KR20200025263A - High strength steel reinforcement and method of manufacturing the same - Google Patents

Abstract

According to an embodiment of the present invention, a reinforcing bar comprises 0.1-0.4 wt% of carbon (C), 0.05-0.5 wt% of silicon (Si), 0.5-2 wt% of manganese (Mn), 0-0.05 wt% (excluding 0 wt%) of phosphorus (P), 0-0.025 wt% (excluding 0 wt%) of sulfur (S), 0-0.4 wt% (excluding 0 wt%) of copper (Cu), 0-0.1 wt% (excluding 0 wt%) of vanadium (V), 0.1-1 wt% of chrome (Cr), 0-0.5 wt% (excluding 0 wt%) of molybdenum (Mo), 0-0.25 wt% (excluding 0 wt%) of nickel (Ni), 0-0.1 wt% (excluding 0 wt%) of tin (Sn), 0.015-0.07 wt% of aluminum (Al), 0.005-0.025 wt% of nitrogen (N), and the remainder consisting of iron (Fe) and inevitable impurities. The reinforcing bar includes a surface layer portion and a center portion excluding the surface layer portion. The reinforcing bar includes a hardened layer substantially consisting of tempered martensite in the surface layer portion and has a composite structure of ferrite and perlite in the center portion.

Description

High Strength Reinforcing Bar and Manufacturing Method Thereof {HIGH STRENGTH STEEL REINFORCEMENT AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to high strength reinforcing bars and a method of manufacturing the same.

Carbon steels are being applied to structures to secure space for human activities. As an example, the carbon steel is a structural steel, and has been widely applied to various fields such as high-rise buildings, long bridges, large marine structures, underground structures, and storage. As an example of the structural steel, rebar is applied.

On the other hand, the carbon steel can be applied to various industries in the form of rebar. As an example, in the case of rebars applied to a structure, it is required to have high strength and high seismic characteristics as the structure becomes ultra high and large. That is, with the recent increase in the compressive strength of concrete, the strength of the reinforcing bar needs to be increased to correspond to the strength of the elevated concrete, even for the structure in which the concrete and the reinforcing bar are mixed.

Background art related to the present invention is Republic of Korea Patent No. 10-1757591.

The present invention provides reinforcing bars having high strength and high seismic properties through alloying components and process control.

Reinforcing bar according to an aspect of the present invention is 0.10% to 0.40% by weight of carbon (C), 0.05% to 0.50% by weight of silicon (Si), 0.50% to 2.0% by weight of manganese (Mn), phosphorus (P) 0 Greater than 0.05 wt% or less, sulfur (S) greater than 0 0.025 wt% or less, copper (Cu) greater than 0 0.40 wt% or less, vanadium (V) greater than 0 0.10 wt% or less, chromium (Cr) 0.10 wt% to 1.00 wt% Or less, molybdenum (Mo) greater than 0, 0.50 wt% or less, nickel (Ni) greater than 0, 0.25 wt% or less, tin (Sn), greater than 0, 0.1 wt% or less, aluminum (Al) 0.015 wt% to 0.070 wt%, nitrogen (N) ) 0.005% to 0.025% by weight, and the remaining iron (Fe) and inevitable impurities. The reinforcing bar has a surface layer portion and a central portion except for the surface layer portion, wherein the reinforcing bar has a hardened layer made of substantially tempered martensite at the surface layer portion, and has a complex structure of ferrite and pearlite at the central portion.

In one embodiment, the reinforcing bar may satisfy the yield strength (YS) of 500 MPa or more, the tensile strength (TS) / yield strength (YS) ratio of 1.25 or more and elongation 10% or more at room temperature.

In one embodiment, in the central portion, the tissue fraction of the ferrite in the composite tissue may be 35% or more.

Method for producing a rebar according to an aspect of the present invention, carbon (C) 0.10% to 0.40% by weight, silicon (Si) 0.05% to 0.50% by weight, manganese (Mn) 0.50% to 2.0% by weight, phosphorus (P) greater than 0 and 0.05 wt% or less, sulfur (S) greater than 0 and 0.025 wt% or less, copper (Cu) greater than 0 and 0.40 wt% or less, vanadium (V) greater than 0 and 0.10 wt% or less, chromium (Cr) 0.10 wt% To 1.00 wt% or less, molybdenum (Mo) greater than 0, 0.50 wt% or less, nickel (Ni) greater than 0, 0.25 wt% or less, tin (Sn) greater than 0, 0.1 wt% or less, aluminum (Al) 0.015 wt% to 0.070 wt% Reheating the cast steel consisting of 0.005% to 0.025% by weight of nitrogen (N) and the remaining iron (Fe) and unavoidable impurities at 1150 ° C to 1250 ° C; Finished rolling temperature of the reheated slab at 950 ° C to 1000 ° C Hot rolling to form a rebar; And cooling the hot rolled reinforcing bar to a temperature below the martensite transformation start temperature (Ms temperature) through the temper core. The temp core process includes regenerating the reinforcing bar at 500 ° C to 700 ° C.

In one embodiment, the reinforcing bar has a central portion except for the surface layer portion and the surface layer portion, it may be provided with a cured layer consisting of tempered martensite at the surface layer portion. In addition, the central portion may have a complex structure of ferrite and pearlite.

In one embodiment, the manufactured reinforcing bar may satisfy the yield strength (YS) of 500 MPa or more, the tensile strength (TS) / yield strength (YS) ratio of 1.25 or more and elongation 10% or more at room temperature.

In one embodiment, the reinforcing bar is the tissue fraction of the ferrite in the complex in the center may be more than 35%.

According to the present invention, high strength and high strength satisfying the yield strength (YS) of 500 MPa or more, the tensile strength (TS) / yield strength (YS) of 1.25 or more and elongation 10% or more at room temperature through optimized alloy composition and process control It is possible to provide a rebar having a seismic characteristic and a method of manufacturing the same.

1 is a flow chart schematically showing a method for manufacturing a rebar according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail to be easily carried out by those of ordinary skill in the art. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Like reference numerals designate like or similar components throughout the specification. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

Embodiments of the present invention described below provide a reinforcing bar having high strength and high seismic characteristics through proper component design and process control. Embodiments of the present invention have a steel grade design with a relatively reduced content of expensive precipitation hardening alloying elements such as vanadium. As a result, high-strength seismic reinforcing bars having stable seismic performance can be manufactured at low cost.

rebar

Reinforcing bar according to an embodiment of the present invention is 0.10% to 0.40% by weight of carbon (C), 0.05% to 0.50% by weight of silicon (Si), 0.50% to 2.0% by weight of manganese (Mn), phosphorus (P) Greater than 0 and 0.05 wt% or less, sulfur (S) greater than 0 and 0.025 wt% or less, copper (Cu) greater than 0 and 0.40 wt% or less, vanadium (V) greater than 0 and 0.10 wt% or less, chromium (Cr) 0.10 wt% and 1.00 wt% % Or less, molybdenum (Mo) greater than 0 0.50% by weight, nickel (Ni) greater than 0 0.25% by weight, tin (Sn) greater than 0, 0.1% by weight, aluminum (Al) 0.015% to 0.070% by weight, nitrogen ( N) 0.005% to 0.025% by weight, and the remaining iron (Fe) and unavoidable impurities.

The rebar may have a central portion except for the surface layer portion and the surface layer portion. The reinforcing bar may be provided with a hardened layer made of temper martensite at the surface layer portion. The reinforcing bar may have a complex structure consisting of ferrite and pearlite at the central portion.

The reinforcing bar may satisfy a yield strength (YS) of 500 MPa or more, a tensile strength (TS) / yield strength (YS) of 1.25 or more and an elongation of 10% or more at room temperature. The reinforcing bar may have a tissue fraction of the ferrite of 35% or more in the complex structure of the central portion.

Hereinafter, the role and content of each component included in the rebar according to the present invention will be described.

Carbon (C)

In the present invention, carbon (C) is added to secure the strength and hardness of the steel. Typically, carbon (C) is dissolved in austenite to form martensite tissue when quenched. In addition, quenching hardness is generally improved as the amount of carbon increases, but deformation due to rapid cooling may occur, or steel elongation and low temperature toughness may decrease.

The carbon (C) is added in an amount of 0.10% to 0.40% by weight of the total rebar weight. If the carbon content is less than 0.10% by weight, it is difficult to secure sufficient strength. Conversely, when the content of carbon (C) exceeds 0.40% by weight, the strength of the steel is increased, but it may be difficult to secure sufficient elongation and low temperature toughness.

Silicon (Si)

In the present invention, silicon (Si) is added as a deoxidizer for removing oxygen in the steel in the steelmaking process. In addition, silicon (Si) is a ferrite stabilizing element having a solid solution strengthening effect and is effective in inducing ferrite formation to improve toughness and ductility of steel.

The silicon (Si) is added in an amount of 0.05 wt% to 0.50 wt% or less of the total rebar weight. On the other hand, when the content of silicon (Si) is less than 0.05% by weight, it is difficult to achieve the above-described effects sufficiently. On the contrary, when the content of silicon (Si) is exceeded, there is a problem in that oxides are formed on the surface of the steel to lower the ductility of the steel.

Manganese (Mn)

Manganese (Mn) is an element that increases the strength and toughness of steel and increases the hardenability of steel. The manganese is added at 0.50% to 2.0% by weight of the total rebar weight. If the content of manganese is less than 0.50% by weight, it may be difficult to secure strength. On the other hand, when the content of manganese exceeds 2.0% by weight, the strength is increased, but due to the increase in the amount of MnS-based non-metallic inclusions may cause defects such as cracks during welding.

Phosphorus (P)

Phosphorus (P) is an element that partially contributes to strength improvement, but when excessively included, deteriorates the ductility of steel and causes a final material deviation due to billet center segregation. P is not a problem if it is uniformly distributed in the steel, but usually forms a harmful compound of Fe ₃ P. The Fe ₃ P is extremely fragile and segregated so that it does not become homogenized even after annealing, but increases in processing such as forging and rolling.

The phosphorus (P) is limited to a content of greater than 0 and 0.05% by weight of the total rebar weight. When the content of phosphorus (P) exceeds 0.05% by weight, it forms a central segregation and fine segregation, which adversely affects the material, and may also worsen the ductility.

Sulfur (S)

Sulfur (S) is an element that contributes in part to the improvement of workability, but when excessively contained, it inhibits the toughness and ductility of the steel, and combines with manganese to form MnS non-metallic inclusions, causing cracks during processing of the steel. Sulfur can combine with iron to form FeS if there is not enough manganese in the steel. The FeS is very fragile and has a low melting point, which may cause cracking during hot and cold working.

The sulfur (S) is limited to a content of more than 0 and less than 0.025% by weight of the total rebar weight. When the content of sulfur (S) exceeds 0.025% by weight, there is a problem that greatly inhibits the ductility and excessively generates the MnS non-metallic inclusions.

Copper (Cu)

Copper (Cu) may serve to improve the hardenability and low temperature impact toughness of the steel. It can also increase the corrosion resistance of the river in the atmosphere or in seawater. Copper (Cu) is limited to a content of more than 0 and no more than 0.40% by weight of the total weight. If the content of copper is added in excess of 0.40% by weight, hot workability may be lowered and red brittleness may be caused.

Vanadium (V)

Vanadium (V) may combine with carbon (C) and nitrogen (N) at high temperatures to form carbides or nitrides. In addition, vanadium (V) may play a role of improving the strength of the steel through the precipitation strengthening effect by the precipitate formation.

The vanadium (V) is added to more than 0 0.10% by weight of the total rebar weight. When the content of vanadium (V) is added in excess of 0.10% by weight, low temperature impact toughness may be lowered.

Chrome (Cr)

Chromium (Cr) may improve hardenability by improving hardenability of steel. In addition, chromium can delay the diffusion of carbon to achieve finer particle size.

The chromium is added at 0.10% to 1.00% by weight of the total rebar weight. If the content of chromium is less than 0.10% by weight, it is difficult to achieve the above-described effects sufficiently, and conversely, when the content of chromium is added in excess of 1.00% by weight, there is a disadvantage in that weldability or heat affected zone toughness may be reduced.

Molybdenum (Mo)

Molybdenum (Mo) improves the strength, toughness and hardenability of the steel. The molybdenum is added at more than 0 and less than 0.50% by weight of the total rebar weight. If the content of molybdenum is added in excess of 0.50% by weight, there is a disadvantage in reducing the weldability.

Nickel (Ni)

Nickel (Ni) increases the strength of the material and ensures a low temperature impact value. The nickel is added at more than 0 and no more than 1.00 weight percent of the total rebar weight. However, when the content of nickel exceeds 1.00% by weight, the room temperature strength is excessively high, which may deteriorate weldability and toughness.

Tin (Sn)

Tin (Sn) may be added to ensure corrosion resistance. However, when the content of tin is added in excess of 0.1%, the elongation may be sharply reduced. Therefore, tin (Sn) is controlled to more than 0 and 0.1% by weight of the total rebar weight.

Aluminum (Al)

Aluminum (Al) may function as a deoxidizer. Aluminum (Al) may be added at 0.015% to 0.070% by weight of the total rebar weight. When the content of aluminum (Al) is added in less than 0.015% by weight, it is difficult to fully exhibit the effect. On the other hand, when the content of aluminum is added in excess of 0.070% by weight, the amount of non-metallic inclusions such as aluminum oxide (Al ₂ O ₃ ) can be increased when added.

Nitrogen (N)

Nitrogen (N) can increase yield strength and tensile strength. Nitrogen makes the austenite grains fine to make steel of fine grains.

Nitrogen (N) may be added at 0.005% to 0.025% by weight of the total rebar weight. However, when the content of nitrogen (N) is less than 0.005% by weight, it is difficult to achieve the above effects. On the contrary, there is a problem that the amount of nitrogen increases when the content of nitrogen (N) exceeds 0.025% by weight, thereby increasing the elongation and formability of the steel.

In addition to the components of the alloy composition described above, the remainder is made of iron (Fe) and impurities inevitably included in the steelmaking process.

Rebar manufacturing method

Hereinafter will be described a method of manufacturing a rebar according to an embodiment of the present invention.

1 is a flow chart schematically showing a method for manufacturing a rebar according to an embodiment of the present invention. Referring to FIG. 1, the method of manufacturing rebar includes a reheating step (S100), a hot rolling step (S200), and a cooling step (S300) of the cast steel. At this time, the reheating step (S100) may be carried out in order to derive the effect of reusing the precipitate. In this case, the cast steel can be obtained through a continuous casting process after obtaining a molten steel of a predetermined composition through a steelmaking process. The cast piece may, for example, have a form of bloom or fillet. The cast steel is 0.10% to 0.40% by weight of carbon (C), 0.05% to 0.50% by weight of silicon (Si), 0.50% to 2.0% by weight of manganese (Mn), and 0.05% by weight or more above 0 of phosphorus (P). , Sulfur (S) greater than 0 0.025% by weight, copper (Cu) greater than 0, 0.40% by weight, vanadium (V) greater than 0, 0.10% by weight, chromium (Cr) 0.10% by weight to 1.00% by weight, molybdenum (Mo) ) Greater than 0 to 0.50 wt% or less, nickel (Ni) greater than 0 to 0.25 wt% or less, tin (Sn) greater than 0 to 0.1 wt% or less, 0.015 wt% to 0.070 wt% aluminum (Al), 0.005 wt% to nitrogen (N) 0.025% by weight, and the remaining iron (Fe) and unavoidable impurities.

Reheating stage

In the reheating step of the cast steel, the cast steel having the above composition is reheated at a temperature range of 1150 ° C to 1250 ° C. Through such reheating, restocking of segregated components and reclaims of precipitates can occur during casting. The cast steel may be a bloom or billet manufactured by a continuous casting process performed before the reheating step (S100).

When the reheating temperature of the cast steel is less than 1150 ° C, the heating temperature may not be sufficient, and the segregation component and the precipitate may not be sufficiently used. Moreover, there exists a problem that rolling load becomes large. On the contrary, when the reheating temperature exceeds 1250 ° C., the austenite grains may coarsen or decarburization may occur to inhibit the strength.

Hot rolling

In the hot rolling step (S200) to start the hot rolled recast slab at a temperature of 1040 ℃ to 1100 ℃, to finish the hot rolling at the finish rolling temperature of 930 ℃ to 1000 ℃ to produce a rebar. When the finish rolling temperature exceeds 1000 ° C., it may be difficult to secure strength by coarse pearlite formation. On the contrary, when the finish rolling temperature is carried out below 950 ° C., the rolling load may be induced to lower productivity and to reduce the heat treatment effect.

Cooling

In the cooling step (S300), in order to secure sufficient strength, the hot rolled rebar is cooled through the temper core process to the surface temperature of the rebar to below the martensite transformation start temperature (Ms temperature). At this time, the cooling rate may be performed at about 5 to 10 ℃ / s. In the temper core process, the cooled steel may be subjected to a recuperation process at a temperature of 500 ° C. to 700 ° C. After reheating the rebar, the rebar may be air cooled.

The recuperative temperature may correspond to the speed at which the hot rolled rebar passes through the bath containing the cooling water during the temp core process. According to one embodiment, the line speed of the reinforcing bar may have a range of 7 to 11 meters / sec. When the flux is less than 7 meters / sec, excessive cooling may occur and the recuperation temperature may be lower than 500 ° C. If the flux exceeds 11 meters / sec, cooling may be insufficient and the recuperation temperature may be higher than 700 ° C. That is, when the recuperation temperature according to the embodiment of the present invention cannot be secured, the thickness of the cured layer in the target surface layer portion cannot be secured.

Reinforcing bars manufactured through the above-described process may have a central portion except for the surface layer portion and the surface layer portion. A hardened layer made of temper martensite may be disposed in the surface layer portion. As an example, the surface layer portion may be formed of the cured layer. The central portion may have a complex structure consisting of ferrite and pearlite.

The reinforcing bar, in the central portion, the tissue fraction of the ferrite in the composite tissue may be 35% or more.

The reinforcing bar may satisfy a yield strength (YS) of 500 MPa or more, a tensile strength (TS) / yield strength (YS) of 1.25 or more and an elongation of 10% or more at room temperature. In particular, according to the present embodiment, the ratio of tensile strength TS / yield strength YS, which is an index of high seismic characteristics, may have an excellent value of 1.25 or more.

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. However, it is presented as a preferred example of the present invention and should not be construed as limiting the present invention by any means.

Details that are not described herein will be omitted because those skilled in the art can sufficiently infer technically.

Example  One

1. Preparation of Specimen

The billet consisting of the alloy composition and the remaining iron (Fe) and inevitable impurities shown in Table 1 were prepared, respectively. The billets were reheated, hot rolled and reheated under the process conditions shown in Table 2 to prepare specimens of Comparative Examples 1 to 6 and Examples 1 to 3.

C Si Mn P S Cu V Cr Mo Ni Sn Al N Comparative example 0.33 0.21 1.29 0.018 0.020 0.21 0.07 0.32 0.05 0.03 0.01 0.019 0.009 Example 1 0.28 0.20 1.20 0.017 0.021 0.20 0.03 0.30 0.05 0.03 0.01 0.020 0.0154 Example 2 0.30 0.20 1.18 0.015 0.019 0.19 0.03 0.32 0.03 0.03 0.01 0.022 0.0234

* Unit of alloy composition is% by weight

Reheating temperature
(℃) Rolling condition Rolling start temperature (℃) Rolling end temperature (℃) Reheating temperature (℃) Cooling rate (℃ / s) Comparative example 1200 1080 937 620 6.0 Example 1 937 615 6.1 Example 2 933 616 6.0

In the case of the comparative example, compared with Examples 1 and 2, the content of vanadium is high. Reheating, hot rolling and reheating conditions were carried out under substantially the same conditions as in Comparative Examples and Examples 1 and 2. In addition, compared with the comparative example, in the case of the example, the content of nitrogen (N) is relatively high.

2. Property evaluation

Table 3 shows the results of evaluation of the mechanical properties of the specimens of Comparative Examples, Examples 1 and 2 prepared according to the conditions of Table 1 and Table 2. Physical properties were evaluated for room temperature characteristics. In addition, Table 4 shows the results of observing the microstructure of the specimens of Comparative Examples, Examples 1 and 2. The microstructure showed the observation result for the center of the rebar.

Room temperature YS
(MPa) TS (MPa) TS / YS EL (%) Comparative example 553 686 1.24 12.5 Example 1 542 715 1.32 17.0 Example 2 567 732 1.28 11.6

Central microstructure ferrite Pearlite Precipitate Comparative example O O O Example 1 O O O Example 2 O O O

Referring to Table 3, the comparative example did not satisfy the target value of the ratio of tensile strength (TS) / yield strength (YS) of 1.25 or more. Examples 1 and 2 satisfy the target value of the tensile strength (TS) / yield strength (YS).

Referring to Table 4, in Comparative Examples, Examples 1 and 2, the central microstructure was composed of a composite structure of ferrite and pearlite, and precipitates such as vanadium carbide (VC) or vanadium nitride (VN) were observed.

However, in the comparative example, the area fraction of the center ferrite was 22.5%, whereas in Examples 1 and 2, the area fraction of the center ferrite was 40.4% and 35.1%, respectively.

As a result, in contrast to the comparative example, Examples 1 and 2 were able to secure the target material properties by increasing the nitrogen content, instead of reducing the content of manganese and vanadium. In other words, the increase of nitrogen may precipitate the vanadium nitride (VN) at the austenite grain boundary at a high temperature to generate a pinning effect (interfering with the grain boundary movement). As a result, grain coarsening can be prevented. In addition, residual vanadium and carbon are combined in the temperature range in which ferrite and pearlite are formed to form vanadium carbide (VC) precipitates in the ferrite, thereby improving material properties. However, when the amount of nitrogen is excessive, it is advantageous to secure the strength, but since the elongation may decrease due to the influence of residual nitrogen, it is necessary to add an appropriate nitrogen content according to the embodiment of the present invention.

In the above description, the embodiment of the present invention has been described, but various changes and modifications can 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. Therefore, the scope of the present invention will be determined by the claims described below.

Reheating S100
S200 Hot Rolled Step
S300 Refrigerant Steps

Claims (7)

0.10 wt% to 0.40 wt% of carbon (C), 0.05 wt% to 0.50 wt% of silicon (Si), 0.50 wt% to 2.0 wt% of manganese (Mn), greater than 0 to 0.05 wt% of phosphorus (P), sulfur (S) ) Greater than 0 0.025 wt% or less, copper (Cu) greater than 0 0.40 wt% or less, vanadium (V) greater than 0 0.10 wt% or less, chromium (Cr) 0.10 wt% to 1.00 wt% or less, molybdenum (Mo) greater than 0 0.50 Weight% or less, nickel (Ni) greater than 0, 0.25 weight% or less, tin (Sn) greater than 0, 0.1 weight% or less, 0.015 weight%-0.070 weight% aluminum (Al), 0.005 weight%-0.025 weight% nitrogen (N), And the remaining iron (Fe) and inevitable impurities,
The rebar has a surface portion and a central portion except for the surface layer portion,
The reinforcing bar has a hardened layer including tempered martensite at the surface layer portion, and has a complex structure composed of ferrite and pearlite at the central portion.
rebar.
According to claim 1,
Yield strength (YS) 500 MPa or more, tensile strength (TS) / yield strength (YS) ratio at room temperature satisfies 1.25 or more and elongation 10% or more
rebar.
According to claim 1,
In the central portion, the tissue fraction of the ferrite in the composite tissue is at least 35%
rebar.
0.10 wt% to 0.40 wt% of carbon (C), 0.05 wt% to 0.50 wt% of silicon (Si), 0.50 wt% to 2.0 wt% of manganese (Mn), greater than 0 to 0.05 wt% of phosphorus (P), sulfur (S) ) Greater than 0 0.025 wt% or less, copper (Cu) greater than 0 0.40 wt% or less, vanadium (V) greater than 0 0.10 wt% or less, chromium (Cr) 0.10 wt% to 1.00 wt% or less, molybdenum (Mo) greater than 0 0.50 Weight% or less, nickel (Ni) greater than 0, 0.25 weight% or less, tin (Sn) greater than 0, 0.1 weight% or less, 0.015 weight%-0.070 weight% aluminum (Al), 0.005 weight%-0.025 weight% nitrogen (N), And reheating the cast steel made of the remaining iron (Fe) and unavoidable impurities at 1150 ° C to 1250 ° C.
Hot-rolling the reheated cast steel to a finish rolling temperature of 930 ° C to 1000 ° C to form reinforcing bars; And
And cooling the hot rolled rebar to a temperature below the martensite transformation start temperature (Ms temperature) of the rebar through a temp core.
The temp core process includes the step of regenerating the reinforcing bar at 500 ° C to 700 ° C
Method of manufacturing rebar.
The method of claim 4, wherein
The rebar is
It has a surface layer and a central portion except for the surface layer,
In the surface layer portion is provided with a cured layer containing tempered martensite,
Having a complex structure consisting of ferrite and pearlite at the center
Method of manufacturing rebar.
The method of claim 4, wherein
Yield strength (YS) 500 MPa or more, tensile strength (TS) / yield strength (YS) ratio at room temperature satisfies 1.25 or more and elongation 10% or more
Method of manufacturing rebar.
The method of claim 4, wherein
In the central portion, the tissue fraction of the ferrite in the composite tissue is 35% or more
rebar.

Images