High strength thick steel plate with excellent low temperature impact toughness and manufacturing method thereof

Abstract

Provided is a thick steel plate having high strength and excellent low-temperature impact toughness, and a method for manufacturing the same. [Solution] The alloy contains, by weight, C: 0.04-0.08%, Si: 0.1-0.35%, Mn: 1.4-1.8%, Sol.Al: 0.01-0.035%, Ni: 0.2-0.5%, Cr: 0.1-0.3%, Mo: 0.05-0.15%, Nb: 0.015-0.035%, Ti: 0.005-0.02%, N: 0.002-0.006%, P: 0.01% or less, S: 0.003% or less, and the remainder being iron. A high-strength thick steel plate having excellent low-temperature impact toughness, characterized in that the steel consists essentially of a mixed structure of acicular ferrite and bainite with a total area percentage of the remaining cementite and MA of 2% or less, and the average grain size of the acicular ferrite at the 1 / 4 thickness point is 25 μm or less. [Equation 1] R = [Ni] + 3 [Mo] + 2 [Cr] (Here, [Ni], [Mo] and [Cr] are the weight percentages of each element.)

Description

[Technical field]

[0001] The present invention relates to a high-strength thick steel plate having excellent low-temperature impact toughness and a manufacturing method thereof, and more particularly to a thick steel plate having high strength and excellent low-temperature impact toughness and a manufacturing method thereof. [Background technology]

[0002] Since the 2000s, attention has been focused on new and renewable energy as a way to address environmental issues and reduce greenhouse gas emissions. New and renewable energy is a term that collectively refers to new energy (hydrogen, fuel cells, etc.) and renewable energy (solar heat, wind power, bio, etc.), of which wind power is an environmentally friendly power generation method that does not produce waste or cause pollution, and is garnering attention as a next-generation energy source. Onshore wind power generation, which is installed on land, is problematic due to noise pollution and limitations on optimal wind formation and space, but recently there has been rapid growth in offshore wind power generation, which is built in the sea, mainly in Europe.

[0003] Offshore wind power was developed later than onshore wind power, but with the development of technology, the relative superiority of offshore wind power over onshore wind power is increasingly emerging due to various advantages such as low wind speed, low concerns about noise generation, and the ability to secure a large area. In particular, offshore wind power has the great advantage of being able to increase the power generation capacity per turbine compared to onshore wind power. In other words, the average power generation capacity is about twice that of onshore wind power, and the average capacity of newly installed turbines per unit in Europe has rapidly increased from 4MW in 2015 to 7.2MW in 2019, and is expected to reach over 10MW within the next 2 to 3 years.

[0004] As a result, the strength of the thick steel plates used has gradually increased, with most having a yield strength of 325MPa for an 80mm thickness, but in the 2020s, yield strengths of 380 and 410MPa have been applied.The substructures of such offshore wind power plants are broadly divided into monopiles and jackets, and the substructures of the jacket type are divided into pin pile and suction bucket types depending on the method of fixing them to the seabed.

[0005] The substructure of a monopile is divided into the monopile section that is inserted into the seabed and the transition piece that connects the monopile to the tower. This structure bears the most weight, and high-strength steel is primarily used for the joint between the monopile and the transition piece. In these important support areas of the substructure of offshore wind power plants, thick steel plates that are not only high-strength but also extremely thick and have guaranteed low-temperature toughness are used. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a thick steel plate having high strength and excellent low-temperature impact toughness, and a method for manufacturing the same.

[0007] The object of the present invention is not limited to the above-mentioned contents, and a person skilled in the art will have no difficulty in understanding further object of the present invention from the entire content of the specification of the present invention. [Means for solving the problem]

[0008] The present invention includes, by weight percent, C: 0.04-0.08%, Si: 0.1-0.35%, Mn: 1.4-1.8%, Sol.Al: 0.01-0.035%, Ni: 0.2-0.5%, Cr: 0.1-0.3%, Mo: 0.05-0.15%, Nb: 0.015-0.035%, Ti: 0.005-0.02%, N: 0.002-0.006%, P: 0.01% or less, S: 0.003% or less, and the balance being iron (Fe) and other unavoidable impurities, The R value defined by the following relational formula 1 is 0.85 to 1.35, The microstructure at the 1 / 4 thickness point is mainly composed of a mixed structure of acicular ferrite and bainite, with the remaining cementite and MA (martensite) being 2% or less by area in total. It is possible to provide a steel sheet in which the average size of acicular ferrite grains at the 1 / 4 thickness point is 25 μm or less. [Equation 1] R = [Ni] + 3 [Mo] + 2 [Cr] (Here, [Ni], [Mo] and [Cr] are the weight percentages of each element.)

[0009] The above steel plate may contain 40 to 60 area % of acicular ferrite and 40 to 60 area % of bainite as a microstructure at the 1 / 4 thickness point.

[0010] The steel plate may contain cementite and MA in a total amount of 1% by area or less.

[0011] The steel sheet may have an average grain size of acicular ferrite at a quarter thickness point of 15 to 25 μm.

[0012] The steel plate may have a thickness of 50 to 100 mm.

[0013] The steel plate may have a yield strength of 460 MPa or more, a tensile strength of 580 MPa or more, and an impact toughness at -50°C of 100 J or more.

[0014] The present invention relates to a process for producing a steel slab having an R value of 0.85 to 1.35, the R value being defined by the following Relation 1, comprising, by weight, 0.04 to 0.08% C, 0.1 to 0.35% Si, 1.4 to 1.8% Mn, 0.01 to 0.035% Sol.Al, 0.2 to 0.5% Ni, 0.1 to 0.3% Cr, 0.05 to 0.15% Mo, 0.015 to 0.035% Nb, 0.005 to 0.02% Ti, 0.002 to 0.006% N, 0.01% or less P, and 0.003% or less S, with the remainder being iron (Fe) and other unavoidable impurities; rolling the reheated steel slab in the recrystallization region at a temperature range of 900°C or higher with a final pass reduction of 15 to 25 mm; The recrystallization region rolled steel sheet is subjected to non-recrystallization region rolling at a rolling end temperature of Ar3+20 to Ar3+60; and The method for manufacturing the steel sheet may include a step of water-cooling the non-recrystallized region rolled steel sheet to a temperature range of 400° C. or less based on a 1 / 4 point of the steel sheet thickness. [Equation 1] R = [Ni] + 3 [Mo] + 2 [Cr] (Here, [Ni], [Mo] and [Cr] are the weight percentages of each element.)

[0015] The above reheating is carried out in the temperature range of 1020 to 1100°C. During the non-recrystallization region rolling, the cumulative rolling reduction may be 30 to 50%.

[0016] During the cooling, the steel sheet may be cooled at a cooling rate of 5 to 10° C. / s based on a 1 / 4 point of the steel sheet thickness.

[0017] The steel plate may have a thickness of 50 to 100 mm. Effect of the Invention

[0018] According to one aspect of the present invention, there is provided a thick steel plate having high strength and excellent low-temperature impact toughness, and a method for manufacturing the same.

[0019] According to one aspect of the present invention, it is possible to provide a thick steel plate and a manufacturing method thereof that have excellent strength and low-temperature impact toughness and can be used as extremely thick steel material for offshore wind power generation and can also be used as structural steel material for the infrastructure industry, such as construction and bridges. [Brief description of the drawings]

[0020] [Figure 1] 1 is a photograph of a microstructure of an example of the present invention observed at a magnification of 500 using an optical microscope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] In the following, preferred embodiments of the present invention will be described. The embodiments of the present invention can be modified in various ways, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments are provided to further explain the present invention in detail to those skilled in the art to which the present invention pertains.

[0022] The present invention will be described in detail below.

[0023] The steel composition of the present invention will be described in detail below.

[0024] In the present invention, unless otherwise specified, % representing the content of each element is based on weight.

[0025] The steel of the present invention contains, by weight, C: 0.04-0.08%, Si: 0.1-0.35%, Mn: 1.4-1.8%, Sol.Al: 0.01-0.035%, Ni: 0.2-0.5%, Cr: 0.1-0.3%, Mo: 0.05-0.15%, Nb: 0.015-0.035%, Ti: 0.005-0.02%, N: 0.002-0.006%, P: 0.01% or less, S: 0.003% or less, and the balance containing iron (Fe) and other unavoidable impurities.

[0026] Carbon (C): 0.04~0.08% Carbon (C) is an element that causes solid solution strengthening and exists as a carbonitride with Nb etc. to ensure tensile strength, and its content can be limited to 0.04% or more. On the other hand, if the carbon (C) content exceeds 0.08%, not only does it promote the formation of MA, but also pearlite is generated, which may deteriorate the impact properties at low temperatures, and there is a risk of deteriorating the welding properties when welding a structure. A more preferable upper limit of carbon (C) can be 0.07%.

[0027] Silicon (Si): 0.1-0.35% Silicon (Si) is an element that assists Al in deoxidizing molten steel and is necessary for ensuring yield strength and tensile strength, and may be contained in an amount of 0.1% or more. However, if the content exceeds 0.35%, there is a possibility that the diffusion of C is hindered and the formation of MA is promoted. Preferably, silicon (Si) may be contained in an amount of 0.15% or more, and more preferably, 0.25% or less.

[0028] Manganese (Mn): 1.4-1.8% Manganese (Mn) is effective in increasing strength through solid solution strengthening, so it is preferable to add 1.4% or more. On the other hand, if the content is excessive, it may cause a decrease in toughness due to the formation of MnS inclusions and segregation in the center, so the upper limit can be limited to 1.8%.

[0029] Aluminum (Sol.Al): 0.01-0.035% Aluminum (Sol.Al) is the main deoxidizing agent for steel, and in order to obtain this effect, it is preferable to add 0.01% or more. However, if the content exceeds 0.035%, it may cause a decrease in low-temperature toughness due to an increase in the fraction and size of Al2O3 inclusions. In addition, similar to Si, it may promote the generation of MA in the base material and the weld heat affected zone, which may decrease the low-temperature toughness characteristics. It may be preferably contained at 0.015% or more, and more preferably 0.03% or less.

[0030] Nickel (Ni): 0.2-0.5% Nickel (Ni) is an element that improves strength without reducing impact toughness, and can promote the formation of an appropriate amount of acicular ferrite to increase strength, so it is preferable to add 0.2% or more. On the other hand, if its content exceeds 0.5%, it may lower the Ar3 temperature and form bainite, which may reduce the impact toughness of extremely thick products. A more preferable lower limit may be 0.3%.

[0031] Chromium (Cr): 0.1-0.3% Chromium (Cr) is an element advantageous in securing strength as a carbide forming element, but in very thick steel materials, it may form coarse carbides depending on the cooling rate of the steel, which may impair impact toughness, so the Cr content may be limited to 0.1 to 0.3%. A more preferable lower limit of the Cr content may be 0.15%.

[0032] Molybdenum (Mo): 0.05~0.15% Molybdenum (Mo) is an element that effectively increases strength with a small amount of addition, and is preferably added at 0.05% or more to form Mo-C series precipitates to improve strength. However, excessive addition of Mo may cause coarsening of precipitates, so the upper limit may be limited to 0.15%. The preferred lower limit of the content may be 0.08%, and the more preferred upper limit of the content may be 0.12%.

[0033] Niobium (Nb): 0.015-0.035% Niobium (Nb) is an element that suppresses recrystallization during rolling or cooling by forming a solid solution or precipitating carbonitrides, thereby refining the structure and increasing strength, and can be added in an amount of 0.015% or more. However, since C concentration occurs due to C affinity, which promotes MA formation and reduces toughness and fracture properties at low temperatures, the upper limit can be limited to 0.035%. The preferred lower limit can be 0.02%, and the more preferred upper limit can be 0.03%.

[0034] Titanium (Ti): 0.005~0.02% Titanium (Ti) can combine with oxygen or nitrogen to form precipitates. Such precipitates suppress coarsening of the structure, contribute to refinement, and play a role in improving toughness, so it is preferable to add 0.005% or more. However, if the content exceeds 0.02%, the precipitates may become coarse and cause fracture. A more preferable lower limit may be 0.01%, and a more preferable upper limit may be 0.018%.

[0035] Nitrogen (N): 0.002-0.006% Nitrogen (N) forms precipitates together with Ti, Nb, Al, etc. and refines the austenite structure when reheated, which helps improve strength and toughness. However, if contained in excess, it can induce surface cracks at high temperatures and form precipitates, and residual nitrogen (N) exists in an atomic state and may reduce toughness, so its content should be limited to 0.002~0.006%.

[0036] Phosphorus (P): 0.01% or less Phosphorus (P) is an element that causes grain boundary segregation and can embrittle steel, so its upper limit can be limited to 0.01%. However, 0% can be excluded in consideration of the level of phosphorus that is unavoidably added to steel.

[0037] Sulfur (S): 0.003% or less Sulfur (S) can mainly combine with Mn to form MnS inclusions, which can be a factor in impairing low-temperature toughness. Therefore, in order to ensure low-temperature toughness and low-temperature fatigue properties, the upper limit can be limited to 0.003%. However, 0% can be excluded in consideration of the level that is inevitably added to steel.

[0038] The steel of the present invention may contain the remaining iron (Fe) and inevitable impurities in addition to the above-mentioned composition. The inevitable impurities cannot be excluded because they may be mixed in unintentionally during normal manufacturing processes. Since such impurities are known to anyone skilled in the art of normal steel manufacturing, the entire contents of the impurities will not be mentioned in this specification.

[0039] In particular, copper (Cu) may be mixed in as an impurity, but in the present invention, the copper (Cu) content can be limited to less than 0.05%.

[0040] The steel of the present invention may have an R value defined by the following relational expression 1 of 0.85 to 1.35.

[0041] In the present invention, Relational formula 1 is proposed to ensure strength and low-temperature toughness at -50°C at the same time. Relational formula 1 relates to a composition formula for ensuring strength and toughness, and the strength and low-temperature toughness at the target level in the present invention can be ensured by controlling the R value of Relational formula 1. If the R value of Relational formula 1 is less than 0.85, there is a problem that the target yield strength cannot be ensured due to insufficient solid solution strengthening, precipitation strengthening, hardening ability, etc., and if the value exceeds 1.35, hard structures such as MA and bainite are formed, which may cause deterioration of impact toughness. [Equation 1] R = [Ni] + 3 [Mo] + 2 [Cr] (Here, [Ni], [Mo] and [Cr] are the weight percentages of each element.)

[0042] In the following, the steel microstructure of the present invention will be described in detail.

[0043] In the present invention, unless otherwise specified, the percentage indicating the fraction of the microstructure is based on the area.

[0044] The steel of the present invention may contain, as a microstructure at the 1 / 4 thickness point, 40 to 60 area % acicular ferrite, 40 to 60 area % bainite, and the remaining cementite and MA in a total amount of 2% or less.

[0045] In the present invention, in order to achieve the -50°C impact toughness at the 1 / 4 thickness point, the size and potential density of acicular ferrite are important, and it is preferable to minimize cementite and MA. More preferably, the cementite and MA may be contained in a total amount of 1% or less. In the present invention, the 1 / 4 thickness point means t / 4, where t means the thickness of the steel sheet.

[0046] The steel of the present invention may have an average acicular ferrite grain size at the quarter thickness point of 25 μm or less.

[0047] In the present invention, in order to ensure low-temperature impact toughness, the average grain size of acicular ferrite can be limited to 25 μm or less. If the grain size exceeds 25 μm, there is a problem that the impact absorption energy value at -50°C decreases. Meanwhile, because of the characteristics of the thick steel plate having a thickness of 50 mm or more, which is the target of the present invention, there is a limit to how fine the grains can be made, so the lower limit of the grain size can be limited to 15 μm.

[0048] The steel production method of the present invention will now be described in detail.

[0049] The steel of the present invention can be produced by reheating, rolling and cooling a steel slab satisfying the alloy composition described above.

[0050] reheating A steel slab satisfying the alloy composition of the present invention can be reheated in the temperature range of 1020 to 1100°C.

[0051] If the reheating temperature exceeds 1100°C, the austenite grains will become coarse, and the increased hardening ability will cause the appearance of bainite structure, which can reduce toughness. On the other hand, if the temperature is less than 1020°C, Ti, Nb, etc. may not be fully dissolved, which can reduce strength.

[0052] Recrystallization zone rolling The reheated steel slab can be subjected to recrystallization region rolling at a temperature range of 900° C. or higher with a final pass reduction of 15 to 25 mm.

[0053] The recrystallization region rolling stage in the present invention is for completely recrystallizing austenite and suppressing the refinement and growth of austenite. The recrystallization region rolling is preferably performed in a temperature range of 900°C or higher for complete recrystallization of austenite, and the final pass reduction can be 15 to 25 mm for initial austenite refinement. If the final pass reduction is less than 15 mm, it is difficult to ensure the desired level of refinement. Meanwhile, the upper limit can be limited to 25 mm during rolling, taking into account the productivity due to the equipment specifications.

[0054] Unrecrystallized area The steel sheet rolled in the recrystallization region can be rolled in the non-recrystallization region at a rolling finish temperature of Ar3+20 to Ar3+60 and a cumulative rolling reduction of 30 to 50%.

[0055] In the present invention, in order to refine the acicular ferrite size, it is preferable that the rolling end temperature is as close as possible to the Ar3 temperature. If the rolling end temperature is less than Ar3+20, the surface before cooling can enter the two-phase region of austenite and ferrite, and when cooling begins, a hard phase is formed on the surface. On the other hand, if the temperature exceeds Ar3+60, there is a problem that the grains cannot be refined by rolling in the non-recrystallized region.

[0056] In addition, for thick materials with a thickness of 50 mm or more, the cumulative rolling reduction is preferably 30 to 50%. If the cumulative rolling reduction is less than 30%, there is a problem that the amount of rolling in the non-recrystallized region decreases, making it difficult to pancaking and refine the structure, and if it exceeds 50%, there is a risk that the amount of rolling in the recrystallized region is insufficient, resulting in deterioration of low-temperature impact toughness. [formula] Ar3=910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo] (Here, [C], [Mn], [Cu], [Cr], [Ni] and [Mo] are the weight percentages of each element.)

[0057] cooling The non-recrystallized rolled steel sheet can be cooled to a temperature range of 400° C. or less at a cooling rate of 5 to 10° C. / s based on the 1 / 4 point of thickness.

[0058] It is preferable that the thick steel plate of the present invention secures impact toughness near the 1 / 4 thickness point. Therefore, the cooling rate limited in the present invention can be based on the 1 / 4 thickness point. If the cooling end temperature exceeds 400°C or the cooling rate exceeds 10°C / s, MA formation may be promoted and impact toughness may deteriorate. On the other hand, if the cooling rate is less than 5°C / s, it is difficult to secure the desired level of strength. In the present invention, water cooling can be used as the cooling method.

[0059] The steel of the present invention manufactured in this manner has a thickness of 50 to 100 mm, a yield strength of 460 MPa or more, a tensile strength of 580 MPa or more, and an impact toughness of 100 J or more at -50°C, and can have excellent low-temperature impact toughness properties while having high strength.

[0060] The present invention will be described in more detail below with reference to examples. However, it should be noted that the following examples are merely intended to illustrate and explain the present invention in more detail, and are not intended to limit the scope of the present invention.

[0061] (Example) After preparing molten steel having the alloy composition shown in Table 1 below, a slab was produced by continuous casting. The slab was reheated, rolled, and cooled under the conditions shown in Table 2 below to produce a steel sheet. The recrystallization region rolling temperatures not disclosed in Table 2 were all similarly applied at temperatures of 900°C or higher, and the cumulative reduction rate during non-recrystallization region rolling was similarly applied within the range of 30 to 50%. Table 1 also shows the Ar3 temperature and R value of Relation 1 calculated according to the alloy composition of each steel type.

[0062] [Table 1] [Equation 1] R = [Ni] + 3 [Mo] + 2 [Cr] (Here, [Ni], [Mo] and [Cr] are the weight percentages of each element.) [formula] Ar3=910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo] (Here, [C], [Mn], [Cu], [Cr], [Ni] and [Mo] are the weight percentages of each element.)

[0063] [Table 2]

[0064] The microstructure of the manufactured steel plate was measured and listed in Table 3 below. The microstructure was measured at 1 / 4 of the steel thickness and shows the acicular ferrite (AF), cementite and MA fractions, respectively, with the remaining fraction being observed as bainite. Also, the acicular ferrite grain size was measured at 1 / 4 of the steel thickness and shown. The microstructure was measured by analyzing at 500x magnification using an optical microscope.

[0065] The physical properties of each test piece are shown in Table 3. Yield strength (YS), tensile strength (TS), and elongation (El) were evaluated by tensile testing, and the average of two tests was measured using a ring test piece taken in the direction perpendicular to the rolling direction at 1 / 4 of the thickness according to the EN-ISO 6892-1 standard. Impact toughness was also measured at -50°C. Impact toughness was measured using an average of three tests using a test piece taken in the direction parallel to the rolling direction at 1 / 4 of the thickness according to the EN ISO 148-1 standard.

[0066] [Table 3]

[0067] As shown in Table 3, in the case of the example satisfying the alloy composition and manufacturing conditions of the present invention, the characteristics of the microstructure proposed in the present invention were satisfied and the physical properties targeted in the present invention were secured. Figure 1 is a photograph of the microstructure of the example according to one embodiment of the present invention, observed at 500 times using an optical microscope.

[0068] On the other hand, Comparative Examples 1 and 2 are examples that do not satisfy the alloy composition of the present invention, and the strength or impact toughness of the level targeted by the present invention could not be ensured. Specifically, Comparative Example 1 is a case where the value of Relation 1 does not satisfy the range of the present invention, and the bainite fraction is reduced, resulting in a decrease in strength. Comparative Example 2 is a case where the value of Relation 1 exceeds the range of the present invention, and bainite is excessively formed, resulting in a decrease in impact toughness.

[0069] Comparative Example 3 is an example in which the cooling end temperature was outside the range of the present invention, and a large amount of cementite and MA fraction were formed, resulting in deterioration of impact toughness properties.

[0070] In Comparative Example 4, the rolling end temperature in the non-recrystallized region is high, and the grain refinement is insufficient, resulting in a decrease in yield strength and poor impact toughness at -50°C.

[0071] In Comparative Example 5, the reduction amount in the final pass of the recrystallization region rolling was insufficient, and the initial austenite could not be refined well. As a result, it was confirmed that the yield strength and impact toughness decreased due to an increase in the final ferrite grain size and the formation of cementite and MA due to an increase in hardenability.

[0072] Comparative Example 6 is a case in which the composition range proposed by the present invention is satisfied but the value of Relational Formula 1 is not satisfied, and the impact toughness was rapidly reduced due to a decrease in acicular ferrite and an excessive increase in bainite.

[0073] Although the present invention has been described in detail with reference to the embodiments, other embodiments may be possible, and therefore the scope of the claims set forth below should not be limited to the embodiments.

Claims

1. In weight percent, it contains C: 0.04-0.08%, Si: 0.1-0.35%, Mn: 1.4-1.8%, Sol. Al: 0.01-0.035%, Ni: 0.2-0.5%, Cr: 0.1-0.3%, Mo: 0.05-0.15%, Nb: 0.015-0.035%, Ti: 0.005-0.02%, N: 0.002-0.006%, P: 0.01% or less, S: 0.003% or less, and the balance is iron (Fe) and other inevitable impurities. The R value defined by the following relational formula 1 is 0.85 to 1.35, The microstructure at the 1 / 4 thickness point is mainly composed of a mixed structure of acicular ferrite and bainite, and contains the remaining cementite and MA in a total amount of 2 area % or less; A high-strength thick steel plate having excellent low-temperature impact toughness, characterized in that the average size of acicular ferrite crystal grains at the 1 / 4 point of the plate thickness is 25 μm or less. [Relationship 1] R=[Ni]+3[Mo]+2[Cr] (Here, [Ni], [Mo] and [Cr] are the weight percentages of each element.)

2. The high strength thick steel plate having excellent low temperature impact toughness according to claim 1, characterized in that the steel plate contains 40 to 60 area % of acicular ferrite and 40 to 60 area % of bainite as a microstructure at a quarter thickness point.

3. 2. The high-strength thick steel plate having excellent low-temperature impact toughness according to claim 1, characterized in that the steel plate contains cementite and MA in a total amount of 1 area % or less.

4. 2. The high strength thick steel plate having excellent low temperature impact toughness according to claim 1, wherein the average grain size of acicular ferrite at a quarter point of the thickness of the steel plate is 15 to 25 μm.

5. The high strength thick steel plate having excellent low temperature impact toughness according to claim 1, characterized in that the steel plate has a thickness of 50 to 100 mm.

6. The high-strength thick steel plate having excellent low-temperature impact toughness according to claim 1, characterized in that the steel plate has a yield strength of 460 MPa or more, a tensile strength of 580 MPa or more, and an impact toughness at -50 ° C. of 100 J or more.

7. A step of reheating a steel slab containing, by weight, C: 0.04-0.08%, Si: 0.1-0.35%, Mn: 1.4-1.8%, Sol. Al: 0.01-0.035%, Ni: 0.2-0.5%, Cr: 0.1-0.3%, Mo: 0.05-0.15%, Nb: 0.015-0.035%, Ti: 0.005-0.02%, N: 0.002-0.006%, P: 0.01% or less, S: 0.003% or less, and the balance being iron (Fe) and other unavoidable impurities, and having an R value defined by the following relational formula 1 of 0.85-1.35; rolling the reheated steel slab in the recrystallization region at a temperature range of 900° C. or more with a final pass reduction of 15 to 25 mm; The recrystallization region rolled steel sheet is subjected to non-recrystallization region rolling at a rolling end temperature of Ar3+20 to Ar3+60; and The method for producing a high strength thick steel plate having excellent low temperature impact toughness comprises water cooling the non-recrystallized rolled steel plate to a temperature range of 400° C. or less based on a 1 / 4 point of the steel plate thickness. [Relationship 1] R=[Ni]+3[Mo]+2[Cr] (Here, [Ni], [Mo] and [Cr] are the weight percentages of each element.)

8. The reheating is performed in a temperature range of 1020 to 1100° C., The method for producing a high strength thick steel plate excellent in low temperature impact toughness according to claim 7, characterized in that the cumulative rolling reduction during the non-recrystallized region rolling is 30 to 50%.

9. The method for producing a high strength thick steel plate having excellent low temperature impact toughness according to claim 7, wherein the cooling is performed at a cooling rate of 5 to 10°C / s based on a 1 / 4 point of the steel plate thickness.

10. The method for producing a high strength thick steel plate having excellent low temperature impact toughness according to claim 7, characterized in that the steel plate has a thickness of 50 to 100 mm.

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