KR20200072353A - High strength medium carbon steel for earthquake-proof and its manufacturing method - Google Patents

Abstract

The present invention discloses high strength earthquake-proof medium carbon steel and a manufacturing method thereof, wherein the high strength earthquake-proof medium carbon steel can be applied to an anchor bolt fixing a building support by being embedded in a concrete floor when a building is constructed or a machine or the like is installed. According to one embodiment, the disclosed medium carbon steel includes: 0.3 to 0.5 wt% of C; 0.5 to 1.0 wt% of Si; 0.5 to 1.5 wt% of Mn; less than 0.02 wt% of P; 0.03 to 0.07 wt% of S; 0.02 to 0.08 wt% of Al; 0.05 to 0.2 wt% of V; 0.01 to 0.08 wt% of Ti; 0.008 to 0.02 wt% of N; and the remaining of Fe and inevitable impurities. A length of a yield shelf is equal to or more than 1.0 wt%.

Description

High strength medium carbon steel for earthquake-proof and its manufacturing method}

The present invention relates to a high strength seismic medium carbon steel and a method for manufacturing the same.

In 2009, the number of earthquakes on the Korean Peninsula observed by the Korea Meteorological Administration was 60, which was the highest since the earthquake began. In addition, in September 2016, an earthquake of magnitude 5.8 occurred in Gyeongju, and in November 2017, an earthquake of magnitude 5.4 occurred in Pohang.

In Japan and the United States, where earthquakes occur frequently, earthquake-resistant steel is used as a structural steel to increase the safety of earthquakes in buildings. In Japan, the SN (Steel New Structure) steel standard (JIS G3136) was enacted in 1994 for the purpose of strengthening seismic design and improving weldability of steel and legislated to prevent steel for general structural use. In the United States, the A992 and A913 steels are specified as seismic steels and their use is recommended.

In Korea, various seismic technologies, such as seismic design, have been developed in order to increase the stability against earthquakes, but research on seismic steel is still insufficient.

Korean Registered Patent Publication No. 10-1684812 (Announcement date: December 8, 2016)

In order to solve the above-mentioned problems, the present invention aims to provide a high-strength seismic medium-carbon steel and a method for manufacturing the same.

Seismic medium carbon steel according to an embodiment of the present invention in weight percent, C: 0.3 to 0.5%, Si: 0.5 to 1.0%, Mn: 0.5 to 1.5%, P: less than 0.02%, S: 0.03 to 0.07%, Al: 0.02 to 0.08%, V: 0.05 to 0.2%, Ti: 0.01 to 0.08%, N: 0.008 to 0.02%, balance Fe and other inevitable impurities, and the yield shelf length is 1.0% or more.

In addition, the medium carbon steel for seismic protection according to an example of the present invention may include 45 or more precipitates having a size of 10 nm or less per 200x200 nm ² as a microstructure.

In addition, the medium carbon steel for seismic protection according to an example of the present invention may include 15 or more precipitates having a size of 10 to 30 nm per 200x200 nm ² as a microstructure.

In addition, the medium carbon steel for seismic protection according to an example of the present invention may include 10 or less precipitates having a size of 30 nm or more per 200x200 nm ² as a microstructure.

In addition, the medium carbon steel for earthquake-proof according to an example of the present invention may include a ferrite structure as a microstructure, and a fraction of the ferrite may be 50% or more.

In addition, the medium carbon steel for earthquake resistance according to an example of the present invention includes a ferrite structure as a microstructure, and the average grain size of the ferrite may be 20 to 30 μm.

In addition, the seismic medium carbon steel according to an embodiment of the present invention may have a yield ratio of 0.75 or less.

In addition, the seismic medium carbon steel according to an example of the present invention may have a tensile strength of 700 MPa or more and a yield strength of 490 MPa or more.

In addition, the medium carbon steel for earthquake-proof according to an example of the present invention may have an elongation of 20% or more.

The present invention can provide a high strength seismic medium carbon steel having excellent seismic properties and a method of manufacturing the same by having a low yield ratio, a high elongation, and increasing the nitrogen content in the alloy composition to secure a yield shelf of an appropriate length.

1 is a microstructure photograph of Inventive Example 1.

Hereinafter, preferred embodiments of the present invention will be described. However, embodiments of the present invention may be modified in various other forms, and the technical idea of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Terms used in the present application are only used to describe specific examples. Thus, for example, a singular expression includes a plural expression unless the context clearly indicates that it should be singular. In addition, terms such as “comprise” or “include” as used in the present application are used to clearly indicate the existence of features, steps, functions, elements, or combinations thereof described in the specification, and other features. It should be noted that it is not used to preliminarily exclude the presence of a field or step, function, component, or combination thereof.

On the other hand, unless defined otherwise, all terms used in this specification should be regarded as having the same meaning as generally understood by a person having ordinary skill in the art to which the present invention pertains. Accordingly, unless specifically defined herein, certain terms should not be construed in excessively ideal or formal sense. For example, in this specification, a singular expression includes a plural expression unless the context clearly has an exception.

In addition, "about", "substantially", and the like in the present specification are used in the sense of or close to the value when manufacturing and substance tolerances unique to the stated meaning are presented, and are used to help understand the present invention. Or, an absolute value is used to prevent unscrupulous use of the disclosed content by unscrupulous intruders.

In addition, "yield shelf" of the present specification means a section that yields elongation (Yield Point Elongation), and "yield shelf" is a section in which uneven deformation occurs in the lower yielding after the upper yielding and then the upper yielding. It means the difference (%) of elongation at the beginning and end of.

In Japan and the United States, where earthquakes occur frequently, earthquake-resistant steel is used as a structural steel to increase the safety of earthquakes in buildings. In Japan, the SN (Steel New Structure) steel standard (JIS G3136) was enacted in 1994 for the purpose of strengthening seismic design and improving weldability of steel and legislated to prevent steel for general structural use. In the United States, the A992 and A913 steels are specified as seismic steels and their use is recommended.

In Korea, various seismic technologies, such as seismic design, have been developed in order to increase the stability against earthquakes, but research on seismic steel is still insufficient.

In order to secure seismic properties, the tensile strength, yield strength, yield ratio, and elongation criteria must be satisfied. The yield ratio of the building moves to the left and right in the event of an earthquake, and the lower it is, the better. However, when the yield ratio is low, in the case of the bolt, since the fastening force itself becomes weak, the length and thickness of the product are increased to improve the fastening force, and the depth of the ground is also deepened.

As a result of repeated studies to solve the above-mentioned problems, the present researchers found that the earthquake input energy can be efficiently absorbed by using the deformation in the yield shelf, so that the seismic properties can be further improved. In addition, by utilizing the deformation in the yield shelf, as a result of controlling the yield ratio low, it is possible to solve the problem of increasing the length and thickness of the product in order to improve the fastening force of the bolt, thereby reducing the cost.

Accordingly, the present invention is to provide a high-strength seismic medium-carbon steel and a method for manufacturing the same, which can secure a yield shelf of elongation and proper length while satisfying a low yield ratio including high tensile and yield strength through alloy component control. do.

In order to control the yield ratio low, since the ferrite structure fraction, which is a soft tissue phase capable of deformation, must be high, it is necessary to appropriately control the content of alloying components such as C.

The yield shelf corresponds to a section in which non-uniform deformation occurs in the lower yield after the upper yield after passing through the elastic region, and corresponds to a section that occurs because intrusive elements such as N and C adhere to dislocations formed in the grain. Therefore, it is necessary to appropriately control the content of alloying components such as N and C added in order to secure a yield shelf of an appropriate length.

Seismic medium carbon steel according to an aspect of the present invention in weight percent, C: 0.3 to 0.5%, Si: 0.5 to 1.0%, Mn: 0.5 to 1.5%, P: 0.02% or less, S: 0.03 to 0.07%, Al: 0.02 to 0.08%, V: 0.05 to 0.2%, Ti: 0.01 to 0.08%, N: 0.008 to 0.02%, balance Fe and other inevitable impurities.

Hereinafter, the reason for limiting the composition of the steel will be described in detail. The following composition of the composition means all weight% unless otherwise specified.

C (carbon): 0.3 to 0.5% by weight

C is a major element for securing strength. C is the main element that forms pearlite and exists as cementite. When the C content increases by 0.1%, the strength increases by about 100 MPa. When C is less than 0.3%, a ferrite fraction may be obtained to have a yield shelf, but a target strength cannot be secured, and when C is more than 0.5%, a yield shelf is not shown due to an increase in the pearlite fraction, and therefore, it is preferred.

Si (silicon): 0.5 to 1.0% by weight

Si is a ferrite solid solution strengthening element, which is dissolved in ferrite, but is also an element segregated in the ferrite/cementite grain boundary. When the Si content increases by 0.1%, the yield strength increases by about 14 to 16 MPa. When Si is less than 0.5%, it is difficult to secure the target strength in the present invention, and when Si exceeds 1.0%, the ductility is lowered, so it is preferable to control below.

Mn (manganese): 0.5 to 1.5% by weight

Mn is an austenite stabilizing element and has a deoxidizing effect. Mn is an element that combines with S present in the steel to form MnS to prevent red brittleness by sulfur. In addition, the strength is also slightly increased, but added to ensure stable quenching. When Mn is less than 0.5%, there is no effect of increasing the strength, and when Mn is more than 1.5%, a low-temperature structure is formed, so it is preferable to control below.

P(phosphorus): less than 0.02%

The smaller the P is, the better it is, but if it is limited to too extreme, the cost of removing impurities in the steelmaking process increases. Accordingly, the content of P is managed to be less than 0.02%.

S (sulfur): 0.03 to 0.07%

S is an impurity, but combines with Mn to form a stretching system MnS. MnS may act as a defect when present in steel, but MnS stretched during rolling is an element that plays a role in improving machinability. When S is less than 0.03%, cutting is not preferred, and when S is more than 0.07%, the cutting effect is not large, so it is preferable to manage it below.

Al (aluminum): 0.02 to 0.08%

Al combines with N present in the steel to form AlN, and is an element that plays a role in inhibiting grain growth because it is present at the austenite grain boundary. When Al is less than 0.02%, the effect of grain refinement is small, and when Al is more than 0.08%, it is preferable to add less than this, since there is a high possibility that uneven grains due to coarse AlN formation are caused.

V (Vanadium): 0.05~0.2%

V is combined with C and N present in the steel to form VC and VN fine precipitates. When V is less than 0.05%, the effect of increasing the strength by the fine precipitates does not appear, and when V is more than 0.2%, it is preferable to control below because the ductility decreases due to the formation of coarse precipitates and the manufacturing cost increases significantly.

Ti (Titanium): 0.01~0.08%

Ti combines C and N present in the steel to form TiC and TiN precipitates, and is an element that serves to increase strength. When Ti is less than 0.01%, the effect of increasing the strength is small and the target strength cannot be secured. When Ti exceeds 0.08%, coarse TiN is formed to weaken the ductility, so it is preferable to control below.

N (nitrogen): 0.008 to 0.02%

N is an element that greatly increases the strength, such as C. When 0.1% is added, the strength increases by 100 MPa. In addition, N can be fixed to the dislocation formed in the crystal grains, and at this time, since it causes yield reduction, N is an element forming the yield shelf to be secured in the present invention. When N is 0.008% or less, the yield shelf length cannot be sufficiently secured, and when N is more than 0.02%, it is preferable to control below because the field control is difficult and not managed.

The remaining component of the invention is iron (Fe). However, in the normal manufacturing process, unintended impurities from the raw material or the surrounding environment may be inevitably mixed, and therefore cannot be excluded. Since the impurities are known to anyone skilled in the ordinary manufacturing process, they are not specifically mentioned in this specification.

Hereinafter, the microstructure of the medium carbon steel of the present invention having the above composition will be described in detail.

Microstructure

The medium carbon steel according to an example of the present invention includes a ferrite structure, the average grain size of the ferrite may be 20 to 30 μm, and the fraction of the ferrite may be 50% or more.

In addition, in the medium carbon steel according to an embodiment of the present invention, regardless of the type of precipitate, 45 or more precipitates having a size of 10 nm or less per 200x200 nm ² , 15 or more precipitates having a size of 10 to 30 nm, and precipitates having a size of 30 nm or more This can be 10 or less. At this time, the precipitate may include VC, VN, TiC, TiN, and the like.

The medium carbon steel according to an example of the present invention having the above-described composition and microstructure may have a tensile strength of 700 MPa or more, and a yield strength of 490 MPa or more.

In addition, the medium carbon steel according to an embodiment of the present invention may have a yield ratio of 0.75 or less.

In addition, the elongation of the medium carbon steel according to an example of the present invention may be 20% or more.

In addition, the medium carbon steel according to an embodiment of the present invention may have a yield shelf length of 1.0% or more.

In addition, the medium carbon steel according to an example of the present invention may be processed into a tensile test piece size, and the energy absorption amount may be 70 kN·mm or more when a constant amplitude is repeatedly applied at a strain rate of 1 to 10%.

Hereinafter, a method for manufacturing the medium carbon steel of the present invention will be described in detail.

The method for manufacturing medium carbon steel according to an embodiment of the present invention is weight %, C: 0.3-0.5%, Si: 0.5-1.0%, Mn: 0.5-1.5%, P: less than 0.02%, S: 0.03-0.07% , Al: 0.02 ~ 0.08%, V: 0.05 ~ 0.2%, Ti: 0.01 ~ 0.08%, N: 0.008 ~ 0.02%, heat-treating the steel containing the balance Fe and other inevitable impurities, the heat-treated steel Hot rolling, and cooling the hot rolled steel.

According to an example, the step of heat-treating the steel containing the composition component may be heat-treated for 90 to 120 minutes in a temperature range of 1000 to 1200°C.

According to an example, the step of hot rolling the heat-treated steel may be performed in a temperature range of 900 to 1000°C.

According to an example, the cooling may cool the steel to 5° C./s or less in an air-cooled table.

Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and reasonably inferred therefrom.

{Example}

In the following examples, 400 x 500 mm ² blooms were manufactured by continuously casting steels of each of the invention examples and comparative examples having the component system shown in Table 1, and 400 x 500 mm ^{2 by} rolling steel pieces under a heating furnace of 1200 to 1250° C. and 300 to 400 minutes. Billets were prepared. The billet was hot-rolled after being maintained at 1020°C for 10 minutes on a heating furnace, and cooled by controlling the temperature at 800-850°C at the time of finishing rolling, and at a cooling rate of 5°C/s in a cooling table.

In addition, Table 2 shows the results of observing the microstructures of the steels of each of the inventive examples and comparative examples having the composition of Table 1.

In addition, with reference to Table 1 and Table 2, the mechanical properties of each of the inventive examples and comparative examples steel are shown in Table 3 below. The machinability in Table 3 is a measure of machinability when cutting both ends of the final rolled steel, and the energy absorption amount is the amplitude of a strain of 1 to 10% by processing each invention example and comparative example steel into a tensile test specimen size. It is a value that measures the amount of energy absorbed during repeated pressing.

Sample Weight (wt.%) C Si Mn P S Al V Ti N Comparative Example 1 0.4 0.8 1.2 0.012 0.02 0.043 0.0 0.00 0.006 Inventive Example 1 0.4 0.8 1.2 0.012 0.06 0.045 0.1 0.02 0.010 Comparative Example 2 0.6 0.8 1.2 0.012 0.06 0.041 0.1 0.02 0.010 Comparative Example 3 0.2 0.8 1.2 0.012 0.06 0.046 0.1 0.02 0.010 Comparative Example 4 0.4 0.4 1.2 0.012 0.06 0.045 0.1 0.02 0.010 Inventive Example 2 0.4 0.6 1.2 0.012 0.06 0.044 0.1 0.02 0.010 Inventive Example 3 0.4 1.0 1.2 0.012 0.06 0.044 0.1 0.02 0.010 Comparative Example 5 0.4 1.2 1.2 0.012 0.06 0.045 0.1 0.02 0.010 Comparative Example 6 0.4 0.8 0.4 0.012 0.06 0.042 0.1 0.02 0.010 Inventive Example 4 0.4 0.8 0.9 0.012 0.06 0.042 0.1 0.02 0.010 Comparative Example 7 0.4 0.8 1.6 0.012 0.06 0.046 0.1 0.02 0.010 Comparative Example 8 0.4 0.8 1.2 0.012 0.02 0.046 0.1 0.02 0.010 Comparative Example 9 0.4 0.8 1.2 0.012 0.09 0.047 0.1 0.02 0.010 Comparative Example 10 0.4 0.8 1.2 0.012 0.06 0.045 0.04 0.02 0.010 Inventive Example 5 0.4 0.8 1.2 0.012 0.06 0.042 0.18 0.02 0.010 Comparative Example 11 0.4 0.8 1.2 0.012 0.06 0.045 0.21 0.02 0.010 Comparative Example 12 0.4 0.8 1.2 0.012 0.06 0.045 0.1 0.005 0.010 Inventive Example 6 0.4 0.8 1.2 0.012 0.06 0.044 0.1 0.04 0.010 Inventive Example 7 0.4 0.8 1.2 0.012 0.06 0.043 0.1 0.07 0.010 Comparative Example 13 0.4 0.8 1.2 0.012 0.06 0.044 0.1 0.09 0.010 Comparative Example 14 0.4 0.8 1.2 0.012 0.06 0.045 0.1 0.02 0.006 Inventive Example 8 0.4 0.8 1.2 0.012 0.06 0.045 0.1 0.02 0.018 Comparative Example 15 0.4 0.8 1.2 0.012 0.06 0.044 0.1 0.02 0.022

Sample ferrite
Fraction (%) Number of observed precipitates by size ≤10nm 10~30nm ≥30nm Comparative Example 1 51 One 0 0 Inventive Example 1 52 48 15 10 Comparative Example 2 43 46 18 12 Comparative Example 3 68 51 12 9 Comparative Example 4 51 49 18 14 Inventive Example 2 53 47 16 8 Inventive Example 3 52 50 18 9 Comparative Example 5 53 49 17 14 Comparative Example 6 54 48 15 13 Inventive Example 4 51 51 19 9 Comparative Example 7 52 52 20 12 Comparative Example 8 51 50 15 11 Comparative Example 9 50 48 17 8 Comparative Example 10 52 30 25 8 Inventive Example 5 53 64 20 9 Comparative Example 11 50 42 27 32 Comparative Example 12 51 28 22 12 Inventive Example 6 52 70 26 7 Inventive Example 7 53 72 28 8 Comparative Example 13 54 39 42 45 Comparative Example 14 51 48 15 14 Inventive Example 8 50 52 17 9 Comparative Example 15 53 37 29 18

Sample The tensile strength
(MPa) Yield strength
(MPa) Surrender Elongation
(%) Yield shelf
Length
(%) Machinability
(Excellent/bad) energy
Absorption
(kNmm) Comparative Example 1 520 440 0.85 28 0.2 Great 12 Inventive Example 1 760 530 0.70 27 1.2 Great 75 Comparative Example 2 890 640 0.72 23 x Great 8 Comparative Example 3 520 340 0.65 29 1.0 Great 64 Comparative Example 4 681 495 0.70 27 0.9 Great 73 Inventive Example 2 752 529 0.70 26 1.1 Great 74 Inventive Example 3 788 532 0.68 24 1.3 Great 73 Comparative Example 5 816 562 0.70 11 1.1 Great 70 Comparative Example 6 616 445 0.72 27 0.9 Great 67 Inventive Example 4 709 521 0.73 26 1.3 Great 74 Comparative Example 7 832 650 0.78 15 1.1 Great 61 Comparative Example 8 758 532 0.70 26 1.2 Bad 75 Comparative Example 9 762 527 0.69 24 1.1 Bad 75 Comparative Example 10 660 529 0.80 25 1.0 Great 74 Inventive Example 5 770 535 0.69 26 1.2 Great 78 Comparative Example 11 Brittle fracture x X x x x X Comparative Example 12 650 526 0.81 28 1.1 Great 70 Inventive Example 6 780 540 0.69 24 1.3 Great 77 Inventive Example 7 810 550 0.68 26 1.2 Great 75 Comparative Example 13 Brittle fracture x X x x x X Comparative Example 14 760 527 0.69 25 0.4 Great 71 Inventive Example 8 765 536 0.70 27 1.4 Great 79 Comparative Example 15 Destruction x x x x x X

Hereinafter, each invention example and comparative example are evaluated with reference to Tables 1-3.

Referring to Table 1, the steels of Inventive Examples 1 to 8 are weight %, C: 0.3 to 0.5%, Si: 0.5 to 1.0%, Mn: 0.5 to 1.5%, P: less than 0.02%, S: 0.03 to 0.07 %, Al: 0.02 ~ 0.08%, V: 0.05 ~ 0.2%, Ti: 0.01 ~ 0.08%, N: 0.008 ~ 0.02%, it can be confirmed that it contains the balance Fe and other inevitable impurities.

Also, referring to Table 2 and FIG. 1, the steels of Inventive Examples 1 to 8 include a ferrite structure as a microstructure, and an average grain size of ferrite is 20 to 30 μm, and the fraction of ferrite is 50% or more. It can be confirmed that it includes 45 or more precipitates having a size of 10 nm or less per 200x200 nm ² , 15 or more precipitates having a size of 10 to 30 nm, and 10 or less precipitates having a size of 30 nm or more.

Further, referring to Table 3, the steels of Inventive Examples 1 to 8 have a tensile strength of 700 MPa or more, a yield strength of 490 MPa or more, a yield ratio of 0.75 or less, an elongation of 20% or more, a yield shelf length of 1.0% or more, and excellent machinability. , It can be confirmed that the energy absorption amount is 70 kNmm or more.

On the other hand, in the steel of Comparative Example 1, Ti and V were not added, the N content was low, the tensile and yield strength was low, the yield ratio was high, the yield shelf length was small as 0.2%, and the energy absorption was measured as small as 12 kNmm. And seismic properties were not good.

The steels of Comparative Examples 2 and 3 correspond to comparative steels in which the carbon content was controlled differently from the composition range of the present invention.

The steel of Comparative Example 2 is a high carbon steel, the tensile strength is higher than that of the invention example, but the yield ratio is high, and since the yield shelf does not exist, the energy absorption amount is measured as small as 8 kNmm and the seismic properties are not good. The steel of Comparative Example 3 was a low-carbon steel, and the tensile and yield strength were not sufficiently secured, and the seismic properties were poor.

The steels of Comparative Examples 4 and 5 correspond to comparative steels in which the silicon content was controlled differently from the composition range of the present invention.

The steel of Comparative Example 4 is a steel having a low silicon content, which satisfies elongation and machinability, but has a lower tensile strength than the present invention. The steel of Comparative Example 5 is a steel having a high silicon content, and has excellent strength and other properties, but has a poor elongation rate, so that the workability is poor.

The steels of Comparative Examples 6 and 7 correspond to comparative steels in which the manganese content was controlled differently from the composition range of the present invention.

The steel of Comparative Example 6 is a low manganese content, low tensile and yield strength, small yield shelf length, and poor seismic properties. The steel of Comparative Example 7 is a high manganese content, high yield ratio, low elongation, and poor seismic properties.

The steels of Comparative Examples 8 and 9 correspond to comparative steels in which the sulfur content was controlled differently from the composition range of the present invention. Comparative Example 8 was a steel with a low sulfur content, and Comparative Example 9 was a steel with a high sulfur content, and was not good due to poor machinability.

The steels of Comparative Examples 10 and 11 correspond to comparative steels in which the vananium content was controlled differently from the composition range of the present invention. The steel of Comparative Example 10 is a steel having a low vanadium content, low tensile strength, high yield ratio, and poor seismic properties. The steel of Comparative Example 11 is a steel having a high vanadium content. Referring to Table 2, it can be seen that as a result of adding a large amount of vanadium, brittle fracture occurred due to the formation of a large number of coarse precipitates having a size of 30 nm or more.

The steels of Comparative Examples 12 and 13 correspond to comparative steels in which the titanium content was controlled differently from the composition range of the present invention. The steel of Comparative Example 12 is a steel with a low titanium content, low tensile strength, high yield ratio, and poor seismic properties. The steel of Comparative Example 13 is a steel with a high titanium content. Referring to Table 2, it can be seen that as a result of adding a large amount of titanium, brittle fracture occurred due to formation of a large number of coarse precipitates having a size of 30 nm or more.

The steels of Comparative Examples 14 and 15 correspond to comparative steels in which the nitrogen content was controlled differently from the composition range of the present invention. The steel of Comparative Example 14 was a steel with a low nitrogen content, and the yield shelf length was small as 0.4%, so that the seismic properties were not good. The steel of Comparative Example 15 is a steel with a high nitrogen content, and destruction occurred during playing.

As described above, the present invention has a low yield ratio, a high elongation, and by increasing the nitrogen content in the alloy composition to secure a yield shelf of an appropriate length, to provide a high strength seismic medium carbon steel having excellent seismic properties and a method for manufacturing the same Can.

In addition, the present invention has an advantage in terms of economy because it can solve the problem of increasing the length and thickness of the product to improve the fastening force of the bolt by securing the yield shelf of an appropriate length. In particular, the present invention can reduce the length and weight of anchor bolts that fix a building support by buried on a concrete floor when building or installing a machine or the like, thereby reducing the production cost of building materials such as anchor bolts.

As described above, although exemplary embodiments of the present invention have been described, the present invention is not limited thereto, and a person having ordinary skill in the art does not depart from the concept and scope of the following claims. It will be understood that various modifications and variations are possible.

Claims (9)

In weight percent, C: 0.3 to 0.5%, Si: 0.5 to 1.0%, Mn: 0.5 to 1.5%, P: less than 0.02%, S: 0.03 to 0.07%, Al: 0.02 to 0.08%, V: 0.05 to 0.2 %, Ti: 0.01~0.08%, N: 0.008~0.02%, the balance contains Fe and other inevitable impurities,
Seismic medium carbon steel with yield shelf length of 1.0% or more. According to claim 1,
As a microstructure, seismic medium carbon steel containing 45 or more precipitates having a size of 10 nm or less per 200x200 nm ² . According to claim 1,
As a microstructure, seismic medium carbon steel containing 15 or more precipitates having a size of 10~30nm per 200x200nm ² . According to claim 1,
As a microstructure, seismic medium carbon steel containing 10 or less precipitates of 30nm or more per 200x200nm ² . According to claim 1,
A medium-strength medium carbon steel comprising a ferrite structure as a microstructure and having a fraction of 50% or more of the ferrite. According to claim 1,
As a microstructure, a ferrite structure, and the average grain size of the ferrite is 20 to 30㎛ seismic medium carbon steel. According to claim 1,
Seismic medium carbon steel with a yield ratio of 0.75 or less. According to claim 1,
Seismic medium carbon steel with tensile strength over 700MPa and yield strength over 490MPa. According to claim 1,
Seismic medium carbon steel with elongation of 20% or more.

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