KR20180138297A - Steel reinforcement and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a method of manufacturing a reinforced bar for providing reinforced bars with high strength and high ductility. The method of manufacturing a reinforced bar according to the present invention comprises the steps of: reheating a cast piece, which consists of 0.10 to 0.50 wt% of carbon (C), 0.15 to 3.0 wt% of manganese (Mn), 0.05 to 0.6 wt% of silicon (Si), 0.10 to 0.50 wt% or less of chrome (Cr), more than 0 to 0.40 wt% or less of copper (Cu), more than 0 to 0.45 wt% or less of molybdenum (Mo), more than 0 to 0.040 wt% or less of aluminum (Al), more than 0 to 0.30 wt% or less of niobium (Nb), more than 0 to 0.020 wt% or less of nitrogen (N), and the remaining of iron (Fe) and inevitable impurities, at 1100°C to 1250°C; manufacturing a reinforced bar by performing hot rolling of the reheated cast piece at temperature of Ar3-70°C to Ar3-30°C; cooling the surface temperature the hot rolled reinforced bar through a temp core to the martensite conversion start temperature (Ms temperature) or less; and recuperating the cooled reinforced bar at 450°C to 600°C.

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 ductility as the structure is made into a superstructure and a giant structure.

A background art related to the present invention is Korean Patent Laid-Open Publication No. 10-2014-0041279.

It is an object of the present invention to provide reinforcing bars having high strength and high ductility 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: 0.10 to 0.50% by weight of carbon (C), 0.15 to 3.0% by weight of manganese (Mn), 0.05 to 0.6% (Al) 0 to 0.040 wt.% Or less, niobium (Nb) 0 or more, and the like. 0.30 wt% or less, nitrogen (N) more than 0 wt% and 0.020 wt% or less, and remaining iron (Fe) and unavoidable impurities at a temperature of 1100 ° C to 1250 ° C; Hot-rolling the reheated cast slab to a finish rolling temperature at a temperature of Ar ₃ -70 캜 to Ar ₃ -30 캜 to produce a rebar; Cooling the hot-rolled steel bar to a martensitic transformation starting temperature (Ms temperature) or lower through a core of the steel; And recovering the cooled reinforcing bar at 450 ° C to 600 ° C; .

In one embodiment, the cast slab may further include at least one of tin (Sn) 0 to 0.50 wt% or less, magnesium (Mg) 0 to 0.005 wt% or less, and calcium (Ca) .

In another embodiment, the finish rolling temperature of the cast slab may satisfy the Ae3 / (4.15 * [C]) requirement. Here, [C] is the weight percentage of carbon in the slab.

In another embodiment, the finishing rolling temperature of the cast steel may be 730 캜 to 780 캜.

In another embodiment, the reinforcing bar has a composite structure of bainite and needle-like ferrite, and may have a particle size of 10 to 20 占 퐉.

The reinforcing bars according to an embodiment of the present invention include 0.10 to 0.50 wt% of carbon (C), 0.15 to 3.0 wt% of manganese (Mn), 0.05 to 0.6 wt% of silicon (Si) (Al) 0 to 0.040 wt.% Or less, niobium (Nb) 0 to 0.30 wt.% Or less, , Nitrogen (N) more than 0 and not more than 0.020 wt%, and the balance of iron (Fe) and unavoidable impurities. The reinforcing bar has a composite structure of bainite and needle-like ferrite, and has a particle size of 10 to 20 占 퐉.

In one embodiment, the reinforcing bars may further include at least one of tin (Sn) in an amount of more than 0 to 0.50 wt%, magnesium (Mg) in an amount of more than 0 to 0.005 wt%, and calcium (Ca) in an amount of more than 0 to 0.005 wt% .

According to the present invention, reinforced bars having high strength and high ductility can be provided through optimized alloy components and process control. 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.
2 is a photograph showing the microstructure of a reinforcing bar according to a comparative example of the present invention.
3A is a photograph showing each microstructure of a reinforcing bar according to an embodiment of the present invention.
FIG. 3B is a partial enlarged view of the reinforcing bar of FIG. 3A. FIG.

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: 0.10 to 0.50% by weight of carbon (C), 0.15 to 3.0% by weight of manganese (Mn), 0.05 to 0.6% (Al) 0 to 0.040 wt% or less, niobium (Nb) 0 to 0.30 wt% or less, nitrogen (molybdenum) N) of more than 0 to 0.020% by weight, and the balance of iron (Fe) and unavoidable impurities.

In another embodiment of the present invention, the reinforcing bars further include at least one of tin (Sn) in an amount of more than 0 to 0.50 wt%, magnesium (Mg) in an amount of more than 0 to 0.005 wt%, and calcium (Ca) in an amount of more than 0 to 0.005 wt% can do.

The reinforcing bar has a composite structure of bainite and needle-like ferrite, and may have a particle size of 10 to 20 占 퐉.

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. It is possible to improve strength and hardness by forming a carbide by bonding with elements such as iron, chromium, molybdenum, and vanadium.

The carbon (C) is added in an amount of 0.10 wt% to 0.50 wt% of the total weight. When the content of carbon is less than 0.10 wt%, it is difficult to secure sufficient strength. On the other hand, when the content of carbon (C) exceeds 0.50% by weight, the strength of the steel increases but the core hardness decreases and it may be difficult to secure a sufficient elongation.

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 0.15 wt% to 3.0 wt% of the total reinforcing bar weight. If the content of manganese is less than 0.15% by weight, it may be difficult to secure strength. On the other hand, when the content of manganese exceeds 3.0% by weight, the strength is increased but the amount of MnS-based nonmetallic inclusions is increased, which may cause defects such as cracks during welding.

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 0.05 wt% to 0.6 wt% of the total weight. When the content of silicon (Si) is less than 0.05% by weight, the effect of adding silicon can not be exhibited properly. On the contrary, when the content of silicon (Si) exceeds 0.6% by weight, oxides are formed on the surface of the steel to lower the ductility of the steel.

chrome( Cr )

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

The chromium is added in an amount of 0.10 wt% to 0.50 wt% of the total weight of the reinforcing bars. When the content of chromium (Cr) is less than 0.10 wt%, the effect of adding chromium can not be exhibited properly. When the content of chromium is more than 1.0% by weight, there is a disadvantage that the weldability and toughness of the heat-affected zone can be lowered.

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 more than 0.40 wt%, it may induce red embrittlement. Therefore, copper (Cu) is controlled to be more than 0 and 0.40 wt% or less of the total weight of the reinforcing bars.

molybdenum( Mo )

Molybdenum (Mo) improves strength and toughness and contributes to ensuring stable strength at room or high temperatures. However, when the molybdenum content exceeds 0.45 wt%, the weldability may be deteriorated. Therefore, molybdenum (Mo) is controlled to be 0 to 0.45 wt% or less of the total reinforcing steel weight.

Aluminum (Al)

Aluminum (Al) can function as a deoxidizer. However, when the content of aluminum is more than 0.040 wt%, the amount of nonmetal inclusions such as aluminum oxide (Al ₂ O ₃ ) can be increased. Therefore, aluminum (Al) is controlled to be not less than 0 to 0.040% by weight of the total reinforcing steel weight.

Niobium ( Nb )

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

The niobium (Nb) is added in an amount of more than 0 to 0.30 wt% of the total weight. When the content of niobium (Nb) exceeds 0.30 wt%, the ductility of the steel is lowered. The strength and the low temperature toughness due to the increase of the niobium content are not improved any more, but are present in a state of being solidified in the ferrite, There is a danger.

Nitrogen (N)

Nitrogen can be combined with other alloying elements such as titanium, vanadium, niobium, aluminum, etc. to form a nitride to function as a fine grain. However, when it is added in a large amount exceeding 0.020%, there is a problem that the amount of nitrogen increases and the elongation and formability of steel are lowered. Therefore, it is preferable that the steel is added in an amount of more than 0 to 0.020% by weight of the total reinforcing steel weight.

According to an embodiment of the present invention, the reinforcing bar having the alloy composition may further include at least one of tin (Sn), magnesium (Mg), and calcium (Ca).

Tin (Sn)

Tin (Sn) may be added to ensure corrosion resistance. However, if the content of tin is added in excess of 0.50%, the elongation can be drastically reduced. Therefore, tin (Sn) is controlled to be not less than 0 and not more than 0.50 wt% of the total reinforcing steel weight.

Magnesium (Mg)

Magnesium (Mg) can serve to improve the toughness and workability of the reinforcing bars. However, when 0.005% by weight or more of magnesium (Mg) is added, the purity of the steel can be deteriorated. Therefore, magnesium (Mg) is controlled to be 0 to 0.005 wt% or less of the total weight of the reinforcing bars.

Calcium (Ca)

Calcium (Ca) can be added for the purpose of improving electrical resistance weldability by inhibiting the formation of MnS inclusions by forming CaS inclusions. That is, calcium (Ca) has a higher affinity with sulfur than manganese (Mn), so CaS inclusions are formed and CaS inclusions are reduced when calcium is added. Such MnS is stretched during hot rolling to cause hook defects and the like in electrical resistance welding (ERW), so that electrical resistance weldability can be improved.

However, when the content of calcium (Ca) exceeds 0.005% by weight, generation of CaO inclusions is excessively generated, which deteriorates performance and electrical resistance weldability. Therefore, calcium (Ca) is controlled to be not less than 0 and not more than 0.005% by weight of the total reinforcing steel weight.

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 reinforcing bar according to the embodiment of the present invention has a composite structure of bainite and needle-like ferrite, and may have a particle size of 10 to 20 탆.

How to make high strength 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, a cooling step S300, and a repetition step S400. 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 slab may contain 0.10 to 0.50 wt% of carbon (C), 0.15 to 3.0 wt% of manganese (Mn), 0.05 to 0.6 wt% of silicon (Si), 0.10 to 0.50 wt% of chromium (Al) 0 to 0.040 wt% or less, niobium (Nb) 0 to 0.30 wt% or less, nitrogen (N) 0, And not more than 0.020 wt%, and the balance iron (Fe) and unavoidable impurities. The cast steel may further contain at least one of tin (Sn) in an amount of more than 0 to 0.50 wt%, magnesium (Mg) in an amount of more than 0 to 0.005 wt%, and calcium (Ca) in an amount of more than 0 to 0.005 wt%.

Reheat step

In the reheating step of the cast steel, the cast steel having the above composition is reheated in the temperature range of 1100 ° C to 1250 ° 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 1100 ° 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 1250 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 temperature of Ar ₃ -70 캜 to Ar ₃ -30 캜 to a finish rolling temperature 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.

When the finish rolling temperature is higher than Ar ₃ -30 ° C, the bainite fraction in the final structure may be decreased or it may become difficult to secure strength by forming coarse pearlite. Further, deformation concentrates on the interface between the cementite and the ferrite, and defects such as voids are generated, and the defects act as crack growth sites, which may lower the workability of the steel. On the contrary, when the finish rolling temperature is lower than Ar ₃ -70 캜, the rolling load is induced to lower the productivity and reduce the heat treatment effect. The r of Ar ₃ means the A ₃ temperature at the time of cooling. In one embodiment, the finishing rolling temperature of the casting may be 730 ° C to 780 ° C.

In one embodiment, the finish rolling temperature of the cast steel may meet the Ae3 / (4.15 * [C]) requirement. Here, [C] may be the weight percentage of carbon in the slab. Accordingly, the coefficient 4.15 may have a unit of [1 / weight%]. 'E' in Ae ₃ means A ₃ temperature in equilibrium state.

Cooling

In the cooling step (S300), the hot-rolled steel bar is cooled to a martensitic transformation start temperature (Ms temperature) through a temper core process so as to secure sufficient strength. At this time, the inner central portion of the reinforcing bar may be formed of needle-like ferrite and bainite. A process of reheating at a temperature of 500 ° C to 700 ° C may be performed on the steel material cooled during the temp core process.

Through the above-described process, a high-strength reinforcing bar having a composite structure of bainite and acicular ferrite can be produced. The reinforcing bar may have a particle size of 10 to 20 占 퐉.

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 Al Cr Mo V Nb Cu N Comparative Example 0.28 0.15 1.20 0.20 0.20 0.03 0.050 - 0.25 0.0090 Example 1 0.26 0.25 1.00 0.20 0.20 0.033 - 0.040 0.24 0.010 Example 2 0.26 0.30 1.05 0.20 0.20 0.41 - 0.038 0.24 0.010

Rolling conditions Reheating temperature (℃) Finishing rolling temperature (캜) Double temperature (℃) Comparative Example 1120 950 570 Example 1 1120 756 521 Example 2 1120 742 490

2. Property evaluation

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

Material evaluation Yield strength (MPa) Tensile Strength (MPa) Elongation Comparative Example 641 780 11.2 Example 1 651 788 13.0 Example 2 674 811 14.6

Comparing the yield strength, the tensile strength and the elongation, the specimens of the conditions of Examples 1 and 2 were superior to those of the comparative specimens. In particular, the specimen under the conditions of Example 2 exhibited a yield strength of 650 MPa or more, a tensile strength of 800 MPa or more, and an elongation of 14 or more.

2 is a photograph showing the microstructure of a reinforcing bar according to a comparative example of the present invention. 3A is a photograph showing each microstructure of a reinforcing bar according to an embodiment of the present invention. FIG. 3B is a partial enlarged view of the reinforcing bar of FIG. 3A. FIG.

The photograph of the comparative example of Fig. 2 is a microstructure photograph of the specimen produced under the conditions of comparative example of Tables 1 and 2 described above, and the photograph of the embodiment of Figs. 3a and 3b was manufactured under the conditions of Example 2 of Tables 1 and 2 The microstructure of the specimen is shown in Fig.

Referring to FIG. 2, the reinforcing steel microstructure according to the comparative example has a composite structure of ferrite and pearlite, and the reinforcing steel microstructure according to the embodiment shown in FIGS. 3A and 3B has a composite structure of bainite structure and needle- As shown in Fig. At this time, the microstructure of the examples was observed to have a particle size of about 10 mu m.

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
Step S400

Claims (7)

0.1 to 0.50 wt% of carbon (C), 0.15 to 3.0 wt% of manganese (Mn), 0.05 to 0.6 wt% of silicon (Si), 0.10 to 0.50 wt% of chromium (Cr) (N) more than 0 and not more than 0.30 wt%, nitrogen (N) more than 0 and not more than 0.020 wt%, molybdenum (Mo) And reheating the cast steel consisting of the remaining iron (Fe) and unavoidable impurities at 1100 ° C to 1250 ° C;
Hot-rolling the reheated cast slab to a finish rolling temperature at a temperature of Ar ₃ -70 캜 to Ar ₃ -30 캜 to produce a rebar;
Cooling the hot-rolled steel bar to a martensitic transformation starting temperature (Ms temperature) or lower through a core of the steel; And
Heating the cooled reinforcing bar at 450 ° C to 600 ° C; Containing
Method of manufacturing reinforcing bars.
The method according to claim 1,
The cast steel
At least one of tin (Sn) 0 to 0.50 wt% or less, magnesium (Mg) 0 to 0.005 wt% or less, and calcium (Ca)
Method of manufacturing reinforcing bars.
The method according to claim 1,
The finish rolling temperature of the cast steel satisfies the requirement of Ae3 / (4.15 * [C])
([C] is the weight percentage of carbon in the slab)
Method of manufacturing reinforcing bars.
The method according to claim 1,
The finish rolling temperature of the cast steel is from 730 캜 to 780 캜
Method of manufacturing reinforcing bars.
The method according to claim 1,
Wherein the reinforcing bars have a composite structure of bainite and needle-like ferrite,
Having a particle size of 10 to 20 mu m
Method of manufacturing reinforcing bars.
0.1 to 0.50 wt% of carbon (C), 0.15 to 3.0 wt% of manganese (Mn), 0.05 to 0.6 wt% of silicon (Si), 0.10 to 0.50 wt% of chromium (Cr) (N) more than 0 and not more than 0.30 wt%, nitrogen (N) more than 0 and not more than 0.020 wt%, molybdenum (Mo) (Fe) and inevitable impurities,
The reinforcing bar has a composite structure of bainite and needle-like ferrite, and has a particle size of 10 to 20 mu m
rebar.
The method according to claim 6,
At least one of tin (Sn) 0 to 0.50 wt% or less, magnesium (Mg) 0 to 0.005 wt% or less, and calcium (Ca)
rebar.

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