Shaped steel and manufacturing method therefor

Abstract

A shaped steel according to an embodiment of the present invention comprises 0.05-0.15 wt% of carbon (C), 0.10-0.30 wt% of silicon (Si), 1.00-1.60 wt% of manganese (Mn), 0.040 wt% or less (excluding 0) of phosphorus (P), 0.040 wt% or less (excluding 0) of sulfur (S), 0.015 wt% or less of aluminum (Al), 0.050-0.100 wt% of vanadium (V), 0.010-0.050 wt% of niobium (Nb), 0.010-0.015 wt% of titanium (Ti), 0.0150-0.0220 wt% of nitrogen (N), and the balance of iron (Fe) and other inevitable impurities, wherein the shaped steel has a yield strength of 400 MPa or more, an elongation of 17% or more, and an impact toughness of 100 J or more as measured at 0°C.

Description

Steel profiles and methods for manufacturing the same

[0001] The present invention relates to a structural steel and a method for manufacturing the same.

[0002] Structural steel generally refers to steel materials with cross-sectional shapes that vary widely. Structural steel is applied as structural steel, such as columns in large buildings; structural steel for automobiles; and temporary construction materials and foundation piles for civil engineering projects like bridges. Structural steel can be manufactured by hot rolling cast slabs, such as blooms, billets, and beam blanks, produced by continuous casting.

[0003] When using structural steel for construction, properties such as high strength, low yield ratio, and low-temperature toughness are required. In particular, as buildings are becoming increasingly tall and massive internationally in recent years, the thick structural steel used in these applications is required to have excellent yield ratio and low-temperature toughness in its surface.

[0004] However, there is a problem in that increasing the strength of the structural steel also increases the yield ratio.

[0005] An increase in the yield ratio means that the stress difference from plastic deformation to the point of failure decreases; consequently, the gap through which the building can absorb energy via deformation to prevent failure is smaller, making it difficult to guarantee structural stability when external forces are applied.

[0006] In addition, increasing the strength of structural steel can reduce low-temperature toughness, so for steel grades that require strength and low-temperature toughness, low-temperature toughness is secured through additional processes such as the TMCP (Thermo-Mechanical Control Process).

[0007] However, in the case of thick materials, it is difficult to apply sufficient reduction and cooling processes at low temperatures, so there is a problem that it is difficult to apply processes such as TMCP.

[0008] Accordingly, there is a need to develop thick structural steel with a thickness of 40 mm or more, excellent strength and low-temperature toughness, and a method for manufacturing the same.

[0009] The purpose is to provide a structural steel with a thickness of 40 mm or more and excellent strength and low-temperature toughness, and a method for manufacturing the same, in order to solve the problems of the aforementioned conventional technology.

[0010] The problems of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0011] A structural steel according to one embodiment of the present invention comprises 0.05 to 0.15 wt% carbon (C), 0.10 to 0.30 wt% silicon (Si), 1.00 to 1.60 wt% manganese (Mn), 0.040 wt% or less phosphorus (P) (excluding 0), 0.040 wt% or less sulfur (S) (excluding 0), 0.015 wt% or less aluminum (Al), 0.050 to 0.100 wt% vanadium (V), 0.010 to 0.050 wt% niobium (Nb), 0.010 to 0.015 wt% titanium (Ti), 0.0150 to 0.0220 wt% nitrogen (N), and the remainder being iron (Fe) and other unavoidable impurities, has a yield strength of 400 MPa or more, an elongation of 17% or more, and is measured at 0°C The impact toughness is 100J or more.

[0012] According to one embodiment of the present invention, the thickness may be 40 to 80 mm.

[0013] According to one embodiment of the present invention, the yield ratio may be 85% or less.

[0014] According to one embodiment of the present invention, the tensile strength may be 550 MPa or more.

[0015] According to one embodiment of the present invention, the impact toughness measured at -20℃ may be 75J or higher.

[0016] According to one embodiment of the present invention, the ratio of impact toughness measured at -20°C to impact toughness measured at 0°C may be 75% or more.

[0017] A method for manufacturing a structural steel according to an embodiment of the present invention comprises the steps of: (S1) preparing a steel material; (S2) reheating the steel material; (S3) hot rolling the steel material to form a hot-rolled material; and (S4) reheating and cooling the hot-rolled material to form a structural steel as a final product, wherein the final product contains carbon (C) 0.05 to 0.15 wt%, silicon (Si) 0.10 to 0.30 wt%, manganese (Mn) 1.00 to 1.60 wt%, phosphorus (P) 0.040 wt% or less (excluding 0), sulfur (S) 0.040 wt% or less (excluding 0), aluminum (Al) 0.015 wt% or less, vanadium (V) 0.050 to 0.100 wt%, niobium (Nb) 0.010 to 0.050 wt%, and titanium (Ti). It contains 0.010 to 0.015 wt%, 0.0150 to 0.0220 wt% nitrogen (N) and the remainder being iron (Fe) and other unavoidable impurities, has a yield strength of 400 MPa or more, an elongation of 17% or more, and an impact toughness of 100 J or more measured at 0°C.

[0018] According to one embodiment of the present invention, the reheating temperature of step (S2) may be 1150 to 1300℃.

[0019] According to one embodiment of the present invention, the rolling start temperature of step (S3) may be 1030 to 1070℃.

[0020] According to one embodiment of the present invention, the rolling end temperature of step (S3) may be 800 to 900℃.

[0021] According to one embodiment of the present invention, the heat temperature of step (S4) may be 650 to 800℃.

[0022] According to one embodiment of the present invention, the thickness of the final product may be 40 to 80 mm.

[0023] According to one embodiment of the present invention, the yield ratio of the final product may be 85% or less.

[0024] According to one embodiment of the present invention, the tensile strength of the final product may be 550 MPa or more.

[0025] According to one embodiment of the present invention, the impact toughness of the final product measured at -20°C may be 75J or higher.

[0026] According to one embodiment of the present invention, the ratio of impact toughness measured at -20°C to impact toughness measured at 0°C of the final product may be 75% or more.

[0027] According to one embodiment of the present invention, a structural steel having a thickness of 40 mm or more and excellent strength and low-temperature toughness, and a method for manufacturing the same can be provided.

[0028] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims.

[0029] FIG. 1 is a flowchart illustrating a method for manufacturing a structural steel section according to one embodiment of the present invention.

[0030] Figure 2 is a drawing showing the tensile test and impact test evaluation method of a structural steel section.

[0031] Hereinafter, preferred embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention is not limited or restricted by the following embodiments.

[0032] Additionally, when it is stated that a component (or area, layer, part, etc.) is "on," "connected," or "combined" with another component, it means that it may be directly placed / connected / combined with the other component, or that a third component may be placed between them.

[0033] Terms such as "include" or "have" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0034] In order to clearly explain the present invention, detailed descriptions of related prior art that are irrelevant to the explanation or that may unnecessarily obscure the essence of the invention have been omitted. Furthermore, when assigning reference numerals to the components of each drawing in this specification, identical or similar reference numerals are assigned to identical or similar components throughout the entire specification.

[0035] Furthermore, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0036] Unless otherwise specified, the notation 'A ~ B' for numerical values ​​A and B shall mean 'A or greater, B or less'. In such notation, if a unit is attached only to numerical value B, that unit shall also apply to numerical value A.

[0037]

[0038] Hereinafter, an embodiment of the present invention will be described in more detail.

[0039]

[0040] Structural steel

[0041] A structural steel according to one embodiment of the present invention may contain 0.05 to 0.15 wt% carbon (C), 0.10 to 0.30 wt% silicon (Si), 1.00 to 1.60 wt% manganese (Mn), 0.040 wt% or less phosphorus (P) (excluding 0), 0.040 wt% or less sulfur (S) (excluding 0), 0.015 wt% or less aluminum (Al), 0.050 to 0.100 wt% vanadium (V), 0.010 to 0.050 wt% niobium (Nb), 0.010 to 0.015 wt% titanium (Ti), 0.0150 to 0.0220 wt% nitrogen (N), and the remainder being iron (Fe) and other unavoidable impurities.

[0042] Hereinafter, the roles and contents of each alloy element included in the structural steel according to one embodiment of the present invention will be described in detail.

[0043]

[0044] Carbon (C)

[0045] Carbon (C) is an indispensable element for securing the necessary strength.

[0046] Carbon can react with elements such as niobium and titanium in steel to precipitate fine carbides. In other words, carbon can contribute to strength improvement through precipitation strengthening.

[0047] If the carbon content is insufficient, the aforementioned effects are lacking, making it difficult to secure sufficient strength. Conversely, if the carbon content is excessive, the impact toughness of the steel may decrease and the yield ratio may increase.

[0048] Accordingly, a structural steel according to one embodiment of the present invention may contain carbon (C) in an amount of 0.05 to 0.15 weight%.

[0049]

[0050] Silicon (Si)

[0051] Silicon (Si) is added along with aluminum as a deoxidizer to remove oxygen from steel during the steelmaking process, and can improve strength through solid solution strengthening effects.

[0052] If the silicon content is insufficient, the aforementioned effects may be negligible. Conversely, if the silicon content is excessive, the weldability and surface quality of the steel may be degraded.

[0053] Accordingly, a structural steel according to one embodiment of the present invention may contain silicon (Si) in an amount of 0.10 to 0.30 weight%.

[0054]

[0055] Manganese (Mn)

[0056] Manganese (Mn) can not only contribute to securing strength as a solid solution strengthening element but also improve the hardenability of steel.

[0057] If the manganese content is insufficient, the aforementioned effects may be negligible. Conversely, if the manganese content is excessive, MnS inclusions may form, which may reduce ductility and corrosion resistance.

[0058] Accordingly, a structural steel according to one embodiment of the present invention may contain 1.00 to 1.60 weight percent of manganese (Mn).

[0059]

[0060] Ph(P)

[0061] Phosphorus (P) is an element that contributes to strength enhancement.

[0062] However, if the phosphorus content exceeds 0.040 weight%, it can form central segregation and microsegregation, which can reduce the ductility of the steel and lower the impact toughness due to precipitation behavior.

[0063] Accordingly, a structural steel according to one embodiment of the present invention may contain phosphorus (P) in an amount of 0.040 weight% or less (excluding 0), and preferably in an amount of 0.020 to 0.040 weight%.

[0064]

[0065] Yellow (S)

[0066] Sulfur (S) improves the machinability of steel by combining with manganese, zinc, titanium, molybdenum, etc., and can improve processability by combining with manganese to form fine precipitates (e.g., MnS).

[0067] However, if the sulfur content exceeds 0.040 weight%, MnS inclusions may be excessively formed, which may reduce weldability and impact toughness.

[0068] Accordingly, a structural steel according to one embodiment of the present invention may contain sulfur (S) in an amount of 0.040 weight% or less (excluding 0), preferably 0.005 to 0.010 weight%, and more preferably 0.006 to 0.007 weight%.

[0069]

[0070] Aluminum (Al)

[0071] Aluminum (Al) acts as a deoxidizer, enabling the steel to maintain a sufficiently low level of dissolved oxygen. Additionally, it can refine the grain size by reacting with nitrogen (N), a solid solution element, to form AlN precipitates.

[0072] However, if the aluminum content exceeds 0.015 weight%, non-metallic inclusions may be excessively formed, which may reduce ductility and toughness.

[0073] Accordingly, a structural steel according to one embodiment of the present invention may contain aluminum (Al) in an amount of 0.015 weight% or less.

[0074]

[0075] Vanadium (V)

[0076] Vanadium (V) can combine with carbon and nitrogen in steel to form precipitates. Vanadium's carbide-forming ability is stronger than that of chromium (Cr), and because it refines the microstructure of steel through precipitates, it causes precipitation strengthening, which helps improve strength. In addition, when vanadium is added, toughness can be improved.

[0077] If the vanadium content is insufficient, the aforementioned effect may be negligible. Conversely, if the vanadium content is excessive, the low-temperature impact toughness of the steel may decrease.

[0078] Accordingly, a structural steel according to one embodiment of the present invention may contain vanadium (V) in an amount of 0.050 to 0.100 weight%, and preferably in an amount of 0.070 to 0.080 weight%.

[0079]

[0080] Niobium (Nb)

[0081] Niobium (Nb) can increase the unrecrystallized region by raising the recrystallization cessation temperature. Consequently, the reduction in the unrecrystallized region increases, which suppresses grain growth and can improve strength and low-temperature impact toughness.

[0082] If the niobium content is insufficient, the aforementioned effect may be negligible. Conversely, if the niobium content is excessive, it may be dissolved within the steel, which could actually reduce impact toughness.

[0083] Accordingly, a structural steel according to one embodiment of the present invention may contain niobium (Nb) in an amount of 0.010 to 0.050 weight%, and preferably in an amount of 0.020 to 0.030 weight%.

[0084]

[0085] Titanium (Ti)

[0086] Titanium (Ti) contributes to strength improvement by forming precipitates in steel.

[0087] In the case of titanium precipitates, as high-temperature precipitates, they can refine the microstructure by inhibiting the growth of austenite grains upon reheating.

[0088] If the titanium content is insufficient, the aforementioned effect may be negligible. Conversely, if the titanium content is excessive, impact toughness may be reduced due to coarse titanium precipitates.

[0089] To this end, a structural steel according to one embodiment of the present invention may contain 0.010 to 0.015 weight percent of titanium (Ti).

[0090]

[0091] Nitrogen (N)

[0092] Even in extremely small amounts, nitrogen (N) can have a significant effect on the mechanical properties of steel.

[0093] Nitrogen can combine with aluminum, vanadium, titanium, and niobium to precipitate nitrides, and because it refines the structure of steel through these precipitates, it causes precipitation strengthening, which helps improve strength.

[0094] If the nitrogen content is insufficient, the aforementioned effects may be negligible. Conversely, if the nitrogen content is excessive, the toughness of the steel may decrease.

[0095] Accordingly, a structural steel according to one embodiment of the present invention may contain nitrogen (N) in an amount of 0.0150 to 0.0220 weight%, and preferably in an amount of 0.0200 to 0.0220 weight%.

[0096]

[0097] In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. If additional elements are included, they may be included to replace the remainder of iron (Fe).

[0098] In addition to the aforementioned steel components, the remainder may contain Fe and unavoidable impurities. Unavoidable impurities are those introduced during the steelmaking stage and the manufacturing process of structural steel; as this is widely known in the field, a detailed explanation is omitted.

[0099] A structural steel section according to one embodiment of the present invention may be a thick structural steel section. Specifically, a structural steel section according to one embodiment of the present invention may have a thickness of 40 to 80 mm. Here, the thickness of the structural steel section refers to the thickness of the flange portion.

[0100] A structural steel according to one embodiment of the present invention may have a yield strength (YS) of 400 MPa or more, and preferably 419 MPa or more.

[0101] A structural steel according to one embodiment of the present invention may have a tensile strength (TS) of 550 MPa or more, preferably 550 to 720 MPa, and more preferably 555 to 594 MPa.

[0102] A structural steel according to one embodiment of the present invention may have a yield ratio (YR), which is the ratio of yield strength (YS) to tensile strength (TS), of 85% or less, and preferably 75% or less.

[0103] A structural steel according to one embodiment of the present invention may have an elongation (EL) of 17% or more, preferably 27% or more, and more preferably 27.5% or more.

[0104] A structural steel according to one embodiment of the present invention may have an impact toughness of 100J or more when measured at 0℃, and preferably 107J or more.

[0105] A structural steel according to one embodiment of the present invention may have an impact toughness of 75J or more when measured at -20℃, preferably 81J or more, and more preferably 75% or more of the toughness when measured at 0℃.

[0106] Hereinafter, a method for manufacturing a structural steel according to one embodiment of the present invention will be described in detail.

[0107]

[0108] Method for manufacturing structural steel

[0109] Hereinafter, a method for manufacturing a structural steel according to an embodiment of the present invention will be described with reference to FIG. 1.

[0110] FIG. 1 is a flowchart illustrating a method for manufacturing a structural steel section according to one embodiment of the present invention.

[0111] A method for manufacturing a structural steel according to one embodiment of the present invention comprises the steps of preparing a steel material that is a semi-finished product (S1), reheating the steel material (S2), hot rolling the steel material to form a hot-rolled material (S3), and cooling the formed hot-rolled material (S4).

[0112] Hereinafter, each step of the method for manufacturing a structural steel section according to one embodiment of the present invention will be described in detail.

[0113] According to one embodiment of the present invention, the step (S1) of preparing a semi-finished steel material is a step of preparing a steel material having the alloy composition range described above in order to manufacture a final product, a structural steel.

[0114] Specifically, the step of preparing steel (S1) may be a step of manufacturing a semi-finished product by designing the alloy composition within the aforementioned alloy composition range. The semi-finished product may be a beam blank, a billet, or a bloom, but is not limited thereto. Furthermore, the manufacturing of the semi-finished product may be carried out by processes known in the relevant technical field, such as a steelmaking process or a continuous casting process.

[0115] According to one embodiment of the present invention, a step (S2) of reheating the steel material may be performed after a step (S1) of preparing the steel material.

[0116] The step of reheating the steel (S2) is a pretreatment process for the rolling step, and may be a step of charging the steel into a heating furnace and heating the steel uniformly to facilitate plastic deformation, thereby allowing segregated components to be re-dissolved during the casting of the steel.

[0117] In the step (S2) of reheating the steel, the steel may be reheated to 1150 to 1300°C. If the reheating temperature is below 1150°C, the re-dissolution of segregated components may not be smooth. Conversely, if the reheating temperature exceeds 1300°C, the austenite grains may coarsen, and the strength may decrease. In addition, increased heating costs and time may lead to increased manufacturing costs and reduced productivity.

[0118] Therefore, in the present invention, steel can be reheated at a temperature of 1150 to 1300°C.

[0119] According to one embodiment of the present invention, after the step (S2) of reheating the steel, the step (S3) of hot rolling the steel to form a hot-rolled material may be performed.

[0120] In the step (S3) of forming the hot-rolled material, the temperature of the reheated steel may drop due to reasons such as transport, and hot rolling may begin in a temperature range of 1030 to 1070°C.

[0121] The above hot rolling may include rough rolling and finishing rolling processes. Here, the rough rolling process may be the process of making the steel into a rolled material having a suitable shape, thickness, and width, and the finishing rolling process may be the process of adjusting the steel to a predetermined size and rolling it at a finishing temperature suitable for the application to obtain a good surface and shape.

[0122] In the step (S3) of forming hot-rolled material, the rolling end temperature may be 800 to 900°C. If the rolling end temperature is less than 800°C, the equipment load may increase and the yield ratio of the final product, the structural steel, may increase.

[0123] Conversely, if the rolling end temperature exceeds 900℃, the grains may grow excessively, which may reduce strength and toughness.

[0124] Consequently, in the method for manufacturing a structural steel according to one embodiment of the present invention, the rolling end temperature may be 800 to 900℃.

[0125] According to one embodiment of the present invention, after performing the step (S3) of forming a hot-rolled material, the step (S4) of cooling the formed hot-rolled material may be performed.

[0126] The step (S4) of cooling the hot-rolled material can be performed by water cooling through a cooling facility. The step (S4) of cooling the hot-rolled material can be a QST (Quenching and Self-Tempering) process. In other words, the hot-rolled material can be reheated using residual heat after being rapidly cooled with cooling water.

[0127] The hot-rolled material, after the step (S4) of cooling the hot-rolled material is performed, may contain a low-temperature structure. Here, the low-temperature structure means at least one of tempered martensite or bainite.

[0128] According to one embodiment of the present invention, the reheat temperature, which is reheated by residual heat after rapid cooling, may be 650 to 800°C.

[0129] If the reheat temperature is below 650℃, the cooling of the hot-rolled material is excessive, which may lead to the excessive formation of a low-temperature structure. Consequently, the resistance to fracture due to crack propagation is reduced, and as a result, the impact toughness of the final product, the structural steel, may be lowered.

[0130] Conversely, if the heat temperature exceeds 800℃, the cooling of the hot-rolled material may be insufficient, resulting in insufficient formation of the low-temperature structure. Consequently, the tensile strength of the final product, the structural steel, may decrease.

[0131] Consequently, the method for manufacturing a structural steel according to one embodiment of the present invention may have a heat temperature of 650 to 800℃.

[0132] After the step (S4) of cooling the hot-rolled material is performed, the final product, a structural steel, can be formed.

[0133] The thickness of the steel section manufactured by the steel section manufacturing method according to one embodiment of the present invention may be 40 to 80 mm.

[0134] A structural steel manufactured by the method for manufacturing structural steel according to one embodiment of the present invention can satisfy all of the aforementioned yield strength (YS), tensile strength (TS), elongation (EL), and impact toughness values.

[0135]

[0136] Comparative Examples and Examples

[0137] Preferred comparative examples and embodiments are presented below to aid in understanding the present invention. However, the following comparative examples and embodiments are intended only to aid in understanding the present invention, and the present invention is not limited by the following embodiments.

[0138] Table 1 shows the alloy element composition of the comparative example and the example, Table 2 shows the process conditions of the comparative example and the example, and Table 3 shows the physical properties of the comparative example and the example.

[0139] The comparative example and the example were each manufactured using a semi-finished product having the alloy composition listed in Table 1 below, and were manufactured using the reheating temperature, rolling start temperature, rolling end temperature, and double heating temperature conditions listed in Table 2.

[0140] Except for the conditions described above, the manufacturing processes of the comparative examples and embodiments of the present invention were controlled as control variables under the same conditions within the range described in the method for manufacturing structural steel according to one embodiment of the present invention.

[0141] In Table 1 below, the unit of the composition of alloy elements is weight%, and in Table 2 below, the units of the reheat temperature, rolling start temperature, rolling end temperature and double heating temperature are °C, and in Table 3, the units of tensile strength (TS) and yield strength (YS) are MPa, the units of yield ratio (YR) and elongation (EL) are %, and the unit of impact toughness (CVN) measured at 0°C and -20°C is J.

[0142] Here, physical properties were measured according to the EN 10025 standard and disclosed in Table 3.

[0143] Figure 2 is further referenced for a detailed explanation of the method for measuring physical properties.

[0144] Figure 2 is a drawing showing the tensile test and impact test evaluation method of a structural steel section.

[0145] According to one embodiment of the present invention, tensile and impact tests of structural steel can be performed in accordance with EN 10025 standards.

[0146] Specifically, for the tensile test, as in (2a), a tensile test specimen with a diameter of 14 mm was taken and measured at a point t / 4 from the surface in the thickness (t) direction of the flange and at a point B / 6 from the end in the length (B) direction.

[0147] Specifically, the size of the tensile test specimen is a diameter of 14 mm, a gauge length of 50 mm, and a shoulder radius of 15 mm.

[0148] In addition, for the impact test, after removing 2 mm from the surface of the flange as in (2b), the surface was made into a cross-section, and a 10 mm × 10 mm impact test specimen was taken with the center at a point B / 6 from the end in the direction of the length (B) of the flange, and a V-notch test was performed.

[0149] Specifically, the length of the impact test specimen is 50 mm, and the overall size is 10 mm × 10 mm × 50 mm.

[0150] Composition CsiMnPSAlVNbTiN Example 10.130.281.500.0200.0070.0110.0730.0220.0120.0209 Example 20.120.271.510.0210.0060.0100.0720.0220.0120.0217 Example 30.120.271.500.0200.0060.0120.0730.0220.0130.0218 Comparative Example 10.120.261.450.0190.0070.0110.0790.0230.0110.0183 Comparative Example 20.130.231.460.0170.0050.0120.0800.0200.0110.0190 Comparative Example 30.140.211.450.0200.0050.0100.0790.0210.0120.0172 Comparative Example 40.140.171.460.0210.0070.0110.0680.0200.0100.0131 Comparative Example 50.130.281.500.0120.0050.0120.0880.0210.0110.0229

[0151] Process Reheating Temperature (°C) Rolling Start Temperature (°C) Rolling End Temperature (°C) Reheating Temperature (°C) Example 1 1 200 10 40 8 70 790 Example 2 1 200 10 40 8 20 779 Example 3 1 200 10 40 8 22 654 Comparative Example 1 1 200 10 40 9 10 707 Comparative Example 2 1 200 10 40 8 70 850 Comparative Example 3 1 200 10 40 8 10 572 Comparative Example 4 1 200 10 40 8 27 770 Comparative Example 5 1 200 10 40 8 30 680

[0152] Material Properties Tensile Strength (TS) Yield Strength (YS) Yield Ratio (YR) Elongation (EL) 0℃ Impact Toughness (CVN) 0℃ )-20℃ Impact Toughness (CVN -20℃ )Ratio of Impact Toughness (CVN) 0℃ / CVN -20℃Example 15944227132.91251170.94 Example 25834197232.81671300.78 Example 35554197527.5107810.76 Comparative Example 15603916934.380430.54 Comparative Example 25553987235.1132780.59 Comparative Example 36585608524.043250.58 Comparative Example 45193737235.81411220.87 Comparative Example 56254797713.751400.78

[0153]

[0154] Referring to Tables 1 to 3 above, Comparative Example 1 is a comparative example in which the alloy composition range satisfies all the ranges according to one embodiment of the present invention, and the rolling end temperature is 910℃.

[0155] In the case of Comparative Example 1, it can be confirmed that the rolling end temperature does not satisfy the range of 800 to 900℃ according to one embodiment of the present invention described above.

[0156] Accordingly, in the case of Comparative Example 1, the values ​​of yield strength (YS), impact toughness at 0°C, and impact toughness at -20°C are 391 MPa, 80 J, and 43 J, respectively, and it can be confirmed that they do not satisfy the target ranges of 400 MPa or more, 100 J or more, and 75 J or more as intended by the present invention.

[0157] In addition, in the case of Comparative Example 1, the ratio of impact toughness at 0°C to impact toughness at -20°C is 54%, which can be seen as not satisfying the target range of 75% or more in the present invention.

[0158] Comparative Example 2 is a comparative example in which the alloy composition range satisfies all the ranges according to one embodiment of the present invention, but the double heating temperature is 850℃.

[0159] In the case of Comparative Example 2, it can be confirmed that the heat temperature does not satisfy the range of 650 to 800℃ according to one embodiment of the present invention described above.

[0160] Accordingly, it can be confirmed that in the case of Comparative Example 2, the yield strength (YS) value does not satisfy the target range of 400 MPa or higher in the present invention.

[0161] In addition, in the case of Comparative Example 2, the ratio of impact toughness at 0°C to impact toughness at -20°C is 59%, which can be seen as not satisfying the target range of 75% or more in the present invention.

[0162] Comparative Example 3 is a comparative example in which the alloy composition range satisfies all the ranges according to one embodiment of the present invention, but the double heating temperature is 572℃.

[0163] In the case of Comparative Example 3, it can be confirmed that the heat temperature does not satisfy the range of 650 to 800℃ according to one embodiment of the present invention described above.

[0164] Accordingly, in the case of Comparative Example 3, the values ​​of impact toughness at 0°C and impact toughness at -20°C are 43J and 25J, respectively, and it can be confirmed that they do not satisfy the target range of 100J or more and 75J or more in the present invention.

[0165] In addition, in the case of Comparative Example 3, the ratio of impact toughness at 0°C to impact toughness at -20°C is 58%, which does not satisfy the target range of 75% or more in the present invention.

[0166] Comparative Example 4 is a comparative example in which the process conditions satisfy all the ranges according to one embodiment of the present invention, but the nitrogen (N) content is 0.0131 weight%.

[0167] In the case of Comparative Example 4, it can be confirmed that the nitrogen (N) content does not satisfy the range of 0.0150 to 0.0220 weight% according to one embodiment of the present invention described above.

[0168] Accordingly, in the case of Comparative Example 4, the yield strength (YS) and tensile strength (TS) values ​​are 373 MPa and 519 MPa, respectively, and it can be confirmed that they do not satisfy the target range of 400 MPa or more and 550 MPa or more in the present invention.

[0169] Comparative Example 5 is a comparative example in which the process conditions satisfy all the ranges according to one embodiment of the present invention, but the nitrogen (N) content is 0.0229 wt%.

[0170] In the case of Comparative Example 5, it can be confirmed that the nitrogen (N) content does not satisfy the range of 0.0150 to 0.0220 weight% according to one embodiment of the present invention described above.

[0171] Accordingly, in the case of Comparative Example 5, the elongation (EL) and 0°C impact toughness values ​​are 13.7% and 51J, respectively, which does not satisfy the target range of 17% or more and 100J or more in the present invention.

[0172] On the other hand, in the case of Examples 1 to 3 according to one embodiment of the present invention, it can be confirmed that the alloy composition including nitrogen (N) satisfies all the ranges targeted by the present invention, and the process conditions including the rolling end temperature and the double-rolling temperature satisfies all the ranges targeted by the present invention. Accordingly, it can be confirmed that the yield strength (YS), tensile strength (TS), elongation (EL), and impact toughness (CVN) measured at 0°C and -20°C satisfy all the ranges targeted by the present invention.

[0173] As described above, preferred embodiments according to the present invention have been examined. It is obvious to those skilled in the art that, in addition to the embodiments described above, the present invention may be embodied in other specific forms without departing from the spirit or scope thereof. Therefore, the embodiments described above should be regarded as illustrative rather than restrictive, and accordingly, the present invention is not limited to the description above but may be modified within the scope of the appended claims and their equivalents.

[0174] [Explanation of the symbol]

[0175] S1: Steel preparation stage

[0176] S2: Steel reheating step

[0177] S3: Hot-rolled material formation stage

[0178] S4: Hot-rolled material cooling stage

Claims

1. comprising carbon (C) 0.05 ~ 0.15 wt%, silicon (Si) 0.10 ~ 0.30 wt%, manganese (Mn) 1.00 ~ 1.60 wt%, phosphorus (P) 0.040 wt% or less (excluding 0), sulfur (S) 0.040 wt% or less (excluding 0), aluminum (Al) 0.015 wt% or less, vanadium (V) 0.050 ~ 0.100 wt%, niobium (Nb) 0.010 ~ 0.050 wt%, titanium (Ti) 0.010 ~ 0.015 wt%, nitrogen (N) 0.0150 ~ 0.0220 wt%, and the remainder being iron (Fe) and other unavoidable impurities, The yield strength is 400 MPa or higher, and The elongation rate is 17% or higher, and Impact toughness of 100J or more measured at 0℃, Structural steel.

2. In Paragraph 1, With a thickness of 40 to 80 mm, Structural steel.

3. In Paragraph 1, with a yield rate of 85% or less, Structural steel.

4. In Paragraph 1, tensile strength of 550 MPa or higher, Structural steel.

5. In Paragraph 1, Impact toughness of 75J or higher measured at -20℃, Structural steel.

6. In Paragraph 5, A ratio of impact toughness measured at -20℃ to impact toughness measured at 0℃ of 75% or more, Structural steel.

7. (S1) Step of preparing steel materials; (S2) Step of reheating the above steel material; (S3) A step of hot-rolling the steel material to form a hot-rolled material; and (S4) A step of reheating and cooling the above hot-rolled material to form a final product, a structural steel; Includes, The above final product comprises 0.05 to 0.15 wt% carbon (C), 0.10 to 0.30 wt% silicon (Si), 1.00 to 1.60 wt% manganese (Mn), 0.040 wt% or less phosphorus (P) (excluding 0), 0.040 wt% or less sulfur (S) (excluding 0), 0.015 wt% or less aluminum (Al), 0.050 to 0.100 wt% vanadium (V), 0.010 to 0.050 wt% niobium (Nb), 0.010 to 0.015 wt% titanium (Ti), 0.0150 to 0.0220 wt% nitrogen (N), and the remainder being iron (Fe) and other unavoidable impurities, The yield strength is 400 MPa or higher, and The elongation rate is 17% or higher, and Impact toughness of 100J or more measured at 0℃, Method for manufacturing structural steel.

8. In Paragraph 7, The reheating temperature of the above (S2) step is 1150 to 1300℃, Method for manufacturing structural steel.

9. In Paragraph 7, The rolling start temperature of the above (S3) step is 1030 to 1070℃, Method for manufacturing structural steel.

10. In Paragraph 7, The rolling end temperature of the above (S3) step is 800 to 900℃, Method for manufacturing structural steel.

11. In Paragraph 7, The double heat temperature of the above (S4) step is 650 to 800℃, Method for manufacturing structural steel.

12. In Paragraph 7, The thickness of the above final product is 40 to 80 mm, Method for manufacturing structural steel.

13. In Paragraph 7, The yield ratio of the above final product is 85% or less, Method for manufacturing structural steel.

14. In Paragraph 7, The tensile strength of the above-mentioned final product is 550 MPa or higher, Method for manufacturing structural steel.

15. In Paragraph 7, The impact toughness of the above final product measured at -20℃ is 75J or higher, Method for manufacturing structural steel.

16. In Paragraph 7, The ratio of the impact toughness measured at -20℃ to the impact toughness measured at 0℃ of the above final product is 75% or more, Method for manufacturing structural steel.

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