KR20190058046A - Steel reinforcement and method of manufacturing the same - Google Patents

Abstract

According to an embodiment of the present invention, a rebar manufacturing method includes: a step of reheating a cast piece, which comprises 0.27-0.31 wt% of carbon (C), more than 0 and equal to or less than 0.30 wt% of silicon (Si), 1.5-1.80 wt% of manganese (Mn), more than 0 and equal to or less than 0.04 wt% of phosphorous (P), more than 0 and equal to or less than 0.04 wt% of sulfur (S), 0.2-0.3 wt% of copper (Cu), 0.080-0.10 wt% of vanadium (V), and the remaining of Fe and inevitable impurities, at 1050-1150°C; a step of manufacturing a rebar by hot-rolling the reheated cast piece at a final rolling temperature which is 980-1030°C; and a step of cooling the hot-rolled rebar via a temp core process to make the surface temperature of the rebar become no more than a martensite transformation start temperature (Ms temperature). At this point, the temp core process includes a step of recuperating the rebar at 555-590°C. Therefore, the present invention is capable of providing a high-strength rebar responding to an increase in concrete compression strength.

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. That is, as the compressive strength of concrete is recently increased, it is necessary to increase the strength of the reinforcing bars so as to correspond to the strength of the raised concrete, even in a structure in which the concrete and the reinforcing bars are mixed.

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 ductility through alloy components and process control.

According to an embodiment of the present invention, there is provided a method of manufacturing a reinforcing bar comprising 0.27 wt% to 0.31 wt% of carbon (C), 0.30 wt% of silicon (Si), 1.5 wt% to 1.80 wt% of manganese (Mn) P) of more than 0 to 0.04% by weight, sulfur (S) of more than 0 to 0.04% by weight, copper (Cu) of 0.2 to 0.3% by weight, vanadium (V) of 0.080 to 0.10% Reheating the slab comprising impurities at a temperature of from 1050 DEG C to 1150 DEG C; Hot rolling the reheated cast slab to a finish rolling temperature of 980 캜 to 1030 캜 to produce a reinforcing bar; And cooling the hot-rolled steel bar to a martensitic transformation starting temperature (Ms temperature) or lower through a core of the steel through a core of the steel. At this time, the temp core process includes a step of reheating the reinforcing bars at 555 to 590 캜.

In one embodiment, the finishing rolling temperature may be in accordance with the following equation.

Finishing rolling temperature (占 폚) <(0.8 × Ae1 / 3.0 × [C] + 15.2 [V]) - Ae3

[C] is the content of carbon in the slab, the unit is weight%, [V] is the content of vanadium in the slab, the unit is weight%, and the coefficient is 0.8 The coefficient 3.0 has a unit of 1 / weight%, and the coefficient 15.2 has a unit of 1 / weight%).

In one embodiment, the produced reinforcing bars have a structure of tempered martensite at the surface portion, and a composite structure of ferrite and pearlite at the center portion.

In one embodiment, the produced reinforcing bar may have a yield strength (YS) of 700 MPa or more, an elongation of 10% or more, and a tensile strength (TS) of 1.08 times or more of the yield strength (YS).

A reinforcing bar according to another embodiment of the present invention comprises 0.27 wt% to 0.31 wt% carbon (C), 0.30 wt% of silicon (Si), 1.5 wt% to 1.80 wt% of manganese (Mn) (Cu), 0.080 to 0.10 wt% of vanadium (V), and the balance of iron (Fe) and unavoidable impurities And has a structure of tempered martensite at the surface portion and a composite structure of ferrite and pearlite at the center portion.

In one embodiment, the reinforcing bar may have a yield strength (YS) of 700 MPa or more, an elongation of 10% or more, and a tensile strength (TS) of 1.08 times or more of the yield strength (YS).

According to the present invention, reinforced bars having high strength and high ductility can be provided through optimized alloy components and process control. Thus, it is possible to provide reinforcing bars of high strength corresponding to the recent increase in the compressive strength of concrete.

1 is a flowchart schematically showing a method of manufacturing 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, which will be described below, present high strength rebars manufactured through appropriate component design and process control.

High strength steel

An embodiment of the present invention is a method of manufacturing a semiconductor device comprising 0.27 wt% to 0.31 wt% of carbon (C), 0.30 wt% of silicon (Si), 1.5 wt% to 1.80 wt% of manganese (Mn) , Iron (S) more than 0, 0.04 wt%, copper (Cu) 0.2 wt% to 0.3 wt%, vanadium (V) 0.080 to 0.10 wt%, and balance of iron (Fe) and unavoidable impurities.

The reinforcing bars have a structure of tempered martensite at the surface portion and may have a complex structure of ferrite and pearlite at the center portion. The reinforcing bar may have a yield strength (YS) of 700 MPa or more, an elongation of 10% or more, and a tensile strength (TS) of 1.08 times or more of a yield strength (YS).

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. Carbon (C) is dissolved in austenite to form martensite structure during quenching. In addition, the quenching hardness is improved as the amount of carbon is increased, and the possibility of deformation during quenching may increase. Iron and vanadium to form a carbide, whereby strength and hardness can be improved.

The carbon (C) is added in an amount of 0.27 wt% to 0.31 wt% of the total weight. When the content of carbon is less than 0.27% by weight, it is difficult to secure sufficient strength. On the other hand, when the content of carbon (C) exceeds 0.31% by weight, the strength of the steel increases but the core hardness decreases and 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 not less than 0.30 wt% of the total weight. On the other hand, when the content of silicon (Si) exceeds 0.30% 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 1.5 wt% to 1.80 wt% of the total reinforcing steel weight. If the content of manganese is less than 1.5% by weight, it may be difficult to secure strength. On the other hand, when the content of manganese exceeds 1.80 wt%, 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) is an element that contributes a little to the strength improvement, but if it is included excessively, the ductility of the steel is deteriorated and the final material deviation is caused by billet center segregation. P 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 weak and segregated, so it does not become homogeneous even after the annealing treatment, and it is elongated at the time of forging, rolling and the like.

The phosphorus (P) is limited to a content of more than 0 to 0.04% by weight of the total weight. When the content of phosphorus (P) exceeds 0.04% by weight, not only center segregation but also fine segregation is formed, which adversely affects the material and may deteriorate ductility and toughness.

Sulfur (S)

Sulfur (S) is an element which contributes partly to the improvement of workability. However, if it is included excessively, sulfur (S) inhibits toughness and ductility of steel and forms MnS nonmetallic inclusion by binding with manganese. Sulfur can combine with iron to form FeS if the amount of manganese in the steel is insufficient.

The sulfur (S) is limited to an amount of more than 0 to 0.04% by weight of the total weight. When the content of sulfur (S) exceeds 0.04% by weight, there is a problem that ductility is greatly deteriorated and MnS non-metallic inclusions are excessively generated.

Copper (Cu)

Copper (Cu) can serve to improve the hardenability of the steel and the impact resistance at low temperatures. However, when the content of copper is less than 0.2% by weight, the above-mentioned effect can not be sufficiently secured. On the other hand, when the content of copper is added in an amount exceeding 0.3% by weight, it is possible to cause a red-hot brittleness. Therefore, copper (Cu) is controlled to 0.2 wt% to 0.3 wt% of the total rebar 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 0.080 wt% to 0.10 wt% of the total weight. If the content of vanadium is less than 0.080 wt%, it may be difficult to exhibit the effect of adding vanadium properly. On the other hand, if the addition amount of vanadium exceeds 0.10% by weight and is added in an excess amount, the low temperature impact toughness may 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.

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 a cooling step (S300). At this time, the reheating step (S100) may be carried out in order to obtain effects such as reuse of precipitates. 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 cast may, for example, be in the form of a bloom or a fillet. The cast steel is composed of 0.27 wt% to 0.31 wt% of carbon (C), 0.30 wt% of silicon (Si), 1.5 wt% to 1.80 wt% of manganese (Mn) S) of more than 0 to 0.04% by weight, copper (Cu) of 0.2 to 0.3% by weight, vanadium (V) of 0.080 to 0.10% 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 980 ° C to 1030 ° C. 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 980 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, if the reheating temperature exceeds 1030 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 finishing rolling temperature of 980 캜 to 1030 캜 to produce a reinforcing bar. The finish rolling can proceed near the vacancy transformation temperature to prevent the formation of continuous cornerstone cementite and to increase nucleation.

If the finish rolling temperature exceeds 1030 DEG C, it may become difficult to secure strength by forming coarse pearlite. On the other hand, when the finish rolling temperature is lower than 980 占 폚, the rolling load is caused to lower the productivity and reduce the heat treatment effect.

In one embodiment, the hot rolling may start rolling at a temperature of 1030 캜 to 1070 캜 after reheating of the cast steel. Then, as described above, the finish rolling may proceed at a temperature of 980 캜 to 1030 캜. The rolling speed can be progressed from 6.0 to 8.0 m / sec.

In one embodiment, the finishing rolling temperature may be subject to the conditions of the following formula (1).

(1): Finishing rolling temperature (° C) <(0.8 × Ae1 / 3.0 × [C] +15.2 [V]) - Ae3

(C) is the content of carbon in the slab, the unit is weight%, [V] is the content of vanadium in the slab, the unit is wt%, and the coefficient 0.8 is non-stationary, coefficient 3.0 has units of 1 / weight%, coefficient 15.2 has units of 1 / weight%).

Ae1 in Equation 1 means a known critical temperature A1 related to the phase transformation of the steel in an equilibrium state and Ae3 means a known critical temperature A3 related to the phase change of the steel in the equilibrium state.

Cooling

In the cooling step (S300), the hot-rolled steel bar is cooled to a martensitic transformation start temperature (Ms temperature) or less through a Temp core process so as to secure sufficient strength. In the process of the temp core, the process of reheating at the temperature of 500 ° C to 700 ° C may be performed in the cooled steel material. After rebuilding of the rebar, the rebar may be air cooled.

Through the above-described process, the produced reinforcing bars have a structure of tempered martensite at the surface portion and a composite structure of ferrite and pearlite at the center portion.

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

A casting composed of the alloy composition shown in Table 1 and the balance of Fe (Fe) and unavoidable impurities was prepared. The cast steel was hot-rolled under the conditions shown in Table 2 below to prepare a plurality of specimens according to the conditions of Examples 1 to 3 and Comparative Examples.

Chemical composition (% by weight) C Si Mn P S Cu V Example 0.29 0.28 1.51 0.018 0.017 0.21 0.081 Comparative Example 1 0.32 0.18 1.30 0.026 0.024 0.23 0.031 Comparative Example 2 0.32 0.18 1.30 0.030 0.030 0.35 0.049

Rolling conditions Reheating temperature (℃) Rolling start temperature (캜) Finishing end temperature (캜) Rolling speed (m / sec) Double temperature (℃) Comparative Example 1120 1040 1010 7.2 570 Example 1 1120 1040 1010 6.5 565 Example 2 1120 1040 1010 8.0 613

In the case of Comparative Example 1, the manganese content was lower than the lower limit of the content range of the examples of the present invention. In the case of Comparative Example 2, the content of manganese was lower than the lower limit of the content range of the examples of the present invention, and the copper content was higher than the upper limit of the content range of the examples of the present invention. In the case of Comparative Example 2, the double heat temperature was higher than the upper limit of the double heat temperature range of the embodiment of the present invention.

2. Property evaluation

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

Material evaluation Yield strength (MPa) Tensile Strength (MPa) Elongation (%) Tensile strength / yield strength ratio Target value 700 or more 756 or more over 10 1.08 or higher Example 707 852 12.05 1.20 Comparative Example 1 689 826 8.4 1.20 Comparative Example 2 733 850 3.2 1.16

Referring to Table 3, in the case of the examples, all of the above-mentioned target values of the mechanical properties were satisfied. On the other hand, in the case of Comparative Example 1, the yield strength was lower than the target value of 700 MPa, and the elongation was lower than the target value of 10%. In the case of Comparative Example 2, the ratio of the yield strength, the tensile strength, and the tensile strength / yield strength satisfied the target value, but the elongation was 3.2%, which was below the target value.

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 Cooling step

Claims (6)

(P) 0 to 0.04% by weight or less, sulfur (S) 0 (carbon), 0.27 to 0.31% by weight of carbon (C), 0.30% (10) to 1150 占 폚 of a cast steel composed of at least 0.04% by weight of copper (Cu), 0.2 to 0.3% by weight of copper (Cu), 0.080 to 0.10% by weight of vanadium ;
Hot rolling the reheated cast slab to a finish rolling temperature of 980 캜 to 1030 캜 to produce a reinforcing bar; And
Cooling the hot-rolled steel bar to a surface temperature of the reinforcing bar through a core of the steel to a martensitic transformation start temperature (Ms temperature) or less,
Wherein the temp core process includes a step of recuperating the reinforcing bars at 555 DEG C to 590 DEG C
Method of manufacturing reinforcing bars.
The method according to claim 1,
The finish rolling temperature is determined according to the conditions of the following formula
Finishing rolling temperature (占 폚) <(0.8 × Ae1 / 3.0 × [C] + 15.2 [V]) - Ae3
[C] is the content of carbon in the slab, the unit is weight%, [V] is the content of vanadium in the slab, the unit is weight%, and the coefficient is 0.8 The coefficient 3.0 has a unit of 1 / weight%, and the coefficient 15.2 has a unit of 1 / weight%).
Method of manufacturing reinforcing bars.
The method according to claim 1,
The produced reinforcing bars have a structure of tempered martensite at the surface portion,
Having a complex structure of ferrite and pearlite in the center
Method of manufacturing reinforcing bars.
The method according to claim 1,
The produced reinforcing bar has a YS of 700 MPa or more, an elongation of 10% or more, and a tensile strength TS of 1.08 times or more of YS
Method of manufacturing reinforcing bars.
(P) 0 to 0.04% by weight or less, sulfur (S) 0 (carbon), 0.27 to 0.31% by weight of carbon (C), 0.30% (Fe) and inevitable impurities, and the amount of the iron (Fe) is not more than 0.04% by weight, the content of copper is from 0.2 to 0.3% by weight,
Having a structure of tempered martensite at the surface portion and having a composite structure of ferrite and pearlite in the center portion
rebar
6. The method of claim 5,
YS of not less than 700 MPa, elongation of not less than 10%, tensile strength (TS) not less than 1.08 times the yield strength (YS)
rebar.

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