JP2862206B2 - High-strength PC steel strand and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-strength PC steel strand and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, as concrete structures have been increased in size, lengthened in span, or reduced in weight with increasing strength of concrete, the strength of concrete steel stranded wires for reinforcing concrete has been increased. The demands are getting stronger.

[0003] Many researches and developments have been conducted on steel wires having high strength and excellent toughness and ductility, and methods for producing the same.
For example, Japanese Patent Publication No. 5-26851 discloses a method for producing a high-strength high-toughness steel wire excellent in toughness and ductility by water cooling immediately after wire drawing.
No. 29 discloses a method for producing a high-strength steel wire by forming a fine pearlite structure not containing pro-eutectoid cementite, and Japanese Unexamined Patent Publication No. 2-197524 discloses a high-strength steel wire for ultrafine use. A manufacturing method is disclosed. FIG. 1 shows the main relationship between the wire diameter and the tensile strength of the steel wires disclosed therein. The horizontal axis in FIG. 1 shows the diameters of the strands and the strands, and the vertical axis shows elongation.
It is shown as a tensile strength when 5% or more is indicated.

The vertical axis indicates the elongation of 3.5% indicated by "JIS G 3536 PC steel wire and PC steel strand" as a measure of ductility. The horizontal axis is shown on a logarithmic scale, and those having a diameter smaller than 9 mm indicate a steel wire strand, and 9 mm
The above shows a steel strand. As can be seen from FIG. 1, in the case of the stranded wire, the tensile strength is 220 to 230 kgf / mm.
^{About 2} . In the case of a strand, the tensile strength is 230 kgf.
/ mm ² or less is common, and there are also 230 to 245 kgf / mm ² , but when these strands are used to manufacture stranded wires,
A shear force acts at the contact point between the strands, causing a break due to shear. Since the maximum shear load shows only about 60% of the tensile breaking load, it is difficult to increase the strength, and the tensile strength as a stranded wire is 230 kgf / mm ² or less.

[0005]

[Problems to be solved by the invention] As shown in "Prestressed Concrete Vol.26, No.3 May 1984",
In the case of a commonly used steel stranded wire having a diameter of 12.7 mm rather than 7, a tensile strength of about 230 kgf / mm ² is industrially close to the upper limit of strength. This is for the following reasons. That is, in general, the production of PC steel strands
After processing the drawn wire into a stranded wire, 300 to 45 is used for removing residual strain and improving relaxation properties.
Although aging treatment is performed at a temperature of about 0 ° C,
As described above, in the case of a high-strength steel wire having a tensile strength exceeding 230 kgf / mm ² , short-time aging treatment after twisting causes insufficient heating, embrittlement due to strain aging, and elongation does not recover . Therefore, in order to recover growth, it is conceivable to perform aging treatment for a long time, for example, several tens of minutes.
In that case, the tensile strength decreases and the productivity is low,
There are also industrial disadvantages. The aging temperature is set to, for example, 7
A method of shortening the heating time by increasing the temperature to 00 ° C. or higher can be considered, but in this case, there is a problem that workability is not good. In other words, the range of time during which the characteristics are good is very narrow, and the characteristics of the product as a product vary greatly due to slight variations in the heating time. As a result, it becomes difficult to increase the strength by mixing low-strength materials. .

The present invention has been made in order to solve such a conventional problem, and a stable strength is obtained, and a tensile strength of 2 is obtained by aging treatment suitable for industrial use.
35 kgf / mm ² or more, high strength P having the above elongation of 3.5%
An object of the present invention is to provide a C steel strand and a method for producing the strand.

[0007]

According to the first aspect of the present invention, there is provided the following:
0.80 to 1.30%, Si: 0.60 to 2.50%,
Mn: 0.30 to 1.50%, with the balance being a pearlite structure wire composed of Fe and inevitable impurities, the cementite portion of which is composed of a mixed structure of fibrous cementite and granular cementite. It has a volume ratio of 10 to 40%, the particle size of the granular cementite is 40 to 300 °, the tensile strength is 235 kgf / mm ² or more, and the elongation is 3.5% or more.

According to a second aspect of the present invention, C is 0.80 to 1.3.
0%, Si: 0.60 to 2.50%, Mn: 0.30
After patenting, drawing, and twisting a wire rod containing 1.5%, with the balance being Fe and unavoidable impurities, hold at a temperature of 200 to 600 ° C. for 2 to 1500 seconds, and hold at that temperature A plastic elongation of 0.4 to 3.0% is imparted therein, and the aging treatment is performed for an appropriate time depending on the applied strain determined by FIGS. Thereby, the tensile strength is 235 kgf / mm ² or more, and the elongation is 3.
A high strength PC steel wire of 5% or more can be obtained.

According to a third aspect of the present invention, C: 0.80 to 1.3.
0%, Si: 0.60 to 2.50%, Mn: 0.30
After patenting, drawing, and twisting a wire rod containing 1.5%, with the balance being Fe and unavoidable impurities, hold at a temperature of 200 to 600 ° C. for 2 to 1500 seconds, and hold at that temperature A plastic elongation of 0.8 to 3.0% is imparted therein, and the aging treatment is performed for an appropriate time depending on the applied strain determined by FIGS. Thereby, the tensile strength is 235 kgf / mm ² or more, and the elongation is 5.
High-strength PC steel wire of 0% or more can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the above components will be described.

C: C is an effective and economical element for increasing the patenting strength. However, if it is less than 0.8%, the required strength cannot be obtained. Since the reticulated cementite precipitates and the ductility of the steel wire significantly decreases, the range is set to 0.80 to 1.30%.

Si: Si is an element necessary as a deoxidizing material, and forms a solid solution with ferrite and shows remarkable solid solution strengthening.
Further, Si in the ferrite has an effect of suppressing a decrease in strength due to aging treatment after stranded wire processing, and is an indispensable element for producing a high-strength steel stranded wire. Therefore, the lower limit is set to 0.60%. However, if added excessively, the amount of SiO ₂ -based inclusions increases, and the ductility of the drawn steel wire is reduced. Therefore, the upper limit is set to 2.50%. Mn: Mn is also an element required as a deoxidizing material, and is effective in improving the hardenability of steel to increase the uniformity of the structure in the cross section of the steel wire. I do. However, if added in excess, the pearlite transformation end time is lengthened in the patenting process,
Since it is not practical, the upper limit is set to 1.5%.

The balance consists of Fe and inevitable impurities.

As for patenting, lead patenting is applied, and the temperature is usually 540 to 570 ° C.
And there is no need for special conditions.

C: 0.94%, Si: 1.45%, M
n: After subjecting a steel wire having a composition of 0.52% to lead patenting, drawing, and twisting, the stranded wire is subjected to aging treatment, the aging temperature and the holding time, and the plastic elongation imparted during holding. FIG. 2 shows the characteristics when the (deformation rate) was changed. The figure shows the characteristics of the stranded wire with respect to the aging treatment temperature and the wire deformation application time at the treatment temperature. Here, the plastic deformation application time refers to a time during which the wire is plastically deformed by applying tension while being heated to a predetermined processing temperature, and the wire after the plastic deformation is maintained at that temperature. If the aging temperature is lower than 200 ° C., it takes a very long time to reduce the industrial value, and if it exceeds 600 ° C., the characteristics change suddenly and it is not suitable for work.

FIG. 5 shows an apparatus for performing a heat treatment or the like on the stranded wire. The stranded wire fed from the stranded wire supply drum 1 is preheated in a preheating furnace 3, and is driven from a driving pulley 4 to a heating and holding furnace 5. After passing through a pulley 6, it is further cooled by a cooling tank 7 and wound up by a winding drum 8. And heated to the extent the preheating furnace 3 at 200 ° C. or less, fed into a heated holding furnace 5 is wound three times the drive pulley 4, wound several times also in the driving pulley 6, the rotational speed V ₁ of the drive pulley 6 driven pulley by slightly faster than the rotation speed V ₀ which 4, is to be able to arbitrarily set the plastic elongation of the strand in the holding at aging temperature, it extends plasticity is expressed by the following formula at that time (epsilon ).

Ε (%) = (V ₁ −V ₀ ) × 100 / V ₀ As a result, when the deformation rate of the applied plastic elongation exceeds 3.0%, there is a possibility that the wire may break during the work. Therefore, the upper limit is set to 3.0%.

In FIG. 2, when the processing temperature is 400 ° C.,
Aging treatment with 3.0% distortion gives only 2.4
A steel stranded wire with excellent properties of tensile strength of 235 kgf / mm ² or more and elongation of 5% or more can be manufactured by processing for more than seconds (point A). At (point B), similarly, excellent characteristics can be achieved in a short time of 12 seconds. If the strain is less than 0.4% (point C), the processing time becomes longer than 650 seconds (10.8 minutes), and the elongation recovers but the tensile strength is 230 kgf /.
mm ² and cannot be strengthened.

Further, in the aging treatment with the application of strain of less than 0.2%, the material of the present invention does not recover its elongation even after aging treatment for about 24 minutes or more (point D) due to the high Si content. Due to the high degree of hardening, the steel breaks early in the elastic range during the tensile test, has low tensile strength, and shows embrittlement. In a normal aging treatment without imparting any distortion, about 29 minutes (E
Point) By the above treatment, the tensile strength is 210-230kgf /
mm ² , it does not become high in strength, and softens rapidly after about 35 minutes (point F) with continued aging treatment. The plastic deformation application time during this aging treatment is shown in FIG.
Depends on the amount of strain as shown in the figure, the greater the applied strain, the faster the softening, so the longest time to satisfy the characteristics is short,
The lower the distortion, the longer the upper limit time. Therefore, the processing time may be appropriately selected according to the applied distortion.

FIG. 4 shows the relationship between the plastic deformation imparting strain and the plastic deformation imparting time in the aging treatment at the aging treatment temperature of 200 to 600 ° C. In the figure, the lower curve shows the minimum aging time as a function of plastic elongation at 600 ° C aging temperature, and the upper curve shows the maximum aging time at 200 ° C aging temperature. From this figure, it can be seen that when the predetermined mechanical properties, that is, the plastic deformation (elongation) rate given to the wire is 3.0%, the tensile strength is 235 kgf /
The minimum time for obtaining mm ² and elongation of 3.5% is 2 seconds at 600 ° C., and the maximum application time for obtaining similar properties is 200 ° C.
5 minutes. If the application time is 5 minutes or longer, the wire is softened. When the plastic deformation (elongation) rate applied to the wire during the aging treatment is 0.4%, the minimum application time for obtaining the above mechanical properties is 200 seconds, and the maximum application time is 150.
0 seconds. If the plastic elongation imparted to the wire is high, softening occurs at an early stage. It can be seen from the figure that the lower the plastic elongation imparted to the wire during the aging treatment, the longer the imparting time for achieving the predetermined mechanical properties such as tensile strength and ductility.

Therefore, the maximum application time for obtaining good properties becomes shorter as the plastic elongation applied during the aging treatment increases. Similarly, the minimum application time for obtaining good properties decreases as the plastic elongation applied during aging increases. Therefore, the aging time can be more suitably determined as a function of the plastic deformation (plastic elongation) rate according to FIG.

Therefore, the condition that the elongation is 3.5% or more and the tensile strength is 235 kgf / mm ² or more from FIG.
At a temperature of 00 to 600 ° C, the minimum processing time is 2 to 1500 seconds, and the applied deformation rate is 0.4 to 3.0% (the area below the curve of 0.4% and above the curve of 3.0% in the figure) )It can be seen that it is. In order to obtain a higher elongation of 5.0% or more, the deformation rate is 0.8 to 3.0% (the area below the curve of 0.8% and above the curve of 3.0%). Indicates that it is desirable.

Therefore, referring to FIGS. 2 and 4, an appropriate aging time can be determined. In FIG. 2, the minimum application time to achieve a given mechanical property can be known as a function of the plastic deformation rate and the aging temperature. Further, in FIG. 4, the range of the application time including the minimum application time and the maximum application time for obtaining specific mechanical properties (tensile strength: 235 kgf / mm ² , elongation: 3.5%) can be known.

A technically important point for realizing high strength and ductility in this high-strength PC steel strand is that it has a characteristic metal structure. That is, this product has a cementite morphology of a mixed structure of fiber cementite and granular cementite.

FIG. 3 shows the relationship between the volume ratio of the granular cementite after treatment to the total cementite, the particle size thereof, and the properties. The product of cementite was extracted by acetylacetone + methanol + tetramethylammonium chloride mixed electrolytic extraction, and the volume fraction of particulate cementite was determined by a line analysis method on an electron micrograph. According to this figure, if the volume fraction of the particulate cementite is 10% or less, sufficient tensile strength and elongation cannot be obtained, and if it exceeds 40%, the average particle size of the particulate cementite tends to be large, so that sufficient tensile strength can be obtained. Hateful. If the average particle size of the particulate cementite is smaller than 40 °, it is difficult to obtain sufficient elongation, and if it is larger than 300 °, it is difficult to obtain sufficient tensile strength. From the above, in order to satisfy both the characteristics of tensile strength of 235 kgf / mm ² or more and elongation of 3.5% or more, the volume ratio of granular cementite to total cementite is also 10 to 40% in the metal structure.
It can be seen that the particle size must be adjusted to 40 to 300 °.

It is to be noted that the fact that the aging treatment is performed in a state in which a certain deformation is imparted, whereby the elongation of the steel stranded wire can be achieved while maintaining high strength by a special metallographic structure has not been known. It was not done.

[0027]

EXAMPLE The wire diameter was 13 mm and the component was C: 0.94.
%, Si: 1.45%, Mn: 0.52%
After lead patenting at 0 ° C., acid pickling, phosphate coating treatment, passing through a die 11 times using a continuous wire drawing machine (11 times drawing), 4 side wires at a speed of 150 m / min. After drawing the core wire to a diameter of 0.22 mm and a diameter of 4.40 mm, the wire was processed into seven 12.7 mm diameter strands. And the aging temperature is 1-6600 at 200-600 ° C.
Hold for 2 seconds, and at the same temperature, the deformation
Tables 1 to 3 show the results obtained by changing the ratio to 3.0%. Table 1 shows the results of tests in which the aging treatment at 200 ° C. and the deformation time due to plastic elongation, the volume ratio of granular cementite, and the particle size of cementite were variously changed. As a result, the elongation of 3.6% or more at a tensile strength of 235 kgf / mm ² or more was caused by a holding time of 11 to 1500.
Second, the deformation ratio was 0.4 to 3.0%, the volume ratio of granular cementite was 10 to 40%, and the particle size of cementite was 40 to 300 °. Table 2 shows the results of the same test as above at an aging treatment of 400 ° C.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

As a result, the elongation of 4.0% or more at a tensile strength of 235 kgf / mm ² or more was caused by a holding time of 2.5 to 9%.
00 sec, deformation ratio 0.4 to 3.0%, volume ratio of granular cementite 10 to 40%, particle size of cementite 50 to 300
Å. Furthermore, in Table 3, the aging treatment was performed at 600 ° C
Shows the result of the same test as described above. As a result, the elongation of 4.0% or more at a tensile strength of 235 kgf / mm ² or more was caused by a holding time of 2 to 500 seconds and a deformation ratio of 0.4.
3.0 to 3.0, a volume fraction of granular cementite of 15 to 40%, and a particle diameter of cementite of 80 to 300 °.

From the above results, the tensile strength was 235 kgf / mm.
² or more, show a higher elongation of 3.5%, the aging temperature 20
At 0 ° C, 400 ° C, and 600 ° C, the treatment time varies depending on the aging temperature, but is 2 to 1500 seconds (25 minutes), the plastic deformation imparting rate is 0.4 to 3.0%, and the volume ratio of granular cementite to all cementite is 10 to 10%. It can be seen that only those satisfying the conditions of 40% and the particle size of granular cementite are 40 to 300 °.

[0033]

According to the first aspect of the present invention, in a pearlite-structured wire containing predetermined amounts of C, Si and Mn, the volume ratio of the particulate cementite to the whole cementite and the particle size of the particulate cementite are set to predetermined ranges. , Tensile strength of 235 kgf / mm ² or more and elongation of 3.5% or more.

According to a second aspect of the present invention, there is provided a method for producing the above-mentioned wire rod, wherein the wire rod is held at a temperature of 200 to 600 ° C. for 2 to 1500 seconds after a patenting process, a drawing process, and a laying process, and During the holding at that temperature, a plastic elongation of 0.4 to 3.0% is imparted, and the aging treatment is performed for an appropriate time. As a result, a high-strength PC steel strand having a tensile strength of 235 kgf / mm ² or more and an elongation of 3.5% or more can be stably obtained, and this aging treatment is industrially suitable.

Further, in the invention according to claim 3, the plastic deformation during aging treatment is set to 0.8 to 3.0% in the above method. Thereby, a high-strength PC steel strand having a tensile strength of 235 kgf / mm ² or more and an elongation of 5.0% or more can be obtained.

[Brief description of the drawings]

FIG. 1 shows the wire diameter and elongation of high-strength steel wire and steel stranded wire.
FIG. 3 is a diagram showing a relationship with tensile strength when indicating% or more.

FIG. 2 is a characteristic diagram of a stranded line with respect to an aging treatment temperature, a plastic deformation application rate at the treatment temperature, and the application time.

FIG. 3 is a graph showing the relationship between the particle size and the properties with respect to the volume fraction, tensile strength and elongation of granular cementite after heating.

FIG. 4 is a diagram showing the relationship between plastic deformation imparting strain and plastic deformation imparting time.

FIG. 5 is an explanatory view showing one example of an apparatus for carrying out the method of the present invention.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaru Kodama 10-1 Nakahamacho, Amagasaki City, Hyogo Prefecture Shinko Steel Wire Industry Co., Ltd. (72) Inventor Toshiki Suwa 10-1 Nakahamacho Amagasaki City, Hyogo Prefecture Shinko Steel Wire Industry (72) Inventor Nobuhiko Ibaraki 1-3-18 Wakihama-cho, Chuo-ku, Kobe Kobe Steel, Ltd.Kobe Head Office (72) Inventor Masato Kaiso 1-3-18, Wakihama-cho, Chuo-ku, Kobe No. Kobe Steel, Ltd. Kobe Head Office (56) References JP-A-8-170150 (JP, A) JP-A 8-120407 (JP, A) JP-A-61-261430 (JP, A) (58 ) Surveyed fields (Int. Cl. ⁶ , DB name) C22C 38/00-38/60 C21D 8/06, 9/52 103 E04C 5/08

Claims (3)

(57) [Claims] 1. C: 0.80 to 1.30%, Si: 0.
In a pearlite wire rod containing 60 to 2.50% and Mn: 0.30 to 1.50%, the balance being Fe and unavoidable impurities, the cementite portion is composed of a mixed structure of fibrous cementite and granular cementite. The volume ratio of the particulate cementite to the entire cementite is 10 to 40%, and the particle size of the particulate cementite is 4%.
A high-strength PC steel stranded wire having a tensile strength of 0 to 300 °, a tensile strength of 235 kgf / mm ² or more, and an elongation of 3.5% or more. 2. C: 0.80 to 1.30%, Si: 0.
Containing 60 to 2.50%, Mn: 0.30 to 1.5%,
After the patenting, wire drawing, and twisting of the wire consisting of Fe and unavoidable impurities, the temperature is 200 to 6%.
Hold at 00 ° C. for 2 to 1500 seconds, and give a plastic elongation of 0.4 to 3.0% during holding at that temperature, and aging at an appropriate time depending on the applied strain determined by FIGS. A method for producing a high-strength PC steel strand. 3. C: 0.80 to 1.30%, Si: 0.
Containing 60 to 2.50%, Mn: 0.30 to 1.5%,
After the patenting, wire drawing, and twisting of the wire consisting of Fe and unavoidable impurities, the temperature is 200 to 6%.
Hold at 00 ° C. for 2 to 1500 seconds, and give 0.8 to 3.0% plastic elongation during holding at that temperature, and aging for an appropriate time depending on the applied strain determined by FIGS. A method for producing a high-strength PC steel strand.