KR101676109B1 - Wire rod having good drawability and high strength, steel wire having high strength and manufacturing method of wire rod - Google Patents

Abstract

The present invention relates to a wire and a steel wire used for a PC steel wire, an anchor rope, and the like, and a method of manufacturing the wire and wire, and more particularly, to a method for manufacturing a high strength wire rod excellent in freshness by controlling an alloy component and finely controlling a pearlite block after intermediate rolling, And to provide a manufacturing method of a steel wire and a wire rod.
According to an aspect of the present invention, there is provided a steel sheet comprising, by weight%, 0.8 to 1.1% of C, 0.5 to 1.5% of Si, 0.2 to 0.7% of Mn, 0.2 to 1.0% of Cr, 0.01% 0.02% or less of S, and the balance Fe and other unavoidable impurities, wherein the microstructure contains 95% or more of pearlite in an area fraction and the pearlite block has an average size of 11 탆 or less, A method of manufacturing a wire rod is provided.
According to the present invention, it is possible not only to provide a high-strength wire rod which is capable of imparting excellent freshness during wire drawing by controlling an alloy component and performing control rolling before finishing rolling after intermediate filament rolling to miniaturize the pearlite block, It is possible to provide a high strength steel wire having twist characteristics of 16 times or more.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high strength wire rod and a high strength steel wire rod,

TECHNICAL FIELD The present invention relates to a wire rod and a steel wire used for a PC steel wire, an anchor rope and the like, and more particularly, to a high-strength wire rod excellent in freshness and a method for manufacturing a high-strength steel wire and a wire rod.

Steel wire used for PC steel wire, bridge wire for anchor and rope for anchor is made of carbon steel of 0.7 wt% or more, tensile strength is 1,700 ~ 1,900 MPa based on steel wire in general use and high strength product up to 2,400 MPa Has been completed. The reason for the continued strength of the steel wire is that the higher the strength of the steel wire, the lighter the product, the shorter the construction period, and the lower the manufacturing cost.

The strengthening of the steel wire was made according to the empirical formula proposed by Fmbury and Fisher in the 1960s. The pearlite steel is not superior in strength and ductility to other microstructures but has a high work hardening rate because it receives a hydrostatic pressure when drawing or drawing and is rearranged in the drawing direction, And the increase in the strength was observed. Accordingly, the high strength steel wire to date has been progressing in the strength of the steel wire based on the pearlite structure.

As a method for increasing the strength, there is an increase in initial strength or heat treatment strength, and a fine grain formation in terms of structure. That is, as the initial strength is higher, the strength is secured in the final steel wire corresponding to the corresponding value, and as the fine pearlite is formed, the probability of occurrence of the cementite segment during the drawing process is lowered.

Factors influencing these factors include process conditions such as alloying elements such as C, Cr and Si and heat treatment and drawing conditions.

The increase in the strength by the alloying element is also effective, but since the annealing temperature, the holding time, and the change in the drawing conditions must be taken into account when changing the alloy amount, the latter method, especially the increase in the amount of drawing processing, may be more effective.

 The latter method is the future direction, but this is also not easy because it is highly dependent on the material properties and requires improvement of the fresh technology. Therefore, it is necessary to strengthen the steel wire through the complementary method of the electronic method and the latter method.

On the other hand, there are various factors that affect the torsional characteristics of the drawability and the final steel wire. These are largely influenced by the ductility of wire rods, such as colonies and nodules. The most ideal structure is that one colony (in this case, a colony = nodule) is formed in one fine austenite grains. This is because the interface between the colony and the colony is defective and can be present as a crack generation site due to an increase in the amount of drawing process, and crack propagation proceeds accordingly.

And another is a pearlite block. The pearlite nodule is slightly different from the pearlite nodule in terms of definition, and when the orientation difference between the colonies is 15 degrees or more, it is determined as another crystal grain and the crystal grain having an azimuth difference of 15 degrees or less between neighboring colonies is defined as one pearlite block. Since the azimuth is difficult to identify with the naked eye, it can be observed using electron beam scattered diffractoin (EBSD).

One aspect of the present invention is to provide a high-strength wire rod excellent in freshness by controlling an alloy component and performing controlled rolling before finishing rolling after intermediate filament rolling to refine the pearlite block.

Another aspect of the present invention is to provide a method of manufacturing a high strength wire rod excellent in freshness by controlling an alloy component and performing control rolling before the finishing rolling after the intermediate finishing rolling to miniaturize the pearlite block.

Another aspect of the present invention is to provide a high-strength steel wire using the high-strength wire rod excellent in the freshness of the present invention.

According to an aspect of the present invention, there is provided a steel sheet comprising, by weight%, 0.8 to 1.1% of C, 0.5 to 1.5% of Si, 0.2 to 0.7% of Mn, 0.2 to 1.0% of Cr, 0.01% Or less and 0.02% or less of S and the balance Fe and other unavoidable impurities, wherein the microstructure contains 95% or more of pearlite in an area fraction and the pearlite block has an average size of 11 탆 or less .

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: C: 0.8 to 1.1%; Si: 0.5 to 1.5%; Mn: 0.2 to 0.7% 0.02% or less of S and the balance Fe and other unavoidable impurities at a temperature of 1000 to 1200 캜 for 60 minutes or more;

Subjecting the heated billet to rough rolling and intermediate finish rolling at 900 to 1000 ° C, subjecting the billet to controlled rolling at (Acm-20) to (Acm + 40) ° C and finishing rolling at 850 to 900 ° C to produce a wire rod; And

There is provided a method of manufacturing a high-strength wire rod excellent in freshness including a step of winding the wire rod (laying head) and cooling the wire rod.

According to another aspect of the present invention, there is provided a ferritic stainless steel comprising, by weight%, 0.8 to 1.1% of C, 0.5 to 1.5% of Si, 0.2 to 0.7% of Mn, 0.2 to 1.0% of Cr, 0.01% % Or less, S: 0.02% or less, and the balance Fe and other unavoidable impurities, and has a tensile strength of 2300 MPa or more.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages and effects of the present invention will become more fully understood with reference to the following specific embodiments.

According to the present invention, it is possible not only to provide a high-strength wire rod which is capable of imparting excellent freshness during wire drawing by controlling an alloy component and performing control rolling before finishing rolling after intermediate filament rolling to miniaturize the pearlite block, It is possible to provide a high strength steel wire having excellent torsion characteristics.

1 is a graph showing the pearlite block size distribution at the center of the wire rope of Comparative Example 1 which is controlled and rolled according to the present invention.

The inventors of the present invention conducted researches and experiments to derive wire rods excellent in freshness and high strength steel wires. As a result, controlling the size of the pearlite block by controlling alloying elements and performing control rolling before intermediate rolling after hot rolling, It is possible to provide an excellent high-strength wire rod and a high-strength steel wire having excellent torsional characteristics using the wire rod. The present invention has been made based on these results.

Hereinafter, the composition of the wire rod and the steel wire of the present invention will be described in detail. At this time, the content of the component elements means all the weight percentages.

C (carbon): 0.8 to 1.1%

C is the main element for securing strength, and most of the added C exists in the form of cementite. Increasing the carbon content reduces the interlayer spacing of the pearlite and increases the fraction of cementite, which has the effect of increasing the strength. When the carbon content increases by 0.1%, for example, the strength of approximately 80 MPa increases. When the C content exceeds 1.1%, the center segregation is severely formed. When the C content is less than 0.8%, it is difficult to secure the target strength. Therefore, the content of C is preferably limited to 0.8-1.1% May be 0.85 to 1.0%.

Si (silicon): 0.5 to 1.5%

Si is one of the effective elements for increasing the strength of the ferrite base solid solution. The Si prevents these effects as well as changes to spherical cementite during the heat treatment. This is because Si is segregated at the ferrite-cementite interface, thereby suppressing diffusion of carbon into ferrite. If the Si content is less than 0.5%, such an effect is unlikely to be expected. If the Si content is more than 1.5%, a scale which adversely affects the peelability of the ferrite or the like is formed, , And more preferably 0.9 to 1.3%.

 Mn (manganese): 0.2 to 0.7%

Mn is an austenite stabilizing element and added for securing entrapmentability. Mn is combined with S to form an MnS inclusion, which is a soft inclusion, but also induces breakage in the drawing. When the content of Mn is less than 0.2%, it is difficult to obtain good entrapment property, and a hard stone cementite is formed in grain boundaries. When the content of Mn is more than 0.7%, the center segregation is significant, so that the content of Mn is limited to 0.2 to 0.7% , And more preferably from 0.3 to 0.6%.

Cr (chrome): 0.2 to 1.0%

Cr is an element which can effectively improve the strength after C and N. It can increase about 40 MPa when the Cr content is increased by 0.1%. The Cr can inhibit the appearance of anomalous part of the cementite after the heat treatment in the fresh yarn and the grain boundary and the formation of the thick cementite of the cemented cementite. However, since the dislocation density in the ferrite can be increased, it is possible to cause disconnection in the case of a very fine line drawing due to a decrease in ferrite ductility. When Cr is added in an amount of less than 0.2%, it is difficult to obtain freshness and strength to be obtained in the present invention. When the Cr content exceeds 1.0%, the completion time of transformation due to formation of carbide increases, The content is preferably limited to 0.2 to 1.0%, more preferably 0.4 to 0.8%.

N: not more than 0.01%

N is an element which is adhered to a potential formed on a ferrite base during drawing to cause age hardening. If the content of N exceeds 0.01%, the increase in strength due to dynamic aging and static aging is large, and delamination occurs in the longitudinal direction at the initial stage when the torsional stress is applied to the final rigidity, Is preferably limited to 0.01% or less, more preferably 0.007% or less.

Phosphorus (P) and sulfur (S): 0.02% or less

The lower the content of P and S is, the better the impurities are. However, if the limit is too high, the cost of removing impurities in the steelmaking process increases. Further, when the content of P and S increases, ductility of the material decreases. Therefore, it is important to control the upper limit of the content of P and S, and in the present invention, the upper limit of P and S is preferably limited to 0.02%, more preferably 0.01% .

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

In addition, the preferred microstructure of the wire according to the present invention preferably contains 95% or more of pearlite and the rest of the structure in terms of area fraction%. The remainder of the other structure may include at least one of a quartz cementite, a pro-eutectoid ferrite, and a ferrite resulting from decarburization at the surface.

If the area fraction of the pearlite is less than 95%, breakage may occur during drawing.

It is more preferable that the cornerstone cementite area fraction is limited to 1% or less. When the amount of the elemental cementite exceeds 1% by area, there is a possibility that breakage occurs during drawing.

The wire may have a tensile strength of 1380 MPa or more, and may have a section reduction ratio of 38% or more after being maintained at room temperature for up to 7 days.

Hereinafter, a method of manufacturing a high-strength wire having excellent freshness, which is another aspect of the present invention, will be described in detail.

Another aspect of the present invention is to provide a method for producing a high-strength wire having excellent freshness, which comprises, by weight, 0.8 to 1.1% of C, 0.5 to 1.5% of Si, 0.2 to 0.7% of Mn, 0.2 to 1.0% : Not more than 0.01%, P: not more than 0.02%, S: not more than 0.02%, and the balance Fe and other unavoidable impurities at a temperature of 1000 to 1200 캜 for 60 minutes or more;

Subjecting the heated billet to rough rolling and intermediate finish rolling at 900 to 1000 ° C, subjecting the billet to controlled rolling at (Acm-20) to (Acm + 40) ° C and finishing rolling at 850 to 900 ° C to produce a wire rod; And a step of winding the wire rod (Laying head) and cooling the wire rod.

Heating step

And the billet satisfying the above-mentioned component system is heated to 1000 to 1200 占 폚. By heating the steel strip in this temperature range, it is possible to maintain the austenite single phase, prevent the coarsening of the austenite grains, and effectively dissolve the remaining segregation, carbides and inclusions. In the present invention, it is preferable to heat the billet at a temperature of 1000 占 폚 or more in order to realize the above effect. On the other hand, when the heating temperature is too high, the austenite grains become very coarse and it is difficult to obtain a high strength and high-strength wire, and the upper limit thereof is preferably controlled to 1200 ° C, to be. Here, the term "steel" refers to all semifinished products such as blooms and billets, which can be produced from wire rods.

Rolling step

The heated steel strip is rolled to produce a wire rod. By positioning the direction of the ferrite parallel to the drawing direction through the rolling, it is possible to draw the wire without breakage without performing a separate heat treatment in the subsequent drawing process.

More preferably, the billet is subjected to rough rolling and intermediate finish rolling at 900 to 1000 占 폚, control rolling at (Acm-20) to (Acm + 40) 占 폚, and finish rolling at 850 to 900 占 폚 to produce a wire rod .

The temperature of the rough rolling and the intermediate filament rolling is preferably limited to 900 to 1000 ° C because if the temperature of the rough rolling and the intermediate filament rolling is less than 900 ° C, the roll wear becomes excessive, And when it exceeds 1000 ° C, there is a problem that the rolling speed must be increased

The control rolling temperature is preferably limited to (Acm-20) to (Acm + 40) ° C because when the controlled rolling temperature is lower than (Acm -20) ° C, the cornerstone cementite is formed in the austenite grain boundary (Acm + 40) < 0 > C, the austenite grain growth is increased.

A more preferable control rolling temperature is 860 to 900 占 폚. Controlled rolling at a temperature of less than 860C results in a smaller crystal grain size, but a quartzite cementite is formed in the austenite grain boundary, and there is a high possibility that disconnection occurs at the final drawing. A more preferred controlled rolling temperature may be 870-890 ° C.

It is preferable that the finishing rolling temperature is limited to 850 to 900 캜, because when the finishing rolling temperature is lower than 850 캜, a corner stone cementite is formed during rolling on grain boundaries. When the finishing rolling temperature exceeds 900 캜 This is because there is a problem that the austenite grain size increases

Laying Head Step

The hot-rolled wire as described above is wound.

It is preferable that the coiling temperature is limited to 840 to 900 占 폚, because when the coiling temperature is lower than 840 占 폚, the quartzite cementite is likely to be formed at the time of continuous transformation, and when it exceeds 900 占 폚, This is because there is a problem.

Cooling step

Followed by a step of cooling after the winding step. At this time, cooling is preferably performed at a rate of 10 ° C / second or higher. If it is less than 10 ° C / second, the formation of the cornerstone cementite becomes active and it may be difficult to obtain the microstructure of the present invention.

The method for manufacturing the steel wire of the present invention is not necessarily limited to this, but it is possible to produce a steel wire by drawing wire material satisfying the composition and the microstructure described above. The steel wire thus obtained can have a tensile strength of 2300 MPa or more, and can have an excellent twisting property of 16 times or more.

At this time, the step of freshness can be carried out according to a usual method, and therefore, the present invention is not particularly limited.

Also, in the case of manufacturing the steel wire by drawing the wire material produced by the above method, the ductility at the time of drawing is not drastically reduced, and the steel wire having the desired diameter can be produced without performing the LP heat treatment. It is possible to solve the environmental problem that arises.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the present invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example 1)

Ingots having a composition of C: 0.98%, Si: 0.6%, Mn: 0.5%, Cr: 0.6%, N: 0.0050%, P: 0.015% and S: 0.012% And hot-rolled into 13 mm wire. From the heating to the intermediate finishing rolling, the rolling temperature of the inventive example is almost the same as that of the comparative example. However, in the case of the invention, the control rolling is carried out, while in the case of the comparative example, the control rolling is not performed.

The tensile strength and RA (section reduction ratio) were measured for the wire rod prepared as described above, and the results are shown in Table 1 below.

At this time, RA is a value obtained by stabilizing at room temperature aging after being maintained at room temperature for 7 days.

Example
NO. Heating furnace temperature (캜) Rough rolling
Temperature
(° C) middle
Finish rolling
Temperature (℃) Control rolling temperature (℃) Finishing rolling temperature (캜) L / H
Temperature
(° C) Cooling
speed
(° C / sec) Seal
burglar
(MPa) RA

(%) Inventory 1 1040 930 960 860 870 860 10 1390 42 Inventory 2 1050 940 955 900 900 900 10 1380 38 Comparative Example 1 1050 940 960 skip 960 900 10 1370 26 Comparative Example 2 1040 950 965 skip 800 860 10 1380 22

As shown in Table 1, in the cases of Examples 1 and 2 and Comparative Examples 1 and 2, the tensile strengths were almost similar, whereas in case of Examples 1 and 2, 2), which is about twice as high as that of the conventional method.

It can be inferred that even if the temperature is maintained at the laying head (L / H) similarly, the control rolling process after the intermediate rolling does not affect the pearlite interlayer spacing to determine the strength, but the factors determining the ductility have changed Do.

On the other hand, the pearlite block size at the center of the section was measured in the wire rods of Inventive Example 1 and Comparative Example 1, and the results are shown in Fig.

In FIG. 1, a pearlite block is defined as a crystal grain having an azimuth difference of 15 degrees or less between neighboring colonies, and is measured using EBSD.

As shown in FIG. 1, the pearlite block sizes of Inventive Example 1 and Comparative Example 1 are significantly different. That is, the average size of the pearlite block existing in the central portion of the inventive example 1 was 11 μm, whereas the comparative example 1 was 17 μm. The difference does not greatly affect the strength of the wire rod, And torsional characteristics.

 (Example 2)

The wire rod of Example 1 was dried in a fresh manner as shown in Table 2 under the usual conditions after scale peeling using saline pickling, and a Ca-based lubricant was used to reduce frictional heat. The total amount of reduction is 83.3%, and the amount of reduction per pass is not the same because it is designed with a low coefficient of friction based on the delta parameter.

The change in the strength (MPa) increase, the work hardening rate and the torsion number according to exp (e / 4) were measured for the steel wire manufactured as described above, and the results are shown in Table 2 below. Here, exp (e / 4) is a factor derived from the equation derived from the EF empirical formula, which is based on Hall-Petch and is based on the consideration of the wire diameter and the throughput (e). When exp (e / 4) is plotted on the X-axis and tensile strength is plotted on the y-axis, the slope indicates the work hardening rate of the steel wire in ky / √2λPo.

Exp
(e / 4) Inventory 1 Inventory 2 Comparative Example 1 Comparative Example 2 1.00 1390 1380 1370 1380 1.06 1460 1405 1410 1420 1.12 1560 1510 1532 1490 1.18 1572 1550 1580 1540 1.25 1704 1620 1724 1680 1.32 1725 1670 1695 1740 1.4 1836 1788 1786 1792 1.48 1996 1945 1966 1870 1.56 2066 1982 2026 1998 1.65 2012 2000 2142 2110 1.7 2250 2230 2180 2170 1.75 2310 2300 2240 2230 Work hardening rate 1246 1220 1142 1130 Torsion number @ 1.7 17.8 16.2 16.4 10.4 @ 1.75 14.8 13.5 2.8 1.9

As can be seen from the above Table 2, when the Exp (e / 4) was fresh to 1.7, the inventive (1 and 2) and comparative examples (1 and 2) can secure a steel wire having a high strength value of 2,200 MPa or more And the inventive examples 1 and 2 are 50 to 70 MPa higher than the comparative examples 1 and 2, but the difference is not large. Torsional evaluation was made in the state of applying a load of TS * sectional area (mm ² ) * 0.008 on the basis of 100D [D: steel wire diameter (mm)] to the steel wire at this time. In the case of the invention example, 16 times or more, to be. However, the comparative example 2 in which the laying head (L / H) temperature is 860 DEG C has a small value.

On the other hand, it can be seen that a large difference is observed in the strength and twist number when the drawing amount is further applied by exp (e / 4): 0.05. Thus, the difference in strength in the wire rods was not large, but it was judged that the difference in the strength in the steel rope was affected to some extent by the pearlite interlayer spacing because the pearlite block size decreased. Particularly, there is a large difference in the number of twist, which is 13 to 14 times in the case of the inventive examples (1 and 2), and 2 to 3 times in the case of the comparative examples (1 and 2). This means that, in the case of inventions (1 and 2), additional drawing is possible.

Claims (9)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet comprises, by weight, 0.8 to 1.1% of C, 0.5 to 1.5% of Si, 0.2 to 0.7% of Mn, 0.2 to 0.8% of Cr, 0.01% A balance Fe and other unavoidable impurities, wherein the microstructure contains 95% or more of pearlite in an area fraction, and the block size of the pearlite is 11 탆 or less.
The high-strength wire according to claim 1, wherein the microstructure of the wire has an area fraction of 1% or less of a cornerstone cementite.
The high strength wire rod according to claim 1, wherein the wire rod has a tensile strength of 1,380 MPa or more and a reduction ratio of 38% or more after being maintained at room temperature for 7 days.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet comprises, by weight, 0.8 to 1.1% of C, 0.5 to 1.5% of Si, 0.2 to 0.7% of Mn, 0.2 to 1.0% of Cr, 0.01% The balance Fe and other unavoidable impurities at a temperature of 1000 to 1200 占 폚 for 60 minutes or more;
Subjecting the heated billet to rough rolling and intermediate finish rolling at 900 to 1000 ° C, subjecting the billet to controlled rolling at (Acm-20) to (Acm + 40) ° C and finishing rolling at 850 to 900 ° C to produce a wire rod; And
And a step of cooling the wire rod (Laying head) and cooling the wire rod.
The method of manufacturing a high strength wire rod according to claim 4, wherein the control rolling temperature of the wire rod is 860 to 900 占 폚.
The method of manufacturing a high-strength wire according to claim 4, wherein the wire has a winding temperature of 840 to 900 캜.
The method of manufacturing a high-strength wire rod according to claim 4, wherein the wire has a cooling rate of 10 ° C / sec or more.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet comprises, by weight, 0.8 to 1.1% of C, 0.5 to 1.5% of Si, 0.2 to 0.7% of Mn, 0.2 to 0.8% of Cr, 0.01% The balance being Fe and other unavoidable impurities and having a tensile strength of 2300 MPa or more and a load of TS * sectional area (mm ² ) * 0.008 on the basis of 100 D [D: steel wire diameter (mm) High strength steel wire with twist number of 16 or more at the time of evaluation. delete

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