KR20120132829A

KR20120132829A - Method for manufacturing high-strength deformed bar with low yield ratio

Info

Publication number: KR20120132829A
Application number: KR1020110051189A
Authority: KR
Inventors: 이철원; 권영준; 윤일성
Original assignee: 현대제철 주식회사
Priority date: 2011-05-30
Filing date: 2011-05-30
Publication date: 2012-12-10

Abstract

PURPOSE: A low-yield ratio earthquake-proof steel reinforcement using a temp core and a manufacturing method thereof are provided to obtain high strength and a low yield ratio by controlling the fraction of a surface hardened layer in a temp core process. CONSTITUTION: A method for manufacturing a low-yield ratio earthquake-proof steel reinforcement comprises the steps of: heating a steel material to a temperature range of 1000-1250°C, hot-rolling the steel material in a rolling finish temperature condition of 950°C-1250°C, rapidly cooling the steel material in a temp core with a heat transfer coefficient of 23000-38000W/m^2K and a feed flux of 312-416m3/h. [Reference numerals] (AA) H[W/m^2K]; (BB) Surface layer fraction

Description

METHODS 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 resistance yield ratio (tensile strength / yield strength) seismic reinforcing bar having a sufficient work hardening ability after yielding.

Generally, Tempcore is used to manufacture high tensile rebar. When using the temp core, the surface of the reinforcing steel bar produced has a martensite structure due to quenching, thereby showing high yield strength.

Therefore, it was difficult to produce high tensile reinforcing bars having a resistive ratio using the temp core.

An object of the present invention is to manufacture steel reinforcement using the temp core process, but to control the fraction of the surface hardened layer, seismic reinforcing steel having a high yield strength of 600 MPa or more and a low yield ratio (tensile strength / yield strength) of 1.25 or more, and its manufacture In providing a method.

In the present invention, C: 0.1 to 0.4%, Si: 0.1 to 0.6%, Mn: 0.4 to 1.5%, P: 0.01 to 0.03%, S: 0.01 to 0.03%, Cu: 0.01 to 0.3%, and V: 0.01 ~ 0.15% and the remainder are heated to 1000 ℃ ~ 1250 ℃ temperature steel, consisting of Fe and other inevitable impurities, and hot-rolled at the end temperature of rolling at 950 ℃ ~ 1250 ℃ through rebar rolling process. After that, while performing quenching in the temp core, it provides a method for manufacturing a resistance to earthquake-resistant seismic reinforcing bar, characterized in that the heat transfer coefficient during cooling to be 23000 ~ 38000W / m ² K.

At this time, the process conditions of the temp core is preferably a supply flow rate of 312 ~ 416m ³ / h range.

In addition, the present invention is produced by the above method, the fraction of the surface layer which is a hardened layer provides a resistance-to-earthquake-resistant reinforcing bar, characterized in that the range.

At this time, the resistance yield ratio seismic reinforcing bar, the hardness of the inner layer is 210Hv or more, yield strength 600MPa or more, yield ratio (yield strength / tensile strength) 0.8 or less.

The present invention has the effect of producing a seismic reinforcing bar having a yield strength of 600MPa or more and a resistance yield ratio of 0.8 or less (yield strength / tensile strength) using the temp core.

The seismic reinforcing bar manufactured in this way effectively absorbs energy, thereby bringing the effect of improving the seismic performance of the building or structure constructed using it.

1 is a graph showing the relationship between the heat transfer coefficient of the seismic reinforcing bar according to the embodiment of the present invention and the fraction of the surface layer which is a hardened layer.

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, a detailed description will be given of a resistance-to-wear ratio seismic reinforcing bar using a temper core according to a preferred embodiment of the present invention and a manufacturing method thereof.

In the present invention, C: 0.1 to 0.4%, Si: 0.1 to 0.6%, Mn: 0.4 to 1.5%, P: 0.01 to 0.03%, S: 0.01 to 0.03%, Cu: 0.01 to 0.3%, and V: 0.01 ~ 0.15% and the remainder are heated to 1000 ℃ ~ 1250 ℃ temperature steel, consisting of Fe and other inevitable impurities, and hot-rolled at the end temperature of rolling at 950 ℃ ~ 1250 ℃ through rebar rolling process. After that, the heat transfer coefficient during cooling in the temp core is heat treated in the range of 23000 ~ 38000W / m ² K, to provide a resistive ratio seismic reinforcing steel bar, characterized in that the fraction of the surface layer of the cured layer is in the range of 19 ~ 29%.

At this time, the resistive-ratio seismic reinforcing bars exhibit physical properties of the hardness of the inner layer of 210 Hv or more, yield strength of 600 MPa or more, and yield ratio (yield strength / tensile strength) of 0.8 or less.

The present invention is to secure the hardness of the inner layer from the alloy composition, and to control the cooling conditions of the temp core process, to control the fraction of the inner layer and the surface layer, the seismic reinforcing steel having a physical property of yield strength 600MPa or more, yield ratio 0.8 or less To provide.

Seismic rebar

The seismic reinforcing steel according to the present invention is characterized by lowering the yield ratio by coordinating high temperature grains by controlling the yield strength of 600MPa or more, yield ratio steel composition, in particular by controlling the content of Zr.

The seismic reinforcing bar according to the present invention has a composition as follows to indicate the mechanical properties of the yield strength (yield strength / tensile strength) of more than 600MPa, 0.8 or less yield strength.

Seismic reinforcing bar according to the present invention by weight% carbon (C): 0.10 ~ 0.40%, silicon (Si): 0.10 ~ 0.60%, manganese (Mn): 0.40 ~ 1.50%, phosphorus (P): 0.03% or less, Sulfur (S): 0.03% or less, copper (Cu): 0.30% or less, vanadium (V): 0.015% or less and the remaining Fe and inevitable 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)

C is an element effective for increasing the strength. However, if the content is less than 0.10%, the desired high strength will not be obtained. Moreover, if it exceeds 0.4%, it is effective for increasing the strength, but deterioration of toughness and ductility is remarkable, so it is necessary to designate it at 0.4% or less and add it. Therefore, it is necessary to add C content in 0.10%-0.4% of range.

Silicon (Si)

Si is an essential element for deoxidation of steel and is an element effective in increasing the strength. However, if the content is 0.1% or less, the desired high strength will not be obtained. Moreover, exceeding 0.6% causes a sharp decrease in toughness and ductility. Therefore, it is necessary to add content of Si in 0.1%-0.6% of range.

Manganese (Mn)

Mn has the effect of increasing the strength during heat treatment by improving the hardenability. In particular, it is also an element that is added essentially for strength compensation according to the addition amount of C as described above. In this case, when Mn is added in an amount of 0.4% or less, there is little effect of improving hardening property, and when Mn exceeds 1.5%, weldability is lowered and the risk of cracking is increased. Therefore, it is preferable to add Mn addition amount in 0.4%-1.5% of range.

Phosphorus (P)

P is an impurity that impairs the impact toughness of the steel material, and it is preferable to minimize it because it accumulates in the central segregation portion during performance, impairs internal quality and workability, and causes hydrogen embrittlement. Therefore, considering the steelmaking facility capability, it is desirable to limit the content to 0.03% or less.

Sulfur (S)

S, like P, is an element harmful to ductility and impact toughness and causes hot cracking and central segregation during continuous casting.

Moreover, since it forms with inclusions, such as MnS, and becomes a cause of poor internal quality, it is preferable to limit the content to 0.03% or less.

Copper (Cu)

Cu is an element that is inevitably contained in steel scrap, which is a steelmaking raw material, and the strength is increased by the precipitation strengthening effect. However, Cu is used to cause surface defects, so the amount thereof is limited to 0.5% or less.

Vanadium (V)

V chemically bonds with C or N at high temperatures to form precipitates that are V (C, N), thereby inducing a precipitation strengthening effect. However, when the content exceeds 0.15%, the degree of increase in strength decreases, and the effect is reduced, and the yield ratio is increased by intensively increasing the yield strength.

In addition, since the addition of V lowers the impact toughness, an appropriate amount of V is limited to 0.15% or less.

Rebar manufacturing method using temp core

The alloying elements as described above are added within the respective weight ratio ranges, and the remainder is billed by continuous casting after the steel material composed of Fe and inevitably contained impurities is produced in an electric furnace.

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.

On the other hand, the hot rolled reinforcing bars are subjected to a heat treatment by passing through the Tempcore (Tempcore), at this time to control the cooling conditions in the water cooling tank, that is, the heat transfer amount and the recuperation temperature within a predetermined range.

In this way, by controlling the cooling conditions within a predetermined range, the hardness of the inside and the surface and the fraction of the hardened layer can be controlled, thereby satisfying the resistive ratio, which is the required physical properties.

Referring to FIG. 1, the higher the heat transfer coefficient, the higher the fraction of the surface layer, and the lower the heat transfer coefficient, the lower the fraction of the surface layer.

Since the inner layer and the surface layer have different physical properties from each other, it is possible to control the physical properties of the entire earthquake-resistant rebar by adjusting the fraction of the surface layer and the hardened layer.

As can be seen in Figure 1, the control of the fraction of the inner layer and the surface layer is dependent on the heat transfer coefficient during cooling in the temp core process, this heat transfer coefficient is directly related to the flow rate supplied to the temp core.

According to the present invention, several times of repeated experiments, when the cured layer fraction is in the range of 19-29%, the required yield strength and yield ratio can be satisfied.

The heat transfer coefficient for the hardened layer fraction to be in the range of 19 to 29% is in the range of 23000 to 38000 W / m ² K from the graph of FIG. 1.

The relationship between the heat transfer coefficient and the flow rate is shown in Equation 1 below.

The heat flow coefficient satisfying heat transfer coefficient: 23000-38000 W / m ² K was derived from Equation 1 above, 312 to 416 m ³ / h.

Table 1 below shows the process conditions and alloy components of the temp core, Table 2 shows the hardness, fractions and mechanical properties results at each process condition.

Looking at the results of Table 2, it is found that when the flow rate ranges from 312 to 416 m ³ / h, the surface layer fraction satisfies the range of 19 to 29%, and satisfies both the yield strength of 600 MPa or more and the yield ratio of 0.8 or less. Can be.

When the flow rate exceeds the above range, the fraction of the surface layer increases, the yield strength decreases, and the yield ratio becomes large,

When the flow rate is less than the above range, the fraction of the surface layer, which is a cured layer, cannot be secured, so that the required yield strength cannot be obtained.

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

By weight% C: 0.1 ~ 0.4%, Si: 0.1 ~ 0.6%, Mn: 0.4 ~ 1.5%, P: 0.01 ~ 0.03%, S: 0.01 ~ 0.03%, Cu: 0.01 ~ 0.3%, V: 0.01 ~ 0.15 % And the remainder are heated to a temperature range of 1000 ℃ to 1250 ℃ consisting of Fe and other unavoidable impurities, and hot rolled to a rolling end temperature condition of 950 ℃ ~ 1250 ℃ through a reinforcing rolling process,
A method for manufacturing a resistance to earthquake-resistant seismic reinforcing bar, characterized in that quenching is performed on the temper core, but the heat transfer coefficient during cooling is 23000 to 38000 W / m ² K.

The method of claim 1,
Process conditions of the temp core
Resistant-ratio earthquake-resistant rebar manufacturing method, characterized in that the supply flow rate is 312 ~ 416m ³ / h range.

By weight% C: 0.1 ~ 0.4%, Si: 0.1 ~ 0.6%, Mn: 0.4 ~ 1.5%, P: 0.01 ~ 0.03%, S: 0.01 ~ 0.03%, Cu: 0.01 ~ 0.3%, V: 0.01 ~ 0.15 % And the remainder are heated to a temperature range of 1000 ℃ to 1250 ℃ consisting of Fe and other unavoidable impurities, and hot rolled to a rolling end temperature condition of 950 ℃ ~ 1250 ℃ through a reinforcing rolling process,
Heat-resistance coefficient during cooling in the temp core is heat-treated in the range of 23000 ~ 38000W / m ² K, the fraction of the surface layer of the hardened layer is characterized in that the range of 19 ~ 29% resistance earthquake-resistant seismic reinforcing steel.

The method of claim 3, wherein
The resistance ratio of the seismic reinforcing bar,
Resistant-ratio seismic reinforcing bars, characterized in that the hardness of the inner layer is 210Hv or more.

The method of claim 3, wherein
The resistive ratio seismic rebar is
A yield strength seismic reinforcing bar, characterized in that the yield strength 600MPa or more, the yield ratio (yield strength / tensile strength) 0.8 or less.