Development of Cold Forging Technology for Beta-Titanium 2018-04-14¢  Development of Cold Forging Technology

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  • 1Kobe Steel, LTD Proprietary Information

    Development of Cold Forging Technology for Beta-Titanium

    October 2006

    NORIKAZU MATSUKURA TITANIUM TECHNOLOGY DEPARTMENT

    KOBE STEEL, LTD.

  • 2Kobe Steel, LTD Proprietary Information (Reference: Japan Titanium Association)

    Various bolts and parts made with titanium

  • 3Kobe Steel, LTD Proprietary Information

    Titanium materials for bolts and parts

    Kind of material Tensile strength Young’s Modulus

    Unalloyed titanium   300 ~ 500 MPa 105 GPa

    Ti-6Al-4V (annealed) 900 MPa   115 GPa (ST-A) 1200 MPa

    Ti-6-4 is generally used for high strength bolts.

  • 4Kobe Steel, LTD Proprietary Information

    Ti-6Al-4V bolts

    Thread rolling or

    machining Hot forging

    (1)

    (2) Machining only

    Manufacturing costs are higher than cold forging.

  • 5Kobe Steel, LTD Proprietary Information

    Feature of Ti-15V-3Cr-3Sn-3Al (1)

    Upset : 20% Upset : 60% Upset : 80%

    Good cold workability

    High tensile strength due to aging Tensile strength 750~800MPa (annealed)

    Aging 1000~1200MPa

    Ti-15-3-3-3 is a good material for high strength bolts.

    - No cracks are generated even if Ti-15-3-3-3 is deformed to 80%. - Ti-15-3-3-3 can be cold forged.

  • 6Kobe Steel, LTD Proprietary Information

    Feature of Ti-15V-3Cr-3Sn-3Al (2) 0.02

    0.01

    0 0 20000 40000 60000 80000 100000

    Time [s]

    To ta

    l s tr

    ai n

    at room temperature CP-Ti (0.8σ0.2)

    Ti-6Al-4V (0.8σ0.2)

    Ti-15V-3Cr-3Sn-3Al (0.8σ0.2)

    Creep curve of titanium materials (annealed) (Ref : E. Sato : J. JILM., 55 (2005), 604-609)

    - Since Ti-15-3-3-3 does not start creep at room temperature, it is suitable for high strength bolts.

  • 7Kobe Steel, LTD Proprietary Information

    Why is cold forging difficult for Ti-15-3-3-3 ? The Young’s modulus is low. (~80GPa / less than half that of steel)

    - It is easy to gall with the die when the reduction and hollowing process are performed.

    die

    material

    reduction

    die material

    hollowing

    Thermal conductivity is low. (8.1W/m K / one tenth that of steel) - The temperature of the contact surface between material

    and die is increased locally by friction heat, so it is easy to gall.

  • 8Kobe Steel, LTD Proprietary Information

    Ti-15V-3Cr-3Sn-3Al bolts POINTS - galling prevention coating for the material

    - cooling the material and the die effectively

    Trial production

    By coating materials with the appropriate oxide layer and lubricant, galling can be prevented.

  • 9Kobe Steel, LTD Proprietary Information

    The cold forging process of the bolts

    Stage 1 chamfer the edge of the shaft Stage 2 reduce the shaft (forward extrusion) Stage 3 upset the head part Stage 4 reduce the head part and form the head shape Stage 5 hollow the head part (backward extrusion) and

    expand the flange

    Stage 1 Stage 2 Stage 3 Stage 4 Stage 5

  • 10Kobe Steel, LTD Proprietary Information

    Parts former

    Production equipment

    Material (Ti-15-3-3-3)

    diepunch

    #1 #2 #3 #4 #5

    #1 #2 #3 #4 #5

    back and forth

    (Reference: SAKAMURA MACHINE CO., LTD)

  • 11Kobe Steel, LTD Proprietary Information

    A bolt made from Ti-15-3-3-3 - Trial production was successful. 10,000 bolts were made by this cold forging process.

    10mm

  • 12Kobe Steel, LTD Proprietary Information

    Relationship between the tensile properties of Ti-15-3-3-3 bolts and aging condition.

    - Tensile strength without aging is about 900 MPa. - Though maximum tensile strength exceeds 1200 MPa, the elongation declines about 1%.

    - Tensile strength of 1000~1100MPa is appropriate for Ti-15-3-3-3 bolts

    Relationship between tensile properties and aging condition in a Ti-15-3-3-3 material

    600

    800

    1000

    1200

    1400

    0 4 8 12 16 20 24 28 aging time [h]

    450°C 480°C

    570°C

    510°C 540°C

    Te ns

    ile s

    tre ng

    th [M

    P a]

    600

    800

    1000

    1200

    1400

    0 4 8 12 16 20 24 28 aging time [h]

    450°C 480°C

    570°C

    510°C 540°C

    0. 2%

    p ro

    of s

    tre ng

    th [M

    P a]

    0 5

    10 15 20

    0 4 8 12 16 20 24 28 Aging time [h]

    E lo

    ng at

    io n

    [% ]

    450°C 480°C

    570°C

    510°C540°C

    0

    800

    900

    1000

    1100

    1200

    1300

    1400

    1 2 3 4 Aging temperature [°C]

    Te ns

    ile s

    tre ng

    th [M

    Pa ] as cold forging800°C ST and aging

    770°C ST and aging aging only

    without aging 570540510

    breaking below the normal

    0

    5

    10

    15

    1 2 3 4 Aging temperature [°C]

    El on

    ga tio

    n [%

    ]

    without aging 570540510

  • 13Kobe Steel, LTD Proprietary Information

    Microstructures of the cross section of screw part (a) 800 degree C solution treatment and 570 degree C aging (b) 570 degree C aging

    - The microstructure of (a) is coarse, so the elongation is low. - The microstructure of (a) is fine, so the elongation is not declined.

    0.2mm

    1mm

    (a)

    1mm

    0.2mm(b)

  • 14Kobe Steel, LTD Proprietary Information

    Relationship between aging temperature and tensile properties of Ti-15-3-3-3 smooth and notch specimens - When the tensile strength of smooth specimen exceeds 1200MPa,

    the tensile strength of notch specimen declines from the peak. Then the bolts cannot be used by the tensile strength over 1200MPa.

    600

    800

    1000

    1200

    1400

    1600

    1 2 3 4 5 6 Aging temperature [°C]

    St re

    ng th

    [M Pa

    ]

    tensile strength (smooth) tensile strength (notch)

    1000MPa class bolt

    1100MPa class bolt

    0 5

    10 15 20 25

    1 2 3 4 5 6 Aging temperature [°C]

    El on

    ga tio

    n [%

    ]

    elongation (smooth)

    540without aging 570 480500510

  • 15Kobe Steel, LTD Proprietary Information

    The relation between temperature and tensile properties of Ti-15-3-3-3 bolts

    - A tensile strength of 1000~1100MPa is appropriate for Ti-15-3-3-3 bolts considering the balance between tensile strength and elongation.

    0

    2

    4

    6

    8

    10

    12

    14

    800 900 1000 1100 1200 1300 Tensile strength [MPa]

    El on

    ga tio

    n [%

    ]

    as cold forged (without heat treatment)

  • 16Kobe Steel, LTD Proprietary Information

    - Cold forging of Ti-15-3-3-3 bolts is enabled by improvements of galling prevention coating, that is the appropriate oxide layer and lubricant.

    - The trial production of 10,000 bolts by cold forging was successful. So, it is expected that the cost of high strength titanium bolts become lower than that of Ti-6-4.

    - Ti-15-3-3-3 bolt has a strength of 1000~1100MPa and it is expected to contributes to weight reduction of the parts.

    Summary

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