KR101950597B1 - Steel reinforcement and method of manufacturing the same - Google Patents

Abstract

According to an embodiment of the present invention, a method of manufacturing reinforcing steel comprises the following steps of: re-heating a slab at 1050°C to 1150°C, wherein the slab comprises 0.26-0.29 wt% of carbon (C), more than 0 to less than or equal to 0.25 wt% of silicon (Si), 1.35-1.40 wt% of manganese (Mn), more than 0 to less than or equal to 0.035 wt% of phosphorus (P), more than 0 to 0.040 wt% of sulfur (S), 0.085-0.15 wt% of vanadium (V), more than 0 to less than or equal to 0.30 wt% of chromium (Cr), and the remainder consisting of iron (Fe) and inevitable impurities; forming a reinforcing steel by hot rolling the re-heated slab with a finish rolling temperature of 950°C to 1050°C; and air-cooling the hot rolled reinforcing bar.

Description

TECHNICAL FIELD [0001] The present invention relates to a reinforcing bar and a method of manufacturing the reinforcing bar.

The present invention relates to a reinforcing bar and a manufacturing method thereof.

Generally, carbon steel has an advantage that it is cheap and the material control by heat treatment is easy. As an example, carbon steel has been applied throughout the industry such as automobiles and machine parts. These carbon steels are also applied to structures for securing space for human activities. As an example, steel for structures has been widely applied to skyscrapers, long bridges, giant marine structures, underground structures, and the like.

On the other hand, the carbon steel can be applied to various industries in the form of reinforcing bars. As an example, in the case of reinforcing bars applied to a structure, it is required to have high strength and high seismic resistance as the structure becomes superstructure and becomes larger.

A background art relating to the present invention is Korean Patent No. 10-1757591.

It is an object of the present invention to provide reinforcing bars having high strength and high seismic resistance through alloy components and process control.

A method of manufacturing a reinforcing bar according to an embodiment of the present invention includes the steps of: 0.26 wt% to 0.29 wt% of carbon (C), 0.25 wt% or less of silicon (Si), 1.35 wt% to 1.40 wt% of manganese (P): more than 0 to 0.035% by weight, sulfur (S): more than 0 to 0.040% by weight, vanadium (V): 0.085 to 0.15% (Fe) and inevitable impurities at 1050 캜 to 1150 캜; Forming a reinforcing bar for hot-rolling the reheated cast steel to a finish rolling temperature of 950 캜 to 1050 캜; And air cooling the hot rolled steel bar.

In one embodiment, the hot rolling of the cast steel may start rolling at a temperature of 1000 to 1100 占 폚.

In another embodiment, after the air cooling, the reinforcing bars have a composite structure of ferrite and pearlite, and the area fraction of the ferrite may be 10% or more.

In another embodiment, after the air cooling, the steel bar may have a yield strength of 550 MPa or more, an elongation of 10% or more, and a ratio of tensile strength / yield strength of 1.25 or more.

The reinforcing bar according to one embodiment of the present invention comprises 0.26 wt% to 0.29 wt% of carbon (C), 0.25 wt% or less of silicon (Si), 1.35 wt% to 1.40 wt% of manganese (Mn) : More than 0 and not more than 0.035 wt%, S: not less than 0 and not more than 0.040 wt%, vanadium (V): 0.085 to 0.15 wt%, Cr: more than 0 and not more than 0.30 wt% And inevitable impurities. The reinforcing bars have a complex structure of ferrite and pearlite.

In one embodiment, the area fraction of the ferrite may be greater than or equal to 10%.

In another embodiment, the reinforcing bar may have a yield strength of 550 MPa or more, an elongation of 10% or more, and a ratio of tensile strength / yield strength of 1.25 or more.

According to the present invention, reinforced bars having high strength and high seismic resistance can be provided through optimized alloy components and process control. In particular, it is possible to secure an alloy component and a manufacturing method capable of manufacturing high-strength seismic reinforcing bars without applying the temp core process. This makes it possible to utilize the reinforcing bars at the time of constructing a large-sized, long-range structure.

1 is a flowchart schematically showing a method of manufacturing a reinforcing bar according to an embodiment of the present invention.
2A and 2B are photographs showing the microstructure of a reinforcing bar according to a comparative example of the present invention.
3A and 3B are photographs showing the microstructure of a reinforcing bar according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. Throughout this specification, the same or similar components are denoted by the same reference numerals. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

The embodiments of the present invention described below provide reinforcing bars having high strength and high seismic resistance properties, which are manufactured through appropriate component design and process control.

rebar

One embodiment of the present invention is a method of manufacturing a semiconductor device comprising 0.26 wt% to 0.29 wt% of carbon (C), 0.25 wt% or less of silicon (Si), 1.35 wt% to 1.40 wt% of manganese (Mn) (Fe): 0.085 to 0.15 wt.%, Cr: more than 0 to 0.30 wt.%, And the balance of iron (Fe) and unavoidable impurities Thereby providing reinforcing bars.

The reinforcing bars have a composite structure of ferrite and pearlite, and the area fraction of the ferrite may be 10% or more.

In a reinforcing bar according to an embodiment of the present invention, vanadium (V) can be applied as an additive element to generate a precipitation strengthening effect. As a result, the carbon content in the reinforcing bars can be reduced, and the weldability can be improved.

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

Carbon (C)

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

The carbon (C) is added in an amount of 0.26 wt% to 0.29 wt% of the total weight. When the content of carbon is less than 0.26% by weight, it is difficult to secure sufficient strength. On the contrary, when the content of carbon (C) exceeds 0.29% by weight, the strength of the steel increases but it may be difficult to secure a sufficient elongation.

Silicon (Si)

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

The silicon (Si) is added in an amount of more than 0 to 0.25 wt% of the total weight. When the content of silicon (Si) exceeds 0.25% by weight, oxides are formed on the surface of the steel to lower the ductility of the steel.

Manganese (Mn)

Manganese (Mn) is an element which increases the strength and toughness of steel and increases the ingotability of steel. The manganese is added in an amount of 1.35 wt% to 1.40 wt% of the total reinforcing bar weight. If the content of manganese is less than 1.35 wt%, it may be difficult to secure strength. On the other hand, when the content of manganese exceeds 1.40% by weight, the strength is increased but the amount of MnS-based nonmetallic inclusions is increased, which may cause defects such as cracking during welding.

In (P)

Phosphorus (P) can inhibit cementite formation and increase strength. However, when the content of phosphorus is more than 0.035% by weight, secondary workability may be lowered. Therefore, the phosphorus (P) is controlled to be 0 to 0.035 wt% or less of the total reinforcing bar weight.

Sulfur (S)

Sulfur (S) can combine with manganese, molybdenum, etc. to improve machinability of steel. However, if the precipitation occurs in the form of MnS, FeS, and the like, and the amount of such precipitates increases, cracking may occur during hot and cold working. Therefore, sulfur (S) is controlled to be more than 0 to 0.040 wt% of the total reinforcing bar weight.

Vanadium (V)

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

The vanadium is added in an amount of 0.085 wt% to 0.15 wt% of the total weight. When the addition amount of vanadium is less than 0.085 wt%, the precipitation hardening effect can not be sufficiently secured. On the other hand, if the addition amount of vanadium exceeds 0.15% by weight, excess precipitates may be generated and brittle fracture may be caused.

chrome( Cr )

Chromium (Cr) improves the hardenability of the steel and improves the hardenability.

The chromium is added in an amount of more than 0 to 0.30 wt% of the total reinforcing steel weight. When the content of chromium is more than 0.30 wt%, there is a drawback that weldability and toughness of the heat-affected zone can be lowered.

In addition to the components of the alloy composition described above, the remainder is composed of iron (Fe) and impurities inevitably included in the steelmaking process and the like. The rebar according to the embodiment of the present invention having the above-described alloy composition may have a yield strength of 550 MPa or more, an elongation of 10% or more, and a ratio of tensile strength / yield strength of 1.25 or more. Thus, high strength and high seismic resistance characteristics can be obtained.

How to make rebar

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

1 is a flowchart schematically showing a method of manufacturing a reinforcing bar according to an embodiment of the present invention. Referring to FIG. 1, a method of manufacturing a reinforcing bar includes a reheating step (S100), a hot rolling step (S200), and an air cooling step (S300). The reheating step (S100) may be carried out in order to obtain effects such as reuse of precipitates and the like. At this time, the cast steel can be obtained through a continuous casting process after molten steel having a predetermined composition is obtained through a steelmaking process. The casting may, for example, take the form of a bloom or billet. The cast steel is composed of 0.26 wt% to 0.29 wt% of carbon (C), 0.25 wt% or less of silicon (Si), 1.35 wt% to 1.40 wt% of manganese (Mn) (S): more than 0 to 0.040% by weight, vanadium (V): 0.085 to 0.15% by weight, chromium (Cr): more than 0 to 0.30% by weight and the balance of iron (Fe) and unavoidable impurities .

Reheat step

In the reheating step of the cast steel, the cast steel having the above composition is reheated in the temperature range of 1050 캜 to 1150 캜. This reheating can result in re-use of the segregated components and re-use of precipitates during casting. The cast steel may be a bloom or billet produced by a continuous casting process carried out before the reheating step (S100).

If the reheating temperature of the cast steel is less than 1050 DEG C, the heating temperature is not sufficient and the segregation component and the precipitate may not be sufficiently reused. Further, there is a problem that the rolling load becomes large. On the other hand, when the reheating temperature exceeds 1150 占 폚, the austenite grains may be coarse or decarburized to deteriorate the strength.

Hot rolling

In the hot rolling step S200, the reheated cast steel is hot-rolled at a finish rolling temperature of 950 占 폚 to 1050 占 폚 to form a reinforcing bar. In one embodiment, the hot rolling of the cast slab can be started at a temperature of 1000 to 1100 占 폚.

On the other hand, when the finish rolling temperature exceeds 1050 DEG C, the austenite grains are coarse, so that it becomes difficult to secure strength after transformation. On the other hand, when the finish rolling temperature is lower than 950 占 폚, the rolling load is induced to lower the productivity and reduce the heat treatment effect.

Air cooling

In the air cooling step (S300), the hot-rolled steel bar is cooled to room temperature in the air. In the embodiment of the present invention, the Temp core process is not applied in the cooling step. When the cooling rate is artificially increased as in the case of the temp core process, the decrease of the ferrite grains may occur and the deterioration of the seismic performance may be caused. Therefore, in the embodiment of the present invention, the hot-rolled steel bar is cooled by an air cooling method.

Proceeding with the above-described process steps, a reinforcing bar according to an embodiment of the present invention is produced. The reinforcing bars produced as a whole have a composite structure of ferrite and pearlite. At this time, the area fraction of the ferrite may be 10% or more of the total area. By including the ferrite having the above-mentioned area fraction, the steel can attain a ratio of elongation of 10% or more and a tensile strength / yield strength ratio of 1.25 or more.

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. Preparation of specimens

Comparative Examples and Example Casts comprising the alloy composition shown in Table 1 and the balance of Fe (Fe) and unavoidable impurities were prepared. The above Comparative Examples and Examples were subjected to hot rolling and cooling under the conditions shown in Table 2 to produce reinforcing bars. In the case of the comparative example, it was cooled in a quenching manner using the Temp core process, and in the case of the examples, it was cooled by air cooling after hot rolling.

Chemical composition (% by weight) C Si Mn P S V Cr Carbon equivalent (Ceq) Comparative Example 0.34 0.21 1.35 0.034 0.031 - 0.16 0.59 Example 0.28 0.22 1.35 0.031 0.028 0.085 0.12 0.52

Process conditions Reheating temperature (℃) Rolling start temperature (캜) Rolling end temperature (캜) Whether temp core is applied Comparative Example 1082 1055 1000 apply Example 1080 1040 980 Unapplied

2. Property evaluation

 Table 3 shows the results of evaluating mechanical properties of reinforcing bars of Comparative Examples and Examples prepared according to the conditions of Tables 1 and 2. The physical properties were evaluated by measuring yield strength (YS), tensile strength (TS), elongation (EL), and yield ratio (YR).

Material evaluation Tensile Strength (MPa) Yield strength (MPa) Elongation Tensile strength / yield strength Target value Yield strength * 1.25 or higher 550 or more over 10 1.25 or higher Comparative Example 827 614 12.6 1.36 Example 762 575 14.8 1.32

The reinforcing bars of the comparative example and the example both satisfied the target values of the ratio of tensile strength, yield strength, elongation, and tensile strength / yield strength.

On the other hand, referring to Table 1, in the case of the comparative example, the carbon equivalent is 0.59, and in the case of the embodiment, the carbon equivalent is 0.52, and the carbon equivalent of the embodiment is relatively low. As described above, the reinforcing bars of the examples can reduce the carbon equivalent and improve the weldability of the reinforcing bars while satisfying the target values in terms of mechanical properties.

2A and 2B are photographs showing the microstructure of a reinforcing bar according to a comparative example of the present invention. 3A and 3B are photographs showing the microstructure of a reinforcing bar according to an embodiment of the present invention.

FIG. 2A shows a surface portion of a comparative reinforcing bar. As the quenching and repetition process proceeds by the Temp core process, the surface portion may have a microstructure of tempered martensite. On the other hand, referring to FIG. 2B, it can be confirmed that the core portion of the comparative reinforcing bar has a composite structure of ferrite (bright portion) and pearlite (dark portion).

FIG. 3A and FIG. 3B show the surface portion and the center portion of the reinforcing bars of the embodiment, respectively, and in the case of the reinforcing bars of the embodiment, the composite structure of ferrite and pearlite is entirely confirmed.

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.

S100 reheat step
S200 Step of hot rolling
S300 air-cooling step

Claims (7)

0.26 wt% to 0.29 wt% of carbon (C), 0.25 wt% or less of silicon (Si), 1.35 wt% to 1.40 wt% of manganese (Mn) ): More than 0 to 0.040 wt%, vanadium (V): 0.085 to 0.15 wt%, chromium (Cr): more than 0 to 0.30 wt%, and the balance Fe and unavoidable impurities, ≪ / RTI >
Forming a reinforcing bar for hot-rolling the reheated cast steel to a finish rolling temperature of 950 캜 to 1050 캜; And
And air-cooling the hot-rolled steel bar
Method of manufacturing reinforcing bars.
The method according to claim 1,
The hot rolling of the cast steel
Rolling at a temperature of 1000 to 1100 < RTI ID = 0.0 >
Method of manufacturing reinforcing bars.
The method according to claim 1,
After the air cooling, the reinforcing bars have a composite structure of ferrite and pearlite,
If the area fraction of the ferrite is not less than 10%
Method of manufacturing reinforcing bars.
The method according to claim 1,
After the air cooling, the reinforcing bar has a yield strength of 550 MPa or more, an elongation of 10% or more, and a ratio of tensile strength / yield strength of 1.25 or more
Method of manufacturing reinforcing bars.
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