JP3978364B2 - High strength steel wire rod excellent in drawability and method for producing the same - Google Patents

Description

【００６６】
【表２】

【００６７】
[実施例２]
表３に、表１中、Ｎｏ．３の組成の鋼を用い、圧延後の引張強度（伸線加工前の引張強度）におよぼす製造条件の影響を調査した結果、表４に更に伸線加工後４８０℃で３０秒の浸漬により亜鉛めっきを施した結果を示す。
【００６８】
表中、Ｎｏ．２０はＮｏ．３の組成の鋼で圧延加熱温度を本発明範囲外で低くし、Ｎｏ．２１はＮｏ．３の組成の鋼で仕上げ温度、冷却速度を本発明範囲外としたものである。
【００６９】
本発明鋼であるＮｏ．３は、圧延後１０００ＭＰａを超える引張強度が得られたが、Ｎｏ．２０，２１はいずれの鋼も析出強化が不充分で十分な強度が得られなかった。
【００７０】
また、４８０℃×３０秒に浸漬される亜鉛めっき後も本発明鋼では強度低下はほとんど観察されなかった。これは、圧延後得られる微細析出物が高温でも安定なためであり、本発明の特徴のひとつである。
【００７１】
【表３】

【００７２】
【表４】

【００７３】
【発明の効果】
本発明によれば、伸線性に優れ且つ高強度な鋼線材およびその製造方法が得られ、産業上極めて有用である。
【図面の簡単な説明】
【図１】 本発明鋼線材の製造工程の一例を示す図。
【図２】 線材の巻取り以降の設備の状況を示す図。
【符号の説明】
１ 巻取り装置
２ 搬送装置
３ 集束装置
４ 鋼材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-strength steel wire used for wire ropes for bridges, PC steel wires, springs, steel cords, and the like, and a method for producing the same, and particularly relates to one having a diameter of 16 mm or less excellent in stretch workability.
[0002]
[Prior art]
Wire ropes for bridges, PC steel wires, springs, steel cords, and high-strength steel wires are drawn from high carbon steels such as JISG3502 (piano wire) and JISG3506 (hard steel wire) after patenting (online and offline). It is manufactured by cold working-heat treatment-finishing wire drawing.
[0003]
When high carbon steel wire is strengthened by adjusting the pearlite lamella spacing by work hardening or adding alloying elements, ductility decreases, so reducing wire breakage during wire drawing and wire breakage during twisting of products is an issue. Yes.
[0004]
As methods for preventing disconnection, JP-A-49-123923 and JP-A-52-12611 disclose a method of improving γ grains by carbonitride to improve ductility, and JP-B-7-11060 discloses a method for improving the ductility. It has been proposed to reduce the segregation peak of Mn in segregation.
[0005]
Japanese Patent Application Laid-Open No. 1-215928 discloses that a blueing treatment is performed before plating in order to improve ductility during the plating treatment of a galvanized steel wire. In addition, Si is added in order to prevent the strength reduction at the time of the plating process of the galvanized steel wire.
[0006]
[Problems to be solved by the invention]
However, the ductility of the steel wire after drawing described in these (drawing at the time of the tensile test) is only less than 50%, which is insufficient for further strengthening the drawing, and the galvanized steel wire. If Si is added to prevent a decrease in strength during the plating process, the drawability is lowered and the product cost is increased.
[0007]
Therefore, the present invention has an object to provide a high strength steel wire material (high strength steel wire) of φ16 mm or less having excellent strength after wire drawing of 2000 MPa or more and drawing of 60% or more, and its production conditions. To do.
[0008]
[Means for Solving the Problems]
The present inventors have intensively studied from the viewpoint of the structure and composition of the steel about the method of improving the strength without impairing the ductility of the drawn steel material, and made the low-carbon steel a ferrite single-phase structure to improve the ductility during the drawing process. It was found that a high-strength steel wire rod can be obtained without impairing the drawability when improved and by hardening by the processing after processing and precipitation hardening by fine precipitates.
[0009]
The present invention is Ru der been made in further studies based on the above findings. That is, the invention according to claim 1 is, in mass%, C ≦ 0.1%, Si ≦ 0.3%, Mn ≦ 2%, Ti: 0.03 to 0.20%, Mo: 0.05 to It consists of 0.6%, the remainder Fe and inevitable impurities, has a ferrite single-phase structure, and fine precipitates having a particle size of less than 10 nm are dispersed and precipitated in the ferrite phase by 90% or more of all precipitates. It is a high-strength steel wire with excellent drawability that has features.
[0010]
The invention described in claim 2 is characterized in that, in the high-strength steel wire rod excellent in drawability described in claim 1, the steel composition further satisfies the formula (1).
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96)} ≦ 1.5 --- (1)
However, each element has a content (% by mass).
[0011]
The invention described in claim 3 is characterized in that, in the high-strength steel wire rod excellent in drawability described in claim 1 or 2, the fine precipitates are made of carbides of Ti and Mo.
[0012]
The invention described in claim 4 is the high strength steel wire rod excellent in drawability according to claim 1, wherein the steel composition is further in mass%, Nb ≦ 0.08%, V ≦ 0.15%, W ≦ 1. It is characterized by containing 5% of one kind or two or more kinds.
[0013]
The invention described in claim 5 is characterized in that, in the high strength steel wire rod excellent in drawability described in claim 4, the steel composition further satisfies the formula (2).
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (Nb / 93) + (V / 51) + (W / 184)} ≦ 1.5 −−− (2 )
However, the content of each element is the content (% by mass), and the content that is not contained is 0.
[0014]
The invention described in claim 6 is the carbide containing the at least one of Ti, Mo, Nb, V, and W in the high-strength steel wire rod excellent in drawability according to claim 4 or 5. It has a special feature.
[0015]
The invention described in claim 7 is a high-strength steel wire having a tensile strength of 2000 MPa or more, characterized by drawing the high-strength steel wire according to any one of claims 1-6.
[0016]
Invention of Claim 8 is a manufacturing method of the high strength steel wire rod excellent in drawability, Comprising: Steel composition consists of a ingredient given in any 1 paragraph of Claims 1, 2, 4, 5, and 7, It is characterized in that a steel bar having a ferrite / pearlite structure is formed into a PC steel bar, quenched and then tempered at 550 to 700 ° C. for 10 minutes or more.
[0017]
Invention of Claim 9 is a manufacturing method of the high strength steel wire rod excellent in drawability, Comprising: Steel which has the composition as described in any one of Claim 1, 2, 4, 5 is 1100 degreeC or more. It is characterized by rolling at a finish rolling temperature of 800 ° C. or higher after heating and cooling 700 to 550 ° C. at a cooling rate of 0.5 ° C./sec or lower in the subsequent cooling.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The microstructure, component composition and production conditions of the steel wire of the present invention will be described in detail below.
[0020]
1. Microstructure The high-strength steel wire according to the present invention defines the microstructure as a single-phase ferrite structure and a fine precipitate having a particle size of less than 10 nm so that a steel wire having a desired strength can be obtained after wire drawing.
[0021]
When the structure before wire drawing is a ferrite single phase structure and fine precipitates are dispersed and precipitated in the structure, a desired strength can be obtained after wire drawing without impairing wire drawing.
[0022]
In the present invention, the ferrite single phase structure is a ferrite area ratio of 95% or more, preferably 98% or more in cross-sectional structure observation (observation of 200 times optical microscope structure).
[0023]
In the present invention, the fine precipitate has a particle size of less than 10 nm. When the particle size of the precipitate is 10 nm or more, the tensile strength necessary for a high-strength steel wire such as a PC steel wire cannot be obtained even by work hardening by wire drawing.
[0024]
The smaller the particle size of the fine precipitates, the more effective for improving the strength, preferably 5 nm, more preferably 3 nm or less. As such fine precipitates, carbides containing a composite of Ti and Mo, and further Nb, V, Carbides containing one or more of W are preferred.
[0025]
Although the distribution form of these fine precipitates is not particularly defined, it is desirable to uniformly disperse (disperse precipitation) in the matrix.
[0026]
Moreover, in this invention, if the magnitude | size of a fine precipitate will satisfy | fill 90% or more of all the precipitates, the target tensile strength after wire drawing will be obtained. However, a precipitate having a size of 10 nm or more consumes a precipitate-forming element and adversely affects the strength.
[0027]
Although the effect of the present invention is not impaired even if a small amount of Fe carbide is contained in addition to the precipitate described above, toughness is inhibited when a large amount of Fe carbide having an average particle size of 1 μm or more is contained, in the present invention The upper limit of the size of Fe carbide contained is preferably 1 μm, and the content is preferably 1% or less of the whole.
[0028]
The ratio of the fine precipitates in the present invention to the total precipitates can be determined by the following method. First, an electron microscope sample is prepared by an electropolishing method using a twin jet method and observed at an acceleration voltage of 200 kV.
[0029]
At that time, the crystal orientation of the parent phase is controlled so that the fine precipitates have a measurable contrast with respect to the parent phase, and the defocus is shifted from the normal focus in order to minimize the counting of the precipitates. Observe by method.
[0030]
Moreover, the thickness of the sample in the region where the precipitate particles are measured is evaluated by measuring the elastic scattering peak and the inelastic scattering peak intensity using electron energy loss spectroscopy.
[0031]
By this method, the measurement of the number of particles and the measurement of the sample thickness can be executed for the same region. The measurement of the number of particles and the particle diameter is carried out for four locations of a 0.5 × 0.5 μm region of the sample, and the precipitates distributed per 1 μm ² are calculated as the number for each particle diameter.
[0032]
From this value and the sample thickness, the number of precipitates distributed per 1 μm ^{3 of} particle diameter is calculated, and the ratio of the precipitates having a diameter of less than 10 nm to the measured total precipitates is calculated.
[0033]
2. Component composition The steel of the present invention can achieve the desired performance with the microstructure described above, but the following component composition is preferred.
[0034]
C
C is added to ensure strength. If the content exceeds 0.1%, the fine precipitates become coarse and the strength decreases, so the content is preferably 0.1% or less.
[0035]
Si
Si is added to ensure strength. If it exceeds 0.3%, the deformation resistance at the time of wire drawing is high and breakage is likely to occur, so the content is made 0.3% or less.
[0036]
Mn
Mn is added because it is effective in improving the strength, but if it exceeds 2%, the cold workability deteriorates, so the content is made 2% or less.
[0037]
Ti
Ti is added to precipitate Ti-Mo carbide precipitates together with Mo to improve the strength. If less than 0.03%, the amount of precipitates is small and the desired strength cannot be obtained, so 0.03% or more. On the other hand, if added over 0.20%, the precipitates become coarse and disconnection occurs. 0.20%.
[0038]
Mo
Mo is added to precipitate Ti-Mo carbide precipitates together with Ti to improve the strength. In order to ensure the desired tensile strength, it is made 0.05% or more. On the other hand, if added over 0.6%, a low-temperature transformation phase such as bainite is formed, precipitation strengthening due to fine precipitates is insufficient, and the strength decreases. Therefore, the content is set to 0.05 to 0.6%.
Mo has a slow diffusion rate, and when it precipitates together with Ti, the growth rate of the precipitate is reduced and a fine precipitate is obtained.
[0039]
(C / 12) / {(Ti / 48) + (Mo / 96)}
This parameter affects the size of the precipitate. When the parameter is 0.5 or more and 1.5 or less, preferably 0.7 or more and 1.2 or less, the formation of fine precipitates having a particle size of less than 10 nm is formed. Becomes easy.
[0040]
For fine Ti-Mo carbides, Ti and Mo in the carbide should be 2.0 ≧ Ti / Mo ≧ 0.2 in atomic ratio, and 1.5 ≧ Ti / Mo ≧ 0.7 for finer carbides. Was observed.
[0041]
Furthermore, when improving the characteristics, it is preferable to add one or more of Nb, V, and W.
[0042]
Nb
Nb forms fine precipitates together with Ti and contributes to an increase in strength. In addition, the structure is refined and the ductility is improved by adjusting the grain size. If it exceeds 0.08%, the precipitates become coarse, the crystal grains become excessively fine, and the ductility is lowered.
[0043]
V
V forms fine precipitates with Ti, but if it exceeds 0.15%, the precipitates become coarse, so 0.15% or less.
[0044]
W
W forms fine precipitates with Ti, but if it exceeds 1.5%, the precipitates become coarse, so 1.5% or less.
[0045]
In the addition of these elements, it is effective to define the atomic ratio of C, Ti, Mo, Nb, V, and W for the refinement of carbides (C / 12) / {(Ti / 48) + (Mo / 96) + (Nb / 93) + (V / 51) + (W / 184)} is 0.5 or more and 1.5 or less, preferably 0.7 or more and 1.2 or less, the particle size is less than 10 nm. It is easy to form fine precipitates.
[0046]
Further, in the fine Ti—Mo— (Nb, V, W) type carbide, each element in the carbide is 2.0 ≧ (Ti + Nb + V) / (Mo + W) ≧ 0.2 in atomic ratio, and 1 in the finer carbide. .5 ≧ (Ti + Nb + V) / (Mo + W) ≧ 0.7 was observed.
[0047]
In the steel of the present invention, the balance other than the above-mentioned additive elements is Fe and inevitable impurities, but Al can be added as a deoxidizer in an amount of 0.1% or less. Further, when improving the strength and ductility, one or two of Ni and Cr may be added in the range of Ni ≦ 2% and Cr ≦ 2%. In order to further improve the drawability, it is desirable to restrict the inevitable impurities P and N to P ≦ 0.040% and N ≦ 0.0080%.
[0048]
In addition, the effect of this invention is not impaired by content of these elements, or the presence or absence of addition.
[0049]
3. Manufacturing Conditions FIG. 1 is a schematic manufacturing process diagram of a hot forged part according to the present invention, in which S1 is a wire manufacturing process, S2 is a conveying process, and S3 is a product finishing process. The steel ingot is hot-rolled in the wire manufacturing process (S1) to obtain a wire having a diameter of 16 mm or less, and in the product finishing process (S3), the wire is formed into a steel wire by drawing to a predetermined size, and is plated as necessary. Desired products such as wire ropes for bridges, PC steel wires and steel cords. A desirable manufacturing process will be described in detail below.
[0050]
Rolling heating temperature Rolling heating temperature shall be 1100 degreeC or more. In this invention, in order to precipitate a fine precipitate during cooling after completion | finish of rolling, the carbide | carbonized_material which remains from the time of melt | dissolution at the time of hot rolling is made into a solid solution.
[0051]
When the rolling heating temperature is less than 1100 ° C., the Ti—Mo-based carbide remaining from the time of melting does not dissolve, so the temperature is set to 1100 ° C. or higher.
[0052]
Rolling finishing temperature When the rolling finishing temperature is less than 800 ° C, the rolling load is high and the roundness is deteriorated, so that the rolling finish temperature is set to 800 ° C or higher.
[0053]
By adjusting the cooling rate after the cooling rate rolling, fine precipitates are deposited before the wire drawing, and a product having a desired strength is obtained by precipitation strengthening by the precipitation and work hardening after the wire drawing. The precipitation temperature range of 700 to 550 ° C. of the fine precipitate is cooled at a critical cooling rate (0.5 ° C./sec) or less at which the fine precipitate is obtained. The regulation of the cooling rate may be satisfied in any of the winding, transporting, and converging processes through which the wire passes after rolling, and the process is not particularly defined. FIG. 2 shows an example of equipment arrangement after winding.
[0054]
【Example】
[Example 1]
Using the steels of various compositions shown in Table 1 (Nos. 1 to 19), the influence of the component composition on the drawability and the strength of the wire was investigated. No. in the table. 1-11 are examples of the present invention (development examples), No. Nos. 12 to 18 are comparative examples. Reference numeral 19 denotes a conventional example.
[0055]
The test steel was melted in a 150 kg vacuum melting furnace, heated at 1100 ° C. or higher, finished at a finishing temperature: 950 ° C. to obtain a wire rod, wound at a winding temperature: 880 ° C., and a cooling rate of 0.1 ° C. / Sec at room temperature.
[0056]
The obtained wire is pickled and treated with a lubricant, and then the primary wire is drawn to φ2 mm with a pass schedule with an average area reduction of 25% in each die, and further wet drawing to φ0.5 mm. I did it. No heat treatment was performed in this step.
[0057]
As-rolled, a tensile test and a twist test were performed after primary wire drawing and wet wire drawing. In the tensile test, tensile strength and drawing were determined.
[0058]
In the twisting test, a portion having a length 100 times the diameter of the wire was twisted until it was disconnected at 30 rpm, and the number of rotations up to the disconnection and the occurrence of vertical cracks were observed. After secondary wire drawing, the drawing in the 0.4 mmφ tensile test is difficult to measure, so the ductility was determined only for the twist value.
[0059]
In the structure observation, the cross section was observed with an optical microscope, the precipitate was observed with a transmission electron microscope (TEM), and the composition was determined with an energy dispersive X-ray spectrometer (EDX).
[0060]
Table 2 shows the test results. Invention Example (Development Example) No. Nos. 1 to 11 have no disconnection during wire drawing, and desired strength and ductility are obtained after wire drawing.
[0061]
On the other hand, no. 12-18, No. of the conventional example. No fine precipitate was obtained for No. 19. No. In No. 12, when C exceeded the upper limit and the structure after rolling was ferrite + pearlite, the ductility was low, wire breakage occurred frequently during wire drawing, and vertical deformation in the twist test was also observed remarkably.
[0062]
No. No. 13 is Ti and Mo. No. 14 is Mo. In No. 15, Ti was outside the scope of the present invention, and the precipitation strengthening amount was insufficient, and the desired strength was not obtained after wire drawing. No. No. 15 is outside the scope of the present invention, and the wire breakage during wire drawing and the twisting value are low and the cold workability is poor.
[0063]
No. In No. 16, Mo, Ti, and V are out of the scope of the present invention, the wire drawability is poor, breakage occurs frequently, and the strength is low. No. In No. 17, Si is high outside the range of the present invention, disconnection during wire drawing is remarkable, and Ti is outside the range of the present invention and precipitation strengthening is insufficient and the strength is low.
[0064]
No. In No. 18, Mo was high outside the scope of the present invention, and wire breakage was observed during wire drawing, and vertical cracks were observed during the twist test. No. No. 19 is a conventional steel (SWRH82 class), and due to insufficient ductility, disconnection frequently occurred even in primary wire drawing, and secondary wire drawing could not be performed.
[0065]
[Table 1]

[0066]
[Table 2]

[0067]
[Example 2]
In Table 3, in Table 1, No. As a result of investigating the influence of manufacturing conditions on the tensile strength after rolling (tensile strength before wire drawing) using steel having a composition of 3, the zinc was further immersed in 480 ° C for 30 seconds after wire drawing. The result of plating is shown.
[0068]
In the table, No. No. 20 is No. No. 3 steel with a rolling heating temperature lower than the scope of the present invention. No. 21 is No. 21. The finishing temperature and cooling rate of the steel of composition 3 are outside the scope of the present invention.
[0069]
No. which is steel of the present invention. No. 3 obtained a tensile strength exceeding 1000 MPa after rolling. No steels 20 and 21 were insufficient in precipitation strengthening, and sufficient strength could not be obtained.
[0070]
Further, even after galvanization immersed in 480 ° C. × 30 seconds, almost no reduction in strength was observed in the steel of the present invention. This is because fine precipitates obtained after rolling are stable even at high temperatures, which is one of the features of the present invention.
[0071]
[Table 3]

[0072]
[Table 4]

[0073]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the steel wire excellent in wire drawing property and high intensity | strength and its manufacturing method are obtained, and it is very useful industrially.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a manufacturing process of a steel wire rod according to the present invention.
FIG. 2 is a diagram showing the situation of equipment after winding of wire.
[Explanation of symbols]
1 Winding device 2 Conveying device 3 Converging device 4 Steel

Claims (9)

% By mass
C ≦ 0.1%,
Si ≦ 0.3%,
Mn ≦ 2%,
Ti: 0.03 to 0.20%,
Mo: 0.05-0.6%
Remaining Fe and inevitable impurities
A high-strength steel excellent in drawability, characterized by having a ferrite single-phase structure and fine precipitates having a particle size of less than 10 nm dispersed and precipitated in the ferrite phase by 90% or more of the total precipitates wire. The high-strength steel wire rod excellent in drawability according to claim 1, wherein the steel composition further satisfies the formula (1) .
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96)} ≦ 1.5 --- (1)
However, each element has a content (% by mass). High strength steel wire fine precipitates were excellent in drawability according to claim 1 or 2, wherein the consist carbide of Ti and Mo. As a steel composition, it is further mass%,
Nb ≦ 0.08%,
V ≦ 0.15%,
W ≦ 1.5%
The high-strength steel wire rod excellent in wire drawing property of Claim 1 containing 1 type (s) or 2 or more types . 5. The high-strength steel wire rod excellent in drawability according to claim 4, wherein the steel composition further satisfies the formula (2) .
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (Nb / 93) + (V / 51) + (W / 184)} ≦ 1.5 −−− (2 )
However, the content of each element is the content (% by mass), and the content that is not contained is 0. The high-strength steel wire rod excellent in drawability according to claim 4 or 5 , wherein the fine precipitate is a carbide containing Ti, Mo, and at least one of Nb, V, and W. A high strength steel wire having a tensile strength of 2000 MPa or more, wherein the high strength steel wire rod according to any one of claims 1 to 6 is drawn. The steel having the composition according to any one of claims 1, 2, 4, and 5 is heated at 1100 ° C or higher and then rolled at a finish rolling temperature of 800 ° C or higher, and 700 to 550 ° C is reduced to 0 in subsequent cooling. A method for producing a high-strength steel wire rod excellent in wire drawing, characterized by cooling at a cooling rate of 5 ° C./sec or less. The steel having the composition according to any one of claims 1, 2, 4, and 5 is heated to 1100 ° C or higher and then rolled at a finish rolling temperature of 800 ° C or higher, and 700 to 550 ° C is reduced to 0 in subsequent cooling. A method for producing a high-strength steel wire excellent in drawability, characterized by drawing a wire cooled at 5 ° C./sec or less.

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