel plate No. 17-20), K _{ca-50 ° C.} is the steel plate No. It was a little inferior compared with 1-16.

Among the comparative steels whose manufacturing conditions do not satisfy the provisions of the present invention, steel plate No. Nos. 21 to 23 are poor in base material toughness, K _{ca-50 ° C.} In 24-31, the base material toughness was equivalent to that of the example of the present invention, but Kca _{-50 ° C} was inferior.

The figure which shows the influence of plate | board thickness on the distribution state of the texture in the plate | board thickness direction of a two-phase area rolling material.

Claims (4)

  Aggregation in which the (100) plane X-ray intensity ratio at the rolled surface in the central portion of the plate thickness is 1.5 or more and the (100) plane X-ray intensity ratio in the rolled surface at the 1/4 thickness portion is 1.5 or more A structural high-strength thick steel plate having a structure having a brittle crack propagation stopping characteristic and having a brittle crack propagation stopping property and having a Charpy fracture surface transition temperature at ¼ part of a thickness of −40 ° C. or less and exceeding 50 mm.   Steel composition is mass%, C: 0.03-0.20%, Si: 0.03-0.5%, Mn: 0.5-2.0%, Al: 0.005-0.08 %, P: 0.03% or less, S: 0.01% or less, N: 0.0050% or less, with the balance consisting of Fe and unavoidable impurities. An excellent structural high-strength thick steel plate having a thickness of more than 50 mm and having a Charpy fracture surface transition temperature of -40 ° C. or lower at a thickness of 1/4 part.   Steel composition is further mass%, Ti: 0.005-0.03%, Nb: 0.005-0.05%, Cu: 0.01-0.5%, Ni: 0.01-1 0.0%, Cr: 0.01-0.5%, Mo: 0.01-0.5%, V: 0.001-0.1%, B: 0.003% or less, Ca: 0.005 % Or less, REM: 0.01% or less of any one kind, or two or more kinds, characterized in having excellent brittle crack propagation stop property according to claim 2, at a thickness of 1/4 part A structural high-strength thick steel plate having a Charpy fracture surface transition temperature of −40 ° C. or less and a plate thickness exceeding 50 mm. The steel material having the composition according to claim 2 or 3 is heated to a temperature of 900 to 1200 ° C., and the temperature of the central portion of the sheet thickness in hot rolling is Ar ₃ or higher, and the cumulative reduction rate is 30% or more, After rolling at a central thickness of _{3 to} −10 ° C. or lower and an Ar _{3 to} −50 ° C. or higher temperature at a cumulative reduction rate of 30% or more and an average pass reduction rate of 8% or more, 2 ° C. / The Charpy fracture surface transition temperature at ¼ part of the plate thickness excellent in brittle crack propagation stopping characteristics characterized by cooling to 600 ° C. or less at a cooling rate of s or more is a plate thickness exceeding 50 mm, which is −40 ° C. or less. A manufacturing method for structural high-strength thick steel plates.

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