KR20220161891A - Thick steel plate and method of manufacturing the same - Google Patents

Abstract

The present invention is to provide a 110t thick steel plate with excellent mechanical properties in the center in the thickness direction while having a reduction ratio of 2.7 : 1 and a method for manufacturing the same. According to one embodiment of the present invention, the thick steel plate comprises 0.045 to 0.075 wt% of carbon (C), 0.15 to 0.25 wt% of silicon (Si), 1.3 to 1.6 wt% of manganese (Mn), 0.02 to 0.05 wt% of aluminum (Al), 0.1 to 0.2 wt% of copper (Cu), 0.015 to 0.025 wt% of niobium (Nb), 0.2 to 0.3 wt% of nickel (Ni), 0.01 to 0.02 wt% of titanium (Ti), 0 to 0.01 wt% (excluding 0 wt%) of phosphorus (P), 0 to 0.002 wt% (excluding 0 wt%) of sulfur (S), and the balance including iron (Fe) and other unavoidable impurities, and satisfies a low temperature impact toughness of 100 to 400 J at -60℃.

Description

Thick steel plate and method of manufacturing the same

The present invention relates to a thick steel plate and a method for manufacturing the same, and more particularly, to a thick steel plate with a yield strength of 400 MPa having excellent toughness at the center in the thickness direction and a method for manufacturing the same.

In accordance with the recent trend of high-rise and large-sized structures, the thickness of steel sheets required is increasing to 80 mm or more, and the use of ultra-thick materials with a thickness of 110 mm (110t) is also increasing. Furthermore, interest in large-size and stabilization of structures is emerging, and the demand for ultra-thick steel materials with high strength and high functionality is increasing. In the case of ultra-thick materials with high strength and high functionality, the reduction ratio from slabs to thick steel plates is traditionally limited to 3:1 or more in order to prevent deterioration of the internal quality of the product. In order to produce an ultra-thick steel plate that meets this reduction ratio limit, a slab of 330 mm or more is required in the case of 110t, and there is a process difficulty in that it must be manufactured separately from 300 mm and 250 mm slabs normally used for manufacturing thick steel plates.

Korean Patent Application No. 10-2018-0073809

Technical problem to be achieved by the technical spirit of the present invention is to provide a 110t thick steel plate having excellent mechanical properties at the center in the thickness direction while having a reduction ratio of 2.7: 1, unlike conventional thick plate materials, and a manufacturing method thereof.

However, these tasks are exemplary, and the technical spirit of the present invention is not limited thereto.

According to one embodiment of the present invention, by weight, carbon (C): 0.045% to 0.075%, silicon (Si): 0.15% to 0.25%, manganese (Mn): 1.3% to 1.6%, aluminum (Al) : 0.02% ~ 0.05%, Copper (Cu): 0.1% ~ 0.2%, Niobium (Nb): 0.015% ~ 0.025%, Nickel (Ni): 0.2% ~ 0.3%, Titanium (Ti): 0.01% ~ 0.02% , Phosphorus (P): greater than 0% to 0.01%, sulfur (S): greater than 0% to 0.002%, the balance including iron (Fe) and other unavoidable impurities, low-temperature impact toughness at -60 ° C: 100 J Provided is a thick steel plate that satisfies ~ 400 J.

The thick steel sheet may satisfy tensile strength (TS): 500 MPa to 570 MPa, yield strength (YS): 400 MPa to 500 MPa, and elongation (EL): 20% to 30%.

The thick steel plate may satisfy low-temperature impact toughness at -60°C: 100 J to 400 J at 1/2 of the thickness.

In the thick steel sheet, the nickel (Ni) content may be 1.4 times or more than the copper (Cu) content.

According to an embodiment of the present invention, (a) by weight, carbon (C): 0.045% to 0.075%, silicon (Si): 0.15% to 0.25%, manganese (Mn): 1.3% to 1.6%, aluminum (Al): 0.02% to 0.05%, Copper (Cu): 0.1% to 0.2%, Niobium (Nb): 0.015% to 0.025%, Nickel (Ni): 0.2% to 0.3%, Titanium (Ti): 0.01% ~ 0.02%, phosphorus (P): more than 0% ~ 0.01%, sulfur (S): more than 0% ~ 0.002%, the balance comprising iron (Fe) and other unavoidable impurities Reheating the steel; (b) first hot-rolling the reheated steel; (c) an air-cooling standby step of air-cooling the first hot-rolled steel material in air; (d) secondarily hot-rolling the steel material waiting for air cooling; and (e) forcibly cooling the secondary hot-rolled steel material.

In the manufacturing method of the thick steel plate, the step (a) includes reheating the steel material at a reheating temperature of 950 ° C to 1050 ° C, and the step (c) heats the first hot-rolled steel material in the air at 300 ° C. An air-cooling standby step of air-cooling for seconds to 600 seconds, and the step (d) includes the step of performing secondary hot rolling so that the air-cooling standby steel material is finished at a hot rolling end temperature of 700 ° C to 800 ° C, wherein the ( Step e) may include forcibly cooling the secondary hot-rolled steel material to 350°C to 450°C.

In the manufacturing method of the thick steel sheet, the reduction ratio of the thick steel sheet subjected to the first hot rolling and the second hot rolling may be 2.7 or more and less than 3.0.

The thick steel plate manufactured by the method for manufacturing a thick steel plate has tensile strength (TS): 500 MPa to 570 MPa, yield strength (YS): 400 MPa to 500 MPa, elongation (EL): 20% to 30%, - Low-temperature impact toughness at 60℃: 100 J ~ 400 J can be satisfied.

In step (a) of the manufacturing method of the thick steel plate, the nickel (Ni) content may be 1.4 times or more than the copper (Cu) content.

According to the technical concept of the present invention, unlike conventional thick plate materials, it is possible to implement a 110t thick steel plate having a reduction ratio of 2.7:1 and excellent mechanical properties at the center in the thickness direction and a manufacturing method thereof. The effects of the present invention described above have been described by way of example, and the scope of the present invention is not limited by these effects.

1 is a process flow chart schematically illustrating a method of manufacturing a thick steel plate according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those skilled in the art, and the following examples may be modified in many different forms, and the The scope of the technical idea is not limited to the following embodiments. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the spirit of the invention to those skilled in the art. Like reference numerals throughout this specification mean like elements. Further, various elements and areas in the drawings are schematically drawn. Therefore, the technical spirit of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

Conventionally, when manufacturing an extremely thick steel plate, the reduction ratio from a slab to a thick steel plate has traditionally been limited to 3:1 or more in order to prevent deterioration of the characteristics of the center of the thick steel plate. For example, when manufacturing a 110mm thick steel plate, a slab of 330mm or more was required. However, it is true that there are still many restrictions in the normal manufacturing and handling of 330mm slabs in the heavy plate manufacturing market, and actual steel companies are expressing their disapproval, demanding minimum order quantities and long lead times for manufacturing thick steel plates.

The present invention relates to a thick steel plate having a yield strength of 400 MPa used for structural steel, particularly for offshore wind towers, and to a thick steel plate having improved economic efficiency and core characteristics and a manufacturing method thereof. In the present invention, a 110mm ultra-thick steel sheet having excellent center toughness even with a reduction ratio of 2.7:1 was manufactured by utilizing low-temperature heating, center pressure reduction, and the addition of toughness enhancing elements.

Hereinafter, a thick steel plate and a manufacturing method thereof according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

steel plate

In the thick steel plate according to an embodiment of the present invention, in weight percent, carbon (C): 0.045% to 0.075%, silicon (Si): 0.15% to 0.25%, manganese (Mn): 1.3% to 1.6%, aluminum (Al): 0.02% to 0.05%, Copper (Cu): 0.1% to 0.2%, Niobium (Nb): 0.015% to 0.025%, Nickel (Ni): 0.2% to 0.3%, Titanium (Ti): 0.01% ~ 0.02%, phosphorus (P): more than 0% ~ 0.01%, sulfur (S): more than 0% ~ 0.002%, the balance includes iron (Fe) and other unavoidable impurities.

The role and content of each component included in the thick steel plate according to an embodiment of the present invention will be described as follows. At this time, the content of component elements all means weight%.

Carbon (C): 0.045% to 0.075%

Carbon is added to ensure strength of steel. When the carbon content is less than 0.045%, the strength may decrease. If the carbon content exceeds 0.075%, the strength of the steel material increases, but low-temperature impact toughness and weldability may be deteriorated. Therefore, it is preferable to add carbon in an amount of 0.045% to 0.075% of the total weight of the steel sheet.

Silicon (Si): 0.15% to 0.25%

Silicon is added as a deoxidizer to remove oxygen in steel in the steelmaking process. In addition, silicon has a solid solution strengthening effect. When the content of silicon is less than 0.15%, the effect of adding silicon cannot be properly exhibited. When the content of silicon exceeds 0.25%, non-metallic inclusions may be excessively formed on the surface of the steel material, thereby reducing toughness. Therefore, silicon is preferably added in an amount of 0.15% to 0.25% of the total weight of the steel sheet.

Manganese (Mn): 1.3% to 1.6%

Manganese, as an austenite stabilizing element, serves to improve strength and toughness by refining crystal grains by rolling by expanding the controlled rolling temperature range by lowering the Ar3 point. When the content of manganese is less than 1.3%, the fraction of the second phase structure is lowered, and it may be difficult to secure strength. When the manganese content exceeds 1.6%, sulfur dissolved in the steel is precipitated as MnS, and low-temperature impact toughness may be reduced. Therefore, manganese is preferably added in an amount of 1.3% to 1.6% of the total weight of the steel sheet.

Aluminum (Al): 0.02% to 0.05%

Aluminum acts as a deoxidizer to remove oxygen in steel. If the aluminum content is less than 0.02%, the above-described effect cannot be expected, and if it exceeds 0.05%, aluminum oxide, which is a non-metallic inclusion, may be formed to reduce low-temperature impact toughness. Therefore, aluminum is preferably added in an amount of 0.02% to 0.05% of the total weight of the thick steel sheet.

Copper (Cu): 0.1% to 0.2%

Copper serves to improve hardenability and low-temperature impact toughness of steel together with nickel. When the copper content is less than 0.1%, the effect of adding copper cannot be exhibited properly. When the copper content exceeds 0.2%, it does not contribute to further increase in strength because it exceeds the solid solution limit, and may cause glowing brittleness. Therefore, copper is preferably added in an amount of 0.1% to 0.2% of the total weight of the steel sheet.

Nickel (Ni): 0.2% to 0.3%

Nickel refines grains and is incorporated into austenite and ferrite to strengthen the matrix. In particular, nickel is an element effective in improving low-temperature impact toughness. When the content of nickel is less than 0.2%, the effect of adding nickel cannot be exhibited properly. If the content of nickel exceeds 0.3%, it may cause red heat brittleness. Therefore, nickel is preferably added in an amount of 0.2% to 0.3% of the total weight of the steel sheet.

Meanwhile, the nickel (Ni) content may be 1.4 times or more than the copper (Cu) content. In the thick steel sheet according to an embodiment of the present invention, copper and nickel are added to improve toughness without reducing strength. However, when only copper is added without sufficient nickel content, a copper-enriched phase is formed at the interface between the scale and the steel. Often, the copper-enriched phase converts to a liquid phase at a sufficiently high heating temperature and invades and precipitates at the austenite grain boundary during hot rolling. It causes cracks on the surface of the steel plate. The addition of sufficient nickel can promote oxidation of the steel surface and increase the solubility of copper in the austenite phase to prevent precipitation of the copper enriched phase at the austenite grain boundary. It was confirmed that the above effect appeared when nickel was added at 1.4 times or more than the amount of copper added.

Niobium (Nb): 0.015% to 0.025%

Niobium combines with carbon and nitrogen at high temperatures to form carbides or nitrides. Niobium-based carbide or nitride improves strength and low-temperature toughness of steel by suppressing crystal grain growth during rolling and refining crystal grains. When the content of niobium is less than 0.015%, the effect of adding niobium cannot be exhibited properly. When the content of niobium exceeds 0.025%, the weldability of the steel is deteriorated, and the strength and low-temperature toughness according to the increase in the niobium content are no longer improved, and exist in a solid solution state in ferrite, rather reducing impact toughness. Therefore, niobium is preferably added in an amount of 0.015% to 0.025% of the total weight of the thick steel sheet.

Titanium (Ti): 0.01% to 0.02%

Titanium has an effect of improving toughness and strength of a hot-rolled steel sheet by generating Ti(C, N) precipitates having high high-temperature stability, thereby hindering the growth of austenite crystal grains during welding to refine the structure of the welded portion. When the content of titanium is less than 0.01%, age hardening may occur due to dissolved carbon and solid nitrogen remaining without precipitation. When the content of titanium exceeds 0.02%, the low-temperature impact properties of the steel are deteriorated by generating coarse precipitates, and the manufacturing cost may be increased without further addition effect. Therefore, titanium is preferably added in an amount of 0.01% to 0.02% of the total weight of the thick steel sheet.

Phosphorus (P): greater than 0% to 0.01%

Phosphorus contributes to the improvement of strength in part, but lowers weld toughness and low-temperature impact toughness, and forms fine segregation as well as center segregation, which can adversely affect the material. Therefore, the lower the phosphorus content, the better. Therefore, in the present invention, phosphorus is limited to more than 0% to 0.01% of the total weight of the thick steel sheet.

Sulfur (S): greater than 0% to 0.002%

Sulfur, together with phosphorus, is an element that is unavoidably contained in the manufacture of steel, forms non-metallic inclusions such as MnS, and has a high possibility of grain boundary segregation as a low-melting element, thereby reducing toughness. If the content of sulfur exceeds 0.002% by weight, the toughness of the base material and welded part may be greatly reduced. Therefore, in the present invention, sulfur is limited to more than 0% to 0.002% of the total weight of the thick steel sheet.

The remaining components of the thick steel sheet are iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in a normal manufacturing process, this cannot be excluded. Since these impurities are known to anyone skilled in the ordinary manufacturing process, not all of them are specifically mentioned in this specification.

The thick steel sheet had tensile strength (TS): 500 MPa to 570 MPa, yield strength (YS): 400 MPa to 500 MPa, elongation (EL): 20% to 30%, low-temperature impact toughness at -60 ° C: 100 Satisfies J ~ 400 J.

The thick steel plate may satisfy low-temperature impact toughness at -60° C.: 100 J to 400 J at 1/2 point (t/2) of the thickness.

Hereinafter, a method for manufacturing a thick steel plate according to the present invention will be described with reference to the accompanying drawings.

Manufacturing method of thick steel plate

1 is a process flow chart showing a method for manufacturing a thick steel plate according to an embodiment of the present invention.

In the method for manufacturing a thick steel plate according to the present invention, the semi-finished product, which is a target steel material, may be illustratively a slab. The semi-finished slab can be secured through a continuous casting process after obtaining molten steel of a predetermined composition through a steelmaking process.

The steel material, in weight percent, carbon (C): 0.045% ~ 0.075%, silicon (Si): 0.15% ~ 0.25%, manganese (Mn): 1.3% ~ 1.6%, aluminum (Al): 0.02% ~ 0.05 %, Copper (Cu): 0.1% ~ 0.2%, Niobium (Nb): 0.015% ~ 0.025%, Nickel (Ni): 0.2% ~ 0.3%, Titanium (Ti): 0.01% ~ 0.02%, Phosphorus (P) : more than 0% to 0.01%, sulfur (S): more than 0% to 0.002%, the balance includes iron (Fe) and other unavoidable impurities.

Referring to FIG. 1 , the method of manufacturing a thick steel sheet according to an embodiment of the present invention includes a reheating step (S10), a first hot rolling step (S20), an air cooling waiting step (S30), a second hot rolling step (S40), and A forced cooling step (S50) is included.

Reheating step (S10)

In the reheating step (S10), the steel material having the above composition, for example, the slab plate material, is reheated at a reheating temperature (Slab Reheating Temperature, SRT) of 950 ° C to 1050 ° C. Through such reheating, re-dissolution of components segregated during casting and re-dissolution of precipitates may occur. When the reheating temperature is less than 950° C., the rolling load may be increased due to the low reheating temperature, and the solid solution temperature of Nb-based precipitates such as NbC and NbN may not be reached, so that fine precipitates may not be re-precipitated during hot rolling, resulting in crystal grain growth of austenite. can cause rapid coarsening of austenite grains. When the reheating temperature exceeds 1050° C., it may be difficult to secure strength and low-temperature toughness of a steel sheet manufactured due to rapid coarsening of austenite crystal grains. In this embodiment, it is characterized in that the reheating process is performed at a low temperature of 1050 ° C. or less to control the initial austenite grain size. On the other hand, the reheating step (S10) is not necessarily performed, but is preferably performed to derive effects such as re-dissolution of the precipitate.

1st hot rolling step (S20)

In the first hot rolling step (S20), the first hot rolling is performed on the reheated steel material. The first hot rolling step may be referred to as a rough rolling step. The primary hot rolling step may include a leveling rolling step, a widthwise rolling step, and a lengthwise rolling step. The leveling rolling can be carried out a minimum number of times, can be carried out once or twice, preferably once. The widthwise rolling may be performed at a frequency of 3 to 5 times. The length betting rolling may be carried out at a frequency of 3 to 5 times.

In the first hot rolling step, the maximum value of the reduction ratio per pass may be 6% or more, for example, 6% to 15%. In particular, in the lengthwise rolling step, a sufficient reduction rate in the recrystallization region can be imparted to the steel by applying a reduction. The "pass" means that the steel material passes through the rolling rolls.

Air cooling standby stage (S30)

In the air-cooling waiting step (S30), after the first hot rolling step (S20) is finished, the steel material is waiting in the air while cooling is performed in the air. The air-cooling standby step (S30) may be performed for, for example, 300 seconds to 600 seconds. By this air-cooling waiting step, a hardened surface layer of the steel material is created and the central portion of the steel material is hardened, enabling subsequent rolling by secondary hot rolling.

2nd hot rolling step (S40)

In the second hot rolling step (S40), the first hot rolled steel is subjected to second hot rolling. The second hot rolling step may be referred to as a finishing rolling step. The secondary hot rolling may be finished at a finish rolling temperature (FRT) of 700 ° C to 800 ° C. The reduction ratio per pass of the secondary hot rolling may be applied to 6% or more. When the hot rolling end temperature is less than 700° C., abnormal reverse rolling occurs and a non-uniform structure is formed, thereby greatly reducing low temperature impact toughness. When the hot rolling end temperature exceeds 800° C., ductility and toughness are excellent, but strength may rapidly decrease.

The first hot rolling step (S20), the air cooling standby step (S30), and the second hot rolling step (S40) may be performed continuously. The steel material may form a thick steel plate by the first hot rolling and the second hot rolling. The reduction ratio of the thick steel sheet subjected to the first hot rolling and the second hot rolling may be 2.7 or more and less than 3.0. The thick steel plate thus formed may have a thickness of, for example, 110 mm (110t).

Forced cooling step (S50)

The secondary hot-rolled steel material may be forcibly cooled to 350 ° C to 450 ° C. Forced cooling means cooling relatively faster than the cooling rate of air cooling while waiting in air. For example, the forced cooling may be water cooling using cooling water. On the other hand, after forced cooling to 350 ° C. to 450 ° C., the steel plate may be naturally cooled to room temperature. At this time, the room temperature may be about 1 ° C to 40 ° C.

Experimental example

Hereinafter, a preferred experimental example is presented to aid understanding of the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited by the following experimental examples. Contents not described herein can be technically inferred by those skilled in the art, so descriptions thereof will be omitted.

Table 1 shows the composition of the thick steel plate used in the manufacturing method of the thick steel plate. In Table 1, the remainder consists of iron (Fe) and impurities inevitably contained in the steelmaking process. The unit is % by weight.

ingredient C Si Mn P S Al Cu Nb Ni Ti comparative example 0.071 0.27 1.55 0.010 0.001 0.028 - 0.018 - 0.016 Example 0.055 0.18 1.35 0.006 0.001 0.024 0.16 0.021 0.23 0.013

Referring to Table 1, examples are in weight percent, carbon (C): 0.045% to 0.075%, silicon (Si): 0.15% to 0.25%, manganese (Mn): 1.3% to 1.6%, aluminum (Al) : 0.02% ~ 0.05%, Copper (Cu): 0.1% ~ 0.2%, Niobium (Nb): 0.015% ~ 0.025%, Nickel (Ni): 0.2% ~ 0.3%, Titanium (Ti): 0.01% ~ 0.02% , Phosphorus (P): greater than 0% to 0.01%, sulfur (S): greater than 0% to 0.002%, the balance satisfies the composition range of iron (Fe). Furthermore, the content of the nickel (Ni) satisfies 1.4 times or more of the content of the copper (Cu). In contrast, the comparative example does not satisfy all of the ranges of silicon (Si): 0.15% to 0.25%, copper (Cu): 0.1% to 0.2%, and nickel (Ni): 0.2% to 0.3%.

Table 2 shows process condition values of Examples and Comparative Examples.

process Abhabi reheat temperature
(℃) before finishing
air cooling standby
time (seconds) rolling
end temperature
(℃) Cooling
stop temperature
(℃) comparative example 3.0:1 1077 261 804 504 Example 2.7:1 1038 365 765 438

Referring to Table 2, the embodiment has a reduction ratio of thick steel sheet: 2.7 or more and less than 3.0, reheating temperature: 950 ℃ ~ 1050 ℃, air cooling waiting time before finishing rolling: 300 seconds ~ 600 seconds, hot rolling end temperature: 　 700 ℃ ~ 800°C, cooling stop temperature: 350°C to 450°C are all satisfied, but the comparative example does not satisfy all of the above process conditions. The embodiment has a slab thickness of 300 mm and a thick steel plate thickness of 110 mm and a reduction ratio of 2.7, whereas the comparative example has a slab thickness of 250 mm and a thick steel plate thickness of 83 mm and a reduction ratio of 3.0.

Table 3 shows the results obtained by measuring yield strength (YS), tensile strength (TS), elongation (EL), and low-temperature impact toughness as mechanical properties of the manufactured thick steel sheet. The three low-temperature impact toughness values shown in Table 3 show the values measured for each of the three specimens obtained from the center of one steel.

texture TS
(MPa) YP
(MPa) EL
(%) center of thickness
Low temperature shock (J@-60℃) comparative example 513 398 27 23, 10, 8 Example 509 410 30 367, 314, 354

Referring to Table 3, the examples have tensile strength (TS): 500 MPa to 570 MPa, yield strength (YS): 400 MPa to 500 MPa, elongation (EL): 20% to 30%, low temperature at -60 ° C. Impact toughness: Satisfies 100 J ~ 400 J. In contrast, the comparative example does not satisfy the yield strength (YS): 400 MPa to 500 MPa, and the low-temperature impact toughness at -60 ° C: 100 J to 400 J.

According to an embodiment of the present invention, an ultra-thick steel sheet having a reduction ratio of less than 3:1, high strength of 400 MPa in yield strength and 500 MPa in tensile strength, and excellent impact absorption energy of 100 J or more in the center in the thickness direction at -60 ° C. can be obtained.

The technical idea of the present invention described above is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope of the technical idea of the present invention. It will be clear to those skilled in the art to which it pertains.

Claims (9)

In weight percent, carbon (C): 0.045% to 0.075%, silicon (Si): 0.15% to 0.25%, manganese (Mn): 1.3% to 1.6%, aluminum (Al): 0.02% to 0.05%, copper ( Cu): 0.1% to 0.2%, Niobium (Nb): 0.015% to 0.025%, Nickel (Ni): 0.2% to 0.3%, Titanium (Ti): 0.01% to 0.02%, Phosphorus (P): greater than 0% ~ 0.01%, sulfur (S): more than 0% ~ 0.002%, the balance including iron (Fe) and other unavoidable impurities,
Low-temperature impact toughness at -60 ° C: satisfies 100 J ~ 400 J,
steel plate. According to claim 1,
The thick steel sheet satisfies tensile strength (TS): 500 MPa to 570 MPa, yield strength (YS): 400 MPa to 500 MPa, elongation (EL): 20% to 30%,
steel plate. According to claim 1,
The thick steel plate satisfies low-temperature impact toughness at -60 ° C: 100 J to 400 J at 1/2 of the thickness,
steel plate. According to claim 1,
Characterized in that the content of nickel (Ni) is 1.4 times or more than the content of copper (Cu),
steel plate. (a) in weight percent, carbon (C): 0.045% to 0.075%, silicon (Si): 0.15% to 0.25%, manganese (Mn): 1.3% to 1.6%, aluminum (Al): 0.02% to 0.05% , Copper (Cu): 0.1% ~ 0.2%, Niobium (Nb): 0.015% ~ 0.025%, Nickel (Ni): 0.2% ~ 0.3%, Titanium (Ti): 0.01% ~ 0.02%, Phosphorus (P): More than 0% to 0.01%, sulfur (S): more than 0% to 0.002%, the balance comprising iron (Fe) and other unavoidable impurities Reheating the steel;
(b) first hot-rolling the reheated steel;
(c) an air-cooling standby step of air-cooling the first hot-rolled steel material in air;
(d) secondarily hot-rolling the air-cooled steel; and
(e) forcibly cooling the secondary hot-rolled steel; including,
A method for manufacturing a thick steel plate. According to claim 1,
The step (a) includes reheating the steel at a reheating temperature of 950 ° C to 1050 ° C,
The step (c) includes an air-cooling standby step of air-cooling the first hot-rolled steel material in air for 300 seconds to 600 seconds,
The step (d) includes the step of secondarily hot rolling the air-cooled steel material to end at a hot rolling end temperature of 700 ° C to 800 ° C,
In the step (e), forcibly cooling the secondary hot-rolled steel material to 350 ° C. to 450 ° C.; Including,
A method for manufacturing a thick steel plate. According to claim 5,
Characterized in that the reduction ratio of the steel sheet subjected to the first hot rolling and the second hot rolling is 2.7 or more and less than 3.0,
A method for manufacturing a thick steel plate. According to claim 5,
The thick steel plate manufactured by the method for manufacturing a thick steel plate,
Tensile strength (TS): 500 MPa ~ 570 MPa, yield strength (YS): 400 MPa ~ 500 MPa, elongation (EL): 20% ~ 30%, low temperature impact toughness at -60℃: 100 J ~ 400 J satisfied,
A method for manufacturing a thick steel plate. According to claim 5,
Characterized in that the content of nickel (Ni) in step (a) is 1.4 times or more than the content of copper (Cu),
A method for manufacturing a thick steel plate.

Images