Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/001—Heat treatment of ferrous alloys containing Ni
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
  • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/54—Furnaces for treating strips or wire
  • C21D9/56—Continuous furnaces for strip or wire
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
  • C22C38/105—Ferrous alloys, e.g. steel alloys containing cobalt containing Co and Ni
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt

Definitions

• the present invention relates to an invar type alloy wire and, more specifically, to an invar type alloy wire excellent in toughness, strength and low thermal expansion property which can be used preferably as strands for overhead conductor cables.
• An invar alloy having the composition of Fe-36 wt% Ni has been known as an alloy having low thermal expansion property, which is used for precision parts, for example. Meanwhile, in order to increase transmission capacity of an aluminum cable steel reinforced (ACSR) as overhead conductor cable, a method of reducing slack of conductor cable caused by increase in temperature during power transmission has been studied. One method has been known in which an alloy wire having low thermal expansion property is used as a steel core to reduce slacking. An invar type alloy wire such as disclosed in Japanese Patent Laying-Open No. 55-119156 has been developed as such alloy wire having low thermal expansion property.
• the alloy wire developed in accordance with Japanese Patent Laying-Open No. 55-119156 is a hard material and exhibits tensile strength of 120 kg/mm 2 . However, it exhibits low toughness property stability such as turns of twisting after it has been finally subjected to zinc or zinc alloy plating, thereby reducing production yield of conductor cables.
• Zinc alloy plating or the like is applied to improve corrosion resistance of the conductor cable.
• an intermetallic compound formed at the interface with the plating tends to lower the twisting property of the alloy wire.
• an object of the present invention is to improve toughness of a conventionally used invar type alloy wire having high strength, and, more particularly, to improve twisting property of the wire in the final wire size.
• the invar type alloy wire in accordance with one aspect of the present invention contains Fe and Ni as main alloy elements, wherein areal ratio of precipitates existing at grain boundary of the wire in the final wire size after processing is at most 4 %, and the wire has superior toughness, strength and low thermal expansion property.
• the precipitates are often carbide.
• the invar type alloy wire in accordance with another aspect of the present invention contains Fe and Ni as main alloy elements, wherein average grain size in transverse direction of the wire in the final wire size after processing is within a range of 1 to 5 ⁇ m, and it has superior toughness, strength and low thermal expansion property.
• a method of manufacturing an invar type alloy wire excellent in toughness, strength and low thermal expansion property in accordance with a still another aspect of the present invention includes the steps of preparing an invar type alloy containing Fe and Ni as main elements, performing hot working and heat treatment in combination to reduce areal ratio of precipitates existing at the grain boundary of the alloy to be at most 2 %, and thereafter, performing cold working and heat treatment in combination to reduce areal ratio of precipitates existing at the grain boundary of the alloy in the final wire size of the wire to be at most 4 %.
• the method of manufacturing an invar type alloy wire excellent in toughness, strength and low thermal expansion property in accordance with a still further aspects of the present invention includes the steps of preparing an invar type alloy containing, as main elements, Fe and Ni, performing hot rolling and heat treatment in combination to process the alloy to a rod shape and to make average grain size in longitudinal direction of the rod to be within the range of 5 to 40 ⁇ m, and thereafter performing cold working and heat treatment in combination to make average grain size in transverse direction of the wire in final wire size to be within the range of 1 to 5 ⁇ m.
• the areal ratio of the precipitates existing at the grain boundary of the wire in the processed final wire size is at most 4 %, and hence twisting property of the wire is improved. Especially when the areal ratio of the precipitates existing at the grain boundary of the wire in the final wire size is at most 2 %, twisting property and reliability of the wire can be remarkably improved.
• the average grain size in the transverse direction of the wire in the processed final wire size is 1 to 5 ⁇ m, and hence twisting property of the wire is improved. Especially when the average grain size in the transverse direction of the wire in the final wire size is within 1.5 to 4 ⁇ m, the twisting property and the reliability of the wire can significantly be improved.
• the areal ratio of the precipitates existing at the grain boundary of the alloy can be set to be at most 2 % by the combination of hot working and heat treatment, and therefore by the subsequent combination of cold working and heat treatment, the areal ratio of precipitates existing at the grain boundary of the alloy in the final wire size can be easily set to be at most 4 %, and hence an invar type alloy wire having superior twisting property can be provided.
• the areal ratio of the precipitates existing at the grain boundary of the alloy is set to be at most 1 to 5 % by the combination of hot working and heat treatment
• the areal ratio of the precipitates existing at the grain boundary of the alloy in the final wire size can be easily set to be at most 2 % by the subsequent combination of cold working and heat treatment, and hence an invar type alloy wire having significantly improved twisting property can be provided.
• the alloy is processed to a rod shape by the combination of hot working and heat treatment, and the average grain size in the longitudinal direction of the rod is set to be within the range of 5 to 40 ⁇ m. Therefore, by the subsequent combination of cold working and heat treatment, the average grain size in the transverse direction of the wire in the final wire size can be easily set to be within the range of 1 to 5 ⁇ m, and hence an invar type alloy wire having superior twisting property can be provided.
• a conventionally used invar type alloy wire having high strength contains, as main elements, Fe and Ni, and Co may partially substitute for Ni.
• such an invar type alloy wire having high strength contains at least one of Mo, Cr, C, W, Nb, Ti, V, Si or the like as strengthing element, and in addition, at least one of Mn, Al, Mg, Ti, Ca or the like as a deoxidizer.
• the inventors performed various investigations to eliminate instabilizing factors related to the toughness of such invar type alloy wire having high strength. As a result, it was found that crystal grain size of the wire, the amount of precipitates at the grain boundary and amount of specific impurity elements have significant effects on the toughness of the wire. It was also found that there is a preferable method of processing and heat treatment for controlling the grain size and the amount of precipitates at the grain boundary.
• the precipitates at the grain boundary here are often carbide.
• any of the following methods may be used: a method in which during hot rolling, cooling is started from solid solution temperature (cooling from the solid solution temperature may be considered to be a kind of heat treatment); a method in which solution heat treatment is performed prior to hot rolling; and a method in which solution heat treatment is performed after hot rolling.
• the smaller the amount of precipitates at the grain boundary after the combined hot working and heat treatment the smaller the amount of precipitates at the grain boundary precipitated during subsequent cold working and heat treatment, and therefore the smaller the amount of precipitates existing at the grain boundary in the wire in the final wire size.
• Table 1 Element C Mn Ni Co Cr Mo P S O N Fe Wt % 0.25 0.30 35.0 3.01 0.98 2.01 0.002 0.001 0.0015 0.0013 remaining part
• Table 2 shows the influence of the temperature at which rolling is started and the rate of cooling during rolling until the temperature reaches 600°C when the invar type alloy shown in Table 1 is subjected to hot rolling, on the average grain size in the longitudinal direction of the rod after rolling and on the areal ratio of the precipitates at the grain boundary.
• the rolled rod was cut along the longitudinal direction, the cut surface is polished and etched for 40 seconds by using 5 % nital solution, and the surface was photographed with the magnification of 4000 by using a scanning type electron microscope.
• the microphotograph was processed by an automatic image processing apparatus, the areal ratio of the precipitates existing at the grain boundary was calculated, and the average grain size in the longitudinal direction was calculated.
• the average grain sizes in the longitudinal direction of samples A, B and C of which rate of cooling during hot working was relatively fast are within the range of 5 to 40 ⁇ m, and the areal ratio of the precipitates at the grain boundary is at most 2.0 %. Meanwhile, the grain sizes of samples D and E of which cooling rate during hot working was slow are far greater than 40 ⁇ m, and the areal ratio of precipitates at the grain boundary exceeds 2.0 %.
• a billet having a square cross section of about 120 x 120 mm 2 was passed through a plurality of shaping rolls and rolled to be a rod having a circular cross section of about 12 mm in diameter.
• the samples softened by the second heat treatment were drawn to have the diameter of about 2 to 5 ⁇ m with the degree of processing of about 85 %, by passing through a plurality of dies, and thereafter the samples were dipped in Zn-5 wt % Al alloy melt.
• the average grain size in the transverse direction, areal ratio of precipitates at the grain boundary and various mechanical properties of the wires having final wire size obtained through these steps are as shown in Table 3.
• samples 1A to 1E are the samples obtained from samples A to E of Table 2.
• the samples 1A to 1E all have similar tensile strength exceeding the target property of 120 kg/mm 2 .
• comparative examples 1D and 1E are inferior in twisting property and elongation as compared with samples 1A, 1B and 1C in accordance with the present invention.
• the twisting property is represented by the number of possible twisting (turns/100d) at about 60 rpm of a single wire having the length one hundred times the diameter d until it breaks.
• the reference character ⁇ represents standard deviation of the turns of twisting of one hundred wires. The smaller the value ⁇ , the higher the reliability, as the twisting property is stable.
• the samples 1A and 1B of which areal ratio of precipitates at the grain boundary is at most 2.0 % and average grain size in the transverse direction is within the range of 1.5 to 4 ⁇ m have superior twisting property exceeding 100 turns, and they have high reliability as represented by the standard deviation ⁇ of at most 10.
• the sample 1C of which areal ratio of the precipitates at the grain boundary exceeds 2 % but not higher than 4 % and the grain size in the cross sectional direction is within a range of 1 to 5 ⁇ m but not higher than 1.5 ⁇ m has slightly inferior twisting property as compared with samples 1A and 1B. However, it can still satisfy the target property in 3 ⁇ management.
• samples 1A to 1E are obtained by performing same cold working and heat treatment on the hot worked samples A to E of Table 2. If would be understood that in order to obtain preferable twisting property, it is preferable that the areal ratio of the precipitates at the grain boundary in the rod after hot working is at most 2 % and the grain size in the longitudinal direction is within the range of 5 to 40 ⁇ m.
• Table 4 shows influence of the degree of processing of the first cold working and the temperature of immediately following first heat treatment on the areal ratio of the precipitates at the grain boundary and various mechanical properties of the wires in the final wire size.
• first cold working with various degrees of processing and first heat treatment at various temperatures were performed on sample A of Table 2.
• the processes after the first heat treatment are the same as those described with reference to Table 3.
• Samples 1A to 7A all have similar tensile strength higher than the target property of 120 kg/mm 2 .
• samples 1A to 6A belonging to the present invention of which areal ratio of the precipitates at the grain boundary in the final state is at most 4 % can satisfy the target value of the twisting property ( ⁇ 16 turns/100d) even under 3 ⁇ management
• sample 4A is processed with the degree of processing of the first cold working being 80 %, exceeding 70 %, and hence the areal ratio of the precipitates at the grain boundary of the final state exceeds 2 %, though not higher than 4 %. Therefore, it is inferior to samples 1A to 3A in twisting property and elongation.
• the degree of processing of the first cold working should more preferably be at most 70 %.
• temperature of the first heat treatment was 570°C, which was not higher than 600°C. Therefore, the amount of precipitates at the grain boundary was small.
• the strain in the wire is not sufficiently removed, the turns of twisting vary as compared with samples 1A to 3A, and as a result, average turns of twisting is low and elongation is degraded.
• the temperature for the first heat treatment should more preferably be at least 600°C.
• the temperature for the first heat treatment should preferably be in the range of 600°C to 700°C.
• Table 5 shows influence of hot working, cold working and heat treatment on the average grain size in the transverse direction of the wire and twisting property of the wire in the final wire size.
• the alphabets (A) to (E) appended to the sample numbers of Table 5 represent that the samples are obtained by performing first cold working, first heat treatment, scraping, second cold working and Zn-5 wt % Al alloy plating on the hot worked samples A to E of Table 2.
• the temperature for the first and second heat treatments before and after scraping is set to be the same temperature.
• samples 11 to 14 belonging to the present invention of which average grain size in the transverse direction in the final wire size is within the range of 1 to 5 ⁇ m can satisfy the target value of twisting property ( ⁇ 16 turns/100d) even at the 3 ⁇ management.
• comparative examples 15 to 17 of which grain size in the transverse direction is out of the range of 1 to 5 ⁇ m cannot satisfy the target value of twisting property at 3 ⁇ management.
• the degree of processing in the first cold working was 80 %, which is higher than 70 %, so that the grain size in the transverse direction at the final state exceeds 4 %, though not higher than 5 %, and twisting property is inferior to samples 11 to 13. Therefore, the degree of processing of the first cold working should desirably be at most 70 %.
• the small grain size in the transverse direction of comparative example 15 may be related to small grain size in the longitudinal direction of sample C in Table 2.
• sample C has relatively large areal ratio of the precipitates at the grain boundary, and areal ratio of the precipitates at the grain boundary at the final wire size of sample 15 was increased to 4.4 %, even though the temperatures for the first and second heat treatments were relatively low.
• Table 7 shows various mechanical properties at the final wire size of the invar type alloy wires having such compositions as shown in Table 6.
• the rolled rods which were hot worked were all subjected to a first cold drawing of 22 %, scraping, heat treatment at 650°C for 10 hours, a second cold drawing of 86 % and plating with Zn-5 wt % Al alloy.
• samples 21 to 27 all have similar tensile strength exceeding the target value of 120 kg/mm 2 . However, it is apparent that comparative examples 24 to 27 are inferior in twisting property and elongation as compared with the samples 21 to 23 belonging to the present invention.
• samples 21 to 23 belonging to the present invention containing P of at most 0.01 percent by weight, S of at most 0.004 percent by weight, O of at most 0.005 percent by weight and N of at most 0.008 percent by weight have superior twisting property.
• samples 21 and 22 which include P of at most 0.005 percent by weight, S of at most 0.002 percent by weight O of at most 0.003 percent by weight and N of at most 0.006 percent by weight only as impurities have superior twisting property and stability (that is, small ⁇ ).
• Comparative examples 24 to 27 all include at least one impurity of P exceeding 0.001 percent by weight, S exceeding 0.004 percent by weight O exceeding 0.005 percent by weight N exceeding 0.008 percent by weight, so that these examples are far inferior in twisting property to the samples 21 to 23 of the present invention, and target value ( ⁇ 16 turns/100d) of the twisting property cannot be achieved.
• toughness, especially twisting property of an invar type alloy wire having high strength can be improved, and by using the same, production yield of overhead conductor cables can be improved.

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• Chemical & Material Sciences (AREA)
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• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Manufacturing & Machinery (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
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• 1995
  • 1995-01-23 JP JP00823695A patent/JP3447830B2/ja not_active Expired - Lifetime
  • 1995-12-01 TW TW084112829A patent/TW344075B/zh not_active IP Right Cessation
• 1996
  • 1996-01-17 DE DE69615874T patent/DE69615874T2/de not_active Expired - Lifetime
  • 1996-01-17 EP EP96100655A patent/EP0723025B1/fr not_active Expired - Lifetime
  • 1996-01-22 KR KR1019960001246A patent/KR100204443B1/ko not_active IP Right Cessation

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