KR101304764B1 - Spiral reinforcing wire rod having excellent strength and ductility and producing method of the same - Google Patents

Abstract

The present invention relates to a wire rod for concrete reinforcement and a method of manufacturing the same, which controls the component system and composition range of the wire rod, controls heating temperature, rolling conditions, cooling conditions, and the like, and has excellent yield strength, tensile strength, elongation, and bending property. Provided is a wire rod for concrete reinforcement and a method of manufacturing the same. Through this, wire rod that satisfies D = 2.5d, 180 ° when the yield strength is 400MPa or more, tensile strength 700MPa or more, elongation 20% or more, and the diameter is 16mm or less during bending test without adding expensive elements such as Cr and Ni. Can provide. In addition, it is possible to increase the adhesion between the concrete and the wire rod by rolling the deformed shape on the outer shape of the wire rod.

Spiral, coiled bar, rebar, billet, concrete, reinforcement

Description

Spiral reinforcing wire rod having excellent strength and ductility and producing method of the same}

The present invention relates to a wire rod for spiral concrete reinforcement and a method for manufacturing the wire rod, and to control the component system and the composition range of the wire rod, and to control the heating temperature, rolling conditions, cooling conditions, etc., which is excellent in yield strength, tensile strength, elongation and bendability. Wire rod can be provided.

The wire rod for concrete reinforcement means a wire rod embedded in concrete for the purpose of reinforcing concrete, and is generally called rebar.

Among steel wires for concrete reinforcement, straight rebar is usually cut to 6 ~ 12m length, which is inefficient because the end of rebar is left during secondary processing, and the ratio of material consumed due to overlapping hypothesis reaches 5 ~ 10%. In addition, the utilization of spiral concrete reinforcing wire (coil reinforcing bar) is required to reduce costs due to the increase in labor costs and the need for reduction of construction costs according to the advanced economy.

Currently, in the developed countries, mainly in Europe, spiral concrete reinforcing wire rods (coil reinforcing bars) using automated processing equipment occupy most of the cases below the reinforcement diameter D16, but in Korea, the market is still unformed. As the economy is expected to change, the utilization of the wire rod is expected to increase rapidly.

In addition, the wire rod for spiral concrete reinforcement having a deformed shape including protrusions in the outer shape of the wire rod can increase the adhesive force between the wire rod and the concrete, and thus it is required to be utilized.

In addition, the spiral concrete reinforcing wire is mainly applied to large structures should have a high strength, high toughness mechanical properties. To date, there are no spiral wire reinforcing wires (coil reinforcing bars) satisfying D = 2.5d, 180 ° when the yield strength is over 400MPa, the tensile strength is over 700MPa, the elongation is over 20% and the diameter is less than 16mm in the bending test.

The present invention relates to a wire rod for concrete reinforcement and a method of manufacturing the same, and more particularly, to control the component system and composition range of the wire rod, and to control the heating temperature, rolling conditions, cooling conditions, and the like, yield strength, tensile strength, elongation and bending. To provide a spiral concrete reinforcing wire having excellent properties and a method of manufacturing the same.

In one embodiment of the present invention, the wire rod for spiral concrete reinforcement is% by weight, C: 0.35-0.65%, Si: 0.10-0.35%, Mn: 0.60-0.90%, P: 0.030% or less, and S: 0.035% or less, It is composed of the remaining Fe and other unavoidable impurities.

The microstructure is preferably composed of 20-40% ferrite and the balance pearlite in an area fraction.

In addition, the average particle diameter of the ferrite is preferably 15 ~ 25㎛.

In addition, the wire rod preferably satisfies D = 2.5d, 180 ° when the yield strength is 400MPa or more, the tensile strength is 700MPa or more, the elongation 20% or more, and the diameter is 16mm or less during the bending test.

In addition, it is preferable that the outer shape of the wire rod is rolled into a release shape.

As another embodiment of the present invention, the manufacturing method of the wire rod for spiral concrete reinforcement is a weight%, C: 0.35 ~ 0.65%, Si: 0.10 ~ 0.35%, Mn: 0.60 ~ 0.90%, P: 0.030% or less, S : Less than 0.035%, billet composed of remaining Fe and other unavoidable impurities is heated at 1000 ~ 1200 ℃ for 90 ~ 150 minutes, multi-stage rolling at 950 ~ 1200 ℃, water-cooled, and then at 850 ~ 950 ℃ After winding up in a form, the step of cooling on a roller conveyor at a cooling rate of 2 ~ 10 ℃ / s.

The multi-stage rolling step is preferably rough rolling, intermediate rolling, finishing rolling and release rolling sequentially.

In addition, the wire rod preferably satisfies D = 2.5d, 180 ° when the yield strength is 400MPa or more, the tensile strength is 700MPa or more, the elongation 20% or more, and the diameter is 16mm or less during the bending test.

As described above, the present invention provides a yield strength of at least 400 MPa, a tensile strength of at least 700 MPa, an elongation of at least 20%, and a diameter of 16 mm or less in a bending test without adding expensive elements such as Cr and Ni. D = 2.5d, 180 ° It can provide a wire for reinforcing spiral concrete that satisfies. In addition, it is possible to increase the adhesion between the concrete and the wire rod by rolling the deformed shape on the outer shape of the wire rod. In addition, it is possible to provide a wire rod for spiral concrete reinforcement with less material loss and economical efficiency as compared with straight bars.

The present invention relates to a wire rod for concrete reinforcement that can be applied to concrete structures used in various construction sites, the surface of the wire rod, and rolled a deformed shape to increase the adhesion strength between the wire rod and the concrete on the surface of the wire rod itself A wire rod having excellent mechanical properties with improved strength and ductility can be provided.

Hereinafter, the component system and composition range of the spiral concrete reinforcing wire of the present invention will be described in detail.

C (carbon): 0.35-0.65 weight%

C is an essential element to be added to secure the strength of the steel. If the content of C is less than 0.35% by weight, the strength intended by the present invention cannot be obtained. On the other hand, when the content of C exceeds 0.65% by weight, high strength can be ensured, but the ductility and bendability intended by the present invention cannot be secured. Therefore, the content of C is preferably limited to 0.35 ~ 0.65%.

Si (silicon): 0.10 to 0.35 wt%

Si is an element necessary for deoxidation of steel materials and can improve yield stress as a solid solution strengthening element. However, when the content of Si is less than 0.10% by weight, the above effects cannot be exhibited. On the other hand, when the content of Si exceeds 0.35% by weight, there is a problem in that ductility and bendability are lowered. Therefore, the content of Si is preferably limited to 0.10 to 0.35% by weight.

Mn (Mn): 0.60 ~ 0.90% by weight

Mn is an element that forms a solid solution to form a solid solution to strengthen the solid solution and is very useful for improving the strength of steel. When the content of Mn is less than 0.6% by weight, the segregation by Mn is hardly affected, but the effect of improving the strength of the steel by solid solution strengthening cannot be obtained. On the other hand, when the Mn content exceeds 0.9% by weight, Mn segregation is generated rather than a solid solution strengthening effect, which adversely affects product characteristics. Therefore, the content of Mn is preferably limited to 0.60 to 0.90% by weight.

P (phosphorus): 0.030 wt% or less

P is an impurity, which is segregated at grain boundaries and may be a major cause of hot embrittlement or deterioration of ductility. Therefore, it is desirable to control P as low as possible. In theory, it is possible to limit P content to 0%, but it is inevitable in manufacturing process. It can only be added. It is important to manage the upper limit, the upper limit of the content of P is preferably limited to 0.035% by weight.

S (sulfur): 0.035% by weight or less

S is an impurity element and is a low melting point element, which precipitates at grain boundaries and causes hot embrittlement, so it is preferable to control it as low as possible. In theory, it may be possible to limit the content of S to 0%, but it is inevitably added in the manufacturing process. It must be. It is important to manage the upper limit, the upper limit of the content of S is preferably limited to 0.035% by weight.

Hereinafter, a method of manufacturing the wire rod of the present invention will be described in detail.

The method for producing a wire rod of the present invention is to heat the billet satisfying the component system and composition range for 90 to 150 minutes at 1000 ~ 1200 ℃, multi-stage rolling the heated billet at 950 ~ 1200 ℃, the rolled wire After cooling the water is wound at 850 ~ 950 ℃ and then cooled at a cooling rate of 2 ~ 10 ℃ / s.

Heating stage: heating at 1000-1200 ° C. for 90-150 minutes

When heating the billet satisfying the component system and composition range controlled by the present invention in the heating temperature range, the austenite single phase is maintained, the austenite grains are not coarsened, and the remaining segregation, carbides and inclusions can be effectively dissolved. have.

If the heating temperature is less than 1000 ° C., sufficient heat cannot be transferred to re-use segregation, carbides, etc., even by heating. On the other hand, when the heating temperature exceeds 1200 ℃ decarburization occurs on the surface of the billet and the austenite grains become very coarse, the fraction of the ferrite in the microstructure after cooling becomes very small, it is unable to secure sufficient ductility. Therefore, the heating temperature is preferably limited to 1000 ~ 1200 ℃.

If the heating time is less than 90 minutes, the temperature of the billet to be heated cannot be made uniform. On the other hand, when the heating time exceeds 150 minutes, decarburization becomes excessive. Therefore, the heating time is preferably limited to 90 to 150 minutes.

Rolling stage: rolling at 950 ~ 1200 ℃

It is preferable to roll the billet heated above to the desired thickness and width by rough rolling, intermediate rolling, finishing rolling in the range of 950-1200 degreeC, and to roll-release to have a reinforcement shape in the final roll.

Winding process: up to 850 ~ 950 ℃

After rolling, the wire rod is cooled to 850 ~ 950 ℃ and wound in a ring form. If the coiling temperature is less than 850 ℃ water cooling is excessive to increase the material strength is difficult to wind up, if the coiling temperature exceeds 950 ℃ microstructure is coarse hard to obtain the desired mechanical properties.

Cooling step: cooling to 2 ~ 10 ° C / s;

The coiled wire rod is cooled after the winding. If the cooling rate is less than 2 ° C./s, the grains grow and it is difficult to obtain the desired strength. On the other hand, if it exceeds 10 ℃ / s it is difficult to secure the desired ductility and bendability to form a low-temperature structure, such as martensite. Therefore, the cooling rate is preferably limited to 2 ~ 10 ℃ / s.

In the course of cooling after the hot rolling, in the austenitic austenite composition, the cornerstone ferrite is first generated, and then the remaining austenite is transformed into a pearlite structure composed of cementite and ferrite.

As a result, the microstructure of the wire rod of the present invention forms a composite structure consisting of ferrite and residual pearlite having an area fraction of 20 to 40% and a grain size of 15 to 25 μm. In addition, if the yield strength is more than 400MPa, the tensile strength is more than 700MPa, the elongation is more than 20%, and the coil reinforcing bar diameter is 16mm or less, the mechanical property of D = 2.5d, 180 ° can be ensured. Inner radius during the test, d is the diameter of the spiral concrete reinforcing wire)

Hereinafter, the present invention will be described in detail by way of examples.

(Example)

The billet having the component system and composition range as shown in Table 1 was reheated at 1000 to 1200 ° C. for 2 hours, and then extracted and hot rolled into a spiral reinforcing wire having a diameter of D13. At this time, the finish hot rolling temperature was 1000 ℃, and then cooled to 900 ~ 940 ℃ and then wound in a ring (ring) was blown and cooled on a roller conveyor at a cooling rate of 2 ~ 10 ℃ / s.

The yield strength, tensile strength, elongation, bendability, and microstructure of the spiral reinforcing wire manufactured by the above manufacturing method are shown in Table 2 below. When the bending test satisfies D = 2.5d and 180 °, it is marked as ○, and when it is not satisfied, it is marked as X.

division C (% by weight) Si (% by weight) Mn (% by weight) P (% by weight) S (% by weight) Inventory 1 0.44 0.26 0.75 0.023 0.028 Inventive Example 2 0.62 0.25 0.74 0.025 0.023 Comparative Example 1 0.33 0.26 0.75 0.028 0.028 Comparative Example 2 0.68 0.40 0.75 0.024 0.025

division Microstructure Yield strength
(MPa) The tensile strength
(MPa) Elongation
(%) Bendability
(D = 2.5d, 180 °) Inventory 1 Ferrite 33% + Balance Pearlite 404 767 25.2 ○ Inventive Example 2 Ferrite 21% + Balance Pearlite 440 923 20.4 ○ Comparative Example 1 Ferrite 48% + Balance Pearlite 355 647 27.2 ○ Comparative Example 2 Ferrite 10% + Balance Pearlite 473 985 16.9 X

The C content of Comparative Example 1 is lower than the content of C to be controlled by the present invention. The low C content indicates that the yield strength of the wire rod is less than 400 MPa and the tensile strength is less than 700 MPa. The content of C and Si of Comparative Example 2 is higher than the content of C and Si to be controlled by the present invention, but the strength of the wire is measured to be high, but the elongation is less than 20%, and the bending property is also poor.

Inventive Examples 1 and 2, which correspond to the component system and composition range intended in the present invention, have a fraction of ferrite within 20 to 40%, yield strength of 400 MPa or more, tensile strength of 700 MPa or more, elongation 20% or more, and a bending test. It showed excellent mechanical properties satisfying D = 2.5d, 180 °.

Claims (8)

By weight, C: 0.35-0.65%, Si: 0.10-0.35%, Mn: 0.60-0.90%, P: 0.030% or less, S: 0.035% or less, remaining Fe and other unavoidable impurities, ferrite and pearlite It comprises a microstructure consisting of, the microstructure is made of ferrite 20 ~ 40% and the remainder pearlite in the area fraction, the spiral concrete reinforcing wire, characterized in that having a tensile strength of 700MPa or more. delete The wire rod for spiral concrete reinforcement according to claim 1, wherein the ferrite has an average particle diameter of 15 to 25 µm. The wire rod for spiral concrete reinforcement according to claim 1, wherein the wire satisfies D = 2.5d, 180 ° when the yield strength is 400MPa or more, the elongation is 20% or more, and the diameter is 16mm or less during the bending test. D is the inner radius in the bending test, d is the diameter of the spiral concrete reinforcing wire) The wire rod for spiral concrete reinforcement according to claim 1, wherein an outer shape of the wire rod is rolled into a deformed shape. By weight%, C: 0.35 to 0.65%, Si: 0.10 to 0.35%, Mn: 0.60 to 0.90%, P: 0.030% or less, S: 0.035% or less, and billet composed of remaining Fe and other unavoidable impurities Heating at 1200 ° C. for 90-150 minutes; Multi-stage rolling the heated billet at 950-1200 ° C .; Winding the rolled wire in water and winding it in the form of a ring at 850-950 ° C .; And The method of producing a spiral concrete reinforcing wire rod comprising the step of cooling the twisted wire rod at a cooling rate of 2 ~ 10 ℃ / s on a roller conveyor (roller conveyor). The method of claim 6, wherein the multi-stage rolling step includes a rough rolling, an intermediate rolling, a finishing rolling, and a release rolling in sequence. The method of claim 6, wherein the wire has a yield strength of 400MPa or more, tensile strength of 700MPa or more, elongation 20% or more, when the diameter is 16mm or less during the bending test, it satisfies D = 2.5d, 180 ° Method for manufacturing wire rod (where D is the inner radius during bending test and d is the diameter of wire rod for spiral concrete reinforcement)