KR102289520B1 - Steel reinforcement and method of manufacturing the same - Google Patents

Abstract

Reinforcing bars according to an embodiment of the present invention are carbon (C): 0.06 to 0.10% by weight, manganese (Mn): 1.2 to 2.0% by weight, silicon (Si): more than 0 0.25% by weight or less, chromium (Cr): 0 More than 0.25 wt%, Copper (Cu): More than 0 0.28 wt% or less, Molybdenum (Mo): 0.01 to 0.125 wt%, Nickel (Ni): 0.5 to 0.65 wt%, Phosphorus (P): More than 0 0.01 Weight % or less, sulfur (S): more than 0 and less than 0.01 wt%, nitrogen (N): more than 0 and less than or equal to 0.01 wt%, and the remaining iron (Fe) and other unavoidable impurities, but with a yield strength (YS) of 600 MPa at room temperature or more, the ratio of tensile strength to yield strength (TS/YS) is 1.08 or more, and the elongation is 12% or more.

Description

Rebar and its manufacturing method

The present invention relates to a reinforcing bar and a method for manufacturing the same, and more particularly, to a high-strength rebar for cryogenic use and a method for manufacturing the same.

As interest in eco-friendliness increases worldwide, interest in natural gas is increasing. LNG is expected to increase by 46.1% from 2.9 billion TOU of the total energy mix in 2013 to 4.2 billion TOU by 2040. Natural gas is transported to and stored in the LNG terminal through the refining-liquefaction process. Natural gas is liquefied at -170°C (cryogenic) or lower to become liquefied natural gas (LNG). An LNG tank for storing cryogenic LNG requires a special structure and materials that can withstand cryogenic temperatures. The LNG Tank is largely composed of an inner shell and an outer shell, each of which is composed of 9% Ni steel and reinforced concrete. The complete protection type design method in which the inner and outer tanks are closely attached is the current trend of the LNG tank design method, and reinforcing bars that guarantee -170°C are used for the outer tank. This is a crack in the inner tank, and when LNG comes into contact with the outer tank, it is known to maintain structural integrity without causing brittle fracture even when the temperature drops rapidly. Such reinforcing bars used as outer walls for LNG tanks are being applied to many LNG tanks and terminals abroad.

As a related prior art, there is Korean Patent Laid-Open Publication No. 10-2003-0095071, title of invention: method for manufacturing high-yield ratio high-strength hot-dip galvanized rebar).

In order to solve the above problems, the technical problem to be achieved by the present invention is a reinforcing bar that has excellent mechanical properties at room temperature strength (YS 600 MPa class), and can also secure cryogenic toughness, ductility, and strength, and a method for manufacturing the same is to provide

Reinforcing bars according to an embodiment of the present invention for achieving the above object is carbon (C): 0.06 to 0.10% by weight, manganese (Mn): 1.2 to 2.0% by weight, silicon (Si): 0 to 0.25% by weight or less, Chromium (Cr): more than 0 0.25% by weight, copper (Cu): more than 0, 0.28% by weight or less, molybdenum (Mo): 0.01 to 0.125% by weight, nickel (Ni): 0.5 to 0.65% by weight, phosphorus ( P): greater than 0 and less than 0.01% by weight, sulfur (S): greater than 0 and less than or equal to 0.01% by weight, nitrogen (N): greater than 0 and less than or equal to 0.01% by weight, and the remaining iron (Fe) and other unavoidable impurities, but yield at room temperature The strength (YS) is 600 MPa or more, the ratio of tensile strength to yield strength (TS/YS) is 1.08 or more, and the elongation is 12% or more.

The reinforcing bar may have a yield strength (YS) of 575 MPa or more at a temperature of -170° C., and an elongation of 3% or more.

In the reinforcing bar, the final microstructure may include ferrite and tempered martensite.

The method of manufacturing a reinforcing bar according to an embodiment of the present invention for achieving the above object is (a) carbon (C): 0.06 to 0.10 wt%, manganese (Mn): 1.2 to 2.0 wt%, silicon (Si): 0 More than 0.25 wt%, Chromium (Cr): More than 0 0.25 wt% or less, Copper (Cu): More than 0, 0.28 wt% or less, Molybdenum (Mo): 0.01 to 0.125 wt%, Nickel (Ni): 0.5 to 0.65% by weight, phosphorus (P): greater than 0 and less than 0.01% by weight, sulfur (S): greater than 0 and less than or equal to 0.01% by weight, nitrogen (N): greater than 0 and less than or equal to 0.01% by weight, and remaining iron (Fe) and other unavoidable impurities Reheating the steel material made at 1000 ~ 1100 ℃; (b) hot-rolling the reheated steel to a final finish rolling temperature condition of 920 ~ 1000 ℃; and (c) performing a temp core process on the hot-rolled steel; includes

In the manufacturing method of the reinforcing bar, the step (c) may include a step of rapidly cooling the surface to a martensite starting temperature (Ms), and then reheating to 570 ~ 580 °C.

In the method of manufacturing the reinforcing bar, after performing step (c), the final microstructure of the reinforcing bar may include ferrite and tempered martensite.

In the method of manufacturing the reinforcing bar, the reinforcing bar implemented by performing the steps (a) to (c) has a yield strength (YS) of 600 MPa or more at room temperature, and a ratio of tensile strength to yield strength (TS/YS) is 1.08 or more, the elongation is 12% or more, the yield strength (YS) at a temperature of -170 ° C. is 575 MPa or more, and the elongation may be 3% or more.

According to an embodiment of the present invention, it is possible to implement a reinforcing bar that has excellent mechanical properties at room temperature strength (YS 600 MPa class), and further, can secure cryogenic toughness, ductility, and strength, 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 schematically showing a method of manufacturing a reinforcing bar according to an embodiment of the present invention.

A reinforcing bar and a method for manufacturing the same according to an embodiment of the present invention will be described in detail. The terms described below are appropriately selected in consideration of their functions in the present invention, and definitions of these terms should be made based on the content throughout this specification. Hereinafter, it is intended to provide specific details for carrying out a large-standard rebar and a method for manufacturing the same while having high strength.

rebar

Reinforcing bars according to an embodiment of the present invention are carbon (C): 0.06 to 0.10% by weight, manganese (Mn): 1.2 to 2.0% by weight, silicon (Si): more than 0 0.25% by weight or less, chromium (Cr): 0 More than 0.25 wt%, Copper (Cu): More than 0 0.28 wt% or less, Molybdenum (Mo): 0.01 to 0.125 wt%, Nickel (Ni): 0.5 to 0.65 wt%, Phosphorus (P): More than 0 0.01 Weight % or less, sulfur (S): more than 0 and 0.01 wt% or less, nitrogen (N): more than 0 and 0.01 wt% or less, and the remaining iron (Fe) and other unavoidable impurities.

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

Carbon (C): 0.06 to 0.10 wt%

Carbon (C) is the most effective and important element for increasing the strength of steel. It is dissolved in austenite to form a martensitic structure during quenching. As the amount of carbon increases, the quenching hardness is improved, but the possibility of deformation during quenching is increased. Combines with elements such as iron, chromium, molybdenum, and vanadium to form carbides, improving strength and hardness. Carbon (C) may be added in a content ratio of 0.06 to 0.10% by weight of the total weight of the reinforcing bar according to an embodiment of the present invention. When the content of carbon is less than 0.06% by weight of the total weight, the above-described effect cannot be realized and it may be difficult to secure sufficient strength. Conversely, when the content of carbon exceeds 0.10% by weight of the total weight, excessive strength and poor weldability may appear.

Manganese (Mn): 1.2 to 2.0 wt%

Manganese (Mn) is partially dissolved in steel and some is combined with sulfur contained in steel to form MnS, a non-metallic inclusion. MnS is ductile and is elongated in the machining direction during plastic working. However, as the sulfur content in the steel decreases due to the formation of Mns, the crystal grains become weak and the formation of FeS, a low-melting-point compound, is suppressed. It inhibits the acid resistance and oxidation resistance of steel, but improves the yield strength by making pearlite finer and strengthening ferrite in solid solution. Manganese may be added in a content ratio of 1.2 to 2.0% by weight of the total weight of the reinforcing bar according to an embodiment of the present invention. When the manganese content is less than 1.2% by weight, the above-described effect of adding manganese cannot be sufficiently exhibited. In addition, when the content of manganese exceeds 2.0% by weight, quenching cracks or deformation is caused, weldability is lowered, MnS inclusions and center segregation occur, so that the ductility of the rebar is lowered and the corrosion resistance is lowered. can

Silicon (Si): greater than 0 0.25% by weight or less

Silicon (Si) is well known as a ferrite stabilizing element and is well known as an element that increases ductility by increasing the ferrite fraction during cooling. On the other hand, silicon is added together with aluminum as a deoxidizer for removing oxygen in steel in the steelmaking process, and may also have a solid solution strengthening effect. Silicon remains from pig iron and deoxidizer, _{and as long as it does not form a compound such as SiO 2} , it is dissolved in ferrite, so it does not significantly affect the mechanical properties of steel. The silicon may be added in a content ratio of greater than 0 and 0.25% by weight or less of the total weight of the reinforcing bar according to an embodiment of the present invention. When the content of silicon exceeds 0.25% by weight of the total weight, when a large amount is added, there is a problem of lowering toughness and lowering plastic workability, lowering weldability of steel, and generating red scale during reheating and hot rolling. It can cause quality problems.

Chromium (Cr): more than 0 0.25 wt% or less

Chromium (Cr) is a ferrite stabilizing element, and when added to C-Mn steel, it 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 greater than 0 and 0.25% by weight or less of the total weight of the reinforcing bar according to an embodiment of the present invention. When the content of chromium exceeds 0.25% by weight of the total weight, when a large amount is added, toughness may be lowered and workability and machinability may deteriorate.

Copper (Cu): More than 0 0.28% by weight or less

Copper (Cu) is an element that improves hardenability and low-temperature impact toughness of steel. Since it is dissolved in ferrite at room temperature and exhibits a solid solution strengthening effect, strength and hardness are slightly improved, but elongation is reduced. The copper may be added in a content ratio of more than 0 and 0.28% by weight or less of the total weight of the reinforcing bar according to an embodiment of the present invention. When the content of copper exceeds 0.28% by weight of the total weight, hot workability deteriorates when a large amount is added, which may cause red hot brittleness and impair product surface quality.

Molybdenum (Mo): 0.01 to 0.125 wt%

Molybdenum (Mo) is an element that can improve hardenability by about 10 times that of nickel, and is an element that provides temper brittle resistance by preventing temper embrittlement. Since molybdenum forms carbide, it has an excellent effect as an alloying element for advanced cutting tools and increases the grain coarsening temperature. To improve hardenability, the effect is better when used with chromium than when used alone. The molybdenum may be added in a content ratio of 0.01 to 0.125% by weight of the total weight of the reinforcing bar according to an embodiment of the present invention. When the content of molybdenum is less than 0.01% by weight of the total weight, the above-described effect does not appear, and when the content of molybdenum exceeds 0.125% by weight of the total weight, when a large amount is added, weldability is lowered and the manufacturing cost of parts is increased. occurs

Nickel (Ni): 0.5 to 0.65 wt%

Nickel (Ni) is an element that increases hardenability and improves toughness. The nickel may be added in a content ratio of 0.5 to 0.65% by weight of the total weight of the reinforcing bar according to an embodiment of the present invention. When the content of nickel is less than 0.5% by weight of the total weight, the above-described effect does not appear, and when the content of nickel exceeds 0.65% by weight of the total weight, when a large amount is added, the manufacturing cost of the part is increased.

Phosphorus (P): greater than 0 0.01% by weight or less

Phosphorus (P) increases the strength of the strength by solid solution strengthening, and may perform a function of suppressing the formation of carbides. Phosphorus is not a problem if it is uniformly distributed in the steel, but usually forms harmful compounds of _{Fe 3 P.} This Fe ₃ P is extremely brittle and segregated, so it does not become homogenized even after annealing, and elongates during processing such as forging and rolling. It lowers impact resistance, promotes temper brittleness, improves machinability in free-cutting steel, but is generally treated as an element harmful to steel. The phosphorus may be added in a content ratio of greater than 0 and 0.01 wt% or less of the total weight of the reinforcing bar according to an embodiment of the present invention. When the phosphorus content exceeds 0.01% by weight, there is a problem in that the low-temperature impact value is lowered by the above-described precipitation behavior.

Sulfur (S): more than 0 0.01% by weight or less

Sulfur (S) combines with manganese, molybdenum, etc. to improve the machinability of steel, and forms MnS inclusions by combining with manganese. If the amount of manganese in steel is insufficient, it combines with iron to form FeS. Because this FeS is very brittle and has a low melting point, it cracks during hot and cold working. Therefore, in order to avoid the formation of such FeS inclusions, the ratio of manganese to sulfur can be set to 5:1. The sulfur may be added in a content ratio of greater than 0 to 0.01% by weight or less of the total weight of the reinforcing bar according to an embodiment of the present invention. When the content of sulfur exceeds 0.01% by weight, toughness and weldability may be impaired, and a low-temperature impact value may be reduced.

Nitrogen (N): greater than 0 and less than or equal to 0.01% by weight

Nitrogen (N) has a great effect on the mechanical properties of steel even in very small amounts. It is an element that increases tensile strength and yield strength while decreasing elongation. In particular, a decrease in the impact value and an increase in the transition temperature are remarkable. Nitrogen, as an interstitial element, has a fast diffusion rate and shows continuous solubility changes in ferrite. In addition, the crystal grains are refined by forming nitrides such as vanadium. In the present invention, for the purpose of refining the high temperature austenite grain size and solid solution strengthening through VN formation, the nitrogen may be added in a content ratio of greater than 0 to 0.01% by weight or less of the total weight of the reinforcing bar according to an embodiment of the present invention. When the content of nitrogen exceeds 0.01% by weight of the total weight, it may act as an element impairing toughness when a large amount is added.

As described above, the final microstructure of the reinforcing bar according to an embodiment of the present invention having an alloy element composition may include ferrite and tempered martensite.

In addition, the reinforcing bar according to an embodiment of the present invention having the alloy element composition as described above has a yield strength (YS) of 600 MPa or more at room temperature, a ratio of tensile strength to yield strength (TS/YS) is 1.08 or more, and an elongation This is 12% or more, the yield strength (YS) at a temperature of -170 ℃ is 575 MPa or more, and the elongation may be 3% or more.

Hereinafter, a method for manufacturing a reinforcing bar according to an embodiment of the present invention having the above-described alloying element composition will be described.

Method of manufacturing rebar

1 is a flowchart schematically showing a method of manufacturing a reinforcing bar according to an embodiment of the present invention.

Referring to Figure 1, the method of manufacturing a reinforcing bar according to an embodiment of the present invention is (a) carbon (C): 0.06 to 0.10 wt%, manganese (Mn): 1.2 to 2.0 wt%, silicon (Si): 0 More than 0.25 wt%, Chromium (Cr): More than 0 0.25 wt% or less, Copper (Cu): More than 0, 0.28 wt% or less, Molybdenum (Mo): 0.01 to 0.125 wt%, Nickel (Ni): 0.5 to 0.65% by weight, phosphorus (P): greater than 0 and less than 0.01% by weight, sulfur (S): greater than 0 and less than or equal to 0.01% by weight, nitrogen (N): greater than 0 and less than or equal to 0.01% by weight, and remaining iron (Fe) and other unavoidable impurities Reheating the steel material made at 1000 ~ 1100 ℃ (S100); (b) hot-rolling the reheated steel to a final finish rolling temperature condition of 920 ~ 1000 °C (S200); and (c) performing a temp core process on the hot-rolled steel (S300); includes

The rebar steelmaking/casting process generally consists of an electric furnace, LF, and casting. In the method of manufacturing rebar according to an embodiment of the present invention, after LF, which is a secondary refining process, a vacuum degassing (VD) process was performed to lower the oxygen content, and then solidified into a semi-material in the casting process to improve fatigue resistance.

The rolling process is manufactured through a reheating process, a hot deformation process, and a cooling process. In the reheating process, the semi-finished billet is reheated to 1000 ~ 1100℃. Next, the hot rolling process goes through each of the rolling rolls (RM, IM, FM) and the final finishing rolling is completed at 920 ~ 1000℃, and then goes through a tempcore and the surface goes through the martensite starting temperature (Ms). After rapid cooling, it is characterized in that it comprises a recuperation step to 570 ~ 580 ℃.

The steel material is carbon (C): 0.06 to 0.10% by weight, manganese (Mn): 1.2 to 2.0% by weight, silicon (Si): more than 0 0.25% by weight, chromium (Cr): more than 0, 0.25% by weight or less, copper (Cu): more than 0 0.28% by weight or less, molybdenum (Mo): 0.01 to 0.125% by weight, nickel (Ni): 0.5 to 0.65% by weight, phosphorus (P): more than 0, 0.01% by weight or less, sulfur (S) ): more than 0 and less than 0.01% by weight, nitrogen (N): greater than 0 and less than or equal to 0.01% by weight, and the remaining iron (Fe) and other unavoidable impurities.

In one embodiment, the steel may be reheated at a temperature of 1000 ~ 1100 ℃. When the steel is re-heated at the above-described temperature, the segregated components may be re-dissolved during the continuous casting process. When the reheating temperature is lower than 1000°C, the solid solution of various carbides may not be sufficient, and there may be a problem that the segregated components are not sufficiently evenly distributed during the continuous casting process. When the reheating temperature exceeds 1100° C., it may be difficult to secure strength because very coarse austenite grains are formed. In addition, when it exceeds 1100° C., heating cost increases and process time is added, which may result in an increase in manufacturing cost and a decrease in productivity.

In the hot rolling step (S200), the reheated steel material is hot rolled. The rolling starts at 1000 ~ 1050 ℃ and the final deformation is finished at 920 ~ 1000 ℃ in the hot deformation finishing temperature range, and a fine austenite structure and precipitates containing vanadium (V) can be formed through dynamic recrystallization.

On the other hand, if the hot rolling temperature is too low, the rolling load is increased during rolling and a mixed structure of the edge (EDGE) portion may be generated, so that the hot finishing temperature may be preferably 920° C. or higher.

In the step (S300) of performing the temp core process, the temp core cooling temperature is in the range of 570 ~ 580 °C. When the temperature increases, the lamellar spacing between ferrite and pearlite increases, making it difficult to act as an obstacle to dislocation movement, resulting in a decrease in strength. Such defects may occur and work as a crack growth site to decrease machinability.

So far, a method for manufacturing a reinforcing bar according to an embodiment of the present invention has been described. According to this, the reinforcing bar is in weight%, carbon (C): 0.06 to 0.10%, silicon (Si): 0.25% or less, manganese (Mn): 1.20 to 2.0%, phosphorus (P): 0.01% or less, S: 0.01% or less, Nickel (Ni): 0.50 to 0.65%, Molybdenum (Mo): 0.010 to 0.125%, Chromium (Cr): 0.25% or less, Copper (Cu): 0.28% or less: Nitrogen (N): 0.01 % or less, and the remainder is characterized in that it consists of iron (Fe) and unavoidable impurities. The cryogenic rebar rolling process is manufactured through a reheating process, a hot rolling process, and a cooling process. It is manufactured through reheating process, hot deformation process, and cooling process. In the reheating process, the semi-finished billet is reheated to 1,000 ~ 1,100℃. Next, the hot rolling process goes through each rolling roll (RM, IM, FM), and the final finishing rolling is completed at 920 ~ 1,000℃, and then goes through a tempcore cooling process, the surface is quenched to Ms, and then again It is characterized in that it comprises a recuperation step to 570 ~ 580 ℃.

One of the technical ideas of the present invention is to reduce the cost by lowering the content of the alloy component while strengthening the strength of the reinforcing bar for the LNG tank. Disclosed is a method capable of reducing Mn and Mo components compared to the prior art and securing mechanical properties at room temperature and cryogenic temperature by controlling the cooling rate. The cryogenic reinforcing bar manufactured through the present invention can secure high strength at room temperature yield strength of 600 MPa or more and cryogenic toughness, so it facilitates securing social safety, so it has a wide range of application as a safety steel material when applied to external structures of LNG tanks, civil engineering and building structures in polar regions. . According to the increase in strength, it is possible to reduce the construction cost by securing the space between rebars and preventing overcrowding, thereby shortening the construction period and reducing the amount of rebars used.

Experimental example

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

In this experimental example, the main alloy element composition (unit: weight ratio %) of Table 1 and the specimens implemented with the process conditions of Table 2 are provided.

C Si Mn P S Cr Cu Ni Mo N, (ppm) Experimental Example 1 0.07 0.06 1.83 0.010 0.010 0.08 0.11 0.59 0.12 90 Experimental Example 2 0.06 0.13 1.53 0.009 0.004 0.09 0.10 0.56 0.02 97

Referring to Table 1, Experimental Example 1 and Experimental Example 2 are carbon (C): 0.06 to 0.10% by weight, manganese (Mn): 1.2 to 2.0% by weight, silicon (Si): more than 0 0.25% by weight or less, chromium ( Cr): more than 0 0.25% by weight, copper (Cu): more than 0, 0.28% by weight or less, molybdenum (Mo): 0.01 to 0.125% by weight, nickel (Ni): 0.5 to 0.65% by weight, phosphorus (P) : 0 more than 0.01 wt%, sulfur (S): more than 0 0.01 wt% or less, nitrogen (N): more than 0 0.01 wt% or less, and the rest of the iron (Fe) composition range is satisfied. However, the content of Mn and Mo is relatively lower in Experimental Example 2 than in Experimental Example 1.

extraction temperature
(℃) final
Finishing rolling temperature (℃) quantity speed
(m/s) recuperation temperature
(℃) Experimental Example 1 1,050 950 1,005 11.0 610 Experimental Example 2 1,050 950 1,005 10.5 580

Referring to Table 2, Experimental Example 1 comprises the steps of reheating the steel at 1000 ~ 1100 ℃; hot rolling the reheated steel material to a final finish rolling temperature condition of 920 ~ 1000 °C; And after quenching to the martensite starting temperature (Ms), the step of recuperating to 610 ~ 620 ℃ is applied. In contrast, Experimental Example 2 comprises the steps of reheating the steel at 1000 ~ 1100 ℃; hot rolling the reheated steel material to a final finish rolling temperature condition of 920 ~ 1000 °C; And after quenching to the martensite starting temperature (Ms), the step of recuperating to 570 ~ 580 ℃ is applied.

Table 3 shows the material evaluation results according to the experimental example of the present invention. Items ① to ③ are room temperature material evaluation results, and items ④ to ⑦ are cryogenic (-170°C) material evaluation results. Specifically, item ① is yield strength at room temperature, item ② is tensile strength at room temperature, item ③ is elongation at room temperature, item ④ is uniform yield strength at cryogenic temperature, item ⑤ is uniform elongation at cryogenic temperature, and item ⑥ is Yield strength at cryogenic temperature, item ⑦ is notch sensitivity.

①
YS
(MPa) ②
TS, (MPa) ③
EL, (%) ④
YS_un, (MPa) ⑤
UE_un, (%) ⑥
TS_n, (MPa) ⑦
NSR Experimental Example 1 564 677 15.4 810 9.0 936 1.12 Experimental Example 2 625 677 14.0 802 8.4 815 1.02

Referring to Table 3, it can be confirmed that in Experimental Example 2, although the content of Mn and Mo is relatively lower than in Experimental Example 1, the material properties can be secured at an almost equal level at room temperature and cryogenic temperature. That is, Experimental Example 2 discloses a method capable of reducing Mn and Mo components compared to Experimental Example 1 and securing mechanical properties at room temperature and cryogenic temperature by controlling the cooling rate. The cryogenic reinforcing bar manufactured by Experimental Example 2 can secure high strength at room temperature yield strength of 600 MPa or higher and cryogenic toughness, thereby facilitating social safety assurance, and the scope of application as a safety steel material when applied to the outer structure of the LNG tank, civil engineering and building structures in the polar region expected to be wide.

Although the above description has been focused on the embodiments of the present invention, various changes or modifications may be made at the level of those skilled in the art. Such changes and modifications can be said to belong to the present invention without departing from the scope of the present invention. Accordingly, the scope of the present invention should be judged by the claims described below.

Claims (7)

Carbon (C): 0.06 to 0.10 wt%, Manganese (Mn): 1.2 to 2.0 wt%, silicon (Si): more than 0 and 0.25 wt% or less, Chromium (Cr): more than 0 to 0.25 wt% or less, copper (Cu) : 0 to 0.28 wt% or less, Molybdenum (Mo): 0.01 to 0.02 wt%, Nickel (Ni): 0.5 to 0.65 wt%, Phosphorus (P): 0 to 0.01 wt% or less, Sulfur (S): 0 Exceeding 0.01% by weight or less, nitrogen (N): more than 0 and 0.01% by weight or less, and the remainder consisting of iron (Fe) and other unavoidable impurities,
The yield strength (YS) at room temperature is 600 MPa or more, the ratio of tensile strength to yield strength (TS/YS) is 1.08 or more, and the elongation is 12% or more,
The yield strength (YS) at a temperature of -170 ℃ is 575 MPa or more, and the elongation is 3% or more,
rebar.
delete The method of claim 1,
The final microstructure contains ferrite and tempered martensite,
rebar. (a) carbon (C): 0.06 to 0.10 wt%, manganese (Mn): 1.2 to 2.0 wt%, silicon (Si): more than 0 and 0.25 wt% or less, chromium (Cr): more than 0 to 0.25 wt% or less, copper (Cu): more than 0 0.28% by weight or less, molybdenum (Mo): 0.01 to 0.02% by weight, nickel (Ni): 0.5 to 0.65% by weight, phosphorus (P): more than 0, 0.01% by weight or less, sulfur (S) ): greater than 0 and less than 0.01% by weight, nitrogen (N): greater than 0 and less than or equal to 0.01% by weight and the remaining iron (Fe) and other unavoidable impurities comprising the steps of reheating the steel at 1000 ~ 1100 ℃;
(b) hot-rolling the reheated steel to a final finish rolling temperature condition of 920 ~ 1000 ℃; and
(c) performing a temp core process on the hot-rolled steel; includes,
The step (c) is a method of manufacturing a reinforcing bar comprising the step of rapidly cooling the surface of the steel material to a martensite starting temperature (Ms), and then reheating to 570 ~ 580 ° C.,
The reinforcing bars implemented by performing steps (a) to (c) have a yield strength (YS) of 600 MPa or more at room temperature, a ratio of tensile strength to yield strength (TS/YS) of 1.08 or more, and an elongation of 12 % or more, the yield strength (YS) at a temperature of -170 ℃ is 575 MPa or more, characterized in that the elongation is 3% or more,
Method of manufacturing rebar.
delete 5. The method of claim 4,
After performing the step (c), the final microstructure of the reinforcing bar comprises ferrite and tempered martensite,
Method of manufacturing rebar. delete

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