JP5267048B2 - Manufacturing method of thick steel plate with excellent weldability and ductility in the thickness direction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a thick steel plate excellent in a weldability and a ductility in the plate thickness direction, used to a building, bridging, ship-building, offshore structure, tank, etc. <P>SOLUTION: After reheating at 1,000-1,350&deg;C a steel material having the steel composition composed by mass% of 0.01-0.20% C, 0.05-0.50% Si, 0.3-3.0% Mn, &le;0.03% P, &le;0.005% S, &le;0.1% Al, &le;0.02% N, and if necessary, one or more elements selected from Cu, Ni, Cr, Mo, Nb, V, Ti, B, REM and Mg, and the balance Fe with inevitable impurities, a hot-working, desirably a hot-forging is applied with 0.05-3/s strain speed at &ge;1,000&deg;C and &ge;15% accumulated pressing-reduction ratio, and further, a hot-rolling and a heat-treatment are suitably applied according to the desirable plate thickness and mechanical characteristics. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a thick steel plate having excellent weldability and ductility in the thickness direction used for buildings, bridges, shipbuilding, offshore structures, tanks, etc., and particularly as a method for producing a thick steel plate having a thickness of 60 mm or more. It relates to a suitable one.

  When steel materials are used in various fields such as architecture, bridges, shipbuilding, offshore structures, tanks, etc., they are finished to a desired shape by welding according to the shape of the steel structure. In recent years, steel structures are becoming larger and their shapes are diversified, and the strength and thickness of steel materials used are increasing.

  It is known that the amount of alloying elements to be added generally increases as the strength of steel materials increases, and this causes deterioration in cold cracking properties of welds.

  In particular, when the steel material used is thickened, not only the tensile stress applied to the welded portion increases, but also the central segregation portion where the alloy elements are concentrated remains in the steel material, and the apparent amount of alloying elements increases. When the welded heat cycle is applied to the center segregated portion, the quench hardenability is remarkably increased, so that the low temperature cracking property of the welded portion is deteriorated.

  In addition, in steel structures welded to complex shapes, tensile stress may act in the thickness direction of the steel material. From the viewpoint of safety, the width direction and length of the steel material used It is required to have excellent mechanical properties in the thickness direction as well as mechanical properties in the direction.

  In particular, ductility with respect to a tensile load in the plate thickness direction is important from the viewpoint of preventing destruction of the steel structure.

  However, when the steel material is thickened, the center porosity and solidification segregation generated at the stage of the steel material may remain in the final product, leading to a reduction in ductility in the thickness direction.

  As steel materials increase in strength, the amount of alloying elements added increases segregation of alloying elements and formation of inclusions, making it more difficult to ensure ductility in the thickness direction. There is a demand for a thick steel plate having excellent ductility in the thickness direction.

In Patent Document 1, as a technique for improving the tensile and compressive deformation performance in the thickness direction of 500 N / mm grade ² steel, when continuously casting a steel material, electromagnetic stirring is performed, and the slab is bulged, and the unsolidified portion is further removed. A continuous casting method for rolling down a slab containing is described.

Patent Document 2 describes that the center porosity and the center segregation are improved by carrying out cross forging on a continuous cast slab and then forming and rolling. Patent Document 3 describes a method for producing a steel sheet that is excellent in strength and toughness by carrying out solution heat treatment of a steel material and then rolling and heat treatment.
Japanese Patent Laid-Open No. 2005-103604 JP 2000-263103 A Japanese Patent Laid-Open No. 2-205629

However, in the manufacturing method described in Patent Document 1, there are large restrictions on the amount of reduction and strain rate control, and the effect of improving weldability and ductility in the plate thickness direction cannot be sufficiently obtained with extremely thick high-strength steel. Since the capacity is limited by the drawing speed of continuous casting, there is a concern that the production efficiency is lowered.

  In the technique described in Patent Document 2, weldability and ductility improvement effect in the plate thickness direction cannot be sufficiently obtained, and further, the forging process needs to be divided into two processes, so that the production efficiency is lowered and the production cost is raised. Is concerned.

  The technique described in Patent Document 3 requires a solution heat treatment for a long time at high temperature before rolling, so there is concern about a decrease in manufacturing efficiency and an increase in manufacturing cost, and an improvement in weldability and ductility in the plate thickness direction. The effect cannot be obtained sufficiently.

  Accordingly, an object of the present invention is to provide a method for producing a thick steel plate that satisfies excellent weldability and stably achieves excellent ductility with respect to a tensile load in the plate thickness direction.

In order to achieve the above-mentioned problems, the present inventors have studied the microstructure control factor inside the steel plate among various factors that determine the weld cold cracking property and the ductility in the plate thickness direction at the center of the plate thickness for the thick steel plate. We conducted intensive research and obtained the following knowledge.
1. In order to achieve excellent weldability of the steel material, it is necessary to appropriately select and strictly control the steel composition.
2. In order to suppress hydrogen accumulation sites that promote cold cracking of welds as much as possible, and to stably achieve excellent ductility in the thickness direction tensile test of thick steel plates, MnS generated in the center of the steel material is as much as possible It is essential to suppress it. When MnS cannot be completely suppressed, it is important to finely control the sulfide in the central portion of the plate thickness by strictly adjusting the amount of Ca added.
3. Furthermore, in order to achieve excellent weldability and ductility in the thickness direction, the lower limit of the total hot rolling reduction and the lower limit of the processing temperature are strictly controlled, and the center porosity disappears completely. This is very important.
4). Furthermore, in order to achieve excellent weldability and ductility in the plate thickness direction, the total segregation amount of hot working and the processing temperature are controlled, and the strain rate is adjusted strictly to reduce the center segregation at the center of the steel material. It is most important to eliminate it.

  By strictly controlling the processing temperature, processing amount and strain rate, various dynamics of austenite are expressed during hot processing, and the movement of grain boundaries is promoted. A steel plate having a uniform composition without segregation can be obtained by efficiently diffusing the alloy elements.

By the above combination, a steel plate free from center metal porosity, coarse non-metallic inclusions such as MnS and center segregation is obtained in the center of the plate thickness of the thick steel plate, and has excellent weldability and ductility in the thickness direction. It can be achieved stably.
5. When the average crystal grain size of the metal structure after hot working exceeds 300 μm, the toughness is lowered and dynamic recrystallization during hot working becomes insufficient, so that segregation is not eliminated. As a result, during the tensile test, stress on the crystal grain boundary is likely to concentrate, which becomes a starting point of voids and causes a significant decrease in ductility. Therefore, it is desirable that the average crystal grain size of the metal structure after hot working be 300 m or less.

The present invention has been made by further studying the obtained knowledge, that is, the present invention
1. Steel composition is mass%,
C: 0.01 to 0.20%
Si: 0.05 to 0.50%
Mn: 0.3 to 3.0%
P: 0.03% or less S: 0.005% or less Al: 0.1% or less N: 0.02% or less, the steel material consisting of Fe and unavoidable impurities in the balance, 1100 to 1350 ° C. Thick steel plate with excellent weldability and ductility in the plate thickness direction, which is subjected to hot working after reheating to a strain rate at 1000 ° C. or higher of 0.05 to 3 / s and a cumulative reduction amount of 15% or higher. Manufacturing method.
In steel composition described in 2.1, in mass%,
Ca: A steel material containing 0.005% or less and the balance consisting of Fe and inevitable impurities is reheated to 1100 to 1350 ° C., and then the strain rate at 1000 ° C. or higher is 0.05 to 3 / s, cumulative reduction A method for producing a thick steel plate excellent in weldability and ductility in the thickness direction, characterized by performing hot working to an amount of 15% or more.
3.1 In addition to the steel composition described in 2 or 2 by mass%,
Cu: 0.01 to 2.0%
Ni: 0.01-3.0%
Cr: 0.01 to 3.0%
Mo: 0.01 to 3.0%
Nb: 0.1% or less,
V: 0.1% or less,
Ti: 0.05% or less,
B: 0.005% or less REM: 0.02% or less Mg: 0.005% or less One or two or more steel materials, the balance being Fe and inevitable impurities are re-used at 1100 to 1350 ° C. After heating, the strain rate of hot working at 1000 ° C. or higher is 0.05 to 3 / s, and the cumulative reduction amount is 15% or more. Production of a thick steel plate excellent in weldability and ductility in the plate thickness direction Method.
4). The method for producing a thick steel plate having excellent weldability and ductility in the plate thickness direction according to any one of 1 to 3, further comprising tempering at 400 to 650 ° C after hot working.
5. The method for producing a thick steel plate having excellent weldability and ductility in the plate thickness direction according to any one of 1 to 3, wherein the steel plate is further reheated to 1000 to 1250 ° C after hot working.
6). 6. The method for producing a thick steel plate having excellent weldability and ductility in the thickness direction according to 5, wherein the steel is further tempered at 400 to 650 ° C. after reheating.
7). After the hot working, it is further reheated to 1000 to 1250 ° C., and hot rolling is performed so that the rolling end temperature is 750 ° C. or more. A method for producing thick steel plates with excellent ductility in the direction.
8). After hot rolling, further Ac ₃ weldability and the plate thickness direction of the manufacturing method of excellent steel plate ductility 7, wherein the reheating above transformation point.
9. 9. The method for producing a thick steel plate having excellent weldability and ductility in the thickness direction according to 8, wherein the steel plate is further tempered at 400 to 650 ° C. after reheating.

  According to the present invention, a method for producing a thick steel plate having a thickness of 60 mm or more excellent in weldability and ductility in the plate thickness direction is obtained, and the steel structure is increased in size, the safety of the steel structure is improved, and the construction efficiency is improved. It greatly contributes to improvement and has a remarkable industrial effect.

In this invention, a component composition and manufacturing conditions are prescribed | regulated.
[Ingredient composition] In the description, “%” means “mass%”.
C: 0.01 to 0.16%
C is an element necessary for increasing the strength of the steel and ensuring the strength required as a structural steel material. To obtain the effect, C is required to be contained in an amount of 0.01% or more.

  On the other hand, the content exceeding 0.16% significantly deteriorates the toughness of the base material and the welded portion. Moreover, in order to degrade the low temperature cracking property of a welding part, it limits to 0.01 to 0.16% of range. Preferably, it is 0.02 to 0.15%.

Si: 0.05 to 0.50%
Si acts as a deoxidizer and needs to be at least 0.05% for steelmaking. However, if it contains more than 0.50%, not only the toughness of the base metal and the welded portion is deteriorated, but also the welded portion. Since low temperature cracking property deteriorates, it limits to 0.05 to 0.50% of range. Preferably, it is 0.10 to 0.40%.

Mn: 0.3 to 3.0%
Mn has the effect of increasing the strength of the steel and needs to contain 0.3% or more. On the other hand, if the content exceeds 3.0%, not only the toughness of the base material deteriorates, but also the low temperature cracking property of the welded portion significantly deteriorates, and the center segregation becomes prominent and the ductility in the thickness direction is deteriorated. , Limited to the range of 0.3-3.0%. Preferably, it is 0.4 to 1.8%.

P: 0.03% or less P is not only an element that increases the strength of steel and deteriorates toughness, but also deteriorates ductility in the thickness direction due to center segregation. It is desirable to reduce as much as possible. In addition, since excessive P reduction raises refining cost and becomes economically disadvantageous, it is desirable to set it as 0.001% or more.

S: 0.005% or less S not only deteriorates the low temperature toughness of the base material, but also produces MnS and deteriorates the ductility in the thickness direction. Therefore, 0.005% can be reduced as much as possible. desirable.

Al: 0.1% or less Al acts as a deoxidizer, and is most commonly used in the molten steel deoxidation process of high-strength steel. In addition, N in the steel is fixed as AlN and contributes to the improvement of the toughness of the base metal. However, if the content exceeds 0.1%, the toughness of the base material decreases, and the weld metal part is mixed during welding, In order to deteriorate the toughness, the content is limited to 0.1% or less.

N: 0.02% or less N is contained in steel as an unavoidable impurity, and if it exceeds 0.02%, the toughness of the base metal and the welded portion is remarkably reduced, so it is limited to 0.02% or less.

  In the present invention, when further improving the characteristics, in addition to the basic component system, one or more of Ca, Cu, Ni, Cr, Mo, Nb, V, Ti, B, REM, and Mg are contained. be able to.

Ca: 0.005% or less Ca is effective in controlling the form of oxysulfide, suppresses the formation of coarse MnS and the like that adversely affects ductility, forms fine Ca oxysulfide and improves toughness It is a useful element.

  If it exceeds 0.005%, Ca oxysulfide becomes coarse and adversely affects toughness, so it is limited to 0.005% or less. In order to acquire the said effect, it is preferable to add 0.0005% or more, and it is preferable to set it as 0.0005 to 0.0045%.

One or more of Cu: 0.01 to 2.0%, Ni: 0.01 to 3.0% Cu and Ni are elements that can increase strength while maintaining high toughness, Since the influence on the HAZ toughness is small, it is an element useful for increasing the strength, and can be selected and contained as necessary.

When adding Cu, it is preferable to contain 0.01% or more, but if it exceeds 2.0%, it causes hot brittleness and deteriorates the surface properties of the steel sheet. %. In addition, Preferably, it is 0.05 to 0.7%.
When adding Ni, it is preferable to contain 0.01% or more, but even if it contains more than 3.0%, the effect is saturated and the effect commensurate with the content cannot be expected, which is economically disadvantageous. Therefore, the content is made 0.01 to 3.0%. In addition, Preferably it is 0.05 to 1.7%.

Cr: 0.01-3.0%, Mo: 0.01-3.0%, Nb: 0.1% or less, V: 0.1% or less, Ti: 0.05% or less, B: 0.0. One or more of 005% or less, Cr, Mo, Nb, V, Ti, and B are elements that contribute to improving the strength of the steel, and can contain one or more of them depending on the desired strength.

  When adding Cr, it is preferable to contain 0.01% or more, but when it exceeds 3.0%, the low temperature cracking property and HAZ toughness of the welded portion are deteriorated. It is desirable to limit it to%.

  When Mo is added, the content is preferably 0.01% or more. However, when the content exceeds 3.0%, the low temperature cracking property, the base metal toughness, and the HAZ toughness of the weld are adversely affected. It is desirable to limit to 01 to 3.0%.

  When Nb is added, it is preferably contained in an amount of 0.005% or more. However, if it exceeds 0.1%, the base material toughness and the HAZ toughness are deteriorated. desirable.

  When V is added, it is preferably contained in an amount of 0.01% or more, but if it exceeds 0.1%, the HAZ toughness is deteriorated, so it is desirable to limit it to 0.1% or less.

  Ti contributes to strength improvement, and has a strong affinity with N, and precipitates as TiN during solidification, thereby suppressing the austenite grain coarsening in HAZ and contributing to the toughness of HAZ, but it exceeds 0.05%. If added, the base material toughness is deteriorated. Therefore, when added, the content is preferably limited to 0.05% or less. In order to acquire the said effect, it contains 0.005% or more.

  B has the effect of improving the hardenability and increasing the strength of the steel, but if contained over 0.005%, the hardenability is remarkably increased, the cold cracking property of the weld zone, the toughness of the base metal and In order to cause deterioration of ductility, the content is made 0.005% or less.

One or two types of REM: 0.02% or less and Mg: 0.005% or less REM and Mg both contribute to improvement of toughness, and are added according to desired properties. When adding REM, even if it exceeds 0.02%, the effect is saturated, so 0.02% is made the upper limit. In order to acquire the said effect, it is preferable to set it as 0.002% or more.

  When adding Mg, the effect is saturated even if it exceeds 0.005%, so 0.005% is made the upper limit. In order to acquire the said effect, it is preferable to set it as 0.001% or more. The balance other than the above components is Fe and inevitable impurities.

[Production conditions]
In the description, the temperature “° C.” means a temperature at half the plate thickness.
In the method for producing a thick steel plate according to the present invention, it is essential to subject the steel material to hot working in order to eliminate casting defects such as center porosity in the steel material.

1. Hot working conditions for steel materials Heating temperature: 1100 ° C to 1350 ° C
A steel material of a slab or steel slab having the composition described above is prepared from molten steel by a generally known method such as a converter, electric furnace, vacuum melting furnace, etc., and reheated to 1100 ° C to 1350 ° C. If the reheating temperature is less than 1100 ° C., the predetermined hot working cumulative rolling amount and the lower temperature limit cannot be secured, the deformation resistance in hot working is high, and the rolling amount per pass cannot be taken sufficiently.

  As a result, the number of passes increases, the production efficiency decreases, and casting defects such as center porosity in the steel material cannot be pressure-bonded.

  On the other hand, if the reheating temperature exceeds 1350 ° C., surface flaws are likely to occur due to the scale during heating, and the maintenance load after hot working increases, so the temperature is set to 1100 to 1350 ° C.

Hot working temperature: 1000 ° C or higher If the hot working temperature is less than 1000 ° C, the diffusion effect of alloying elements due to the dynamic recrystallization of austenite during hot working cannot be sufficiently obtained. Is not eliminated, and the cold cracking property of the welded portion and the ductility decrease in the thickness direction are caused. Further, since the deformation resistance is increased, the load to be applied is increased and the burden on the hot working machine is increased, so that the temperature is set to 1000 ° C. or higher.

Cumulative reduction amount of hot working: 15% or more When the cumulative reduction amount of hot working is less than 15%, casting defects such as center porosity in the steel material cannot be crimped. Furthermore, since the diffusion effect of the alloy element due to the dynamic recrystallization of austenite during hot working cannot be sufficiently obtained, the center segregation is not eliminated, and the cold cracking property of the welded portion and the ductility reduction in the plate thickness direction are caused.

  In the case of an extremely thick steel plate having a thickness exceeding 80 mm, it is desirable to secure at least one pass with a reduction rate of 5% or more per pass for center porosity pressure bonding.

Hot working strain rate: 0.05-3 / s
When the strain rate of hot working is less than 0.05 / s, due to the temperature drop during hot working, the predetermined cumulative reduction amount and the lower temperature limit cannot be secured, and the production efficiency is lowered.

  On the other hand, if it exceeds 3 / s, the diffusion effect of the alloy element due to dynamic recrystallization of austenite during hot working cannot be sufficiently obtained, so that center segregation is not eliminated and cold cracking property of the welded portion, plate thickness In order to reduce the ductility in the direction, the strain rate of hot working is set to 0.05 to 3 / s.

  In addition, it is preferable to reduce the casting conditions when manufacturing the steel material from the molten steel as much as possible because coarse non-metallic inclusions in the metal structure cause low-temperature crackability of the welded portion and reduced ductility in the plate thickness direction. It is desirable to adjust so that the area fraction is 5% or less and the maximum equivalent circle diameter is 100 μm or less.

  In addition, although a publicly known method, such as hot forging and hot rolling, can be used for hot working, hot forging is preferable in consideration of economy, controllability, and the like.

After hot working, reheating treatment or tempering is carried out alone or in combination depending on the desired mechanical properties. When the reheating treatment is performed, heating is performed to a temperature range equal to or higher than the Ac ₃ transformation point. The upper limit of the heating temperature is not specified, but if it exceeds 1100 ° C., the surface properties of the steel sheet deteriorate, so the upper limit is preferably set to 1100 ° C. or less.

Also, the holding time is not specified, but if it exceeds 1 hr, the toughness of the base material deteriorates due to coarsening of austenite grains, so that it is preferably within 1 hr. . Note that the Ac ₃ point (° C.) can be roughly correlated with the chemical composition by the following equation.
Ac ₃ points (° C.) = 854-180C + 44Si-14Mn-17.8Ni-1.7Cr
(However, C, Si, Mn, Ni, Cr: content of each alloy element (mass%))
When tempering is performed after hot working or after reheating, heating is performed at 400 ° C. or more and 650 ° C. or less. In order to obtain the effect of improving the toughness and ductility of the base material, the heating temperature is set to 400 ° C. or higher, and if it exceeds 650 ° C., the strength of the base material is greatly reduced.

  The cooling after the hot working is appropriately selected according to the desired mechanical characteristics, such as air cooling, accelerated cooling, and water cooling.

  In the present invention, hot rolling is performed after hot working to obtain a steel plate having a desired thickness, and the obtained steel plate is kept in hot rolling or subjected to reheating treatment or tempering treatment alone depending on the desired mechanical properties. Or they can be applied in combination.

2. Hot rolling conditions Reheating temperature: 1000 ° C to 1250 ° C
For hot rolling, reheating is performed at 1000 ° C. to 1250 ° C. after hot working. If the reheating temperature is less than 1000 ° C, the deformation resistance in hot rolling is high, and the amount of rolling reduction per pass cannot be increased. Therefore, the number of rolling passes increases and the rolling efficiency decreases, and the steel material ( In some cases, the casting defect in the slab cannot be crimped.

  On the other hand, if the reheating temperature exceeds 1250 ° C., surface flaws are likely to occur due to the scale during heating, and the maintenance load after rolling increases, so the temperature is set to 1000 to 1250 ° C.

Rolling end temperature: 750 ° C. or higher When the rolling end temperature is lower than 750 ° C., the deformation resistance increases, so the rolling load increases and the burden on the rolling mill increases. Moreover, in order to reduce the thick material to a rolling temperature of less than 750 ° C., it is necessary to wait in the middle of rolling, which greatly impedes productivity. For this reason, rolling end temperature shall be 750 degreeC or more.

When the rolling is left as it is, if the cooling rate after the rolling is over 60 ° C./s, it becomes difficult to control the temperature depending on the position of the steel sheet, and material variations tend to occur. The cooling rate is an average cooling rate obtained by averaging the cooling rates at the respective positions in the thickness direction.
3. Heat treatment conditions
The heat treatment after rolling is as follows: 1. Reheat to temperature range above Ac ₃ transformation point and normalize. 2. Reheating to a temperature range above the Ac ₃ transformation point and quenching, or Either direct quenching after the end of rolling. After any of these heat treatments, appropriate tempering is performed according to the tempering conditions after hot working.

  Note that the microstructure of the steel sheet obtained by hot rolling after hot working is either a ferrite, pearlite, bainite, martensite, or the like, or a multiphase by heat treatment performed according to the desired mechanical properties. A mixed tissue is obtained.

  A steel slab (steel material) with a thickness of 310 mm prepared in various components by the converter-ladder refining-continuous casting method is hot-forged under various conditions to form a steel plate. After hot forging, hot rolling and / or heat treatment was performed. Table 1 shows the component composition of the steel sheet, and Table 2 shows the hot forging, hot rolling and heat treatment conditions.

  A JIS No. 4 tensile test piece was sampled from the C direction at a thickness of 1/2 of the obtained steel sheet, and a tensile test was performed in accordance with the default of JIS Z 2241 (1998) to investigate the tensile properties.

For base metal toughness, V-notch specimens were collected from the C direction at a thickness of 1/4 of each steel plate according to JIS Z 2202 (1998), and conformed to JIS Z 2242 (1998). Then, a Charpy impact test was carried out, and the absorbed energy (vE ₀ ) at 0 ° C. was obtained and evaluated.

  The ductility in the plate thickness direction is determined from the plate thickness direction of each steel plate in accordance with JIS G 3199 (1992) by collecting a thickness direction tensile test piece (type b), and JIS Z 2241 (1998). Was subjected to a tensile test, and a drawing value (RA) was obtained and evaluated.

  Furthermore, each steel plate was subjected to a y-type weld cracking test in accordance with JIS Z 3158 (1993), and the weldability was evaluated by obtaining the root crack generation rate at room temperature (25 ° C.). The supply wire used was JIS Z 3212 equivalent.

The results obtained are shown in Table 3. In all of the inventive examples, it is recognized that high toughness with an absorbed energy of 100 J or more by a Charpy impact test at 0 ° C. and high ductility of 60% or more by a drawing value by a sheet thickness direction tensile test are obtained. Furthermore, in the y-type weld crack test, cracks at the root do not occur.
On the other hand, in the comparative example outside the scope of the present invention, the toughness or the ductility in the thickness direction does not satisfy the target value, or cracks occur at the root portion in the y-type weld crack test.

Claims (9)

Steel composition is mass%,
C: 0.01 to 0.20%
Si: 0.05 to 0.50%
Mn: 0.3 to 3.0%
P: 0.03% or less S: 0.005% or less Al: 0.1% or less N: 0.02% or less, the steel material consisting of Fe and unavoidable impurities in the balance, 1100 to 1350 ° C. Thick steel plate with excellent weldability and ductility in the plate thickness direction, which is subjected to hot working after reheating to a strain rate at 1000 ° C. or higher of 0.05 to 3 / s and a cumulative reduction amount of 15% or higher. Manufacturing method. The steel composition according to claim 1, further in mass%,
Ca: A steel material containing 0.005% or less and the balance consisting of Fe and inevitable impurities is reheated to 1100 to 1350 ° C., and then the strain rate at 1000 ° C. or higher is 0.05 to 3 / s, cumulative reduction A method for producing a thick steel plate excellent in weldability and ductility in the thickness direction, characterized by performing hot working to an amount of 15% or more. In the steel composition according to claim 1 or 2, further in mass%,
Cu: 0.01 to 2.0%
Ni: 0.01-3.0%
Cr: 0.01 to 3.0%
Mo: 0.01 to 3.0%
Nb: 0.1% or less,
V: 0.1% or less,
Ti: 0.05% or less,
B: 0.005% or less REM: 0.02% or less Mg: 0.005% or less One or two or more steel materials, the balance being Fe and inevitable impurities are re-used at 1100 to 1350 ° C. After heating, the strain rate of hot working at 1000 ° C. or higher is 0.05 to 3 / s, and the cumulative reduction amount is 15% or more. Production of a thick steel plate excellent in weldability and ductility in the plate thickness direction Method.   The method for producing a thick steel plate excellent in weldability and ductility in the plate thickness direction according to any one of claims 1 to 3, further comprising tempering at 400 to 650 ° C after hot working.   The method for producing a thick steel plate excellent in weldability and ductility in the plate thickness direction according to any one of claims 1 to 3, further comprising reheating to 1000 to 1250 ° C after hot working.   6. The method for producing a thick steel plate excellent in weldability and ductility in the plate thickness direction according to claim 5, further comprising tempering at 400 to 650 ° C. after reheating.   The weldability according to any one of claims 1 to 3, wherein after hot working, the steel is further reheated to 1000 to 1250 ° C, and hot rolling is performed so that the rolling end temperature is 750 ° C or higher. A method for producing a thick steel plate having excellent ductility in the thickness direction. The method for producing a thick steel plate excellent in weldability and ductility in the plate thickness direction according to claim 7, wherein after the hot rolling, reheating is further performed to an Ac ₃ transformation point or higher.   The method for producing a thick steel plate excellent in weldability and ductility in the plate thickness direction according to claim 8, further tempered at 400 to 650 ° C. after reheating.