KR102089167B1 - Shape steel and method of manufacturing the same - Google Patents

Abstract

The method of manufacturing a section steel according to an embodiment of the present invention is (a) carbon (C): 0.06 ~ 0.20% by weight, manganese (Mn): 0.60 ~ 2.0% by weight, silicon (Si): 0.05 ~ 0.25% by weight, chromium (Cr): 0.5 to 1.30% by weight, copper (Cu): more than 0 to 0.4% by weight or less, molybdenum (Mo): more than 0 to 0.50% by weight or less, aluminum (Al): 0.015 to 0.070% by weight, nickel (Ni): More than 0 0.10% by weight or less, phosphorus (P): more than 0 0.02% by weight or less, sulfur (S): more than 0 0.008% by weight or less, nitrogen (N): more than 0 0.02% by weight or less, tin (Sn): more than 0 Reheating the steel material consisting of less than 0.1% by weight and the remaining iron (Fe) and other inevitable impurities to 1150 to 1250 ℃; (b) hot rolling the steel material to a rolling end temperature of 910 to 960 ° C; And (c) quenching & self-tempering (QST) the hot rolled steel; It includes.

Description

SHAPE STEEL AND METHOD OF MANUFACTURING THE SAME

The present invention relates to a shape steel and a method for manufacturing the same, and more particularly, to a high-strength and high-performance shape steel having a fire / seismic performance and a method for manufacturing the same.

The section steel generally refers to a steel material having a multi-faceted cross-sectional shape. In recent years, the section steel is applied as structural steel such as pillars of large buildings, and is also applied as a temporary construction material for civil works such as subways and bridges, and foundation piles. The section steel can be produced by hot rolling a cast piece such as a bloom, billet, or beam blank produced by continuous casting.

Related prior art is Republic of Korea Patent Publication No. 10-2014-0056765 (2014.05.12 published, the name of the invention: section steel and its manufacturing method).

The problem to be solved by the present invention is to provide a high strength and high performance section steel having a fireproof / seismic performance and a method for manufacturing the same.

The shape steel according to an embodiment of the present invention for achieving the above object is carbon (C): 0.06 ~ 0.20% by weight, manganese (Mn): 0.60 ~ 2.0% by weight, silicon (Si) 0.05 ~ 0.25% by weight, chromium ( Cr): 0.5 to 1.30% by weight, copper (Cu): more than 0 to 0.4% by weight, molybdenum (Mo): more than 0 to 0.50% by weight, aluminum (Al): 0.015 to 0.070% by weight, nickel (Ni): 0 More than 0.10% by weight, phosphorus (P): more than 0 and less than 0.02% by weight, sulfur (S): more than 0 and less than 0.008% by weight, nitrogen (N): more than 0 and less than 0.02% by weight, tin (Sn): more than 0 0.1 Consists of less than weight percent and the rest of iron (Fe) and other inevitable impurities, the normal temperature microstructure of the surface includes tempered martensite and bainite, and the normal temperature microstructure of the center includes acicular ferrite, bainite and pearlite. do.

The section steel may further include at least one or more selected from calcium (Ca) and boron (B), but calcium (Ca): greater than 0 and 0.005% by weight or less, and boron (B): greater than 0 and 0.003% by weight or less.

In the section steel, the average particle size of the ferrite may be 10 to 20 μm, and the bainite in the center may have a fraction of 15 to 25%.

Method for producing a section steel according to an embodiment of the present invention for achieving the above object is (a) carbon (C): 0.06 ~ 0.20% by weight, manganese (Mn): 0.60 ~ 2.0% by weight, silicon (Si): 0.05 ~ 0.25 wt%, Chromium (Cr): 0.5 ~ 1.30 wt%, Copper (Cu): over 0 0.4 wt%, Molybdenum (Mo): Over 0 0.50 wt%, Aluminum (Al): 0.015 ~ 0.070 wt% , Nickel (Ni): more than 0, 0.10% by weight or less, phosphorus (P): more than 0, 0.02% by weight or less, sulfur (S): more than 0, 0.008% by weight, nitrogen (N): more than 0, 0.02% by weight or less, tin (Sn): reheating the steel material consisting of more than 0 and 0.1% by weight or less and the remaining iron (Fe) and other unavoidable impurities to 1150 to 1250 ° C; (b) hot rolling the steel material to a rolling end temperature of 910 to 960 ° C; And (c) quenching & self-tempering (QST) the hot rolled steel; It includes.

In the method of manufacturing the section steel, the steel material further comprises at least one or more selected from calcium (Ca) and boron (B), calcium (Ca): more than 0 0.005% by weight or less, boron (B): more than 0 0.003 It may be less than or equal to weight percent.

In the method of manufacturing the section steel, the QST cooling is performed while controlling the surface recuperation temperature from 630 to 810 ° C.

According to an embodiment of the present invention, it is possible to implement a high strength and high performance section steel having a fireproof / seismic performance and a method for manufacturing the same. Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart illustrating a method of manufacturing a section steel according to an embodiment of the present invention.
Figure 2 is a photograph of the central microstructure of the section steel according to a comparative example of the present invention.
3 and 4 are photographs of the central microstructure of the section steel according to the embodiments of the present invention.

Hereinafter, the section steel according to an embodiment of the present invention and a method of manufacturing the same will be described in detail. Terms to be described later are terms appropriately selected in consideration of functions in the present invention, and definitions of these terms should be made based on contents throughout the present specification.

In recent years, in the trend of high-rise building structures, it is essential to design structures safely against disasters such as fires and earthquakes, and development of high-functional construction materials such as fire resistance and earthquake resistance is urgently needed. Meanwhile, the demand for safety design for securing disaster safety of buildings in the event of a fire is also intensifying. In Europe, the United States, Australia, the United Kingdom, etc., the level of safety design requirements is increasing through the maintenance of laws and regulations for fire-resistant design of skyscrapers. In Japan, which has a similar construction law regulation system to that of Korea, the Building Standards Act is amended to introduce performance regulations for fire-resistant structures and to apply fire-resistant performance regulations. In Korea, refractory thick plates have been developed, but they have not been commercialized, and the development and performance evaluation of refractory steels for shaped structural steels (H-beams, etc.) has not been completed. Hereinafter, a high-strength high-performance section steel having stable fire-resistance / seismic performance and a method of manufacturing the same are provided.

Section steel

The steel according to an embodiment of the present invention is carbon (C): 0.06 ~ 0.20% by weight, manganese (Mn): 0.60 ~ 2.0% by weight, silicon (Si) 0.05 ~ 0.25% by weight, chromium (Cr): 0.5 ~ 1.30 Weight percent, copper (Cu): more than 0 and 0.4 weight percent or less, molybdenum (Mo): more than 0 0.50 weight percent, aluminum (Al): 0.015 to 0.070 weight percent, nickel (Ni): more than 0 and 0.10 weight percent or less, Phosphorus (P): more than 0 and 0.02% by weight or less, sulfur (S): more than 0 and 0.008% or less, nitrogen (N): more than 0 and 0.02% or less, tin (Sn): more than 0 and 0.1% or less by weight (Fe) and other inevitable impurities.

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

Carbon (C)

Carbon (C) is added to secure strength and is the element that has the greatest influence on weldability. The carbon (C) may be added in a content ratio of 0.06 to 0.20% by weight of the total weight of the section steel according to an embodiment of the present invention. If the carbon content is less than 0.06% by weight of the total weight, it may be difficult to secure sufficient strength. Conversely, when the carbon content exceeds 0.20% by weight of the total weight, the impact toughness of the base material may be deteriorated, and there may be a problem that deterioration of weldability during electric resistance welding (ERW).

Manganese (Mn)

Manganese (Mn) is effective in strengthening employment. In addition, manganese (Mn) can increase the hardenability of the steel. Manganese may be added in a content ratio of 0.60 to 2.0% by weight of the total weight of the section steel according to an embodiment of the present invention. When the content of manganese is less than 0.60% by weight, the effect of solid solution strengthening cannot be sufficiently exhibited. In addition, when the content of manganese exceeds 2.0% by weight, weldability decreases, MnS inclusions and center segregation occur, and ductility of the shaped steel may decrease and corrosion resistance may deteriorate.

Silicon (Si)

Silicon (Si) is added with aluminum as a deoxidizer to remove oxygen in the steel in the steelmaking process. In addition, silicon may also have a solid solution strengthening effect. The silicone may be added in a content ratio of 0.05 to 0.25% by weight of the total weight of the section steel according to an embodiment of the present invention. When the content of silicone is less than 0.05% by weight of the total weight, the effect of adding silicone cannot be properly exhibited. Conversely, the content of silicon exceeds 0.25% by weight of the total weight, which decreases the weldability of steel when added in large quantities, and may cause a problem in surface quality by generating a red scale during reheating and hot rolling.

Chrome (Cr)

Chromium (Cr) is a ferrite stabilizing element that, when added to C-Mn steel, delays the diffusion of carbon due to a solute interference effect, thereby affecting particle size refinement. The chromium may be added in a content ratio of 0.5 to 1.30% by weight of the total weight of the section steel according to an embodiment of the present invention. If the content of chromium is less than 0.5% by weight of the total weight, the effect of adding chromium cannot be properly exhibited. Conversely, when the content of chromium exceeds 1.30% by weight of the total weight, when added in large amounts, it may give a problem that the properties of steel are deteriorated from the viewpoint of toughness and curability.

Copper (Cu)

Copper (Cu) is an element exhibiting solid solution strengthening effect by being dissolved in ferrite. In addition, in the bainite transformation, supersaturated copper is not dissolved in the solid solution at room temperature, and the copper phase is precipitated on the electric potential introduced by the bainite transformation upon heating at a working temperature of 600 ° C. as a refractory steel. By increasing the strength of the base material. The copper may be added in a content ratio of more than 0 to 0.4% by weight or less of the total weight of the section steel according to an embodiment of the present invention. When the content of copper exceeds 0.4% by weight of the total weight, when it is added in large quantities, hot working is difficult, precipitation strengthening is saturated, toughness is lowered, and problems causing red brittleness occur.

Molybdenum (Mo)

Molybdenum (Mo) is an element effective for securing the base material strength and high temperature strength. The molybdenum may be added in a content ratio of greater than 0 to 0.50% by weight or less of the total weight of the section steel according to an embodiment of the present invention. When the content of molybdenum exceeds 0.50% by weight of the total weight, the quenching property is excessively increased when a large amount is added, resulting in a deterioration in the toughness of the base material and the welding heat-affected zone.

Aluminum (Al)

Aluminum (Al) is added to the steelmaking process as a deoxidizer to remove oxygen from the steel. In addition, it can be precipitated in the steel with AlN to contribute to grain refinement. The aluminum may be added in a content ratio of 0.015 to 0.070% by weight of the weight of the section steel according to an embodiment of the present invention. The content of aluminum tteurimyeo decrease productivity it is difficult to play when it is more than 0.015% by weight, lack a deoxidation effect, and 0.070% by weight is below, to form the non-metallic inclusions of alumina (Al ₂ O ₃₎ that ductility and toughness decrease There may be problems.

Nickel (Ni)

Nickel (Ni) is a tramp element of electric furnace scrap, which increases the strength of the material and ensures low-temperature impact values. The nickel may be added in a content ratio of more than 0 to 0.10% by weight or less of the total weight of the section steel according to an embodiment of the present invention. When the content of nickel exceeds 0.10% by weight of the total weight, the strength at room temperature is excessively high, resulting in a problem that weldability and toughness deteriorate.

Phosphorus (P)

Phosphorus (P) increases the strength of the strength by strengthening the solid solution, and can function to suppress the formation of carbides. The phosphorus may be added in a content ratio of more than 0 to 0.020% by weight or less of the total weight of the section steel according to an embodiment of the present invention. When the phosphorus content exceeds 0.020% by weight, there is a problem that the low-temperature impact value is lowered due to the precipitation behavior.

Sulfur (S)

Sulfur (S) can form a precipitate of fine MnS to improve processability. The sulfur may be added in a content ratio of more than 0 to 0.008% by weight or less of the total weight of the section steel according to an embodiment of the present invention. When the sulfur content exceeds 0.008% by weight, toughness and weldability may be impaired and low-temperature impact values may be reduced.

Nitrogen (N)

Nitrogen (N) may form nitride-based precipitates such as AlN to contribute to grain refinement and to secure high temperature strength. The nitrogen may be added in a content ratio of more than 0 to 0.02% by weight or less of the total weight of the section steel according to an embodiment of the present invention. When the nitrogen content exceeds 0.02% by weight, the toughness of the weld portion may decrease, and the impact value may decrease.

Tin (Sn)

Tin (Sn) is an element that has a solid solution strengthening effect and prevents a reduction in elongation. However, when tin is added in excess of 0.1% by weight in the total weight of the section steel according to an embodiment of the present invention, there is a problem that the ductility of the steel is rapidly reduced. Therefore, the content of tin in the total weight of the section steel according to an embodiment of the present invention was limited to 0.1% by weight or less of the total weight of the steel.

Meanwhile, the section steel according to an embodiment of the present invention may optionally further include at least one or more selected from calcium (Ca) and boron (B). In this case, calcium (Ca): more than 0 to 0.005% by weight or less and / or boron (B): more than 0 to 0.003% by weight or less in the total weight of the section steel.

Calcium (Ca)

Calcium (Ca) can be added to control the shape of the sulfide or oxide. Calcium in the section steel according to an embodiment of the present invention can be optionally added to more than 0 to less than 0.005% by weight. If, if the content of calcium exceeds 0.005% by weight of the total weight of the section steel according to an embodiment of the present invention, there is a problem in that the oxide coarsens and the toughness and ductility decrease.

Boron (B)

Boron (B) is a strong quenchable element that contributes to the improvement of the strength of the steel. Boron in the section steel according to an embodiment of the present invention may optionally be added to more than 0 to less than 0.003% by weight. If, if the content of boron exceeds 0.003% by weight of the total weight of the section steel according to an embodiment of the present invention, there is a problem that material deviation due to grain boundary segregation.

As described above, the section steel according to an embodiment of the present invention having an alloy element composition has a yield strength at room temperature (YS) of 355 MPa or more, a tensile strength (TS) of 490 MPa or more, a yield ratio (YR) of 0.80 or less, and an elongation rate (EL). It has 10% or more, and the yield strength at a high temperature of 600 ° C. may be 2/3 or more of the yield strength at room temperature.

In addition, in the section steel according to an embodiment of the present invention having the alloy element composition as described above, the normal temperature microstructure of the surface portion includes tempered martensite and bainite, and the normal temperature microstructure of the center portion is acicular ferrite, bainite And pearlite. The average particle size of the ferrite may be 10 to 20㎛, and the fraction of bainite in the center may be 15 to 25%.

Hereinafter, a method of manufacturing a section steel according to an embodiment of the present invention having the above-described alloy element composition will be described.

Method of manufacturing the section steel

1 is a flowchart schematically showing a method of manufacturing a section steel according to an embodiment of the present invention. Referring to FIG. 1, a method of manufacturing a section steel having excellent fire resistance according to an embodiment of the present invention includes a reheating step (S100), a hot rolling step (S200), and a QST (Quenching & Self-Tempering) step (S300). Includes.

First, in the reheating step (S100), the steel having a predetermined composition as described above is reheated. The steel material may be manufactured through a continuous casting process after obtaining molten steel having a desired composition through a steelmaking process. The steel material may be, for example, a billet or a beam blank.

The steel material is carbon (C): 0.06 ~ 0.20% by weight, manganese (Mn): 0.60 ~ 2.0% by weight, silicon (Si): 0.05 ~ 0.25% by weight, chromium (Cr): 0.5 ~ 1.30% by weight, copper (Cu ): More than 0 and less than 0.4% by weight, molybdenum (Mo): more than 0 and 0.50% by weight, aluminum (Al): 0.015 to 0.070% by weight, nickel (Ni): more than 0 and 0.10% by weight or less, phosphorus (P): 0 More than 0.02% by weight, sulfur (S): more than 0 and less than 0.008% by weight, nitrogen (N): more than 0 and less than 0.02% by weight, tin (Sn): more than 0 and less than 0.1% by weight and the rest of iron (Fe) and other inevitable It can be made of impurities.

Meanwhile, the steel material may further include at least one or more selected from calcium (Ca) and boron (B). In this case, the composition may be calcium (Ca): more than 0 and 0.005% by weight or less, boron (B): more than 0 and 0.003% or less by weight.

In one embodiment, the steel material may be reheated at a temperature of 1150 to 1250 ℃. When the steel is reheated at the above-mentioned temperature, components segregated during the continuous casting process may be re-used. When the reheating temperature is lower than 1150 ° C, the solid solution may not be sufficiently dissolved, and there may be a problem that segregated components are not evenly distributed during the continuous casting process. When the reheating temperature exceeds 1250 ° C, very coarse austenite grains may be formed, which may make it difficult to secure strength. In addition, when the temperature exceeds 1250 ° C, the heating cost increases and the process time is added, which may lead to an increase in manufacturing cost and a decrease in productivity.

In the hot rolling step (S200), the reheated steel is hot rolled. The hot rolling may be controlled such that the rolling end temperature is 910 to 960 ° C. When the rolling end temperature is less than 910 ° C., rolling progresses in the unrecrystallized region, whereby the rolling addition may be increased, and the yield ratio of the section steel as a result of rolling may be increased. In addition, when the rolling end temperature exceeds 960 ° C, it may be difficult to secure target strength and toughness.

In the QST (Quenching & Self-Tempering) step (S300), the hot-rolled section steel is cooled and self-tempered. For the cooling, a quenching method of spraying cooling water to the section steel is applied. In addition, the QST step, by controlling the feed rate of the section steel, or the amount of cooling water to be injected, can be performed in a controlled state of the recuperative temperature of the section steel to 630 ~ 810 ℃.

Summarizing the above-described steel material manufacturing process, it is manufactured through a reheating process, a hot deformation process, and a cooling process. In the reheating process, the semi-finished billets and beam blanks are reheated at 1150 to 1250 ° C. Next, after the hot rolling of the reheated material and the final finish rolling is deformed at 910 to 960 ° C, some surfaces are formed of martensite by an external cooling facility, and the center is a temperature at which needle-shaped ferrite and bainite can be formed. After rapid cooling to 250 ~ 300 ℃, characterized in that it comprises a surface recuperation step to 630 ~ 810 ℃. In order to satisfy the required characteristics, it is necessary to secure a bainite fraction of 15 to 25%.

In an embodiment of the present invention, chromium (Cr) and some alloy elements are added so that strength and toughness can be improved simultaneously without using niobium (Nb) or titanium (Ti), which are commonly used expensive precipitation hardening alloy elements. One steel design and process conditions apply. In addition, securing low-temperature toughness can be performed through the control of the recuperative temperature during the cooling.

Through the above-described manufacturing method, a section steel according to an embodiment of the present invention can be manufactured. The prepared section steel has a yield strength at room temperature (YS) of 355 MPa or higher, a tensile strength (TS) of 490 MPa or higher, a yield ratio (YR) of 0.80 or lower, an elongation (EL) of 10% or higher, and yield strength at a high temperature of 600 ° C. May be 2/3 or more of the yield strength at room temperature. In addition, in the section steel according to an embodiment of the present invention, the normal temperature microstructure of the surface portion includes tempered martensite and bainite, and the normal temperature microstructure of the center portion may include acicular ferrite, bainite and pearlite. The average particle size of the ferrite may be 10 to 20㎛, and the fraction of bainite in the center may be 15 to 25%.

Experimental example

Hereinafter, a preferred experimental example is presented to help understanding of the present invention. However, the following experimental examples are only to aid the understanding of the present invention, and the present invention is not limited by the following experimental examples.

1. Preparation of Specimen

The specimens of Comparative Examples 1 to 2 and Examples 1 to 2 having the main alloy element composition (unit: weight ratio%) of Table 1 were prepared by proceeding with the process conditions of Table 2, respectively.

division C Si Mn P S Cu Nb Cr Mo Ni Sn Al N Comparative Example 1 0.08 0.21 1.29 0.018 0.017 0.21 0.031 0.32 0.32 0.03 0.01 0.019 0.008 Comparative Example 2 0.06 0.15 1.30 0.019 0.009 0.22 0.020 0.20 0.70 0.05 0.01 0.020 0.008 Example 1 0.14 0.20 0.70 0.017 0.005 0.20 - 1.00 0.011 0.09 0.03 0.020 0.006 Example 2 0.15 0.10 1.05 0.015 0.005 0.19 - 0.85 0.010 0.08 0.05 0.042 0.006

division Reheating temperature Rolling start temperature Rolling end temperature Double heat temperature Cooling rate (℃ / s) Comparative Example 1 1200 ℃ 1050 ℃ 937 ℃ 676 ℃ 5.3 Comparative Example 2 1200 ℃ 1050 ℃ 934 ℃ 628 ℃ 6.1 Example 1 1200 ℃ 1050 ℃ 937 ℃ 636 ℃ 6.1 Example 2 1200 ℃ 1050 ℃ 933 ℃ 644 ℃ 6.0

Referring to Table 3 and Table 4, in Example 1 and Example 2, carbon (C): 0.06 to 0.20 wt%, manganese (Mn): 0.60 to 2.0 wt%, silicon (Si) 0.05 to 0.25 wt%, chromium (Cr): 0.5 to 1.30% by weight, copper (Cu): more than 0 to 0.4% by weight or less, molybdenum (Mo): more than 0 to 0.50% by weight or less, aluminum (Al): 0.015 to 0.070% by weight, nickel (Ni): More than 0 0.10% by weight or less, phosphorus (P): more than 0 0.02% by weight or less, sulfur (S): more than 0 0.008% by weight or less, nitrogen (N): more than 0 0.02% by weight or less, tin (Sn): more than 0 It satisfies the composition range of 0.1% by weight or less. On the other hand, in Comparative Example 1, the composition of sulfur exceeds 0.008% by weight, niobium (Nb) is included as an alloying element, and chromium (Cr) is less than 0.50% by weight, and in Comparative Example 2, sulfur has a composition of 0.008% by weight. Exceeding, containing niobium (Nb) as an alloying element, chromium (Cr) is less than 0.50% by weight, and molybdenum (Mo) is more than 0.50% by weight.

After the rolling of each of the specimens, QST treatment was performed while maintaining the recuperation temperature of Table 2.

2. Mechanical property evaluation

Tables 3 and 4 show the results of evaluation of mechanical properties of the specimens according to Comparative Examples 1 and 2 and Examples 1 and 2, and observations at room temperature microstructure.

division Room temperature
YS (MPa) Room temperature
TS (MPa) Room temperature
YR Ratio Room temperature
EL (%) High temperature (600 ℃)
YS (MPa) Comparative Example 1 455 639 0.71 17.5 302 Comparative Example 2 506 675 0.75 15.0 326 Example 1 481 675 0.71 23.9 337 Example 2 527 729 0.72 20.6 384

Microstructure of the surface at room temperature Microstructure in the center of room temperature division Tempered martensite Bainite ferrite
(shape) Bainite
(Fraction) Pearlite Precipitate Comparative Example 1 ○ ○ ○
(polygonal) ○
(16.8) ○ ○ Comparative Example 2 ○ ○ ○
(polygonal) ○
(17.5) ○ ○ Example 1 ○ ○ ○
(acicular) ○
(19.2) ○ - Example 2 ○ ○ ○
(acicular) ○
(22.7) ○ -

Referring to Table 3 and Table 4, it can be seen that the elongation is relatively higher in Example 1 and Example 2 than Comparative Example 1 and Comparative Example 2, and the high temperature yield strength (YS) is also relatively higher. In addition, it can be seen that the shape of the ferrite appearing in the microstructure of the central part of the room temperature of the section steel is a polygonal shape in Comparative Example 1 and Comparative Example 2, whereas in Example 1 and Example 2, the shape of the ferrite is acicular. Furthermore, it can be seen that the shape of ferrite appearing in the microstructure of the normal temperature center of the section steel has a relatively higher bainite fraction in Example 1 and Example 2 than in Comparative Example 1 and Comparative Example 2.

The above-described difference in high temperature yield strength is also understood as one of the main causes of the ferrite shape of the microstructure in the center of the room temperature.

2 is a photograph of the central microstructure of the section steel according to Comparative Example 2 of the present invention, and FIGS. 3 and 4 are photographs of the central microstructure of the section steel according to Examples 1 and 2 of the present invention .

2 to 4, it can be seen that the ferrite particle size is finer in the central microstructure of the embodiment than in the comparative example of the present invention.

The hot-deformation finish temperature range is deformed near the vacancy transformation temperature to prevent continuous formation of cementite cementite and cause explosive nucleation. Looking at the microstructure, it can be confirmed that in the case of Example 1 and Example 2 compared to the comparative example, fine bainite structure or ferrite and pearlite were rapidly formed under a wide hot deformation temperature, and thus it was generated without formation of cornerstone ferrite. However, if the hot rolling temperature is too low, the rolling load increases during rolling and some mixed structures may occur, so that the finishing temperature is A3 + (30 to 50 ° C). On the other hand, as the temperature increases, the bainite fraction decreases or the pearlite structure spacing increases, making it difficult to act as an obstacle to dislocation movement, resulting in a decrease in strength and deformation at the interface between coarse cementite and ferrite. As it is concentrated, defects such as voids are generated, and it can act as a crack growth site and deteriorate processability. In addition, in the case of the comparative example, it is a typical (ferrite + pearlite) structure, whereas in the case of the example, the particle size of ferrite was ultra-fine from 30 to 40 μm to 10 μm through final strain temperature control and cooling control, and the complex structure (bainite + acicular ferrite) It can be seen that this was formed, which also affected mechanical properties.

So far, the shape steel according to the embodiments of the present invention and a method of manufacturing the same have been described. The high-functional section steel and its manufacturing method according to the present invention provide suitable mechanical properties, and thus, when constructing a large-sized / large-sized structure, it is possible to simultaneously contribute to the reduction of the construction member cost and the improvement of the fire resistance and seismic performance due to the reduction in the cost of inserting expensive alloy elements. Accordingly, it is possible to reduce manufacturing cost and provide an effect of increasing production efficiency.

That is, the highly functional refractory seismic steel according to the present invention and its manufacturing method provide a high level of mechanical properties compared to the comparative steel produced by the existing components and manufacturing methods. Particularly, in the present invention, it is possible to reduce the expensive alloy iron and increase the chromium (Cr) content for the purpose of forming bainite and acicular ferrite with stable high temperature characteristics, and increase the carbon to an unfavorable level in terms of carbon equivalent to secure weldability together. You can. In addition, since there is no significant change in terms of production of the existing section steel, there is no need for additional equipment, and thus, there is an advantage of manufacturing a high-performance high-strength section steel having fireproof and seismic properties without increasing costs. When the high-functional section steel manufactured through the present invention is applied to a building structure, it will play a large role in human safety by delaying the collapse point compared to the normal section steel even in the event of an earthquake or fire, and it can also minimize the application of expensive refractory paints, thus shortening construction air. It has the advantage of reducing the effect and construction cost.

In the above, the description has been mainly focused on the embodiment of the present invention, but various changes or modifications can be made at the level of those skilled in the art. It can be said that such modifications and variations belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

Claims (6)

Carbon (C): 0.06 to 0.20% by weight, manganese (Mn): 0.60 to 2.0% by weight, silicon (Si): 0.05 to 0.25% by weight, chromium (Cr): 0.5 to 1.30% by weight, copper (Cu): 0 More than 0.4% by weight, molybdenum (Mo): more than 0 0.50% by weight, aluminum (Al): 0.015 to 0.070% by weight, nickel (Ni): more than 0 0.10% by weight or less, phosphorus (P): more than 0 0.02% % Or less, sulfur (S): more than 0 0.008% by weight, nitrogen (N): more than 0 and 0.02% by weight, tin (Sn): more than 0 and 0.1% by weight or less, and remaining iron (Fe) and other inevitable impurities Lose,
The normal temperature microstructure of the surface portion includes tempered martensite and bainite, and the normal temperature microstructure of the center portion includes acicular ferrite, bainite and pearlite.
Section steel. The method of claim 1,
At least one or more selected from calcium (Ca) and boron (B),
Calcium (Ca): more than 0 0.005% by weight or less, boron (B): characterized by being more than 0 and 0.003% by weight or less,
Section steel. The method of claim 1,
The average particle size of the ferrite is 10 ~ 20㎛, characterized in that the fraction of bainite in the center is 15-25%,
Section steel. (a) Carbon (C): 0.06 to 0.20% by weight, manganese (Mn): 0.60 to 2.0% by weight, silicon (Si) 0.05 to 0.25% by weight, chromium (Cr): 0.5 to 1.30% by weight, copper (Cu) : More than 0 0.4% by weight or less, Molybdenum (Mo): More than 0 0.50% by weight or less, Aluminum (Al): 0.015 to 0.070% by weight, Nickel (Ni): More than 0 0.10% by weight or less, Phosphorus (P): More than 0 0.02% by weight or less, sulfur (S): more than 0 0.008% by weight or less, nitrogen (N): more than 0 0.02% by weight or less, tin (Sn): more than 0 and 0.1% by weight or less and the rest of iron (Fe) and other unavoidable impurities Re-heating the steel consisting of 1150 to 1250 ℃;
(b) hot rolling the steel material to a rolling end temperature of 910 to 960 ° C; And
(c) cooling the hot rolled steel with QST (Quenching &Self-Tempering); Containing,
Method of manufacturing a section steel. The method of claim 4, wherein
The steel material further comprises at least one or more selected from calcium (Ca) and boron (B), characterized in that the calcium (Ca): more than 0 0.005% by weight, boron (B): more than 0 and 0.003% by weight or less ,
Method for manufacturing a section steel. The method of claim 4, wherein
The QST cooling is performed while controlling the surface recuperation temperature to 630 ~ 810 ℃,
Method for manufacturing a section steel.

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