JPH0255495B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a low thermal expansion alloy wire that has high strength and high twisting characteristics and is used as a steel core wire for ACSR. Generally, an ACSR has a sagging line called a catenary curve caused by the overhead wires, so it is necessary to leave a certain amount of space around the ACSR, mainly for safety reasons, and there are space constraints, especially in urban areas. Therefore, it was necessary to reduce the sagging as much as possible. Conventional ACSR has a 7-strand high carbon steel core wire for reinforcement, but this core wire has a tensile strength (120Kg/mm2 ^or more).
Although it is excellent in terms of and twist value (20 times or more),
Since the coefficient of thermal expansion is as large as 13×10 ^-6 /°C, it expands greatly due to temperature rise due to power transmission, and tends to cause large sag. In particular, due to the recent increase in power consumption, there has been a demand for an increase in the amount of power transmitted in urban areas, and this has led to the need for ACSRs to have larger diameters. For this reason, the ACSR will sag even more, and the vacant land for the existing tower will have to be expanded accordingly.However, in the current situation, securing land will increase the cost significantly, and the existing ACSR will need to be expanded.
It is considered difficult to increase the diameter of the chisel. Therefore, as a means to reduce drooping,
Attempts have been made to use core wires with a small coefficient of thermal expansion. As an alloy with smaller thermal expansion than conventional ones,
Invar (Fe-36Ni alloy) and Super Invar (Fe-35Ni-2Co alloy) are known, but these have a tensile strength of 100% even after high-strength wire drawing.
Even if the tensile strength is not exceeded by Kg/mm ² and the tensile strength is simply added as a reinforcing measure, the torsion value will be low, and wire breakage will occur during the stranding process when manufacturing the steel core wire.
In practical terms, it is impossible to apply to ACSR due to its low toughness. The present invention was made to eliminate such conventional drawbacks, and provides an alloy wire with excellent tensile strength and twist value. That is, this invention uses Ni: 30 to 45%, Mo: 0.5 to 4.5%,
C: 0.31 to 0.45%, Co: 1 to 10%, the balance being Fe and 0.5% Si, which is usually included as a deoxidizing element.
% or less, Mn is 1% or less and unavoidable impurities, and the relationship between Ni and Co is Co≦8−0.3.
(Ni−35) ² is processed to an area reduction rate of 20 to 50%, annealed to precipitate molybdenum carbide (Mo ₂ C), and then reduced to a predetermined wire diameter. It is designed to be processed to a rate of 70% or more. Ni is 30~40%, Co is 1~10%, Co≦8−
The reason for setting 0.3 (Ni−35) to ² is as follows. In other words, Fig. 1 A shows the Fe-Ni-Co alloy at 0 to 300°C.
The figure shows the change in the average thermal expansion coefficient of Ni.The numerical value of each curve indicates the thermal expansion coefficient (x10 ^-6 /℃)
There is a composition with low thermal expansion around 30-40% and 1-10% Co. FIG. 1B is a partial enlarged view of FIG. 1A, and in order to suppress the thermal expansion coefficient to 3×10 ⁻⁶ /° C. or less, the composition must be within the range of curve 1. Therefore, it is necessary to set the balance between Ni and Co to Co≦8−0.3(Ni−35) ^2, which is the expression of curve 1. When the balance of Ni and Co deviates from this formula,
It is not preferable because the coefficient of thermal expansion exceeds 3.0×10 ^-6 /°C. The lower the C content, the better the coefficient of thermal expansion. However, as shown in Figure 2, if the C content is less than 0.3%, the tensile strength will not reach 130 Kg/mm ² . It is practically impractical. On the other hand, if the C content is too high, the coefficient of thermal expansion will increase, and C will be 0.45
%, the average coefficient of thermal expansion from 0 to 300℃ is 3.5
Since it no longer satisfies ×10 ^-6 /℃, C is 0.31~
It is necessary to specify within the range of 0.45. With regard to Mo, the strength increases with the addition of Mo, and rather than Mo becoming a solid solution in the matrix, in the case of this alloy, it combines with C and precipitates Mo ₂ C carbide, and the precipitation of this carbide causes high twisting. You will be able to obtain the characteristics. Figure 3 shows this situation, and shows the relationship between the Mo content, twist value, and thermal expansion coefficient of a wire with a diameter of 3 mm and a tensile strength of 130 Kg/mm ² or more. Curve 2 shows the torsion value, and curve 3 shows the coefficient of thermal expansion. From this, those with a twist value of 20 times or more and a thermal expansion coefficient of 3.5×10 ^-6 /°C or less are
The Mo content is 0.5 to 4.5%, and if the Mo content is 4.5 or more, the expansion will be large and it will be impractical. Since the coefficient of thermal expansion of Si increases as the content increases, it is necessary to set it at 0.5% or less as required for steel manufacturing, and Mn also needs to be set at 1% or less due to problems in melting. Further, P, S, etc. exist as unavoidable impurities during melting. Examples The alloys shown in Table 1 were rolled into wire rods with a diameter of 12 mm, and after pickling and phosphate coating, the wire rods were processed to a diameter of 9 mm using a wire drawing machine. Thereafter, annealing was performed at 850° C. for 5 hours in an air annealing furnace to remove machining strain and soften the material, and at the same time precipitate Mo ₂ C carbide, resulting in a structure suitable for exhibiting a high torsion value. After annealing, pickling, coating, and expansion and contraction
A wire with a diameter of 3 mm was produced with 89% processing. Table 2 shows the results of measuring the tensile strength, torsion value, and coefficient of thermal expansion of this wire. The reason why light processing is added before annealing in the above process is as follows. Mild (area reduction rate 20-50
%), dislocations (crystal defects) are uniformly introduced into the material, so the subsequent 850
By annealing at ℃, Mo carbides preferentially precipitate on these dislocations. This has the effect of making the distribution of Mo carbides uniform. On the other hand, if light processing is not applied, Mo carbides will preferentially precipitate at grain boundaries, leading to embrittlement of the material. FIG. 4 shows the precipitation characteristics of Mo carbides, where 6 shows the precipitation start line and 7 the precipitation end line, which shows that precipitation is most likely to occur at 850°C.

【table】

[Table] As shown in Tables 1 and 2 above, alloys No. 1 to 4 of the present invention both have a tensile strength of 130 Kg/mm ²
More than 20 twists, thermal expansion coefficient 3.5×
It exhibits characteristics that are highly practical at temperatures below 10 ^-6 /℃. On the other hand, comparative steel No. 5 has a low tensile strength due to its low C content, No. 6 has a low torsion value due to the absence of Mo, and No. 7 has a low tensile strength due to its high Mo content. The expansion coefficient is large, and No. 8 has a low C content, so the tensile strength is less than 120 Kg/mm ² , and both values are poor in practical use. As explained above, this invention sets the balance of Ni-C-Mo-Co appropriately for the steel core wire for ACSR, precipitates Mo ₂ C carbide in the manufacturing process, and creates a metal structure suitable for high twisting. By doing so, the tensile strength is 130Kg/mm2 ^or more, the twist value is 20 times or more, and the
This makes it possible to manufacture wires with an average coefficient of thermal expansion of 3.5×10 ^-6 /°C or less at temperatures up to 300°C. Therefore, by using this, it is possible to increase the cross-sectional area of the ACSR to cope with an increase in the amount of power transmitted without having to rebuild the current transmission tower, and it is possible to increase the diameter and
This makes it possible to suppress the drooping of the ACSR due to temperature rise to the same level as before or to a lower level.

[Brief explanation of drawings]

Figure 1A is a characteristic diagram of the thermal expansion coefficient of Fe-Ni-Co alloy, Figure 1B is a partially enlarged diagram, Figure 2 is a diagram of the relationship between C content and tensile strength, and Figure 3 is Mo content. Figure 4 shows the relationship between the torsion value and thermal expansion coefficient.
It is a precipitation characteristic diagram of Mo carbide. 1... Co-Ni relationship curve, 2... Torsion value curve,
3...Curve of thermal expansion coefficient.

Claims (1)

[Claims] 1 Ni: 35-45%, Mo: 0.5-4.5%, C: 0.31
~0.45%, Co: 1~10%, the balance is Fe and Si, which is normally included as a deoxidizing element, is 0.5% or less.
A rolled wire rod consisting of 1% or less Mn and unavoidable impurities is processed with an area reduction rate of 20 to 50%, annealed to precipitate molybdenum carbide (Mo ₂ C), and then processed to a predetermined wire diameter. A high-strength, high-twist, low-thermal-expansion alloy wire that has been processed with an area reduction rate of 70% or more.