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(11) | EP 4 800 140 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 153(4) EPC |
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| (54) | WIRE ROD, STEEL WIRE AND METHOD FOR MANUFACTURING SAME |
(57) A wire rod according to an example of the present disclosure comprises, in percent
by weight (wt%)in percent by weight (wt%): C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn:
0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.020% to 0.105%, N: 0.0021% to 0.0205%, Al/N:
2.00 to 11.00, the balance of Fe and other unavoidable impurities.
A manufacturing method of a wire rod according to another example of the present disclosure comprises: preparing a billet comprising, in percent by weight (wt%): C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al/N: 2.00 to 11.00, and the balance of Fe and other unavoidable impurities; reheating and hot-rolling the billet; coiling at Acm-80°C to 760°C; cooling from the coiling temperature to 650°C to 620°C, which is a pearlite transformation entry temperature, at 10°C/s to 20°C/s; and maintaining for 200 seconds or more by setting a conveyor speed to 0.30 m/s or less from the cooling temperature to a temperature range of 600°C to 560°C.
A manufacturing method of a wire rod according to another example of the present disclosure comprises: preparing a billet comprising, in percent by weight (wt%): C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al/N: 2.00 to 11.00, and the balance of Fe and other unavoidable impurities; reheating and hot-rolling the billet; coiling at Acm-80°C to 760°C; cooling from the coiling temperature to 650°C to 620°C, which is a pearlite transformation entry temperature, at 10°C/s to 20°C/s; and maintaining for 200 seconds or more by setting a conveyor speed to 0.30 m/s or less from the cooling temperature to a temperature range of 600°C to 560°C.
[Technical Field]
[0001] The present disclosure relates to a wire rod, a steel wire, and a manufacturing method thereof, which are applicable for use in bridge cables such as suspension bridges.
[Background Art]
[0002] Cables connecting a deck and a main tower directly or indirectly are used in bridges such as suspension bridges. Despite variations based on cable type, the cable is placed in an environment directly or indirectly contacting water, thereby requiring galvanizing after final wire-drawing, and Zn, Zn-Al, or the like are used depending on the application. The manufacturing process and purpose of a steel wire for cables are as follows.
[0003] The strength of steel wires for cables has continuously increased from 1660 MPa in the past to 1960 MPa at present. This is due to the ability to obtain effects of reduced material usage and shortened construction periods through an increase in cable strength. Accordingly, the high-strength development of steel wires for cables is expected to continue through joint development among steel mills, wire drawing companies, and construction companies.
[0004] Steel wire strengthening proceeds based on an experimental formula proposed by Embury-Fisher in the 1960s. The achievability of high strength involves increasing strength through an increase in alloying elements such as C and Cr, pearlite refinement via lead patenting heat treatment, an increase in total reduction during wire drawing, and prevention of strength degradation during plating. Carbon is an inexpensive and the most effective element for improving strength. However, a limitation exists in compositions of eutectoid steel or more, due to a high possibility of cementite, which degrades initial formability during cooling, forming at grain boundaries.
[0005] Additionally, Al is used in conjunction with Si in cable wire rods for steel deoxidation. Furthermore, Al is known as an element suppressing proeutectoid cementite formation in hypereutectoid steel. However, an increase in Al content is limited due to the formation of complex inclusions, such as Al2O3 and Al-Si-O, which leads to nozzle clogging issues.
[0006] Meanwhile, Al combines with N in steel to form AlN. The AlN's presence at austenitic grain boundaries retards grain growth and increases a drawing limit during final wire-drawing, making Al an important element. Nevertheless, Al/N control being necessary, technology acquisition for this is required.
[Disclosure]
[Technical Problem]
[0007] The present disclosure aims to provide a wire rod with improved nodule refinement and wire-drawability, and a steel wire having excellent high strength and torsion properties without LP (Lead Patenting) heat treatment, through control of Al/N to 2.00 to 11.00 in high carbon steel with 0.94% or more and through multi-stage cooling control during Stelmor cooling.
[Technical Solution]
[0008] A wire rod according to an example of the present disclosure comprises, in percent by weight (wt%): C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.020% to 0.105%, N: 0.0021% to 0.0205%, Al/N: 2.00 to 11.00, the balance of Fe and other unavoidable impurities.
[0009] Additionally, an example wire rod of the present disclosure has a density of AlN precipitates having a size of 50 nm or less of 2.4x 1011/mm2 or less.
[0010] The wire rod according to an example of the present disclosure may have an average nodule size is 16 µm or less.
[0011] Furthermore, a wire rod according to an example of the present disclosure may have an average pearlite lamellar spacing of 80 nm to 120 nm at 1/4D (D: diameter) of a cross-section of the wire rod.
[0012] Also, a wire rod according to an example embodiment of the present disclosure has an average tensile strength of 1600 MPa or more and a reduction of area of 28% or more.
[0013] A manufacturing method of a wire rod, according to another example of the present disclosure, comprising: preparing a billet comprising, in percent by weight (wt%): C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al/N: 2.00 to 11.00, and the balance of Fe and other unavoidable impurities; reheating and hot-rolling the billet; coiling at Acm-80°C to 760°C; cooling from the coiling temperature to 650°C to 620°C, which is a pearlite transformation entry temperature, at 10°C/s to 20°C/s; and maintaining for 200 seconds or more by setting a conveyor speed to 0.30 m/s or less from the cooling temperature to a temperature range of 600°C to 560°C.
[0014] The manufacturing method of a wire rod according to an example of the present disclosure further comprises: cooling to an R/T (reforming tube) charging temperature of 470°C to 440°C at 5°C/s to 10°C/s after the maintaining.
[0015] Furthermore, in the manufacturing method of a wire rod according to an example of the present disclosure, the reheating and rolling the billet can comprise heating to 950°C to 1050°C, maintaining for 90 minutes to 120 minutes, and then rolling.
[0016] Furthermore, in the manufacturing method of a wire rod according to an example of the present disclosure, an average pearlite lamellar spacing at 1/4D (D: diameter) of a cross-section of the wire rod after the maintaining is 80 nm to 120 nm.
[0017] Further, in the manufacturing method of a wire rod according to an example of the present disclosure, a tensile strength of the wire rod after the maintaining may be 1600 MPa or more and a reduction of area may be 28% or more.
[0018] A manufacturing method of a steel wire according to another example of the present disclosure, comprising: wire-drawing the manufactured wire rod with a total reduction ratio of 77% to 85% without LP (Lead Patenting) heat treatment after pickling.
[0019] Further, a manufacturing method of a steel wire according to an example of the present disclosure can further comprise a step of performing a Zn hot-dip galvanizing treatment.
[0020] A steel wire according to another example of the present disclosure, wherein a tensile strength is 2270 MPa or more and torsion (100D, D: diameter) is 26 times or more.
[0021] Furthermore, in a steel wire according to an example of the present disclosure, after the Zn hot-dip galvanizing treatment, a tensile strength of a galvanized wire is 2130 MPa or more and torsion is 16 times or more.
[Advantageous Effects]
[0022] According to the present disclosure, the manufacturing of a wire rod having improved nodule refinement and wire-drawing formability, and a steel wire having excellent high strength and torsion characteristics without LP (Lead Patenting) heat treatment, is enabled. This enablement provides CO2 reduction through the omission of LP heat treatment, material quantity reduction through the securing of high strength, and construction period shortening.
[Description of Drawings]
[0023]
FIG. 1 is a diagram illustrating a pearlite lamellar spacing according to an example of the present disclosure.
FIG. 2 is a schematic diagram illustrating a method for measuring a density of AlN precipitates.
[Modes of the Invention]
[0024] Hereinafter, preferred embodiments of the present disclosure are described. However, the embodiments of the present disclosure may be modified into various different forms, and the technical spirit of the present disclosure is not limited to the embodiments described hereinafter. Further, the embodiments of the present disclosure are provided to more completely describe the present disclosure to those having ordinary skill in the art.
[0025] Terms used in the present disclosure are for describing specific examples. Accordingly, a singular expression includes a plural expression unless contextually requiring a singular meaning. Additionally, terms such as "comprising" or "having," used in the present disclosure, are for clearly designating the existence of features, steps, functions, components, or combinations thereof described in the disclosure, and are not for preliminarily excluding the existence of other features, steps, functions, components, or combinations thereof.
[0026] Meanwhile, unless otherwise defined, all terms used in the present disclosure should be understood as having the same meaning as generally understood by those of ordinary skill in the technical field to which the present disclosure pertains. Therefore, unless clearly defined in the present disclosure, a specific term should not be construed in an excessively idealistic or formal sense.
[0027] Further, in the present disclosure, terms such as "approximately" and "substantially" are used to mean at or close to the numerical value, given manufacturing and material tolerances inherent in the stated meaning, and are also used to prevent unscrupulous infringers from unfairly exploiting disclosed contents mentioning accurate or absolute numerical values for aiding understanding of the present disclosure.
[0028] Absent specific mention to the contrary in the present disclosure, the percentages representing the content of each element are by weight.
[0029] First, a description of the wire rod according to an example of the present disclosure is provided.
[0030] A wire rod according to an example of the present disclosure comprises, in percent by weight (wt%): C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al/N: 2.00 to 11.00, the balance of Fe and other unavoidable impurities.
[0031] Hereinafter, the reasons for the numerical limitations of the alloy component content in the example of the present disclosure are described.
C: 0.94% to 1.04%
[0032] Carbon is an element most effectively increasing material strength. An increase of 0.1% C provides a strength increase effect of 100 MPa. However, an addition of less than 0.94% makes achievement of a target product strength difficult. An excess of 1.04% causes grain boundary cementite formation and central segregation deterioration, decreasing wire-drawability, therefore, the content is preferably maintained at 1.04% or less. Further, the content can more preferably be 0.96% to 1.00%.
Si: 0.9% to 1.5%
[0033] Si segregates at cementite grain boundaries, making it suitable for preventing strength reduction during hot-dip galvanizing. A Si content of less than 0.9% results in a large strength reduction rate. A Si content of greater than 1.5% leads to inferior drawability. Therefore, controlling the content to 0.9% to 1.5% is desirable. More preferably, the Si content may be 1.20% to 1.30%.
Mn: 0.2% to 0.8%
[0034] An increase in Mn content by 0.1% increases strength by 20 MPa, and Mn addition is for providing sufficient hardenability during heat treatment. Mn addition in the present disclosure is 0.2% or more for removing S in steel. However, a large amount of addition promotes segregation. The upper limit of Mn is 0.8% or less, preferably 0.6% or less, and more preferably 0.3% to 0.5%.
Cr: 0.2% to 0.8%
[0035] Cr is an advantageous element, providing a 30-40 MPa increase in tensile strength through solid solution strengthening upon addition of 0.1%, and improvements in wire drawability through pearlite refinement. Specifically, a large hardenability effect enables stable pearlite formation through transformation nose delay and pearlite lamellar spacing refinement. However, a Cr content of less than 0.2% makes securing tensile strength difficult. A Cr content greater than 0.8% can cause coarse proeutectoid carbides to form at grain boundaries, potentially leading to inferior wire drawability. Therefore, controlling the Cr content to 0.8% or less is desirable. Additionally, a more preferable content can be 0.5% to 0.7%.
Al: 0.020% to 0.105%
[0036] Al, as an element suppressing proeutectoid cementite formation in hypereutectoid steel, combines with N in steel to form AlN. The AlN existing at austenite grain boundaries retards grain growth and increases the wire-drawing limit during final wire-drawing. A content of 0.020% or more is added. However, excessive addition causes a nozzle clogging problem due to the formation of complex inclusions such as Al2O3 and Al-Si-O, making controlling the upper limit to 0.105% desirable.
N: 0.0021% to 0.0205%
[0037] N is an element effective for strength improvement. N combines with Al in steel to form AlN. The presence of said AlN at austenite grain boundaries retards grain growth and increases the wire-drawing limit during final wire-drawing. The addition of N is 0.0021% or more. However, excessive addition causes inferiority in workability. Controlling the upper limit to 0.0205% is desirable.
Al/N: 2.00 to 11.00
[0038] Refinement of austenitic grain size or refinement of nodules is required for improvement of wire-drawability. For securing nodules with an average size of 10 to 20 µm, fine formation of AlN precipitates having a size of 50 nm or less is required. An Al/N ratio less than 2.00 results in a low number of precipitates, preventing nodule refinement. An Al/N ratio greater than 11.00 prevents the resulting effect from AlN coarsening; thus, control to that or less is desirable. Furthermore, more desirably, the Al/N ratio can be 2.08 to 10.88.
[0039] Additionally, in the wire rod of an example of the present disclosure, the density of AlN precipitates having a size of 50 nm or less may be 2.4x1011/mm2 or less. A density of AlN precipitates having a size of 50 nm or less greater than 2.4x10^11/mm^2 results in an average nodule size greater than 16 µm. A larger average nodule size increases stress concentration during wire-drawing. Therefore, controlling the density of the AlN precipitates to 2.4x1011/mm2 or less and controlling the average nodule size to 16 µm or less is desirable.
[0040] The balance of Fe and other unavoidable impurities. These impurities are known to those skilled in the art of typical manufacturing processes. Therefore, specific mention of all their details is omitted from the present disclosure.
[0041] Further, the wire rod of an example of the present disclosure has an average pearlite lamellar spacing at 1/4D (D: diameter) of a cross-section of 80 nm to 120 nm. Controlling the pearlite lamellar spacing to less than 80 nm is difficult due to equipment limitations. A pearlite lamellar spacing exceeding 120 nm results in a relatively low tensile strength, a decreased reduction of area, and also degraded mechanical properties after wire-drawing. Therefore, controlling the pearlite lamellar spacing to 120 nm or less is desirable.
[0042] Also, the wire rod according to an example of the present disclosure has an average tensile strength of 1600 MPa or more and a reduction of area of 28% or more. Tensile strength greater than 1600 MPa may cause a decrease in a service life of a die during wire-drawing, and the inability to increase a processing speed may result in inferior productivity.
[0043] Hereinafter, a description of a manufacturing method of a wire rod according to an example of the present disclosure is provided.
[0044] A manufacturing method of a wire rod according to an example of the present disclosure, comprising: preparing a billet comprising, in percent by weight (wt%): C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al/N: 2.00 to 11.00, and the balance of Fe and other unavoidable impurities; reheating and hot-rolling the billet; coiling at Acm-80°C to 760°C; cooling from the coiling temperature to 650°C to 620°C, which is a pearlite transformation entry temperature, at 10°C/s to 20°C/s; and maintaining for 200 seconds or more by setting a conveyor speed to 0.30 m/s or less from the cooling temperature to a temperature range of 600°C to 560°C.
[0046] A step of preparing a billet is a conventional billet manufacturing process, and the billet is manufactured with a size of 160x160 mm2.
[0047] Further, the reheating and rolling of the billet can occur by a conventional process. For example, after manufacturing a billet having the aforementioned alloy composition, the billet can be heated to a furnace temperature of 950°C to 1050°C, maintained for 90 minutes to 120 minutes for normalization and austenite formation, and then rolled. Maintaining the billet at less than 950°C causes a problem of increased charging time. Maintaining the billet at a temperature greater than 1050°C causes a furnace load. Therefore, controlling the temperature to 950°C to 1050°C is desirable. Further, maintaining the billet for less than 90 minutes may result in difficult austenite formation in the core. Maintaining the billet for greater than 120 minutes may result in coarse grain growth.
Coiling temperature: Acm-80°C to 760°C
[0048] The Stelmor is a cooling zone utilizing air blowing. For cooling as rapidly as possible to the pearlite transformation nose temperature of 650°C, lowering the coiling temperature as much as possible is required. A maximum coiling temperature is Acm-80°C. A coiling temperature greater than this delays reaching a target temperature, consequently preventing uniform pearlite refinement. Since 760°C is the lowest temperature due to equipment performance, controlling at Acm-80°C to 760°C is desirable.
Stelmor cooling control.
[0049] The cooling from the coiling temperature to 650°C to 620°C, which is a pearlite transformation entry temperature, can be controlled at a cooling rate of 10°C/s to 20°C/s. Cooling at less than 10°C/s presents difficulties in uniform pearlite formation. Cooling at greater than 20°C/s presents equipment limitations. Therefore, controlling at 20°C/s or less is desirable.
[0050] Subsequently, all Stelmor covers are engaged up to a temperature range of 600°C to 560°C, the conveyor speed is set to 0.30 m/s or less, and maintaining for 200 seconds or more in that section is possible, considering pearlite transformation. A conveyor speed greater than 0.30 m/s causes a reduction in transformation time, forming low-temperature structures such as martensite, resulting in inferior formability; therefore, control to 0.30 m/s or less is desirable. Further, desirably, the conveyor speed can be 0.25 m/s or less, and the pearlite transformation can be maintained for 200 seconds to 230 seconds.
[0051] Wherein, after the maintaining, an average pearlite lamellar spacing at 1/4D (D: diameter) of a cross-section of the wire rod is 80 nm to 120 nm, a tensile strength is 1600 MPa or more, and a reduction of area is 28% or more.
[0052] Thereafter, for improved workability, a step of cooling to an R/T (reforming tube) charging temperature of 470°C to 440°C at 5°C/s to 10°C/s may be performed. Cooling at less than 5°C/s does not satisfy a target temperature. Cooling at greater than 10°C/s has equipment limit restrictions, thus controlling to be less than that is desirable. Additionally, the cooling rate may desirably be 5°C/s to 8°C/s.
[0053] Description is provided for a steel wire and its manufacturing method according to an example of the present disclosure.
[0054] According to the present disclosure, a steel wire is manufactured by wire-drawing the wire rod manufactured by the manufacturing method after pickling, without LP (Lead Patenting) heat treatment, with a total reduction ratio of 77% to 85%. The steel wire manufactured thereby has a tensile strength of 2270 MPa or more and torsion (100D, D: diameter) of 26 times or more.
[0055] Furthermore, the manufacturing method of a steel wire according to an example of the present disclosure may further comprise performing a Zn hot-dip galvanizing treatment, wherein after the Zn hot-dip galvanizing treatment, a tensile strength of a galvanized wire may be 2130 MPa or more and torsion may be 16 times or more.
[0056] An increase in strength by 100 MPa can reduce the material usage for cables by up to 5%. Meanwhile, a tensile strength of the drawn wire less than 2270 MPa presents limitations, such as a reduced cable cutting force, problems with cable stability, and a smaller reduction in material usage for cables, thereby restricting application to steel wires for cables.
[0057] A torsion of the steel wire less than 26 times indicates a high density of internal defects. The condition presents a problem of difficulty in securing a target galvanized wire torsion of 16 times or more, even with a Zn hot-dip galvanizing treatment, thereby restricting application to steel wire for cables.
(Example)
[0059] In the present disclosure, specimens were manufactured based on a 0.96C-1.25Si-0.4Mn-0.6Cr component system in percent by weight (wt%), as shown in Table 1 below, with individual control of the Al/N ratio, and billets having a size of 160x160 mm2 were prepared. Subsequently, for low-temperature rolling and coiling, a furnace temperature was maintained at 990 °C for 80 minutes. Thereafter, cooling control was performed under the conditions as shown in Table 2, wherein Table 2 presents the temperature and holding time for each section. Additionally, the manufactured wire rod, after pickling and without LP (Lead Patenting) heat treatment, was wire-drawn using a dry wire drawing machine to approximately 5.0 mm at a speed of 200 m/m, and finished by immersion at a hot-dip galvanizing temperature of 450 °C for approximately 1 minute.
[0060] Further, the tensile strength, reduction of area (RA), wire-drawing amount, torsion times, and delamination occurrence of the manufactured wire rod and steel wire at room temperature were measured and are shown in Table 3 below.
[0061] The average pearlite nodule size is represented by an average of three arbitrary points, obtained by measuring crystal orientations of a ferritic structure in a cross-section of the wire rod using Electron Back Scatter Diffraction (EBSD) equipment, defining a nodule boundary as a misorientation of 10° or more between adjacent ferrite grains, and then measuring a size of grains formed by the boundaries.
[0062] The measurement of the tensile strength of the wire rod involved cutting a 40 cm length from two rings (circumference: 3.2m) at the rear end of the coil and performing a tensile test. The tensile speed (crosshead speed) was 70 m/m, and the gauge length was 30 cm. Using a stereo projector, measurement of the diameter before the tensile test and the diameter of the necked portion after the tensile test was performed to determine the reduction of area, calculated by [1-(diameter after tensile test / diameter before tensile test)2]*100.
[0063] For tensile strength measurement of the steel wire according to the present disclosure, a tensile test piece length is 40 cm, a crosshead speed is 100 mm/min, and a gauge length is 30 cm, which is the same as the wire rod. Elongation is determined as a percentage of an elongated length relative to an initial length of 30 cm. For torsion, a back load is load (kg) × 0.008, a length is 100D (D: diameter), and a number of fractures is confirmed while rotating an unfixed chuck in the same direction with one chuck fixed.
[0064] The density of AlN precipitates having a size of 50 nm or less was measured by the following method.
[0065] A wire rod (A) manufactured as shown in FIG. 2 underwent mechanical milling to its center. After the cutting of the center, polishing was performed to prepare a specimen (B). Regarding the observed surface microstructure (C) having cementite and grain boundaries formed therein, electropolishing was performed, followed by film deposition to extract only AlN precipitates, and a TEM (transmission electron microscope) analysis of the precipitates was performed (D). The polishing solution was 3% picric acid, and the film was carbon (C). The TEM analysis field of view was 500 nm x 500 nm. Measurements were taken from a total of 20 random regions to confirm the number of precipitates, and an average value was derived.
[0066] The pearlite lamellar spacing was identified using an SEM (Scanning Electron Microscope) by selecting a region perpendicular to the incident beam, taking 10 measurements at x5000 magnification, and averaging the measurements.
[TABLE 1]
| C | Si | Mn | Cr | Al | N | Al/N | |
| Inventive Example 1 | 0.96 | 1.25 | 0.4 | 0.6 | 0.022 | 0.0021 | 5.44 |
| Inventive Example 2 | 0.96 | 1.25 | 0.4 | 0.6 | 0.021 | 0.0052 | 2.10 |
| Comparative Example 1 | 0.96 | 1.25 | 0.4 | 0.6 | 0.023 | 0.0110 | 1.09 |
| Comparative Example 2 | 0.96 | 1.25 | 0.4 | 0.6 | 0.022 | 0.0220 | 0.52 |
| Inventive Example 3 | 0.96 | 1.25 | 0.4 | 0.6 | 0.044 | 0.0021 | 10.88 |
| Inventive Example 4 | 0.96 | 1.25 | 0.4 | 0.6 | 0.043 | 0.0050 | 4.46 |
| Inventive Example 5 | 0.96 | 1.25 | 0.4 | 0.6 | 0.043 | 0.0103 | 2.17 |
| Comparative Example 3 | 0.96 | 1.25 | 0.4 | 0.6 | 0.042 | 0.0202 | 1.08 |
| Comparative Example 4 | 0.96 | 1.25 | 0.4 | 0.6 | 0.061 | 0.0025 | 12.67 |
| Inventive Example 6 | 0.96 | 1.25 | 0.4 | 0.6 | 0.062 | 0.0050 | 6.44 |
| Inventive Example 7 | 0.96 | 1.25 | 0.4 | 0.6 | 0.062 | 0.0100 | 3.22 |
| Comparative Example 5 | 0.96 | 1.25 | 0.4 | 0.6 | 0.063 | 0.0220 | 1.49 |
| Comparative Example 6 | 0.96 | 1.25 | 0.4 | 0.6 | 0.081 | 0.0022 | 19.11 |
| Inventive Example 8 | 0.96 | 1.25 | 0.4 | 0.6 | 0.081 | 0.0053 | 7.93 |
| Inventive Example 9 | 0.96 | 1.25 | 0.4 | 0.6 | 0.080 | 0.0100 | 4.15 |
| Inventive Example 10 | 0.96 | 1.25 | 0.4 | 0.6 | 0.082 | 0.0205 | 2.08 |
| Comparative Example 7 | 0.96 | 1.25 | 0.4 | 0.6 | 0.101 | 0.0021 | 24.97 |
| Inventive Example 11 | 0.96 | 1.25 | 0.4 | 0.6 | 0.102 | 0.0050 | 10.59 |
| Inventive Example 12 | 0.96 | 1.25 | 0.4 | 0.6 | 0.101 | 0.0102 | 5.14 |
| Inventive Example 13 | 0.96 | 1.25 | 0.4 | 0.6 | 0.100 | 0.0204 | 2.54 |
| Comparative Example 8 Comparative | 0.96 | 1.25 | 0.4 | 0.6 | 0.042 | 0.0050 | 4.36 |
| Comparative Example 9 | 0.96 | 1.25 | 0.4 | 0.6 | 0.043 | 0.0050 | 4.46 |
| Inventive Example 14 | 0.96 | 1.25 | 0.4 | 0.6 | 0.040 | 0.0051 | 4.07 |
[TABLE 2]
| Coiling Temperature (°C) | Pearlite Transformation Entry Temperature (°C) | Maintenance Time (s) | Maintenance End Temperature(°C) | RT Entry Temperature(°C) | Nodule Size (µm) | Pearlite Lamellar Spacing (nm) | Number of Precipitates of 50 nm or less (mm2) | |
| Inventive Example 1 | 790 | 630 | 220 | 580 | 450 | 8 | 98 | 2.2x1011 |
| Inventive Example 2 | 800 | 640 | 205 | 582 | 460 | 10 | 89 | 1.9x1011 |
| Comparative Example 1 | 795 | 625 | 210 | 578 | 450 | 23 | 97 | 2.2x103 |
| Comparative Example 2 | 805 | 630 | 230 | 568 | 450 | 25 | 102 | 4.0x102 |
| Inventiv e Example 3 | 800 | 640 | 225 | 580 | 460 | 7 | 99 | 5.8x1010 |
| Inventive Example 4 | 790 | 620 | 220 | 582 | 465 | 9 | 98 | 2.0x1011 |
| Inventive Example 5 | 805 | 630 | 230 | 586 | 455 | 10 | 92 | 7.8x1010 |
| Comparative Example 3 | 795 | 625 | 235 | 588 | 445 | 25 | 95 | 2.1x1011 |
| Comparative Example 4 | 790 | 630 | 215 | 585 | 450 | 27 | 94 | 2.4x1011 |
| Inventive Example 6 | 780 | 640 | 220 | 580 | 450 | 9 | 90 | 1.1x1011 |
| Inventive Example 7 | 800 | 650 | 230 | 582 | 450 | 7 | 89 | 9.7x1010 |
| Comparative Example 5 | 790 | 640 | 220 | 586 | 460 | 28 | 90 | 2.2x1011 |
| Comparative Example 6 | 780 | 630 | 210 | 581 | 440 | 22 | 93 | 2.4x1011 |
| Inventive Example 8 | 800 | 640 | 200 | 584 | 440 | 9 | 88 | 4.7x1010 |
| Inventive Example 9 | 800 | 630 | 220 | 578 | 442 | 8 | 85 | 1.3x1011 |
| Inventive Example 10 | 795 | 620 | 200 | 583 | 450 | 9 | 86 | 1.7x1011 |
| Comparative Example 7 | 790 | 640 | 205 | 580 | 452 | 17 | 105 | 8.9x108 |
| Inventive Example 11 | 780 | 630 | 215 | 580 | 461 | 11 | 90 | 7.2x1010 |
| Inventive Example 12 | 790 | 650 | 200 | 586 | 452 | 8 | 92 | 5.8x1010 |
| Inventive Example 13 | 800 | 630 | 220 | 584 | 447 | 12 | 87 | 2.2x1010 |
| Comparative Example 8 | 890 | 730 | 210 | 640 | 554 | 19 | 167 | 1.2x1010 |
| Comparative Example 9 | 790 | 620 | 105 | 485 | 450 | 10 | 142 | 2.1x109 |
| Inventive Example 14 | 790 | 620 | 220 | 582 | 465 | 9 | 98 | 5.8x1010 |
[TABLE 3]
| Tensile Strength (MPa) | RA (%) | Drawing Reduction Ratio (%) | Tensile Strength of Drawn Wire (MPa) | Torsion (times/10 0D) | Tensile Strength of Galvanize d Wire (MPa) | Occurrence of Delamination | Torsion of Galvanized Wire (times/ 100D) | |
| Inventive Example 1 | 1620 | 32 | 77.5 | 2290 | 28 | 2150 | Non-occurrence | 18 |
| Inventive Example 2 | 1630 | 31 | 77.5 | 2290 | 29 | 2150 | Non-occurrence | 17 |
| Comparative Example 1 | 1590 | 26 | 77.5 | 2270 | 22 | 2130 | Occurrence | 0 |
| Comparative Example 2 | 1610 | 22 | 77.5 | 2270 | 19 | 2130 | Non-occurrence | 3 |
| Inventive Example 3 | 1600 | 29 | 77.5 | 2300 | 27 | 2160 | Non-occurrence | 18 |
| Inventive Example 4 | 1620 | 28 | 77.5 | 2310 | 26 | 2170 | Non-occurrence | 16 |
| Inventive Example 5 | 1610 | 30 | 77.5 | 2280 | 28 | 2140 | Non-occurrence | 19 |
| Comparative Example 3 | 1590 | 24 | 77.5 | 2250 | 18 | 2110 | Occurrence | 0 |
| Comparative Example 4 | 1600 | 26 | 77.5 | 2630 | 22 | 1490 | Occurrence | 0 |
| Inventive Example 6 | 1630 | 31 | 77.5 | 2280 | 29 | 2140 | Non-occurrence | 20 |
| Inventive Example 7 | 1620 | 29 | 77.5 | 2290 | 30 | 2150 | Non-occurrence | 16 |
| Comparative Example 5 | 1600 | 24 | 77.5 | 2270 | 24 | 2130 | Non-occurrence | 3 |
| Comparative Example 6 | 1610 | 25 | 77.5 | 2250 | 24 | 2110 | Non-occurrence | 2 |
| Inventive Example 8 | 1650 | 29 | 77.5 | 2300 | 27 | 2160 | Non-occurrence | 18 |
| Inventive Example 9 | 1600 | 29 | 77.5 | 2280 | 28 | 2140 | Non-occurrence | 17 |
| Inventive Example 10 | 1610 | 30 | 77.5 | 2270 | 30 | 2130 | Non-occurrence | 18 |
| Comparative Example 7 | 1600 | 26 | 77.5 | 2270 | 23 | 2130 | Occurrence | 0 |
| Inventive Example 11 | 1620 | 29 | 77.5 | 2290 | 28 | 2150 | Non-occurrence | 20 |
| Inventive Example 12 | 1630 | 30 | 77.5 | 2300 | 29 | 2160 | Non-occurrence | 16 |
| Inventive Example 13 | 1600 | 30 | 77.5 | 2270 | 29 | 2130 | Non-occurrence | 17 |
| Comparative Example 8 | 1480 | 25 | 77.5 | 2020 | 12 | 1880 | Non-occurrence | 7 |
| Comparative Example 9 | 1540 | 27 | 77.5 | 2050 | 15 | 1910 | Non-occurrence | 5 |
| Inventive Example 14 | 1620 | 28 | 84.3 | 2380 | 24 | 2240 | Non-occurrence | 14 |
[0067] Inventive Examples 1 to 13 satisfy the entire range of compositions, and the Al/N ratio satisfies 2.00 to 11.00. Additionally, the coiling was performed at a low temperature of 790°C to 805°C, and the pearlite transformation entry temperature was 620°C to 650°C. Maintaining for 200 seconds to 230 seconds occurred in the pearlite formation range. After exiting the Stelmor cover, the maintaining stage end temperature was 578°C to 586°C, cooled at 10°C/s or less. The temperature at R/T (reforming tube) charging was confirmed to be 440°C to 465°C. Nodule size is known to be influenced by the Al/N ratio. A size of 11 µm or less was obtained when measured by EBSD (tolerance angle: 10°). As confirmed in FIG. 1, the pearlite lamellar spacing was 80 nm to 100 nm. The wire rod exhibited a tensile strength of 1600 MPa or more and a reduction of area of 28% or more.
[0068] The processing evaluation for the coil is shown in Table 3. After descaling, the total applied reduction ratio is 77.5%. A tensile strength after wire-drawing is 2270 MPa or more, and torsion (100D, D: diameter) is 26 times or more without delamination during a torsion test. This is subjected to a Zn hot-dip galvanizing treatment after maintaining at 450°C for a predetermined time. It is confirmed that the galvanized wire has suitable characteristics for cables, showing a tensile strength of 2130 MPa or more and torsion of 16 times or more without delamination.
[0069] In contrast, Comparative Examples 1 to 7 have the same component system as Inventive Examples 1 to 13, but the Al/N ratio is less than 2.00 or greater than 11.00, not satisfying the range of the present disclosure. Accordingly, Comparative Examples 1 to 7, despite undergoing the same manufacturing process as Inventive Examples 1 to 13, are confirmed to have an average nodule size greater than 16 µm, and a reduction of area is less than 28%, confirming an influence by the Al/N ratio.
[0070] Additionally, even with the application of the same amount of wire-drawing, the tensile strength and the torsion count of the comparative examples in the drawn wire are confirmed to be lower than those of the inventive examples. In particular, delamination occurs during torsion in the galvanized wires of comparative examples 1, 3, 4, and 7. In the galvanized wires of comparative examples 2, 5, and 6, even without the occurrence of delamination, the torsion count is significantly lower, being less than 16, thereby confirming the effect of AlN.
[0071] Furthermore, the presence or absence of changes in the mechanical properties of the galvanized wire due to process differences was compared using Invention Example 4 and Comparative Example 8. Specifically, Invention Example 4 and Comparative Example 8 are for comparing the effect due to coiling temperature control. For Comparative Example 8, the coiling temperature was increased to 890°C. The minimal change in the cooling rate results in a high isothermal transformation initiation temperature of 730°C. The temperature upon passing through the cover after maintaining for 210 seconds is 640°C, which is higher than that of Invention Example 4. The temperature upon R/T entry is also high at 554°C, making it unsuitable for workability. Furthermore, the pearlite lamellar spacing being wide at 167 nm results in a relatively low tensile strength of 1480 MPa. The reduction of area property is also decreased to 25%, and the mechanical properties after wire-drawing are also confirmed to deteriorate. Furthermore, the galvanized wire does not exhibit delamination. However, the tensile strength is low at 1880 MPa, confirming its unsuitability for high-strength applications.
[0072] Comparative Example 9 involved manufacturing with the maintaining time reduced to 105 seconds. The tensile strength was 1540 MPa, and the reduction of area was merely 27%. The mechanical properties after wire-drawing showed a non-high tensile strength of 2050 MPa and a likewise low torsion value. These characteristics present some difficulty for field application.
[0073] Finally, Inventive Example 14 concerns the wire-drawing limit. The amount of wire-drawing increased by 6.8% compared to Inventive Example 4. The test evaluated suitability for processing ultra-high strength products. An increase in the amount of wire-drawing showed no issues during processing. The tensile strength of the galvanized wire is 2240 MPa, with the strength increasing by approximately 70 MPa, while the torsion value only decreased by approximately 2 times.
[0074] While the foregoing description has described exemplary embodiments of the present disclosure, the present disclosure is not limited thereto. A person of ordinary skill in the art's understanding confirms that various changes and modifications are possible within the concept and scope of the claims described below without departing from the present disclosure.
1. A wire rod comprising, in percent by weight (wt%): C: 0.94% to 1.04%, Si: 0.9% to
1.5%, Mn: 0.2% to 0.8%, Cr: 0.2% to 0.8%, Al: 0.020% to 0.105%, N: 0.0021% to 0.0205%,
Al/N: 2.00 to 11.00, the balance of Fe and other unavoidable impurities.
2. The wire rod of claim 1,
wherein a density of AlN precipitates having a size of 50 nm or less is 2.4x 1011/mm2 or less.
wherein a density of AlN precipitates having a size of 50 nm or less is 2.4x 1011/mm2 or less.
3. The wire rod of claim 1,
wherein an average nodule size is 16 µm or less.
wherein an average nodule size is 16 µm or less.
4. The wire rod of claim 1,
wherein an average pearlite lamellar spacing at 1/4D (D: diameter) of a cross-section of the wire rod is 80 nm to 120 nm.
wherein an average pearlite lamellar spacing at 1/4D (D: diameter) of a cross-section of the wire rod is 80 nm to 120 nm.
5. The wire rod of claim 1,
wherein an average tensile strength is 1600 MPa or more and a reduction of area is 28% or more.
wherein an average tensile strength is 1600 MPa or more and a reduction of area is 28% or more.
6. A manufacturing method of a wire rod, comprising: preparing a billet comprising, in
percent by weight (wt%): C: 0.94% to 1.04%, Si: 0.9% to 1.5%, Mn: 0.2% to 0.8%, Cr:
0.2% to 0.8%, Al: 0.021% to 0.102%, N: 0.0021% to 0.0205%, Al/N: 2.00 to 11.00, and
the balance of Fe and other unavoidable impurities;
reheating and hot-rolling the billet;
coiling at Acm-80°C to 760°C;
cooling from the coiling temperature to 650°C to 620°C, which is a pearlite transformation entry temperature, at 10°C/s to 20°C/s; and
maintaining for 200 seconds or more by setting a conveyor speed to 0.30 m/s or less from the cooling temperature to a temperature range of 600°C to 560°C.
7. The manufacturing method of claim 6,
further comprising: cooling to an R/T (reforming tube) charging temperature of 470°C to 440°C at 5°C/s to 10°C/s after the maintaining.
further comprising: cooling to an R/T (reforming tube) charging temperature of 470°C to 440°C at 5°C/s to 10°C/s after the maintaining.
8. The manufacturing method of claim 6,
wherein the reheating and rolling the billet comprises heating to 950°C to 1050°C, maintaining for 90 minutes to 120 minutes, and then rolling.
wherein the reheating and rolling the billet comprises heating to 950°C to 1050°C, maintaining for 90 minutes to 120 minutes, and then rolling.
9. The manufacturing method of claim 6,
wherein an average pearlite lamellar spacing at 1/4D (D: diameter) of a cross-section of the wire rod after the maintaining is 80 nm to 120 nm.
wherein an average pearlite lamellar spacing at 1/4D (D: diameter) of a cross-section of the wire rod after the maintaining is 80 nm to 120 nm.
10. The manufacturing method of claim 6,
wherein a tensile strength of the wire rod after the maintaining is 1600 MPa or more and a reduction of area is 28% or more.
wherein a tensile strength of the wire rod after the maintaining is 1600 MPa or more and a reduction of area is 28% or more.
11. A manufacturing method of a steel wire, comprising: wire-drawing the wire rod of Claim
1 with a total reduction ratio of 77% to 85% without LP (Lead Patenting) heat treatment
after pickling.
12. The manufacturing method of claim 11,
further comprising: performing a Zn hot-dip galvanizing treatment.
further comprising: performing a Zn hot-dip galvanizing treatment.
13. A steel wire manufactured by the method of claim 11,
wherein a tensile strength is 2270 MPa or more and torsion (100D, D: diameter) is 26 times or more.
wherein a tensile strength is 2270 MPa or more and torsion (100D, D: diameter) is 26 times or more.
14. The steel wire of claim 12,wherein, after the Zn hot-dip galvanizing treatment, a
tensile strength of a galvanized wire is 2130 MPa or more and torsion is 16 times
or more.