JPH0565581B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in high-strength steel wires for steel core Al stranded wires (hereinafter referred to as ACSR) used in overhead power transmission lines. In recent years, ACSR for overhead power transmission lines has been used to improve the mechanical properties of steel core wires, such as not only static strength such as tensile strength, but also dynamic It is essential to improve fatigue properties, which are high strength. That is, as overhead power transmission lines are increasingly being installed over long distances in mountainous areas, the overhead lines tend to be longer spans and have height differences unique to mountains, resulting in extremely high overhead line tension. In order to increase the power transmission capacity in order to meet the increasing demand for electricity, the diameter of ACSR has been increased, and the weight of the overhead wires has increased, resulting in a significant increase in the tension of the overhead wires. Due to the intense wind and snow that is typical of mountainous areas, increasing the diameter causes an increase in tension due to ice and snow accumulation and wind pressure, as well as an increase in complex dynamic tension loads due to various vibrations and the like. Furthermore, in order to increase the above-mentioned power transmission capacity, high power transmission (for example, high voltage transmission of 75 to 1 million KV) is performed, so the temperature of ACSR due to Joule heat increases sharply (sometimes reaching 400 to 500 degrees Celsius).
Therefore, it is necessary to increase the tensile strength and improve fatigue properties, and it is also desired to ensure tensile strength in a high temperature range (hereinafter referred to as high temperature strength). In addition, current ACSR is designed as a composite stranded wire of the steel core wire and the Al stranded wire wound on the outside so that tension acts on both.
Some are designed so that the aluminum strands are freed from sharing the tension and the steel core wire alone carries the tension. However, the former type of ACSR with multiple tension sharing
However, due to temperature rise during power transmission, cases are often experienced in which the steel core wire actually bears most of the total tension, so almost all of the mechanical properties of ACSR are determined by the steel core wire. It is no exaggeration to say that it depends on the characteristics of Conventionally, the steel core wire of ACSR mentioned above is
Galvanized steel stranded wire as specified in JISG3537 is used, but such conventional steel wire has not only tensile strength but also fatigue properties and other mechanical properties that are not subject to recent harsh conditions such as those mentioned above. It is simply impossible to satisfy the requirement to withstand the usage conditions. The present inventors previously published a patent application No. 57-3607 (``High tensile strength steel wire for steel core of steel core Al stranded wire'').
A new steel composition for ACSR was proposed. According to it, the tensile strength exceeds that of wire compared to conventional galvanized steel.
A high-strength steel wire for an ACSR steel core, which has both winding and unwinding characteristics, extremely good fatigue strength, and high-temperature strength, and satisfies the following (a) to (d) can be obtained. (a) In order to increase the tensile strength of overhead wires, the standard tensile strength of steel wires will be increased to 130 to 260 Kgf/ ^mm2 . (b) To ensure safety under harsh usage environments, the fatigue strength is higher than before, and the fatigue limit ≦ tensile strength (TS) × 0.19. (c) In order to ensure safe tension when the ACSR temperature rises during normal and abnormal conditions,
-450℃) tensile strength is as follows. TS _(T) ≧TS _(R) × (1.42−0.0028T) Preferably TS _(T) ≧T _(R) × (1.29−0.0019T) However, TS (T): TS TS _{(S )} : TS at room temperature (d) When manufacturing ACSR or constructing overhead line work,
In order to prevent breakage and cracking, the winding and unwinding characteristics are higher than conventional ones, and in a winding test where the winding curvature radius is 3.0 times the wire radius, preferably 1.5 times the wire radius, no breakage or cracks occur. The probability (hereinafter referred to as defective rate) shall be 50% or less. The present invention aims to further improve the fatigue strength of such high-tensile steel wire, and its features are as follows: C: 0.6 to 1.2%, Si: 2% or less, Mn: 2% or less, Al: 0.1% or less, and Cr: 5 if necessary
% or less, the remainder consists of Fe and unavoidable impurities, and the impurities are P, S, N and oxygen: P≦0.025% S≦0.015% P+S≦0.03%, N
≦0 005% Oxygen ≦0.002% Steel having a steel composition that satisfies the following conditions, the thickness of the Fe-Zn alloy layer is 15 μm or less, the tensile strength is 180 Kgf/mm ² or more, and the fatigue strength is 40 Kgf/mm ² or more High tensile strength Zn plated steel wire for steel core with Al stranded wire. The plated steel wire of the present invention is produced by subjecting a wire rod made of a material having the above-mentioned steel composition to an austenitic structure by subjecting it to a patenting process, and after pearlitic transformation, pickling and lubrication treatment, and then wire drawing. ) Can be produced by immersion galvanizing at a bath temperature of 15 seconds or less at a bath temperature of 450°C or higher. In addition, in order to further improve dynamic properties such as fatigue strength, (i) the austenite grain size of the austenite structure is set to 20 to 60 μm, and the area reduction rate during the wire drawing is set to 70 to 95%. (ii) The lamella spacing of the pearlite structure obtained by the pearlite transformation is 0.2 μm or less, and the area reduction rate during the wire drawing process is 70 to 95%; (iii) The patent lengthening process is a lead patenting process, and the lead patenting process is managed so that the decarburization state of the wire surface layer after the lead patenting process is such that the total decarburization depth is ≦150μm and the ferrite decarburization depth is ≦50μm, (iv ) The lubrication treatment prior to the wire drawing process is performed using a zinc phosphate base lubricant, and the amount of the lubricant applied is 3 to 7 g/m ² , and (v) After the immersion galvanizing treatment 5 Within seconds, obtained
When the Zn-plated steel wire is water-cooled, it is preferable to carry out the following in an appropriate combination. Thus, according to the invention, the tensile strength is 180Kg
f/mm ² or more, fatigue strength 40Kgf/mm ² or more, which meets the current requirements as already mentioned.
A Zn-plated steel wire is obtained. The reasons for limiting the ingredients in the present invention will be described in detail below. C: A useful component for securing the tensile strength necessary for high-tensile steel wires that require heat resistance. If it is less than 0.6%, the target strength of 180 Kgf/mm ² or more cannot be achieved, and if it is 1.2%. If it exceeds this, the winding and unwinding characteristics will be adversely affected, so it was set at 0.6 to 1.2%. Si: It is an effective component for increasing fatigue properties and high-temperature strength in high-carbon high-tensile steel wires, but if it exceeds 2%, the ductility decreases significantly and the winding and unwinding characteristics are adversely affected, so 2% The following was made. Mn: Effective for improving the tensile strength of large-diameter steel wires, but when added in large amounts, the pearlite becomes coarse and the strength actually decreases. If it exceeds 2%, it becomes difficult to secure the necessary tensile strength, so it is set to 2% or less. Al: Effective as a deoxidizing material for steel, and in the present invention, it is set at 0.1% or less in order to perform sufficient deoxidation. P: A component that has a significant influence on the winding and unwinding characteristics.In high carbon steel, where the winding and unwinding characteristics deteriorate as the tensile strength increases, this deterioration can be prevented and the necessary winding can be achieved. In order to ensure good loading and unwinding characteristics, it is necessary to suppress the amount of P to an extremely low level. Generally, P exists in a relatively large amount in high carbon steel due to P returned from slag during refining, but
If it exceeds 0.025%, it becomes difficult to secure the above-mentioned necessary winding and unwinding characteristics, so it is set to 0.025% or less. S: A component that has a significant influence on the winding, unwinding properties and fatigue properties, and in high carbon steel, where the winding, unwinding properties and fatigue properties deteriorate as the tensile strength increases, these deterioration In order to prevent this and ensure the necessary winding, unwinding and fatigue characteristics,
It is necessary to suppress the amount of S to an extremely low level. The amount of S in ordinary high carbon steel is about 0.02%,
If it exceeds 0.015%, it will be difficult to secure the above-mentioned necessary winding, unwinding and fatigue characteristics.
It was set to 0.015% or less. P+S: If it exceeds 0.03%, it may be difficult to ensure both the necessary winding and unwinding characteristics and the necessary fatigue characteristics, so it is set to 0.03% or less. Further, in order to further improve winding and unwinding characteristics and fatigue characteristics, the content is preferably 0.028% or less. N: A component that has a large influence on winding and unwinding characteristics, and a lower N is desirable. Especially tensile strength (TS)
If it exceeds 0.005%, winding and unwinding characteristics may be extremely deteriorated when the amount is 180 Kgf/mm ² or more, so it is set to 0.005% or less. Oxygen: A component that has a large influence on both winding and unwinding characteristics and fatigue characteristics. If it exceeds 0.002%,
The failure rate in a winding test with a diameter 3.0 times the wire diameter exceeds 50%, and the fatigue limit of a high carbon steel wire with a tensile strength (TS) of 180 Kgf/ ^mm2 or more cannot achieve the above TS x 0.19. , 0.002% or less.
In addition, if it is 0.002 to 0.0010%, the defective rate in the above 3.0 diameter winding test will be 0% and 1.5%.
If the defective rate in the double diameter winding test is improved to 50% and is 0.0010% or less, the defective rate in the above 1.5 times diameter winding test is improved to 30% or less, so the lower one is possible. is a preferred component. Cr: An element added as necessary to improve the tensile strength, especially the tensile strength of large diameter steel wires. Cr is thus an effective component for improving tensile strength, and is particularly effective in large-diameter steel wires, and the addition of Cr also provides significant high-temperature strength. However, if it exceeds 5%, it becomes difficult to secure the necessary winding, unwinding and fatigue characteristics, so it is set at 5% or less. Next, in the present invention, Fe after galvanizing
- The thickness of the Zn alloy layer is limited to 15 μm or less, which is in contrast to the Fe-Zn alloy layer of conventional products, which has a thickness of 20 to 25 μm. It is preferable to make it as small as possible in order to improve fatigue strength. In particular, by regulating the steel composition as described above, the fatigue strength can be increased to 40 kgf/mm ² or more.
Preferably, it is synergistically improved by, for example, 44 Kgf/mm ² or more. To limit the thickness of the Fe-Zn alloy layer to 15 μm or less, the plating bath temperature can be lowered or the immersion plating time can be shortened, but in general, the plating bath temperature It is sufficient to control the temperature to 450℃ or less and the immersion plating time to 15 seconds or less. However, in order to stabilize the melting of the galvanizing bath, the temperature of the galvanizing bath should be at least 10°C above the melting point of zinc. Figure 1 is a graph that generally shows the relationship between the thickness of the Fe-Zn alloy layer and fatigue strength for Zn-plated steel wires with the following steel compositions, based on data obtained through a series of experiments. Figure 2 is a similar graph showing the relationship between the thickness of the Fe-Zn alloy layer and the immersion time in the plating bath. The cases where water cooling was applied 4 seconds after plating at 450°C are indicated by △.) And Figure 3 is a similar graph showing the relationship with bath temperature (in the figure, the subscripts are immersion time (sec),
The three curves have immersion times (t) of 9 seconds, 15 seconds, and
This is a diagram of the relationship in the case of 30 seconds. ). Steel composition C Si Mi Al P S N O 0.82 0.27 0.75 0.034 0.017 0.010 0
.004 0.001 As is clear from the data shown in Figures 1 to 3, in order to obtain a fatigue strength of 40Kgf/mm ² or more,
The thickness of the Fe-Zn alloy layer is 18 μm or less, preferably
Particularly critical improvements have been made by limiting the bath temperature to 450 μm or less.
It is desirable for purposes of the present invention to limit the temperature to below 0.degree. C. and the immersion time to 15 seconds or less. In other words, if these two conditions are taken into account, the thickness of the Fe--Zn alloy layer can be controlled with a practical level of precision. Next, after being immersed in a plating bath for 12 seconds, the specimens were left to cool after various periods of time, and the formation of the alloy layer was examined. The results are shown in Figure 4. The growth of the alloy layer is the thickness
It can be seen that up to 15 μm, the process is almost completed in 5 seconds. That is, in order to prevent the formation of an alloy layer by water cooling after plating, it is necessary to perform water cooling within 5 seconds after plating. By the way, in order to prevent steel wire from breaking or cracking during ACSR manufacturing or overhead line construction, we have made the twisting characteristics higher than before, and in a twisting test with a grip spacing 100 times the wire diameter, no breakage or cracking occurred. The number of twists (hereinafter referred to as twist value) required to occur is required to be, for example, 20 or more times. Therefore, in a preferred embodiment of the present invention, the austenite grain size of the austenite structure obtained by performing the patenting treatment is set to 20 to 60μ.
It is desirable to further improve the dynamic fatigue properties by setting the wire to m and/or setting the lamella spacing of the pearlite structure to 0.20 μm or less, and setting the area reduction rate during wire drawing to 70 to 95%. In order to improve fatigue strength, it is better to have a smaller austenite grain size, but if the grain size is too small, the twisting properties will actually deteriorate. Therefore,
In the present invention, the austenite grain size is preferably 20~
The range is 60μm. Note that, conventionally, the austenite grain size is generally about 100 μm. Figure 5 is a graph that generally shows the relationship between pearlite lamella spacing (μm) and twist value (turns) when manufacturing Zn-plated steel wire with the same steel composition as above, based on a series of experimental data. It is. The austenite grain size at this time was approximately 97 μm. twist value
It can be seen that in order to achieve 20 times or more, it is necessary to set the lamella spacing to 0.24 μm or less, preferably 0.20 μm or less. The austenite grain size and pearlite lamella spacing can generally be adjusted by appropriately adjusting the steel type components and manufacturing conditions. For example, lead patenting treatment is performed by appropriately controlling the heating rate, heating temperature, heating time, and lead bath temperature. In addition, instead of the lead patenting described above, various other patenting processing methods (for example, various direct patenting processing methods in which controlled cooling is performed after hot rolling) are used, and the composition of the steel and the hot rolling conditions are further adjusted and optimized. It can also be carried out by a method such as a controlled rolling method, used alone or in combination of two or more, and by appropriately controlling the respective conditions.
Such means for adjusting the austenite grain size and pearlite lamella spacing will be obvious to those skilled in the art. Note that the wire drawing processing rate, expressed as the area reduction rate of the steel wire, is less than 70%, and the tensile strength of carbon steel and low alloy steel with C content of 0.6 to 1.2% is 180Kgf/
mm ² and the target value of durability ratio
It becomes difficult to achieve 0.19. Also, the wire drawing processing rate is 95%
If the
When the value is lower than 0.18, there is also an adverse effect on the winding and unwinding characteristics. Similarly, if it exceeds 95%, uniform twisting will not proceed in the twisting test, and abnormal breakage may occur at an extremely low number of twists, which is undesirable. In a preferred embodiment of the steel wire manufacturing method of the present invention,
A lead patenting process is used as the patenting process, and the degree of decarburization of the surface layer of the wire after the lead patenting process is largely related to the quality of the fatigue strength. In other words, lead patenting is a process that increases the deformability of the wire and makes it easier to draw.It is generally held at 900 to 1000°C in a heating furnace for about 1 hour, and then cooled in a lead bath at 530°C. However, when subjected to this lead patenting, the decarburized state of the wire is such that the outermost layer is a ferrite decarburized layer that does not contain any carbide, and below that a ferrite decarburized layer that contains some carbide, so to speak. The decarburized layer appears to be expanding. The depth of the above ferrite decarburization is indicated by the symbol DmF, while the total decarburization depth including the incomplete decarburized layer is indicated by the symbol DmT. These two decarburization indexes and the fatigue strength of Zn-plated steel wire The relationship between the two is as shown in FIGS. 6 and 7. The steel composition at this time is as described above, and the bath temperature
This is experimental data on a Zn-plated steel wire obtained by immersion Zn-plating at 450°C for 12 seconds. In the illustrated example,
40Kg if total decarburization depth exceeds 150μm or ferrite decarburization depth exceeds 50μm
Fatigue strength of f/mm ² or higher cannot be obtained. In the case of the example shown in FIG. 6, the DmF was 10 μm. In the case of FIG. 7, DmT was 150 μm. Therefore, in a preferred embodiment of the method of the present invention employing lead patenting treatment, DmT≦150 μm and
Must be DmF≦50μm. Decarburization management as described above can be achieved by adjusting the setting of processing conditions in the lead patenting process. This can be done by controlling the combination of heating temperature and holding time, as well as the atmosphere (air-fuel ratio, etc.).
In general, if you lower the heating temperature, shorten the holding time, and reduce the O ₂ component in the atmosphere,
Although decarburization is suppressed in each case, the adoption of such a method for managing decarburization as described above as one preferred embodiment of the present invention prevents lead patenting from achieving its original purpose. There is no need to worry about something like this happening. Conventionally, for this type of Zn-plated steel wire, DmT exceeds 150 μm and is about 170 to 200 μm, and DmF also usually exceeds 50 μm to about 60 to 70 μm. The wire thus obtained is subjected to a lubrication treatment prior to wire drawing. Here, lubrication treatment generally refers to the first step after lead patenting and pickling.
A zinc phosphate-based base lubricant, such as Bonderite (trade name: Nippon Parker Co., Ltd.), is applied by dipping or the like, and a sodium stearate-based lubricant, such as Bondaryuve (same as above), is applied on top of this. A layer of sodium stearate is formed between the two layers. Regarding lubrication treatment, the present inventors have found that the durability ratio exhibits the best value when the amount of base lubricant attached is 7 g/m ² or less. On the other hand, if the amount of the base lubricant applied is less than 3 g/m ² , the original function of lubrication will be impaired and there will be a risk of seizure during wire drawing. In addition, in the conventional method, the amount of the base lubricant deposited is 10 g/m ² or more, and excellent fatigue properties cannot be expected with this. Conventionally, the application of such lubricant has generally been carried out with the sole purpose of preventing seizing during wire drawing, and for this reason, from the standpoint of safety, the amount of lubricant applied has been greater than necessary, at 10 g/m ² or more. It was. Next, the present invention will be further explained with reference to Examples. Example 1 Four steel types No. 1 to 18 having the steel composition shown in Table 1 were used.
It was melted in an electric furnace and hot rolled into a wire rod with a diameter of 8.0 mm. This wire was heated to 900°C and subjected to lead patenting treatment. A patented material was obtained in which the austenite grain size during patenting was 30 μm, the lamella spacing of the pearlite structure after patenting was 0.15 μm, the total decarburized layer depth (DmT) was 50 μm, and the ferrite decarburized layer depth was zero. Next, after pickling, lubrication treatment was performed so that the amount of zinc phosphate coating as a base lubricant was 6 g/ ^m2 , and the diameter
Continuously drawn to 3.11mm wire (area reduction rate = 85.9
%). Zinc immersion plating was carried out at a Zn plating bath temperature of 450° C., immersion plating time of 12 seconds, and water cooling after 4 seconds of plating. Table 2 summarizes the mechanical properties of each steel sample. From the same table, it can be seen that the mechanical properties of the steel of the present invention are clearly superior to each comparative steel.

【table】

【table】

【table】 [Brief explanation of the drawing]

Figure 1 is a graph generally showing the relationship between the thickness of the Fe-Zn alloy layer and fatigue strength in Zn-plated steel wire; Figure 2 is a graph showing the relationship between the thickness of the Fe-Zn alloy layer and the immersion time in the plating bath. Figure 3 is a similar graph showing the relationship between Fe-Zn alloy layer thickness and bath temperature; Figure 4 is a similar graph showing the relationship between Fe-Zn alloy layer growth and cooling time. Figure 5 is a graph showing the relationship between the lamella spacing of the pearlite structure before wire drawing and the torsion value; Figure 6 is the graph showing the relationship between the total decarburization depth by lead patenting treatment and the steel obtained at that time. A graph showing the relationship between the line and the fatigue strength; and a seventh
The figure is also a graph showing the relationship between decarburization depth and fatigue strength of ferrite.

Claims (1)

[Claims] 1 C: 0.6 to 1.2%, Si: 2% or less, Mn: 2%
Hereinafter, Al: 0.1% or less, the balance consists of Fe and unavoidable impurities, and the impurities of P, S, N and oxygen are P≦0.025%, S≦0.015%, P+S≦0.03%,
It has a steel composition that satisfies the following conditions: N≦0.005%, oxygen≦0.002%, and has a tensile strength of 180Kg.
f/mm ² or more, fatigue strength 40Kgf/mm ² or more,
A high-strength Zn-plated steel wire for use in a steel core Al stranded wire, which is a Zn-plated steel wire, characterized in that the thickness of the Fe-Zn alloy layer of the plating coating is 15 μm or less. 2 C: 0.6-1.2%, Si: 2% or less, Mn: 2%
Hereinafter, Al: 0.1% or less, Cr: 5% or less, the balance consists of Fe and unavoidable impurities, P, S, N and oxygen as impurities are P≦0.025%, S≦0.015%, P+S ≦0.03%,
It has a steel composition that satisfies the following conditions: N≦0.005%, oxygen≦0.002%, and has a tensile strength of 180Kg.
f/mm ² or more, fatigue strength 40Kgf/mm ² or more,
A high-strength Zn-plated steel wire for use in a steel core Al stranded wire, which is a Zn-plated steel wire, characterized in that the thickness of the Fe-Zn alloy layer of the plating coating is 15 μm or less.