KR100548729B1 - High strength invar alloy - Google Patents

Abstract

The present invention relates to a high strength invar alloy suitable for power transmission lines, in weight%, C: 0.15-0.45%, Si: 0.1-0.35%, Mn: 1.5% or less, Cr: 0.3-2.0%, Ni: 33-38 %, Co: 5% or less, Mo: 0.5 to 4.5%, V: 0.1 to 0.5%, Nb: 0.3% or less, Al: 1 to 5% preferably 2 to 4%, the remainder as Fe and other unavoidable impurities It provides a high strength Invar alloy, characterized in that the composition.

Description

High Strength Invar Alloy {HIGH STRENGTH INVAR ALLOY}

The present invention relates to an Invar alloy used for the core wire of a high-strength transmission line, and more particularly, to the strength improvement of such an Invar alloy.

Invar alloys have a lower coefficient of thermal expansion than other steels and have been widely used in electronic components such as precision measuring instruments, thermostatic bimetals, and shadow masks of color TVs. Since the invention of Invar alloy, Colin, Mo, W, Ti, Al, Cr, C, etc. have been added to the basic composition for the last 100 years to compensate for the elastic change due to temperature changes. Various types of Invar alloys have been developed and used, including Intel (Metelinvar), which combines reinforcement effects, and Fixinvar, which offsets the temporal / dimensional instability, one of the problems of existing Invar alloys. have.

Recently, the demand for electricity is increasing rapidly due to the high economic growth, and the demand for power supply in suburban cities is increasing due to the overcrowding of cities due to industrial expansion. Is required. In order to increase the amount of transmission, it is necessary to install transmission towers for the construction of new transmission lines. In this case, it is difficult to add new transmission lines due to excessive installation cost due to land shortage and land price increase caused by the urbanization near the city. to be.

As an alternative to the increase in power transmission requirements, there is a method of increasing power transmission using existing power transmission lines.However, when power is increased by boosting an existing power transmission line, the temperature of the wire increases and sagging of the wire due to thermal expansion. There is a risk that the height required for safety from ground level cannot be obtained when high voltage current passes. In developed countries, ACIR (Aluminum Conductor) using invar alloy (Invar, 36% Ni-Fe-Co) wire with low thermal expansion coefficient (1/10 of carbon steel) instead of high carbon steel is used in advanced countries. Invar Reinforced) Power transmission lines are used to carry out boosted power transmission by utilizing existing transmission lines.

Therefore, the Invar alloy for high-strength high-voltage transmission lines should have a low coefficient of thermal expansion of 10 ^-6 and a high strength of 1000 MPa or more in the hot rolling state. If the strength is low, the diameter of the wire rod should be increased, which in turn increases the load of the wire rod, which causes a disadvantage of giving a large load to the transmission tower. And when the wind blows badly, especially when a typhoon passes, the larger the diameter of the wire rod, the greater the force acting on the transmission line, such as a disconnection.

Accordingly, an object of the present invention is to provide an Invar alloy with improved strength that can effectively solve the problems of the prior art as described above.

Hereinafter, the present invention for achieving the above object will be described in detail.

In the present invention, by weight%, C: 0.15-0.45%, Si: 0.1-0.35%, Mn: 1.5% or less, Cr: 0.3-2.0%, Ni: 33-38%, Co: 5% or less, Mo: 0.5 ˜4.5%, V: 0.1-0.5%, Al: 1-5%, Nb: 0.3% or less, and provides an Invar alloy, which is composed of the remaining Fe and other unavoidable impurities.

In the preferred heat treatment method for the Invar alloy of the present invention, the alloy prepared as described above is preheated for a predetermined time at 1000-1100 ℃ to ensure a uniform temperature over the entire large ingot, the decomposition treatment of Mo solid precipitate The first homogenization treatment at 1250-1300 ° C. and the second homogenization treatment at 1100-1150 ° C. for faster re-dissolution at Si, effectively decomposes the coarse Mo solids precipitate in the Invar alloy casting and then processes it. Heat treatment is performed to precipitate fine Mo2C carbides which are beneficial for hardening by hardening.

The inventors of the present invention conducted the research to effectively remove coarse precipitates by using an invar alloy casting material for a high-voltage power transmission line, and confirmed the following facts.

(1) Complete redissolution of coarse precipitates occurs at a holding time of 2 hours in the temperature range of 1250-1300 ° C.

(2) Even when kept in the temperature range of 1100-1150 ° C for a long time, a considerable amount of coarse precipitates remain and the strength is higher than that maintained in the temperature range of 1250-1300 ° C.

Therefore, it was found that, with proper attention to the above two facts, the proper homogenization heat treatment procedure can achieve both the complete decomposition of the coarse precipitate and the strengthening effect at the same time.

Invar alloy of the present invention is characterized by being able to achieve both the complete decomposition of the coarse precipitate inherent in the invar alloy ingot material for high-voltage transmission line by a suitable heat treatment, and at the same time, the strengthening effect, the composition limitation range of the alloy to be applied to A suitable heat treatment method will be described.

[Composition Limitation Range of the Alloy of the Invention]

C: 0.15 to 0.45 wt%

The carbon content of the Invar alloy is a factor determined by the contents of the carbide forming elements Mo, V, Nb and Cr, and forms various carbides by combining with various carbide forming elements such as V, Cr, Mo, and Nb. As a necessary basic component, the addition of less than 0.15% by weight is difficult to form a sufficient amount of carbide, and when added in excess of 0.45% by weight lowers the thermal expansion characteristics, it is preferable to limit the content to 0.15 to 0.45% by weight.

Si: 0.1 ~ 0.35 wt%

Said Si is a component added as a deoxidizer and contributes to the improvement of hardness by further increasing carbide precipitation. If the content of Si is less than 0.1% by weight, there is almost no inherent deoxidation effect of Si, and if it is added in excess of 0.35% by weight, the coefficient of thermal expansion on the high temperature side is increased, so that the content is preferably limited to 0.1 to 0.35% by weight. .

Mn: 1.5 wt% or less

The Mn is an austenite stabilizing element, and when added in excess of 1.5% by weight, the thermal expansion coefficient increase transition temperature is lowered, it is preferable to limit the content to 1.5% by weight or less.

Cr: 0.3-2.0 wt%

The Cr is a component having a very high strength improvement effect in Fe-Ni-based alloys, and when the content is less than 0.3% by weight, the reinforcing effect is small. It is preferable to limit to 2.0% by weight.

Ni: 33-38 wt%

Ni has the lowest coefficient of thermal expansion at 36% by weight. If less than 33% by weight or more than 38% by weight is added to the Invar alloy is difficult to use for the transmission line, it is preferable to limit the content to 33 to 38% by weight.

Co: 5.0 wt% or less

Co has the effect of lowering the coefficient of thermal expansion without changing the thermal expansion coefficient increase transition temperature by substituting a part of Ni. However, if it exceeds 5.0% by weight, the effect is saturated and the price is very expensive, so it is preferable to limit the content to 5.0% by weight or less.

Mo: 0.5-4.5 wt%

The Mo is a component added to form a carbide of the M2C type, but the effect of strengthening the Fe-Ni-based alloy, but less than 0.5% by weight is less effective, when added in excess of 4.5% by weight is unnecessary raw material costs Since to increase, it is preferable to limit the content to 0.5 to 4.5% by weight.

V: 0.1-0.5 wt%

The V is added for the formation of MC-type carbide, if less than 0.1% by weight it is difficult to secure sufficient carbide, when it is added more than 0.5% by weight is left in the matrix to reduce the hot workability of the matrix, It is preferable to limit it to 0.1-0.5 weight%.

Al: 1.0-5.0 wt%

The Al combines with Ni to form an intermetallic compound, thereby improving the strength. Less than 1% by weight of the effect is insignificant and the addition of more than 5.0% by weight has a disadvantage in that the elongation is lowered, the content is preferably limited to 1.0 to 5.0% by weight.

Nb: 0.3 wt% or less

Nb is added to form MC in the same manner as V, and when added in an amount of 0.1 wt% or more, it remains in the matrix and degrades hot workability of the matrix. Thus, the content is preferably limited to 0.3 wt% or less.

In addition to the above compositions, the remainder is composed of Fe and other unavoidable impurities.

[Heat treatment method of invention alloy]

The alloy formed as described above is first preheated for a predetermined time at 1000-1100 ° C. in order to ensure a uniform temperature throughout the large ingot. Subsequently, the first homogenization treatment at 1250-1300 ° C. and the second homogenization treatment at 1100-1150 ° C. in order to achieve complete redissolution of the coarse Mo solid solution precipitate are performed. Effective carbide can be effectively distributed.

The reason for the first homogenization treatment in the homogenization treatment temperature range is 1250-1300 ° C. is less than 1250 ° C., in order to re-dissolve the coarse Mo solid solution precipitate produced during casting, it is difficult to apply practically, and 1300 ° C. This is because it is difficult to apply in the field and re-dissolves even carbides effective for improving strength.

The second homogenization temperature is 1100-1150 ℃. If the temperature is less than 1100 ℃, the load of the roll or press hammer increases due to the temperature drop during hot wire rolling or forging. Since it is difficult to nucleate the carbide to help improve the strength to cause a problem to secure the strength in the future, the hot working temperature is preferably limited to 1100 ~ 1150 ℃.

Hereinafter, the present invention will be described through examples.

(Example)

Table 1 shows the composition of the comparative and development materials. The prepared ingot was preheated at 1000 to 1100 ° C. for 2 hours in a heat treatment furnace, and then maintained at 1130, 1200, and 1280 ° C. for 3-9 hours for homogenization.

Table 2 shows the tensile strength characteristics of the hot rolled material, and it can be seen that the strength of the Al-added development material is higher than that of the comparative material.

Table 3 shows the tensile properties after cold rolling of the development material, and the tensile strength can be increased up to 1676 MPa.

<Table 1> Composition of Development and Comparative Materials

division Ni Mo Co Cr C Mn Si Nb V Cu Al [P] [S] [N] [O] Comparison H01 36 2.8 2 0.8 0.32 0.22 0.15 0.06 0.11 0 - -5 -5 -20 -20 H02 36 2.8 2 0.8 0.32 0.22 0.15 0.06 0.11 0.5 - -5 -5 -20 -20 H03 36 2.8 2 0.8 0.32 0.22 0.15 0.06 0.11 One - -5 -5 -20 -20 H04 36 2.8 2 0.8 0.25 0.22 0.15 0.06 0.11 0 - -5 -5 -20 -20 H05 36 2.8 2 0.8 0.4 0.22 0.15 0.06 0.11 0 - -5 -5 -20 -20 H06 34 2.8 2 0.8 0.32 0.22 0.15 0.06 0.11 0 - -5 -5 -20 -20 H07 34 2.8 2 0.8 0.32 0.22 0.15 0.06 0.11 0.5 - -5 -5 -20 -20 H08 34 2.8 2 0.8 0.32 0.22 0.15 0.06 0.11 One - -5 -5 -20 -20 H09 36 2.8 2 0.8 0.32 0.22 0.15 0.03 0.11 0 - -5 -5 -20 -20 H10 36 2.8 2 0.8 0.32 0.22 0.15 0.1 0.11 0 - -5 -5 -20 -20 Dog paw HA1 36 2.8 2 0.8 0.32 0.22 0.15 0.06 0.11 0.5 One - - - - HA2 36 2.8 2 0.8 0.32 0.22 0.15 0.06 0.11 0.5 3 - - - - YA3 36 2.8 2 0.8 0.32 0.22 0.15 0.06 0.11 0.5 5 - - - -

<Table 2> Mechanical Properties of Hot Rolled Sheet Using Comparative and Development Materials

No YS UTS Elong. (%) H01-1 413 1057 42 H01-2 410 1062 43 H01-3 429 1085 43 H02-1 493 1050 34 H02-2 460 1054 37 H02-3 530 1065 31 H03-1 475 1045 34 H03-2 530 1075 33 H03-3 476 1051 34 H04-1 418 978 39 H04-2 436 976 37 H04-3 422 977 39 H05-1 460 1122 40 H05-2 460 1122 38 H05-3 446 1108 38 H06-1 483 1049 34 H06-2 527 1072 35 H06-3 486 1075 35 H07-1 485 1043 34 H07-2 505 1076 36 H07-3 474 1058 37 H08-1 452 1054 38 H08-2 458 1050 37 H08-3 458 1046 38 H09-1 397 1098 49 H09-2 385 1083 46 H09-3 386 1085 48 H10-1 471 1075 37 H10-2 426 1060 40 H10-3 428 1066 40 A1-1 422 1057 52 A1-2 412 1056 51 A1-3 408 1088 53 A2-1 458 1190 53 A2-2 474 1179 54 A2-3 456 1185 56 A3-1 702 1215 20 A3-2 707 1370 29 A3-3 701 1202 20

<Table 3> Tensile Properties after Cold Rolling

No Cold rolling pressure (%) YS (MPa) UTS (MPa) Elong. (%) HA1 50 437 1254.3 13.9 67 1036.5 1313.4 10.4 78 1132.5 1367.9 7.7 HA2 50 363.5 1345.2 15 67 1078 1394.4 9.3 78 1138 1427.7 7.2 HA3 50 393.5 1487.1 9.9 67 450 1537.1 7.7 78 1223.5 1676.3 5.1 HC0 50 442 1223.8 16.2 67 965 1297.1 11.2 78 1077 1353 8

As described above, the invar alloy of the present invention is remarkably improved in strength, and has an effect suitable for high strength transmission lines.

Claims (1)

Invar alloy for power transmission lines, in weight%, C: 0.15 to 0.45%, Si: 0.1 to 0.35%, Mn: 1.5% or less, Cr: 0.3 to 2.0%, Ni: 33 to 38%, Co: 5% or less , Mo: 0.5-4.5%, V: 0.1-0.5%, Nb: 0.3% or less, Al: 1-5%, preferably 2-4%, the remainder is composed of Fe and other unavoidable impurities, The invar alloy is subjected to a preheating treatment in the ingot state, a high-strength invar alloy characterized in that the first homogenization treatment at 1250 ~ 1300 ℃ and the second homogenization treatment at 1100 ~ 1150 ℃ .