[0001]
The present invention relates to a method for producing a titanium casting
10 product for hot rolling made of titanium alloy, particularly to a titanium casting
product that can keep excellent surface properties after hot rolling even when a
breakdown process such as slabing, forging, or the like is omitted and a method for
producing the same.
15
[0002]
lo
Backgli-ound Art
In general, titanium material uses titanium sponge or titanium scrap as a raw
material. It is melted by non-consumable electrode arc remelting, electron-beam
remelting, plasma arc remelting, or the like into a titanium ingot (titanium casting
20 product). Non-consumable arc remelting uses titanium sponge pressed into a
I
briquette as an electrode, and causes arc discharge between the electrode and a mold
to melt the electrode itself and. cast it into the mold, thereby obtaining an ingot.
Therefore, uniform discharge between the electrode and the mold is necessary, which
limits the shape of the. m old to a cylindrical shape; accordingly, the shape of the in~ot .. . .
25 after casting is a cylindrical shape. On the other hand, electron-beam remelting and
plasma arc remelting, which use electron beams and plasma arc, respectively, differ
in melting method, but both the methods pour molt\)n titanium melted on a hearth
into a mold, and this allbws free s~lection . of the shape of the mold; tl:njs, it is
'
possible to produce ingots with various shapes, such as a rectangular shape and a .
30 ·billet, shape, as well as a C)'lihdrical shape.
[0003}
- --"-----------------------
. PCT/JP2014/076083
2/25
In the current titanium material production process, after this, a hot working
process, such as slabing or forging, which is called an ingot breakdown process, is
carried out and then hot rolling is performed; the breakdown process is necessary.
However, according to the shapes, it is considered that the breakdown process can be
5 omitted in producing a sheet material for a rectangular ingot (slab) and in producing
a bar or a wire rod for a cylindrical ingot and a billet ingot, and a technology of
performing hot rolling without the breakdown process has been under study. If this
technology is established, it can be expected that cost will be improved by omission
of a process and an enhancement in yield.
10 [0004]
However, a titanium casting product produced by electron-beam remelting
or plasma arc remelting is as-cast and therefore comprises coarse grains with sizes as
large as several tens of millimeters. In regard to such a titanium casting product,
when hot rolling is performed without a breakdown process, because of the coarse
15 grains, the influence of deformation anisotropy in a grain and between crystal grains
causes surface unevenness, leading to surface defects. In order to remove surface
defects that occur in hot rolling, it is necessary to increase the amount of pickling of
the s)lfface of a hot-rolled material in a pickling process, which is the following
process, and accordingly yield is worsened and may result in an increase in cost.
20 [0005]
Accordingly, for a titanium ingot produced by electron-beam remelting or
plasma arc remelting, while it is expected that cost will be improved by omission of a
breakdown process carried out by slabing, forging, or the like, there is a concern that
an increase in surface defects may cause an increase in cost. This has inhibited
25 practical utilization of a titanium casting product obtained without a breakdown
process.
[0006]
Patent Literature 1 discloses a method that provides an excellent casting
surface and can improve surface defects after hot rolling even when an ingot
30 breakdown process is omitted in the following case: in a cross-sectional
microstructure of a titanium slab produced in an electron-beam remelting furnace and
PCT/JP20 14/076083
3/25
extracted directly from a mold, an angle e formed by the solidification direction from
the surface layer toward the interior and the casting direction of the slab is in the
range of 45 to 90°, or in the crystal orientation distribution of the surface layer, an
angle formed by the c-axis of hcp and the normal to the slab surface layer is in the
5 range of 35 to 90°. That is, controlling the shape and crystal orientation of crystal
grains of the surface suppresses occurrence of defects due to coarse crystal grains.
[0007]
In Patent Literature 2, as a method for .directly performing hot rolling
without an ingot breakdown process for a titanium material, the surface layer at a
10 surface corresponding to a surface to be rolled is subjected to melting and
resolidification by high-frequency induction heating, arc heating, plasma heating,
electron-beam heating, laser heating, and the like; thus, a portion from the surface
layer to a depth of 1 mm or more undergoes grain refining. This slab surface layer
is quenched and solidified to have fine and irregular crystal orientation distribution,
15 which prevents occurrence of surface defects.
Patent Literature
[0008]
20 Patent Literature 1:
Patent Literature 2:
Technical Problem
Citation List
W0/2010/090353
JP 2007-332420A
Sunnnary of Invention
25 [0009]
The present invention provides a titanium casting product and a method for
producing the same, where the titanium casting product is obtained without any need
of either a cutting and conditioning process for an as-cast titanium casting product
surface layer or any breakdown process and the occurrence of the surface defects is
30 suppressed in a titanium material after subsequent hot rolling.
-- ------ ----
PCT/JP2014/076083
4/25
Solution to Problem
[0010]
The present inventors carried out extensive studies in order to achieve the
object. The resulting findings are as follows. When an as-cast titanium casting
5 product produced by electron-beam remelting or plasma arc remelting, as a method
for melting a titanium casting product made of titanium alloy, is subjected to hot
rolling without a breakdown process, which has been conventionally necessary, a
material (powder, a chip, wire, or foil) containing a.~ stabilizer element is placed or
applied on the surface layer at a surface to be rolled of the as-cast titanium casting
10 product, and the surface layer of a titanium material is melted with the material as a
pre-process of hot rolling. In this manner, a layer having a higher ~ stabilizer
element concentration than a base material, i.e., a ~ stabilizer element-rich layer, is
formed in the surface layer of the titanium material. This makes it possible to keep
excellent surface properties after hot rolling.
15 [0011]
That is, the present invention is as described below.
(1)
A titanium casting product made of titanium alloy, comprising:
a layer containing one or more kinds of~ stabilizer elements in a range of 1
20 mm or more in depth at a surface serving as a surface to be rolled,
wherein an average value of ~ stabilizer element concentration in a range of
within 1 mm in depth is higher than ~ stabilizer element concentration in a base
material by, in mass%, equal to or more than 0.08 mass% and equal to or less than
1.50mass%.
25 (2)
The titanium casting product according to (1 ),
wherein the~ stabilizer element(s) is/are one or more of Fe, Ni, and Cr.
(3)
The titanium casting product according to (1 ), containing one or more kinds
30 of a stabilizer elements or neutral elements together with the~ stabilizer element(s).
(4)
PCT/JP2014/076083
5/25
A method for producing a titanium casting product, comprising:
melting a surface serving as a surface to be rolled of a titanium casting
product made of titanium alloy together with a material containing a ~ stabilizer
element and then solidifying the surface to make an average value of ~ stabilizer
5 element concentration in a range of within 1 mm in depth higher than ~ stabilizer
element concentration in a base material by, in mass%, equal to or more than 0.08
mass% and equal to or less than 1.50 mass%.
10
(5)
The method for producing a titanium casting product according to ( 4),
wherein the material containing the ~ stabilizer element is in a form of any
of powder, a chip, wire, and foil.
(6)
The method for producing a titanium casting product according to ( 4),
wherein the surface serving as the surface to be rolled of the titanium
15 casting product made of titanium alloy is melted by electron-beam heating or plasma
heating.
Advantageous Effects of Invention
[0012]
20 With a titanium casting product according to the present invention, even
when hot rolling is performed without a breakdown process such as slabing, forging,
or the like, which has been conventionally necessary, a titanium material having
surface properties equivalent to those of a conventional material can be produced.
A reduction in heating time due to omission of the breakdown process, a reduction in
25 cutting treatment achieved by smoothing of the surface layer of the titanium casting
product due to surface layer melting, a reduction in the amount of scarfmg in
pickling due to an enhancement in surface properties of the titanium material after
hot rolling, and the like lead to an enhancement in yield, producing an effect of
reducing production cost; the present invention offers a great effect in industry.
30
Brief Description of Drawings
5
10
PCT/JP2014/076083
6/25
[0013]
[FIG. 1] FIG. 1 schematically shows a change m concentration of a moltenresolidified
layer.
Description of Embodiments
[0014]
Hereinafter, the present invention will be described in detail.
[0015]
In general, titanium alloy is subjected to hot rolling and cold rolling, so that
a sheet material, a wire rod, a bar, or the like is produced. In the present invention,
titanium alloy refers to a titanium alloy and a+~ titanium alloy.
[0016]
Titanium casting products of interest in the present invention include
15 rectangular ingots (slab), cylindrical ingots, and billet ingots. The surface layer of a
titanium casting product with such a shape is melted together with a material
containing a ~ stabilizer element, so that surface defects are suppressed for a titanium
material after hot rolling.
[0017]
20 In the present invention, only a surface layer part of an as-cast titanium
casting product is heated to be melted 1 mm or more in depth. The surface layer
part of the titanium casting product melted in this manner is quenched and
resolidified after melting, and a cross-sectional microstructure of a molten -
resolidified layer cooled to room temperature (a solidified layer that is obtained by
25 melting only a surface layer part of an as-cast titanium casting product by heating
and then performing quenching and resolidification in this manner is called a
"molten - resolidified layer") is a fine acicular microstructure or a martensite
microstructure. Moreover, in melting the surface layer, a base material is melted
concurrently with a ~ stabilizer element; thus, the ~ stabilizer element concentration
30 in the molten - resolidified layer becomes higher than that in the base material, and
consequently, an enhancement in hardenability due to the addition of the ~ stabilizer
PCT/JP2014/076083
7/25
element causes a transformation or martensite transformation during cooling and
thus makes the molten - resolidified layer have an even finer microstructure. The
"enhancement in hardenability" here refers to low temperature a transformation or
martensite transformation achieved by shifting the nose of transformation in
5 continuous cooling to the long-time side by containing the p stabilizer element in the
surface layer of the titanium casting product. The purpose of the low temperature
transformation is to increase nucleation sites to make crystal grains finer.
[0018]
Furthermore, the titanium casting product subjected to the above-described
10 melting and resolidification has high p stabilizing ability in the molten - resolidified
layer, which brings the interior of the molten - resolidified layer into the state of
a+pregion in heating for hot rolling. Since there exist two phases of a phase and p
phase, grain growth is suppressed, so that fine crystal grains after the melting and
resolidification can maintain the fine grains until hot rolling after heating for hot
15 rolling. Accordingly, unevenness of the surface of the titanium material due to
coarse crystal grains can be suppressed, and thus a titanium hot-rolled material
without surface defects can be produced.
[0019]
As will be described in detail later, in the present invention, the formed
20 molten - resolidified layer includes a deep portion and a shallow portion. In the
present invention, the specified depth of the molten - resolidified layer is 1 mm or
more; this depth refers to the depth of the shallowest portion as viewed in a crosssection
in a direction perpendicular to a scanning direction of a molten bead.
25
[0020]
When the surface layer of the titanium casting product is remelted l mm or
more in depth as described above and then solidified, a portion from the surface layer
to a depth of 1 mm or more has a fine acicular microstructure or a martensite
microstructure, whereas the center side in the sheet thickness direction of the
titanium material with respect to the molten - resolidified layer and a portion
30 thermally influenced thereby keeps the microstructure as-cast. In the present
invention, at least the surface layer corresponding to a surface to be rolled of the
---------------~ ~-------- .
PCT/JP20 14/076083
8/25
titanium casting product is remelted together with a material containing a ~ stabilizer
element and then solidified, so that the average value of concentrations of the ~
stabilizer element in a portion from the surface layer to a depth of 1 mm in the
molten - resolidified layer is higher than the ~ stabilizer element concentration in the
5 base material by a certain amount. Even if melting and resolidification treatment is
performed without adding a ~ stabilizer element, a+~ titanium alloy containing a ~
stabilizer element in its alloy composition has the effect of making crystal grains of
the molten - resolidified layer finer. In this treatment, however, in the composition
of a molten portion in the melting and resolidification treatment, when the surface
10 layer is melted together with a ~ stabilizer element, solidification starts immediately
after the melting, and thus sufficient diffusion does not occur in the molten portion,
so that ununiformity of~ stabilizer element concentration remains. Such remaining
ununiformity causes a region with high ~ stabilizer element concentration, which
makes the microstructure even finer. Moreover, in the case where the base material
15 is remelted as it is, even if a fme microstructure is obtained in melting and
resolidification, a colony, which is an aggregate of crystal grains having the same
crystal orientation, may be formed. Because of the same crystal orientation, such a
colony behaves like a coarse grain. Accordingly, this may lead to hot rolling
defects due to the influence of deformation anisotropy. However, with the
20 ununiformity of ~ stabilizer element concentration, the difference in ~ stabilizer
element concentration creates fine crystal grains locally as described above, which
suppresses occurrence of the colony and suppresses growth of the colony in heating
for hot rolling. The average value of concentrations of the ~ stabilizer element in a
portion from the surface layer to a depth of 1 mm in the molten - resolidified layer is
25 higher than the ~ stabilizer element concentration in the base material by, in mass%,
equal to or more than 0.08 mass% and equal to or less than 1.50 mass%. As the ~
stabilizer element, a plurality of ~ stabilizer elements may be added in combination,
in which case the ~ stabilizer element concentration refers to the sum of the
concentrations of the contained ~ stabilizer elements. Since an effect is obtained by
30 only adding the ~ stabilizer element to make the base material and the molten -
resolidified layer have a difference in ~ stabilizer element concentration of 0.08
-------- -----~~------~ ~
PCT/JP20141076083
9/25
mass% or more, this value is set as a lower limit. In order to further exert the effect
of suppressing surface defects, the ~ stabilizer element concentration difference
preferably exceeds 0.2 mass%, and it is most preferable that the ~ stabilizer element
difference exceed 0. 5 mass%. Moreover, when the difference in ~ stabilizer
5 element concentration between the base material and the molten- resolidified layer is
within the aforementioned range, the ~ stabilizer element-enriched layer at the
surface layer is removed by shot blasting and pickling, which are processes after hot
rolling, and the ~ stabilizer element enriched in the molten - resolidified layer is
detoxified. That is, the processes of shot blasting and pickling removes the ~
10 stabilizer element-enriched layer, making it possible to obtain components and
mechanical properties equivalent to those of a cold-rolled sheet produced by a
normal method. However, if the difference in ~ stabilizer element concentration
between the base material and the molten - resolidified layer is more than 1.50
mass%, the volume fraction of the ~ phase, which undergoes significant oxidation, in
15 the surface layer of the titanium casting product increases, so that the amount of
oxidation increases greatly as compared with the base material. Furthermore, a
difference in hot deformation resistance increases between the molten - resolidified
layer at the surface layer of the titanium casting product and the base material in hot
rolling, which may cause crack or the like in the surface layer or this boundary
20 portion. These causes make it necessary to increase the amount of scarfing of the
surface in a pickling process, which significantly reduces yield. In addition, it
becomes difficult to detoxify the ~ stabilizer element-enriched layer in a post-process.
Hence, the average value of concentrations of the ~ stabilizer element in a portion
from the surface layer to a depth of 1 mm may be made to differ from the ~ stabilizer
25 element concentration in the base material by 1.50 mass% or less. In addition,
although the specified melting depth is 1 mm or more, too deep melting depth may
cause the ~ stabilizer element-enriched layer to remain after the processes of shot
blasting and pickling; hence, it is desirable that the melting depth be approximately 5
mmorless.
30 [0021]
Moreover, normally, a titanium casting product m casting undergoes
PCT/JP2014/076083
10/25
solidification from a surface layer part of the titanium casting product in contact with
the mold; therefore, components slightly differ between the surface layer and the
interior of the titanium casting product depending on distribution of a solute for each
element. Since a ~-stabilizer, such as Fe, exhibits normal segregation, in
5 solidification or in transformation, the Fe concentration in the surface layer part of
the titanium casting product decreases and the Fe concentration tends to become
higher toward the interior of the titanium casting product. Therefore, it is very
effective to make the ~-stabilizer concentration in the molten and resolidified layer
equal to or higher than that in the parent metal by melting the ~-stabilizer and the
10 parent metal concurrently. This effect is especially significant with a titanium alloy.
[0022]
In addition, in casting of the titanium material, components are adjusted to
be uniform in the entire slab by controlling input of raw materials. However,
fluctuation of components or the like may occur partially. Therefore, in an alloy
15 originally having a low ~-stabilizer concentration, a region may exist in which
crystal grains are not sufficiently fine in the molten and resolidified layer, according
to component fluctuation of the ~-stabilizer, and surface defects may occur partially
after hot rolling. Hence, it is effective to add a ~-stabilizer in melting and
resolidification to raise the amount of the ~-stabilizer added; thus, partial surface
20 defects can also be suppressed. In addition, as mentioned above, component
fluctuation of the ~-stabilizer in the molten and resolidified phase is greater than
component fluctuation in the parent metal also in an alloy originally having a high ~stabilizer
concentration; thus, the effect of splitting a colony further mcreases,
making it possible to suppress partial surface defects.
25 [0023]
In a cross-section in a direction perpendicular to a scanning direction of a
molten bead, the molten and resolidified layer tends to be deepest at the center of the
molten bead in remelting of the surface layer of the titanium casting product, and,
when molten beads are overlapped, is shallowest at a portion midway between
30 adjacent molten beads, the deepest portion and the shallowest portion being repeated
periodically. Here, if a difference between the deepest portion and the shallowest
PCT/JP2014/076083
11/25
portion is large, this difference causes a difference in deformation resistance in hot
rolling, which may cause defects. Hence, it is desirable that the above difference be
less than 2 mm. Note that in the present invention, the specified depth of the
molten and resolidified layer is 1 mm or more; this depth refers to the depth of the
5 shallowest portion as viewed in a cross-section in a direction perpendicular to a
scanning direction of a molten bead.
[0024]
Description will be given on a method for measuring the depth of the molten
and resolidified layer and ununiformity in melting and resolidification. A portion
10 cut out from the surface layer portion of the titanium casting product in a crosssection
in a direction perpendicular to a scanning direction of a molten bead is used
as an embedding and polishing sample for scanning electron microscopy (SEM)/ an
electron probe microanalyser (EPMA); thus, the molten and resolidified layer can be
distinguished easily. In the present invention, since the depth of the molten and
15 resolidified layer is defmed as the depth of the shallowest portion, a melting depth
can be simply obtained by elemental mapping analysis. FIG. 1 shows an example
of measured values of changes in concentration of the parent metal and the molten
and resolidified layer. This is obtained by linear analysis of P-stabilizer
concentration in the thickness direction from a parent metal portion near the surface
20 layer at a surface to be rolled of the titanium casting product toward the surface to be
rolled. In the base material, the P stabilizer element concentration is low and
substantially uniform, whereas in the molten - resolidified layer, the p stabilizer
element concentration is high and also exhibits concentration fluctuation, which
indicates ununiformity.
25 [0025)
Examples of the p stabilizer element include V, Mo, Fe, Cr, Mn, Ta, Nb, Ni,
Co, Cu, and W. In titanium, however, an element such as W or Ta having a high
melting point causes high density inclusion (HDI), and serves as a starting point of
fatigue when it remains in the titanium material without being melted or without
30 being diffused sufficiently; therefore, such an element needs to be used with care.
Moreover, Mo, Nb, and the like have lower melting points than W and Ta, but still
It
PCT/JP20 14/076083
12/25
have melting points of 2000°C or higher; therefore, when using Mo or Nb, it is
desirable to alloy it with an element such as Ti in advance to make the melting point
lower and add the resulting alloy. ~ stabilizer elements can be classified into a
complete solid solution type, such as V, Mo, Ta, and Nb, and an eutectoid type, such
5 as Fe, Cr, Mn, Co, Ni, and Cu. ~ stabilizer elements of the eutectoid type have low
solid solubility but have high ~ stabilizing ability; therefore, addition of a ~ stabilizer
element of the eutectoid type is effective even in a small amount. In regard to Fe,
Cr, Mn, Co, Ni, and Cu, which are of the eutectoid type, surface defects after hot
rolling can be suppressed when ~ stabilizer element concentration in the molten -
10 resolidified layer is higher than that in the base material by approximately 0.10 to
0.60 mass%; hence, this range is preferable. In regard to V, Mo, Ta, and Nb, which
are of the complete solid solution type, which have low ~ stabilizing ability as
compared with the eutectoid type, it is desirable to add a ~ stabilizer element in a
large amount such that ~ stabilizer element concentration in the molten - resolidified
15 layer is higher than that in the base material by approximately 0.60 to 1.50 mass%.
Even when a ~ stabilizer element of the eutectoid type is used, since quenching is
performed in solidification after remelting, cooling rate is high and no precipitate
occurs, and also in heating for hot rolling, no precipitate occurs because the state is
the a+~region. Furthermore, the material containing the ~ stabilizer element may
20 contain a a-stabilizer typified by AI, or a neutral element, such as Sn or Zr. Either
one or both of a a-stabilizer and a neutral element may be contained. The total
amount of a a-stabilizer and a neutral element in the molten - resolidified layer is
preferably 2.0 mass% or less with respect to the base material. Fe, Ni, and Cr,
which are relatively inexpensive ~ stabilizer elements, are preferably used as the
25 material to be melted together with the surface layer of the as-cast titanium casting
product. It is also effective to use Fe powder or the like or stainless steel powder or
the like, or utilize crushed scrap of ordinary steel or stainless steel. Similarly,
crushed scrap oftitanium alloy may be used.
30
[0026]
The material used for adding the ~ stabilizer element to the surface layer of
the casting product may have any of the shapes of powder, a chip, wire, and foil, and
PCT/JP2014/076083
13/25
it is desirable that the material be in a small piece. It is effective to use any of the
following materials: powder with a particle size in a range of 1 !LID to 0.5 mm, a chip
with a size in a range of 2 mm square to 5 mm square, wire with a diameter in a
range of 0.5 mm to 5 mm, and foil with a thickness in a range of 1 J.lffi to 0.1 mm.
5 Such a material is disposed uniformly on the surface of the casting product when
placed or applied on the surface of the casting product; thus, it can be added
uniformly to the surface layer of the titanium casting product, which provides a
titanium casting product with more excellent surface. properties.
10
[0027]
Methods for melting the surface layer together with the ~ stabilizer element
include electron-beam heating, arc heating, laser heating, and induction heating.
Titanium is active metal, and when the surface layer is melted in atmospheric air, a
molten portion is oxidized significantly. Hence, the following methods are suitable:
electron-beam heating, arc heating (in particular, a heating method using inert gas,
15 such as plasma arc heating or tungsten inert gas (TIG) welding), laser heating, and
20
25
the like, which can perform treatment in a vacuum atmosphere or an inert gas
atmosphere. The aforementioned treatment can be performed by any of these
methods. Of these, electron-beam heating or plasma arc heating, which can apply
high energy at once, is suitable for industry and preferred to be used.
[Examples]
[0028]
Hereinafter, the present invention will be described m more detail m
Examples.
'0
"
"
"
"
"
"
'" "
'"
'"
"
"
"
"
"
"
o ... d.
Ti-IFa-0.3~0
THFe-0.350
THFe-0.350
THFe-0.350
THFe-0.350
Ti-1 Fe-0.350
THFe-0.350
n-1 F e-0.350
n-1Fe-0.350
THFe-0.350
Ti-1Fe-0.350
THFe-0.350
n-lFe-0.350
n-1Fe-0.350
THFe-Q.350
THFe-0.350
Ti-lFe-0.350
THFe-0.350
THFe-0.350
Ti-lFe-0.350
Ti-1 Fe-0.350
Ti-0.06Pd
TI-Q.5Ni-0.05Ru
Ti-5AI-1Fe
TI-5AI-1 F e-0.25Si
26 ! Ti-3AI-2.5V
21 I n-o.sou
28 I THOu
29 I Ti-1Cu-0.5Nb
30 I n-1Cu-1Sn-0.3Si-Q.2Nb
" TI-3AHV
" Ti-3AI-2.5V
" Ti-3AI-2.5V
" TI-3AI-2.5V
" TI-3AI-2.5V
" TI-3AI-2.5V
" n-3AI-2.5V
" Ti-3AT-2.5V
" Ti-3AT-2.5V
" Ti-3AI-2.5V
" Ti-3AI-2.5V
between base material end molten - resolldified Ioyer (surface layer 1 mm) e~t Difference In /3 stabilil~r element concentration (mass%) 0 I 0 " f
All a Melting meth<>d '"""~;;;,:~ ~ayer I Slabing
Fonn of additive I Fe I Cr I Ni I Mo I V I Mn I Co I Cu I Nb I Or I stablll:ter
~
!l.OJ!
ll.QJl
Fe powder lo.2e
Fe powder /0.83
Fe powder /1.50
F~ powder I 0.42
Fe chip I 0.08
Fewl~ 10.87
Fe foil us
Cr chip o.oo I o.s1
Ni cllip I o.oo
Ti-Me clllp I o.oo
V chip I 0.00
Mn chip I 0.00
Co chip I 0.00
Cu chip I 0.00
Fe-Nb chip 10.11
"'
SUS304 powder I 0.44 I 0.11 I 0.05
6-4 chip I 0.00
15-3-3-3 chip 10.00
Fe powder I 0.68
Fe powder I 0.59 I - I 0.00
Fo powder 10.31
Fe powder I 0.12
Fe powder /0.17
Fe powder 10.11
Fa powder I 0.73
Fe powder 10.55
Fe powder I 0.64
Fe powder I 0.22
none lll.l!.O.
none lll..O.O.
none I !l.Q2
Fe foil I 0.52
Fe foil I 0.67
Fe foil 11.42
Fe foil 10.16
or chip I - I 0.84
Nichip I- I - 11.33
susao4 powder I 0.59 I 0.15 I o.os
1.38
'"
0.14
0,20
0.82
0.00
0.00
0.00
0.00
0.00
o.oo
0.00
0"
elements
!WO_ I none
l;l!W. none
n.aQ I electron beam
"' electron beam
"' electron beam
'" ~lectron beam
0.42 plume ere
o.oa electron beam
0.87 electron bum
1.22 electron boom
0" electron beom
"' electron beam
1.38 electron beam
1.03 electron beam
0.14 electron beem
O.S6 0.86 electron beam
0.57 0.57 electron beom
0.21 "' electron beom
0.60 electron beam
0.20 electron beam
0.16 0>8 electron beam
0.68 electron beam
"' ~lectron beam
"' electron beam
0.12 electron beam
0.17 electron beam
0.00 0.11 electron beam
o.oo 0.73 electron beam
o.oo I o.oo "' electron beam
o.oo I o.oo 0.64 electron beam
"' electron beam
!l.OJ! none
!l.OJ! none
ll.IIJl electron beam
0.52 electron beam
O.e7 eleotron beam
1.42 electron beam
0.16 plasma arc
0.84 electron beam
"' el~ctron beam
0.80 electron beam
(mm)
''o"
'0
"' 'o
'o
'o
'0
No
No
No
'0
'0
No
No
'0
No
'0
'0
'0
'o
'o
'0
'0
'0
'0
'0
'0
'0
'0
'o
'o
''0"
No
"' No
No
No
No
'0
'0
'0
Ingot cutting
treatment
'"
'"
'"
'"
'" No
'o
'0
'o
'o
No
No
'0
'0
'0
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
'"
'"
'"
'"
''0"
No
No
No
No
Surface defects Evaluation Remarks
~ ;;;'
g:
" ~
minor
coarBO defects
Good I Reference Example I 1---1
~a;r I uompar&tive Example
partially somewhat coarse defects Fair I Comparative Example
partially somewhat coer .. defects Fair I ComparatJve Example
minor Good Example
minor Geed E~ample
miMor Good Example
minor Good Example
minor Good Example
minor Good Example
minor Good Example
minor Geed Example
minor Good Example
minor Good Example
minor Good Example
minor Good Example
rilinor Good Example
minor Good Example
miner Good Example
minor Good Example
miner Good Example
minor Good Example
minor Good Example
minor Good Example
minor Good Example
minor Good Example
minor Good Example
minor Good Example
minor Good Example
minor Good Example
minor Good I Example
minor Good I Reference Example
coor•e defects Fair I Comparative Example
partially somewhat coarse defect& I Fair I Comparative Example
pa>tially oomowhat coarse defects I Fair I Comparative Example
miMr Good I Exomple
minor I Good I Example
minor I Good I Example
minor I Good Eumple
minor Good Eumple
minor Good I Example
§
\0
~
~
~ V>
'"d
S§
,~
0
>-'
~_,
<:r>
0
00
00
PCT/JP2014/076083
15/25
[0030]
In each of Reference Examples, Examples, and Comparative Examples
shown in Table 1, a titanium casting product was produced using a rectangular mold
or a cylindrical mold made of titanium alloy of various grades by electron-beam
5 remelting. . A hot-rolled sheet with a thickness of 4 mm was produced by hot rolling
from an ingot with a size of thickness 200 mm x width 1000 mm x length 4500 mm
produced using a rectangular mold, and a wire rod with a diameter of 13 mm was
produced by hot rolling from an ingot with a size o[diameter 170 mm x length 12 m
produced using a cylindrical mold. Hot rolling was performed using hot rolling
10 equipment for steel material. As a material containing a ~ stabilizer element, any of
powder (particle size: 100 J.!m or less), a chip (2 mm square, 1 mm thick), wire
(diameter: 1mm), and foil (20 J.!ffi) was used. Titanium casting products fabricated
included two kinds: those not subjected to cutting treatment and those subjected to
cutting treatment. In containing the ~ stabilizer element, the material containing the
15 ~ stabilizer element was placed or applied on the as-cast surface (without cutting
treatment on casting surface) or the cut surface (with cutting treatment on casting
surface), both of which are surfaces to be rolled. A slab surface layer was heated
from above the material, and a surface to be rolled was entirely treated by scanning a
portion to be heated with electron beams and plasma arc; thus, the material
20 containing the ~ stabilizer element and the surface to be rolled included no portion
remaining urunelted. In addition, an as-cast titanium casting product with a
relatively excellent casting surface was used to prevent occurrence of an urunelted
portion due to the casting surface in melting of the surface layer. Moreover, the
material containing the ~ stabilizer element was dispersed uniformly on the entire
25 surface to be rolled of the titanium casting product so that the ~ stabilizer element
was added uniformly to the entire slab. As a method for measuring the depth of the
molten - resolidified layer, a titanium casting product obtained by remelting and then
solidifYing the surface layer was partly cut out and an embedding sample was
fabricated and subjected to polishing for scanning electron microscopy (SEM)/
30 electron probe microanalyser (EPMA), and elemental mapping was performed,
whereby the depth of the shallowest portion of the molten - resolidified part of the
PCT/JP2014/076083
16/25
embedding sample was obtained as the depth of the molten - resolidified layer.
Moreover, here, analysis samples were taken from within 1 mm of the surface layer
at any ten spots of the surface to be rolled of the titanium casting product and were
subjected to ICP-atomic emission spectrometry, and the average value of the ten
5 spots was obtained. In addition, for comparison, analysis samples were taken from
within 20 mm of the surface layer at any three spots of the surface to be rolled of the
titanium casting product before remelting of the surface layer of the titanium casting
product, and were subjected to ICP-atomic emission spectrometry similarly, and the
average value of the three spots was obtained. Regarding these two kinds of
10 analysis results, a difference between the average value of the ~ stabilizer element
concentration in a range of within 1 mm in depth of the molten - resolidified layer
and the average value of the ~ stabilizer element concentration in the base material
was investigated. The situation of occurrence of surface defects was evaluated by
visually observing the surface of the titanium material (hot-rolled sheet) after the hot-
15 rolled sheet was subjected to shot blasting and pickling after hot rolling. Pickling
was performed to scarf one side of the surface to be rolled approximately 50 1-1m
(approximately 100 j.1ffi for both sides) per once. After the sheet underwent
pickling once or twice, surface properties of the hot-rolled sheet were evaluated.
Note that an analysis sample was taken from within 1 mm of the surface layer for
20 Comparative Example not subjected to surface layer melting treatment, and an
analysis sample was taken from the interior of the molten - resolidified layer for
Comparative Example with a thickness of the molten - resolidified layer of less than
lmm.
25
[0031]
Nos. 1 to 31 were examples for sheet materials.
[0032]
In Reference Example, Comparative Examples, and Example of Nos. 1 to 5,
cutting treatment was performed on a casting surface after ingot casting to remove
the casting surface, whereas in Examples of Nos. 6 to 31, cutting treatment was not
30 performed on a casting surface after ingot casting.
[0033]
I
PCT/JP2014/076083
17/25
In Reference Example, Comparative Examples, and Examples of Nos. 1 to
21, an ingot ofTi-1Fe-0.350 was used.
[0034]
Reference Example of No. 1 was produced with slabbing performed as in a
5 conventional production method. Because of the slabbing, surface defects that
occurred in a hot-rolled sheet after pickling were minor.
[0035]
Comparative Example of No. 2was produced without performing slabbing
after ingot cutting treatment. Because of no slabbing, coarse defects occurred in a
10 hot-rolled sheet after pickling.
[0036]
In Comparative Example of No. 3, melting and resolidification treatment
was performed by electron-beam heating without adding a ~ stabilizer element, after
ingot cutting treatment. The molten - resolidified layer had a depth of 1 mm or
15 more, and surface defects after hot rolling and pickling were basically minor, but
somewhat coarse defects occurred partially.
[0037]
In Comparative Example of No. 4, melting and resolidification treatment
was performed by electron-beam heating using Fe powder as the ~ stabilizer element,
20 after ingot cutting treatment. The molten - resolidified layer had a depth of less
than I mm, and somewhat coarse defects occurred partially as surface defects after
hot rolling and pickling.
[0038]
In Example of No. 5, melting and resolidification treatment was performed
25 by electron"beam heating using Fe powder as the ~ stabilizer element, after ingot
cutting treatment. The molten - resolidified layer had a depth of 1 mm or more and
the difference in ~ stabilizer element concentration between the base material and the
molten- resolidified layer was equal to or more than 0.08 mass% and equal to or less
than 1.50 mass%, and surface defects after hot rolling and pickling were minor.
30 [0039]
In Example of No. 6, melting and resolidification treatment was performed
PCT/JP20 14/076083
18/25
by electron-beam heating using Fe powder as the ~ stabilizer element, without
performing ingot cutting treatment. The molten - resolidified layer had a depth of 1
mm or more and the difference in ~ stabilizer element concentration between the
base material and the molten - resolidified layer was equal to or more than 0.08
5 mass% and equal to or less than 1.50 mass%, and surface defects after hot rolling and
pickling were minor.
[0040]
In Example of No. 7, melting and resolidification treatment was performed
by plasma arc heating using Fe powder .as the ~ stabilizer element, without
10 performing ingot cutting treatment. The molten- resolidified layer had a depth of 1
mm or more and the difference in ~ stabilizer element concentration between the
base material and the molten - resolidified layer was equal to or more than 0.08
mass% and equal to or less than 1.50 mass%, and surface defects after hot rolling and
pickling were minor.
15 [0041]
In Examples of Nos. 8 to 10, melting and resolidification treatment was
performed by electron-beam heating using a Fe chip, Fe wire, and Fe foil,
respectively, as the ~ stabilizer element, without performing ingot cutting treatment.
In each case, the molten - resolidified layer had a depth of 1 mm or more and the
20 difference in ~ stabilizer element concentration between the base material and the
molten- resolidified layer was equal to or more than 0.08 mass% and equal to or less
than 1.50 mass%, and surface defects after hot rolling and pickling were minor.
[0042]
In Examples of Nos. 11 to 17, melting and resolidification treatment was
· 25 performed by electron-beam heating with the kinds of ~ stabilizer elements changed
by using a Cr chip, aNi chip, a Ti-Mo chip, a V chip, a Mn chip, a Co chip, and a Cu
chip as the ~ stabilizer element, without performing ingot cutting treatment. In each
case, the molten - resolidified layer had a depth of 1 mm or more and the difference
in ~ stabilizer element concentration between the base material and the molten -
30 resolidified layer was equal to or more than 0.08 mass% and equal to or less than
1.50 mass%, and surface defects after hot rolling and pickling were minor.
PCT/JP2014/076083
19/25
[0043]
In Examples of Nos. 18 to 21, melting and resolidification treatment was
performed by electron-beam heating using materials containing several kinds of ~
stabilizer elements and a stabilizer elements of a Fe-Nb chip, SUS304 powder, a chip
5 (6-4V chip) obtained by crushing Ti-6mass%Al-4mass%V scrap, and a chip (15-3-3-
3 chip) obtained by crushing Ti-15mass%V-3mass%Cr-3mass%Sn-3mass%Al scrap,
respectively, as the ~ stabilizer element, without performing ingot cutting treatment.
In each case, the molten - resolidified layer had a depth of 1 mm or more and the
difference in ~ stabilizer element concentration between the base material and the
10 molten- resolidified layer was equal to or more than 0.08 mass% and equal to or less
than 1.50 mass%, and surface defects after hot rolling and pickling were minor.
[0044]
In Examples of Nos. 22 to 31, the kinds of titanium alloy ingots were
changed. No. 22 used Ti-0.06mass%Pd, No. 23 used Ti-0.5mass%Ni-
15 0.05mass%Ru, No. 24 used Ti-5mass%Al-1mass%Fe, No. 25 used Ti-5mass%Al-
1mass%Fe-0.25mass%Si, No. 26 used Ti-3mass%Al-2.5mass%V, No. 27 used Ti-
0.5mass%Cu, No. 28 used Ti-1mass%Cu, No. 29 used titanium alloy of Ti-
1mass%Cu-0.5mass%Nb, No. 30 used Ti-1mass%Cu-1mass%Sn-0.3mass%Si-
0.2mass%Nb, and No. 31 used Ti-3mass%Al-5mass%V. In each case, melting and
20 resolidification treatment was performed by electron-beam heating using Fe powder
as the ~ stabilizer element, without performing ingot cutting treatment. In each case,
the molten - resolidified layer had a depth of 1 mm or more and the difference in ~
stabilizer element concentration between the base material and the molten -
resolidified layer was equal to or more than 0.08 mass% and equal to or less than
25 1.50 mass%, and surface defects after hot rolling and pickling were minor.
[0045]
Nos. 32 to 41 were examples for wire rods.
[0046]
In Reference Example, Comparative Examples, and Example of Nos. 32 to
30 36, cutting treatment was performed on a casting surface after ingot casting to
remove the casting surface, whereas in Examples of Nos. 37 to 41, cutting treatment
20/25
was not performed on a casting surface after ingot casting.
[0047]
PCT/JP2014/076083
In Reference Example, Comparative Examples, and Examples of Nos. 32 to
41, an ingot ofTi-3mass%Al-2.5mass%V was used.
5 [0048]
10
Reference Example of No. 32 was produced with slabing performed as in a
conventional production method. Because of the slabing, surface defects that
occurred in a hot-rolled sheet after pickling were minor.
[0049]
Comparative Example ofNo. 33 was produced without performing slabing
after ingot cutting treatment. Because of no slabing, coarse defects occurred in a
hot-rolled sheet after pickling.
[0050]
In Comparative Example of No. 34, melting and resolidification treatment
15 was performed by electron-beam heating without adding a ~ stabilizer element, after
ingot cutting treatment. The molten - resolidified layer had a depth of 1 mm or
more, and surface defects after hot rolling and pickling were basically minor, but
somewhat coarse defects occurred partial! y.
20
[0051]
In Comparative Example of No. 35, melting and resolidification treatment
was performed by electron-beam heating using Fe foil as the ~ stabilizer element,
after ingot cutting treatment. The molten - resolidified layer had a depth of less
than 1 mm, and somewhat coarse defects occurred partially as surface defects after
hot rolling and pickling.
25 [0052]
In Example of No. 36, melting and resolidification treatment was performed
by electron-beam heating using Fe foil as the ~ stabilizer element, after ingot cutting
treatment. The molten - resolidified layer had a depth of 1 mm or more and the
difference in ~ stabilizer element concentration between the base material and the
30 molten - resolidified layer was equal to or more than 0.08 mass% and equal to or less
than 1.50 mass%, and surface defects after hot rolling and pickling were minor.
PCT/JP2014/076083
21/25
[0053]
In Example of No. 37, melting and resolidification treatment was performed
by electron-beam heating using Fe foil as the ~ stabilizer element, without
performing ingot cutting treatment. The molten - resolidified layer had a depth of 1
5 mm or more and the difference in ~ stabilizer element concentration between the
base material and the molten - resolidified layer was equal to or more than 0.08
mass% and equal to or less than 1.50 mass%, and surface defects after hot rolling and
pickling were minor.
[0054]
10 In Example of No. 38, melting and resolidification treatment was performed
by plasma arc heating using Fe foil as the ~ stabilizer element, without performing
ingot cutting treatment. The molten - resolidified layer had a depth of 1 mm or
more and the difference in ~ stabilizer element concentration between the base
material and the molten - resolidified layer was equal to or more than 0.08 mass%
15 and equal to or less than 1.50 mass%, and surface defects after hot rolling and
pickling were minor.
[0055]
In Examples of Nos. 39 and 40, melting and resolidification treatment was
performed by electron-beam heating with the kinds of ~ stabilizer elements changed
20 by using a Cr chip and aNi chip as the ~ stabilizer element, without performing ingot
cutting treatment. In each case, the molten - resolidified layer had a depth of 1 mm
or more and the difference in ~ stabilizer element concentration between the base
material and the molten - resolidified layer was equal to or more than 0.08 mass%
and equal to or less than 1.50 mass%, and surface defects after hot rolling and
25 pickling were minor.
[0056]
In Example of No. 41, melting and resolidification treatment was performed
by electron-beam heating using SUS304 powder containing a plurality of~ stabilizer
elements as the ~ stabilizer element, without performing ingot cutting treatment. In
30 each case, the molten - resolidified layer had a depth of 1 mm or more and the
difference in ~ stabilizer element concentration between the base material and the
PCT/JP20 14/076083
22/25
molten- resolidified layer was equal to or more than 0.08 mass% and equal to or less
than 1.50 mass%, and surface defects after hot rolling and pickling were minor.

CLAIMS
Claim 1
A titanium casting product made of titanium alloy, comprising:
a layer containing one or more kinds of ~ stabilizer elements in a range of 1
mm or more in depth at a surface serving as a surface to be rolled,
wherein an average value of ~ stabilizer element concentration in a range of
within 1 mm in depth is higher than ~ stabilizer element concentration in a base
material by, in mass%, equal to or more than 0.08 mass% and equal to or less than
10 1.50 mass%.
15
20
Claim2
The titanium casting product according to claim 1,
wherein the~ stabilizer element(s) is/are one or more of Fe, Ni, and Cr.
Claim 3
The titanium casting product according to claim 1, containing one or more
kinds of a stabilizer elements or neutral elements together with the ~ stabilizer
element(s).
Claim4
A method for producing a titanium casting product, comprising:
melting a surface serving as a surface to be rolled of a titanium casting
product made of titanium alloy together with a material containing a ~ stabilizer
25 element and then solidifYing the surface to make an average value of ~ stabilizer
element concentration in a range of within 1 mm in depth higher than ~ stabilizer
element concentration in a base material by, in mass%, equal to or more than 0.08
mass% and equal to or less than 1.50 mass%.
30 Claim 5
The method for producing a titanium casting product according to claim 4,
5
PCT/JP2014/076083
24/25
wherein the material containing the ~ stabilizer element is in a form of any
of powder, a chip, wire, and foil.
Claim 6
The method for producing a titanium casting product according to claim 4,
wherein the surface serving as the surface to be rolled of the titanium
casting product made of titanium alloy is melted by electron-beam heating or plasma
heating.