KR20200035524A - Steel reinforcement and method of manufacturing the same - Google Patents

Abstract

The present invention provides a high-strength reinforcing bar with excellent fatigue resistance, comprising 0.1-0.45 wt% of carbon (C), 0.15-3 wt% of manganese (Mn), 0.05-1 wt% of silicon (Si), 0.1-1 wt% of chrome (Cr), 0-0.4 wt% (excluding 0 wt%) of copper (Cu), 0-0.25 wt% (excluding 0 wt%) of nickel (Ni), 0-0.45 wt% (excluding 0 wt%) of molybdenum (Mo), 0-0.04 wt% (excluding 0 wt%) of aluminum (Al), 0-0.2 wt% (excluding 0 wt%) of vanadium (V), 0-0.15 wt% (excluding 0 wt%) of niobium (Nb), 0-0.05 wt% (excluding 0 wt%) of titanium (Ti), 0-0.02 wt% (excluding 0 wt%) of nitrogen (N), 0-0.1 wt% (excluding 0 wt%) of antimony (Sb), 0-0.1 wt% (excluding 0 wt%) of tin (Sn), 0-0.03 wt% (excluding 0 wt%) of phosphorus (P), 0-0.03 wt% (excluding 0 wt%) of sulfur (S), and the remainder consisting of iron (Fe) and inevitable impurities. The center portion of the final microstructure consists of perlite and acicular ferrite or consists of perlite, bainite, and acicular ferrite, and the surface portion includes tempered martensite.

Description

Rebar and its manufacturing method {STEEL REINFORCEMENT AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to a reinforcing bar and a method for manufacturing the same, and more particularly, to a high strength reinforcing bar having excellent fatigue resistance and a method for manufacturing the same.

In recent years, in order to increase the utilization of space in the installation of structures, the structures installed are becoming larger and longer. It is analyzed that the cause of unexpected natural disasters or climate change is that global warming continues to occur due to pollution of the global environment. Meanwhile, it is pointed out that the main factor of global warming is CO ₂ generation. When reinforcing high-strength rebar, over-reinforcement can be eliminated by reducing the amount of reinforcing bar, and through this, 0.4 tons of CO ₂ generated when producing 1 ton of rebar can be reduced to 0.2 tons per household when ultra-high strength rebar is applied. Accordingly, reinforcing bars having higher strength than before are required. For example, what was required up to 500 MPa based on yield strength has recently been requested from 600 to 700 MPa, and the demand for reinforcing bars of 1.0 GPa is expected in the future. However, it is also important to not only achieve reinforcement of reinforced steel bars, but also to secure safety even among natural disasters such as earthquakes and loads caused by the weight of the building itself, which is becoming larger and longer. By simply increasing the amount of alloying elements added, there is a problem that it is unclear to secure cost stability due to the addition of high alloys and to secure external force.

Related prior art is Republic of Korea Patent Publication No. 10-2003-0095071, the name of the invention: high yield ratio type high strength hot-dip galvanized rebar manufacturing method).

In order to solve the above problems, the technical problem to be achieved by the present invention is to reduce the cost in manufacturing high-strength reinforcing bars and to provide high-strength reinforcing bars and methods for manufacturing the same with fatigue resistance, which prevents new equipment from being input and productivity. Is to provide.

Rebar according to an embodiment of the present invention for achieving the above object is carbon (C): 0.10 ~ 0.45% by weight, manganese (Mn): 0.15 ~ 3.0% by weight, silicon (Si): 0.05 ~ 1.0% by weight, chromium (Cr): 0.1 to 1.0% by weight, copper (Cu): more than 0 to 0.40% by weight, nickel (Ni): more than 0 to 0.25% by weight, molybdenum (Mo): more than 0 to 0.45% by weight, aluminum ( Al): more than 0 0.04% by weight or less, vanadium (V): more than 0 0.20% by weight, niobium (Nb): more than 0 0.15% by weight, titanium (Ti): more than 0 and 0.05% by weight or less, nitrogen (N) : More than 0 0.020% by weight or less, Antimony (Sb): More than 0 0.1% by weight, Tin (Sn): More than 0 0.1% by weight, Phosphorus (P): More than 0 0.03% by weight or less, Sulfur (S): 0 Exceeding 0.03% by weight or less and remaining iron (Fe) and other inevitable impurities, the center of the final microstructure is composed of pearlite and acicular ferrite, or pearlite, bainite and acicular ferrite, and the surface part is tempered It includes ten sites.

The reinforcing bar may further include one or more of magnesium (Mg): more than 0 and less than 0.005% by weight and calcium (Ca): more than 0 and less than 0.005% by weight.

The reinforcing bar may have a yield strength (YS) of 650 MPa or higher, a tensile strength (TS) of 850 MPa or higher, an elongation of 19% or higher, and a tensile strength ratio (TS / YS) of 1.25 or higher.

Method for manufacturing a rebar according to an embodiment of the present invention for achieving the above object is (a) carbon (C): 0.10 ~ 0.45% by weight, manganese (Mn): 0.15 ~ 3.0% by weight, silicon (Si): 0.05 ~ 1.0% by weight, chromium (Cr): 0.1 to 1.0% by weight, copper (Cu): more than 0 and less than 0.40% by weight, nickel (Ni): more than 0 and less than 0.25% by weight, molybdenum (Mo): more than 0 and 0.45 % By weight or less, aluminum (Al): more than 0 0.04% by weight or less, vanadium (V): more than 0 0.20% by weight or less, niobium (Nb): more than 0 0.15% by weight or less, titanium (Ti): more than 0 and 0.05% by weight Nitrogen (N): more than 0 and 0.020 wt% or less, antimony (Sb): more than 0 and 0.1 wt% or less, tin (Sn): more than 0 and 0.1 wt% or less, phosphorus (P): more than 0 and 0.03 wt% or less, Sulfur (S): reheating the steel material consisting of more than 0 and 0.03% by weight or less and the remaining iron (Fe) and other inevitable impurities at 1050 to 1250 ° C; (b) hot rolling the reheated steel under the conditions of the finish rolling temperature (Ae3 + 50 ° C) to (Ae3 + 100 ° C); And (c) performing a tempcore process on the hot-rolled steel.

In the method of manufacturing the reinforcing bar, the temp core process may include a reheating step of 550 to 650 ° C. after quenching the surface to a martensite starting temperature (Ms).

In the method of manufacturing the reinforcing bar, the steel of step (a) is controlled by controlling the oxygen content in the molten steel to 20 ppm or less by performing VD (Vacuum Degassing) process after LF treatment of molten steel exiting the electric furnace; And solidifying the molten steel by a continuous casting process; may be a steel material implemented by performing.

In the method of manufacturing the reinforcing bar, the steel material may further include at least one of magnesium (Mg): more than 0 and 0.005% by weight or less and calcium (Ca): more than 0 and 0.005% by weight or less.

According to the embodiment of the present invention, it is possible to implement a high-strength reinforcing bar and a method of manufacturing the same as fatigue resistance, which is made to prevent costly decreases in productivity and reduce productivity. Of course, the scope of the present invention is not limited by these effects.

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 of a microstructure of reinforcing bars according to a comparative example among experimental examples of the present invention.
3 is a photograph of a microstructure of a reinforcing bar according to Example 1 among experimental examples of the present invention.
Figure 4 is a photograph of the microstructure of the reinforcing bar according to Example 2 among the experimental examples of the present invention.

Reinforcing bars according to an embodiment of the present invention and its manufacturing method will be described in detail. Terms to be described later are terms appropriately selected in consideration of functions in the present invention, and definitions of these terms should be made based on contents throughout the present specification. Hereinafter, to reduce the cost of some of the expensive alloy elements, such as V, Nb, and to improve the strength and fatigue properties at the same time, to provide a steel-type design and manufacturing method of the alloy-reduced rebar.

rebar

Rebar according to an embodiment of the present invention is carbon (C): 0.10 ~ 0.45% by weight, manganese (Mn): 0.15 ~ 3.0% by weight, silicon (Si): 0.05 ~ 1.0% by weight, chromium (Cr): 0.1 ~ 1.0% by weight, copper (Cu): more than 0 and less than 0.40% by weight, nickel (Ni): more than 0 and less than 0.25% by weight, molybdenum (Mo): more than 0 and less than 0.45% by weight, aluminum (Al): more than 0 and 0.04 % By weight or less, vanadium (V): more than 0 0.20% by weight or less, niobium (Nb): more than 0 0.15% by weight, titanium (Ti): more than 0 0.05% by weight or less, nitrogen (N): more than 0 0.020% by weight Or less, antimony (Sb): more than 0 to 0.1% by weight, tin (Sn): more than 0 to 0.1% by weight, phosphorus (P): more than 0 to 0.03% by weight, sulfur (S): more than 0 to 0.03% by weight, and It consists of the remaining iron (Fe) and other inevitable impurities.

Hereinafter, the role and content of each component included in the rebar according to an embodiment of the present invention will be described.

Carbon (C)

Carbon (C) is the most effective and important element for increasing the strength of steel. In addition, it is dissolved in austenite by the addition of carbon to form a martensite structure upon quenching. As the carbon amount increases, the hardening hardness is improved, but the possibility of deformation during quenching is greatly increased. Furthermore, it forms a carbide by combining with elements such as iron, chromium, molybdenum, and vanadium to improve strength and hardness. Carbon (C) may be added in a content ratio of 0.10 to 0.45% by weight of the total weight of the rebar according to an embodiment of the present invention. When the content of carbon is less than 0.01% by weight of the total weight, the above-described effect cannot be realized and difficulty in securing sufficient strength may follow. Conversely, when the carbon content exceeds 0.45% by weight of the total weight, excessive strength and weldability deterioration may occur.

Manganese (Mn)

Manganese (Mn) is partly dissolved in the steel, and some is combined with sulfur contained in the steel to form a non-metallic inclusion, MnS, which is ductile and elongated in the machining direction during plastic working. However, the formation of MnS reduces the sulfur content in the steel, making the grains vulnerable and inhibiting the formation of the low-melting compound FeS. It inhibits the acid and oxidation resistance of steel, but improves yield strength by making pearlite fine and ferrite hardened. Manganese may be added in a content ratio of 0.15 to 3.0% by weight of the total weight of the rebar according to an embodiment of the present invention. When the content of manganese is less than 0.15% by weight, the above-described effect of adding manganese cannot be sufficiently exhibited. In addition, when the content of manganese exceeds 3.0% by weight, it causes quenching cracking or deformation, weldability deteriorates, and MnS inclusions and center segregation occur, deteriorating the ductility of reinforcing bars and deteriorating corrosion resistance. You can.

Silicon (Si)

Silicon (Si) is well known as a ferrite stabilizing element and is known as an element that increases ductility by increasing the ferrite fraction during cooling. On the other hand, silicon is added as a deoxidizer for removing oxygen in the steel in the steelmaking process together with aluminum, and may also have a solid solution strengthening effect. The silicone may be added in a content ratio of 0.05 to 1.0% by weight of the total weight of the rebar according to an embodiment of the present invention. When the content of silicone is less than 0.05% by weight of the total weight, the above-described effect of adding silicone cannot be properly exhibited. Conversely, when the content of silicon exceeds 1.0% by weight of the total weight, when added in large quantities, there is a problem that the toughness decreases and the plastic workability decreases, the weldability of the steel decreases, and red scale is generated during reheating and hot rolling. By doing so, it can give problems to the surface quality.

Chrome (Cr)

Chromium (Cr) is a ferrite stabilizing element that, when added to C-Mn steel, delays the diffusion of carbon due to a solute interference effect, thereby affecting particle size refinement. The chromium may be added in a content ratio of 0.1 to 1.0% by weight of the total weight of the rebar according to an embodiment of the present invention. When the content of chromium is less than 0.1% by weight of the total weight, the above-described effect of adding chromium cannot be properly exhibited. Conversely, when the content of chromium exceeds 1.0% by weight of the total weight, when added in large amounts, the toughness is lowered and the workability and machinability may be deteriorated.

Copper (Cu)

Copper (Cu) is an element that improves the hardenability and low-temperature impact toughness of steel. It is employed in ferrite at room temperature and exhibits a solid solution strengthening effect, so its strength and hardness are slightly improved, but its elongation is lowered. The copper may be added in a content ratio of more than 0 to 0.40% by weight or less of the total weight of the rebar according to an embodiment of the present invention. When the content of copper exceeds 0.40% by weight of the total weight, when added in large quantities, hot workability deteriorates, causes red brittleness, and may impair product surface quality.

Nickel (Ni)

Nickel (Ni) is an element that increases hardenability and improves toughness. The nickel may be added in a content ratio of more than 0 to 0.25% by weight of the total weight of the rebar according to an embodiment of the present invention. When the content of nickel exceeds 0.25% by weight of the total weight, when a large amount is added, a problem arises in that the manufacturing cost of parts increases.

Molybdenum (Mo)

Molybdenum (Mo) is an element that can improve hardenability about 10 times more than nickel, and is an element that prevents temperability and imparts temperability. Because molybdenum forms carbide, it has an excellent effect as an alloying element of high-end cutting tools and increases the grain coarsening temperature. The effect is better when used together with chromium rather than alone to improve the hardenability. The molybdenum may be added in a content ratio of more than 0 to 0.45% by weight of the total weight of the reinforcing bar according to an embodiment of the present invention. When the content of molybdenum exceeds 0.45% by weight of the total weight, when a large amount is added, the weldability decreases and the manufacturing cost of the parts increases.

Aluminum (Al)

Aluminum (Al) is an element that inhibits ferrite stabilization and carbide formation, such as silicon. In addition, aluminum is added to the steelmaking process as a deoxidizer for removing oxygen in the steel, and can be precipitated in the steel with AlN to contribute to grain refinement. The aluminum may be added in a content ratio of more than 0 to 0.04% by weight or less of the rebar weight according to an embodiment of the present invention. When the aluminum content exceeds 0.04% by weight, alumina (Al ₂ O ₃ ), which is a non-metallic inclusion, increases, and the bending processability decreases as a starting point during bending processing, and process loads such as increased steelmaking and annealing temperatures occur, leading to performance. There may be a problem that productivity is lowered due to difficulty.

Vanadium (V)

Vanadium (V) is an element that contributes to strength improvement by acting as a pinning of grain boundaries. The vanadium may be added in a content ratio of more than 0 to 0.20% by weight or less of the total weight of the rebar according to an embodiment of the present invention. When the content of vanadium exceeds 0.20% by weight of the total weight, and when a large amount is added, there is a problem in that the manufacturing cost of steel is excessively increased compared to the effect of improving the strength.

Niobium (Nb)

Niobium (Nb) is an element that precipitates in the form of NbC or Nb (C, N) to improve the strength of the base material and the weld. The niobium may be added in a content ratio of more than 0 to 0.15% by weight of the total weight of the rebar according to an embodiment of the present invention. When the content of niobium exceeds 0.15% by weight of the total weight, a large amount of brittle cracks occurs.

Titanium (Ti)

Titanium (Ti) is an element that suppresses the formation of AlN through the formation of high temperature TiN and has the effect of miniaturizing grain size through the formation of Ti (C, N). The titanium may be added in a content ratio of greater than 0 and less than or equal to 0.05% by weight of the total weight of the rebar according to an embodiment of the present invention. When the content of titanium exceeds 0.05% by weight of the total weight, when a large amount is added, the carbon content in the mother phase decreases, which may cause a problem of deterioration of steel properties.

Nitrogen (N)

Nitrogen (N) is an element that increases strength by depositing vanadium and nitride or carbonitride. The nitrogen may be added in a content ratio of more than 0 to 0.02% by weight or less of the total weight of the rebar according to an embodiment of the invention. When the content of nitrogen exceeds 0.02% by weight of the total weight, a large amount may act as an element that inhibits toughness.

Antimony (Sb)

Antimony (Sb) is an element that inhibits the growth of various subscales produced in the hot rolling process. The antimony may be added in a content ratio of more than 0 to 0.1% by weight or less of the total weight of the rebar according to an embodiment of the invention. When the content of antimony exceeds 0.1% by weight of the total weight, a large amount may act as an element that induces embrittlement of the material.

Tin (Sn)

Tin (Sn) is an element added to the electric steelmaking method. The tin may be added in a content ratio of more than 0 and 0.1% by weight or less of the total weight of the rebar according to an embodiment of the invention. When the content of tin exceeds 0.1% by weight of the total weight, the elongation may decrease when added in large amounts.

Phosphorus (P)

Phosphorus (P) increases the strength of the strength by strengthening the solid solution, and can function to suppress the formation of carbides. The phosphorus may be added in a content ratio of more than 0 to 0.03% by weight or less of the total weight of the rebar according to an embodiment of the present invention. When the phosphorus content exceeds 0.03% by weight, there is a problem that the low-temperature impact value is lowered due to the precipitation behavior.

Sulfur (S)

Sulfur (S) can form a precipitate of fine MnS to improve processability. The sulfur may be added in a content ratio of more than 0 to 0.03% by weight or less of the total weight of the rebar according to an embodiment of the present invention. When the sulfur content exceeds 0.03% by weight, toughness and weldability may be impaired and low-temperature impact values may be reduced.

On the other hand, the rebar according to the modified embodiment of the present invention may further include at least one of magnesium (Mg): more than 0 and 0.005% by weight or less and calcium (Ca): more than 0.005% by weight or less in addition to the above-described composition range. It might be.

Magnesium (Mg)

Magnesium (Mg) has an effect of controlling the form of the emulsion in the steel and reducing the toughness of the base material due to the emulsion. The magnesium may be further added in a content ratio of more than 0 to 0.005% by weight or less of the total weight of the rebar according to an embodiment of the present invention. When the content of magnesium exceeds 0.005% by weight, the additive effect is saturated and only the manufacturing cost can be increased.

Calcium (Ca)

Calcium (Ca) may be added for the purpose of improving the electrical resistance weldability by preventing the formation of MnS inclusions by forming CaS inclusions. That is, since calcium (Ca) has a higher affinity with sulfur than manganese (Mn), when calcium is added, CaS inclusions are generated and MnS inclusions are reduced. However, when the content of calcium (Ca) exceeds 0.005% by weight, there is a problem in that the production of CaO inclusions becomes excessive, resulting in poor performance and electrical resistance weldability. Therefore, calcium (Ca) is controlled to be greater than 0 and less than 0.005% by weight of the total rebar weight.

As described above, the reinforcing bar according to an embodiment of the present invention having an alloy element composition has a central portion of the final microstructure composed of pearlite and acicular ferrite, or pearlite, bainite and acicular ferrite, and the surface portion is tempered marten Sites may be included.

In addition, the rebar according to an embodiment of the present invention having an alloy element composition as described above has a yield strength (YS) of 650 MPa or higher, a tensile strength (TS) of 850 MPa or higher, an elongation of 19% or higher, and tensile strength. The ratio of yield strength (TS / YS) may be 1.25 or more.

Hereinafter, a method for manufacturing a reinforcing bar according to an embodiment of the present invention having the above-described alloy element composition will be described.

Method of manufacturing rebar

1 is a flowchart schematically showing a method of manufacturing a reinforcing bar according to an embodiment of the present invention.

Referring to Figure 1, the method of manufacturing a rebar according to an embodiment of the present invention (a) carbon (C): 0.10 ~ 0.45% by weight, manganese (Mn): 0.15 ~ 3.0% by weight, silicon (Si): 0.05 ~ 1.0% by weight, chromium (Cr): 0.1 to 1.0% by weight, copper (Cu): more than 0 and less than 0.40% by weight, nickel (Ni): more than 0 and less than 0.25% by weight, molybdenum (Mo): more than 0 and 0.45 % By weight or less, aluminum (Al): more than 0 0.04% by weight or less, vanadium (V): more than 0 0.20% by weight or less, niobium (Nb): more than 0 0.15% by weight or less, titanium (Ti): more than 0 and 0.05% by weight Nitrogen (N): more than 0 and 0.020 wt% or less, antimony (Sb): more than 0 and 0.1 wt% or less, tin (Sn): more than 0 and 0.1 wt% or less, phosphorus (P): more than 0 and 0.03 wt% or less, Sulfur (S): Step of reheating the steel consisting of more than 0 0.03% by weight or less and the remaining iron (Fe) and other inevitable impurities at 1050 ~ 1250 ℃ (S100); (b) hot rolling the reheated steel under the conditions of the finish rolling temperature (Ae3 + 50 ° C) to (Ae3 + 100 ° C) (S200); And (c) performing a tempcore process on the hot-rolled steel (S300); It includes.

The rebar steel / casting process generally consists of electric furnace, LF, and performance. In the method for manufacturing reinforcing bars according to an embodiment of the present invention, after the LF, a second refining process, and a VD (vacuum degassing) process for lowering fatigue properties, the oxygen content was lowered to 20 ppm or less, and then solidified as a semi-material in the performance process. .

The rolling process is manufactured through a reheating process, a hot deformation process, and a cooling process. In the reheating process, the semi-finished billet is reheated to 1,050 ~ 1,250 ℃. Next, the hot rolling process goes through each rolling roll (RM, IM, FM), and after the final finish rolling is deformed in Ae3 (837 ℃) + (50 ~ 100 ℃), the surface is passed through Tempcore. After quenching to the starting temperature (Ms) of martensite, characterized in that it comprises a recuperation step to 550 ~ 650 ℃.

The steel material is carbon (C): 0.10 ~ 0.45% by weight, manganese (Mn): 0.15 ~ 3.0% by weight, silicon (Si): 0.05 ~ 1.0% by weight, chromium (Cr): 0.1 ~ 1.0% by weight, copper (Cu ): More than 0 and less than 0.40% by weight, nickel (Ni): more than 0 and less than 0.25% by weight, molybdenum (Mo): more than 0 and less than 0.45% by weight, aluminum (Al): more than 0 and less than 0.04% by weight, vanadium (V) ): More than 0 and less than 0.20% by weight, niobium (Nb): more than 0 and 0.15% by weight, titanium (Ti): more than 0 and 0.05% by weight, nitrogen (N): more than 0 and 0.020% by weight or less, antimony (Sb): More than 0 and less than 0.1% by weight, tin (Sn): more than 0 and less than 0.1% by weight, phosphorus (P): more than 0 and less than 0.03% by weight, sulfur (S): more than 0 and less than 0.03% by weight and the rest of iron (Fe) and others It can be made of inevitable impurities. In addition, the steel material may further include at least one of magnesium (Mg): more than 0 and less than 0.005% by weight and calcium (Ca): more than 0 and less than 0.005% by weight.

In one embodiment, the steel material may be reheated at a temperature of 1050 ~ 1250 ℃. When the steel is reheated at the above-mentioned temperature, components segregated during the continuous casting process may be re-used. When the reheating temperature is lower than 1050 ° C, the solid solution may not be sufficiently dissolved, and there may be a problem that segregated components are not evenly distributed during the continuous casting process. When the reheating temperature exceeds 1250 ° C, very coarse austenite grains may be formed, which may make it difficult to secure strength. In addition, when the temperature exceeds 1250 ° C, the heating cost increases and the process time is added, which may lead to an increase in manufacturing cost and a decrease in productivity.

In the hot rolling step (S200), the reheated steel is hot rolled. The temperature range of the hot-deformed finish can be finalized at Ae3 (837 ° C) + (50 to 100 ° C) to form a final fine austenite structure and fine Ti (C, N) precipitates through dynamic recrystallization. That is, when the amount of deformation is increased from the critical temperature at which the dynamic recrystallization occurs to the critical deformation amount, the austenite particle size is refined and the particle size growth by fine Ti-carbonitride starting to form from high temperature is delayed to form fine ferrite and bainite during cooling. A fine ferrite having a size of 10 μm can be formed. The ultra-fine ferrite thus formed maximizes the driving force of pearlite transformation, and as a result, it has an ultra-fine ferrite-pearlite-bainite structure.

When observing the microstructure of the reinforcing bar according to an embodiment of the present invention, it can be confirmed that fine ferrite and pearlite are rapidly formed under a relatively wide hot deformation temperature. However, if the hot rolling temperature is too low, the rolling load increases during rolling and an edge (EDGE) mixed structure may occur, so it can be said that the hot finishing temperature is preferably A3 temperature.

In the step (S300) of performing the tempcore process, the tempcore cooling temperature is in the range of 550 ~ 650 ℃. As the temperature increases, the spacing between ferrite and pearlite lamellae increases, making it difficult to act as an obstacle to dislocation movement, resulting in a decrease in strength. Voids are concentrated due to deformation at the interface between coarse cementite and ferrite. Defects such as these occur and can act as a crack growth site, degrading processability.

The rebar according to an embodiment of the present invention implemented by performing the above-described process shows that it is possible to increase the strength while simultaneously exhibiting excellent fatigue properties and seismic performance, and is expected to further improve the stability of the building structure. .

Experimental example

Hereinafter, a preferred experimental example is presented to help understanding of the present invention. However, the following experimental examples are only to aid the understanding of the present invention, and the present invention is not limited by the following experimental examples.

1. Preparation of Specimen

In this experimental example, the main alloy element composition (unit: weight ratio%) of Table 1 and specimens implemented with process conditions are provided.

Examples 1 and 2 in Table 1 are carbon (C): 0.10 to 0.45 wt%, manganese (Mn): 0.15 to 3.0 wt%, silicon (Si): 0.05 to 1.0 wt%, chromium (Cr): 0.1 ~ 1.0% by weight, copper (Cu): more than 0 and less than 0.40% by weight, nickel (Ni): more than 0 and less than 0.25% by weight, molybdenum (Mo): more than 0 and 0.45% by weight or less, aluminum (Al): more than 0 0.04% by weight or less, vanadium (V): more than 0 0.20% by weight or less, niobium (Nb): more than 0 0.15% by weight, titanium (Ti): more than 0, 0.05% by weight or less, nitrogen (N): more than 0 0.020% % Or less, antimony (Sb): more than 0 to 0.1% by weight, tin (Sn): more than 0 to 0.1% by weight, phosphorus (P): more than 0 to 0.03% by weight, sulfur (S): more than 0 to 0.03% by weight or less And the remaining iron (Fe), while the comparative example in Table 1 is molybdenum (Mo): more than 0 and 0.45% by weight or less, niobium (Nb): more than 0 and 0.15% by weight or less, titanium ( Ti): more than 0 and 0.05% by weight or less, antimony (Sb): more than 0 and 0.1% by weight or less, tin (Sn): more than 0 and 0.1% by weight or less Does not satisfy the gender range.

In addition, Example 1 and Example 2 of Table 1 controls the oxygen content in the molten steel to 20 ppm or less by performing a VD (Vacuum Degassing) process, whereas the Comparative Example of Table 1 does not perform a VD (Vacuum Degassing) process. Therefore, the oxygen content in the molten steel exceeds 20 ppm.

In addition, Example 1 and Example 2 of Table 1, while performing the hot rolling having a finish rolling temperature within the range of the finish rolling temperature (Ae3 + 50 ℃) to (Ae3 + 100 ℃), while comparing Table 1 For example, finish rolling is performed at a temperature higher than (Ae3 + 100 ° C).

2. Evaluation of physical properties and microstructure

Table 2 shows the physical properties and central microstructure observation results for the specimens in Table 1.

Referring to Table 2, Examples 1 and 2 have a yield strength (YS) of 650 MPa or more, a tensile strength (TS) of 850 MPa or more, an elongation of 19% or more, a hardness of 200 Hv or more, and a tensile strength. It can be seen that the ratio of yield strength (TS / YS) is 1.25 or more, and it can be understood that these properties have better yield strength, tensile strength, elongation, and hardness characteristics than the comparative example.

2 to 4 are photographs of the central microstructure of the rebar according to the experimental example of the present invention. Specifically, FIG. 2 relates to a comparative example of Table 2, FIG. 3 relates to Example 1 of Table 2, and FIG. 4 relates to Example 2 of Table 2.

3 and 4, it can be seen that the center of the reinforcing bar according to the embodiment of the present invention is made of pearlite and acicular ferrite, or pearlite, bainite and acicular ferrite. On the other hand, referring to Figure 2, it can be seen that the final microstructure of the center of the rebar according to the comparative example of the present invention is made of equiaxed ferrite and pearlite.

In comparison with microstructure, the ferrite particle size was ultra-fine from 30 µm to less than 10 µm through the final deformation temperature control and the cooling process control in the case of the comparative ferrite and pearlite structures in the case of the comparative example. It can be seen that (bainite, acicular ferrite and pearlite) were formed, which also influenced the improvement of mechanical properties.

Such results also show the superiority through the fatigue test results. Table 3 shows the fatigue test results for the specimens of Table 1 and Table 2.

Referring to Table 3, according to the increase in the load of the fatigue test shows that the life of Example 2 can secure twice or more repetitive fatigue characteristics despite being a high strength material (46,244cycle) compared to the comparative example (19,936cycle). It can be seen that it has been implemented by reducing the number of non-metallic inclusions through the VD described above and securing a fine composite structure. These results show that it is possible to increase the strength through this technology while simultaneously exhibiting excellent fatigue resistance and seismic performance, and it is expected that the stability of building structures can be further improved.

In the above, the description has been mainly focused on the embodiment of the present invention, but various changes or modifications can be made at the level of those skilled in the art. It can be said that such modifications and variations belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should be judged by the claims set forth below.

Claims (7)

Carbon (C): 0.10 to 0.45% by weight, manganese (Mn): 0.15 to 3.0% by weight, silicon (Si): 0.05 to 1.0% by weight, chromium (Cr): 0.1 to 1.0% by weight, copper (Cu): 0 More than 0.40% by weight, nickel (Ni): more than 0, 0.25% by weight or less, molybdenum (Mo): more than 0 0.45% by weight or less, aluminum (Al): more than 0, 0.04% by weight or less, vanadium (V): 0 More than 0.20% by weight, niobium (Nb): more than 0 0.15% by weight, titanium (Ti): more than 0 0.05% by weight, nitrogen (N): more than 0 0.020% by weight, antimony (Sb): more than 0 0.1 % By weight or less, tin (Sn): more than 0 and 0.1% by weight or less, phosphorus (P): more than 0 and 0.03% by weight or less, sulfur (S): more than 0 and 0.03% by weight or less, and the rest of iron (Fe) and other unavoidable impurities Done,
The central portion of the final microstructure is composed of pearlite and acicular ferrite or pearlite, bainite and acicular ferrite, characterized in that the surface portion comprises tempered martensite,
rebar. According to claim 1,
Magnesium (Mg): more than 0 0.005% by weight or less and calcium (Ca): more than 0 0.005% by weight or less, further comprising at least one,
rebar. According to claim 1,
Yield strength (YS) is 650 MPa or higher, tensile strength (TS) is 850 MPa or higher, elongation is 19% or higher, and tensile strength ratio (TS / YS) is 1.25 or higher,
rebar. (a) Carbon (C): 0.10 to 0.45 wt%, Manganese (Mn): 0.15 to 3.0 wt%, Silicon (Si): 0.05 to 1.0 wt%, Chromium (Cr): 0.1 to 1.0 wt%, Copper (Cu ): More than 0 and less than 0.40% by weight, nickel (Ni): more than 0 and 0.25% by weight, molybdenum (Mo): more than 0 and 0.45% by weight, aluminum (Al): more than 0 and 0.04% by weight or less, vanadium (V ): More than 0 and less than 0.20% by weight, niobium (Nb): more than 0 and less than 0.15% by weight, titanium (Ti): more than 0 and less than 0.05% by weight, nitrogen (N): more than 0 and less than 0.020% by weight, antimony (Sb): More than 0 and less than 0.1% by weight, tin (Sn): more than 0 and less than 0.1% by weight, phosphorus (P): more than 0 and less than 0.03% by weight, sulfur (S): more than 0 and less than 0.03% by weight and the rest of iron (Fe) and others Reheating the steel made of unavoidable impurities at 1050 to 1250 ° C;
(b) hot rolling the reheated steel under the conditions of the finish rolling temperature (Ae3 + 50 ° C) to (Ae3 + 100 ° C); And
(c) performing a tempcore process on the hot-rolled steel;
Containing,
Method of manufacturing reinforcing bars. The method of claim 4,
The tempcore process comprises a reheating step to 550 ~ 650 ℃ after quenching the surface to the martensite starting temperature (Ms),
Method of manufacturing reinforcing bars. The method of claim 4,
The step (a) of the steel material is a step of controlling the oxygen content in the molten steel to 20 ppm or less by performing a VD (Vacuum Degassing) process after LF treatment of molten steel exiting the electric furnace; And solidifying the molten steel by a continuous casting process.
Method of manufacturing reinforcing bars. The method of claim 4,
The steel material further comprises one or more of magnesium (Mg): more than 0 0.005% by weight or less and calcium (Ca): more than 0 0.005% by weight or less,
Method of manufacturing reinforcing bars.

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