KR101748968B1

KR101748968B1 - Shape steel and method of manufacturing the shape steel

Info

Publication number: KR101748968B1
Application number: KR1020150185680A
Authority: KR
Inventors: 이철원; 구본승; 이명규; 임영훈; 정승훈
Original assignee: 현대제철 주식회사
Priority date: 2015-12-24
Filing date: 2015-12-24
Publication date: 2017-06-20

Abstract

Embodiments of the present invention may include (a) 0.08 wt% to 0.14 wt% carbon (C), 0.15 wt% to 0.40 wt% silicon (Si), 1.25 wt% to 1.60 wt% manganese 0.001 wt% to 0.025 wt% sulfur, 0.001 wt% to 0.025 wt% sulfur, 0.001 wt% to 0.055 wt% aluminum (Al), 0.001 wt% to 0.050 wt% niobium (Nb) (V): 0.001 wt.% To 0.100 wt.%, Ti: 0.001 wt.% To 0.025 wt.%, Nitrogen: 0.0001 wt.% To 0.0120 wt.% And the balance iron (Fe) and unavoidable impurities , Reheating the steel having an alloy composition having a weight ratio of titanium to nitrogen (Ti: N) of 1: 1 to 2.5: 1 to 1050 to 1250 占 폚; (b) a hot rolling step of rolling the reheated steel to a finishing rolling temperature (FRT) of 800 to 850 占 폚 to produce a rolled material having a thickness of 12 to 40 mm; And (c) After the hot rolling step, the rolled material having a thickness of 12 mm to 24 mm is cooled to a temperature of 670 to 700 캜 under a finishing cooling temperature (FCT), and a finishing cooling temperature (FCT) of 630 And a cooling step in which the steel sheet is cooled at a temperature in the range of from 0 DEG C to 670 DEG C, and a steel sheet produced by the method.

Description

TECHNICAL FIELD [0001] The present invention relates to a steel sheet and a method of manufacturing the steel sheet,

More particularly, the present invention relates to a steel sheet for low temperature impact assurance which can be applied to an architectural structure due to low physical property deviations due to its shape and high strength and toughness, and a method for manufacturing the same.

Recent architectural structures are becoming larger and larger. As described above, steel materials used for superstructures and large-scale building structures are required to have higher strength and toughness than conventional ones. In particular, high-rise building structures and super-large building structures are required to withstand external forces due to earthquakes and strong winds. Therefore, steels having a good balance between strength and toughness as well as elongation and strength are required. Such steels are subjected to natural disasters and high- A low temperature impact toughness is also required.

A TMCP (thermo-mechanical control process) process is mainly used as a manufacturing method of a steel material capable of ensuring impact toughness even at a low temperature. However, it is difficult to produce high strength high strength steel in the TMCP process due to large variation of physical properties depending on the size and thickness due to geometrical factors.

A related prior art is Korean Patent Publication No. 10-2004-0004137 (published on Jan. 13, 2004).

(YS), a tensile strength (TS), an elongation (EL), and an elongation (EL) of the TMCP process, which can be applied to the TMCP process through control of alloy components and process conditions, And a method of manufacturing a steel having impact absorption energy of -20 占 폚.

(YS) of 490 MPa or more, a tensile strength (TS) of 600 MPa or more, an elongation (EL) of 22% or more, and a tensile strength of -20 Lt; RTI ID = 0.0 > 100 J < / RTI >

One embodiment of the present invention is directed to a method of making a carbon nanowhisker comprising the steps of: (a) providing 0.08 wt% to 0.14 wt% carbon, 0.15 wt% to 0.40 wt% silicon, 1.25 wt% to 1.60 wt% manganese, 0.001 wt% to 0.025 wt% sulfur (P), 0.001 wt% to 0.025 wt% sulfur (S), 0.001 wt% to 0.055 wt% aluminum (Al), 0.001 wt% to 0.050 wt% niobium (Nb) , 0.001 wt% to 0.100 wt% of vanadium (V), 0.001 wt% to 0.025 wt% of titanium (Ti), 0.0001 wt% to 0.0120 wt% of nitrogen (N) and unavoidable impurities And reheating the steel having an alloy composition having a weight ratio of titanium to nitrogen (Ti: N) of 1: 1 to 2.5: 1 to a temperature of 1050 to 1250 占 폚; (b) a hot rolling step of rolling the reheated steel to a finishing rolling temperature (FRT) of 800 to 850 占 폚 to produce a rolled material having a thickness of 12 to 40 mm; And (c) After the hot rolling step, the rolled material having a thickness of 12 mm to 24 mm is cooled to a temperature of 670 to 700 캜 under a finishing cooling temperature (FCT), and a finishing cooling temperature (FCT) of 630 Deg.] C to 670 [deg.] C.

Wherein the step (b) comprises controlling the rolling speed from 5.2 m / s to 8.8 m / s to produce a rolled material having a thickness of 12 mm to 24 mm, wherein the step (c) With a feed rate of 2.0 m / s to 3.0 m / s and a main feed of 300 m 3 / h to 1,000 m 3 / h.

Wherein the step (b) comprises controlling the rolling speed from 3.0 m / s to 4.4 m / s to produce a rolled material having a thickness greater than 24 mm to 40 mm, wherein step (c) Cooling the strip at a feed rate of 1.0 m / s to 1.9 m / s and a main feed of 1,000 m / h to 1,500 m / h.

Another embodiment of the present invention is a process for the preparation of a catalyst composition comprising (a) from 0.08 to 0.14% by weight of carbon (C), from 0.15 to 0.40% by weight of silicon (Si), from 1.25 to 1.60% by weight of manganese 0.001 wt% to 0.025 wt% sulfur (P), 0.001 wt% to 0.025 wt% sulfur (S), 0.001 wt% to 0.055 wt% aluminum (Al), 0.001 wt% to 0.050 wt% niobium (Nb) , 0.001 wt% to 0.100 wt% of vanadium (V), 0.001 wt% to 0.025 wt% of titanium (Ti), 0.0001 wt% to 0.0120 wt% of nitrogen (N) and unavoidable impurities (YS) of not less than 490 MPa, a tensile strength (TS) of not less than 600 MPa, a tensile strength (TS) of not less than 600 MPa, and a weight ratio of titanium to nitrogen , An elongation (EL) of 22% or more, and a shock absorption energy of 100 J or more at -20 캜.

The weight ratio of Ti: N in the alloy composition may be 1: 1 to 2: 1.

The section steel may have a volume fraction of low-temperature structure in the thickness direction of 10% to 40%, and the low-temperature structure in the thickness direction may include martensite and bainite.

(YS) of 490 MPa or more, a tensile strength (TS) of 600 MPa or more, an elongation (EL) of 22% or more, and a temperature of -20 DEG C A shock absorbing energy of 100 J or more, and a method of manufacturing such a section.

1 is a flow chart showing a method of manufacturing a steel sheet according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

One embodiment of the present invention is directed to a method of making a carbon nanowhisker comprising the steps of: (a) providing 0.08 wt% to 0.14 wt% carbon, 0.15 wt% to 0.40 wt% silicon, 1.25 wt% to 1.60 wt% manganese, 0.001 wt% to 0.025 wt% sulfur (P), 0.001 wt% to 0.025 wt% sulfur (S), 0.001 wt% to 0.055 wt% aluminum (Al), 0.001 wt% to 0.050 wt% niobium (Nb) , 0.001 wt% to 0.100 wt% of vanadium (V), 0.001 wt% to 0.025 wt% of titanium (Ti), 0.0001 wt% to 0.0120 wt% of nitrogen (N) and unavoidable impurities And reheating the steel having an alloy composition having a weight ratio of titanium to nitrogen (Ti: N) of 1: 1 to 2.5: 1 to a temperature of 1050 to 1250 占 폚; (b) a hot rolling step of rolling the reheated steel at a finishing rolling temperature (FRT) of 800 ° C to 850 ° C to produce a rolled material having a thickness of 12 mm to 40 mm; And (c) After the hot rolling step, the rolled material having a thickness of 12 mm to 24 mm is cooled to a temperature of 670 to 700 캜 under a finishing cooling temperature (FCT), and a finishing cooling temperature (FCT) of 630 Deg.] C to 670 [deg.] C.

As a result, the steel sheet manufacturing method of one embodiment of the present invention is capable of applying the TMCP process and has a yield strength (YS) of not less than 490 MPa, a tensile strength (TS) of not less than 600 MPa, an elongation EL) of 22% or more and a shock absorption energy of 100 J or more at -20 캜.

Hereinafter, the role and content of each component included in the alloy composition used in the steel sheet forming method according to the present invention will be described.

Carbon (C)

In the present invention, carbon (C) is added to secure the strength of the steel.

The carbon (C) is added in a content ratio of 0.08 wt% to 0.14 wt% of the total weight of the steel according to the present invention. If the content of carbon is less than 0.08% by weight, it may be difficult to secure strength. On the contrary, when the content of carbon (C) exceeds 0.14% by weight, the strength of the steel increases but the core hardness and weldability are deteriorated.

silicon( Si )

In the present invention, silicon (Si) is added as a deoxidizer to remove oxygen in the steel in the steelmaking process. Silicon (Si) also has a solid solution strengthening effect.

The silicon (Si) is added at a content ratio of 0.15 wt% to 0.40 wt% of the total weight of the steel according to the present invention. If the content of silicon (Si) is less than 0.15 wt%, the effect of adding silicon can not be exhibited properly. On the other hand, when the content of silicon (Si) exceeds 0.40% by weight, oxides are formed on the surface of the steel, thereby deteriorating the weldability of the steel.

Manganese (Mn)

Manganese (Mn) is an element which increases the strength and toughness of steel and increases the incombustibility of steel. Addition of manganese (Mn) causes less deterioration of ductility when the strength is higher than that of carbon (C). Further, manganese (Mn) contributes to improvement of the hardenability of the steel.

The manganese (Mn) is added at a content ratio of 1.25 wt% to 1.60 wt% of the total weight of the steel according to the present invention. When the content of manganese (Mn) is less than 1.25 wt%, it may be difficult to secure strength even if the content of carbon (C) is high. On the contrary, when the content of manganese (Mn) exceeds 1.60% by weight, the amount of MnS-based nonmetallic inclusions increases, which may cause defects such as cracks during welding.

In (P)

Phosphorus (P) is an element contributing to strength improvement.

The phosphorus (P) is limited to a content ratio of 0.001 wt% to 0.025 wt% of the total weight of the steel according to the present invention. If the content of phosphorus (P) is less than 0.001% by weight, the effect of improving the strength due to the addition of phosphorus can not be exhibited properly because the amount of phosphorus (P) added is insignificant. On the contrary, when the content of phosphorus (P) exceeds 0.025% by weight, not only center segregation but also fine segregation is formed, which adversely affects the material and may deteriorate the weldability.

Sulfur (S)

Sulfur (S) is an element contributing to improvement of processability.

The sulfur (S) is limited to a content ratio of 0.001 wt% to 0.025 wt% of the total weight of the steel according to the present invention. When the content of sulfur (S) is less than 0.001% by weight, it is difficult to improve workability due to sulfur, and the content of sulfur must be controlled to a minimum, resulting in an increase in steel production cost. On the contrary, when the content of sulfur (S) exceeds 0.025% by weight, there is a problem that the weldability is greatly deteriorated.

Aluminum (Al)

Aluminum (Al) acts as a deoxidizer to remove oxygen in the steel.

The aluminum (Al) is added in a content ratio of 0.001 wt% to 0.055 wt% of the total weight of the steel according to the present invention. When the content of aluminum (Al) is less than 0.001% by weight, the effect of deoxidation is insufficient. On the contrary, when the content of aluminum (Al) exceeds 0.055% by weight, Al ₂ O ₃ is formed to deteriorate toughness.

Niobium ( Nb )

Niobium (Nb) combines with carbon (C) and nitrogen (N) at high temperatures to form carbides or nitrides. Niobium-based carbides or nitrides improve grain strength and low-temperature toughness by suppressing grain growth during rolling and making crystal grains finer.

The niobium (Nb) is added at a content ratio of 0.001 wt% to 0.050 wt% of the total weight of the steel according to the present invention. When the content of niobium (Nb) is less than 0.001% by weight, the effect of adding niobium can not be exhibited properly. On the contrary, when the content of niobium (Nb) exceeds 0.050 wt%, the weldability of steel is deteriorated. If the content of niobium exceeds 0.050 wt%, the strength and low temperature toughness due to the increase in niobium content are not further improved but exist in a solid state in the ferrite, which may lower the impact toughness.

Vanadium (V)

Vanadium (V) plays a role in improving the strength of steel through precipitation strengthening effect by precipitate formation.

The vanadium is added in a content ratio of 0.001 wt% to 0.100 wt% of the total weight of the steel according to the present invention. If the content of vanadium is less than 0.001% by weight, it may be difficult to exhibit the effect of adding vanadium properly. On the other hand, if the addition amount of vanadium exceeds 0.100 wt%, it may become a factor to lower the impact resistance at low temperature.

titanium( Ti )

In the present invention, titanium (Ti) plays a role of suppressing the growth of austenite crystal grains by forming carbide upon reheating, and finely structuring the steel structure.

The titanium (Ti) is added in a content ratio of 0.001 wt% to 0.025 wt% of the total weight of the steel according to the present invention. When the content of titanium (Ti) is less than 0.001% by weight, the titanium addition effect can not be exhibited properly. On the contrary, when the content of titanium (Ti) exceeds 0.025% by weight, carbonized precipitates become coarse and the effect of suppressing grain growth is lowered.

Nitrogen (N)

Nitrogen (N) is an inevitable impurity, and there is a problem that inclusions such as AlN and TiN are formed and the quality of the steel is deteriorated.

The nitrogen (N) is limited to a content ratio of 0.0001% by weight to 0.0120% by weight of the total weight of the steel according to the present invention. If the content of nitrogen (N) is less than 0.0001% by weight, the nitrogen content must be controlled to a very small amount, resulting in an increase in manufacturing cost and difficulties in management. On the contrary, when the content of nitrogen (N) exceeds 0.0120% by weight, the solid solution nitrogen is increased and the impact characteristics and elongation rate of the steel are lowered and the toughness of the welded portion is greatly lowered.

Titanium: nitrogen (Ti: N)

The titanium and the nitrogen (Ti: N) are contained in a weight ratio of 1: 1 to 2.5: 1. When the weight of titanium is less than 1.0 weight ratio with respect to the weight of nitrogen (Ti: N), the effect of inhibiting grain growth by the TiN precipitates during reheating is reduced and austenite coarsening occurs. Also, the free N in the steel is increased, and the impact toughness may be lowered. On the contrary, when the weight of titanium is more than 2.5 weight% with respect to the weight of nitrogen (Ti: N), the content of nitrogen (N) binding to elements such as Al, V and Nb is insufficient, and the precipitation strengthening effect and grain refinement effect are deteriorated do.

In one embodiment, the titanium and the nitrogen (Ti: N) may be included in a weight ratio of 1: 1 to 2.0: 1. In this case, the precipitation strengthening effect and grain refinement effect are more excellent, and the strength and impact toughness can be further improved.

Section steel Manufacturing method

1 is a flowchart schematically showing a method of manufacturing a steel sheet according to an embodiment of the present invention. Referring to FIG. 1, the steel sheet manufacturing method includes a reheating step (S110), a hot rolling step (S120), and a cooling step (S130). At this time, the reheating step (S110) is not necessarily performed, but a reheating step (S110) is performed in order to derive effects such as reuse of the precipitate.

The semi-finished steel to be subjected to the hot rolling process in the steel forming method according to the present invention has the above-described alloy composition.

Reheating

In the reheating step (S110), the steel having the above alloy composition is reheated to 1050 캜 to 1250 캜. The steel having the alloy composition may be obtained through a continuous casting process after obtaining a molten steel having a desired composition through a steelmaking process. By reheating these steels, segregated components can be reused in casting.

If the reheating temperature is less than 1050 DEG C in this step, there is a problem that the segregated components are not sufficiently reused during casting. On the other hand, if the reheating temperature is higher than 1250 ° C, the austenite grain size may increase and the strength of the steel may be difficult to secure, and the steel manufacturing cost may be increased due to the excessive heating process.

Hot rolling

In the hot rolling step (S120), the reheated steel is hot-rolled to FRT (Finishing Rolling Temperature): 800 to 850 占 폚. In the present invention, the finishing hot rolling finishing temperature is relatively low at 800 ° C. to 850 ° C. If the finishing hot rolling finishing temperature is lowered as described above, crystal grains can be finer due to repetition of recovery and recrystallization during rolling.

If the finish rolling temperature (FRT) is lower than 800 ° C, coarse erosion ferrite is formed on the surface of the steel, and the strength may be lowered. On the other hand, when the finishing rolling temperature (FRT) exceeds 850 占 폚, the amount of reduction in the non-recrystallized region becomes 30% or less, and the impact toughness of the steel is rapidly deteriorated.

Although not shown in the drawing, universal rolling can be used for hot rolling. By this universal rolling, it can be rolled into a specific shape such as 'H' or 'I'. At this time, the universal rolling is performed in such a manner that the web and the flange of the steel are pressed in the up, down, left and right directions. That is, the universal rolling can be performed in such a manner that the universal rolling is pressed at a constant speed along a universal stand having a horizontal roll for pressing the steel web and a vertical roll for pressing the steel flange.

In the hot rolling step, a rolled material having a thickness of 12 mm to 40 mm is produced. In this case, variations in the physical properties depending on the shape generated when the steel sheet is rolled into a specific shape such as 'H' or 'I' can be reduced.

In one embodiment, the hot rolling step may comprise controlling the rolling speed from 5.2 m / s to 8.8 m / s to produce a rolled material having a thickness of 12 mm to 24 mm. In this case, the strength and impact toughness of the rolled material having a thickness of 12 mm to 24 mm can be further improved by acting in combination with the cooling step described later. At this time, the rolling starting temperature in the hot rolling step may be 1000 占 폚 to 1100 占 폚, for example, 1050 占 폚. In this case, the physical properties of the rolled material can be further improved at the rolling speed, and the deviation can be reduced.

In another embodiment, the hot rolling step may comprise controlling the rolling speed from 3.0 m / s to 4.4 m / s to produce a rolled material having a thickness greater than 24 mm and less than 40 mm. In this case, the strength and impact toughness of the rolled material having a thickness exceeding 24 mm to 40 mm can be further improved by acting in combination with the cooling step to be described later. More specifically, the rolling speed in the production of the rolled material having a thickness exceeding 24 mm to 40 mm may be 3.7 m / s to 4.4 m / s. The effect of improving the physical properties in the above range is more excellent.

At this time, the rolling starting temperature in the hot rolling step may be 1000 占 폚 to 1100 占 폚, for example, 1050 占 폚. In this case, the physical properties of the rolled material can be further improved at the rolling speed, and the deviation can be reduced.

Cooling

In the cooling step (S130), by controlling the cooling process according to the thickness of the rolled material, even when the section steel is manufactured by applying the TMCP process, variation in physical properties according to the shape can be reduced and strength and impact toughness can do.

In one embodiment, after the hot rolling step (S120), the rolled material having a thickness of 12 mm to 24 mm is cooled to a finishing cooling temperature (FCT) of 670 캜 to 700 캜. As a result, the strength and impact toughness of the section steel can be improved, and variations in physical properties according to the shape can be reduced. If the rolled material having the thickness of 12 to 24 mm has an FCT of less than 670 DEG C, the low temperature structure is excessively formed on the surface, the fraction of the low temperature structure is increased to 40% or more, and the elongation is reduced. On the contrary, when the rolled material having a thickness of 12 mm to 24 mm has an FCT of 700 ° C or higher, the effect of grain refinement due to cooling is deteriorated and a low-temperature transformed structure is not formed.

Specifically, the rolled material having the thickness of 12 mm to 24 mm can be cooled at a feed rate of 2.0 m / s to 3.0 m / s and a main feed quantity of 300 m / h to 1,000 m / h. In such a case, the shape of the steel sheet having a thickness of 12 mm to 24 mm can be reduced in variation in physical properties, and the strength and impact toughness can be further improved.

In another embodiment, after the hot rolling step (S120), the rolled material having a thickness exceeding 24 mm to 40 mm is cooled to a condition of 630 to 670 ° C (Finish Cooling Temperature). As a result, the strength and impact toughness of the section steel can be improved, and variations in physical properties according to the shape can be reduced. If the rolled material having a thickness of more than 24 mm and less than 40 mm has an FCT of less than 630 ° C, the low-temperature structure is excessively formed on the surface, the fraction of the low-temperature structure is increased to 40% or more, and the elongation is decreased. On the contrary, when the rolled material having a thickness of more than 24 mm and less than 40 mm has an FCT of more than 670 ° C, the effect of grain refinement due to cooling is deteriorated and a low temperature transformation structure is not formed.

Specifically, the rolled material having a thickness exceeding 24 mm to 40 mm may be cooled at a feed rate of 1.0 m / s to 1.9 m / s and a main feed quantity of 1,000 m / h to 1,500 m / h. In such a case, the section steel having a thickness of more than 24 mm and less than 40 mm can reduce the variation of physical properties depending on the shape, and the strength and impact toughness can be further improved.

In the method of manufacturing a steel sheet according to one embodiment, the volume fraction of the low-temperature structure in the thickness direction of the formed steel is 10% to 40%, and the low-temperature structure in the thickness direction may be controlled to include martensite and bainite. Not only the low-temperature impact toughness is further improved in the above-mentioned range, but also the lowering of the elongation can be prevented. In addition, it is more advantageous to achieve the desired yield strength, tensile strength and elongation. In this case, it is possible to provide a section steel for a building structure, in particular, a section steel suitable for application to a superstructure or an enlarged building structure.

Such a section steel can be manufactured through the method (S110 to S130) of the embodiment of the present invention. In addition, the section steel has the advantage of being applicable to the TMCP process and having a small variation in physical properties depending on the shape.

The weight ratio of Ti: N in the alloy composition may be 1: 1 to 2: 1. In this case, the precipitation strengthening effect and grain refinement effect are more excellent, and the strength and impact toughness can be further improved.

The yield strength (YS) of the section steel may be, for example, 490 MPa to 550 MPa or 497 MPa to 530 MPa.

The tensile strength (TS) of the section steel may be, for example, 600 MPa to 650 MPa or 602 MPa to 639 MPa.

The elongation (EL) of the section steel may be, for example, 22% to 30% or 22% to 28%.

The -20 占 폚 impact absorption energy of the section steel may be, for example, 100 J to 250 J, or 138 J to 225 J.

In the yield strength, the tensile strength, the elongation, and the impact absorption energy range of -20 占 폚, the shape steel can attain both the strength and the impact toughness at the same time while the variation of physical properties according to the shape is further reduced. In this case, due to the physical property variation according to the shape, the TMCP process is applied instead of the conventional technique of assembling the steel plates such as 'H' and 'I' in a built-up manner using a thick plate It is possible to provide a steel having excellent strength and impact toughness with less variation in physical properties even when it is produced by rolling in the form of 'H' or 'I'.

The section steel may have a volume fraction of low-temperature structure in the thickness direction of 10% to 40%, and the low-temperature structure in the thickness direction may include martensite and bainite. It is further advantageous to attain the desired yield strength, tensile strength and elongation, because the low temperature impact toughness of the section steel is further improved and the elongation is excellent in the above range.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Specimen Manufacturing

The steels of Examples 1 to 6 and Comparative Examples 1 to 7 satisfying the alloy composition shown in Table 1 and satisfying the weight ratio of Ti: N shown in Table 2 were produced. Then, the steel was hot-rolled and cooled under the process conditions shown in Table 2 to prepare specimens.

ingredient C Si Mn P S Al Nb V Ti N Minimum content 0.08 0.15 1.25 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Maximum content 0.14 0.4 1.6 0.025 0.025 0.055 0.05 0.1 0.025 0.012

(Unit: wt%)

Product thickness Ti: N Rolling end temperature Rolling speed Cooling end temperature Feeding speed Quantity (m ³ / h) Example 1 15 1.9: 1 825 8.8 682 2.8 620 Example 2 17 2.1: 1 811 5.8 686 2.7 760 Example 3 21 2.5: 1 819 5 675 2.8 980 Example 4 35 1.6: 1 839 3.5 645 1.3 1200 Example 5 37 1.9: 1 849 3.2 638 1.1 1390 Example 6 32 1.3: 1 834 4.2 651 1.5 1050 Comparative Example 1 15 1.3: 1 830 8.8 - - 0 (air cooling) Comparative Example 2 21 1.5: 1 907 8.8 - - 0 (air cooling) Comparative Example 3 35 2.1: 1 928 8.8 - - 0 (air cooling) Comparative Example 4 35 1.2: 1 839 3.5 721 1.5 800 Comparative Example 5 21 0.7: 1 832 5 699 2 980 Comparative Example 6 35 3.2: 1 840 3.5 663 1.4 1200 Comparative Example 7 21 1.6: 1 817 5 610 1.9 980

2. Evaluation of mechanical properties

Table 3 shows the results of evaluation of mechanical properties of the samples prepared according to Examples 1 to 6 and Comparative Examples 1 to 7.

The physical properties were measured by measuring tensile strength, yield strength, elongation, impact absorption energy at -20 ° C, and physical property deviations of sections.

The specimens of Examples 1 to 6 and Comparative Examples 1 to 7 were produced as "H" shaped steel, and the physical properties of the both ends in the longitudinal direction of the section steel and the center portion of the section steel were separately measured , And the difference between them was measured as a mean value converted to a percentage. When the deviation of the physical properties of the section steel is 15% or less, the symbol is marked with & cir &, 10% or less when the section is 15% or less.

TS (MPa) YS (MPa) EL (MPa) J @ -20 C Physical property deviation Low temperature tissue volume fraction (%) Example 1 629 497 25 178 ◎ 17 Example 2 602 523 28 225 ◎ 19 Example 3 628 522 22 186 ◎ 18 Example 4 611 518 27 158 ◎ 27 Example 5 639 536 24 138 ◎ 32 Example 6 635 530 24 190 ◎ 29 Comparative Example 1 563 469 29 222 X 0 Comparative Example 2 540 436 29 116 X 0 Comparative Example 3 537 424 33 78 X 0 Comparative Example 4 543 459 28 110 X 7 Comparative Example 5 597 492 25 88 X 12 Comparative Example 6 570 466 28 65 X 24 Comparative Example 7 713 602 18 203 X 45

Tables 1 to 3 show that the specimens prepared according to Examples 1 to 6 can be applied to the TMCP process and have a yield strength (YS) of 490 MPa or more, a tensile strength (TS) of 600 MPa or more, an elongation (EL) 22% or more and a shock absorption energy of 100 J or more at -20 ℃. In addition, the specimens prepared according to Examples 1 to 6 satisfied the volume fraction of the low-temperature structure in the range of 10% to 40%, and even when formed into the shape steel after the application of the TMCP process, the deviation of the property between the end portion and the center portion was 10% Respectively.

On the other hand, the specimens of Comparative Examples 1 to 3, in which the air cooling was performed differently from the cooling process shown in the present invention in the cooling step, did not produce cold structure and the yield strength was below the target value.

In the case of Comparative Examples 4 and 7 in which the cooling termination temperature (FCT) according to the thickness was out of the range suggested by the present invention, the tensile strength TS and the yield strength YS were less than the target value, This was below the target value.

Further, in the case of Comparative Examples 5 and 6 in which the weight ratio of Ti: N in the alloy composition was out of the range suggested by the present invention, the tensile strength (TS), the yield strength (YS) Respectively.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

S110: Reheating step
S120: Hot rolling step
S130: cooling step

Claims

(a) carbon: 0.08 wt.% to 0.14 wt.% silicon, 0.15 wt.% to 0.40 wt.% silicon, 1.25 wt.% to 1.60 wt.% manganese, 0.001 wt.% phosphorus, 0.001 wt% to 0.025 wt% of aluminum (Al), 0.001 wt% to 0.050 wt% of niobium (Nb), 0.001 wt% of vanadium (V) (Ti): 0.001 to 0.025 wt.%, Nitrogen (N): 0.0001 wt.% To 0.0120 wt.% And the balance of iron (Fe) and unavoidable impurities, wherein the titanium and nitrogen Reheating the steel of an alloy composition having a weight ratio (Ti: N) of 1: 1 to 2: 1 to 1050 캜 to 1250 캜;
(b) a hot rolling step of rolling the reheated steel to a finishing rolling temperature (FRT) of 800 to 850 占 폚 to produce a rolled material having a thickness of 12 to 40 mm; And
(c) After the hot rolling step, the rolled material having a thickness of 12 mm to 24 mm has a conveying speed of 2.0 m / s to 3.0 m / s at a finishing cooling temperature (FCT) of 670 캜 to 700 캜, / h, and the rolled material having a thickness exceeding 24 mm to 40 mm has a conveying speed of 1.0 m / s to 1.9 m / s and a conveying speed of 1,000 m / h to 1,500 m / s at 630 to 670 ° C under finishing cooling temperature (FCT) M < 3 > / h,
In the step (b), rolling material having a thickness of 12 mm to 24 mm is manufactured by controlling the rolling speed from 5.2 m / s to 8.8 m / s, or rolling speed is controlled from 3.0 m / s to 4.4 m / To 40 mm in diameter,
(YS) 497 MPa to 536 MPa, a tensile strength (TS) of 600, and a tensile strength (TS) of 600 MPa to 650 MPa, an elongation (EL) of 22% to 30%, and a -20 占 폚 shock absorption energy of 100J to 250J.

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(a) carbon: 0.08 wt.% to 0.14 wt.% silicon, 0.15 wt.% to 0.40 wt.% silicon, 1.25 wt.% to 1.60 wt.% manganese, 0.001 wt.% phosphorus, 0.001 wt% to 0.025 wt% of aluminum (Al), 0.001 wt% to 0.050 wt% of niobium (Nb), 0.001 wt% of vanadium (V) (Ti): 0.001 to 0.025 wt.%, Nitrogen (N): 0.0001 wt.% To 0.0120 wt.% And the balance of iron (Fe) and unavoidable impurities, wherein the titanium and nitrogen Wherein the thickness direction low-temperature structure has an alloy composition having a weight ratio (Ti: N) of 1: 1 to 2: 1, a thickness of 12 mm to 40 mm, (YS) of 497 MPa to 536 MPa, a tensile strength (TS) of 600 MPa to 650 MPa, an elongation (EL) of 22% to 30% and an impact absorption energy of 100 J to 250 J Satisfactory section.

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