WO2024091054A1 - Steel section and method for manufacturing same - Google Patents

Abstract

A method for manufacturing a steel section, according to an embodiment of the present invention, comprises the steps of: (a) reheating steel to 1150-1300 °C, the steel comprising 0.04-0.14 wt% of carbon (C), 0.10-0.55 wt% of silicon (Si), 0.90-1.65 wt% of manganese (Mn), 0.020 wt% or less of phosphorus (P), 0.007 wt% or less of sulfur (S), 0.015-0.055 wt% of aluminum (Al), 0.010-0.080 wt% of vanadium (V), 0.005-0.025 wt% of titanium (Ti), 0.010-0.050 wt% of niobium (Nb), and the remainder of iron (Fe) and other inevitable impurities; and (b) rolling the steel, wherein the rolling start temperature is 900-1100 °C, the rolling medium temperature is 850-1000 °C, and the rolling end temperature is 800-900 °C. Accordingly, it is possible to realize a high-performance steel section which achieves uniform physical properties while securing low-temperature impact toughness and a method for manufacturing the steel section.

Description

Section steel and section steel manufacturing method

The present invention relates to section steel and a method of manufacturing section steel.

Section steel generally refers to a steel material whose cross-sectional shape varies in various ways. Section steel can be manufactured by hot rolling casts such as blooms, billets, and beam blanks manufactured through continuous casting, and is applied as structural steel such as pillars of large buildings, subways, and bridges. It is also used as temporary material for civil engineering and foundation piles.

Recently, as the marine plant industry develops, the demand for section steel with light weight and high strength and guaranteed low-temperature impact toughness that can withstand external impacts even below -40℃ is increasing in the field of steel materials for marine structures.

The TMCP (thermo-mechanical control process) process using QST (Quenching and Self-Tempering), an accelerated cooling facility, is mainly used as a manufacturing method for steel materials that can secure high strength and impact toughness even at low temperatures.

However, when hot rolling is performed using the TMCP process, a grain refinement effect can be obtained, but there are problems with temperature deviation and deformation occurring during cooling due to differences in the three-dimensional shape of the section steel and the thickness of the flange and web.

In addition, in the process of manufacturing medium- or small-sized section steel, the size of the beam blank is relatively small, so when using the TMCP process, cooling may proceed too quickly and there is a risk that the cooling rate may not be precisely controlled.

Accordingly, the demand for high-strength section steel and its manufacturing method that can minimize the occurrence of deformation and physical property deviation while ensuring low-temperature impact toughness is increasing.

In order to solve the problems of the prior art described above, the purpose of the section steel and section steel manufacturing method according to the present invention is to provide a high-performance section steel and section steel manufacturing method that achieves homogenization of the physical properties of the section steel while securing low-temperature impact toughness.

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

The method of manufacturing section steel according to an embodiment of the present invention is (a) 0.04 to 0.14 wt% of carbon (C), 0.10 to 0.55 wt% of silicon (Si), 0.90 to 1.65 wt% of manganese (Mn), and 0.020 wt% of phosphorus (P). Weight% or less, sulfur (S) 0.007 weight% or less, aluminum (Al) 0.015 to 0.055 weight%, vanadium (V) 0.010 to 0.080 weight%, titanium (Ti) 0.005 to 0.025 weight%, niobium (Nb) 0.010 to 0.050 % by weight, reheating the steel containing the remaining iron (Fe) and other inevitable impurities to 1150 ~ 1300 ℃; and (b) rolling the steel, wherein the rolling start temperature is 900 ~ 1100 ℃ and the rolling middle temperature is 850 ~ 1300 ℃. It includes the step of performing rolling at 1000°C and the rolling end temperature is 800 to 900°C.

In addition, in step (b), coolant is sprayed from an S/C (Selective Cooling) device to control the rolling temperature, but the waiting time is 0 to 120 seconds, the water quantity is 50 to 300 m ³ /hr, and the transfer speed is can be performed under the conditions of 2.0 to 4.0 m/s.

In addition, the steel material subjected to step (b) may have a room temperature microstructure in the center containing ferrite and pearlite, and the F.G.S. (Ferrite grain size) may be 10 ㎛ or less.

In addition, the steel material that performed step (b) above has a yield strength (YS) of 420 MPa or more, a low-temperature impact toughness at -40°C of 50 J or more, a yield ratio (YR) of 0.90 or less, and an elongation (EL) of 19% or more. You can.

The steel material performed in step (b) is manufactured as H-beam steel including a web and a flange, and the yield strength (YS) deviation of the upper and lower parts of the flange based on the web may be 15 MPa or less.

In addition, the steel material contains 0.1 to 0.2% by weight of silicon (Si), 1.57 to 1.65% by weight of manganese (Mn), 0.015 to 0.021% by weight of aluminum (Al), 0.040 to 0.045% by weight of vanadium (V), and 0.005 to 0.005% by weight of titanium (Ti). It may be 0.008% by weight, and niobium (Nb) may be 0.040 to 0.045% by weight.

The section steel according to an embodiment of the present invention contains 0.04 to 0.14 wt% of carbon (C), 0.10 to 0.55 wt% of silicon (Si), 0.90 to 1.65 wt% of manganese (Mn), and 0.020 wt% or less of phosphorus (P). Sulfur (S) 0.007% by weight or less, aluminum (Al) 0.015 to 0.055% by weight, vanadium (V) 0.010 to 0.080% by weight, titanium (Ti) 0.005 to 0.025% by weight, niobium (Nb) 0.010 to 0.050% by weight, remainder It contains iron (Fe) and other inevitable impurities, and the yield strength (YS) satisfies 420 MPa or more.

Additionally, low-temperature impact toughness at -40°C can satisfy more than 50J.

Additionally, a yield ratio (YR) of 0.90 or less can be satisfied.

Additionally, the elongation (EL) may be 19% or more.

In addition, it has the shape of an H-beam steel including a web and a flange, and the yield strength (YS) deviation of the upper and lower parts of the flange with respect to the web may be 15 MPa or less.

In addition, the room temperature microstructure in the center includes ferrite and pearlite, and the F.G.S. (Ferrite grain size) may be 10 ㎛ or less.

In addition, the steel material contains 0.1 to 0.2 wt% of silicon (Si), 1.57 to 1.65 wt% of manganese (Mn), 0.015 to 0.021 wt% of aluminum (Al), 0.040 to 0.045 wt% of vanadium (V), and 0.005 wt% of titanium (Ti). ~ 0.008% by weight, niobium (Nb) may be 0.040 ~ 0.045% by weight.

The section steel according to an embodiment of the present invention contains 0.04 to 0.14 wt% of carbon (C), 0.10 to 0.55 wt% of silicon (Si), 0.90 to 1.65 wt% of manganese (Mn), and 0.020 wt% or less of phosphorus (P). Sulfur (S) 0.007% by weight or less, aluminum (Al) 0.015 to 0.055% by weight, vanadium (V) 0.010 to 0.080% by weight, titanium (Ti) 0.005 to 0.025% by weight, niobium (Nb) 0.010 to 0.050% by weight, remainder Contains iron (Fe) and other inevitable impurities, reheats to 1150 ~ 1300 ℃ and then rolls, with rolling start temperature controlled at 900 ~ 1100 ℃, rolling middle temperature at 850 ~ 1000 ℃, and rolling end temperature at 800 ~ 900 ℃. It can be manufactured by this method.

In addition, to control the temperature in the middle of rolling, coolant is sprayed from the S/C (Selective Cooling) device, with a waiting time of 0 to 120 seconds, a water quantity of 50 to 300 m ³ /hr, and a transfer speed of 2.0 to 4.0 m/hr. It can be manufactured using a method controlled by s.

According to an embodiment of the present invention, it is possible to implement a high-performance section steel and a method for manufacturing section steel that achieves homogenization of physical properties while securing low-temperature impact toughness.

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

1 is a flowchart showing a method for manufacturing section steel according to the present invention.

Figure 2 is a diagram showing the S/C device and the section steel used in the section steel manufacturing method according to the present invention.

Figures 3(a) to 3(c) are tissue observation photographs of specimens at the center of the flange of section steel according to comparative examples and experimental examples. In detail, Figure 3(a) is a photograph of the microstructure according to Comparative Example 1, Figure 3(b) is a photograph of the microstructure according to Comparative Example 2, and Figure 3(c) is a photograph of the microstructure according to Experimental Example 1.

In this specification, when a component (or region, layer, portion, etc.) is referred to as being “on,” “connected to,” or “coupled to” another component, it is directly placed/on the other component. This means that they can be connected/combined or a third component can be placed between them.

Like reference numerals refer to like elements. Additionally, in the drawings, the thickness, proportions, and dimensions of components are exaggerated for effective explanation of technical content.

“And/or” includes all combinations of one or more that the associated configurations may define.

Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, a first component may be named a second component, and similarly, the second component may also be named a first component without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

Additionally, terms such as “below,” “on the lower side,” “above,” and “on the upper side” are used to describe the relationship between the components shown in the drawings. The above terms are relative concepts and are explained based on the direction indicated in the drawings.

Unless otherwise defined, all terms (including technical terms and scientific terms) used in this specification have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Additionally, terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and unless interpreted in an idealized or overly formal sense, are explicitly defined herein. do.

Terms such as “include” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but do not include one or more other features, numbers, or steps. , it should be understood that it does not exclude in advance the possibility of the existence or addition of operations, components, parts, or combinations thereof.

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

section steel

The section steel according to an embodiment of the present invention contains 0.04 to 0.14 wt% of carbon (C), 0.10 to 0.55 wt% of silicon (Si), 0.90 to 1.65 wt% of manganese (Mn), 0.020 wt% or less of phosphorus (P), and sulfur. (S) 0.007% by weight or less, aluminum (Al) 0.015 to 0.055% by weight, vanadium (V) 0.010 to 0.080% by weight, titanium (Ti) 0.005 to 0.025% by weight, niobium (Nb) 0.010 to 0.050% by weight, remaining iron (Fe) and other inevitable impurities, and the yield strength (YS) satisfies 420 MPa or more. Here, the yield strength (YS) may mean the yield strength at room temperature.

More preferably, the silicon (Si) is 0.1 to 0.2% by weight, the manganese (Mn) is 1.57 to 1.65% by weight, the aluminum (Al) is 0.015 to 0.021% by weight, and the vanadium (V) is 0.040 to 0.045% by weight. %, the titanium (Ti) may be 0.005 to 0.008 wt%, and the niobium (Nb) may be 0.040 to 0.045 wt%.

The section steel having the above-described alloy composition can satisfy low-temperature impact toughness at -40°C of 50J or more, yield ratio (YR) of 0.90 or less, and elongation (EL) of 19% or more.

Preferably, the yield strength (YS) at room temperature may be 435 MPa or more, the yield ratio (YR) may be 0.85 or less, and the elongation may be 21% or more. More preferably, the yield strength (YS) at room temperature may be 445 MPa or more, - Low-temperature impact toughness at 40°C can satisfy 160J or more, yield ratio (YR) 0.81 or less, and elongation (EL) 29.9% or more.

In addition, the section steel has the shape of an H-section steel including a web and a flange, and the yield strength (YS) deviation of the upper and lower parts of the flange with respect to the web may be 15 MPa or less. Preferably, the yield strength (YS) deviation between the upper and lower parts of the flange may be 12 MPa, more preferably 8 MPa or less.

In addition, the section steel having the above-described alloy composition includes ferrite and pearlite in the room temperature microstructure at the center, and the F.G.S. (Ferrite grain size) may be 10 ㎛ or less. More specifically, F.G.S may be 9.5 μm or less.

As a result, it is possible to implement a high-performance section steel and a section steel manufacturing method that achieves homogenization of the physical properties of the section steel while securing low-temperature impact toughness according to an embodiment of the present invention.

In particular, precipitation strengthening and grain refinement can be achieved through the addition of vanadium (V) and niobium (Nb) in the above-mentioned composition range, and sufficient cooling effect can be obtained. In addition, through V-Nb composite design, high strength, stability, and mass production can be secured compared to conventional 355 MPa yield strength section steel.

Additionally, austenite grain growth can be delayed and welding performance can be improved by adding titanium (Ti) in the above-mentioned composition range.

Hereinafter, the role and content of each alloy element included in the section steel according to an embodiment of the present invention will be described in detail.

Carbon (C)

Carbon is the most effective and important element in increasing the strength of steel. It reacts with Nb, Ti, etc. to promote the creation of fine carbides, effectively contributing to improving strength through precipitation strengthening. Therefore, the section steel according to an embodiment of the present invention may contain 0.04% by weight to 0.14% by weight of carbon.

In other words, if the carbon content is less than 0.04% by weight of the total weight, it may be difficult to secure sufficient strength. Conversely, if the carbon content exceeds 0.14% by weight of the total weight, coarse carbides are generated, which may deteriorate impact characteristics and cause problems with deterioration of weldability.

Silicon (Si)

Silicon (Si) is added along with aluminum as a deoxidizer to remove oxygen in steel during the steelmaking process. Additionally, silicon can also have a solid solution strengthening effect.

Silicon may be added in an amount of 0.10 to 0.55% by weight of the total weight of the section steel according to an embodiment of the present invention. If the silicone content is less than 0.10% by weight of the total weight, the effect of adding silicone cannot be properly achieved. Conversely, if the silicon content exceeds 0.55% by weight of the total weight, adding a large amount may deteriorate the weldability of the steel and cause problems with surface quality by generating red scale during reheating and hot rolling.

Manganese (Mn)

As a solid solution strengthening element, manganese not only contributes to securing strength but can also improve the hardenability of steel. In addition, it impairs the acid resistance and oxidation resistance of steel, but improves yield strength by making pearlite finer and strengthening ferrite in solid solution. Therefore, the section steel according to an embodiment of the present invention may contain 0.90 wt% to 1.65 wt% of manganese, and preferably 1.57 wt% to 1.65 wt%.

If the manganese content is less than 0.90% by weight of the total weight, the solid solution strengthening effect cannot be sufficiently exerted, and if it exceeds 1.65% by weight, it may combine with sulfur to create MnS inclusions or cause central segregation in the ingot. As a result, the ductility of the section steel may decrease and corrosion resistance may decrease.

Phosphorus (P)

Phosphorus (P) increases strength through solid solution strengthening and can perform the function of suppressing the formation of carbides. The phosphorus may be added in an amount of 0.020% by weight or less of the total weight of the section steel according to an embodiment of the present invention. If the phosphorus content exceeds 0.020% by weight, inclusions such as tramp elements may be created, which may reduce the ductility of the steel, and there is a problem of low-temperature impact value being lowered due to precipitation behavior.

Hwang (S)

Sulfur (S) can improve processability by forming fine MnS precipitates. The sulfur may be added in an amount of 0.007% by weight or less of the total weight of the section steel according to an embodiment of the present invention. If the sulfur content exceeds 0.007% by weight, inclusions such as tramp elements are generated, which may impair the ductility, toughness and weldability of the steel, and lower the low-temperature impact value.

Aluminum (Al)

Aluminum (Al) is added in the steelmaking process as a deoxidizer to remove oxygen in steel. In addition, AlN can precipitate in steel and contribute to grain refinement. The aluminum may be added at an amount of 0.015 to 0.055% by weight of the weight of the section steel according to an embodiment of the present invention, and preferably at an amount of 0.015 to 0.021% by weight. If the aluminum content is less than 0.015% by weight, the deoxidation effect is insufficient, and if it exceeds 0.055% by weight, it makes playing difficult, reducing productivity, and forms alumina (Al ₂ O ₃ ), a non-metallic inclusion, which reduces ductility and toughness. There may be a problem.

Vanadium (V)

Vanadium (V) has a large carbide-forming ability, so it creates fine-grained carbides, which has the effect of refining the structure of steel and increasing strength by forming precipitates during rolling. In particular, the amount of precipitation can be controlled according to the amount of nitrogen added. Additionally, vanadium can contribute to improving strength by acting as a pinning agent on grain boundaries.

The vanadium may be added at an amount of 0.010 to 0.080% by weight of the weight of the section steel according to an embodiment of the present invention, and preferably at an amount of 0.040 to 0.045% by weight. If the vanadium content is less than 0.010% by weight, it is difficult to sufficiently secure the above effect. On the other hand, if the vanadium content exceeds 0.080% by weight, there may be a problem in that low-temperature impact toughness deteriorates.

Titanium (Ti)

Titanium (Ti) can produce Ti(C, N) precipitates with high high temperature stability. As a result, the growth of austenite grains is hindered during welding, thereby refining the structure of the weld zone, thereby improving the toughness and strength of the steel. The titanium may be added at an content ratio of 0.005 to 0.025% by weight of the weight of the section steel according to an embodiment of the present invention, and preferably at an content ratio of 0.005 to 0.008% by weight. If the titanium content is less than 0.005% by weight, it is difficult to sufficiently secure the above effect. On the other hand, if the titanium content exceeds 0.025% by weight, the low-temperature impact toughness of the steel may be reduced by generating coarse precipitates.

Niobium (Nb)

Niobium is an element that, when dissolved in an austenite structure, suppresses grain growth and creates a fine grain size. In particular, recrystallization can be delayed by allowing the steel to quickly reach below the non-recrystallization temperature (Tnr). In addition, it is effective in improving strength through precipitation strengthening by reacting with carbon and promoting the creation of fine carbides. However, if added excessively, it can reduce the impact properties of the steel.

Therefore, the section steel according to an embodiment of the present invention may contain 0.01 to 0.05% by weight of niobium, and preferably 0.040 to 0.045% by weight. In other words, if niobium is added in less than 0.01% by weight of the total weight, the effect of adding niobium cannot be properly exhibited, and if it is added in a large amount exceeding 0.05% by weight, the shock absorption energy of the steel can be reduced. On the other hand, when the niobium content is 0.040 to 0.045% by weight, the effect of adding niobium described above can be maximized while the reduction in the shock absorption energy of the steel can be minimized.

Nitrogen (N)

Even in extremely small amounts, it has a significant impact on the mechanical properties of steel and can increase tensile strength and yield strength while decreasing elongation. However, if nitrogen is added excessively, the toughness of the weld zone may decrease and the impact value may decrease. The section steel according to an embodiment of the present invention may contain 110 to 120 ppm of nitrogen.

Meanwhile, the section steel according to an embodiment of the present invention contains 0.04 to 0.14 wt% of carbon (C), 0.10 to 0.55 wt% of silicon (Si), 0.90 to 1.65 wt% of manganese (Mn), and 0.020 wt% or less of phosphorus (P). , sulfur (S) 0.007% by weight or less, aluminum (Al) 0.015 to 0.055% by weight, vanadium (V) 0.010 to 0.080% by weight, titanium (Ti) 0.005 to 0.025% by weight, niobium (Nb) 0.010 to 0.050% by weight, It contains the remaining iron (Fe) and other inevitable impurities, and is reheated to 1150 ~ 1300 ℃ and then rolled. The rolling start temperature is 900 ~ 1100 ℃, the middle rolling temperature is 850 ~ 1000 ℃, and the rolling end temperature is 800 ~ 900 ℃. Manufactured using a controlled method.

In addition, in order to control the intermediate rolling temperature, coolant is sprayed from the S/C (Selective Cooling) device shown in FIG. 2, with a waiting time of 0 to 120 seconds, a water quantity of 50 to 300 m ³ /hr, and a transfer speed of 0 to 120 seconds. It can be manufactured by controlling the speed from 2.0 to 4.0 m/s. The S/C device will be described in detail in the section steel manufacturing method below.

The section steel containing the above-described alloy composition and manufactured by the above-described method can satisfy low-temperature impact toughness at -40°C of 50J or more, yield ratio (YR) of 0.90 or less, and elongation (EL) of 19% or more. Preferably, the yield strength (YS) at room temperature may be 435 MPa or more, the yield ratio (YR) may be 0.85 or less, and the elongation may be 21% or more. More preferably, the yield strength (YS) at room temperature may be 445 MPa or more, - Low-temperature impact toughness at 40°C can satisfy 160J or more, yield ratio (YR) 0.81 or less, and elongation (EL) 29.9% or more.

In addition, the section steel has the shape of an H-section steel including a web and a flange, and the yield strength (YS) deviation of the upper and lower parts of the flange with respect to the web may be 15 MPa or less. Preferably, the yield strength (YS) deviation between the upper and lower parts of the flange may be 12 MPa, more preferably 8 MPa or less.

In addition, the section steel having the above-described alloy composition and manufactured by the above-described method may have a room temperature microstructure at the center containing ferrite and pearlite (F+P), and the F.G.S. (Ferrite grain size) may be 10 ㎛ or less. More specifically, F.G.S may be 9.5 μm or less.

As a result, the section steel according to an embodiment of the present invention can implement a high-performance section steel and section steel manufacturing method that secures low-temperature impact toughness, minimizes temperature deviation, and achieves homogenization of physical properties.

In particular, precipitation strengthening and grain refinement can be achieved through the addition of vanadium (V) and niobium (Nb) in the above-mentioned composition range and control of the temperature in the middle of rolling through a S/C (Selective Cooling) device, and an accelerated cooling effect can be obtained. there is. In addition, through V-Nb composite design, high strength, stability, and mass production can be secured compared to conventional 355 MPa yield strength section steel.

Additionally, austenite grain growth can be delayed and welding performance can be improved by adding titanium (Ti) in the above-mentioned composition range.

Section steel manufacturing method

The method of manufacturing section steel according to an embodiment of the present invention includes (a) a reheating step and (b) a rolling step, as shown in FIG. 1. In Aha, the method of manufacturing section steel will be described in detail with reference to FIGS. 1 and 2.

First, the steel contains 0.04 to 0.14 wt% of carbon (C), 0.10 to 0.55 wt% of silicon (Si), 0.90 to 1.65 wt% of manganese (Mn), 0.020 wt% or less of phosphorus (P), and 0.007 wt% of sulfur (S). Hereinafter, aluminum (Al) 0.015 ~ 0.055% by weight, vanadium (V) 0.010 ~ 0.080% by weight, titanium (Ti) 0.005 ~ 0.025% by weight, niobium (Nb) 0.010 ~ 0.050% by weight, the remaining iron (Fe) and other inevitable A step of containing impurities and reheating the steel to 1150 to 1300° C. is performed. Next, the steel material is rolled, with the starting temperature of rolling being 900 to 1100°C, the middle temperature of rolling being 850 to 1000°C, and the rolling ending temperature being 800 to 900°C.

As a result, the section steel 10 according to an embodiment of the present invention can implement a high-performance section steel and section steel manufacturing method that secures low-temperature impact toughness, minimizes temperature deviation, and achieves homogenization of physical properties by securing the target microstructure and grain size. You can.

In particular, precipitation strengthening and grain refinement can be achieved and an appropriate cooling effect can be obtained through the addition of vanadium (V) and niobium (Nb) in the above-mentioned composition range and control of the temperature during rolling. In addition, through V-Nb composite design, high strength, stability, and mass production can be secured compared to conventional 355 MPa yield strength section steel. Additionally, austenite grain growth can be delayed and welding performance can be improved by adding titanium (Ti) in the above-mentioned composition range.

Hereinafter, a method for manufacturing section steel according to an embodiment of the present invention will be described in detail.

First, in the reheating step, the steel material of the above composition is reheated at 1150°C or higher. If the reheating temperature is lower than 1150°C, the solid solution of various carbides may not be sufficient, and the segregated components may not be distributed sufficiently evenly during the continuous casting process. Additionally, the reheating temperature may not exceed 1300°C. If the reheating temperature exceeds 1300°C, coarse austenite grains may be formed, making it difficult to secure strength, and increased heating costs and time may lead to increased manufacturing costs and reduced productivity.

Meanwhile, the steel may be manufactured through a continuous casting process after obtaining molten steel of a desired composition through a steelmaking process. The steel may be, for example, a beam blank, but is not necessarily limited thereto.

Meanwhile, the composition range of the steel is more preferably 0.1 to 0.2% by weight of silicon (Si), 1.57 to 1.65% by weight of manganese (Mn), 0.015 to 0.021% by weight of aluminum (Al), and 0.040 to 0.045% by weight of vanadium (V). %, titanium (Ti) may be 0.005 to 0.008 wt%, and niobium (Nb) may be 0.040 to 0.045 wt%. As a result, the deviation in room temperature yield strength and low temperature impact toughness of the upper and lower ends of the flange can be further reduced, and the microstructure grain size can be secured to 10 ㎛ or less.

(b) In the rolling step, coolant is sprayed from the S/C (Selective Cooling) device 100 shown in FIG. 2 to control the above-mentioned rolling intermediate temperature, with a waiting time of 0 to 120 seconds and a quantity of 50 to 50 seconds. It can be performed at 300 m ³ /hr and the transfer speed is 2.0 ~ 4.0 m/s.

The TMCP process is mainly used to ensure high-strength impact toughness, but one embodiment of the present invention is used in medium-sized or small-sized manufacturing processes without accelerated cooling facilities such as QST equipment in the TMCP process. A S/C (Selective Cooling) device 100 can be used along with a CM (Continuous Mill).

The QST equipment is characterized by not only a side cooler, but also an upper cooling box and a lower cooling nozzle. Since it uses high-pressure coolant, the cooling speed is fast and it is used for large-sized section steel. On the other hand, in the case of the S/C device 100, as shown in FIG. 2, it consists only of the side cooler 110 and the lower cooling nozzle 120, so it has the advantage of easier cooling rate and temperature control.

In the case of the CM device, since H-beam products are continuously attached to the rolling mill, coolant accumulates in the upper part of the beam and is exposed to the air, resulting in rolling temperature deviation and the upper (12a) and lower portions of the flange (12) of the beam (10). This causes deviation in the physical properties of (12b). In order to improve this, the lower part is intensively cooled through the S/C device 100 and the operating conditions of the S/C device 100, and the cooling temperature and speed are precisely controlled to homogenize temperature deviation and physical properties, and improve some physical properties. can be obtained.

In this way, the steel material that has undergone the rolling step according to the above process conditions has a room temperature microstructure in the center containing ferrite and pearlite, but the F.G.S. (Ferrite grain size) may be 10 ㎛ or less, and as shown in FIG. 2, the web 11 In the H-beam 10 including the flange 12, the F.G.S grain size deviation of the upper part 12a and the lower part 12b of the flange 12 based on the web 11 may be reduced. In this way, in the case of the section steel manufacturing method according to an embodiment of the present invention, the target microstructure and grain size can be secured, and a high-strength section steel can be manufactured.

In addition, the steel that performed the rolling step (b) according to the above process conditions has a yield strength (YS) of 420 MPa or more, a low-temperature impact toughness at -40°C of 50 J or more, a yield ratio (YR) of 0.90 or less, and an elongation ( EL) may be 19% or more. In this way, by using the section steel manufacturing method according to an embodiment of the present invention, high-performance section steel with impact toughness secured at low temperatures can be manufactured.

In addition, the steel material that has performed the rolling step (b) according to the above process conditions is manufactured as H-beam steel 10 including a web 11 and a flange 12, and the flange ( The yield strength (YS) deviation between the upper part 12a and the lower part 12b of 12) may be 15 MPa or less. In this way, in the case of the section steel manufacturing method according to an embodiment of the present invention, quality and mass production can be improved by securing uniform quality and stable physical properties compared to the prior art.

Comparative and experimental examples

Below, preferred comparative examples and experimental examples are presented to aid understanding of the present invention. However, the following experimental examples are only intended to aid understanding of the present invention, and the present invention is not limited by the following experimental examples.

Table 1 below shows the main alloy element composition (unit: weight %) of this experimental example and comparative example, and Table 2 shows the process conditions for manufacturing the specimens of this experimental example and comparative example (temperature unit: ℃, time unit: sec) , S/C quantity unit: m ³ /hr, speed unit: m/s), and Table 3 shows the results of measuring the mechanical properties of the specimen implemented according to the process conditions in Table 2. A beam blank with the composition shown in Table 1 was manufactured using an electric furnace and then hot rolled to produce H-beam steel with a flange thickness of 15 mm.

Process conditions are reheating temperature 1150~1300℃, waiting time 0~120 seconds, rolling start temperature 900~1100℃, rolling middle temperature 850~1000℃, rolling end temperature 800~900℃, S/C quantity 50~300 m ³ /hr, the transfer speed was in the range of 2.0 to 4.0 m/s, and Table 2 lists the process conditions under which the actual experimental data was obtained. Through this, the physical properties to be targeted in the experimental example are tensile strength (TS) of 500 to 660 MPa, room temperature yield strength (YS) of 420 MPa or more, elongation (EL) of 19% or more, and yield ratio (YR) of 90% or less -40 The goal was to observe low-temperature impact toughness at ℃ of 50J or more based on the flange part, and in the case of microstructure, F+P (composite structure of ferrite and pearlite) with a grain size of 10 ㎛ or less in the deep part. In addition, the goal was to reduce the deviation of room temperature yield strength (YS) to 15 MPa, preferably 12 MPa or less, at the top and bottom of the flange.

Comparative Example 1 and Experimental Example 1

Referring to Tables 1 to 3, Comparative Example 1 has a difference in composition compared to Experimental Example 1, and there is a difference in whether the rolling temperature is controlled or cooled using the S/C device 100 shown in FIG. 2. Figure 3(a) is a photograph of the microstructure according to Comparative Example 1, and Figure 3(c) is a photograph of the microstructure according to Experimental Example 1.

First, referring to Table 1, in the case of Comparative Example 1, the composition range of vanadium and niobium was set to 0.035 to 0.039% by weight, and the actual experimental data included 0.036% by weight of vanadium and 0.035% by weight of niobium; The temperature was controlled without using a separate device.

Meanwhile, in the case of Experimental Example 1, the composition range of vanadium and niobium was aimed to be 0.040 to 0.045% by weight, and the actual experimental data included 0.040% by weight of vanadium and 0.044% by weight of niobium, and the S/C device was used. The rolling intermediate temperature was controlled using the process conditions shown in Table 2.

Referring to Table 3 and Figure 3, it can be seen that Experimental Example 1 has a yield strength (YS) deviation of 8MPa and an impact toughness deviation of 21J between the top and bottom of the flange, which are significantly smaller than Comparative Example 1, and the grain size of the microstructure As expected, the deviation is small and both the top and bottom of the flange are within 10 ㎛, so it can be seen that the physical property deviation has been improved.

Comparative Example 2 and Experimental Example 1

Referring to Tables 1 to 3, Comparative Example 1 has a difference in composition compared to Experimental Example 1, but the temperature control or cooling in the middle of rolling using the S/C device 100 shown in FIG. 2 is the same. Figure 3(b) is a microstructure photograph according to Comparative Example 2, and Figure 3(c) is a microstructure photograph according to Experimental Example 1.

First, referring to Table 1, in the case of Comparative Example 2, the composition range of vanadium and niobium was set to 0.035 to 0.039% by weight, and the actual experimental data included 0.037% by weight of vanadium and 0.036% by weight of niobium; The rolling intermediate temperature was controlled using the S/C device under the process conditions shown in Table 2.

Meanwhile, in the case of Experimental Example 1, the composition range of vanadium and niobium was aimed to be 0.040 to 0.045% by weight, and the actual experimental data included 0.040% by weight of vanadium and 0.044% by weight of niobium, and the S/C device was used. The rolling intermediate temperature was controlled using the process conditions shown in Table 2.

Referring to Table 3, the room temperature yield strength (YS) of Comparative Example 2 is 432 MPa (top of flange) and 419 MPa (bottom of flange), and the room temperature yield strength (YS) of Experimental Example 1 is 447 MPa (top of flange) and 455 MPa (bottom of flange). It can be seen that it is smaller than (bottom), and in particular, the yield strength of the bottom of the flange of Comparative Example 2 is less than 420 MPa. In addition, it can be seen that the yield strength (YS) deviation between the top and bottom of the flange in Comparative Example 2 is 13MPa and the impact toughness deviation is 62J, which is significantly larger than the yield strength (YS) deviation of 8MPa and impact toughness deviation of 21J in Experimental Example 1. there is. Therefore, in the case of Experimental Example 1, it can be confirmed that not only are the physical properties of yield strength (YS) and impact toughness better than Comparative Example 2, but also the deviation is small.

Meanwhile, in the case of the grain size of the microstructure, Comparative Example 2 not only exceeded 10 ㎛ at 10.0 ㎛ and 10.6 ㎛ at the top and bottom of the flange, respectively, but also the deviation was 0.6 ㎛, which was larger than that of Experimental Example 1.

Therefore, in the case of the section steel and section steel manufacturing method according to an embodiment of the present invention, as confirmed in the data of Experimental Example 1, it has excellent quality by securing the target high strength, low-temperature impact toughness, microstructure, and grain size, and the upper part of the flange It is possible to realize high-performance, deep-sea special section steel with uniform quality and little variation in physical properties of the upper and lower parts.

As described above, preferred embodiments, experimental examples, and comparative examples according to the present invention have been examined, and the fact that the present invention can be embodied in other specific forms in addition to the above-described embodiments without departing from the spirit or scope of the relevant technology It is self-evident to those with ordinary knowledge. Therefore, the above-described embodiments are to be regarded as illustrative and not restrictive, and thus the present invention is not limited to the above description but may be modified within the scope of the appended claims and their equivalents.

[Explanation of symbols]

S10: Reheating step

S20: rolling step

10: section steel

11: web

12: Flange

12a: Top of flange

12b: Flange lower part

100: S/C device

110: Side cooler

120: Lower cooling nozzle

Claims (15)

1. (a) Carbon (C) 0.04 to 0.14% by weight, silicon (Si) 0.10 to 0.55% by weight, manganese (Mn) 0.90 to 1.65% by weight, phosphorus (P) 0.020% by weight or less, sulfur (S) 0.007% by weight or less , Aluminum (Al) 0.015 ~ 0.055% by weight, Vanadium (V) 0.010 ~ 0.080% by weight, Titanium (Ti) 0.005 ~ 0.025% by weight, Niobium (Nb) 0.010 ~ 0.050% by weight, the remaining iron (Fe) and other inevitable impurities. Reheating the steel containing to 1150 ~ 1300 ℃; and

   (b) Rolling the steel material at a starting temperature of 900 to 1100°C, a middle rolling temperature of 850 to 1000°C, and a rolling end temperature of 800 to 900°C.
2. According to paragraph 1,

   In step (b) above,

   To control the temperature in the middle of rolling, coolant is sprayed from an S/C (Selective Cooling) device, with a waiting time of 0 to 120 seconds, a water quantity of 50 to 300 m ³ /hr, and a transfer speed of 2.0 to 4.0 m/s. A method of manufacturing section steel that is carried out under certain conditions.
3. According to paragraph 1,

   The steel material that performed step (b) above has a room temperature microstructure in the center containing ferrite and pearlite,

   F.G.S (Ferrite grain size) is a method of manufacturing section steel of 10 ㎛ or less.
4. According to paragraph 1,

   The steel that performed step (b) above is,

   A method of manufacturing section steel with a yield strength (YS) of 420 MPa or more, a low-temperature impact toughness at -40°C of 50 J or more, a yield ratio (YR) of 0.90 or less, and an elongation (EL) of 19% or more.
5. According to paragraph 1,

   The steel that performed step (b) above is,

   A method of manufacturing a section steel made of H-beam including a web and a flange, wherein the yield strength (YS) deviation of the upper and lower parts of the flange based on the web is 15 MPa or less.
6. According to paragraph 1,

   The steel,

   Silicon (Si) 0.1 to 0.2% by weight, manganese (Mn) 1.57 to 1.65% by weight, aluminum (Al) 0.015 to 0.021% by weight, vanadium (V) 0.040 to 0.045% by weight, titanium (Ti) 0.005 to 0.008% by weight, Method for manufacturing section steel containing 0.040 to 0.045% by weight of niobium (Nb).
7. Carbon (C) 0.04 to 0.14% by weight, silicon (Si) 0.10 to 0.55% by weight, manganese (Mn) 0.90 to 1.65% by weight, phosphorus (P) 0.020% by weight or less, sulfur (S) 0.007% by weight or less, aluminum ( Al) 0.015 to 0.055% by weight, vanadium (V) 0.010 to 0.080% by weight, titanium (Ti) 0.005 to 0.025% by weight, niobium (Nb) 0.010 to 0.050% by weight, and the remaining iron (Fe) and other inevitable impurities. ,

   A section steel that satisfies the yield strength (YS) of 420 MPa or more.
8. In clause 7,

   A section steel that satisfies the low-temperature impact toughness of 50J or more at -40℃.
9. In clause 7,

   Section steel that satisfies the yield ratio (YR) of 0.90 or less.
10. In clause 7,

    Section steel with an elongation (EL) of 19% or more.
11. In clause 7,

    A section steel having the shape of an H-beam including a web and a flange, wherein the yield strength (YS) deviation of the upper and lower parts of the flange with respect to the web is 15 MPa or less.
12. In clause 7,

    A section steel whose room temperature microstructure in the center contains ferrite and pearlite, but whose F.G.S (Ferrite grain size) is 10 ㎛ or less.
13. In clause 7,

    Silicon (Si) 0.1 to 0.2% by weight, manganese (Mn) 1.57 to 1.65% by weight, aluminum (Al) 0.015 to 0.021% by weight, vanadium (V) 0.040 to 0.045% by weight, titanium (Ti) 0.005 to 0.008% by weight. , section steel containing 0.040 to 0.045% by weight of niobium (Nb).
14. Carbon (C) 0.04 to 0.14% by weight, silicon (Si) 0.10 to 0.55% by weight, manganese (Mn) 0.90 to 1.65% by weight, phosphorus (P) 0.020% by weight or less, sulfur (S) 0.007% by weight or less, aluminum ( Al) 0.015 to 0.055% by weight, vanadium (V) 0.010 to 0.080% by weight, titanium (Ti) 0.005 to 0.025% by weight, niobium (Nb) 0.010 to 0.050% by weight, and the remaining iron (Fe) and other inevitable impurities. ,

    Section steel manufactured by reheating to 1150 ~ 1300 ℃ and then rolling, with the rolling start temperature controlled at 900 ~ 1100 ℃, the rolling middle temperature at 850 ~ 1000 ℃, and the rolling end temperature at 800 ~ 900 ℃.
15. According to clause 14,

    To control the temperature in the middle of rolling, coolant is sprayed from an S/C (Selective Cooling) device, with a waiting time of 0 to 120 seconds, a water quantity of 50 to 300 m ³ /hr, and a transfer speed of 2.0 to 4.0 m/s. Section steel manufactured using a controlled method.

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