JP3457494B2 - High-strength PC steel bar and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PC steel rod which is widely used as a reinforcing material for prestressed concrete structures such as poles, piles and buildings, bridges, etc. 1230
The present invention relates to a high-strength PC steel bar excellent in delayed fracture property and uniform elongation, which is not less than MPa, and a manufacturing method thereof.

[0002]

2. Description of the Related Art PC steel, which is widely used as a reinforcing material for prestressed concrete structures such as poles, piles, buildings and bridges, is usually PC steel wire, PC steel stranded wire, or PC steel rod. . The PC steel wire is manufactured by performing a patenting treatment and then drawing.

On the other hand, the PC steel rod is, for example, Japanese Patent Publication No. 5-41.
As described in Japanese Patent No. 684, the amount of C is 0.25.
~ 0.35% medium carbon steel after hot rolling, quenching
It is manufactured by tempering. Although the strength of PC steel wire is higher than that of PC steel bar, it has the drawback that spot welding cannot be performed because of the high C content.

On the other hand, although the spot weldability of the PC steel bar is better than that of the PC steel wire, the "prestressed concrete design and construction standard / commentary" (edited by the Architectural Institute of Japan,
Maruzen, pp. 43-45, high-strength PC steel rods having a strength exceeding 1275 MPa (130 kgf / mm ² ) have inferior delayed fracture properties as compared with PC steel wire.

Further, as described in Japanese Patent Publication No. 5-59967, the spot-welded portion is rapidly cooled, so that it has a structure mainly composed of martensite, and delayed fracture tends to occur in the spot-welded portion. There is a point. Further, recently, as described in Japanese Patent Application Laid-Open No. 7-3396, development of a PC steel rod excellent in uniform elongation has been demanded in order to improve bending toughness for applications such as piles. .

As a conventional finding for improving the delayed fracture property of PC steel rods, for example, Japanese Patent Publication No. 5-59967 proposes that it is effective to reduce the P and S contents. Certainly, lowering P and lowering S is effective for delayed fracture, but the P and S contents of the current PC steel bar are already around 0.01%. Although it is possible to further reduce the P and S contents, there is a drawback that the manufacturing cost becomes high. In Japanese Patent Publication No. 5-41684, Si, Mn
It has been proposed to control the content and perform bending or drawing in the tempering process after quenching. Further, Japanese Patent Laid-Open No. 5-7963 proposes to provide a resin coating layer around the spot welded portion between the PC steel rod and the iron wire to reduce the susceptibility to delayed fracture. Further, Japanese Patent Laid-Open No. 6-212346 proposes a means for improving delayed fracture characteristics by adding an alloying element such as Ni. However, none of the proposals has significantly improved delayed fracture characteristics.

On the other hand, as a conventional finding for improving the uniform elongation of PC steel rods, for example, Japanese Patent Laid-Open No. 7-3396 proposes a method of performing tempering at a high temperature of 500 ° C. or higher. Has a defect that spot welding cannot be performed because of a high value of 0.45% or more. In addition, JP-A-8-
Japanese Patent No. 158010 describes that addition of a large amount of Si and Al is effective for improving uniform elongation. However, if Si and Al are added in a large amount, there is a drawback that the delayed fracture property of the spot welded portion is deteriorated and the manufacturing cost is increased.

As described above, according to the prior art, in the high strength PC steel bar capable of spot welding, not only the individual problems of delayed fracture property and uniform elongation but also the high strength of which both are drastically improved. There were limits to the production of PC steel rods.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and is capable of spot welding, has a delayed fracture characteristic and a good strength of uniform elongation of 1230M.
It is an object of the present invention to realize a high-strength PC steel bar of Pa or more and to provide a manufacturing method thereof.

[0010]

Means for Solving the Problems The present inventors first analyzed delayed fracture behavior in detail using PC steel rods of various strength levels produced by quenching and tempering after rolling. It has already been clarified that the delayed fracture is caused by hydrogen in the steel material. Therefore, in this analysis, the delayed fracture characteristics are defined as "critical diffusible hydrogen content" at which delayed fracture does not occur.
It was evaluated by determining. In this method, various amounts of diffusible hydrogen are contained in a sample by electrolytic hydrogen charging, and then Cd plating is performed to prevent hydrogen from being released from the sample to the atmosphere during a delayed fracture test, and then,
This is to evaluate the amount of diffusible hydrogen at which a prescribed load is applied in the atmosphere and delayed fracture does not occur.

FIG. 1 shows an example of analysis of the relationship between the amount of diffusible hydrogen and the fracture time until delayed fracture. It can be seen that as the amount of diffusible hydrogen contained in the sample decreases, the time until delayed fracture becomes longer, and when the amount of diffusible hydrogen is below a certain value, delayed fracture does not occur. This amount of hydrogen is defined as the “limit diffusible hydrogen amount”. The higher the critical diffusible hydrogen content is, the better the delayed fracture resistance of the steel material is, which is a value peculiar to the steel material determined by the composition of the steel material and the manufacturing conditions such as heat treatment. The amount of diffusible hydrogen in the sample can be easily measured with a gas chromatograph.

[0012] As a result of various investigations from the viewpoint of the microstructure in order to increase the critical diffusible hydrogen content of a high strength PC steel rod, that is, to improve delayed fracture characteristics and uniform elongation, the longitudinal length of the PC steel rod was determined. If a layered structure composed of ferrite with martensite or tempered martensite oriented in the direction (L direction) is formed, the critical diffusible hydrogen content is high even in a high strength region exceeding 1230 MPa, and delayed fracture characteristics are significantly increased. We have found a completely new finding that it will improve. Moreover, it was found that uniform elongation was remarkably improved by controlling such a layered structure. Furthermore, the relationship between the layered structure consisting of martensite or tempered martensite and ferrite oriented in the longitudinal direction of the PC steel rod, delayed fracture characteristics and uniform elongation was analyzed in detail, and optimum manufacturing conditions thereof were established. It was made.

The present invention was made based on the above findings, and the gist of the invention is as follows.

(1) % by mass, C: 0.2 to 0.4%, Si: 3.0% or less, Mn: 0.2 to 2.0%, Al: 0.005 to 0.1% The balance of Fe and unavoidable impurities,
Of the organization Ri Do from substantially martensite and ferrite of the lamellar structure oriented in the longitudinal direction of the PC steel rod, martensite
High strength PC steel rod average spacing between sites is characterized der Rukoto below 10 [mu] m.

(2) % by mass, C: 0.2 to 0.4%, Si: 3.0% or less, Mn: 0.2 to 2.0%, Al: 0.005 to 0.1% The balance of Fe and unavoidable impurities,
Of the organization Ri Do from substantially tempered martensite and ferrite of the lamellar structure oriented in the longitudinal direction of the PC steel rod, circle
High strength PC steel rod average spacing between ten sites is characterized der Rukoto below 10 [mu] m.

(3) In mass%, (A) Cr : 0.05 to 2.0%, Mo: 0.05 to 1.0%, Ni: 0.05 to 5.0%, Cu: 0 0.05 to 1.0%, W: 0.05 to 0.5%, B: 0.0003 to 0.0050% , one or more kinds, or (B) V: 0.05 to 0.3. %, Nb: 0.005 to 0.1%, Ti: 0.005 to 0.05%, Ta: 0.005 to 0.5% of one or more kinds of (A) and (B) One side of the group
Is a high-strength PC steel rod according to the above (1) or (2), characterized in that it contains both and the balance consists of Fe and unavoidable impurities.

(4) The ferrite fraction is in the range of 10 to 70%.
Above, wherein the 囲Dea Rukoto (1) internal Izu to (3)
The high-strength PC steel rod described in one of them .

(5) In mass%, C: 0.2 to 0.4%, Si: 3.0% or less, Mn: 0.2 to 2.0%, Al: 0.005 to 0.1% A steel containing Al and the balance Fe and unavoidable impurities
_C1 is heated to a temperature range of to A _C3, after the hot working at a reduction ratio of 20% or more, the method of producing a high strength PC steel bar, characterized in that the cooling at a cooling rate of more than 20 ° C. / sec .

(6) A method for producing a high-strength PC steel rod, which comprises tempering in a temperature range of 200 to 600 ° C. following the production method described in (5 ) above .

(7) Following the production method described in (5) above, a plastic strain of 0.3% or more is applied, and then 200-
A method for producing a high-strength PC steel rod, which comprises tempering in a temperature range of 600 ° C.

(8) High strength characterized by applying a plastic strain of 0.3% or more by heating to a temperature range of 200 to 600 ° C. following the manufacturing method described in (5 ) above. Method for manufacturing PC steel rod.

(9) In mass%, (A) C: 0.2 to 0.4%, Si: 3.0% or less, Cr: 0.05 to 2.0%, Mo: 0.05 to 1 0.0%, Ni: 0.05 to 5.0%, Cu: 0.05 to 1.0%, W: 0.05 to 0.5%, B: 0.0003 to 0.0050%, one kind Or 2 or more types, or (B) V: 0.05-0.3%, Nb: 0.005-0.1%, Ti: 0.005-0.05%, Ta: 0.005-0. (5) characterized by containing 5% of one or more of (A) and / or (B).
(6), (7), The method for producing a high-strength PC steel rod according to any one of (8).

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described.

First, the reason for limiting the morphology of the structure, which is the most important point for the delayed fracture property and the improvement of uniform elongation of the high strength PC steel rod aimed at by the present invention, will be described. An example of a scanning electron micrograph of the layered structure of martensite or tempered martensite and ferrite oriented in the longitudinal direction (L direction) of the PC steel bar limited in the present invention is shown in FIG.

FIG. 2 shows the case of martensite and ferrite. The martensite and ferrite have a fine layered structure, and moreover, the longitudinal direction (L direction) of the PC steel bar.
It can be seen that they are oriented in. When this structure is tempered, it becomes a layered structure of tempered martensite and ferrite. By controlling the fine layered structure of martensite or tempered martensite and ferrite, both delayed fracture characteristics and uniform elongation can be improved at the same time.

An example of the analysis of the influence of the structure morphology on delayed fracture characteristics and uniform elongation is shown in FIGS. 3 and 4. PC
It can be seen that the limit diffusible hydrogen content is high and the uniform elongation is significantly improved by forming the layered structure of martensite or tempered martensite and ferrite oriented in the longitudinal direction of the steel rod. On the other hand, the single structure of tempered martensite obtained by the conventional quenching and tempering method has low critical diffusible hydrogen content and low uniform elongation. In order to significantly improve the high strength and delayed fracture characteristics and uniform elongation, in the layered structure of martensite or tempered martensite and ferrite, the average distance between martensites or between tempered martensites is 10 μm or less. A more preferable condition is 5 μm or less.
The average interval can be measured by the cutting method in the direction perpendicular to the longitudinal direction (L direction) in the photograph shown in FIG.

Even if residual austenite or a small amount of bainite or pearlite is present in martensite or tempered martensite having a layered structure, there is no problem with respect to uniform elongation and delayed fracture properties. The layered structure of martensite or tempered martensite and ferrite does not have to be formed over the entire cross section of the PC steel rod, and may be formed in the region of at least 15% of the radius of the PC steel rod from the surface layer of the PC steel rod. For example, it has an effect of improving delayed fracture characteristics and uniform elongation.

In the layered structure of martensite or tempered martensite, the ferrite fraction is 10
The preferable range is ˜70%. This is because if the ferrite fraction is less than 10%, a significant improvement in uniform elongation cannot be expected, while if it exceeds 70%, it becomes difficult to achieve a high strength of 1230 MPa or more. From the viewpoint of simultaneously achieving high strength and delayed fracture properties and improvement of uniform elongation of the PC steel rod, the more preferable ferrite fraction range is 20 to 60%.

Next, the reasons for limiting the components of the steel targeted by the present invention will be described.

C: C is an essential element for ensuring the strength of the PC steel rod, but if it is less than 0.2%, the desired high-strength PC steel rod cannot be obtained, while 0.4% is used. If it exceeds the range, the spot weldability deteriorates significantly, so the range was limited to 0.2 to 0.4%.

Si: Si has the effect of improving the relaxation characteristics and also of increasing the strength by the solid solution hardening effect. Even if it exceeds 3%, the effect commensurate with the added amount cannot be expected, and the delayed fracture property of the spot welded part deteriorates.
The range was limited to 3% or less. The preferred range is 0.2 to
It is 2.5%.

Mn: Mn is an element effective not only for deoxidizing and desulfurizing but also for improving hardenability, but if it is less than 0.2%, the above effect cannot be obtained. If it exceeds 2.0%, spot weldability deteriorates.
The range was limited to 0.2 to 2.0%.

Al: Al has the effect of preventing coarsening of austenite grains by deoxidizing and forming AlN, but if it is less than 0.005%, these effects are not exhibited, and 0.1%. The effect is saturated even if it exceeds 0.
It was limited to the range of 005 to 0.1%.

The above is the basic composition of the steel to which the present invention is applied. In the present invention, however, (A) Cr: 0.05-2.0%, Mo: 0.05-1. 0
%, Ni: 0.05 to 5.0%, Cu: 0.05 to 1.
0%, W: 0.05 to 0.5%, B: 0.0003 to
0.0050% of 1 type or 2 types or more, or (B) V: 0.05 to 0.3%, Nb: 0.005 to 0.1
%, Ti: 0.005 to 0.05%, Ta: 0.005
.About.0.5% of one or more of (A) and / or (B) can be contained. (A)
The elements of the group are added mainly for the purpose of improving hardenability and delayed fracture characteristics. On the other hand, the elements of the group (B) are mainly for refining the crystal grains, and in the layered structure of martensite or tempered martensite and ferrite, carbonitrides are generated in the ferrite to increase yield strength and relaxation characteristics. It is added for the purpose of improving.

Cr: Cr is an effective element for improving hardenability and delayed fracture characteristics and increasing softening resistance during tempering treatment, but if it is less than 0.05%, its effect cannot be sufficiently exhibited. On the other hand, if the content exceeds 2.0%, the spot weldability deteriorates, so the content is limited to 0.05 to 2.0%.

Mo: Mo is an element that improves hardenability and delayed fracture characteristics similarly to Cr, has a strong temper softening resistance, and is effective in increasing tensile strength after heat treatment, and further improves relaxation characteristics. It also has an effect,
If it is less than 0.05%, its effect is small. On the other hand, if it exceeds 1.0%, its effect is saturated.
The range was limited to 1.0%.

Ni: Ni is added in order to improve hardenability and delayed fracture characteristics. If it is less than 0.05%, its effect is small, while if it exceeds 5.0%, the effect of matching the added amount is exhibited. Since it cannot be done, it was limited to the range of 0.05 to 5.0%.

Cu: Cu is an element effective for increasing the hardenability and the strength of tempered martensite, but 0.0
If it is less than 5%, the effect cannot be exhibited, and if it exceeds 1.0%, the hot workability deteriorates, so the content is limited to 0.05 to 1.0%.

B: B has an effect of improving delayed fracture characteristics and also has an effect of remarkably enhancing hardenability, but if B is less than 0.0003%, the above effect is not exhibited and 0 Even if it exceeds 0.0050%, the effect will be saturated, so that
It was limited to 0003 to 0.0050%.

V: V has the effect of refining the crystal grains by forming carbonitrides and increasing the yield strength and improving the relaxation characteristics, but if it is less than 0.05%, the above-mentioned effect is obtained. On the other hand, the effect is saturated even if it exceeds 0.3%, so the content is limited to 0.05 to 0.3%.

Similar to V, Nb: Nb also has the effect of forming carbonitrides to make the crystal grains finer and to increase the yield strength and improve relaxation characteristics.
If it is less than 0.005%, the above effect is insufficient, while if it exceeds 0.1%, the effect is saturated, so 0.005
Limited to ~ 0.1%.

Ti: Ti is an element effective in preventing the coarsening of crystal grains by forming deoxidation and forming carbonitride, and effective in increasing the yield strength and improving the relaxation characteristics, but less than 0.005%. However, these effects are not exhibited, and the effect is saturated even if it exceeds 0.05%.
It was limited to the range of 005 to 0.05%.

Ta: Ta, like V, also has the effect of refining crystal grains by forming carbonitrides, increasing yield strength and improving relaxation characteristics. The effect is not exhibited,
The effect is saturated even if added over 0.5%, so
It was limited to 005 to 0.5%.

Although P and S are not particularly limited,
From the viewpoint of improving the delayed fracture characteristics of PC steel rods, 0.015% or less is a preferable range. Further, N has the effect of refining crystal grains, increasing yield strength, and improving relaxation characteristics by forming nitrides of Al, V, Nb, and Ti, so 0.002 to 0.015% is preferable. It is a range.

In the method for producing a high strength PC steel rod of the present invention,
20% by heating the steel of the above components to the temperature range of Ac ₁ to Ac _3.
After performing hot working at the above reduction rate, cooling is performed at a cooling rate of 20 ° C./sec or more, or 200 to 60 after cooling.
0.3% after tempering in the temperature range of 0 ° C or cooling
The above plastic strain is applied and subsequently tempered in the temperature range of 200 to 600 ° C., or 200 to 600 after cooling.
It is heated to a temperature range of ° C to give a plastic strain of 0.3% or more. The reasons for limiting the manufacturing conditions will be described below.

The steel material is heated in the two-phase region of ferrite and austenite. At this time, the heating temperature is Ac ₁
If it is less than or more than Ac ₃ , a layered structure of martensite or tempered martensite and ferrite cannot be finally obtained. Therefore, the heating temperature range is limited to Ac ₁ to Ac ₃ . Incidentally, it is more preferable condition range _{℃ (Ac 1 +10) ~ (} Ac 3 -10). Further, in order to refine the layered structure of martensite or tempered martensite and ferrite, the steel before heating may be adjusted to a structure mainly composed of martensite or tempered martensite or bainite or pearlite. Desirably, the ferrite fraction at this time is less than 10%, which is a more preferable condition. As the means for controlling the microstructure before heating, there are adjustment of the cooling rate after hot rolling, ordinary quenching / tempering, adjustment of the cooling rate after austenitizing treatment, and any method may be used.

The reduction ratio (section reduction ratio) of hot working is 20.
If it is less than%, a layered structure oriented in the longitudinal direction of the PC steel rod cannot be obtained, so the lower limit of the rolling reduction was limited to 20%.
From the viewpoint of forming a fine layered structure, a reduction rate of 30% or more is a preferable condition. Further, when using a steel having an ordinary ferrite-pearlite structure, it is preferable to perform hot working at a reduction ratio of 50% or more in order to realize a fine lamellar structure. Any method may be used for hot working.

If the cooling rate after hot working is less than 20 ° C./sec, a large amount of ferrite, pearlite, and bainite are generated during cooling, and the strength is likely to decrease.
The lower limit of the cooling rate was limited to 20 ° C / sec. From the viewpoint of preventing ferrite, pearlite, and bainite that are likely to be generated during cooling as much as possible, the preferable cooling rate is 50 ° C./second or more. The cooling end temperature is equal to or lower than the martensitic transformation temperature (Ms point or lower).

The tempering after cooling is performed in order to increase the yield strength and improve the relaxation characteristics.
In particular, in steels containing V, Nb, Ti, and Ta, carbonitrides of these alloying elements are generated in ferrite by tempering treatment, so that the yield strength is increased and the relaxation characteristics are improved. At this time, if the temperature is less than 200 ° C., the effect of tempering is small, while if it exceeds 600 ° C., the strength decreases and it becomes difficult to manufacture a high-strength PC steel rod, so the tempering temperature range is limited to 200 to 600 ° C. From the viewpoint of improving the delayed fracture property, the heating rate during tempering is preferably 20 ° C./sec or more.

In the present invention, the PC steel bar has a 0.3% content after cooling.
The above plastic strain may be applied and then tempered, or a plastic strain of 0.3% or more may be applied during tempering. The purpose is to increase the yield strength and improve relaxation characteristics. If it is less than 0.3%, the above effect is small, so the lower limit is limited to 0.3%. The means for imparting plastic strain may be any method such as tensile strain and strain due to straightening.

In the present invention, delayed fracture characteristics and uniform even after light wire drawing or plastic working for the purpose of adjusting wire diameter, deforming, etc. before hot working, after hot working, after cooling or after tempering treatment. There is no remarkable deterioration in elongation, and there is no restriction.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

EXAMPLES The effects of the present invention will be described more specifically below with reference to examples.

Steels having the chemical compositions shown in Table 1 were formed into various microstructures by adjusting the cooling rate after hot rolling or by quenching and tempering after austenitizing treatment.
It was heated to a temperature range of c ₁ to Ac ₃ performs hot working, then cooled. Tempering was performed by high frequency heating, and plastic strain was applied using a tensile tester.

Using the above samples, the structure morphology, mechanical properties, delayed fracture properties and relaxation properties were evaluated. The delayed fracture characteristic was evaluated by using the sample subjected to spot welding with the amount of limiting diffusible hydrogen described above, and the load stress was carried out under the condition of 80% of the tensile strength. The relaxation test was performed by the method of JIS G3137.
The results are shown in Tables 2 and 3.

Test No. 2 in Table 2 1 to 16 are examples of the present invention,
No. of Table 3 17 to 24 are comparative examples. As can be seen from the table, in all the examples of the present invention, the tensile strength of the PC steel bar was 12
Along with 30 MPa or more, a fine layered structure of martensite or tempered martensite and ferrite oriented in the longitudinal direction of the PC steel rod provides a higher limit diffusible hydrogen content than conventional PC steel rods and delayed fracture characteristics. A PC steel bar with excellent and high uniform elongation has been realized. Moreover, relaxation is at the same level as conventional PC steel bars.

On the other hand, No. which is a comparative example. 17, 1
Nos. 8 and 19 are manufactured by the conventional manufacturing method. That is, it is manufactured by normal quenching and tempering treatment, and the structure is an example of tempered martensite. Therefore, the critical diffusible hydrogen content is low and the delayed fracture characteristics of the spot welds are inferior to those of the examples of the present invention. Also, the uniform elongation is low.

No. 6 which is a comparative example. Nos. 20 and 21 are examples in which the heating temperature during hot working is inappropriate. No. 20 is
This is an example in which the heating temperature exceeds Ac ₃ and it becomes a single phase of austenite, and the layered structure of tempered martensite and ferrite could not be achieved, and delayed fracture characteristics and uniform elongation could be greatly improved. Not not. In addition, No.
Since _No. 21 had a heating temperature of Ac ₁ or less, it had a pearlite structure spherical with ferrite and could not achieve high strength.

In addition, No. No. 22 is an example in which the reduction rate of hot working is inappropriate. That is, since the rolling reduction is too small, the layered structure of tempered martensite and ferrite oriented in the longitudinal direction of the PC steel bar does not occur, and the effect of improving delayed fracture characteristics and uniform elongation is small.

No. No. 23 is an example in which the cooling rate after hot working was too low, so that a large amount of ferrite and pearlite were generated during cooling and the strength was reduced.

Further, No. 1 which is a comparative example. 24 is steel C
This is an example in which the spot weldability deteriorates and the cracks occur in the spot welds because the content is too high. As a result, the critical diffusible hydrogen content is significantly reduced, and the delayed fracture characteristics of the spot welds are deteriorated.

[0064]

As is clear from the above examples, the present invention enables spot welding by forming a fine layered structure of martensite or tempered martensite and ferrite oriented in the longitudinal direction of a PC steel rod. It is possible to significantly improve the delayed fracture characteristics and uniform elongation of high-strength PC steel bars, and to manufacture them by optimally selecting the chemical composition of steel, hot working conditions, heat treatment conditions, etc. The method has been established, and the industrial effect is extremely remarkable.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of the relationship between the amount of diffusible hydrogen and delayed fracture time.

FIG. 2 is a scanning electron micrograph showing an example of a layered structure of martensite and ferrite oriented in the longitudinal direction of a PC steel rod.

FIG. 3 is a diagram showing an example of a relationship between delayed fracture characteristics and a microstructure of a PC steel rod.

FIG. 4 is a diagram showing an example of a relationship between uniform elongation and a microstructure of a PC steel rod.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 8/08 C21D 9/00

Claims (9)

(57) [Claims] 1. In mass%, C: 0.2 to 0.4%, Si: 3.0% or less, Mn: 0.2 to 2.0%, Al: 0.005 to 0.1% Contains, balance Fe and unavoidable impurities, steel
Of the organization Ri Do from substantially martensite and ferrite of the lamellar structure oriented in the longitudinal direction of the PC steel rod, martensite
High strength PC steel rod average spacing between sites is characterized der Rukoto below 10 [mu] m. 2. In mass%, C: 0.2 to 0.4%, Si: 3.0% or less, Mn: 0.2 to 2.0%, Al: 0.005 to 0.1% Contains, balance Fe and unavoidable impurities, steel
Of the organization Ri Do from substantially tempered martensite and ferrite of the lamellar structure oriented in the longitudinal direction of the PC steel rod, circle
High strength PC steel rod average spacing between ten sites is characterized der Rukoto below 10 [mu] m. 3. In mass%, (A) Cr: 0.05 to 2.0%, Mo: 0.05 to 1.0%, Ni: 0.05 to 5.0%, Cu: 0. 05 to 1.0%, W: 0.05 to 0.5%, B: 0.0003 to 0.0050%, one or more kinds, or (B) V: 0.05 to 0.3% , Nb: 0.005 to 0.1%, Ti: 0.005 to 0.05%, Ta: 0.005 to 0.5%, one or more types of (A) and (B) group The high-strength PC steel rod according to claim 1 or 2, characterized in that it contains one or both of, and the balance consists of Fe and unavoidable impurities. 4. Ferrite fraction in the range of 10-70%
Any one of claims 1, 2, and 3 characterized in that
High-strength PC steel rod described in. 5. In mass%, C: 0.2 to 0.4%, Si: 3.0% or less, Mn: 0.2 to 2.0%, Al: 0.005 to 0.1% A containing steel with the balance being Fe and unavoidable impurities
_C1 is heated to a temperature range of to A _C3, after the hot working at a reduction ratio of 20% or more, the method of producing a high strength PC steel bar, characterized in that the cooling at a cooling rate of more than 20 ° C. / sec . 6. The manufacturing method according to claim 5 , further comprising 200
A method for producing a high-strength PC steel rod, which comprises tempering in a temperature range of up to 600 ° C. 7. The method as set forth in claim 5 is followed by 0.3.
% Or more plastic strain is applied, and then 200-600 ℃
A method for producing a high-strength PC steel rod, characterized by tempering in the temperature range of. 8. The manufacturing method according to claim 5 , further comprising 200
A method for producing a high-strength PC steel rod, which comprises heating to a temperature range of up to 600 ° C to impart a plastic strain of 0.3% or more. 9. In mass%, (A) Cr: 0.05 to 2.0%, Mo: 0.05 to 1.0%, Ni: 0.05 to 5.0%, Cu: 0.05 ~ 1.0%, W: 0.05 to 0.5%, B: 0.0003 to 0.0050%, one or more kinds, or (B) V: 0.05 to 0.3%, Nb: 0.005 to 0.1%, Ti: 0.005 to 0.05%, Ta: 0.005 to 0.5%, one or more of (A) and (B) group One or both are contained, Claim 5, 6, 7,
8. The method for manufacturing a high-strength PC steel rod according to any one of 8.