KR980009479A - Manufacturing method of PC steel bar with excellent elongation and high temperature relaxation characteristics and PC steel bar with high temperature relaxation characteristics with high uniform extension and resistance ratio - Google Patents

Abstract

The present invention quenched steel containing 160% by weight of C: 0.5-0.7%, Mn: 0.2-2.0%, 2.0% ≤Si + A1≤5.0% of Si and A1 at 160 ° C to 1300 ° C, and then tempering. By processing, high uniform elongation and low yield ratio of high temperature relaxation with a tensile strength of 1080 N / mm2 or more that can be manufactured by a conventional process without requiring a strain imparting process The present invention relates to a method of manufacturing a PC steel bar having excellent characteristics.

Description

Manufacturing method of PC steel bar with excellent elongation and high temperature relaxation characteristics and PC steel bar with high temperature relaxation characteristics with high uniform extension and resistance ratio

1 is a diagram showing a temperature cycle in a high temperature relaxation test.

[Technical Field to which the Invention belongs and Prior Art in the Field]

The present invention is used for uniform elongation, which is used in PC structures, including PC poles or PC piles.

n) and PC steel rods with excellent high temperature relaxation characteristics, and high temperature relaxation with high uniform extension and resistance ratio

The present invention relates to a method for producing a PC steel bar having excellent characteristics.

PC steel rod is a high strength member used for PS concrete (prestressed concrete). PC steel rod is Class B (tensile strength ≥ 1080N / mm 2, proof strength ≥ 930N / mm 2, elongation: 5% or more, relaxation value: 4% or less (at room temperature measurement, load) in JIS G 3109 and JIS G 3137 Stress: 0.7 x tensile strength, 1000 hours value and Class C (tensile strength ≥ 1230 N / mm2, yield strength ≥1080 N / mm2, elongation: 5% or more, relaxation value: 4% or less (at room temperature measurement, load stress: 0.7 Tensile strength and 1000 hours value are standardized, and according to JIS G 3137, Class D (tensile strength ≥ 1420 N / mm 2, proof strength ≥ 1275 N / mm 2, elongation: 5% or more, relaxation value: 4% or less (at room temperature measurement) , Load stress: 0.7 x tensile strength, 1000 hours), however, uniform elongation, yield ratio and high temperature relaxation values are not standardized.

The PS concrete structure may be bent and destroyed at the time of an earthquake. In order to prevent it, it is effective to increase bending toughness using a highly uniform PC steel rod. In recent years, from the standpoint of shock resistance, PC steel bars are required to have a high yield ratio and high uniformity. This is because if the yield ratio is high, even if the PC steel rod is excellent in uniform elongation, when a crack occurs in the concrete, the PC steel rod in the region is locally deformed and fracture occurs.

In these PC steel bars, the horizontal restraint of concrete may be used together. In this case, since it is used in the form of spot-welding the transversely constrained band steel to the PC steel rod, there is a need for a PC steel rod that is excellent not only in uniform elongation characteristics before spot welding but also in uniform elongation characteristics after welding.

In addition, in order to shorten the curing period of the concrete during the production of the PS concrete pile or pole, autoclave curing (autoclave curing) that is carried out in an atmosphere of about 10 atm at 180 to 200 ℃ is used. However, autoclave curing has the drawback that the relaxation of PC steel rods in concrete is increased. Therefore, a PC steel rod with a low relaxation at high temperatures as described above is desired.

Conventionally, the improvement technique is established separately in each characteristic of uniform elongation and high temperature relaxation. However, although several proposals have been made for PC steel bars excellent in both uniform elongation and high temperature relaxation characteristics, they have not yet been established.

The method disclosed in Japanese Patent Laid-Open No. 3-79410 is a method of imparting a slight bending deformation of 2% or less during tempering, and Japanese Patent Laid-Open No. 3-28351 Process to increase temperature and reverse transformation while processing at -400 ℃ or plastic processing to make ultra-fine structure, Japanese Patent Laid-Open No. 58-1207

Publication 38 uses a wet straightener to cool during calibration.

Japanese Patent Application Laid-Open No. 8-158010 discloses a method of adding Si + A1 in a large amount from 2% to 5%. However, in the methods disclosed in each of Japanese Patent Application Laid-Open No. 3-79410, Japanese Patent Application Laid-Open No. 3-28351, and Japanese Patent Laid-Open No. 58-120738, all of them require a step for imparting deformation and thus productivity. This has a deteriorating drawback. In addition, the method disclosed in Japanese Patent Application Laid-Open No. 8-158010 has excellent productivity, excellent elongation and high temperature relaxation characteristics, but has a uniform elongation of about 5% at a strength level of 450 N / mm 2. This is not a significant improvement over%. In addition, the yield ratio is higher than 0.95, there is a problem that there is a possibility that the high uniform elongation characteristics are not actually activated in the concrete structure water. In addition, none of these publications mentions a technique for realizing a resistance ratio.

On the other hand, earthquake-resistant designs have attracted attention in earthquake-bonding sections, in which plastic girders are made to bond without breaking pillars, thereby absorbing the energy of earthquakes. According to this, a PC steel bar having a uniform elongation of 8% or more is required for the strength level of JIS G 3109 (JIS G 3137) or higher, but when looking at the prior art from the viewpoint of the strength level, it is 1420 N / mm 2 or more. Most of them are aimed at. Japanese Patent Laid-Open No. 55-8577 and Japanese Patent Laid-Open No. 56-21811 as proposals for PC steel bars having a tensile strength of 1080 N / mm 2 or more and less than 1420 N / mm 2 corresponding to the Class B or C standard. There is. However, the ductility achieved by the techniques disclosed in Japanese Patent Laid-Open No. 55-8577 and Japanese Patent Laid-Open No. 56-21811 is 8 to 9% elongation at break in the former, and 3.3 in the latter. It is about 4.6%, and this strength level does not satisfy | fill the 8% of uniform elongation actually required.

[Technical problem to be achieved]

An object of the present invention is a PC steel rod, which is excellent in both uniform elongation and high temperature relaxation characteristics, which can be manufactured in a normal process without requiring a strain imparting step: 1080 N / mm 2 or more and less than 1420 N / mm 2. To provide.

In addition, an object of the present invention is a PC steel rod having a tensile strength of 1080 N / mm 2 or more, which is excellent in both the uniform extension of the resistance ratio and the high temperature relaxation characteristics, which can be manufactured in a normal process without requiring a strain imparting step. It is to provide a method of manufacturing.

It is also an object of the present invention to provide a PC steel rod excellent in uniform elongation properties after spot welding and a method of manufacturing the same.

In order to achieve this object, the present inventors conducted research. As a result, in order to have excellent uniform elongation and high temperature relaxation characteristics, it is effective to add a large amount of Si and A1, and to have high uniform elongation and excellent both high temperature relaxation characteristics at a resistance ratio. In order to quench at high temperature, it was found that especially the C content is especially effective.

The present invention has been made based on these findings, and the PC steel rod of the present invention is first and in weight%, C: 0.2 to 0.7%, Mn: 0.2 to 3.0%, and (S1% + A1%): 2.0 to Steel containing 5.0%, composed of tempered martensite, and carbides in the martensite are fine grains with an average diameter of 0.1 µm or less, and tensile strength: 1080N / mm2 or more and less than 1420N / mm2. PC steel rod having excellent uniform elongation and high temperature relaxation characteristics, and second, as a steel component, in weight%, Nb: 0.01 to 0.1%, Ti: 0.01 to 0.05%, B: 0.0003 to 0.0055, Ni: PC having excellent uniform elongation and high temperature relaxation characteristics containing one or two or more selected from the group of 0.2 to 1.0%, Cr: 0.1 to 1.0%, Mo: 0.05 to 0.5%, and Cu: 0.2 to 1.0% Steel rod, third, steel component, in weight percent, C: 0.2 to 0.7%, Mn: 0.2 to 3.0%, (Si% + A1%): 2.0 to 5.0%, and Nb: 0.01 to 0.1% Ti: 0.01-0.05%, B: 0.0003-0.005%, Ni: 0.2-1.0%, Cr: 0.1-1.0%, Mo: 0.0 A carbide consisting of one or two or more selected from the group of 5 to 0.5% and Cu: 0.2 to 1.0% and a residual portion of Fe and unavoidable impurities and substantially consisting of marten tempering and also carbide during martens tempering PC steel rods having excellent uniform elongation and high temperature relaxation characteristics with a fine grain having an average diameter of 0.1 μm or less and a tensile strength of not less than 1080 N / mm 2 but less than 1420 N / mm 2, and the fourth and PC steel bars have tensile strength ≥ 1080 N. PC steel rod, fifth, PC steel rod with resistance ≥ 930 N / mm2, PC steel rod with tensile strength ≥1230 N / mm2, proof strength ≥1080 N / mm2, sixth, PC steel rod, C amount: 0.2 It is -0.5 weight%, and it is a PC steel rod used for the use which carries out spot welding and tempering treatment energization.

Next, the manufacturing method of the PC steel rod of this invention contains C: 0.5-0.7%, Mn: 0.2-2.0%, Si, and A1 2.0% <Si + A1≤5.0% by the 1st, weight%. A method for producing a PC steel rod having excellent high temperature relaxation characteristics of high uniform elongation and resistance ratio, having a tensile strength of 1080 N / mm 2 or more, which is quenched at 1160 ° C to 1300 ° C, and then tempered. 2, by weight, C: 0.5-0.7%, Mn: 0.2-2.0%, Si and A1 containing 2.0% ≤Si + A1≤5.0%, and further Nb: 0.01-0.1%, Ti: 0.01-0.05 Steel containing 1 or 2 or more of%, B: 0.0003 to 0.005%, Ni: 0.2 to 1.0%, Cr: 0.1 to 1.0%, Mo: 0.05 to 0.5%, and Cu: 0.2 to 1.0% A third method for producing a PC steel rod having a high uniform elongation and a high temperature relaxation property of a resistance ratio, which is quenched at 1 ° C. to 1300 ° C. and then tempered. , C: 0.5-0.7%, Mn: 0.2-2.0%, Si and A1 2.0% ≤Si + A1≤5.0%, Nb: 0.01-0.1%, Ti: 0.01-0.05%, B: One or two or more of 0.0003 to 0.005%, Ni: 0.2 to 1.0%, Cr: 0.1 to 1.0%, Mo: 0.05 to 0.5%, and Cu: 0.2 to 1.0%, and remaining portions of Fe and unavoidable impurities It is characterized by quenching the steel made at 1160 ° C to 1300 ° C, and then tempering it. Method 4, high uniform elongation and resistance yield ratio at a strength level of tensile strength ≥ 1230 N / mm 2 and proof strength ≥ 1080 N / mm 2 with a uniform elongation of not less than 8.0%, a yield ratio of not more than 0.87, and a high temperature relaxation of not more than 8%. Method for manufacturing PC steel rod with excellent retraction characteristics, No. 5, at a strength level of tensile strength ≥ 1420 N / mm 2 and proof strength ≥ 1275 N / mm 2, uniform elongation of not less than 8.0%, yield ratio of not more than 0.90, and high temperature relaxation 8 Manufacturing method of PC steel rod with excellent high temperature relaxation characteristics of less than% high uniformity and resistive ratio, No. 6, tensile steel PC having excellent high-temperature relaxation characteristics of high uniform extension and resistance yield ratio with uniform elongation of 11.0% or more, yield ratio of 0.85 or less, and high temperature relaxation of 8% or less The manufacturing method of steel rod, 7th, The manufacturing method of PC steel rod which is excellent in the high-uniform extension | strength of a temper treatment temperature more than 600 degreeC, and the high temperature relaxation characteristic of a resistance ratio.

Hereinafter, the reason which limited the component of this invention and manufacturing conditions are demonstrated.

C

C is an element necessary for improving hardenability and increasing strength. If it is less than 0.2 weight%, the strength level as a PC steel bar cannot be ensured. In addition, when more than 0.7% by weight, the ductility is reduced. Therefore, the amount of C is made into 0.2 to 0.7 weight%. On the other hand, in the case of using spot welding, if it exceeds 0.5% by weight, spot weldability is deteriorated. Therefore, when spot-welding a PC steel rod, C amount is made into 0.2 to 0.5 weight%. C is also an element that raises the tempering treatment temperature, and greatly contributes to lowering the yield ratio and improving the uniform elongation under conditions in which a large amount of Si + A1 is added. If it is less than 0.5 weight%, such a ductility improvement cannot be expected.

Si, A1

Si and A1 are used as deoxidizers and are not only effective for relaxation characteristics but also greatly contribute to the improvement of uniform elongation. However, when the value of Si + A1 is less than 2.0% by weight, the effect is small. On the other hand, when the value of Si + A1 is more than 5.0% by weight, relaxation characteristics and spot weldability are deteriorated. Therefore, the value of Si + A1 is made 2.0 weight%-5.0 weight%.

Mn

Mn is a deoxidizer like Si, and like C, is an element necessary for increasing hardenability and improving strength. However, when the amount is less than 0.2% by weight, the effect is small. On the other hand, when the amount exceeds 3.0% by weight, the workability is significantly reduced. Therefore, Mn amount is made into 0.2 to 3.0 weight%. In order to obtain particularly favorable workability, Mn is preferably 2.0% by weight or less.

Nb, Ti, B, Ni, Cr, Mo, Cu

Each element of Nb, Ti, B, Ni, Cr, Mo, and Cu is an element contributing to the improvement of hardenability, and it adds 1 type, or 2 or more types according to the objective of the strength and toughness of a steel bar. However, when these amounts are too small, such an effect cannot be acquired, and even if too large, an effect will become saturated. Accordingly, Nb: 0.01% to 0.1%, Ti: 0.01% to 0.05%, B: 0.0003% to 0.005%, Ni: 0.2% to 1.0%, Cr: 0.1% to 1.0%, Mo: 0.05% to 0.5%, and Cu: Let it be 0.2 to 1.0 weight%.

Metal texture

The PC steel rod of this invention consists of the structure | tissue which consists of martensium tempering substantially, and the carbide in a martens tempering is micro granule of 0.1 micrometer or less in uniform diameter. Substantially the structure of marten tempering includes the thing which has another structure, for example, bainite and ferrite, as long as the characteristic of marten tempering is not impaired.

The change in carbide form during martens tempering greatly affects the uniform elongation through the effect of easy void generation or work hardening progress. If the carbide form is rod-shaped or plate-shaped, it is easy to break by itself, the stress concentration at the tip end is large, and voids are easily generated, so that uniform elongation is lowered. Thus, the carbide form needs to be granular. In addition, even if the carbide form is granular, if the average diameter exceeds 0.1 mu m, the work hardening becomes difficult, so that the size of the granular carbide is 0.1 mu m or less.

Manufacturing method

The method for producing a PC steel rod of the present invention is a steel bar material obtained by solvent-forming steel having the above-described composition according to a conventional method, hot-rolled with a round bar, or subjected to cold working such as drawing. A series of heat treatment fences are not necessary for this steel bar material.

Quenching temperature greatly influences the yield ratio through the change of particle diameter. In addition, the uniform elongation also improves sequentially. When the quenching temperature is less than 1160 ° C, the particle diameter is small and the yield ratio does not decrease significantly. Therefore, the quenching temperature is 1160 ° C or more. In addition, since decarburization becomes remarkable when it exceeds 1300 degreeC, it shall be 1300 degreeC or less.

It is preferable to make tempering treatment temperature 600 degreeC or more, in order to improve uniform elongation drastically.

Characteristics of PC Steel Rod

The PC steel rod obtained by this manufacturing process has a uniform elongation of 8.0% or more at the strength level (1080N / mm2 or more) of class B standard, and a uniform elongation of 6% or more at high strength level (1230N / mm2 or more) of class C standard. It is possible to achieve relaxation of 8% or less. In addition, by quenching the high C content at high temperature, at the strength level (tensile strength ≥ 1080N / mm2, yield strength ≥930N / mm2) of class B standard, uniform elongation of 11.0% or more, yield ratio 0.85 or less, high temperature relaxation 8% or less At the strength level (tensile strength ≥1230N / mm2, proof strength ≥1080N / mm2) of class C standard, achieve uniform elongation of more than 10.0%, yield ratio 0.87, high temperature relaxation of 8% or less, At the strength level (tensile strength ≥ 1420 N / mm 2, proof strength ≥ 1275 N / mm 2), it is possible to achieve a uniform elongation of 8.0% or more, a yield ratio of 0.90 or less, and a high temperature relaxation of 8% or less.

In the case of spot welding the PC steel rod of the present invention, it is possible to secure excellent uniform elongation and high temperature relaxation characteristics by applying tempering treatment after spot welding.

According to the production method of the present invention, it is possible to manufacture in a normal process without adding a process such as strain addition, and excellent in high temperature relaxation characteristics of high uniform elongation and resistance ratio with a tensile strength of 1080N / mm 2 or more. Can provide PC steel rod. Therefore, it is very useful industrially, for example, to improve productivity significantly and to raise the reliability of PS concrete structure dramatically.

[Configuration and Function of Invention]

Example 1

Using the inventive steels (Nos. 1 to 13) and comparative steels (Nos. 14 to 19) of the composition shown in Table 1 as a sample steel, they were rolled on round bars of 24 mm in diameter and drawn on round bars of 23 mm in diameter. Then, the quenching tempering process by high frequency heating was performed. In addition, heat processing is not limited to high frequency heating. Here, the quenching heating temperature is 930 ° C to 1100 ° C, and tempering is performed at two levels for each sample steel so as to obtain the strength levels of Class B and Class C standards in JIS G 3109 (JIS G 3137). It was. Then they were subjected to a stretch test. Uniform elongation was measured by marking 2d (d is diameter) on the sample material and measuring 10d as the gauge distance at a distance of 5d or more from the break. The results of the tensile test are shown in Table 2. The relaxation test was carried out by JIS G 3109 (JIS G 3137 also) at room temperature. However, since 1994, 1000 hours have been standardized, but this time, a simple method was used to evaluate the previous 10 hours. That is, 70% of the standard tensile strength is loaded at room temperature, and the load change amount is measured after 10 hours. 70% of the standard tensile strength is loaded at the room temperature, and the load change amount is measured after 10 hours. It evaluated by ratio. In addition, the high temperature relaxation test was carried out at 180 ° C, loaded with a stress of 70% of the standard tensile strength, heat-cooled in the pattern shown in FIG. 1, and measuring the load change amount 23 hours after the test was started. It evaluated by the ratio with an initial load. The carbide form and size during martensite tempering were investigated by using a transmission electron microscope with an extraction residue method. The diameter of the carbide was observed at 5,000 times at 89000 times, and calculated as an average value. The results are shown in Table 2.

As shown in Table 2, all of the steels of the present invention Nos. 1 to 13 have a uniform elongation of 8.0% or more at high strength levels (tensile strength ≥ 1080 N / mm 2 and proof strength ≥ 930 N / mm 2) of class B standards. Achievement of 8% or less is achieved, and uniform strength of 6% or more and high temperature relaxation of 8% or less are achieved at the strength level (tensile strength ≥1230N / mm2 and proof strength ≥1080N / mm2) of Class C standard. All were found to be significantly superior to conventional steel properties. In addition, the carbide in a marten tempering process was granular, and all the diameters were 0.1 micrometer or less.

On the other hand, comparative steel No. 14 has excellent relaxation characteristics and, while the amount of C exceeds 0.7% by weight, carbides become grainy and rough, resulting in poor ductility. No. 15 is inferior in ductility because Mn exceeds 3.0% by weight. In No. 16, since the amount of Si + A1 is not 2% by weight, sufficient uniform elongation cannot be obtained, and the relaxation characteristics are also inferior. In this comparative steel, carbides were rod-shaped. Moreover, since No.17 amount of Si + A1 exceeds 5 weight%, relaxation is reduced. Nos. 18 and 19 are all suitable for chemical composition, but in No. 18, the carbide form is rod-shaped, and in No. 19, the granule is granular.

Example 2

Among the steels (Nos. 1 to 13) and comparative steels (Nos. 14 to 19) of the present invention shown in Table 1, a sample steel having a C composition of 0.5% by weight or less is rolled to a round rod having a diameter of 8 mm. It was then drawn to a release round rod having a diameter of 7.1 mm, and then quenched and tempered by high frequency heating. In addition, heat processing is not limited to high frequency heating. Here, the quenching heating temperature was performed at 930 ° C. to 1100 ° C., and tempering was performed under optimum conditions so that the strength level of Class B standard in JIS G 3109 (JISG 3137) was obtained. The obtained steel rods were subjected to spot welding under the welding conditions shown below, and then subjected to tempering treatment after welding to provide a tensile test and a relaxation test.

Welding and tempering conditions: welding current = 2500A, tempering current = 2700A, energizing cycles = 2, additional input = 410N, spiral band steel = SWRM8-3.2mm φ.

Uniform elongation and relaxation test methods are as described above. The results are shown in Table 3. In this table, it can be seen that the steel of the present invention is subjected to tempering treatment even after spot welding, thereby ensuring uniform elongation of 6% or more, and having excellent relaxation characteristics.

Table 1 (% by weight)

TABLE 2

TABLE 3

Example 3

Using the steel of the component composition shown in Table 4 as a sample steel, it rolled with the round rod of diameter 8mm, was drawing with the release round rod of diameter 7.1mm, and the quenching tempering process by high frequency heating was performed after that. In addition, heat processing is not limited to high frequency heating. Here, quenching heating temperature was 1160 degreeC to 1300 degreeC (invention example), and tempering process was performed so that the intensity | strength level of the C class or D class standard in JIS G 3109 (JIS G 3137) may be obtained. Then they were subjected to tensile testing. Uniform elongation was measured by 2d (d is the diameter) of each sample material and measured at 10d as the gage distance from 3d or more away from the break. The results of the tensile test are shown in Table 5. The relaxation test was carried out by JIS G 3109 (JIS G 3137 also) at room temperature. However, although the 1000-hour value was standardized since 1994, it evaluated this time using the previous 10-hour value as a simple method like Example 1 this time. In addition, at a high temperature, it is carried out at 180 ° C., and a stress of 70% of the standard tensile strength is added, cooled by a heating pattern shown in FIG. 1, the load change amount after 23 hours is measured, and evaluated as a ratio with the initial load. It was. The results are shown in Table 5.

As shown in Table 5, the invention examples of Nos. 1 to 13 are all equal to or greater than 10.0% of uniform elongation at the strength level (tensile strength ≥ 1230 N / mm 2 and proof strength ≥ 1080 N / mm 2) of the class C standard. 0.87 or less, high temperature relaxation 8% or less, at the strength level (tensile strength ≥ 1420 N / mm2, proof strength ≥ 1275 N / mm2) of class D standards, uniform elongation of 8% or more, yield ratio 0.90 or less, high temperature relaxation 8% The following was achieved and it was confirmed that both characteristics are also significantly superior to the conventional steel characteristics.

In addition, in order to improve the uniform elongation, it is preferable that the tempering treatment temperature is 600 ° C. or higher, but if the steel of the component of the present invention is tempered at a high temperature of 600 ° C. or higher, it is possible to obtain a Class D standard, and to achieve uniform elongation of 8% or more. It can be seen that it is easily secured.

In contrast, in Comparative Example No. 14, the amount of C was insufficient, and in No. 16, the amount of Si + A1 was insufficient, the tempering treatment temperature was lowered, and the yield ratio did not decrease significantly. It will drop significantly around 5% and 7% in Class C specifications. No. 15 and No. 17 have a higher tempering treatment temperature and a resistance ratio, but since the amount of C and Mn exceed the appropriate amounts, respectively, the uniform elongation is slightly lower than that of the example of the present invention, and the uniform elongation is made according to the target class C standard. It was not possible to achieve more than 10.0% of uniform height and more than 8% of uniform height in class D specification. Although No. 18 had a suitable chemical composition, the yield ratio did not decrease because the quenching temperature was as low as 1100 ° C., and thus the uniform elongation target could not be achieved.

Example 4

Using the steel of the composition shown in Table 4 as a sample steel, it was rolled with a round rod having a diameter of 24 mm, drawn with a round rod having a diameter of 23 mm, and then quenched and tempered by high frequency heating. In addition, heat processing is not limited to high frequency heating. Here, quenching heating temperature was performed at 1160 degreeC to 1300 degreeC (example of this invention), and tempering was performed so that the intensity level of the class B standard in JIS G 3109 (JIS G 3137) may be obtained. Then they were subjected to tensile and retraction tests. The test method is the same as in Example 3.

The heat treatment conditions and obtainable mechanical properties are shown in Table 6. All of the steels of the present invention from No. 1 to No. 13 achieve a uniform elongation of 11.0% or more, a yield ratio of 0.85 or less, and a high temperature relaxation of 8% or less at the strength level of Class B standard, and both characteristics are conventional steels. It was confirmed that it was significantly superior to the characteristics. In contrast, in Comparative Example No. 14, the amount of C was insufficient, and in No. 16, the amount of "Si + A1" was insufficient, so that the tempering treatment temperature was lower than that of the present invention, and the yield ratio was remarkably similar to that of Example 3. Even if it does not go down, the uniform elongation will fall by 8%. No. 15 and No. 17 have a high tempering treatment temperature and a resistance ratio, but the amount of C and Mn exceed the appropriate values, respectively, so that the uniform elongation is slightly reduced compared to the example of the present invention. Uniform elongation of more than 11.0% could not be achieved. No. 18 also had the same chemical composition as in Example 3, but because the quenching temperature was low at 1100 ° C., the yield ratio did not fall, and uniform elongation could not achieve the target value.

Table 4

Chemical Composition of Sample Steels

Table 5

Table 6

[Effects of the Invention]

According to the production method of the present invention, it is possible to manufacture in a normal process without adding a process such as strain addition, and excellent in high temperature relaxation characteristics of high uniform elongation and resistance ratio with a tensile strength of 1080N / mm 2 or more. Can provide PC steel rod. Therefore, it is possible to provide a PC steel bar having excellent high temperature relaxation characteristics of the live yield ratio. Therefore, it is very useful industrially, for example, to improve productivity significantly and to raise the reliability of PS concrete structure dramatically.

Claims (13)

A steel containing C: 0.2 to 0.7%, Mn: 0.2 to 3..0%, and (Si% + A1%): 2.0 to 5.0% by weight, and is a structure substantially composed of marten tempering. A PC steel rod having excellent uniform elongation and high temperature relaxation characteristics, characterized in that the carbides in the martens tempering process have fine grains with an average diameter of 0.1 µm or less and a tensile strength of 1080N / mm 2 or more and less than 1420N / mm 2. The steel component according to claim 1, wherein the steel component is, by weight%, Nb: 0.01 to 0.1%, Ti: 0.01 to 0.05%, B: 0.0003 to 0.005%, Ni: 0.2 to 1.0%, Cr: 0.1 to 1.0%, Mo PC steel bars excellent in uniform elongation and high temperature relaxation characteristics characterized by containing one or two or more selected from the group of: 0.05 to 0.5% and Cu: 0.2 to 1.0%. As a steel component, by weight%, C: 0.2-0.7%, Mn: 0.2-3..0%, (Si% + A1%): 2.0-5.0%, Nb: 0.01-0.1%, Ti: 0.01- 0.05%, B: 0.0003 to 0.005%, Ni: 0.2 to 1.0%, Cr: 0.1 to 1.0%, Mo: 0.05 to 0.5% and Cu: 0.2 to 1.0% A structure composed of Fe and unavoidable impurities and substantially composed of martensium tempering, wherein the carbides in martensium tempering have a fine-positioned state of 0.1 µm or less in average diameter and a tensile strength of 1080N / mm 2 or more and less than 1420N / mm 2. PC steel bar with excellent elongation and high temperature relaxation characteristics. The PC steel rod according to any one of claims 1 to 3, wherein the PC steel rod is excellent in uniform elongation and high temperature relaxation characteristics in which tensile strength ≥ 1080 N / mm 2 and proof strength ≥ 930 N / mm 2. The PC steel rod according to any one of claims 1 to 3, wherein the PC steel rod is excellent in uniform elongation and high temperature relaxation characteristics, in which tensile strength ≥ 1230 N / mm 2 and proof strength ≥ 1080 N / mm 2. The PC steel rod is uniformly elongated according to any one of claims 1 to 5, wherein the amount of C steel is 0.2% to 0.5% by weight and is used for the purpose of performing spot welding and subsequent tempering treatment energization. And PC steel rods with high temperature relaxation characteristics. By weight%, steel containing C: 0.5% to 0.7%, Mn: 0.2 to 2.0%, and Si and A1 of 2.0% ≦ Si + A1 ≦ 5.0% was quenched at 1160 ° C to 1300 ° C, and then tempered. A method for producing a PC steel rod having a high uniform elongation and resistance ratio with high temperature relaxation characteristics, characterized in that it has a tensile strength of 1080 N / mm 2 or more. By weight, C: 0.5% to 0.7%, Mn: 0.2 to 2.0%, Si and A1 contain 2.0% ≦ Si + A1 ≦ 5.0%, and further Nb: 0.01 to 0.1%, Ti: 0.01 to 0.05% Steel containing 1 or 2 or more of B: 0.0003 to 0.005%, Ni: 0.2 to 1.0%, Cr: 0.1 to 1.0%, Mo: 0.05 to 0.5%, and Cu: 0.2 to 1.0% A method of producing a PC steel rod having excellent high temperature relaxation characteristics with high uniform elongation and resistance ratio, characterized by quenching at ˜1300 ° C. and tempering thereafter. By weight%, C: 0.5% -0.7%, Mn: 0.2-2.0%, Si and A1 are 2.0% ≤Si + A1≤5.0%, Nb: 0.01-0.1%, Ti: 0.01-0.05%, B: It is composed of one or two or more of 0.0003 to 0.005%, Ni: 0.2 to 1.0%, Cr: 0.1 to 1.0%, Mo: 0.05 to 0.5%, and Cu: 0.2 to 1.0%, and the remaining portions of Fe and unavoidable impurities. Manufacture of PC steel bars with excellent high temperature relaxation characteristics with high uniform elongation and resistance ratio, characterized in that the steel is quenched at 1160 ° C to 1300 ° C and then tempered. Way. The method according to any one of claims 7 to 9, wherein the tensile strength is greater than 10.0%, the yield ratio is 0.87 or less, and the high temperature relaxation is 8% or less at strength levels of tensile strength ≥ 1230 N / mm 2 and proof strength ≥ 1080 N / mm 2. Method for manufacturing PC steel rods with excellent high temperature relaxation characteristics due to high uniform elongation and resistance ratio. The method according to any one of claims 7 to 9, wherein the tensile strength is not less than 8.0%, the yield ratio is not more than 0.90, and the high temperature relaxation is not more than 8% at the strength level of tensile strength ≥ 1420 N / mm 2 and proof strength ≥ 1275 N / mm 2. Method for manufacturing PC steel rods with excellent high temperature relaxation characteristics due to high uniform elongation and resistance ratio. The method according to any one of claims 7 to 9, wherein the tensile strength is higher than 11.0%, the yield ratio is 0.85 or less, and the high temperature relaxation is 8% or less at strength levels of tensile strength ≥1080 N / mm 2 and proof strength ≥930 N / mm 2. Method for manufacturing PC steel rods with excellent high temperature relaxation characteristics due to high uniform elongation and resistance ratio. The method for producing a PC steel rod according to any one of claims 7 to 12, which is excellent in high temperature relaxation characteristics due to its high uniform elongation and resistance ratio where the tempering temperature is 600 ° C or higher. ※ Note: The disclosure is based on the initial application.