KR20120132825A - Method for manufacturing high-strength deformed bar with low yield ratio - Google Patents

Abstract

PURPOSE: An earthquake-resistant reinforced steel with a low yield ratio and a manufacturing method thereof are provided to improve the earthquake resistance of a structure or building by securing a yield strength of 700MPa or greater and a yield ratio of 0.6 or less. CONSTITUTION: An earthquake-resistant reinforced steel comprises 0.30-0.50 weight% of C, 0.10-0.70 weight% of Si, 0.50-1.80 weight% of Mn, 0.03 weight% or less of P, 0.03 weight% or less of S, 0.20-0.30 weight% of Cu, 0.3 weight% or less of Ni, 0.7-1.80 weight% of Cr, 0.5weight% or less of Mo, 0.05 weight% or less of Al, 0.02-0.10 weight% of Zr, 0.001-0.005 weight% of B, 30ppm or less of oxygen, 80ppm or less of N, and the remaining amount of Fe and inevitable impurities. The earthquake-proof steel reinforcement has a yield strength of 700MPa or greater and a yield ratio(yield strength/tensile strength) of 60% or less.

Description

Earthquake-resistant reinforcing bars having a resistive ratio and manufacturing method thereof {METHOD FOR MANUFACTURING HIGH-STRENGTH DEFORMED BAR WITH LOW YIELD RATIO}

The present invention relates to a seismic reinforcing bar and a method for manufacturing the same, and more particularly, to a seismic reinforcing bar and a method for manufacturing the seismic resistance is improved by reducing the yield ratio (yield strength / tensile strength).

Recently, the frequency of earthquakes is increasing due to changes in the global environment. Accordingly, the concept of seismic design is being introduced into architectural and civil engineering structures.

The seismic design is to delay the complete collapse of the structure by absorbing seismic force.

According to the report of the Korea Concrete Institute and the Civil Society, seismic forces are exhibited when the yield ratio of rebars used in seismic design is 0.80 or less.

An object of the present invention to reduce the yield ratio (yield strength / tensile strength) to provide an earthquake-resistant reinforcing steel and a method of manufacturing the same that can improve the seismic strength of the structure during an earthquake.

Another object of the present invention is to provide a seismic reinforcing steel having a yield strength of 700MPa or more and a yield ratio of 0.6 or less, and a method of manufacturing the same.

In the present invention, carbon (C): 0.30 to 0.50%, silicon (Si): 0.10 to 0.70%, manganese (Mn): 0.50 to 1.80%, phosphorus (P): 0.03% or less, sulfur (S): 0.03% or less, Copper (Cu): 0.20 to 0.30%, Nickel (Ni): 0.3% or less, Chromium (Cr): 0.7 to 1.80%, Molybdenum (Mo): 0.5% or less, Aluminum (Al): 0.05% or less , Zirconium (Zr): 0.02 ~ 0.10%, Boron (B): 0.001 ~ 0.005%, Oxygen (O): 30ppm or less, Nitrogen (N): 80ppm or less do.

At this time, the seismic reinforcing bar exhibits a yield strength of 700 MPa or more, a yield ratio (yield strength / tensile strength) of 60% or less, and an elongation of 12% or more.

In the present invention, carbon (C): 0.30 to 0.50%, silicon (Si): 0.10 to 0.70%, manganese (Mn): 0.50 to 1.80%, phosphorus (P): 0.03% or less, sulfur (S) ): 0.03% or less, Copper (Cu): 0.20 to 0.30%, Nickel (Ni): 0.3% or less, Chromium (Cr): 0.7 to 1.80%, Molybdenum (Mo): 0.5% or less, Aluminum (Al): 0.05 % Or less, Zirconium (Zr): 0.02 to 0.10%, Boron (B): 0.001 to 0.005%, Oxygen (O): 30 ppm or less, Nitrogen (N): 80 ppm or less, and the rest of Fe and unavoidable impurities It provides a method for producing a seismic reinforcing bar, characterized in that the heating in the temperature range of ℃ ~ 1250 ℃, and hot rolling under the rolling end temperature conditions at 950 ℃ ~ 1250 ℃ through the reinforcing steel rolling process.

Seismic reinforcing bar according to the present invention has a yield strength of 700MPa or more and a yield ratio of 0.6 or less, thereby bringing an effect of improving the seismic performance of the building or civil engineering structure built using it.

SEM picture of the non-metallic inclusions of the earthquake-resistant rebar according to the embodiment of the present invention of FIG.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the earthquake-resistant reinforcing bar having a resistive ratio and a method of manufacturing the same according to the preferred embodiment of the present invention.

Seismic rebar

The seismic reinforcing bar according to the present invention is characterized by lowering the yield ratio by coordinating high temperature grains by controlling the steel composition, in particular by controlling the content of Zr.

The seismic reinforcing bar according to the present invention exhibits mechanical properties of yield strength of 700 MPa or more and yield ratio (yield strength / tensile strength) of 0.6 or less.

To this end, the earthquake-resistant reinforcing bar according to the present invention is carbon (C): 0.30 to 0.50%, silicon (Si): 0.10 to 0.70%, manganese (Mn): 0.50 to 1.80%, phosphorus (P): 0.03 % Or less, sulfur (S): 0.03% or less, copper (Cu): 0.20 to 0.30%, nickel (Ni): 0.3% or less, chromium (Cr): 0.7 to 1.80%, molybdenum (Mo): 0.5% or less, Aluminum (Al): 0.05% or less, Zirconium (Zr): 0.02 ~ 0.10%, Boron (B): 0.001 ~ 0.005%, Oxygen (O): 30ppm or less, Nitrogen (N): 80ppm or less and inevitable with the rest of Fe Contains impurities.

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

Carbon (C)

Carbon (C) is a major element that determines the strength and hardness of steel when added. The higher the content, the lower the toughness, which increases strength. In addition, as the cold workability increases, tensile strength and yield point increase and elongation decreases. Therefore, in the seismic reinforcing bar according to the present invention, it is preferable to add 0.3 to 0.5% by weight of the total weight.

If the carbon content is less than 0.3% by weight, the required strength cannot be secured. If the carbon content is more than 0.5% by weight, the required yield ratio is not satisfied.

Silicon (Si)

Silicon contributes to strength and, in particular, serves as a deoxidizer to remove oxygen in the steel.

The silicon is preferably added in an amount of 0.1 to 0.7% by weight of the total weight of the seismic reinforcing bar according to the present invention in consideration of inherent deoxidation effect and surface quality. If the content of silicon is less than 0.1% by weight, the deoxidation effect due to the addition of silicon is insufficient. On the contrary, when the content of silicon exceeds 0.7% by weight, toughness and weldability are inhibited.

Manganese (Mn)

Manganese (Mn) improves the hardenability and strength of the steel, and increases the plasticity at high temperatures to improve castability. In particular, it forms a MnS in combination with the harmful component S to prevent redness brittleness. However, when the excess is added, the toughness is lowered, so it is preferable to limit the amount to 0.5 to 1.8 wt%.

Phosphorus (P)

Phosphorous (P) is added to inhibit cementite formation and increase strength.

In addition, phosphorus deteriorates toughness and creates fragile segregation such as Fe ₃ P.

In addition, since phosphorus inhibits weldability and impact toughness and causes final material variation due to slab center segregation, the phosphorus (P) is 0.03 weight of the total weight of the earthquake-resistant rebar according to the present invention. It is preferable to add restrictively within the range of% or less.

Sulfur (S)

Sulfur (S) forms a MnS and is a major circle or excessive addition that improves the machinability of the steel and inhibits hot workability and causes tearing. In addition, excessive addition may cause defects during surface treatment due to the formation of large inclusions.

Therefore, the addition amount of sulfur is preferably limited to 0.03% by weight or less of the total weight of the earthquake-resistant rebar.

Copper (Cu)

Copper (Cu) increases the strength as a solid solution strengthening element, but when excessively added, it degrades hot workability.

When copper is added at least 0.02% by weight of the total weight of the seismic reinforcing bar to obtain the effect of increasing the strength, it is preferable to limit it to 0.30% by weight or less because excessive addition causes a significant decrease in toughness and deterioration due to hot working.

Nickel (Ni)

Nickel (Ni) is an element that increases the hardenability, improves toughness but increases the manufacturing cost of parts and decreases the manufacturability, and therefore it is preferably limited to 0.3 wt% or less.

Chrome (Cr)

Together with Mn, it acts as an element to improve the strength of steel, to refine pearlite colonies and to improve ductility. However, excessive addition lowers toughness and degrades workability and machinability. Therefore, it is preferable to limit to 0.7 to 1.8% by weight.

Molybdenum (Mo)

Molybdenum is effective in improving strength and toughness, but it significantly increases hardness during heat treatment such as normalizing, increases manufacturing cost and decreases part workability. Therefore, it is desirable to limit it to 0.5 wt% or less.

Aluminum (Al)

Aluminum is used as a fine particle deoxidant in combination with N as a strong deoxidizer, but excessive addition increases the amount of non-metallic inclusions such as Al ₂ O ₃ , so it is preferable to limit it to 0.05% by weight or less.

Zirconium (Zr)

Zirconium is a strong nitride-forming element that has an excellent effect on high temperature grain coarsening and forms ZrN prior to the formation of carbonitride, which refines grains. High temperature grain coarsening was found to be highly effective in reducing yield ratio. ZrN acts as a nucleation site of the MnS inclusions, thereby reducing the microstructure and elongation of the inclusions, thereby reducing impact anisotropy. However, excessive addition of needle-like Zr carbide leads to precipitation, which adversely affects the physical properties. Therefore, it is preferable to limit the amount to 0.02 to 0.10 wt%.

Boron (B)

Boron is known as an element that stabilizes the B grain boundary in steel and greatly improves the hardenability by addition of a small amount, but when B is excessively added, it is segregated at the grain boundary and lowers the toughness of the steel, such as lowering the physical properties. It is preferred to limit to 0.005% by weight.

Oxygen (O)

Since oxygen forms an oxide-based inclusion and excessively degrades toughness, it is preferable to limit it to 30 ppm or less of the total weight of the earthquake-resistant rebar.

Nitrogen (N)

Nitrogen is effective for finer grains by the production of AlN, but when added excessively, the toughness deteriorates, so it is preferable to limit it to 80 ppm or less of the total weight of the earthquake-resistant rebar.

Resistant Steel Ratio Seismic Rebar Manufacturing Method

According to the present invention, carbon (C): 0.30 to 0.50%, silicon (Si): 0.10 to 0.70%, manganese (Mn): 0.50 to 1.80%, phosphorus (P): 0.03% or less, sulfur (S) : 0.03% or less, Copper (Cu): 0.20 to 0.30%, Nickel (Ni): 0.3% or less, Chromium (Cr): 0.7 to 1.80%, Molybdenum (Mo): 0.5% or less, Aluminum (Al): 0.05% Below, zirconium (Zr): 0.02 ~ 0.10%, boron (B): 0.001 ~ 0.005%, oxygen (O): 30ppm or less, nitrogen (N): 80ppm or less, and the steel material consisting of the remaining Fe and unavoidable impurities 1000 ℃ It provides a method for producing a seismic reinforcing bar, characterized in that the heating in the temperature range of ~ 1250 ℃, hot rolling at the end temperature conditions of the end of rolling at 950 ℃ ~ 1250 ℃ through the reinforcing steel rolling process.

Alloying elements as described above are added within the respective weight ratio ranges, and the remainder is produced in an electric furnace made of steel composed of Fe and inevitably contained impurities, and then billeted by continuous casting.

Thereafter, the cast billet is reheated and extracted in a heating range of 1000 ° C. to 1250 ° C. in a heating furnace, followed by hot rolling in accordance with a conventional rebar rolling process.

At this time, the hot rolling conditions are not particularly limited, but considering the load and productivity of the rolling roll, it is preferable to finish the rolling at the highest possible temperature, so that the end rolling temperature is preferably applied at a temperature of 950 ° C. or higher. .

As described above, when the end temperature of the rolling is high, the grain size of the final reinforcement product is relatively coarse, which is advantageous in lowering the yield ratio than when the grain is fine.

Thereafter, the step of quenching using Tempcore may be further performed.

Example

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. 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.

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

1. Preparation of Reinforcing Bar Specimen

Alloy compositions applied to the rebar specimens according to Example 1 and Comparative Example 1 are shown in Table 1 below.

main
ingredient C Si Mn Cr V Al B Zr N Comparative Example 1 0.40% 0.56% 1.45% 0.15% 0.19% 90 ppm - - 100 ppm Example 1 0.32% 0.60% 1.42% 1.45% - 60 ppm 38 ppm 200 ppm 70 ppm

As described in Table 1, steels having a composition of Example 1 and Comparative 1 were heated to a temperature range of 1200 ° C., and hot rolled to a rolling end temperature condition of 1150 ° C. through a reinforcing rolling process to prepare reinforcing bar specimens.

2. Property evaluation

Table 2 shows the mechanical properties of the reinforcing bar specimens according to Example 1 and Comparative Example 1.

Yield strength The tensile strength Yield ratio Elongation Comparative Example 1 723 MPa 1,090 MPa 66.3% 10.01% Example 1 721 MPa 1,247 MPa 57.8% 13.2%

Referring to Table 2, it can be seen that in the case of Example 1, the target yield strength is 700 MP or more and the yield ratio is 60% or less. This may be because ZrN acts as a nucleation site of the MnS inclusions, thereby reducing the fineness and elongation of the inclusions, since the added zirconium forms ZrN prior to the formation of carbonitride, which refines the grains.

This can also be seen through the SEM image of the nonmetallic inclusions of FIG. 1.

The upper left shows the shape of the entire nonmetallic inclusion, the upper right shows the area occupied by Zr, the lower left shows the area occupied by Mn, and the lower right shows the area occupied by S.

It can be seen from this that ZrN was generated prior to carbonitride formation and then served as nucleation site of MnS.

As described above, in the case of the resistance yield ratio seismic reinforcing bar according to the present invention, a yield strength of 700 MPa and a resistance yield ratio of 0.6 or less can be simultaneously achieved.

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 may 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.

Claims (4)

By weight% Carbon (C): 0.30 ~ 0.50%, Silicon (Si): 0.10 ~ 0.70%, Manganese (Mn): 0.50 ~ 1.80%, Phosphorus (P): 0.03% or less, Sulfur (S): 0.03% or less , Copper (Cu): 0.20 to 0.30%, nickel (Ni): 0.3% or less, chromium (Cr): 0.7 to 1.80%, molybdenum (Mo): 0.5% or less, aluminum (Al): 0.05% or less, zirconium ( Zr): 0.02 to 0.10%, boron (B): 0.001 to 0.005%, oxygen (O): 30 ppm or less, nitrogen (N): 80 ppm or less, and the seismic reinforcing steel bar consisting of remaining Fe and unavoidable impurities.
The method of claim 1,
The seismic reinforcing bar is
Yield strength 700MPa or more, yield ratio (yield strength / tensile strength) 60% or less, characterized in that the rebar.
The method of claim 2,
The seismic reinforcing bar is an earthquake-resistant reinforcement, characterized in that more than 12% elongation.
By weight% Carbon (C): 0.30 ~ 0.50%, Silicon (Si): 0.10 ~ 0.70%, Manganese (Mn): 0.50 ~ 1.80%, Phosphorus (P): 0.03% or less, Sulfur (S): 0.03% or less , Copper (Cu): 0.20 to 0.30%, nickel (Ni): 0.3% or less, chromium (Cr): 0.7 to 1.80%, molybdenum (Mo): 0.5% or less, aluminum (Al): 0.05% or less, zirconium ( Zr): 0.02 ~ 0.10%, Boron (B): 0.001 ~ 0.005%, Oxygen (O): 30ppm or less, Nitrogen (N): 80ppm or less, and the rest of Fe and unavoidable impurities A method of manufacturing a seismic reinforcing steel bar, characterized in that the heating is carried out at a temperature range, and the steel sheet is hot rolled at a temperature condition of end of rolling at 950 ° C to 1250 ° C through a rebar rolling process.

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