JP5692305B2 - Thick steel plate with excellent heat input welding characteristics and material homogeneity, and its manufacturing method - Google Patents

Description

  The present invention relates to a steel plate that is used in various steel structures such as ships, offshore structures, architecture, and steel pipe fields, and that is particularly suitable as a manufacturing method thereof to which large heat input welding is applied.

  Generally, steel structures used in the fields of ships, offshore structures, architecture, steel pipes, etc. are finished into structures of a desired shape by welding. Therefore, from the viewpoint of ensuring safety, these structures are based on the base material characteristics that are the basis of the steel materials used, that is, in addition to ensuring strength, toughness, and elongation, as well as characteristics of welds, mainly joint strength, There is a demand for excellent joint toughness.

Furthermore, in recent years, the ships and steel structures tend to be larger, so that the steel materials used are required to have higher strength and thickness, while the procurement cost has increased due to a significant increase in steel weight. The viewpoint of suppression is also attracting attention. For this reason, a design that prevents the strength and thickness of the steel sheet to be applied from being excessive is adopted, and for welding work, a high-efficiency, high-heat-input welding method such as submerged arc welding, electrogas welding, or electroslag welding is used. It has become more oriented towards streamlining overall manufacturing costs. Specifically, assuming the application of large heat input welding described above, not very excessive strength and thickness, until ^secondary approximately 550~750N / mm in tensile strength as a strength class, the thickness is below 50mm Application of steel sheets is expected to expand.

  In general, thick steel plates with the above strength classes and thicknesses are manufactured by the so-called TMCP technology that combines controlled rolling and accelerated cooling for the purpose of improving the properties of steel plates, reducing alloy elements, and omitting heat treatment. The Since the TMCP technology can secure a high cooling rate, there is an advantage that the strength of the base material can be secured with a relatively low component. On the other hand, since the surface of the steel plate is rapidly cooled compared to the inside of the steel plate, the hardness in the vicinity of the steel plate surface is higher than that inside the steel plate, and the hardness distribution in the thickness direction may vary. In addition, accelerated cooling may not be uniform over the entire surface of the steel sheet, and there is a concern about the influence on the material uniformity within the steel sheet, specifically the elongation characteristics of the steel sheet.

  In order to solve the above problems, various solutions have been proposed as part of the TMCP technology. For example, Patent Document 1 discloses a relatively low cooling rate of 3 to 12 ° C./s for accelerated cooling. By controlling the speed, a method of suppressing the increase in surface hardness with respect to the center portion of the plate thickness is disclosed in Patent Document 2, and in the cooling process, the structure of the steel plate is obtained by waiting in the temperature range where ferrite precipitates. Has a two-phase structure of ferrite and bainite, and a method for manufacturing a steel sheet having a small material difference in the thickness direction in which the difference in hardness between the surface layer and the thickness center portion is reduced is disclosed. Furthermore, from the viewpoint of paying attention to the scale properties of the steel sheet surface and the cooling rate during accelerated cooling of the steel sheet, Patent Documents 3 and 4 reduce the uneven cooling due to the scale characteristics by performing descaling immediately before cooling. A method for improving the steel plate shape is disclosed. All of these techniques are interpreted as techniques capable of ensuring material uniformity and simultaneously achieving high toughness by refining crystal grains.

  On the other hand, as described above, high heat input welding with high construction efficiency tends to be applied to the welding work of the steel sheet, but the welding heat affected zone (HAZ [Heat Affected Zone]) formed by high heat input welding is also known. )) Joint toughness due to the disappearance of the grain refinement effect by the various controlled rolling / accelerated cooling processes described above and joint strength reduction due to the formation of the joint softening region occur simultaneously. Measures to resolve together are also required.

  Among them, as a widely known measure, a technique for suppressing austenite grain coarsening by finely dispersing TiN, which is relatively stable in a high temperature range during welding, as described in Patent Document 5, There is a method of compensating for the decrease in joint low temperature toughness by adding appropriate amounts of Ti and B therein.

  Furthermore, as described in Patent Document 6, a method is disclosed in which the Nb addition amount in the steel is optimized to achieve both high strength of the steel sheet and joint characteristics, particularly HAZ toughness. However, the effect of the high heat input welding countermeasure techniques represented by Documents 5 and 6 on the homogeneity of the steel sheet material has not been verified.

Japanese Patent Publication No.7-116504 Japanese Patent No. 3911834 JP-A-9-57327 Japanese Patent No. 3796133 JP 2005-2476 A JP 2011-074448 A

  The present invention was developed in view of the above-described present situation, and has various characteristics required for a high heat input welded joint, and reduces variations in hardness in the plate thickness direction and the plate width direction of the steel plate. Therefore, it is to provide a thick steel plate having a thickness of 50 mm or less with improved material properties, particularly its total thickness elongation characteristic, together with its advantageous manufacturing method.

In order to solve the above-mentioned problems, the present invention, in addition to optimizing the component design as a measure against large heat input welding, to examine the manufacturing conditions for improving the material homogeneity in the steel sheet, and to satisfy the predetermined homogeneity It was obtained after many experiments and examinations regarding the material threshold value to be included in That is, the present invention
1. In mass%, C: 0.030 to 0.080%, Si: 0.01 to 0.10%, Mn: 1.20 to 2.40%, P: 0.008% or less, S: 0.0005 -0.0040%, Al: 0.005-0.080%, Nb: 0.003-0.040%, Ti: 0.003-0.040%, N: 0.0030-0.0100%, B: 0.0003 to 0.0030% contained, the remainder having a component composition consisting of Fe and inevitable impurities, and fluctuations in Vickers hardness (HV) in each of the plate thickness direction and the plate width direction Width: A thick steel plate excellent in high heat input welding characteristics and material homogeneity, wherein ΔHV is 30 or less.
2. Further, by mass%, Cu: 1.00% or less, Ni: 1.00% or less, Cr: 1.00% or less, Mo: 0.50% or less, V: 0.10% or less, or 1 or 2 2. A thick steel plate excellent in high heat input welding characteristics and material homogeneity according to 1, characterized by containing at least a seed.
3. Furthermore, it contains one or more of Ca: 0.0005 to 0.0050%, Zr: 0.001 to 0.020%, REM: 0.001 to 0.020% in mass%. A thick steel plate having excellent high heat input welding characteristics and material homogeneity as described in 1 or 2.
The steel material having the composition described in any one of 4.1 to 3 is heated to 1000 to 1300 ° C. and then hot-rolled, and the jet flow is performed under the condition that the collision pressure of the jet flow on the steel plate surface is 1 MPa or more. The descaling is performed by colliding with the steel plate surface, and then accelerated cooling is immediately performed at an average cooling rate of the steel plate of 10 ° C./s or more and an average cooling stop temperature of the steel plate of 200 to 600 ° C. Vickers hardness (HV) fluctuation width in each of the thickness direction and the plate width direction: ΔHV is 30 or less, A method for producing a thick steel plate excellent in high heat input welding characteristics and material homogeneity.
5. 5. The method for producing a thick steel plate according to 4, wherein after accelerating cooling is stopped, tempering is performed below the Ac1 transformation point.

  According to the present invention, a thick steel plate excellent in both material homogeneity and high heat input weld joint characteristics and a method for producing the same can be obtained, which is extremely useful industrially.

Hereinafter, the limiting conditions of the present invention will be described. In addition, all% in a chemical component shall be the mass%.
C: 0.030 to 0.080%
C is an element that increases the strength of the steel material, and 0.030% or more of addition is necessary in order to ensure the strength necessary for structural steel. On the other hand, if it exceeds 0.080%, island martensite is likely to be generated in the high heat input welding HAZ, so the upper limit is made 0.080%. Preferably, it is 0.040 to 0.070% of range.

Si: 0.01-0.10%
Si is an element added as a deoxidizer when melting steel, and it is necessary to add 0.01% or more. However, if it exceeds 0.10%, island martensite is generated in the high heat input welding HAZ, and the toughness is liable to be lowered. Therefore, Si is taken as 0.01 to 0.10% of range.

Mn: 1.20 to 2.40%
Mn, like C, is an element that enhances the strength of the steel plate base material, and it needs to be added in an amount of 1.20% or more in order to ensure the strength necessary for structural steel. Moreover, since it is inexpensive compared with other alloy components, aggressive addition is effective. However, if it exceeds 2.40%, the hardenability becomes excessive, the base metal toughness is lowered and the weldability is impaired. . Therefore, the Mn content is 1.20 to 2.40%. Preferably it is 1.50% to 2.20% of range.

P: 0.008% or less P is one of the elements contained in steel as an impurity, but is 0.008% or less in order to reduce the toughness of the steel plate base material and the high heat input HAZ part. It is preferable to reduce as much as possible in consideration of economics at the time of melting the material.

S: 0.0005 to 0.0040%
Like P, S is one of the elements contained in steel as an impurity, but unlike P, when it exists as sulfides such as MnS, CaS, and REM-S, it becomes a nucleus of ferrite formation, resulting in a large heat input. The effect of improving the toughness of the HAZ part is exhibited. This effect is effective when 0.0005% or more is added. On the other hand, excessive addition leads to a large amount of sulfide formation, and lowers the base material toughness. Therefore, the S amount is in the range of 0.0005 to 0.0040%.

Al: 0.005-0.080%
Al is an element added for deoxidation of steel, and it is necessary to contain 0.005% or more. On the other hand, if added over 0.080%, the amount of inclusions becomes excessive and the toughness of the base material is lowered. Therefore, Al is made 0.005 to 0.080% of range. Preferably, the content is 0.010 to 0.060%.

Nb: 0.003-0.040%
Nb has an effect of expanding the non-recrystallization temperature region by addition, and is an element effective for ensuring the strength toughness of the steel plate base material. However, if the addition is less than 0.003%, the above effect is small. On the other hand, if the addition exceeds 0.040%, island martensite is generated in the high heat input welding HAZ, and the toughness is lowered. For this reason, Nb is taken as 0.003 to 0.040% of range. Preferably, it is 0.005 to 0.025% of range.

Ti: 0.003-0.040%
Ti precipitates as TiN during solidification, and is an extremely useful element for increasing the toughness of high heat input weld HAZ, particularly suppressing the coarsening of austenite grains in the weld heat affected zone and becoming a transformation nucleus of ferrite. is there. In order to obtain this effect, addition of 0.003% or more is necessary. On the other hand, if the addition exceeds 0.040%, the precipitated TiN becomes coarse and the above effect is hardly obtained. Therefore, Ti is taken as 0.003 to 0.040% of range. Preferably, it is 0.005 to 0.025% of range.

N: 0.0030 to 0.0100%
N is an element necessary for the formation of TiN described above and the formation of B nitride described later, and is one of the most important elements in the present invention. In order to generate these nitrides in the high heat input welded HAZ part and effectively contribute to the improvement of toughness, it is necessary to contain 0.0030% or more. On the other hand, if added over 0.0100%, depending on the welding heat input conditions, the amount of solute N in the region where TiN dissolves may increase, and the toughness of the welded HAZ part may be reduced. Therefore, N is set to a range of 0.0030 to 0.0100%. Preferably, it is 0.0040 to 0.0070% of range.

B: 0.0003 to 0.0030%
When B exists in a solid solution state, it is unevenly distributed at grain boundaries to ensure hardenability and contribute to ensuring the strength of the base material, and when it exists as B nitride, it acts as a ferrite nucleus and has a large heat input. It is one of the most important elements in the present invention that contributes to both the effects of increasing welded HAZ toughness. If the content is less than 0.0003%, the former effect cannot be obtained. If the content exceeds 0.0030%, a large amount of solid solution B exceeding B nitride exists, and high heat input welding HAZ. Reduce toughness. Therefore, B is in the range of 0.0003 to 0.0030%.

  The basic component composition of the present invention is as described above, and the balance is composed of Fe and unavoidable impurities. In order to further improve desired characteristics, one of Cu, Ni, Cr, Mo, V, Ca, Zr, and REM is used. Two or more kinds can be added as selective elements.

Cu: 1.00% or less Cu is an element that can be added in order to increase the strength, but if added over 1.00%, the properties of the surface of the steel sheet base material deteriorate due to hot brittleness. When added, the amount is preferably in the range of 1.00% or less.

Ni: 1.00% or less Ni is an element capable of improving the toughness while increasing the strength of the base material. When added over 1.00%, the effect is saturated and economically disadvantageous, so when added, the amount is preferably in the range of 1.00% or less.

Cr: 1.00% or less Cr is an effective element for increasing the strength. However, if added over 1.00%, the base metal toughness is deteriorated, so when added, the amount is 1.00. % Or less is preferable.

Mo: 0.50% or less Mo is an element effective for increasing the strength of the base metal. However, if added over 0.50%, the toughness is significantly deteriorated and the economy is impaired. The amount is preferably in the range of 0.50% or less.

V: 0.10% or less V is an element effective for increasing the strength of the base metal. However, if added over 0.10%, the toughness is remarkably deteriorated. A range of 10% or less is preferable.

Ca: 0.0005-0.0050%, Zr: 0.001-0.020% and REM: 0.001-0.020%
Ca, Zr, and REM have the effect of fixing S in the steel to improve the toughness of the steel sheet. Ca, which is a strong sulfide-forming element, is 0.0005% or more, and 0.001 for Zr and REM. The effect can be obtained by adding more than%. However, if the amount of each of Ca, Zr, and REM exceeds 0.0050%, 0.020%, and 0.020%, the amount of inclusions in the steel increases and the toughness is deteriorated. Therefore, when these elements are added, it is preferable that Ca is 0.0005 to 0.0050%, Zr is 0.001 to 0.020%, and REM is 0.001 to 0.020%.

Vickers hardness (HV) fluctuation range in each of the plate thickness direction and the plate width direction: ΔHV is 30 or less This specification is one of the most important requirements in the present invention. It has a great influence on the elongation characteristics of the full thickness of the steel sheet. Steel plates with a fluctuation range (ΔHV) of more than 30 in the Vickers hardness (HV) in each of the plate thickness direction and the plate width direction are given priority in areas where the hardness is relatively low during the tensile test of the base plate. Since the constriction occurs, the elongation characteristic of the entire thickness is remarkably deteriorated. For this reason, the fluctuation range (variation) of the hardness is set to a range of 30 or less, preferably 20 or less in terms of Vickers hardness. Such a steel plate is a steel plate excellent in material homogeneity in the steel plate. The hardness test method will be described in detail in Examples.

  Steels such as slabs for the production of steel sheets are produced by melting steels having the above-described composition using conventional methods such as converters or electric furnaces, and using conventional processes such as continuous casting or ingot casting. It is preferable to use a raw material. Hereinafter, the reason for limiting the steel sheet manufacturing conditions defined in the present invention will be described. The steel material temperature in the present invention is the average temperature of the steel material surface and the center (1/2 part of the plate thickness).

Heating temperature: 1000-1300 ° C
A steel material such as a slab after casting is charged into a heating furnace after being cooled to room temperature or in a high temperature state, and the steel material temperature is set to 1000 ° C. or higher. The lower limit of the heating temperature of the steel material was set to 1000 ° C. from the viewpoint of mainly dissolving Nb carbonitride and ensuring sufficient solid solution Nb. In addition, when the steel material temperature exceeds 1300 ° C., the austenite grains become coarse during heating and adversely affect the base material toughness, so the upper limit is set to 1300 ° C. In addition, desirable steel raw material temperature is 1000-1250 degreeC, More desirably, it is 1050-1200 degreeC.

The steel slab that is rolled and heated with a cumulative reduction ratio of 40% or more in the non-recrystallization temperature range is subjected to controlled rolling in the non-recrystallization temperature range after hot rolling in the recrystallization temperature range. Rolling in the recrystallization temperature region is preferably performed in order to refine the austenite grains at the time of heating, and it is desirable to perform one pass or more, preferably 20% or more of the cumulative rolling reduction. When the rolling reduction in the non-recrystallization temperature range after the hot rolling in the recrystallization temperature range is small, the predetermined base material toughness cannot be obtained. For this reason, the lower limit of the rolling rolling reduction ratio in the non-recrystallization temperature region is defined as 40%. Moreover, although the one where a rolling reduction is higher is preferable, about 80% becomes an upper limit industrially.

  The lower limit temperature of the recrystallization temperature range is influenced by the crystal grain size, processing history, strain amount, etc. in addition to the steel composition, but is generally in the range of 800 to 950 ° C. By conducting a preliminary test and investigating in advance, the lower limit temperature can be estimated.

  Moreover, it is preferable that rolling completion temperature is more than Ar3 transformation point from a viewpoint of the uniformity of structure | tissue.

Implementation of descaling before accelerated cooling Descaling is performed by causing a high collision pressure jet stream to collide with the steel plate surface immediately before accelerated cooling. In order to make a thick steel plate with excellent material uniformity within the steel plate, it is necessary to reduce the variation in hardness within the steel plate, and in particular, while maintaining the strength inside the steel plate, the variation in hardness of the surface layer is reduced. It is important to suppress.

  In a steel sheet after rolling, unevenness in the thickness of the scale may occur in the width direction due to descaling or the like before rolling and during rolling. Further, when the scale is thick, the scale may be partially peeled off. If the scale thickness varies during cooling after rolling, the cooling rate of the steel sheet surface changes according to the thickness, and the hardness of the steel sheet surface also changes according to the cooling rate. To increase the strength of steel sheets, it is effective to increase the cooling rate during accelerated cooling, but the effect of scale thickness on the surface hardness becomes significant when cooling at a high cooling rate. If the thickness is uneven, the variation in hardness increases and the material uniformity in the steel sheet deteriorates.

  In the present invention, the descaling by the high collision pressure jet flow is performed immediately before the acceleration cooling, and the scale thickness is uniformly thinned to 15 μm or less without causing a large difference in the cooling rate. That is, when the scale thickness of the steel sheet after accelerated cooling is 15 μm or less, the hardness variation in the plate thickness direction is ΔHV30 or less, and the hardness variation in the plate width direction is also ΔHV30 or less.

  Although it is difficult to measure the scale thickness of the steel plate immediately before accelerated cooling, the scale thickness before accelerated cooling can be estimated by the scale thickness after accelerated cooling, and the scale thickness of the steel plate after cooling is 15 μm or less. Thus, it has been clarified that the desired effect can be obtained by performing descaling immediately before cooling. By descaling by the jet flow of high impact pressure immediately before cooling, both strength at high cooling speed and material uniformity in the steel sheet can be achieved.

Descaling pressure (impact pressure of jet flow on steel plate surface): 1 MPa or more In the present invention, the impact pressure of jet flow on the steel plate surface immediately before accelerated cooling is such that the scale thickness of the steel plate after cooling is 15 μm or less. Descaling is performed under conditions of 1 MPa or more. If the collision pressure of the jet flow on the surface of the steel sheet is less than 1 MPa, the descaling may be insufficient and unevenness in scale may occur, resulting in variations in surface hardness. Therefore, the collision pressure of the jet flow is 1 MPa or more. Although descaling is performed using high-pressure water, there is no problem even if another jet flow is used as long as the collision pressure of the jet flow on the steel plate surface is 1 MPa or more. More preferably, it is 2 MPa or more.

Average cooling rate of steel plate: 10 ° C./s or more Accelerated cooling after descaling is carried out in order to ensure the strength of the steel plate, but it is necessary to select conditions that simultaneously ensure the material homogeneity of the steel plate surface layer part. . When the average cooling rate of the steel sheet is less than 10 ° C./s, even in the descaled surface layer, the cooling of the surface layer region becomes non-uniform, and the variation in hardness with the inside of the steel plate becomes large. For this reason, an average cooling rate is prescribed | regulated to 10 degrees C / s or more. A more preferable average cooling rate is 15 ° C./s or more. It should be noted that the cooling start temperature is ideally not less than the Ar3 transformation point from the viewpoint of the uniformity of the obtained metal structure. For example, when the plate thickness is thin, the descaling is performed after completion of rolling. In some cases, the temperature is lowered while being transported to the accelerated cooling facility, and the cooling start temperature is lower than the Ar3 transformation point. In order that this influence does not hinder the homogeneity of hardness as the object of the present invention, it is desirable that the accelerated cooling start temperature is within the range of the rolling end temperature to (rolling end temperature −30 ° C.).

Cooling stop temperature: 200 to 600 ° C. at the average steel plate temperature
In the accelerated cooling, cooling is performed to 200 to 600 ° C., which is a temperature range of bainite transformation, and the inside of the steel sheet is transformed (bainite transformation in the present invention) into a microstructure capable of obtaining a predetermined strength. When the cooling stop temperature exceeds 600 ° C., the bainite transformation is incomplete and sufficient strength cannot be obtained. If the cooling stop temperature is less than 200 ° C., part of martensite or island martensite (MA) is generated particularly in the surface layer portion, and material uniformity in the steel sheet cannot be obtained, resulting in a reduction in the elongation characteristics of the entire thickness. For this reason, the cooling stop temperature of accelerated cooling is set to 200 to 600 ° C. in terms of the average steel plate temperature. It may be tempered at the Ac1 transformation point or lower after the accelerated cooling is stopped so as to obtain desired strength toughness. The Ac1 transformation point can be obtained by the following equation. However, in the formula, each element symbol indicates the content (% by mass) of each element.
Ac1 = 751-26.6C + 17.6Si-11.6Mn-169Al-23Cu-23Ni + 24.1Cr + 22.5Mo + 233Nb-39.7V-5.7Ti-895B

  Hereinafter, the effects of the present invention will be described in detail with reference to examples. Steels having the compositions shown in Table 1 were melted in a converter and then made into slabs (steel materials) by a continuous casting method, and steel plates having a thickness of 20 to 50 mm were produced by controlled rolling and accelerated cooling conditions shown in Table 2. In Table 1, steel numbers 1 to 10 are examples of the present invention, and steel numbers 11 to 15 are comparative examples in which any of the component compositions falls outside the scope of the present invention. In Table 2, the branch number A following the steel number is based on the controlled rolling / cooling conditions according to the present invention, and the branch numbers B1 and B2 are comparative examples in which any of the manufacturing conditions is outside the scope of the present invention. It is.

About the thick steel plate manufactured through the above-mentioned composition and manufacturing process, a full thickness tensile test piece having a parallel part width of 25 mm is sampled and subjected to a tensile test in accordance with the provisions of JIS Z 2241 (1998). (Hereinafter referred to as TS) and total thickness elongation (total elongation) were determined. Since the present invention assumes a high-strength steel plate as the object, the strength target is TS: 550 N / mm ² or more, and the total thickness elongation value is generally required for steel materials of the same strength class. The target was 20% or more.

  Further, in order to clarify the correlation between the elongation value in the full thickness tensile test and the hardness variation value of the steel sheet, Vickers hardness was measured in accordance with JIS Z 2244 for a cross section perpendicular to the rolling direction. The hardness distribution in the plate thickness direction and the hardness distribution in the plate width direction were determined. For the plate thickness direction, the hardness of the entire thickness was measured at a pitch of 1 mm, and for the plate width direction, the hardness of the full width was measured at a pitch of 20 mm. In addition, although the hardness in the plate width direction was measured at the surface layer 1 mm position (position 1 mm inside from the surface layer), t / 4 position (plate thickness 1/4 position), t / 2 position (plate thickness center), Since all the steel sheets showed the largest variation in hardness at the surface layer of 1 mm, the variation in hardness in the plate width direction was evaluated at the surface layer of 1 mm. In addition, the test load at the time of hardness measurement was made constant at 10 kgf (98 N).

  Furthermore, in order to evaluate the toughness of the high heat input welding HAZ, a test piece having a width of 80 mm, a length of 80 mm and a thickness of 15 mm is taken from the thick steel plate, heated to 1450 ° C., and then cooled to 800 to 500 ° C. in 250 seconds. After the heat treatment, three 2 mm V notch Charpy test pieces were collected and subjected to the Charpy impact test in the same manner as described above. The impact test temperature was −40 ° C., and the toughness target was 50 J or more in terms of the average absorbed energy at −40 ° C. (hereinafter referred to as vE-40 ° C.).

Table 4 shows the steel plate base material characteristics and the high heat input welding HAZ toughness evaluation results. Vickers hardness (HV) fluctuation width in each of the plate thickness direction and the plate width direction: ΔHV is 30 or less, TS: 550 N / mm ² or more, total thickness elongation value: 20% or more did. In steel numbers 1 to 10 and branch number A, which are examples of the present invention, good values are obtained for both the base material and high heat input welding HAZ characteristics, whereas in steel numbers 1 to 10 and branch numbers B1 and B2. Although the chemical composition definition is within the scope of the present invention, the high heat input HAZ characteristics are satisfied, but the manufacturing conditions are out of the range, so the characteristics of the base material are inferior. On the other hand, steel numbers 11 to 15 (branch numbers) In A and B1 and B2), since the component range is outside the range of the present invention, the toughness of the high heat input HAZ part is inferior.

Claims (5)

  In mass%, C: 0.030 to 0.080%, Si: 0.01 to 0.10%, Mn: 1.20 to 2.40%, P: 0.008% or less, S: 0.0005 -0.0040%, Al: 0.005-0.080%, Nb: 0.003-0.040%, Ti: 0.003-0.040%, N: 0.0030-0.0100%, B: 0.0003 to 0.0030% contained, the remainder having a component composition consisting of Fe and inevitable impurities, and fluctuations in Vickers hardness (HV) in each of the plate thickness direction and the plate width direction Width: A thick steel plate excellent in high heat input welding characteristics and material homogeneity, wherein ΔHV is 30 or less.   Further, by mass%, Cu: 1.00% or less, Ni: 1.00% or less, Cr: 1.00% or less, Mo: 0.50% or less, V: 0.10% or less, or 1 or 2 The thick steel plate excellent in high heat input welding characteristics and material homogeneity according to claim 1, comprising at least a seed.   Furthermore, it contains one or more of Ca: 0.0005 to 0.0050%, Zr: 0.001 to 0.020%, REM: 0.001 to 0.020% in mass%. The thick steel plate excellent in high heat input welding characteristics and material homogeneity according to claim 1 or 2.   The steel material having the component composition according to any one of claims 1 to 3 is heated to 1000 to 1300 ° C and then hot-rolled, and the jet flow is performed under a condition that the collision pressure of the jet flow on the steel plate surface is 1 MPa or more. The descaling is performed by colliding with the steel plate surface, and then accelerated cooling is immediately performed at an average cooling rate of the steel plate of 10 ° C./s or more and an average cooling stop temperature of the steel plate of 200 to 600 ° C. Vickers hardness (HV) fluctuation width in each of the thickness direction and the plate width direction: ΔHV is 30 or less, A method for producing a thick steel plate excellent in high heat input welding characteristics and material homogeneity.   The method for producing a thick steel plate according to claim 4, wherein after the accelerated cooling is stopped, tempering is performed at a temperature equal to or lower than the Ac1 transformation point.