KR20110066637A - Method for manufacturing high strength steel wire for prestressed concrete stranded wire and high strength steel wire for prestressed concrete stranded wire produced by the same - Google Patents

Abstract

PURPOSE: A method for manufacturing a high strength prestressing wire and a high strength prestressing wire manufactured thereby are provided to reduce construction costs by slimming and lightening a structure. CONSTITUTION: A method for manufacturing a high strength prestressing wire is as follows. A wire member is re-heated with 950~1150°C. The reheated wire member is cooled to the transformation starting temperature of perlite. The cooled wire member is maintained in the transformation starting temperature of perlite for 1 to 3 minutes. The wire member comprises Cr 0.1~0.5 weight%, C 0.80~0.95 weight%, Si 0.8~1.6 weight%, Mn 0.3~0.8 weight%, P less than 0.015 weight%, and S less than 0.015 weight%.

Description

Method for manufacturing high strength steel wire for prestressed concrete stranded wire and high strength steel wire for prestressed concrete stranded wire produced by the same}

The present invention relates to a method for manufacturing a high strength PC steel wire and a PC steel wire produced thereby, and more particularly, by applying a small amount of fresh processing amount at the beginning of the wire drawing process to improve the ductility of the steel wire and to apply more fresh amount than the conventional one. The present invention relates to a method for producing a high strength PC steel wire and a PC steel wire produced thereby, which enables the strength to be improved and prevents the decrease in strength during the bluing heat treatment.

PC steel wire is a steel used as tension material in prestressed concrete. It is manufactured by stranding PC steel wire and should have excellent adhesion and tensile strength.

Briefly, the method of processing the PC steel wire is as follows.

The molten steel having a carbon concentration of about vacancy is rolled into bloom or billet, reheated at 1000 to 1200 ° C. for about 2 hours, and then rolled to a wire having a desired diameter. At this time, the finish rolling temperature is 950 ~ 1200 ℃, and then cooled to 800 ~ 900 ℃ and then wound in the form of a ring (ring) to cool on the Stelmor (stelmor) cooling table. After pickling the surface of the produced 10 ~ 14mm wire rod and then remove the residual stress through the high-frequency heat treatment (blue heat treatment) during the drawing process to produce a PC steel wire having excellent relaxation characteristics (relaxation).

The method of acquiring the strength of the PC steel wire includes a method of increasing the strength of the wire rod state, a method of increasing the work hardening rate or the amount of drawing, and a method of suppressing the decrease in strength during the bluing heat treatment.

Increasing the carbon content in PC steel wire to improve the strength and work hardening rate of wire rod, it is impossible to secure uniform product properties due to high strength and processing deviation by site. As a result, the problem of failing to secure the strength of the final product.

The reason that the uniform product properties cannot be secured is that as the strength of the wire increases, the load applied during the drawing process increases, so the probability of causing cracks in uneven microstructure parts in the material or external defects that may be generated due to drawing processing problems. Because it increases. Therefore, if the microstructure of the material is not more uniform, it is difficult to secure uniform quality after drawing the high strength wire.

In addition, pursuing the increase in strength by increasing the work hardening rate is effective in the case where the processing amount such as tire cord is very large, but it is not effective in the case where the processing amount is relatively small such as PC steel wire. In addition, increasing the amount of fresh processing seriously lowers the ductility of the material, so strength can be easily achieved, but it causes processing problems.

In addition, as the tensile strength required for the final product increases, high strength is required even in the state of wire rods before drawing. In other words, the strength imbalance for each part of the material due to work hardening during the fresh processing is intensified and the fresh processing is often not properly performed, which causes a problem of poor quality of the final product.

The present invention is to solve the above-mentioned problems, by applying a small amount of fresh processing at the beginning of the drawing process to improve the ductility of the steel wire to enable the application of a large amount of fresh processing than conventional to improve the strength, bluing heat treatment By doing so to prevent the decrease in strength is to improve the strength of the wire rod.

In the present invention, in drawing the wire rod, the wire is produced by drawing a small amount of drawing in the range of 3 to 10% during the initial drawing pass, and the drawing material is heat-blured at 200 to 450 ° C. .

In addition, the wire rod before the fresh processing is reheated to 950 ~ 1150 ℃, the reheated wire rod is cooled to the pearlite transformation start temperature at a cooling rate of 10 ℃ / s or more, and then the cooled wire rod 1 ~ at the pearlite transformation start temperature It is preferable to keep constant temperature for 3 minutes.

At this time, it is advantageous to include the constant temperature holding by putting in a bath at 560 ~ 640 ℃ constant transformation (LP heat treatment).

In order to obtain the advantageous effect of the present invention, the wire rod preferably contains 0.1 to 0.5% by weight of Cr.

In addition to the above components, it is advantageous to further include C: 0.80 to 0.95% by weight, Si: 0.8 to 1.6% by weight, Mn: 0.3 to 0.8% by weight, P: 0.015% by weight or less, and S: 0.015% by weight or less. Do.

PC steel wire with a high strength of 2300MPa or more can be manufactured, through which it can be applied to large concrete structures in the future, it is possible to reduce the construction cost by reducing the weight of the structure, slimming and construction period.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present inventors have conducted in-depth studies to solve the above-described problems of the prior art, and then, after a small amount of drawing is applied to the wire rod during the initial drawing pass, additional drawing is performed, followed by bluing heat treatment, and then the strength of the steel wire. And improved the present invention.

In addition, the present inventors have found that it is effective to range the fresh processing in the range of 3 to 10% during the initial fresh pass. If less than 3% of fresh processing does not show the effect of increasing the strength to obtain in the present invention, if it exceeds 10% the pearlite lamellar microstructure near the wire surface is not easily rearranged in the fresh direction, the final fresh This is because the lamellar microstructures tend to be segmented. Accordingly, after the initial drawing pass is performed and additional drawing is performed, the amount of drawing processing at the first drawing pass is preferably in the range of 3 to 10% in manufacturing the drawing material.

After the initial drawing pass, additional drawing is made, which may vary the drawing rate according to the wire diameter and strength required for each final PC steel wire.

In addition, it is preferable to perform the bluing heat treatment of the drawn material after the drawing process, in order to improve the relaxation characteristics of the final product by removing residual stress caused by too much drawing amount during the final drawing process. . More preferably it is effective to bluing the wire in the temperature range of 200 ~ 450 ℃, which can not sufficiently resolve the residual stress at a temperature below 200 ℃, at a temperature exceeding 450 ℃ This is because the strength may be degraded by causing collapse of the freshly processed pearlite microstructure. Therefore, the bluing heat treatment temperature is preferably limited to 200 ~ 450 ℃. In addition, the bluing heat treatment is preferably a high frequency heat treatment for 10 ~ 300 seconds.

In addition, it is preferable to reheat the wire rod rolled wire, cool the reheated wire rod to the pearlite transformation start temperature, and then maintain the temperature at the cooled wire rod at the pearlite transformation start temperature. At this time, the wire rolling is manufactured through a process of hot rolling, cooling and winding, and these processes are to be in accordance with the conventional wire rolling process, so a special description will be omitted.

The above heat treatment process is to improve the strength by minimizing the layer spacing of the pearlite of the wire rod, and at the same time to increase the ductility. The reheating temperature is preferably 950 ~ 1150 ℃, less than 950 ℃ effective austenitization does not occur, it is difficult to secure a homogeneous austenite, and if it exceeds 1150 ℃ austenite grains become too coarse to adversely affect the strength and ductility Because.

In addition, the reheated wire is preferably cooled to the pearlite transformation start temperature at a cooling rate of 10 ° C / s or more. When cooling at a cooling rate of less than 10 ° C / s, it is difficult to refine the sufficient pearlite structure, because the lamellar structure is coarsened and the strength is lowered.

In addition, it is preferable to keep the cooled wire at constant temperature for 1 to 3 minutes at the pearlite transformation start temperature. Through this, the pearlite layer spacing can be miniaturized and the desired strength can be obtained, and the variation of the wire rod can be suppressed as much as possible. Because. If the constant temperature holding time is less than 1 minute, the above effects are insignificant. If the constant temperature is longer than 3 minutes, the microstructure of the wire rod tends to coarsen.

At this time, in the constant temperature holding step, the wire rod is introduced into a lead bath at 560 to 640 ° C. for constant temperature transformation (LP heat treatment). If the temperature is lower than 560 ° C., bainite is partially formed, resulting in poor workability. This is because the lamellar spacing increases if the strength is exceeded.

The steel wire to be provided by the present invention may be manufactured using a billet or bloom having a conventional component system through the above-described manufacturing process, but in order to manufacture more effectively, the wire rod may include the following components.

As described above, the wire is more preferably containing Cr: 0.1 ~ 0.5% by weight, Cr is finer perlite layer spacing, and the miniaturization effect is maximized by the constant temperature heat treatment to reduce the content of C This is because the strength can be increased efficiently. In addition, as in Si, there is an effect of minimizing the strength reduction by suppressing the segment of cementite during bluing heat treatment, and it is preferable to add 0.1% or more in order to fully exhibit the effect. However, when the content of Cr exceeds 0.5%, there is a concern that the hardenability during addition is greatly increased to produce martensite during the continuous cooling process.

In addition, the wire rod is advantageously further included in weight%, C: 0.80-0.95%, Si: 0.8-1.6%, Mn: 0.3-0.8%, P: 0.015% or less, and S: 0.015% or less.

C: 0.80 to 0.95% by weight

C is mostly in the form of cementite in the roughened steel wire. Cementite forms a layered pearlite together with ferrite, which is higher in strength than ferrite, so as the fraction of cementite increases, the strength of the wire increases. Increasing the content of C increases the fraction of cementite and makes the layer spacing fine, which is very effective in increasing the strength of the wire rod.

Therefore, in order to secure tensile strength of 2300 MPa or more, the content of C is preferably included at 0.80% or more. However, when the cooling rate is not sufficient, the problem occurs that the cornerstone cementite is generated at the austenite grain boundary, thereby lowering the freshness. Therefore, the C content is preferably limited to 0.95% or less.

Si: 0.8-1.6 wt%

Si may be dissolved in ferrite, which is a base structure, to exhibit an effect of solid solution strengthening. However, Si may also inhibit strength degradation by preventing cementite structure collapse during bluing heat treatment. When bluing heat treatment, the steel wire temperature is increased to 300 ° C or higher, and the cementite is spheroidized and coarsened to decrease the strength.Si addition of Si forms a Si-concentrated layer at the ferrite / cementite interface of the pearlite microstructure. The collapse of cementite can be suppressed.

When the content of Si is less than 0.8%, the above effect is insignificant. In addition, when the content of Si exceeds 1.6%, decarburization is easily generated on the surface of the material during reheating for incubation and fresh workability is lowered, making it difficult to obtain the target strength of the present invention.

Mn: 0.3-0.8 wt%

Mn is a very useful element that forms a solid solution in the matrix structure and solidifies it. In addition, since the perlite transformation is delayed, it is preferable to add 0.3% or more so that fine perlite is easily produced even at a slightly slow cooling rate. However, when the content exceeds 0.8%, Mn segregation occurs rather than a solid solution strengthening effect, and the grain boundary of the tissue on the surface of the material is easily oxidized during heat treatment, which adversely affects product characteristics.

S: 0.015% by weight or less

S is an element that is inevitably contained during manufacture, and is preferably limited to 0.015% or less because it precipitates at grain boundaries in the form of low melting point precipitates, causing hot embrittlement.

P: 0.015% by weight or less

P is an element that is inevitably contained during manufacture, and segregates between columnar tissues to cause hot embrittlement, and also causes cracking during cold drawing, so it is preferably limited to 0.015% or less.

Steel wire manufactured by the PC steel wire manufacturing method of the present invention described above is characterized in that it has a high strength of 2300MPa or more.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following examples.

[Example]

A steel material satisfying the component system and composition range as shown in Table 1 below was cast into a 50 kg ingot, welded to a billet, heated at 1150 ° C. for 2 hours, and extracted and hot rolled into a wire having a diameter of 12 mm. At this time, the finish hot rolling temperature was 1000 ° C., after which water was cooled to 850 ° C., and then wound in a ring to cool at a cooling rate of 10 ° C./s on a roller conveyor. Subsequently, the wire was reheated to 1000 ° C., cooled to 580 ° C. at a cooling rate of 20 ° C./s, and then incubated for 1 minute and 30 seconds. The tensile strength (TS) and Section reduction rate (RA) was measured and shown in Table 2 below.

division C (% by weight) Si (% by weight) Mn (% by weight) Cr (% by weight) P (wt%) S (% by weight) Inventive Steel 1 0.90 1.30 0.50 0.30 0.011 0.012 Inventive Steel 2 0.89 1.59 0.48 0.31 0.010 0.011 Comparative Steel 1 0.90 0.62 0.51 0.30 0.009 0.011 Comparative Steel 2 0.91 1.30 0.51 - 0.010 0.009

division Wire rod before incubation Wire rod after incubation TS (MPa) RA (%) TS (MPa) RA (%) Inventive Steel 1 1312 25 1465 30 Inventive Steel 2 1356 22 1481 27 Comparative Steel 1 1231 29 1303 33 Comparative Steel 2 1228 25 1295 31

As shown in Table 1 and 2, the invention steel 1 subjected to the incubation was increased by 153MPa tensile strength, and the cross-sectional reduction rate was also increased by 5% compared to the case without the incubation. Inventive steel 2 also showed that the tensile strength increased by 125 MPa and the cross-sectional reduction rate increased by 5%, depending on whether or not constant temperature heat treatment was performed.

In addition, Comparative steel 1, the content of Si is 0.62% by weight, the content of Si intended to be lower than the content of Si intended for the present invention can not be prevented from decreasing the strength, the tensile strength of the wire was measured low. In addition, the comparative steel 2 did not contain Cr, so the strength improvement effect of the wire rod was insignificant even after incubation, and it was confirmed that the tensile strength of the wire rod was lower than that of the inventive steels 1 and 2.

After the incubation, the initial drawing pass was performed at 5% and 20%, so that the wire rod having a diameter of 12 mm became 11.7 mm and 10.7 mm after the first drawing pass, respectively, and the wire diameter of the final product was added to 4.25 mm. Fresh process was applied. Then, the bluing heat treatment was performed at 250 ° C., and the tensile strength and cross-sectional reduction rate of the inventive example and the comparative example which passed through the above process were measured, and are shown in Table 3 below.

division First fresh pass
Fresh Processing Volume (%) TS (MPa) RA (%) Inventive Steel 1
Inventory 1 5 2307 45 Comparative Example 1 20 2254 43 Inventive Steel 2 Inventory 2 5 2336 42 Comparative Example 2 20 2285 40 Comparative Steel 1 Comparative Example 3 5 2109 49 Comparative Example 4 20 2072 48 Comparative Steel 2 Comparative Example 5 5 2054 52 Comparative Example 6 20 2013 50

As shown in Table 3, in the initial drawing pass, when the processing amount is 5%, the strength of Inventive Examples 1 and 2 is increased by 51 to 53 MPa, as compared with the 20%. It was also found that the reduction rate of the cross section was also improved.

In addition, Inventive Examples 1 and 2 satisfy the component system and composition range controlled by the present invention, and it can be confirmed that the tensile strength and cross-sectional reduction rate of the wire material correspond to the intended purpose of the present invention by applying a small amount of wire processing at the initial stage of the wire drawing. there was.

In addition to the above Inventive Examples 1 and 2, Comparative Examples 3 and 5 also had an effect of increasing the strength compared to the case where the fresh processing was carried out at 20% by setting the fresh processing amount at 5% during the initial drawing pass (Comparative Examples 4 and 6). appear. However, although the Comparative Examples 3 and 5 went through the same manufacturing process as Inventive Examples 1 and 2, it did not satisfy the component system and composition range proposed by the present invention, the tensile strength was measured to be less than 2300MPa.

Claims (6)

In the case of drawing the wire, the process of drawing the wire in the range of 3 to 10% during the initial drawing pass (pass) to prepare a fresh material and the step of bluing heat treatment (bluing) at 200 ~ 450 ℃ Manufacturing method of high strength PC steel wire. According to claim 1, Reheating the wire before the wire processing at 950 ~ 1150 ℃, after cooling the reheated wire to a pearlite transformation start temperature at a cooling rate of 10 ° C / s or more, the cooled wire is initiated perlite transformation Method for producing a high-strength PC steel wire comprising maintaining constant temperature for 1 to 3 minutes. The method of manufacturing a high strength PC steel wire according to claim 2, wherein the constant temperature holding is put into a lead bath at 560 to 640 ° C. for constant temperature transformation (LP heat treatment). The method of manufacturing a high strength PC steel wire according to claim 1 or 2, wherein the wire comprises 0.1 wt% to 0.5 wt% of Cr. The method of claim 4, wherein the wire further comprises a weight%, C: 0.80-0.95%, Si: 0.8-1.6%, Mn: 0.3-0.8%, P: 0.015% or less, S: 0.015% or less Method for producing high strength PC steel wire, characterized in that. A high-strength PC steel wire manufactured by the manufacturing method of any one of claims 1 to 5, wherein the high-strength PC steel wire, characterized in that the tensile strength of 2300MPa or more.