WO2015119247A1 - 鋼線 - Google Patents
鋼線 Download PDFInfo
- Publication number
- WO2015119247A1 WO2015119247A1 PCT/JP2015/053387 JP2015053387W WO2015119247A1 WO 2015119247 A1 WO2015119247 A1 WO 2015119247A1 JP 2015053387 W JP2015053387 W JP 2015053387W WO 2015119247 A1 WO2015119247 A1 WO 2015119247A1
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- WO
- WIPO (PCT)
- Prior art keywords
- steel wire
- less
- pearlite
- wire
- steel
- Prior art date
Links
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 507
- 239000010959 steel Substances 0.000 title claims abstract description 507
- 229910001562 pearlite Inorganic materials 0.000 claims abstract description 120
- 241000446313 Lamella Species 0.000 claims abstract description 111
- 239000000203 mixture Substances 0.000 claims abstract description 16
- 239000012535 impurity Substances 0.000 claims description 13
- 239000004615 ingredient Substances 0.000 claims 1
- 230000007547 defect Effects 0.000 abstract description 10
- 238000010438 heat treatment Methods 0.000 description 99
- 239000002344 surface layer Substances 0.000 description 66
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- 238000005259 measurement Methods 0.000 description 42
- 230000000694 effects Effects 0.000 description 37
- 238000004519 manufacturing process Methods 0.000 description 36
- 230000000052 comparative effect Effects 0.000 description 34
- 238000001816 cooling Methods 0.000 description 29
- 229910001566 austenite Inorganic materials 0.000 description 28
- 238000005491 wire drawing Methods 0.000 description 28
- 229910001567 cementite Inorganic materials 0.000 description 25
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 25
- 230000009466 transformation Effects 0.000 description 24
- 230000032798 delamination Effects 0.000 description 21
- 238000012545 processing Methods 0.000 description 20
- 230000008569 process Effects 0.000 description 18
- 229910052761 rare earth metal Inorganic materials 0.000 description 18
- 150000002910 rare earth metals Chemical class 0.000 description 18
- 239000010410 layer Substances 0.000 description 12
- 229910001369 Brass Inorganic materials 0.000 description 11
- 239000010951 brass Substances 0.000 description 11
- 150000004767 nitrides Chemical class 0.000 description 11
- 238000007747 plating Methods 0.000 description 11
- 229910000859 α-Fe Inorganic materials 0.000 description 11
- 238000000635 electron micrograph Methods 0.000 description 9
- 229920001971 elastomer Polymers 0.000 description 8
- 238000007654 immersion Methods 0.000 description 8
- 229910052804 chromium Inorganic materials 0.000 description 7
- 229910052802 copper Inorganic materials 0.000 description 7
- 238000009826 distribution Methods 0.000 description 7
- 229910001563 bainite Inorganic materials 0.000 description 6
- 229910052796 boron Inorganic materials 0.000 description 6
- 230000007423 decrease Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 229910052750 molybdenum Inorganic materials 0.000 description 6
- 229910052758 niobium Inorganic materials 0.000 description 6
- 238000007670 refining Methods 0.000 description 6
- 239000012779 reinforcing material Substances 0.000 description 6
- 229910052721 tungsten Inorganic materials 0.000 description 6
- 229910052720 vanadium Inorganic materials 0.000 description 6
- 230000009471 action Effects 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 5
- 238000007542 hardness measurement Methods 0.000 description 5
- 238000007373 indentation Methods 0.000 description 5
- 229910052698 phosphorus Inorganic materials 0.000 description 5
- 238000012935 Averaging Methods 0.000 description 4
- 208000010392 Bone Fractures Diseases 0.000 description 4
- 230000002411 adverse Effects 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 229910052748 manganese Inorganic materials 0.000 description 4
- 229910000734 martensite Inorganic materials 0.000 description 4
- 229910052757 nitrogen Inorganic materials 0.000 description 4
- 235000019362 perlite Nutrition 0.000 description 4
- 239000010451 perlite Substances 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 239000000446 fuel Substances 0.000 description 3
- 238000000879 optical micrograph Methods 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 239000012141 concentrate Substances 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 229910052726 zirconium Inorganic materials 0.000 description 2
- 229910001122 Mischmetal Inorganic materials 0.000 description 1
- 239000004677 Nylon Substances 0.000 description 1
- 229920000297 Rayon Polymers 0.000 description 1
- -1 automobile tires Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
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- 230000002349 favourable effect Effects 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229920001778 nylon Polymers 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- OXNIZHLAWKMVMX-UHFFFAOYSA-N picric acid Chemical compound OC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O OXNIZHLAWKMVMX-UHFFFAOYSA-N 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 229920000728 polyester Polymers 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000002964 rayon Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 229910052706 scandium Inorganic materials 0.000 description 1
- SIXSYDAISGFNSX-UHFFFAOYSA-N scandium atom Chemical compound [Sc] SIXSYDAISGFNSX-UHFFFAOYSA-N 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
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- 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
-
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
- B60C9/0007—Reinforcements made of metallic elements, e.g. cords, yarns, filaments or fibres made from metal
-
- 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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- 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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- 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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- 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
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- 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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- 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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- 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
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- 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
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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- 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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- 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
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- 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
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- 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
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
-
- 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
- C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
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- 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
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- D—TEXTILES; PAPER
- D02—YARNS; MECHANICAL FINISHING OF YARNS OR ROPES; WARPING OR BEAMING
- D02G—CRIMPING OR CURLING FIBRES, FILAMENTS, THREADS, OR YARNS; YARNS OR THREADS
- D02G3/00—Yarns or threads, e.g. fancy yarns; Processes or apparatus for the production thereof, not otherwise provided for
- D02G3/44—Yarns or threads characterised by the purpose for which they are designed
- D02G3/48—Tyre cords
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- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B1/00—Constructional features of ropes or cables
- D07B1/06—Ropes or cables built-up from metal wires, e.g. of section wires around a hemp core
- D07B1/0606—Reinforcing cords for rubber or plastic articles
- D07B1/066—Reinforcing cords for rubber or plastic articles the wires being made from special alloy or special steel composition
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B2201/00—Ropes or cables
- D07B2201/20—Rope or cable components
- D07B2201/2001—Wires or filaments
- D07B2201/2014—Compound wires or compound filaments
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- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B2205/00—Rope or cable materials
- D07B2205/30—Inorganic materials
- D07B2205/3021—Metals
- D07B2205/3025—Steel
- D07B2205/3035—Pearlite
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- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B2205/00—Rope or cable materials
- D07B2205/30—Inorganic materials
- D07B2205/3021—Metals
- D07B2205/3025—Steel
- D07B2205/3046—Steel characterised by the carbon content
- D07B2205/3053—Steel characterised by the carbon content having a medium carbon content, e.g. greater than 0,5 percent and lower than 0.8 percent respectively HT wires
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- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B2205/00—Rope or cable materials
- D07B2205/30—Inorganic materials
- D07B2205/3021—Metals
- D07B2205/3025—Steel
- D07B2205/3046—Steel characterised by the carbon content
- D07B2205/3057—Steel characterised by the carbon content having a high carbon content, e.g. greater than 0,8 percent respectively SHT or UHT wires
Definitions
- the present invention relates to a steel wire that is a material of a high-strength steel cord used as a reinforcing material for rubber products such as automobile tires, high-pressure rubber hoses, and conveyor belts.
- steel cords made of chemical fibers such as rayon, nylon, polyester, or steel wires are used as reinforcing materials.
- These reinforcing materials play the role of the framework of automobile tires, and have a great influence on the fuel consumption, high-speed durability, and steering stability of a vehicle equipped with the automobile tires.
- the use ratio of steel cords as a reinforcing material has increased.
- a steel cord having a twisted wire structure in which a plurality of steel strands (filaments) are twisted is widely proposed.
- Such a steel cord is manufactured through the following processes. First, dry drawing is performed on a wire having a wire diameter of 5 to 6 mm to obtain a steel wire having a wire diameter of about 1.0 to 4.0 mm. The steel wire is softened by performing a heat treatment called patenting treatment on the steel wire. Then, brass plating is formed on the surface of the softened steel wire, and wet drawing (finish drawing) is further performed on the steel wire to obtain a filament having a wire diameter of about 0.1 to 0.5 mm. And the steel cord of a strand wire structure is manufactured by carrying out the strand wire process of the filament obtained in this way. The brass plating is formed in order to improve the adhesion between the rubber and the steel cord.
- the present invention has been made in view of the above-described situation, and provides a steel wire having high strength, excellent workability, and capable of stably producing a high-strength steel cord. Objective.
- the gist of the present invention for solving the above problems is as follows.
- a component composition is the mass%, C: 0.70% or more and 1.20% or less, Si: 0.15% or more and 0.60% or less, Mn: 0.10% to 1.00%, N: 0.0010% to 0.0050%, Al: 0% to 0.010%, Ti: 0% to 0.10%, Cr: 0% 0.50% or less, Co: 0% or more and 0.50% or less, V: 0% or more and 0.50% or less, Cu: 0% or more and 0.20% or less, Nb: 0% or more and 0.100% or less , Mo: 0% to 0.20%, W: 0% to 0.200%, B: 0% to 0.0030%, REM: 0% to 0.0050%, Ca: 0% or more 0.0050% or less, Mg: 0% or more and 0.0050% or less, and Zr: 0% or more and 0.0100% or less, the balance being e and impurities, the wire diameter R of
- the thickness of the soft portion may be not less than 10 ⁇ m and not more than 0.08 ⁇ Rmm.
- the average lamella spacing from the surface of the steel wire to the portion having a depth of 5 ⁇ m and the average lamella spacing at the center of the steel wire may be 40 nm or less.
- the component composition is, by mass, Ti: 0.005% or more and 0.10% or less, Cr: more than 0% 0.50% or less, Co: more than 0% to 0.50% or less, V: more than 0% to 0.50% or less, Cu: more than 0% to 0.20% or less, Nb: more than 0% to 0.100% or less, Mo: more than 0% to 0.20% or less, W: more than 0% to 0.20% or less, B: more than 0% to 0.0030% or less, REM: more than 0% to 0.0050% or less, Ca: 0.0005% One or more of more than 0.0050%, Mg: more than 0.0005% and 0.0050% or less, and Zr: more than 0.0005% and 0.0100% or less may be included.
- the steel wire having the above-described configuration has a soft portion, and in this soft portion, the average lamella spacing is finer than that of the center portion of the steel wire, and the average lamella spacing in the center portion of the steel wire and the surface to depth of the steel wire.
- the difference from the average lamella spacing in the 5 ⁇ m region is 60 nm or less.
- the Vickers hardness of the soft part of the steel wire which has the above-mentioned structure is Hv30 or more lower than the Vickers hardness in the depth of 1/4 of the wire diameter R of a steel wire. The lower the Vickers hardness, the higher the ductility.
- the present inventors have found that a steel wire having such a soft part on its surface has a tensile strength increased by a central part having a high hardness, and a ductility is remarkably improved by a soft part having a low hardness. Furthermore, the inventors reduced the cementite thickness in the pearlite structure by making the average lamella spacing of the pearlite from the surface of the steel wire to a depth of 5 ⁇ m smaller than the average lamella spacing of the pearlite at the center of the steel wire. It has been found that the cementite cracks that become the starting point of the disconnection become fine. In finish wire drawing and stranded wire processing, the soft part of the steel wire is mainly deformed. Good workability is required for steel wires for steel cords.
- the above-mentioned composition it can control that defects, such as a crack, occur in a steel wire in finish wire drawing and strand wire processing. Since the steel wire having the above-described steel wire can be satisfactorily processed by twisting, it is possible to provide a high-quality steel cord in which the occurrence of twisting defects is suppressed by the above-described configuration.
- the component composition of the steel wire which has the above-mentioned structure is the mass%, C: 0.70% or more and 1.20% or less, Si: 0.15% or more and 0.60% or less, Mn: 0.10% 1.00% or less, N: 0.0010% or more and 0.0050% or less, Al: 0% or more and 0.010% or less, Ti: 0% or more and 0.10% or less, Cr: 0% or more and 0.50 or less %: Co: 0% to 0.50%, V: 0% to 0.50%, Cu: 0% to 0.20%, Nb: 0% to 0.100%, Mo: 0 % To 0.20%, W: 0% to 0.200%, B: 0% to 0.0030%, REM: 0% to 0.0050%, Ca: 0% to 0.0050%
- Mg 0% to 0.0050% and Zr: 0% to 0.0100%, with the balance being Fe Are as fine impurities, tissue in the center of the steel wire having
- the thickness of the soft part of the steel wire having the above-described configuration is 5 ⁇ m or more and 0.1 ⁇ R mm.
- R is the diameter (wire diameter) of the steel wire. Since the thickness of the soft part is 5 ⁇ m or more, the steel wire having the above-described configuration has sufficiently good workability and suppresses the occurrence of defects such as cracks in finish drawing and stranded wire processing. Is done. Moreover, since the thickness of a soft part is 0.1xRmm or less, the tensile strength of the steel wire which has the above-mentioned structure is kept high, and the intensity
- the steel wire 10 which concerns on this embodiment is used as a raw material at the time of manufacturing the high intensity
- the steel wire 10 has a wire diameter R of 1.0 mm ⁇ R ⁇ 3.5 mm, the component composition is mass%, and C: 0.70% or more and 1.20% or less, Si: 0.15% to 0.60%, Mn: 0.10% to 1.00%, N: 0.0010% to 0.0050%, Al: 0% to 0.010%, Ti: 0% to 0.10%, Cr: 0% to 0.50%, Co: 0% to 0.50%, V: 0% to 0.50%, Cu: 0% to 0 20% or less, Nb: 0% to 0.100%, Mo: 0% to 0.20%, W: 0% to 0.200%, B: 0% to 0.0030%, REM : 0% to 0.0050%, Ca: 0% to 0.0050%, Mg: 0% to 0.0050%, and r: 0% or more include 0.0100% or less, the balance being the Fe and impurities.
- the steel wire 10 which concerns on this embodiment has the soft part 11 and the center part 12, as shown in FIG.
- the soft part 11 is formed along the outer periphery of the steel wire 10.
- the Vickers hardness of the soft part 11 is Hv30 or more lower than the Vickers hardness at a depth of 1/4 of the wire diameter R of the steel wire 10, and the thickness of the soft part is 5 ⁇ m or more and 0.1 ⁇ Rmm or less.
- the average lamella spacing of the pearlite from the surface of the steel wire 10 to a depth of 5 ⁇ m is smaller than the average lamella spacing of the pearlite at the center of the steel wire 10, and the average lamella of pearlite from the surface of the steel wire 10 to a depth of 5 ⁇ m.
- the difference between the distance and the average lamella distance of the pearlite at the center of the steel wire 10 is not less than 3.0 nm and not more than 60.0 nm. Furthermore, the tensile strength of the steel wire 10 is 1100 MPa or more.
- the steel wire 10 according to the present embodiment has a soft portion 11 formed along the outer periphery thereof.
- a region softer than the Vickers hardness at a depth of 1 ⁇ 4 of the wire diameter R of the steel wire by Hv30 or more is defined as the soft portion 11. That is, the Vickers hardness of the soft part 11 is Hv30 or less lower than the Vickers hardness at a depth of 1/4 of the wire diameter R of the steel wire.
- symbol 16 shows the location of 1/4 depth of the wire diameter R of a steel wire.
- the part which is not the soft part 11 among the steel wires 10 which concern on this embodiment is defined as the center part 12.
- FIG. The difference between the hardness of the soft portion 11 and the hardness of the central portion 12 is due to the difference in dislocation density and the form of cementite.
- the structure of the central portion 12 includes 95 to 100% pearlite, and the structure of the soft portion 11 also includes a similar amount of pearlite, but most of the dislocations introduced into the structure after the pearlite transformation are in the soft portion 11. Has been removed.
- the soft part 11 has a ductility higher than that of the central part 12 because its hardness is lower than that of the central part 12.
- the thickness t of the soft part 11 of the steel wire 10 according to the present embodiment is in the range of 5 ⁇ m ⁇ t ⁇ 0.1 ⁇ Rmm. That is, in the steel wire 10 according to the present embodiment, a region that is softer than the Vickers hardness of the portion 16 having a depth of 1/4 of the wire diameter R by Hv30 or more is in a region from the outer peripheral surface of the steel wire 10 to the depth t. Is formed. For example, when the wire diameter R is 3.0 mm, the thickness t of the soft part 11 is not less than 5 ⁇ m and not more than 0.3 mm (300 ⁇ m).
- the steel wire 10 Since the soft part 11 having higher ductility than the center part 12 is formed along the outer periphery of the steel wire 10, the steel wire 10 is mainly used in finish wire drawing and stranded wire processing in which significant deformation is applied to the outer periphery. Demonstrates good workability.
- the central portion 12 since the central portion 12 has a sufficiently high hardness, the steel wire 10 has a high tensile strength of 1100 MPa or more.
- the thickness t of the soft part 11 is 5 ⁇ m or less, processing defects such as disconnection tend to occur in finish wire drawing and stranded wire processing.
- the thickness t of the soft part 11 exceeds 0.1 ⁇ R mm, the tensile strength decreases.
- the thickness t of the soft part 11 is set in the range of 5 ⁇ m ⁇ t ⁇ 0.1 ⁇ Rmm.
- a preferable range of the thickness t of the soft part 11 is 10 ⁇ m or more and 0.08 ⁇ R mm or less.
- the method for measuring the thickness of the soft portion 11 of the steel wire 10 according to the present embodiment is not particularly limited.
- the thickness of the soft part 11 can be determined from the hardness distribution in the depth direction of the steel wire 10 obtained by measuring the hardness of the steel wire 10. For example, by appropriately preparing a cut surface (C cross section) obtained by cutting the steel wire 10 perpendicularly to the wire drawing direction, and continuously measuring the hardness from the outer periphery to the center of the cut surface, FIG.
- the graph which shows the relationship between the depth and the hardness of the steel wire 10 as shown in FIG. From this graph, it can be seen that the thickness of the region lower than the Vickers hardness at the depth of 1/4 of the wire diameter R of the steel wire 10 by Hv30 or more.
- the measurement points can be set as shown in FIG. 4 or FIG.
- a hardness at a depth of 1 ⁇ m can be obtained by measuring the hardness at intervals of 2 ⁇ m along the major axis of the cross section.
- the structure of the center portion 12 of the steel wire 10 according to the present embodiment includes 95-100% pearlite in terms of area ratio.
- the structure of the central portion 12 contains 95% or more of pearlite so that the tensile strength of the steel wire 10 is 1100 MPa or more, and the workability of the steel wire 10 in the finishing wire drawing step S07 described later is improved. It is essential. Since it is preferable that the amount of pearlite is large, the upper limit of the amount of pearlite in the central portion 12 of the steel wire 10 is 100%.
- Pseudo pearlite is a structure composed of granular cementite and granular ferrite, and is a normal pearlite having a shape in which layered cementite and layered ferrite overlap (perlite 20 shown in FIG. 8). Differentiated. “Perlite” according to the present embodiment means “normal pearlite”. Although it is not necessary to define the amount of pearlite in the soft portion 11 of the steel wire, it is usually a value similar to the amount of pearlite in the central portion 12 of the steel wire.
- the means for measuring the amount of pearlite in the central portion 12 of the steel wire 10 is not particularly limited. For example, by polishing and etching the C cross section of the steel wire 10, a pearlite structure of the C cross section of the steel wire 10 is revealed, and then an optical micrograph or an electron micrograph of the C cross section is taken, and The amount of pearlite may be obtained by obtaining the area of pearlite contained.
- the location at which the optical micrograph or electron micrograph of the C cross section is taken is, for example, 45 degrees with respect to the center of the steel wire 10 at the center of the C cross section of the steel wire 10 and 1 ⁇ 4 depth of the C cross section of the steel wire 10. It is preferable that the number of pearlites at these photographing locations is determined and the average value of the amount of pearlite at each location is the pearlite amount of the steel wire 10.
- the average lamella spacing of pearlite from the surface to the depth of 5 ⁇ m of the steel wire 10 according to this embodiment is smaller than the average lamella spacing of pearlite at the center of the steel wire 10.
- the difference between the average lamella spacing of pearlite from the surface of the steel wire 10 to a depth of 5 ⁇ m and the average lamella spacing of pearlite at the center of the steel wire 10 hereinafter sometimes abbreviated as “average lamella spacing difference”).
- interval of the soft part 11 is smaller than the center average lamella space
- the cementite in the pearlite is refined and the ductility is increased.
- dislocations are introduced into the steel wire 10 by heat treatment for reducing the average lamella spacing, and this dislocation reduces the ductility of the steel wire 10.
- the effect of introducing dislocations exceeds the effect of cementite refinement, so that the ductility of the steel wire 10 is lowered.
- most of the dislocations disappear due to surface layer heating described later.
- the average lamella spacing of the pearlite of the steel wire 10 according to the present embodiment is reduced, the influence of dislocation introduction is suppressed, so that an effect of improving ductility by cementite refinement can be obtained.
- the average lamella spacing difference is less than 3 nm, cementite in the pearlite from the surface to a depth of 5 ⁇ m is not sufficiently refined, so that the ductility of the surface layer portion of the steel wire 10 is lowered and workability is lowered.
- the lower limit of the difference in average lamella spacing is preferably 5 nm, 8 nm, or 10 nm.
- the present inventors have found that delamination occurs at a high frequency when the average lamellar spacing difference of the steel wire 10 exceeds 60 nm. Therefore, in the steel wire 10 which concerns on this embodiment, it is necessary to make an average lamella space
- the upper limit value of the difference in average lamella spacing is preferably 40 nm, 30 nm, or 25 nm.
- the surface average lamella spacing measurement region 14 is a square of 5 ⁇ m in length and breadth, and one side of this square coincides with the surface of the steel wire 10.
- the electron micrograph may be a square of 5 ⁇ m in length and breadth, and one side of the photograph may be matched with the surface of the steel wire 10, and this photograph may be used as the surface average lamella spacing measurement region 14.
- the pearlite having the smallest lamella interval is selected from the plurality of pearlites included in the surface layer average lamella interval measurement region 14 and included in this pearlite 20.
- the line segment 23 having a length of 2 ⁇ m perpendicular to the ferrite phase layer 21 and the cementite phase layer 22 is drawn, the number of the cementite phase layers 22 intersecting the line segment 23 is counted, and the length of the line segment (2 ⁇ m) Is divided by the number of the layers 22 of the cementite phase to obtain the lamella interval related to the surface average lamella interval measurement region 14.
- the average lamellar spacing of the pearlite from the surface of the steel wire 10 to a depth of 5 ⁇ m is obtained by obtaining the lamellar spacing for each of the eight surface layer average lamellar spacing measuring regions 14 and averaging the lamella spacing.
- Each of the twelve central average lamella interval measurement regions 15 have one of the line segments connecting the midpoints of the opposing sides coincide with the central axis of the steel wire 10.
- Eight of the twelve center average lamella distance measurement regions 15 are ones of the line segments connecting the midpoints of the opposite sides, and the region having a depth of 1/4 of the wire diameter R from the surface of the steel wire 10.
- Match. The values obtained by obtaining the lamella intervals for each of the 12 center average lamella interval measurement regions 15 and averaging these lamella intervals can be regarded as the average lamella interval at the center of the steel wire 10.
- the average lamella spacing may be measured in a cross section (C cross section) perpendicular to the drawing direction of the steel wire 10.
- C cross section cross section
- the method for obtaining the average lamella spacing of the pearlite from the surface of the steel wire 10 to the portion having a depth of 5 ⁇ m is the same as the measurement method on the L cross section.
- the center average lamella interval measurement region 15 for obtaining the average lamella interval at the center of the steel wire 10 is set to 1 ⁇ 4 depth of the central axis of the steel wire 10 and the wire diameter R of the steel wire 10. It can be arranged in the place.
- the lamellar spacing in this embodiment is an average value of the distances between the center lines of the cementite phase layers 22 adjacent to each other with the ferrite phase layer 21 interposed therebetween.
- C is an element that improves the strength of the steel wire 10.
- the C content is preferably set to around 0.80%.
- the steel wire 10 becomes hypoeutectoid steel and steel with a large amount of non-pearlite structure.
- the C content exceeds 1.20%, proeutectoid cementite is precipitated, and the workability of the steel wire 10 may be reduced. For this reason, C content was set in the range of 0.70% or more and 1.20% or less.
- Si 0.15% to 0.60%
- Si is an element that is effective for deoxidation of the steel wire 10, and further has an effect of improving the strength of the steel wire 10 by being dissolved in ferrite.
- Si content is less than 0.15%, there exists a possibility that the effect
- Si content exceeds 0.60%, the workability of the steel wire 10 may be reduced. For this reason, Si content was set in the range of 0.15% or more and 0.60% or less.
- a preferable lower limit value of the Si content is 0.20%, and a preferable upper limit value of the Si content is 0.50%.
- Mn 0.10 to 1.00%
- Mn is effective for deoxidation of the steel wire 10, and further has an action of fixing S in the steel wire 10 and suppressing embrittlement of the steel.
- Mn content is less than 0.10%, there exists a possibility that the effect
- Mn content exceeds 1.00%, the workability of the steel wire 10 may be reduced. For this reason, Mn content was set in the range of 0.10% or more and 1.00% or less.
- N is an element that forms a nitride when combined with Al and / or Ti.
- This nitride has the effect of suppressing the coarsening of austenite contained in the intermediate steel wire before the start of the patenting step S04 described later.
- the average lamella spacing difference of the steel wire 10 can be suppressed to 60 nm or less as described later, and the pearlite of the steel wire 10 is refined to improve the ductility of the steel wire 10. Can be made.
- N content is less than 0.0010%, there exists a possibility that the effect
- N content exceeds 0.0050%, there exists a possibility that the ductility of the steel wire 10 may fall. For this reason, N content was set in the range of 0.0010% or more and 0.0050% or less.
- the preferable lower limit of N content is 0.0015%, and the preferable upper limit of N content is 0.0045%.
- P and S may be contained in the steel wire 10 as impurities. Although it is not necessary to specify the contents of P and S in particular, in order to give the steel wire 10 the same level of ductility as that of the conventional steel wire, the contents of P and S are set to 0% or more and 0.02 respectively. % Or less, more preferably 0% or more and 0.01% or less, respectively. Such contents of S and P are considered to be impurities.
- the steel wire 10 according to this embodiment further includes Al, Ti, Cr, Co, V, Cu, Nb, Mo, W, B, REM, and Ca as selective components. , Mg, Zr may be contained.
- the numerical limitation range of the selected component and the reason for limitation will be described.
- the described% is mass%.
- the upper limit value of the Al content is preferably 0.010%. Moreover, it is good also considering the upper limit of Al content as 0.008%. Since Al does not need to be included in the steel wire 10 according to the present embodiment, the lower limit value of the Al content is 0%. However, Al has a function of forming a nitride by being combined with N, and this nitride suppresses the average lamella spacing difference to 60 nm or less as described above, and the ductility of the steel wire 10 by refining the pearlite. Has the effect of improving. In order to obtain these effects, the lower limit value of the Al content may be 0.003%.
- the lower limit value of the Ti content is 0%.
- Ti is an element having a deoxidizing action.
- Ti has a function of forming a nitride by being combined with N, and this nitride suppresses the average lamella spacing difference to 60 nm or less as described above, and the ductility of the steel wire 10 by refining pearlite. Has the effect of improving. In order to obtain these effects, 0.005% or more of Ti may be contained.
- the upper limit of the Ti content is preferably 0.100%.
- the lower limit value of the Cr content is 0%.
- Cr has an effect of improving the tensile strength of the steel wire 10 by reducing the average lamella spacing of pearlite.
- the Cr content is preferably more than 0%, and more preferably 0.0010% or more.
- the Cr content is more than 0.50%, pearlite transformation is suppressed and austenite may remain in the structure of the intermediate steel wire during the patenting treatment. Residual austenite becomes a supercooled structure such as martensite and bainite after the patenting treatment, and deteriorates the properties of the steel wire 10.
- the Cr content is preferably 0.50% or less.
- the lower limit value of the Co content is 0%.
- Co is an element having an effect of improving the properties of the steel wire 10 by suppressing the precipitation of proeutectoid cementite.
- the Co content is preferably more than 0%, and more preferably 0.0010% or more.
- the Co content is preferably 0.50% or less, and more preferably 0.40% or less.
- V (V: 0% to 0.50%) Since V may not be included in the steel wire 10 according to the present embodiment, the lower limit value of the V content is 0%. However, V has a function of forming fine carbonitride by being combined with N. As described above, this nitride has an effect of suppressing the difference in average lamella spacing to 60 nm or less and an effect of improving the ductility of the steel wire 10 by refining pearlite. In order to obtain these effects, the V content is preferably more than 0%, and more preferably 0.0010% or more. On the other hand, when the V content is more than 0.50%, the amount of carbonitride formed may be excessive, and the particle size of the carbonitride may be increased. Such carbonitrides may reduce the ductility of the steel wire. Therefore, the V content is preferably 0.50% or less, and more preferably 0.40% or less.
- the lower limit value of the Cu content is 0%.
- Cu is an element that improves the corrosion resistance of the steel wire 10.
- the Cu content is preferably more than 0%, and more preferably 0.0001% or more.
- the Cu content is preferably 0.20% or less, and more preferably 0.10% or less.
- Nb 0% to 0.100% Since Nb may not be included in the steel wire 10 according to the present embodiment, the lower limit value of the Nb content is 0%. However, Nb has the effect of increasing the corrosion resistance of the steel wire 10. Nb has a function of forming carbides and / or nitrides. As described above, this carbide and / or nitride has an effect of suppressing the difference in average lamella spacing to 60 nm or less and an effect of improving the ductility of the steel wire 10 by refining pearlite. In order to obtain these effects, the Nb content is preferably more than 0%, and more preferably 0.0005% or more.
- the Nb content is more than 0.100%, austenite may remain due to suppression of pearlite transformation during the patenting process. Residual austenite becomes a supercooled structure such as martensite and bainite after the patenting treatment, and deteriorates the properties of the steel wire 10. Therefore, the Nb content is preferably 0.100% or less, and more preferably 0.050% or less.
- Mo 0% to 0.20% Since Mo may not be included in the steel wire 10 according to the present embodiment, the lower limit value of the Mo content is 0%. However, Mo is an element that concentrates at the pearlite growth interface and suppresses the growth of pearlite by the so-called solution drag effect. Thereby, a pearlite can be refined
- the Mo content is more than 0.20%, the pearlite growth is excessively suppressed, the patenting process takes a long time, and the productivity of the steel wire 10 may be reduced. Moreover, when Mo content is more than 0.20%, coarse Mo carbide precipitates, and the wire drawing workability of the steel wire 10 may deteriorate. Therefore, the Mo content is preferably 0.20% or less, and more preferably 0.06% or less.
- W 0% to 0.200% Since W may not be included in the steel wire 10 according to the present embodiment, the lower limit value of the W content is 0%.
- W like Mo, is an element that concentrates at the pearlite growth interface and suppresses the growth of pearlite by the so-called solution drag effect. Thereby, a pearlite can be refined
- W is an element that reduces the non-pearlite structure that adversely affects the properties of the steel wire 10 by suppressing the formation of ferrite. In order to obtain these effects, the W content is preferably more than 0%, and more preferably 0.0005% or more.
- the W content is more than 0.200%, the pearlite growth is excessively suppressed, and it takes a long time for the patenting process, which may lead to a decrease in the productivity of the steel wire 10.
- W content is more than 0.200%, coarse W carbide precipitates, and the wire drawing workability of the steel wire 10 may deteriorate. Accordingly, the W content is preferably 0.200% or less, and more preferably 0.060% or less.
- the lower limit value of the B content is 0%.
- B is an element that suppresses the formation of non-pearlite structures such as ferrite, pseudo pearlite, and bainite.
- B has a function of forming carbide and / or nitride. As described above, this carbide and / or nitride has an effect of suppressing the difference in average lamella spacing to 60 nm or less and an effect of improving the ductility of the steel wire 10 by refining pearlite.
- the B content is preferably more than 0%, more preferably 0.0004% or more, or 0.0006% or more.
- the B content is preferably 0.0030% or less, more preferably 0.0025% or less, 0.0015% or less, or 0.0012% or less.
- the lower limit of the REM content is 0%.
- REM is a deoxidizing element.
- REM is an element that renders S, an impurity, harmless by forming sulfides.
- the REM content is preferably more than 0%, and more preferably 0.0005% or more.
- the REM content is preferably 0.0050% or less, and more preferably 0.0020% or less.
- REM is a generic name for a total of 17 elements including 15 elements from lanthanum with atomic number 57 to lutesium with 71, plus scandium with atomic number 21 and yttrium with atomic number 39.
- REM is supplied in the form of misch metal, which is a mixture of these elements, and is added to the steel.
- the content of REM mentioned above is the total content of these elements.
- the lower limit value of the Ca content is 0%.
- Ca is an element that reduces hard alumina inclusions that deteriorate the properties of the steel wire 10.
- Ca is an element that generates fine oxides. This fine oxide refines the pearlite block size of the steel wire 10, thereby improving the ductility of the steel wire 10.
- the Ca content is preferably more than 0.0005%.
- the Ca content is preferably 0.0050% or less, and more preferably 0.0040% or less. Note that, under normal operating conditions, Ca may be contained at about 0.0003%.
- the lower limit value of the Mg content is 0%.
- Mg is an element that generates fine oxides. This fine oxide refines the pearlite block size of the steel wire 10, thereby improving the ductility of the steel wire 10.
- the Mg content is preferably more than 0.0005%.
- the Mg content is preferably 0.0050% or less, and more preferably 0.0040% or less. Note that, under normal operating conditions, Mg may be contained in an amount of about 0.0001%.
- the lower limit value of the Zr content is 0%.
- Zr crystallizes as ZrO and becomes a crystallization nucleus of austenite. Therefore, Zr is an element that increases the equiaxed ratio of austenite and refines austenite grains.
- the pearlite block size of the steel wire 10 is refined by refining the austenite before the patenting treatment, and thereby the ductility of the steel wire 10. Will improve.
- the Zr content is preferably more than 0.0005%.
- the Zr content is more than 0.0100%, a coarse oxide may be formed, causing disconnection when the steel wire 10 is drawn. Therefore, the Zr content is preferably 0.0100% or less, and more preferably 0.0050% or less.
- the balance of the component composition of the steel wire 10 according to the present embodiment includes Fe and impurities.
- Impurities are components that are mixed due to various factors of raw materials such as ore or scrap, or manufacturing processes when industrially manufacturing steel materials, and adversely affect the characteristics of the steel wire 10 according to the present embodiment. It means that it is allowed in the range that does not give.
- the tensile strength of the steel wire 10 according to this embodiment is 1100 MPa or more.
- a steel cord obtained using a steel wire 10 having a tensile strength of 1100 MPa or more is suitable as a reinforcing material for rubber products such as automobile tires, high-pressure rubber hoses, and conveyor belts.
- the manufacturing method of the steel wire 10 according to the present embodiment has been descaled in order to obtain an intermediate steel wire and a step of descaling the wire to remove the oxide scale on the surface of the wire (descaling step S01).
- a step of rough-drawing the wire (rough drawing step S02), a step of heating the rough-drawn intermediate steel wire (heating step S03), and a step of performing a patenting treatment on the heated intermediate steel wire (patent A heating step S04), a step of surface heating the patented intermediate steel wire (surface layer heating step S05), and a step of cooling the surface heated intermediate steel wire (cooling step S06).
- the intermediate steel wire is a steel wire 10 being manufactured. Surface heating is heating only the surface layer of the steel wire.
- the manufacturing method of the filament obtained using the steel wire 10 which concerns on this embodiment finishes the process (brass plating process S07) of carrying out the brass plating of the steel wire 10 which concerns on this embodiment, and finishes the steel wire 10 by which brass plating was carried out.
- a wire drawing step finish wire drawing step S08).
- strength steel cord obtained using the steel wire 10 which concerns on this embodiment performs the process (stranded wire processing process S09) which performs a strand wire to the filament obtained using the steel wire 10 which concerns on this embodiment. Including.
- the wire which has the component composition mentioned above is used as a raw material.
- the kind of wire is not particularly limited, it is preferably a hot rolled wire.
- the diameter of the wire is not particularly limited, but is preferably about 5.5 mm.
- the oxide scale formed on the surface of the wire is removed by chemical treatment such as pickling or mechanical treatment. Such processing is called descaling.
- the descaling method is not particularly limited.
- the wire rod from which the oxide scale has been removed is roughly drawn, thereby forming an intermediate steel wire having a wire diameter of 1.0 mm to 3.5 mm (rough drawing step S02).
- the method of rough drawing is not particularly limited, but the rough drawing is preferably performed by dry drawing.
- the steel wire finally obtained that is, the steel wire 10 according to the present embodiment
- the steel wire may be referred to as an intermediate steel wire.
- Heating step S03 Next, both the central portion and the soft portion of the intermediate steel wire obtained in the rough wire drawing step S02 are heated within a temperature range of 850 ° C. to 1350 ° C. (heating step S03).
- the heating step S03 the structure of the intermediate steel wire becomes austenite, and this austenite undergoes pearlite transformation in the patenting step S04 described later. Therefore, the state of pearlite contained in the final steel wire obtained after the patenting step S04 is affected by the state of austenite generated in the intermediate steel wire in the heating step S03.
- the heating temperature in the heating step S03 is less than 850 ° C.
- cementite remains undissolved in the intermediate steel wire, and further, ferrite is generated in the intermediate steel wire.
- a sufficient amount of austenite cannot be obtained, a sufficient amount of pearlite cannot be generated in the intermediate steel wire in the subsequent patenting step S04, and the amount of pearlite in the structure of the center portion of the final steel wire is small. Below 95%.
- the heating temperature in the heating step S03 is higher than 1350 ° C., the austenite grain size becomes coarse and the hardenability is improved, so that the average lamellar spacing difference of the final steel wire may exceed 60 nm.
- FIG. 10 is a schematic CCT diagram (Continuous-Cooling-Transformation diagram) of the steel wire according to the present embodiment.
- Two curves from Ps to Pf are transformation curves indicating the start and end of the pearlite transformation.
- the left transformation curve is a transformation curve relating to an intermediate steel wire having a small austenite grain size
- the right transformation curve is a transformation curve relating to an intermediate steel wire having a large austenite grain size.
- the transformation curve related to the intermediate steel wire with the larger austenite grain size is located on the right side.
- Two curves extending from the upper left to the lower right of the CCT diagram are curves indicating the cooling state of the intermediate steel wire in the patenting step S04 performed after the heating step S03.
- the left curve is a curve indicating the cooling state of the surface layer of the intermediate steel wire
- the right curve is a curve indicating the cooling state of the center of the intermediate steel wire.
- T 1 described in FIG. 10 is the temperature at which the transformation curve relating to the intermediate steel wire having a small austenite grain size first intersects with the curve indicating the cooling state of the surface layer of the intermediate steel wire, and the middle having the small austenite grain size.
- the difference between the temperature at which the transformation curve for the steel wire and the curve indicating the cooling state at the center of the intermediate steel wire first intersect, that is, the difference in the pearlite transformation start temperature at the surface layer and center of the intermediate steel wire with a small austenite grain size is there.
- the difference between the temperature at which the transformation curve related to the steel wire and the curve indicating the cooling state at the center of the intermediate steel wire first intersect, that is, the difference in the pearlite transformation start temperature at the surface layer and center of the intermediate steel wire having a large austenite grain is there.
- T 2 is greater than T 1.
- the austenite of the intermediate steel wire heated in the heating step S03 is coarsened
- the subsequent patenting step S04 the difference in average lamella spacing between the intermediate steel wire surface layer and the center of the intermediate steel wire is increased
- the difference in the average lamella spacing between the final steel wire surface layer and the final steel wire center also increases.
- the present inventors have found that when the heating temperature exceeds 1350 ° C., the average lamellar spacing difference of the final steel wire is 60 nm due to the coarsening of the austenite grain size of the intermediate steel wire. It has been found that there is a very high risk of this. For the reasons described above, it is necessary to set the heating temperature in the heating step S03 to 850 ° C. to 1350 ° C.
- Patenting process S04 a patenting process is performed in which the intermediate steel wire heated in the heating step S03 is immersed in a molten lead bath (lead bath) after the heating step S03 is completed (patenting step S04).
- the temperature of the lead bath is 530 ° C. or more and 580 ° C. or less, and the time for immersing the intermediate steel wire in the lead bath is 5 to 45 seconds.
- the time between the end of the heating step S03 and the start of the patenting step S04 is about 5 seconds.
- Patenting may be performed using molten salt instead of molten lead.
- the reason for defining the temperature of molten lead in the patenting step S04 is as follows.
- the temperature of the lead bath is less than 530 ° C.
- a bainite structure is generated in the surface layer of the intermediate steel wire, and thereby the tensile strength of the final steel wire is lowered.
- the temperature of a lead bath exceeds 580 degreeC, the tensile strength of the last steel wire falls.
- the temperature of the lead bath is preferably set to 530 ° C. or higher and 580 ° C. or lower.
- the reason why the intermediate steel wire is immersed in the lead bath in the patenting step S04 is as follows.
- the immersion time is less than 5 seconds, the pearlite transformation is not completely completed, and the pearlite fraction of the final steel wire is lowered.
- immersion time is 45 second or more, a part of cementite in the lamella of pearlite is parted, and thereby the tensile strength of the final steel wire is lowered.
- the intermediate steel wire taken out from the lead bath in the patenting step S04 is then cooled to room temperature.
- the cooling rate at this time is 10 ° C./second or more.
- the cooling rate of the intermediate steel wire is less than 10 ° C./second, the strength of the final steel wire may be reduced.
- the surface layer heating step S05 it is necessary to sufficiently heat the surface layer of the intermediate steel wire and suppress the temperature rise inside the intermediate steel wire as much as possible.
- the inside of the intermediate steel wire is excessively heated, the final steel wire having the soft portion 11 having a thickness of 5 ⁇ m or more cannot be obtained.
- the best heating method for forming the predetermined soft portion 11 is high-frequency heating.
- the frequency of the high frequency applied to the intermediate steel wire needs to be 50 kHz or more.
- the inside of the intermediate steel wire is also heated, so that the final steel wire having the soft part 11 having a thickness of 5 ⁇ m or more cannot be obtained.
- the upper limit value of the high frequency applied to the intermediate steel wire is not particularly limited, but it is preferable to set the upper limit value of the high frequency to about 100 kHz in consideration of equipment capacity. Since high-frequency heating can be performed by continuously passing the intermediate steel wire through the high-frequency coil, production efficiency is favorable in addition to the above-described heating rate, which is preferable. Moreover, since uniform heating can be performed by high frequency heating, the depth of the soft part 11 obtained by high frequency heating is substantially constant.
- the surface temperature of the intermediate steel wire needs to be 500 ° C. or higher.
- the surface temperature of the intermediate steel wire is less than 500 ° C., dislocations on the surface layer of the intermediate steel wire are not sufficiently removed, so that the soft portion 11 having a thickness of 5 ⁇ m or more cannot be formed.
- the surface temperature of the intermediate steel wire exceeds 700 ° C. in the surface layer heating step S05, the cementite in the pearlite lamella is divided and spheroidized, thereby reducing the tensile strength of the final steel wire.
- the heating time in the surface layer heating step S05 needs to be within 5 seconds.
- the heating time is the time for the intermediate steel wire to pass through the high frequency coil, and this time is obtained by dividing the length of the high frequency coil by the passing speed of the intermediate steel wire. It is not necessary to define the temperature at which surface heating starts. However, in order to make the surface temperature of the intermediate steel wire 500 ° C. or higher within 5 seconds, it is desirable that the temperature at which the surface layer heating is started be 10 ° C. or higher.
- the soft portion 11 having a thickness of 5 ⁇ m or more and 0.1 ⁇ R mm or less is used. Can not form.
- the intermediate steel wire in which only the surface layer is heated in the surface layer heating step S05 is cooled in the cooling step S06.
- the surface temperature of the intermediate steel wire needs to be 500 ° C. or less within 3.0 seconds after the completion of the surface layer heating step S05.
- the surface temperature of the intermediate steel wire is set to 500 ° C. or less within 2.0 seconds after the completion of the surface layer heating step S05.
- the surface layer heating step S05 is performed by high frequency heating
- the time point when the surface layer heating step S05 ends is the time point when the intermediate steel wire leaves the high frequency heating coil. If the above-mentioned cooling conditions are not achieved, the inside of the intermediate steel wire is also softened, so that the soft part 11 having a thickness of 5 ⁇ m or more and 0.1 ⁇ Rmm or less cannot be formed.
- the cooling means in the cooling step S06 is not particularly limited as long as the above cooling conditions are achieved. If the surface heating temperature in the surface layer heating step S05 is about 500 ° C. or slightly higher than 500 ° C., the above cooling conditions can be achieved by air cooling. However, due to disturbance factors such as ambient temperature, the surface temperature of the intermediate steel wire at the end of the surface heating step S05 is unexpectedly much higher than 500 ° C., thereby achieving the above cooling conditions by air cooling. There are cases where it is not possible. On the other hand, the above-mentioned cooling conditions can be reliably achieved by water-cooling the intermediate steel wire within 3.0 seconds after the surface layer heating step S05 ends.
- the steel wire 10 (final steel wire) according to the present embodiment is manufactured by the above-described S01 to S06. Note that it is not preferable to perform additional heat treatment on the steel wire 10 after the cooling step S06 is completed. When the inside of the steel wire 10 is heated by the additional heat treatment, the hardness of the inside of the steel wire 10 is lowered and the soft part 11 having a thickness of 5 ⁇ m or more and 0.1 ⁇ Rmm or less may be lost. is there.
- the steel wire 10 according to the present embodiment is preferably subjected to brass plating on the surface (brass plating step S07). Brass plating is formed in order to improve adhesion between rubber and a steel cord.
- FIG. 13 is a graph showing the relationship between the amount of wire drawing strain applied to the steel wire and the hardness of the central portion 12 and the hardness of the soft portion 11.
- FIG. 13 shows that the difference between the hardness of the central portion 12 and the hardness of the soft portion 11 increases as the wire drawing strain increases.
- the steel wire 10 which concerns on this embodiment, the manufacturing method of the steel wire 10 which concerns on this embodiment, and the method of creating a steel cord using the steel wire 10 which concerns on this embodiment were demonstrated.
- the steel wire 10 according to the present embodiment configured as described above has a soft part 11 and a center part 12, and the soft part 11 has a lower Vickers hardness than the center part 12, and the Vickers of the soft part 11.
- the difference between the hardness and the Vickers hardness at a quarter depth of the diameter R of the steel wire 10 is Hv30 or more.
- the ductility is improved in the soft part 11, and the tensile strength is kept high in the central part 12.
- the steel wire 10 which concerns on this embodiment it is suppressed that defects, such as a crack, generate
- the component composition of the steel wire 10 which concerns on this embodiment is the mass%, C: 0.70% or more and 1.20% or less, Si: 0.15% or more and 0.60% or less, Mn: 0.10 %: 1.00% or less, N: 0.0010% or more, 0.0050% or less, Al: 0% or more, 0.010% or less, Ti: 0% or more, 0.10% or less, Cr: 0% or more, 0.
- the tissue of the central portion 12 of the steel wire 10 according to the present embodiment are contained in a proportion of less than 100% 95% perlite by area%. Therefore, the tensile strength is kept sufficiently high in the central portion 12 of the steel wire 10 according to the present embodiment, and the steel cord manufactured using the steel wire 10 according to the present embodiment also has a high tensile strength. Can have.
- the finishing wire drawing step S08 and the stranded wire processing step S09 it is possible to suppress the occurrence of defects such as cracks and to sufficiently ensure the strength of the steel wire 10.
- the manufacturing method of the steel wire 10 which concerns on this embodiment is surface layer heating which heats the surface temperature of a steel wire to 500 degreeC or more by performing the high frequency heating of the frequency of 50 kHz or more to the steel wire which passed through the patenting process step S04, for example. Step S05 is included. Therefore, according to the manufacturing method of the steel wire 10 according to the present embodiment, a temperature difference is generated between the inside of the steel wire and the surface layer, and the soft portion 11 and the central portion 12 having different hardness and lamella spacing are formed. It becomes possible to do.
- the steel wire 10 which concerns on this embodiment was demonstrated, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
- the thickness of the soft part is not limited to this embodiment.
- the wire diameter of the wire, the wire diameter of the filament, and the like are not limited to the present embodiment, and may be appropriately changed.
- Steel wires having the component compositions shown in Table 1-1, Table 1-2, Table 2-1, and Table 2-2 were produced.
- the amounts of P and S contained in the component compositions of the steel wires of Examples 1 to 25 and the steel wires of Comparative Examples 26 to 46 were at a level that can be regarded as impurities.
- the steel wires of Examples 1 to 25 and the steel wires of Comparative Examples 26 to 36 were produced by the steel wire manufacturing method according to this embodiment described above.
- the steel wire of the comparative example 37 was produced by the manufacturing method based on the manufacturing method of the steel wire which concerns on this embodiment mentioned above except the surface layer heating process S05 being abbreviate
- the steel wire of Comparative Example 38 is produced by a manufacturing method based on the above-described manufacturing method of the steel wire according to the present embodiment except that the heating temperature in the heating step S03 is 1380 ° C. (that is, higher than 1350 ° C.). did.
- the steel wire of Comparative Example 39 is produced by a manufacturing method based on the above-described manufacturing method of the steel wire according to the present embodiment except that the heating temperature in the heating step S03 is 830 ° C. (that is, less than 850 ° C.). did.
- the steel wire of Comparative Example 40 is the same as the steel wire manufacturing method according to the present embodiment described above except that the immersion time in the lead bath in the patenting step S04 is 4 seconds (that is, less than 5 seconds).
- the steel wire of Comparative Example 41 is the same as the steel wire manufacturing method according to the present embodiment described above except that the immersion time in the lead bath in the patenting step S04 is 50 seconds (that is, more than 45 seconds). It was produced by a compliant manufacturing method.
- the steel wire of Comparative Example 42 is the same as the above-described embodiment except that the cooling rate after immersion in the lead bath in the patenting step S04 is 8 ° C./second (ie, less than 10 ° C./second). It produced by the manufacturing method based on the manufacturing method of the steel wire which concerns.
- the steel wire of Comparative Example 43 is manufactured in accordance with the above-described method for manufacturing a steel wire according to the present embodiment except that the frequency of the high-frequency heating performed in the surface layer heating step S05 is 30 kHz (that is, less than 50 kHz). Prepared by the method.
- the steel wire of Comparative Example 44 is a manufacturing method based on the above-described manufacturing method of the steel wire according to the present embodiment except that the surface heating temperature in the surface heating step S05 is 480 ° C. (that is, less than 500 ° C.). It was produced by.
- the steel wire of Comparative Example 45 is a manufacturing method based on the above-described manufacturing method of the steel wire according to the present embodiment except that the surface heating temperature in the surface heating step S05 is 730 ° C. (that is, more than 700 ° C.). It was produced by.
- the steel wire of Comparative Example 46 is the steel wire according to this embodiment described above, except that the time until the surface layer temperature in the cooling step S06 becomes 500 ° C. or less is 4 seconds (that is, more than 2 seconds). It produced by the manufacturing method based on a manufacturing method.
- the tensile strength TS was evaluated.
- the amount of pearlite at the center of the steel wire is the amount of pearlite at the center of the C cross section of the steel wire and at 8 locations arranged at 45 degrees with respect to the steel wire center at 1 ⁇ 4 depth of the C cross section of the steel wire. The average value was used.
- the amount of pearlite at each measurement location was determined based on an optical micrograph or SEM photograph of a C cross section of a steel wire in which a pearlite structure was revealed.
- the soft part thickness was determined based on the hardness distribution in the depth direction of the steel wire obtained by measuring the hardness of the steel wire.
- the surface layer hardness was an average value of Vickers hardness at 8 locations arranged at every 45 degrees with respect to the center of the steel wire at a depth of 2 ⁇ m from the surface of the steel wire.
- the center hardness is a portion having a depth of 1/4 of the wire diameter R of the steel wire from the surface of the steel wire, and 8 locations arranged every 45 degrees with respect to the center of the steel wire, and the center of the steel wire It was set as the average value of Vickers hardness.
- the surface layer average lamella spacing was determined by the procedure described below. First, a pearlite structure was revealed on the L cross section of the steel wire.
- the surface layer average lamella interval measurement region was a square of 5 ⁇ m in length and width, and one side of the square was made to coincide with the surface of the steel wire.
- a pearlite having the smallest lamella interval is selected from among a plurality of pearlites included in the surface average lamella interval measurement region, and the ferrite phase layer and the cementite phase included in the pearlite are selected.
- the surface average is obtained by drawing a line segment with a length of 2 ⁇ m perpendicular to the layer, counting the number of cementite phase layers intersecting this line segment, and dividing the length of the line segment (2 ⁇ m) by the number of cementite phase layers.
- the lamella interval related to the lamella interval measurement region was determined.
- the average lamella spacing of pearlite from the surface of the steel wire to a depth of 5 ⁇ m was obtained by determining the lamella spacing for each of the eight surface layer average lamella spacing measurement regions and averaging the lamella spacing.
- the center average lamella spacing was determined by the procedure described below.
- an L cross section of a steel wire is prepared, an electron micrograph of a region including the central axis of the steel wire, and a 1/4 depth of the wire diameter R of the steel wire.
- region containing a location was image
- regions which are 5 micrometers in length and width square was calculated
- one of the line segments connecting the midpoints of the opposing sides coincided with the central axis of the steel wire.
- the average lamella spacing at the center of the steel wire was obtained by obtaining the lamella spacing for each of the 12 central average lamella spacing measurement regions and averaging these lamella spacings.
- the presence or absence of delamination was determined by conducting a twist test on the steel wire. When a torsion test is performed on a steel wire with delamination, the fracture surface caused by torsion fracture is not a shear fracture surface but a fracture surface along a vertical crack. By inspecting with, it is possible to determine the presence or absence of delamination.
- the tensile strength TS was obtained by a tensile test in accordance with JIS Z 2241 “Tensile test method for metal material”. The evaluation results are shown in Table 1-3 and Table 2-3.
- the pearlite fraction of Comparative Example 26 in which the C content was insufficient was less than 95 area%. Thereby, the tensile strength of the comparative example 26 became lower than 1100 MPa.
- the tensile strength of Comparative Example 28 in which the Si content was insufficient was lower than 1100 MPa.
- Comparative Example 27 in which the C content was excessive and in Comparative Example 29 in which the Si content was excessive delamination occurred due to a decrease in workability.
- Comparative Example 30 in which the Mn content was insufficient deoxidation and S fixation were not sufficiently performed, and thus delamination occurred.
- Comparative Example 31 in which the Mn content was excessive delamination occurred due to a decrease in workability.
- Comparative Example 32 in which the Mo content was excessive, delamination occurred because the wire drawing workability decreased due to precipitation of Mo carbides.
- Comparative Example 33 in which the Al content was excessive, delamination occurred due to the occurrence of alumina inclusions that caused the ductility deterioration and the wire drawing deterioration of the steel wire.
- Comparative Example 34 in which the B content was excessive, delamination occurred due to the generation of coarse Fe 23 (CB) 6 that caused a reduction in the ductility of the steel wire.
- Comparative Example 35 in which the N content was excessive, a decrease in ductility occurred, and thus delamination occurred.
- Comparative Example 36 in which the contents of Cr and Mo were excessive, a large amount of upper bainite or martensite was generated, and the pearlite fraction was lowered and the wire drawing workability was lowered, so that delamination occurred. .
- Comparative Example 37 In Comparative Example 37 in which the surface layer heating was not performed, since the soft part was not formed, the workability was lowered and delamination occurred.
- Comparative Example 38 In Comparative Example 38, in which the heating temperature before patenting was excessive, the average lamellar gap difference was excessive, so delamination occurred.
- Comparative Example 39 in which the heating temperature before patenting was insufficient, delamination occurred because the amount of pearlite decreased and the wire drawing workability decreased.
- the steel wire of Comparative Example 40 In the steel wire of Comparative Example 40 in which the immersion time in the lead bath in patenting was insufficient, the pearlite fraction was reduced and delamination occurred.
- the tensile strength was as high as 1150 MPa or more, and no delamination was observed.
- a steel wire having high strength and excellent workability can be provided.
- Such a steel wire is suitable for producing a high-strength steel cord with a high yield.
- the steel wire according to the present invention has industrial applicability because the high-strength steel cord is very useful for promoting the reduction in fuel consumption of automobiles by reducing the weight of automobile tires.
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Abstract
Description
本願は、2014年2月6日に、日本に出願された特願2014-021684号に基づき優先権を主張し、その内容をここに援用する。
図1に示されているように、本実施形態に係る鋼線10は、その外周に沿って形成された軟質部11を有する。本実施形態に係る鋼線10では、鋼線の線径Rの1/4の深さにおけるビッカース硬度よりもHv30以上柔らかい領域が、軟質部11と定義される。すなわち、軟質部11のビッカース硬度は、鋼線の線径Rの1/4の深さにおけるビッカース硬度よりもHv30以上低い。図1において、符号16が付された破線は、鋼線の線径Rの1/4の深さの箇所を示す。また、本実施形態に係る鋼線10のうち軟質部11ではない部分が、中心部12と定義される。軟質部11の硬度と中心部12との硬度の差は、転位密度、およびセメンタイトの形態の差に起因する。中心部12の組織は95~100%のパーライトを含み、軟質部11の組織も同様の量のパーライトを含むが、パーライト変態後の組織に導入されている転位の大半が、軟質部11においては除去されている。軟質部11は、その硬度が中心部12よりも低いので、中心部12よりも高い延性を有する。
本実施形態に係る鋼線10の軟質部11の厚さtは、5μm≦t≦0.1×Rmmの範囲内とされている。すなわち、本実施形態に係る鋼線10では、線径Rの1/4の深さの箇所16のビッカース硬さよりもHv30以上軟らかい領域が、鋼線10の外周面から深さtまでの領域に形成されている。例えば、線径Rが3.0mmである場合、軟質部11の厚さtは5μm以上0.3mm(300μm)以下である。中心部12よりも高い延性を有する軟質部11が鋼線10の外周に沿って形成されているので、鋼線10は、主に外周に著しい変形が加えられる仕上伸線加工および撚り線加工において、良好な加工性を発揮する。一方、中心部12が十分に高い硬度を有しているので、鋼線10は、1100MPa以上の高い引張強さを有している。軟質部11の厚さtが5μm以下である場合、仕上伸線加工および撚り線加工等において、断線等の加工不良が生じやすくなる。また、軟質部11の厚さtが0.1×Rmm超となった場合、引張強さが低下する。従って、軟質部11の厚さtを5μm≦t≦0.1×Rmmの範囲内とする。軟質部11の厚さtの好ましい範囲は10μm以上0.08×Rmm以下である。
本実施形態に係る鋼線10の中心部12の組織(すなわち、鋼線10の軟質部11以外の組織)は、面積率で、95~100%のパーライトを含む。中心部12の組織が95%以上のパーライトを含有することは、鋼線10の引張強度を1100MPa以上とし、且つ後述する仕上伸線工程S07などでの鋼線10の加工性を良くするために必須である。パーライト量が多い方が好ましいので、鋼線10の中心部12におけるパーライト量の上限値は100%である。マルテンサイト、ベイナイト、セメンタイト、および疑似パーライト等の、パーライト以外の組織の含有は、パーライト量の規定が満たされている限り許容される。疑似パーライトとは、粒状のセメンタイトと粒状のフェライトとから構成される組織であり、層状のセメンタイトと層状のフェライトとが重なっている形状を有する通常のパーライト(図8に示されるパーライト20)とは区別される。本実施形態に係る「パーライト」とは、「通常のパーライト」を意味する。鋼線の軟質部11のパーライト量を規定する必要はないが、通常、鋼線の中心部12のパーライト量と同様の値となる。
本実施形態に係る鋼線10の、表面から深さ5μmまでのパーライトの平均ラメラ間隔は、鋼線10の中心におけるパーライトの平均ラメラ間隔よりも小さい。また、鋼線10の表面から深さ5μmまでのパーライトの平均ラメラ間隔と、鋼線10の中心におけるパーライトの平均ラメラ間隔との差(以下、「平均ラメラ間隔差」と略する場合がある)は、3nm以上60nm以下である。なお、鋼線10の表面から深さ5μmまでの領域は、軟質部11に含まれる。従って、本実施形態に係る鋼線10においては、軟質部11の平均ラメラ間隔が中心の平均ラメラ間隔よりも小さい。
Cは、鋼線10の強度を向上させる元素である。共析組織であるパーライト組織を得るためには、C含有量を0.80%近傍とすることが好ましい。C含有量が0.70%未満である場合、鋼線10が亜共析鋼となり、非パーライト組織が多く存在する鋼になる。一方、C含有量が1.20%を超える場合、初析セメンタイトが析出し、鋼線10の加工性が低下するおそれがある。このため、C含有量を、0.70%以上1.20%以下の範囲内に設定した。
Siは、鋼線10の脱酸のために有効であり、さらに、フェライト中に固溶して鋼線10の強度を向上させる作用を有する元素である。ここで、Si含有量が0.15%未満である場合、上述した作用が十分に得られないおそれがある。一方、Si含有量が0.60%を超える場合、鋼線10の加工性が低下するおそれがある。このため、Si含有量を、0.15%以上0.60%以下の範囲内に設定した。Si含有量の好ましい下限値は0.20%であり、Si含有量の好ましい上限値は0.50%である。
Mnは、鋼線10の脱酸のために有効であり、さらに、鋼線10中のSを固定して鋼の脆化を抑制する作用を有する。ここで、Mn含有量が0.10%未満である場合、上述した作用が十分に得られないおそれがある。一方、Mn含有量が1.00%を超える場合、鋼線10の加工性が低下するおそれがある。このため、Mn含有量を、0.10%以上1.00%以下の範囲内に設定した。
Nは、Alおよび/またはTiと結びつくことにより窒化物を形成する元素である。この窒化物は、後述するパテンティング工程S04の開始前の中間鋼線に含まれるオーステナイトの粗大化を抑制する作用を有する。オーステナイトの粗大化を抑制することにより、後述するように鋼線10の平均ラメラ間隔差を60nm以下に抑制することができ、さらに、鋼線10のパーライトを微細化して鋼線10の延性を向上させることができる。N含有量が0.0010%未満である場合、上述した作用が十分に得られないおそれがある。一方、N含有量が0.0050%を超える場合、鋼線10の延性が低下するおそれがある。このため、N含有量を、0.0010%以上0.0050%以下の範囲内に設定した。N含有量の好ましい下限値は0.0015%であり、N含有量の好ましい上限値は0.0045%である。
Alは、硬質であり変形が生じにくいアルミナ系介在物となり、この介在物は鋼線10の延性劣化と伸線性劣化とを引き起こすおそれがある。従って、Al含有量の上限値を0.010%とすることが好ましい。また、Al含有量の上限値を0.008%としてもよい。Alは、本実施形態に係る鋼線10に含まれなくてもよいので、Al含有量の下限値は0%である。しかしながら、AlはNと結びつくことにより窒化物を形成する働きを有し、この窒化物は上述のように平均ラメラ間隔差を60nm以下に抑制する効果と、パーライトを微細化して鋼線10の延性を向上させる効果とを有する。これら効果を得るために、Al含有量の下限値を0.003%としてもよい。
Tiは、本実施形態に係る鋼線10に含まれなくてもよいので、Ti含有量の下限値は0%である。しかし、Tiは、脱酸作用を有する元素である。また、TiはNと結びつくことにより窒化物を形成する働きを有し、この窒化物は上述のように平均ラメラ間隔差を60nm以下に抑制する効果と、パーライトを微細化して鋼線10の延性を向上させる効果とを有する。これら効果を得るために、Tiを0.005%以上含有してもよい。一方、Ti含有量が0.100%を超える場合、粗大な炭窒化物(TiCN等)が形成されることによって加工性が低下するおそれがある。従って、Ti含有量の上限を、0.100%とすることが好ましい。
Crは、本実施形態に係る鋼線10に含まれなくてもよいので、Cr含有量の下限値は0%である。しかしCrは、パーライトの平均ラメラ間隔を微細化することにより鋼線10の引張強度を向上させる効果を有する。この効果を得るためには、Cr含有量が0%超であることが好ましく、0.0010%以上であることがさらに好ましい。一方、Cr含有量が0.50%超である場合、パーライト変態が抑制されることによりパテンティング処理中の中間鋼線の組織にオーステナイトが残留するおそれがある。残留オーステナイトは、パテンティング処理後にマルテンサイトおよびベイナイトなどの過冷組織となり、鋼線10の特性を悪化させる。また、0.50%超のCrは、メカニカルデスケーリングによる表面酸化物の除去が困難になる場合がある。従って、Cr含有量が0.50%以下であることが好ましい。
Coは、本実施形態に係る鋼線10に含まれなくてもよいので、Co含有量の下限値は0%である。しかしCoは、初析セメンタイトの析出を抑制することにより鋼線10の特性を向上させる効果を有する元素である。この効果を得るためには、Co含有量が0%超であることが好ましく、0.0010%以上であることがさらに好ましい。一方、Co含有量が0.50%超である場合、上述の効果が飽和して、過剰な生産コストが生じる場合がある。従って、Co含有量が0.50%以下であることが好ましく、0.40%以下であることがさらに好ましい。
Vは、本実施形態に係る鋼線10に含まれなくてもよいので、V含有量の下限値は0%である。しかしVは、Nと結びつくことにより微細な炭窒化物を形成する働きを有する。この窒化物は上述のように平均ラメラ間隔差を60nm以下に抑制する効果と、パーライトを微細化して鋼線10の延性を向上させる効果とを有する。これらの効果を得るためには、V含有量が0%超であることが好ましく、0.0010%以上であることがさらに好ましい。一方、V含有量が0.50%超である場合、炭窒化物の形成量が過剰となるおそれがあり、さらに炭窒化物の粒子径が大きくなるおそれがある。このような炭窒化物は鋼線の延性を低下させる場合がある。従って、V含有量が0.50%以下であることが好ましく、0.40%以下であることがさらに好ましい。
Cuは、本実施形態に係る鋼線10に含まれなくてもよいので、Cu含有量の下限値は0%である。しかしCuは、鋼線10の耐食性を高める元素である。この効果を得るためには、Cu含有量が0%超であることが好ましく、0.0001%以上であることがさらに好ましい。一方、Cu含有量が0.20%超である場合、CuとSとが反応することにより粒界にCuSが偏析し、このCuSが鋼線10に疵を発生させる場合がある。従ってCu含有量が0.20%以下であることが好ましく、0.10%以下であることがさらに好ましい。
Nbは、本実施形態に係る鋼線10に含まれなくてもよいので、Nb含有量の下限値は0%である。しかしNbは、鋼線10の耐食性を高める効果がある。また、Nbは、炭化物および/または窒化物を形成する働きを有する。この炭化物および/または窒化物は上述のように平均ラメラ間隔差を60nm以下に抑制する効果と、パーライトを微細化して鋼線10の延性を向上させる効果とを有する。これらの効果を得るためには、Nb含有量が0%超であることが好ましく、0.0005%以上であることがさらに好ましい。一方、Nb含有量が0.100%超である場合、パテンティング処理中のパーライト変態が抑制されることによりオーステナイトが残留するおそれがある。残留オーステナイトは、パテンティング処理後にマルテンサイトおよびベイナイトなどの過冷組織となり、鋼線10の特性を悪化させる。従って、Nb含有量が0.100%以下であることが好ましく、0.050%以下であることがさらに好ましい。
Moは、本実施形態に係る鋼線10に含まれなくてもよいので、Mo含有量の下限値は0%である。しかしMoは、パーライト成長界面に濃縮し、いわゆるソリュートドラッグ効果によりパーライトの成長を抑制する元素である。これにより、パーライトを微細化し、鋼線10の強度を向上させることができる。また、Moは、フェライト生成を抑制することにより、鋼線10の特性に悪影響を与える非パーライト組織を低減させる元素である。これらの効果を得るためには、Mo含有量が0%超であることが好ましく、0.0010%以上、または0.005%以上であることがさらに好ましい。一方、Mo含有量が0.20%超である場合、パーライト成長が過剰に抑制され、パテンティング処理に長時間を要し、鋼線10の生産性の低下を招く場合がある。また、Mo含有量が0.20%超である場合、粗大なMo炭化物が析出し、鋼線10の伸線加工性が低下する場合がある。従って、Mo含有量が0.20%以下であることが好ましく、0.06%以下であることがさらに好ましい。
Wは、本実施形態に係る鋼線10に含まれなくてもよいので、W含有量の下限値は0%である。しかしWは、Moと同様に、パーライト成長界面に濃縮し、いわゆるソリュートドラッグ効果によりパーライトの成長を抑制する元素である。これにより、パーライトを微細化し、鋼線10の強度を向上させることができる。また、Wは、フェライト生成を抑制することにより、鋼線10の特性に悪影響を与える非パーライト組織を低減させる元素である。これらの効果を得るためには、W含有量が0%超であることが好ましく、0.0005%以上であることがさらに好ましい。一方、W含有量が0.200%超である場合、パーライト成長が過剰に抑制され、パテンティング処理に長時間を要し、鋼線10の生産性の低下を招く場合がある。また、W含有量が0.200%超である場合、粗大なW炭化物が析出し、鋼線10の伸線加工性が低下する場合がある。従って、W含有量が0.200%以下であることが好ましく、0.060%以下であることがさらに好ましい。
Bは、本実施形態に係る鋼線10に含まれなくてもよいので、B含有量の下限値は0%である。しかしBは、フェライト、擬似パーライト、ベイナイト等の非パーライト組織の生成を抑制する元素である。また、Bは、炭化物および/または窒化物を形成する働きを有する。この炭化物および/または窒化物は上述のように平均ラメラ間隔差を60nm以下に抑制する効果と、パーライトを微細化して鋼線10の延性を向上させる効果とを有する。これらの効果を得るためには、B含有量が0%超であることが好ましく、0.0004%以上、または0.0006%以上であることがさらに好ましい。一方、B含有量が0.0030%超である場合、粗大なFe23(CB)6の析出を促進し、鋼線10の延性に悪影響を及ぼす場合がある。従って、B含有量が0.0030%以下であることが好ましく、0.0025%以下、0.0015%以下、または0.0012%以下であることがさらに好ましい。
REM(Rare Earth Metal)は、本実施形態に係る鋼線10に含まれなくてもよいので、REM含有量の下限値は0%である。しかしREMは、脱酸元素である。また、REMは、硫化物を形成することで、不純物であるSを無害化する元素である。この効果を得るためには、REM含有量が0%超であることが好ましく、0.0005%以上であることがさらに好ましい。一方、REM含有量が0.0050%超である場合、粗大な酸化物が形成されて、鋼線10の伸線時に断線を引き起こす場合がある。従って、REM含有量が0.0050%以下であることが好ましく、0.0020%以下であることがさらに好ましい。
Caは、本実施形態に係る鋼線10に含まれなくてもよいので、Ca含有量の下限値は0%である。しかしCaは、鋼線10の特性を悪化させる硬質なアルミナ系介在物を低減する元素である。また、Caは、微細な酸化物を生成する元素である。この微細な酸化物は、鋼線10のパーライトブロックサイズを微細化させ、これにより鋼線10の延性を向上させる。これら効果を得るためには、Ca含有量が0.0005%超であることが好ましい。一方、Ca含有量が0.0050%超である場合、粗大な酸化物が形成されて、鋼線10の伸線時に断線を引き起こす場合がある。従って、Ca含有量は0.0050%以下であることが好ましく、0.0040%以下であることがさらに好ましい。なお、通常の操業条件下では、Caが0.0003%程度含有される場合がある。
Mgは、本実施形態に係る鋼線10に含まれなくてもよいので、Mg含有量の下限値は0%である。しかしMgは、微細な酸化物を生成する元素である。この微細な酸化物は、鋼線10のパーライトブロックサイズを微細化させ、これにより鋼線10の延性を向上させる。この効果を得るためには、Mg含有量が0.0005%超であることが好ましい。しかしながら、Mg含有量が0.0050%超である場合、粗大な酸化物が形成されて、鋼線10の伸線時に断線を引き起こす場合がある。従って、Mg含有量は0.0050%以下であることが好ましく、0.0040%以下であることがさらに好ましい。なお、通常の操業条件下では、Mgが0.0001%程度含有される場合がある。
Zrは、本実施形態に係る鋼線10に含まれなくてもよいので、Zr含有量の下限値は0%である。しかしZrは、ZrOとして晶出してオーステナイトの晶出核となるので、オーステナイトの等軸率を高め、オーステナイト粒を微細化する元素である。本実施形態に係る鋼線10にZrが含まれている場合、パテンティング処理前のオーステナイトが微細化されることにより、鋼線10のパーライトブロックサイズが微細化され、これにより鋼線10の延性が向上する。この効果を得るためには、Zr含有量が0.0005%超であることが好ましい。一方、Zr含有量が0.0100%超である場合、粗大な酸化物が形成されて、鋼線10の伸線時に断線を引き起こす場合がある。従って、Zr含有量は0.0100%以下であることが好ましく、0.0050%以下であることがさらに好ましい。
本実施形態に係る鋼線10の成分組成の残部は、Feおよび不純物を含む。不純物とは、鋼材を工業的に製造する際に、鉱石若しくはスクラップ等のような原料、又は製造工程の種々の要因によって混入する成分であって、本実施形態に係る鋼線10の特性に悪影響を与えない範囲で許容されるものを意味する。
本実施形態に係る鋼線10の引張強度は1100MPa以上である。引張強度が1100MPa以上である鋼線10を用いて得られたスチールコードは、自動車用タイヤ、高圧ゴムホース、コンベアベルト等のゴム製品の補強材として好適である。
本実施形態に係る鋼線10の製造方法においては、上述した成分組成を有する線材を原料として用いる。線材の種類は特に限定されないが、熱間圧延線材であることが好ましい。線材の径は特に限定されないが、約5.5mm程度であることが好ましい。この線材の表面に形成された酸化スケールを酸洗等の化学処理、または機械処理によって除去する。このような処理は、デスケーリングと称されている。デスケーリングの方法は特に限定されない。
次に、酸化スケールを除去した線材を粗伸線して、これにより線径1.0mm以上3.5mm以下の中間鋼線を形成する(粗伸線工程S02)。粗伸線の方法は特に限定されないが、粗伸線は乾式伸線によって行われることが好ましい。以降、最終的に得られる鋼線と製造途中の鋼線とを区別するために、最終的に得られる鋼線(即ち本実施形態に係る鋼線10)を最終鋼線と称し、製造途中の鋼線を中間鋼線と称する場合がある。
次に、粗伸線工程S02において得られた中間鋼線の中心部および軟質部の両方が、850℃~1350℃の温度範囲内に加熱される(加熱工程S03)。加熱工程S03によって、中間鋼線の組織がオーステナイトとなり、このオーステナイトは、後述されるパテンティング工程S04においてパーライト変態する。従って、加熱工程S03において中間鋼線に生成したオーステナイトの状態によって、パテンティング工程S04の後に得られる最終鋼線に含まれるパーライトの状態が影響される。
次に、加熱工程S03によって加熱された中間鋼線を、加熱工程S03の終了後、溶融鉛浴(鉛浴)内に浸漬するパテンティング処理を行う(パテンティング工程S04)。鉛浴の温度は530℃以上580℃以下とし、鉛浴内に中間鋼線を浸漬する時間を5~45秒とする。また、加熱工程S03の終了とパテンティング工程S04の開始との間の時間は5秒程度とする。溶融鉛の代わりに溶融塩を用いてパテンティングを行っても良い。
そして、パテンティング工程S04を経た中間鋼線に対して、周波数50kHz以上の高周波加熱により、中間鋼線の表面温度を500℃以上700℃以下の温度範囲まで加熱する表層加熱を行う(表層加熱工程S05)。この際、加熱を行う時間を5秒以下とする必要がある。この表層加熱工程S05においては、中間鋼線の表層のみが加熱される。これにより、パテンティング工程S04におけるパーライト変態の際に生じた転位のうち、中間鋼線の表層の転位の大部分が消滅するので、中間鋼線の中心付近と表層部分とで硬度差が生じ、5μm以上の厚さを有する軟質部11が形成されることになる。
表層加熱工程S05において表層のみが加熱された中間鋼線は、冷却工程S06において冷却される。この際、図12に示されるように、表層加熱工程S05が終了してから3.0秒以内に中間鋼線の表面温度を500℃以下にする必要がある。好ましくは、表層加熱工程S05が終了してから2.0秒以内に中間鋼線の表面温度を500℃以下にする。表層加熱工程S05が高周波加熱によって行われる場合、表層加熱工程S05の終了の時点とは、中間鋼線が高周波加熱コイルを出た時点である。上述の冷却条件が達成されなかった場合、中間鋼線の内部も軟化されてしまうので、5μm以上0.1×Rmm以下の厚さの軟質部11を形成することができない。
本実施形態に係る鋼線10は、表面にブラスめっきが施されることが好ましい(ブラスめっき工程S07)。ブラスめっきは、ゴムとスチールコードとの密着性を高めるために形成されるものである。
そして、ブラスめっき工程S07においてブラスめっきされた鋼線10に対して湿式伸線を行い、その線径を0.15mm以上0.35mm以下のフィラメントを形成する(仕上伸線工程S08)。なお。中心部12と軟質部11とを有する鋼線10に対して伸線加工を実施した場合には、中心部12と軟質部11との硬さの差がさらに大きくなる。図13は、鋼線に付加された伸線加工歪みの量と、中心部12の硬さおよび軟質部11の硬さとの関係を示すグラフである。図13には、伸線加工歪み量の増大に従って、中心部12の硬さと軟質部11の硬さとの差が増大することが示されている。
次に、複数のフィラメントを用いて撚り線加工を行う(撚り線加工工程S09)。これにより、撚り線構造とされた高強度スチールコードが製造されることになる。
実施例1~実施例25の鋼線及び比較例26~36の鋼線は、上述した本実施形態に係る鋼線の製造方法によって作製した。
比較例37の鋼線は、表層加熱工程S05が省略されていることを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
比較例38の鋼線は、加熱工程S03における加熱温度が1380℃である(すなわち1350℃超である)ことを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
比較例39の鋼線は、加熱工程S03における加熱温度が830℃である(すなわち850℃未満である)ことを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
比較例40の鋼線は、パテンティング工程S04における鉛浴中への浸漬時間が4秒である(すなわち5秒未満である)ことを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
比較例41の鋼線は、パテンティング工程S04における鉛浴中への浸漬時間が50秒である(すなわち45秒超である)ことを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
比較例42の鋼線は、パテンティング工程S04における鉛浴中への浸漬後の冷却速度が8℃/秒である(すなわち10℃/秒未満である)ことを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
比較例43の鋼線は、表層加熱工程S05において行われる高周波加熱の周波数が30kHzである(すなわち50kHz未満である)ことを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
比較例44の鋼線は、表層加熱工程S05における表層加熱温度が480℃である(すなわち500℃未満である)ことを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
比較例45の鋼線は、表層加熱工程S05における表層加熱温度が730℃である(すなわち700℃超である)ことを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
比較例46の鋼線は、冷却工程S06における表層温度が500℃以下になるまでの時間が4秒である(すなわち2秒超である)ことを除き、上述した本実施形態に係る鋼線の製造方法に準拠した製造方法によって作製した。
鋼線の中心部のパーライト量は、鋼線のC断面の中心と、鋼線のC断面の1/4深さにおける、鋼線中心に関して45度ごとに配置された8箇所とにおけるパーライト量の平均値とした。各測定箇所におけるパーライト量は、鋼線の、パーライト組織を現出させたC断面の光学顕微鏡写真またはSEM写真に基づいて求めた。
軟質部厚さは、鋼線の硬度を測定することにより得られる、鋼線の深さ方向の硬度分布に基づいて求めた。鋼線のC断面を適宜調製し、切断面の外周から中心に向けて連続的に硬度測定を行うことにより、図2に示されるような、鋼線の深さと硬度との関係を示すグラフを得た。このグラフから、鋼線の線径Rの1/4の深さにおけるビッカース硬度よりもHv30以上低い領域の厚さを求めた。硬度測定の深さ間隔は、1μmとした。
表層硬度は、鋼線の表面から2μmの深さの箇所であって、鋼線の中心に関し45度ごとに配置された8箇所におけるビッカース硬さの平均値とした。
中心部硬度は、鋼線の表面から鋼線の線径Rの1/4の深さの箇所であって、鋼線の中心に関し45度ごとに配置された8箇所と、鋼線の中心とにおけるビッカース硬さの平均値とした。
表層部平均ラメラ間隔(表層ラメラ間隔)は、以下に説明する手順により求めた。まず、鋼線のL断面にパーライト組織を現出させた。次に、このL断面における、鋼線の表面から深さ5μmまでを含む領域の電子顕微鏡写真を撮影した。そして、この写真から、図6に示される表層平均ラメラ間隔測定領域を切り出した。表層平均ラメラ間隔測定領域は、縦横5μmの正方形であり、この正方形の1つの辺は、鋼線の表面と一致するようにされた。次に、図8に示されているように、表層平均ラメラ間隔測定領域に含まれる複数のパーライトのうち最もラメラ間隔が小さいパーライトを選択し、このパーライトに含まれるフェライト相の層およびセメンタイト相の層に直交する長さ2μmの線分を引き、この線分と交差するセメンタイト相の層の数を数え、線分の長さ(2μm)をセメンタイト相の層の数で割ることにより、表層平均ラメラ間隔測定領域に係るラメラ間隔を求めた。8つの表層平均ラメラ間隔測定領域それぞれにかかるラメラ間隔を求め、これらラメラ間隔を平均することにより、鋼線の表面から深さ5μmまでのパーライトの平均ラメラ間隔を得た。
中心部平均ラメラ間隔(中心部ラメラ間隔)は、以下に説明する手順により求めた。上述の表層部平均ラメラ間隔の測定方法と同様に、鋼線のL断面を調製し、鋼線の中心軸を含む領域の電子顕微鏡写真、および鋼線の線径Rの1/4深さの箇所を含む領域の電子顕微鏡写真を撮影した。次いで、縦横5μmの正方形である12箇所の中心平均ラメラ間隔測定領域に係るラメラ間隔を求めた。12箇所の中心平均ラメラ間隔測定領域のうち4箇所は、その向かい合う辺の中点同士を結ぶ線分のうち片方が、鋼線の中心軸と一致していた。12箇所の中心平均ラメラ間隔測定領域のうち8箇所は、その向かい合う辺の中点同士を結ぶ線分のうち片方が、鋼線の表面から線径Rの1/4深さの領域と一致した。12箇所の中心平均ラメラ間隔測定領域それぞれに係るラメラ間隔を求め、これらラメラ間隔を平均することにより、鋼線の中心の平均ラメラ間隔を得た。
デラミネーションの発生の有無は、鋼線に捻り試験を行うことにより判定した。デラミネーションが発生している鋼線に捻り試験を行った場合、捻り破断により生じる破面がせん断破面ではなく縦割れに沿った破面となるので、捻り破断した鋼線の破断形状を目視で検査することにより、デラミネーションの有無を判定することができる。
引張強度TSは、JIS Z 2241「金属材料の引張試験方法」に準拠した引張試験によって求めた。
評価結果を表1-3および表2-3に示す。
Si含有量が不足した比較例28の引張強度は、1100MPaよりも低くなった。
C含有量が過剰であった比較例27、およびSi含有量が過剰であった比較例29には、加工性の低下によって、デラミネーションが発生した。
Mn含有量が不足した比較例30には、脱酸およびSの固定が十分に行われなかったので、デラミネーションが発生した。
Mn含有量が過剰であった比較例31には、加工性の低下によって、デラミネーションが発生した。
Mo含有量が過剰であった比較例32には、Mo炭化物の析出による伸線加工性の低下が生じたので、デラミネーションが発生した。
Al含有量が過剰であった比較例33には、鋼線の延性劣化および伸線性劣化を引き起こすアルミナ系介在物の発生によって、デラミネーションが発生した。
B含有量が過剰であった比較例34には、鋼線の延性低下を引き起こす粗大なFe23(CB)6の発生によって、デラミネーションが発生した。
N含有量が過剰であった比較例35には、延性の低下が生じたので、デラミネーションが発生した。
CrおよびMo含有量が過剰であった比較例36には、上部ベイナイト、もしくはマルテンサイトが多く生成し、パーライト分率が低下して伸線加工性の低下が生じたので、デラミネーションが発生した。
パテンティング前の加熱温度が過剰であった比較例38は、平均ラメラ間隔差が過剰であったので、デラミネーションが発生した。
パテンティング前の加熱温度が不足した比較例39は、パーライトの量が低下して伸線加工性の低下が生じたので、デラミネーションが発生した。
パテンティングにおける鉛浴中への浸漬時間が不足した比較例40の鋼線は、パーライト分率が低下してデラミネーションが発生した。
パテンティングにおける鉛浴中への浸漬時間が過剰であった比較例41の鋼線は、パーライト中のセメンタイトが分断化されてパーライト量が不足し、これにより伸線加工性および引張強度が低下した。
パテンティングにおける鉛浴中への浸漬後の冷却速度が不足した比較例42の鋼線は、引張強度が低下した。
表層加熱において行われる高周波加熱の周波数が不足した比較例43の鋼線は、鋼線の内部まで加熱が行われることにより軟質部厚さが不足したので、デラミネーションが発生した。
表層加熱における表層加熱温度が不足した比較例44の鋼線は、表層の硬さが低下せず軟質部厚さが不足したので、デラミネーションが発生した。
表層加熱における表層加熱温度が過剰であった比較例45の鋼線は、鋼線の内部まで加熱が行われることによりパーライト中のセメンタイトが分断されパーライト量が不足したので、引張強度および引張強度が低下した。
表層加熱後の冷却における、表層温度が500℃以下になるまでの時間が過剰であった比較例46の鋼線は、軟質部深さが過剰になったので、引張強度が不足した。
11 軟質部
12 中心部
13 圧痕
14 表層平均ラメラ間隔測定領域
15 中心平均ラメラ間隔測定領域
16 鋼線の線径Rの1/4の深さの箇所
20 パーライト
21 フェライト相の層
22 セメンタイト相の層
23 線分
Claims (4)
- 鋼線であって、
成分組成が、質量%で、
C:0.70%以上1.20%以下、
Si:0.15%以上0.60%以下、
Mn:0.10%以上1.00%以下、
N:0.0010%以上0.0050%以下、
Al:0%以上0.010%以下、
Ti:0%以上0.10%以下、
Cr:0%以上0.50%以下、
Co:0%以上0.50%以下、
V:0%以上0.50%以下、
Cu:0%以上0.20%以下、
Nb:0%以上0.100%以下、
Mo:0%以上0.20%以下、
W:0%以上0.200%以下、
B:0%以上0.0030%以下、
REM:0%以上0.0050%以下、
Ca:0%以上0.0050%以下、
Mg:0%以上0.0050%以下、および
Zr:0%以上0.0100%以下
を含み、
残部がFe及び不純物からなり、
前記鋼線の線径Rが1.0mm以上3.5mm以下であり、
前記鋼線の外周に沿って軟質部が形成されており、前記軟質部のビッカース硬度は、前記鋼線の前記線径Rの1/4の深さにおける前記ビッカース硬度よりもHv30以上低く、前記軟質部の厚さが、5μm以上0.1×Rmm以下であり、
前記軟質部以外の前記鋼線の組織は、パーライトを面積%で95%以上100%以下の割合で含有しており、
前記鋼線の表面から深さ5μmまでの前記パーライトの平均ラメラ間隔は、前記鋼線の中心の前記パーライトの前記平均ラメラ間隔よりも小さく、前記鋼線の前記表面から深さ5μmまでの前記パーライトの前記平均ラメラ間隔と前記鋼線の前記中心の前記パーライトの前記平均ラメラ間隔との差が3nm以上60nm以下であり、さらに、
引張強さが1100MPa以上である
ことを特徴とする鋼線。 - 前記軟質部の厚さが、10μm以上0.08×Rmm以下であることを特徴とする請求項1に記載の鋼線。
- 前記鋼線の前記表面から深さ5μmの前記箇所までの前記平均ラメラ間隔と前記鋼線の前記中心の前記平均ラメラ間隔との差が40nm以下であることを特徴とする請求項1または2に記載の鋼線。
- 前記成分組成が、質量%で、
Ti:0.005%以上0.10%以下、
Cr:0%超0.50%以下、
Co:0%超0.50%以下、
V:0%超0.50%以下、
Cu:0%超0.20%以下、
Nb:0%超0.100%以下、
Mo:0%超0.20%以下、
W:0%超0.20%以下、
B:0%超0.0030%以下、
REM:0%超0.0050%以下、
Ca:0.0005%超0.0050%以下、
Mg:0.0005%超0.0050%以下、および
Zr:0.0005%超0.0100%以下のうちの1種または2種以上
を含むことを特徴とする請求項1~3のいずれか一項に記載の鋼線。
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