Composite performance steel bar and method for manufacturing the same

Abstract

A composite performance structural steel according to one embodiment of the present invention comprises carbon (C) 0.08 to 0.17 wt%, silicon (Si) 0.10 to 0.50 wt%, manganese (Mn) 0.50 to 1.60 wt%, phosphorus (P) 0.020 wt% or less (excluding 0), sulfur (S) 0.010 wt% or less (excluding 0), chromium (Cr) 0.10 to 0.35 wt%, molybdenum (Mo) 0.15 to 0.73 wt%, copper (Cu) 0.50 wt% or less (excluding 0), niobium (Nb) 0.04 to 0.06 wt%, nitrogen (N) 0.012 wt% or less (excluding 0), and the remainder being iron (Fe) and unavoidable impurities, and has a high temperature yield strength (YS-600℃) of 280 MPa or more.

Description

Technology Field

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

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

[0003] Public interest in safety steel is rising due to the recent frequent earthquakes on the Korean Peninsula and fires in high-rise buildings. In particular, as the increasing size of buildings is linked to the number of fires caused by electrical short circuits during earthquakes, there is an urgent need for practical solutions.

[0004] In conjunction with this environment, various movements are underway to strengthen domestic seismic design standards, and there is a demand for composite performance of structural steel to enhance disaster response capabilities to the level of developed countries.

[0005] Therefore, there is a need to develop composite structural steel capable of possessing excellent strength and seismic and fire-resistant performance, as well as a method for manufacturing the same. The problem to be solved

[0006] According to one embodiment of the present invention, the objective is to provide a structural steel with composite performance capable of securing yield strength in a high-temperature environment as well as tensile strength and yield strength in a room-temperature environment, and a method for manufacturing the same.

[0007] 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. means of solving the problem

[0008] A composite performance structural steel according to one embodiment of the present invention comprises 0.08 to 0.17 wt% carbon (C), 0.10 to 0.50 wt% silicon (Si), 0.50 to 1.60 wt% manganese (Mn), 0.020 wt% or less phosphorus (P) (excluding 0), 0.010 wt% or less sulfur (S) (excluding 0), 0.10 to 0.35 wt% chromium (Cr), 0.15 to 0.73 wt% molybdenum (Mo), 0.50 wt% or less copper (Cu) (excluding 0), 0.04 to 0.06 wt% niobium (Nb), 0.012 wt% or less nitrogen (N) (excluding 0), and the remainder being iron (Fe) and unavoidable impurities, and may have a high temperature yield strength (YS, 600℃) of 280 MPa or more.

[0009] At this time, the room temperature tensile strength (TS) may be 520 MPa or higher.

[0010] Alternatively, the room temperature yield strength (YS) may be 420 MPa or higher.

[0011] Alternatively, the room temperature yield ratio (YR) may be 85% or less.

[0012] Alternatively, the room temperature elongation (EL) may be 15% or more.

[0013] Alternatively, low-temperature impact toughness (CVN-5℃ may be 45J or higher.

[0014] Alternatively, replacing the remainder Fe, it may further include one or more of titanium (Ti) 0.001 wt% or less (excluding 0) and boron (B) 0.0001 to 0.0004 wt%.

[0015] Alternatively, the above composite performance steel may be an H-shaped steel including a web section and flange sections disposed on both sides of the web section.

[0016] And a method for manufacturing a composite performance structural steel according to one embodiment of the present invention comprises: (S1) a step of preparing a steel material; (S2) a step of reheating the steel material; (S3) a step of hot-rolling the steel material to form a hot-rolled material; and (S4) a step of cooling the hot-rolled material to form a final product, wherein the final product comprises carbon (C) 0.08 ~ 0.17 wt%, silicon (Si) 0.10 ~ 0.50 wt%, manganese (Mn) 0.50 ~ 1.60 wt%, phosphorus (P) 0.020 wt% or less (excluding 0), sulfur (S) 0.010 wt% or less (excluding 0), chromium (Cr) 0.10 ~ 0.35 wt%, molybdenum (Mo) 0.15 ~ 0.73 wt%, copper (Cu) 0.50 wt% or less (excluding 0), niobium (Nb) 0.04 ~ It contains 0.06 wt% or less (excluding 0), 0.012 wt% or less (excluding 0) of nitrogen (N) and the remainder being iron (Fe) and unavoidable impurities, and may have a high temperature yield strength (YS, 600℃) of 280 MPa or more.

[0017] At this time, the reheating temperature of the above (S2) step may be 1200 to 1250℃.

[0018] Alternatively, the rolling start temperature of the above (S3) step may be 1050 to 1100℃.

[0019] Alternatively, the rolling end temperature of the above (S3) step may be 725 to 780℃.

[0020] Alternatively, the cooling of the above step (S4) can be performed by air cooling.

[0021] At this time, the cooling rate of the above (S4) step may be 1 to 5℃.

[0022] And the above final product may further include one or more of titanium (Ti) 0.001 wt% or less (excluding 0) and boron (B) 0.0001 to 0.0004 wt% in place of the remainder Fe. Effects of the invention

[0023] It is possible to provide a structural steel with composite performance capable of securing yield strength and tensile strength in a room temperature environment, as well as yield strength in a high temperature environment, and a method for manufacturing the same.

[0024] 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. Brief explanation of the drawing

[0025] FIG. 1 is a flowchart illustrating a method for manufacturing a composite performance structural steel according to one embodiment of the present invention. Specific details for implementing the invention

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0034] Composite performance structural steel

[0035] A composite performance steel section according to one embodiment of the present invention may be a steel section applied to buildings or structures. For example, the composite performance steel section may be an H-shaped steel section comprising a web section and flange sections disposed on both sides of the web section. However, the type of steel section is not limited to that described above.

[0036] A composite performance structural steel according to one embodiment of the present invention may contain 0.08 to 0.17 wt% carbon (C), 0.10 to 0.50 wt% silicon (Si), 0.50 to 1.60 wt% manganese (Mn), 0.020 wt% or less phosphorus (P) (excluding 0), 0.010 wt% or less sulfur (S) (excluding 0), 0.10 to 0.35 wt% chromium (Cr), 0.30 to 0.70 wt% molybdenum (Mo), 0.50 wt% or less copper (Cu) (excluding 0), 0.04 to 0.06 wt% niobium (Nb), 0.012 wt% or less nitrogen (N) (excluding 0), and the remainder being iron (Fe) and unavoidable impurities.

[0037] Hereinafter, the roles and contents of each alloy element included in the composite performance structural steel according to one embodiment of the present invention will be described in detail.

[0039] Carbon (C)

[0040] Carbon (C) is the most effective and important element for increasing the strength of steel.

[0041] Carbon is dissolved in austenite and can form a martensite structure upon quenching. Additionally, hardness can be improved as the carbon content increases.

[0042] In addition, carbon effectively contributes to strength enhancement through precipitation strengthening by reacting with niobium (Nb), titanium (Ti), etc., to promote the formation of fine carbides, while also being effective in securing fire-resistant performance by improving high-temperature strength through hindering dislocation movement at high temperatures.

[0043] In this case, if the carbon content is insufficient, the aforementioned effects may be lacking, making it difficult to secure sufficient strength. Conversely, if the carbon content is excessive, it may cause deformation during quenching or lead to a decrease in the steel's elongation and low-temperature toughness.

[0044] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain carbon (C) in an amount of 0.08 to 0.17 weight%, preferably 0.08 to 0.1 weight%.

[0046] Silicon (Si)

[0047] Silicon (Si) is added as a deoxidizer to remove oxygen from steel in the steelmaking process along with aluminum, and as a ferrite stabilizing element with a solid solution strengthening effect, it can induce ferrite formation to improve the hardenability and softening resistance of steel.

[0048] If the silicon content is insufficient, the aforementioned effects may be negligible. Conversely, if the silicon content is excessive, toughness may be reduced and plastic workability may be impaired.

[0049] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain silicon (Si) in an amount of 0.1 to 0.5 weight%, preferably 0.1 to 0.28 weight%.

[0051] Manganese (Mn)

[0052] Manganese (Mn) contributes to securing strength as a solid solution strengthening element, and can also be effective in forming a bainite structure by improving the hardenability of steel. In addition, as the manganese content increases, the pearlite becomes finer and the ferrite is solid solution strengthened, which can improve yield strength.

[0053] If the manganese content is insufficient, the aforementioned effects may be negligible. Conversely, if the manganese content is excessive, it may combine with sulfur (S) to form MnS inclusions or cause central segregation in the ingot, and the austenite structure may remain, which may actually lower the strength and toughness.

[0054] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain manganese (Mn) in an amount of 0.5 to 1.60 weight%, preferably 0.5 to 1.52 weight%.

[0056] Ph(P)

[0057] Phosphorus (P) is an element that contributes to strength improvement. However, if it is included in excessive amounts, it can worsen the ductility of steel and cause variations in the final material due to billet center segregation. If the phosphorus content exceeds 0.02 weight%, it can form center segregation and microsegregation, which can reduce the ductility of steel and lower impact strength due to precipitation behavior.

[0058] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain phosphorus (P) in an amount of 0.02 weight% or less (excluding 0).

[0060] Yellow (S)

[0061] Sulfur (S) improves the machinability of steel by combining with manganese, zinc, titanium, molybdenum, etc., and can improve workability by forming fine precipitates (e.g., MnS) by combining with manganese. However, if the amount of manganese in the steel is insufficient, it can form sulfides (e.g., FeS) by combining with iron, which may cause cracking during hot and cold working. If the sulfur content exceeds 0.01 weight%, it may reduce the ductility of the steel and lower its toughness and weldability.

[0062] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain sulfur (S) in an amount of 0.01 weight% or less (excluding 0).

[0064] Chrome (Cr)

[0065] Chromium (Cr) is a ferrite-stabilizing element; when added to C-Mn steel, it delays carbon diffusion through a solute interference effect, thereby influencing grain size refinement. Additionally, chromium can improve the hardenability of steel and contribute to the formation of a bainite microstructure, which can enhance hardenability. However, excessive chromium content can lead to the formation of coarse carbides at grain boundaries, which may reduce the ductility of the steel at room and low temperatures and increase manufacturing costs.

[0066] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain chromium (Cr) in an amount of 0.10 to 0.35 weight%.

[0068] Molybdenum (Mo)

[0069] Molybdenum (Mo) can improve the hardenability of steel, contribute to securing a bainite microstructure, and be very effective in securing high-temperature strength. Specifically, even with the addition of a small amount, molybdenum (Mo) can improve hardenability by up to 10 times compared to nickel (Ni) and prevent temper brittleness, thereby providing resistance to temper brittleness.

[0070] Furthermore, since molybdenum (Mo) forms carbides, it is highly effective as an alloying element for high-grade cutting tools and raises the grain coarsening temperature. To enhance hardenability, it is more effective when used in combination with chromium rather than alone.

[0071] Molybdenum (Mo) possesses very high heat resistance at high temperatures and maintains metallic strength and hardness. Due to its high melting point, it can exist in a stable form even at high temperatures. Furthermore, molybdenum plays an important role in high-temperature properties, such as improving corrosion resistance in high-temperature oxidizing environments through its excellent resistance to oxidation at high temperatures.

[0072] If the molybdenum content is insufficient, the aforementioned effects may be negligible. Conversely, if the molybdenum content is excessive, the manufacturing cost of the steel increases, weldability may deteriorate, and, in particular, the impact absorption energy of the steel may decrease, making it unsuitable for achieving seismic resistance.

[0073] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain molybdenum (Mo) in an amount of 0.15 to 0.70 weight%, preferably 0.30 to 0.70 weight%, and more preferably 0.30 to 0.40 weight%.

[0075] Copper (Cu)

[0076] Copper (Cu) is usually contained in steel at a weight of about 0.1 to 0.3 percent, which can increase corrosion resistance in the atmosphere or seawater.

[0077] Copper is dissolved in ferrite up to 0.35 wt% at room temperature and exhibits a solid solution strengthening effect, so strength and hardness can be improved. When copper is added in an amount of 0.35 wt% or more, it exhibits a precipitation hardening effect due to the fine precipitation of copper, so hardness can be further improved.

[0078] However, if the copper content is excessive, the elongation may decrease and it may cause red-hot brittleness.

[0079] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain copper (Cu) in an amount of 0.50 weight% or less (excluding 0), preferably 0.16 to 0.50 weight%.

[0081] Niobium (Nb)

[0082] Niobium (Nb) can increase hardness by combining with carbon to form precipitates such as NbC within the grains.

[0083] In addition, it is an element that is advantageous for improving strength by refining the grain size. If the niobium content is excessively low, the aforementioned effect does not appear, and if the niobium content exceeds 0.06 weight%, the precipitation strengthening effect is excessive, which may cause problems such as increased strength but decreased ductility.

[0084] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain niobium in an amount of 0.04 to 0.06 weight%, preferably 0.04 to 0.045 weight%.

[0086] Nitrogen (N)

[0087] Nitrogen (N) significantly affects the mechanical properties of steel even in extremely small amounts; as the nitrogen content increases, tensile strength and yield strength increase, while elongation decreases. In particular, the decrease in impact strength and the increase in transition temperature are notable.

[0088] When nitrogen is added, it forms nitrides to refine the grain size; however, if the nitrogen content is excessive, it can lead to a decrease in high-temperature toughness and intergranular brittleness due to nitride precipitation at austenite grain boundaries.

[0089] Accordingly, a composite performance structural steel according to one embodiment of the present invention may contain nitrogen (N) in an amount of 0.012 weight% or less (excluding 0).

[0091] A composite performance structural steel according to one embodiment of the present invention may optionally include one or more additional alloying elements, such as titanium (Ti) and boron (B), in addition to the aforementioned alloying elements. The optional elements may be added to replace the remainder, iron (Fe).

[0093] Titanium (Ti)

[0094] Titanium can form TiN together with nitrogen. In the present invention, the formation of proeutectoid ferrite in austenite grains is suppressed by adding boron as a method to improve the hardenability of steel. However, if BN is formed by the combination of boron and nitrogen during the steelmaking process, the mechanism for improving hardenability cannot be implemented. Therefore, it is necessary to limit the nitrogen content to 100 ppm or less by applying a Vacuum Degassing (VD) process during the steelmaking process. Additionally, to suppress the combination of residual nitrogen and boron, titanium can be added to form TiN first, thereby ultimately playing a role in improving the hardenability of the steel.

[0095] To this end, a composite performance structural steel according to one embodiment of the present invention may contain titanium (Ti) in an amount of 0.001 weight% or less (excluding 0).

[0097] Boron (B)

[0098] Boron preferentially segregates at austenite grain boundaries, inhibiting the formation of ferrite, a soft structure, upon cooling, thereby improving hardenability. However, excessive addition can lead to the problem of intergranular brittleness.

[0099] To this end, a composite performance structural steel according to one embodiment of the present invention may contain boron (B) in an amount of 0.002 weight% or less (excluding), preferably 0.0004 weight% or less (excluding 0).

[0101] In addition to the steel components described above, the remainder may contain iron (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.

[0102] 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).

[0103] A composite performance structural steel according to one embodiment of the present invention may have a high temperature yield strength (YS) of 280 MPa or more. Here, high temperature means 600℃.

[0104] A composite performance structural steel according to one embodiment of the present invention may have a room temperature tensile strength (TS) of 520 MPa or more, preferably 520 to 640 MPa. Here, room temperature means 20℃.

[0105] In addition, the composite performance structural steel according to one embodiment of the present invention may have a room temperature yield strength (YS) of 420 MPa or more, preferably 420 to 540 MPa.

[0106] In addition, the composite performance structural steel according to one embodiment of the present invention may have a room temperature yield ratio (YR) of 85% or less, preferably 70% or less.

[0107] In addition, the composite performance structural steel according to one embodiment of the present invention may have a room temperature elongation (EL) of 19% or more, preferably 20% or more.

[0108] In addition, a composite performance structural steel according to one embodiment of the present invention may have a low-temperature impact toughness (CVN) of 47 J or more, preferably 70 to 80 J. Here, low temperature means -5℃.

[0109] Hereinafter, a method for manufacturing a composite performance structural steel according to one embodiment of the present invention will be described in detail.

[0111] Method for manufacturing composite performance steel sections

[0112] Hereinafter, a method for manufacturing a composite performance structural steel according to an embodiment of the present invention will be described with reference to FIG. 1.

[0113] FIG. 1 is a flowchart illustrating a method for manufacturing a composite performance structural steel according to one embodiment of the present invention.

[0114] A method for manufacturing a composite performance structural steel according to one embodiment of the present invention includes 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).

[0115] Hereinafter, each step of the method for manufacturing composite performance steel sections according to one embodiment of the present invention will be described in detail.

[0116] According to one embodiment of the present invention, the step (S1) of preparing a steel material that is a semi-finished product is a step of preparing a steel material having the alloy composition range described above in order to manufacture a composite performance structural steel that is a final product.

[0117] 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 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.

[0118] According to one embodiment of the present invention, a step of reheating the steel (S2) may be performed after a step of preparing the steel (S1).

[0119] 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.

[0120] In the step (S2) of reheating the steel, the steel may be reheated to 1200 to 1250°C. If the reheating temperature is below 1200°C, the rolling load may increase. Conversely, if the reheating temperature exceeds 1250°C, the austenite grains may coarsen or decarburization may occur, which may impair strength. In addition, increased heating costs and time may lead to increased manufacturing costs and reduced productivity.

[0121] Accordingly, in the present invention, the steel can be reheated at a temperature of 1200 to 1250°C, and preferably at 1230 to 1235°C.

[0122] 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.

[0123] 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 1050 to 1100°C.

[0124] 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.

[0125] In the step (S3) of forming the hot-rolled material, if the finishing rolling temperature is below a preset range, the rolling load increases, productivity decreases, and the heat treatment effect may be reduced. Conversely, if the finishing rolling temperature exceeds a preset range, the pearlite structure is formed coarsely, and the strength may decrease rapidly.

[0126] In other words, the finish rolling temperature plays a crucial role in the formation of hot-rolled materials, significantly influencing the microstructure and physical properties of the metal. Specifically, when the finish rolling temperature is high, the internal crystal grains can grow larger, which tends to decrease hardness but increase toughness; this implies that the material becomes more ductile and resistant to fracture in high-temperature environments.

[0127] These characteristics can be ideal, particularly for components in high-temperature environments. Conversely, if the finish rolling temperature is lower, the internal grains of the metal remain smaller; while this increases the metal's hardness, it may reduce toughness. This implies that although the material possesses higher strength, its resistance to fracture at high temperatures may decrease. Therefore, the finish rolling temperature significantly affects the high-temperature properties of hot-rolled materials, which can have a critical impact on their final applications and performance.

[0128] In one embodiment of the present invention, the finish rolling temperature may be 725 to 780°C, and preferably 740 to 780°C.

[0129] 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.

[0130] The step (S4) of cooling the hot-rolled material can be performed by air cooling. At this time, the hot-rolled material can be cooled at a rate of 1 to 5°C.

[0131] After the step (S4) of cooling the hot-rolled material is performed, the final product, a composite performance structural steel, can be formed.

[0132] The composite performance structural steel manufactured by the method for manufacturing composite performance structural steel according to one embodiment of the present invention exhibits the aforementioned room temperature yield strength (YS), room temperature tensile strength (TS), room temperature yield ratio (%), room temperature elongation (EL), and low temperature impact toughness (CVN). -5℃ ) and high temperature yield strength (YS 600℃ Can satisfy all ) values.

[0134] Comparative Examples and Examples

[0135] 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.

[0136] Table 1 shows the alloy element composition of the comparative example and the example, and Table 2 shows the process conditions of the comparative example and the example. And Table 3 shows the physical property values ​​of the comparative example and the example.

[0137] 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 composite performance structural steel according to one embodiment of the present invention.

[0138] In addition, the room temperature properties of the comparative example and the example were measured in an environment of 20℃.

[0139] In Table 1 below, the unit of the composition of alloy elements is weight%, and in Table 2 below, the units of room temperature yield strength (YS), room temperature tensile strength (TS), and high temperature yield strength (YS) are MPa, the units of room temperature yield ratio and room temperature elongation (EL) are %, and the unit of low temperature impact toughness (CVN) is J.

[0141] division Chemical composition [wt.%] C Si Mn P S Cr Mo Cu Nb Ti B N Example 1 0.09 0.24 1.43 0.012 0.001 0.32 0.40 0.16 0.043 0.001 0.0003 0.0097 Real-life example 2 0.08 0.26 1.39 0.010 0.001 0.30 0.40 0.20 0.045 0.001 0.0004 0.0101 Comparative Example 1 0.11 0.32 1.53 0.010 0.001 0.31 0.14 0.15 0.050 0.001 0.002 0.0096 Comparative Example 2 0.11 0.29 1.55 0.011 0.001 0.30 0.74 0.15 0.049 0.001 0.002 0.0093 Comparative Example 3 0.08 0.26 1.39 0.010 0.001 0.30 0.40 0.20 0.045 0.001 0.0004 0.0103 Comparative Example 4 0.09 0.24 1.43 0.012 0.001 0.32 0.40 0.16 0.043 0.001 0.0003 0.0097

[0142] division Heating (°C) Rolling start temperature (°C) Rolling end temperature (°C) Cooling / Reheating Temperature (°C / sec) Thickness (mm) Example 1 1230 1053 748 Air cooling / 1~5 24 Example 2 1235 1062 779 Air cooling / 1~5 24 Comparative Example 1 1221 1057 768 Air cooling / 1~5 24 Comparative Example 2 1226 1072 773 Air cooling / 1~5 24 Comparative Example 3 1237 1060 724 Air cooling / 1~5 24 Comparative Example 4 1242 1066 783 Air cooling / 1~5 24

[0143] division Room temperature properties High-temperature properties TS YS Surrender monument EL CVN YS Example 1 633 426 67 20 79 290 Example 2 621 419 67 22 72 298 Comparative Example 1 546 436 80 27 112 176 Comparative Example 2 755 544 72 14 16 369 Comparative Example 3 598 361 60 24 83 231 Comparative Example 4 639 400 63 23 57 280

[0144] Referring to Tables 1 to 3 above, Comparative Example 1 is a comparative example in which other alloy composition ranges satisfy all the ranges according to one embodiment of the present invention, but the molybdenum (Mo) content is 0.14 wt%.

[0145] In the case of Comparative Example 1, it can be confirmed that the high temperature yield strength (YS) value is 176 MPa because the molybdenum (Mo) content does not satisfy the range of 0.15 to 0.73 weight% according to one embodiment of the present invention described above. In other words, it can be confirmed that in the case of Comparative Example 1, the high temperature yield strength (YS) value does not satisfy the range of 280 MPa or higher targeted by the present invention.

[0146] Comparative Example 2 is a comparative example in which the other alloy composition ranges satisfy all the ranges according to one embodiment of the present invention, except that the molybdenum (Mo) content is 0.74 wt%.

[0147] In the case of Comparative Example 2, the molybdenum (Mo) content did not satisfy the range of 0.15 to 0.73 weight% according to one embodiment of the present invention described above, and thus the room temperature elongation (EL) and low temperature impact toughness (CVN) -5℃ It can be confirmed that the values ​​were 14% and 16J, respectively.

[0148] In other words, it can be seen that in the case of Comparative Example 2, the room temperature elongation (EL) and low temperature impact toughness (CVN-5℃ value) do not satisfy the ranges targeted in the present invention, which are 15% or more and 45J or more, respectively.

[0149] On the other hand, in the case of Example 1 and Example 2 according to one embodiment of the present invention, it can be confirmed that the alloy composition range satisfies all of the embodiments of the present invention. Through this, it can be confirmed that the room temperature yield strength (YS), room temperature tensile strength (TS), room temperature yield ratio, room temperature elongation (EL), and low temperature impact toughness (CVN, -5℃ value) satisfy all the ranges targeted in the present invention.

[0150] 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 rolling end temperature is 724℃.

[0151] In the case of Comparative Example 3, the rolling end temperature did not satisfy the range of 725 to 780°C according to one embodiment of the present invention described above, and it can be seen that the room temperature yield strength (YS) and high temperature yield strength (YS, 600°C) values ​​were 361 MPa and 231 MPa, respectively.

[0152] In other words, it can be seen that in the case of Comparative Example 3, the room temperature yield strength (YS) and high temperature yield strength (YS, 600℃) values ​​do not satisfy the target ranges of 420 MPa or more and 280 MPa or more, respectively, as intended in the present invention.

[0153] Comparative Example 4 is a comparative example in which the alloy composition range satisfies all the ranges according to one embodiment of the present invention, but the rolling end temperature is 783℃.

[0154] In the case of Comparative Example 4, the rolling end temperature did not satisfy the range of 725 to 780°C according to one embodiment of the present invention described above, and it can be confirmed that the room temperature yield strength (YS) value was 400 MPa.

[0155] In other words, it can be confirmed that in the case of Comparative Example 4, the room temperature yield strength (YS) value does not satisfy the range of 420 MPa or higher targeted in the present invention.

[0156] On the other hand, in the case of Example 1 and Example 2 according to one embodiment of the present invention, it can be confirmed that the process range satisfies all of the one embodiment of the present invention. Through this, it can be confirmed that the room temperature yield strength (YS), room temperature tensile strength (TS), room temperature yield ratio, room temperature elongation (EL), and low temperature impact toughness (CVN, -5℃ value) satisfy all the ranges targeted in the present invention.

[0157] 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 its spirit or scope. 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.

Claims

Claim 1 It comprises 0.08 to 0.17 wt% carbon (C), 0.10 to 0.50 wt% silicon (Si), 0.50 to 1.60 wt% manganese (Mn), 0.020 wt% or less phosphorus (P) (excluding 0), 0.010 wt% or less sulfur (S) (excluding 0), 0.10 to 0.32 wt% chromium (Cr), 0.15 to 0.73 wt% molybdenum (Mo), 0.50 wt% or less copper (Cu) (excluding 0), greater than 0.04 to 0.06 wt% niobium (Nb), 0.012 wt% or less nitrogen (N) (excluding 0), 0.001 wt% or less titanium (Ti) (excluding 0), 0.0001 to 0.0004 wt% boron (B), and the remainder being iron (Fe) and unavoidable impurities, and at room temperature Composite performance structural steel having a yield strength (YS) of 420 MPa or more, a low-temperature impact toughness (CVN, -5℃) of 45 J or more, and a high-temperature yield strength (YS, 600℃) of 280 MPa or more. Claim 2 A composite performance structural steel having a room temperature tensile strength (TS) of 520 MPa or more, according to claim 1. Claim 3 delete Claim 4 A composite performance structural steel having a room temperature yield ratio (YR) of 85% or less, according to claim 1. Claim 5 A composite performance structural steel having a room temperature elongation (EL) of 15% or more in claim 1. Claim 6 delete Claim 7 delete Claim 8 In claim 1, the composite performance steel section is an H-shaped steel section comprising a web section and flange sections disposed on both sides of the web section. Claim 9 (S1) a step of preparing steel; (S2) a step of reheating the steel; (S3) a step of hot-rolling the steel to form a hot-rolled material; and (S4) a step of air-cooling the hot-rolled material at a rate of 1 to 5℃ / sec to form a final product; The above-mentioned final product comprises 0.08 to 0.17 wt% carbon (C), 0.10 to 0.50 wt% silicon (Si), 0.50 to 1.60 wt% manganese (Mn), 0.020 wt% or less phosphorus (P) (excluding 0), 0.010 wt% or less sulfur (S) (excluding 0), 0.10 to 0.32 wt% chromium (Cr), 0.15 to 0.73 wt% molybdenum (Mo), 0.50 wt% or less copper (Cu) (excluding 0), greater than 0.04 to 0.06 wt% niobium (Nb), 0.012 wt% or less nitrogen (N) (excluding 0), 0.001 wt% or less titanium (Ti) (excluding 0), 0.0001 to 0.0004 wt% boron (B), and the remainder being iron (Fe) and A method for manufacturing a composite performance structural steel containing unavoidable impurities, having a room temperature yield strength (YS) of 420 MPa or more, a low temperature impact toughness (CVN, -5℃) of 45 J or more, and a high temperature yield strength (YS, 600℃) of 280 MPa or more. Claim 10 A method for manufacturing a composite performance structural steel, wherein, in claim 9, the reheating temperature of step (S2) is 1200 to 1250℃. Claim 11 A method for manufacturing a composite performance structural steel, wherein, in claim 9, the rolling start temperature of step (S3) is 1050 to 1100℃. Claim 12 A method for manufacturing a composite performance structural steel, wherein, in claim 9, the rolling end temperature of step (S3) is 725 to 780℃. Claim 13 delete Claim 14 delete Claim 15 delete

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