The present invention relates to a titanium cast product for hot rolling and a
10 method of manufacturing the same, and relates particularly to a titanium cast product
for hot rolling that can keep surface properties after hot rolling satisfactory even
when a slabing step and a finishing step are omitted, and a method of manufacturing
the same.
15 Background Art
[0002)
A titanium material is generally manufactured by making an ingot obtained
through a melting step into a shape of a slab or a billet, mending the surface,
performing hot rolling, and then subjecting the resultant to annealing or cold working.
20 The melting step includes, in addition to a vacuum arc remelting (VAR) method
which is being used widely, an electron beam remelting (EBR) method or a plasma
arc melting method involving performing melting at a place other than a mold and
pouring the resultant into the mold. Since. the shape of the mold is limited to a
cylindrical shape in the former, a slabing step or a forging step is required for
25 manufacturing a sheet material. The latter has high flexibility regarding the shape
of the mold, hence can use a square-shaped mold in addition to the cylindrical mold.
Accordingly, using the electron beam remelting method or the plasma arc melting
method, the square-shaped ingot or the cylindrical ingot can be cast directly.
Therefore, in the case of manufacturing a sheet material from a square-shaped ingot
30 or in the case of manufacturing a wire material or a bar material from a cylindrical
ingot, the slabing step can be omitted from the viewpoint of the shape of the ingot.
2/25
In this case, since the cost and time spent for the slabing step can be reduced,
remarkable improvements in production efficiency can be expected.
[0003]
However, an as-cast structure of a large-sized ingot that is industrially used
5 has coarse grains each having a grain size of several tens of millimeters. In the case
where such an ingot is directly subjected to hot rolling without undergoing the
slabing step, concavities and convexities are formed on the surface by the influence
of deformation anisotropy in grains and between crystal grains due to coarse crystal
grains and become surface defects. Accordingly, in the case where the square-
10 shaped ingot or the cylindrical ingot is directly manufactured by the electron beam
remelting metl10d or the plasma arc melting method and the slabing step is omitted,
surface defects occur in the hot rolling which is performed thereafter. In order to
remove the surface defects occurred in the hot rolling, it is necessary that the amount
of the surface of the hot-rolled sheet to be molten off in a pickling step be increased,
15 and there arise problems that the cost is increased and the yield is reduced. That is,
it is necessary that a finishing step for removing the surface defects be newly
introduced. Therefore, there is a concern that the expected improvements in
production efficiency owing to the omission of the slabing step may be cancelled due
to the newly introduced finishing step. In regard to such a concern, there are
20 proposed a method of manufacturing a material for hot rolling and a method of
reducing the surface defects by performing fashioning or heat treatment after the
manufacturing.
[0004]
Patent Literature 1 proposes a method including, in the case where an ingot
25 of a titanium material is not subjected to a slabing step and is directly subjected to a
hot rolling process, in order to make crystal grains near an surface layer fine,
providing a strain to the surface layer, and then performing heating to higher than or
equal to recrystallization temperature and performing recrystallization on the surface
to a depth of more than or equal to 2 mm. As means to provide a strain, there are
30 given forging, roll reduction, shot blasting, and the like.
[0005]
3/25
Patent Literature 2 proposes a method of reducing waviness or creases on
the surface formed during rolling due to deformation anisotropy of coarse grains and
reducing surface defects, by heating an ingot of a titanium material to higher than or
equal to T~+50°C, then cooling the ingot to lower than or equal to T~-50°C, and then
5 performing hot rolling.
[0006]
Patent Literature 3 proposes, as a method of reducing surface defects of a
rolled product in the case where the titanium material undergoes a slabing step, a
method involving setting temperature at the end of a slabing step to an a region or
10 performing heating before hot rolling in the temperature in the a phase, thereby
rendering a portion more than or equal to 60 !J.m from the surface equiaxed crystals.
In this way, Patent Literature 3 mentions that forming of a partly deep oxygen-rich
layer can be avoided, the oxygen-rich layer can be removed in a descaling step, and
hence, unuuiform part in regard to hardness and ductility is eliminated, so the surface
15 properties after cold working is improved.
[0007]
Patent Literature 4 proposes a method in which, in the case where an ingot
of a titanium material is not subjected to a hot working step and is directly subjected
to hot rolling, an surface layer serving as a rolling surface of the ingot is molten and
20 resolidified by high-frequency induction heating, arc heating, plasma heating,
electron beam heating, laser heating, and the like, to thereby be turned into fine
grains to a depth of more than or equal to 1 mm from the surface layer, and- an
surface layer structure after the hot rolling is improved. In the above, the surface
layer portion is subjected to quench solidification to form a solidified structure
25 having a fine structure with random orientations, and thus, the occurrence of the
surface defects is prevented. Examples of methods for melting the surface layer
structure of titanium slab include high-frequency induction heating, arc heating,
plasma heating, electron beam heating, and laser heating.
30 Citation List
Patent Literature
5
10
[0008]
Patent Literature 1:
Patent Literature 2:
Patent Literature 3:
Patent Literature 4:
Technical Problem
[0009]
4/25
JP H01-156456A
JP HOS-060317 A
JP H07-102351A
JP 2007-332420A
Summary of Invention
However, although the method of Patent Literature 1 gives the shot blasting
as means to provide a strain, the depth of the strain provided by general shot blasting
is approximately 300 to 500 J.lm, which is not sufficient for forming the recrystallized
layer having a depth of more than or equal to 2 mm that is necessary for improving
the quality. Accordingly, it is practically necessary that the strain be provided to a
15 deeper position by the forging or the roll reduction, but a large plant is required for
20
performing the forging or the roll reduction on a large-sized ingot for hot rolling,
therefore, the cost is not reduced compared to the case of performing an ordinary
slabing step.
[0010]
Further, the method of Patent Literature 2 has an effect that coarse crystal
grains recrystallize and are made fine by heating to a temperature in the ~ phase.
However, in the case where the slabing step is omitted, there are few recrystallized
nuclei since no work strain is applied and the. sizes of the crystal grains become large
since the whole ingot is heated so the cooling rate after the heating is reduced.
25 Therefore, effects obtained by fine-making owing to recrystallization are limitative,
and the reduction of the deformation anisotropy is not sufficient. It is also a factor
of not being able to eliminate the deformation anisotropy that crystal orientations of
the original coarse grains have influence over the recrystallized grains. On the
contrary, moderate fine-making increases grain boundaries which cause concavities
30 and convexities of the surface, and the occurrence of the surface defects is increased.
[0011]
5/25
Still further, the method of Patent Literature 3 is performed from the
assumption that the cast structure is broken to be turned into fine and equiaxed grains
by undergoing the slabing step, and makes no sense in the case where the slabing
step is omitted. If the slabing step is omitted and only heat treatment is performed
5 to form equiaxed grains to a depth of more than or equal to 60 f.Lm from the surface,
it is a simple recrystallization, and the crystal orientation of the recrystallization is
influenced by the original crystal orientation. Accordingly, the method is
insufficient for preventing concavities and convexities due to deformation anisotropy
of coarse grains of the as-cast structure, and it is apparent that problems caused by
10 the surface defects occur.
[0012]
Moreover, in the method of Patent Literature 4, modification is performed
on the structure of the ingot surface layer portion, and this has an effect of improving
the surface properties after hot rolling.
15 [0013]
20
Accordingly, the present invention aims to provide an commercially pure
titanium ingot that can keep surface properties after hot rolling satisfactory even
when a slabing step and a finishing step are omitted, and a method of manufacturing
the same.
Solution to Problem
[0014]
In order to attain the above object, the inventors of the present invention
have conducted intensive studies and have found the following. In manufacturing
25 an commercially pure titanium product from an ingot by performing hot rolling and
omitting a slabing step and a finishing step, an a stabilizer element or a neutral
element is caused to be contained in a slab surface layer by placing or scattering a
material (powder, chips, a wire, a thin film, and the like) containing the a stabilizer
element or the neutral element on a rolling surface surface layer of an as-cast
30 titanium material and remelting the slab surface layer together with the material as
the previous step of hot rolling, hence, a structure of the slab surface layer portion
6/25
can be kept fine even during hot rolling heating, and as a result, surface defects due
to an influence of deformation anisotropy of an original coarse solidified structure
are reduced, and the same surface properties as the case of undergoing the slabing
step and the finishing step can be obtained.
5 [0015]
10
The gist of the present invention is as follows.
(1)
A titanium cast product made of commercially pure titanium, the titanium
cast product including:
a layer in a range of more than or equal to 1 mm in depth on a surface
serving as a rolling surface, the layer containing one or more elements out of any one
of or both of at least one a stabilizer element and at least one neutral element,
wherein a total concentration of the at least one a stabilizer element and the
at least one neutral element in the range of more than or equal to 1 mm in depth is
15 higher than a total concentration of the at least one a stabilizer element and the at
20
least one neutral element in a base metal by, in mass%, more than or equal to 0.1%
and less than 2.0%.
(2)
The titanium cast product according to (1 ),
wherein the at least one a stabilizer element and the at least one neutral
element each include AI, Sn, and Zr.
(3)
The titanium cast product according to ( 1 ),
wherein the layer containing one or more elements out ofany one of or both
25 of the at least one a stabilizer element and the at least one neutral element further
contains, in mass%, less than or equal to 1.5% of one or more p stabilizer elements.
30
(4)
(5)
A method of manufacturing a titanium cast product, the method including:
melting a surface serving as a rolling surface of the titanium cast product
together with a material containing one or more elements out of any one of or both of
7/25
at least one a stabilizer element and at least one neutral element, and then solidifYing
the surface,
wherein a total concentration of the at least one a stabilizer element and the
at least one neutral element in the range of more than or equal to I mm in depth is
5 made higher than a total concentration of the at least one a stabilizer element and the
at least one neutral element in a base metal by, in mass%, more than or equal to 0.1%
and less than 2.0%.
(6)
The method of manufacturing a titanium cast product according to (5),
10 wherein the material containing one or more elements out of any one of or
15
20
25
both of the at least one a stabilizer element and the at least one neutral element
includes one or more of powder, chips, a wire, a thin film, and swarf.
(7)
The method of manufacturing a titanium cast product according to (5),
wherein the surface of the titanium cast product is molten by using one or
more of electron beam heating, arc heating, laser heating, plasma heating, and
induction heating.
(8)
The method of manufacturing a titanium cast product according to (5),
wherein the surface of the titanium cast product is molten in a vacuum
atmosphere or an inert gas atmosphere.
Advantageous Effects ofinvention
[0016]
The titanium cast product for hot rolling and the method of manufacturing
the same according to the present invention make it possible to manufacture a
titanium material having surface properties that are higher than or equal to the case
of undergoing a slabing step and a finishing step, even when, in manufacturing a
titaniwn material, a hot working step such as slabing and forging and a finishing step
30 to be performed thereafter, which have been necessary in the past, are omitted.
Since improvements in the yield can be achieved by reduction in heating time owing
8/25
to omission of a hot working step, reduction in cutting mending owing to slab surface
smoothing, reduction in an amount of pickling owing to improvements in surface
quality, and the like, great effects can be expected not only on reduction of
manufacturing cost but also on improvements in energy efficiency, and industrial
5 effects are immeasurable.
Brief Description of Drawings
[0017]
[FIG. I] FIG. I shows a schematic view of change in concentrations of a melted-
10 resolidified layer.
Description of Embodiments
[0018]
Hereinafter, the present invention will be described in detail.
15 [0019]
[Thickness of melted-resolidified layer]
In the present invention, a titanium material made of commercially pure
titanium has, on a surface serving as a rolling surface, a melted-resolidified layer
having a depth of more than or equal to 1 mm. As described above, the occurrence
20 of surface defects after hot rolling is caused by concavities and convexities of the
surface of the titanium material, which occur due to a structure having coarse crystal
grains. Accordingly, the crystal grain size only in an ingot surface layer portion
may be made as small as possible. In order to suppress crystal grain growth during
hot rolling heating by adding an a stabilizer element and/or a neutral element to be
25 mentioned below and to thereby suppress the occurrence of surface defects, it is
necessary that the thickness of the melted-resolidified layer containing the a
stabilizer element and/or the neutral element be more than or equal to 1 mm. In the
case where the thickness of the melted-resolidified layer is less than 1 mm, surface
defects occur by being influenced by a cast structure of a lower structure, and the
30 surface properties are not improved. Note that the maximum depth is not
particularly defined, but if the melting depth is too large, there is a risk that a layer
9/25
containing an alloying element may remain even after a shot pickling step which is
performed after hot rolling, therefore, the melting depth is desirably up to
approximately 5 mm. Note that, examples of the titanium materials to be subjected
to hot rolling include an ingot, a slab, and a billet.
5 [0020]
The melted-resolidified layer is formed by melting a surface of a titanium
cast product, and then quenching and resolidifying the surface. Viewing a crosssection
in a direction perpendicular to a scanning direction of a molten bead, the
shape of the melted-resolidified layer tends to be the deepest at the center of the
10 molten bead in remelting of the titanium cast product surface layer. When the
molten beads are overlapped, a portion midway between adjacent molten beads is the
shallowest, and the deepest part and the shallowest part are periodically repeated.
In this case, if the difference between the deepest part and the shallowest part is large,
this difference causes a difference in deformation resistances in hot rolling, which
15 may cause defects. Accordingly, the difference is desirably less than 2 mm. Note
that the depth of the melted-resolidified layer according to the present invention is set
to more than or equal to I mm, and the depth indicates the depth of the shallowest
part as viewed in a cross-section in a direction perpendicular to a scanning direction
of a molten bead.
20 [0021]
Here, the commercially pure titanium includes commercially pure titanium
provided by class I to class 4 of the JIS standard, and their corresponding
commercially pure titanium provided by Grades I to 4 of the ASTM standard and
3·7025 of the DIN standard. That is, it can be said that the commercially pure
25 titanium dealt with in the present invention is an commercially pure titanium
consisting of, in mass%, C: less than or equal to 0.1 %, H: less than or equal to
0.015%, 0: less than or equal to 0.4%, N: less than or equal to 0.07%, Fe: less than
or equal to 0.5%, and the balance: Ti.
[0022]
30 [Content of u stabilizer element or neutral element]
In the present invention, the melted-resolidified layer contains one or more
10/25
elements out of a stabilizer elements or neutral elements, the content of the one or
more elements being higher than the content in the base metal portion by more than
or equal to a certain content. Those elements can suppress crystal grain growth in a
temperature in a phase when the elements are contained in titanium to some extent.
5 Therefore, when the crystal grains are heated to an high temperature in the a phase
range, which is a heating temperature range for hot rolling the commercially pure
titanium, the crystal grains can generally be kept fine. In the present invention, as
will be described later, in order to concentrate one or more elements out of a
stabilizer elements or neutral elements, a technique is used that the ingot surface
10 layer portion is molten together with a material made of one or more elements out of
those elements. In this way, when the surface layer is molten with the material
containing those elements, the elements in the surface layer portion in particular
among the molten portion can be concentrated owing to influences such as
solidification segregation. Therefore, by concentrating the elements in the surface
15 layer by adding the elements in an amount more than the amount of the elements to
be added, effects on making the structure finer can be exhibited more strongly. In
addition, by concentrating the elements only in the surface layer portion of the
melted-resolidified layer, diffusion of the alloying element contained in the surface
layer portion into the interior during heat treatment such as hot rolling heating can be
20 reduced, and deterioration of the quality of the material of the product can be
suppressed. When the a stabilizer element(s) or neutral element(s) is/are added
such .that the average concentration of the a stabilizer element( s) or neutral
element(s) in the melted-resolidified layer is higher by more than or equal to 0.1% in
total than the concentration in the base metal portion, the element(s) is/are more
25 concentrated near the surface layer portion and the crystal grain growth can be
suppressed sufficiently, therefore, the lower limit is set to 0.1 %. On the other hand,
when the average concentration in the melted-resolidified layer is higher by more
than or equal to 2.0% than the concentration in the base metal portion, there are risks
that a difference of hot workability may occur between the surface layer portion
30 containing the alloying element and the interior, that a crack may occur during hot
rolling due to further concentrating of the element(s) in the surface layer portion, and
11/25
that the quality of the material of the product may be deteriorated since the addition
amount is large even when the elements are concentrated in the surface layer portion
and a large amount of alloying element contained in the surface layer portion is
diffused into the interior during heat treatment such as hot rolling heating, therefore,
5 the upper limit is set to 2.0%. Two or more of the a stabilizer element(s) and/or the
neutral element( s) may be added in combination, and the concentration of the a
stabilizer element(s) and the neutral element(s) in that case is the total concentration
of the concentrations of the respective elements.
[0023)
10 [Types of a stabilizer element and neutral element]
In the present invention, as the a stabilizer element( s) and the neutral
element(s), there may be used AI, Sn, and Zr. Those elements are each dissolved as
a solid solution in the a phase, and suppress crystal grain growth in the heating
temperature range during hot rolling.
15 [0024)
[~ stabilizer element]
In the present invention, a ~ stabilizer may be contained together with the a
stabilizer element(s) and/or the neutral element(s). When the ~ stabilizer is
contained, not only the above-mentioned crystal grain growth, but also further
20 strncture-fine-malcing can be expected, since the ~ phase, which is the second phase
in the heating temperature range during hot rolling, is easily generated, so that the
crystal grain growth is further suppressed. In addition, by using titanium alloy
scrap containing those alloying elements as an addition material, cost reduction can
be expected.
25 [0025)
[Method of measuring thickness of melted-resolidified layer]
The present invention defines that the melted-resolidified layer in which
alloying element(s) of the a stabilizer element(s) or the neutral element(s) is/are
concentrated has a depth of more than or equal to I mm. The method of measuring
30 the thickness of the melted-resolidified layer will be described. An embedded
polishing sample of the cross-section of the concentrated layer can be easily
12/25
determined by scanning electron microscopy (SEM)Ielectron probe microanalyser
(EPMA). FIG. 1 shows a schematic view of change in concentrations of the meltedresolidified
layer. Owing to the addition of the a stabilizer element(s) and/or the
neutral element(s), the melted-resolidified layer has higher concentration of the a
5 stabilizer element(s) and/or the neutral element(s) in comparison to the base metal
portion, and the thickness of the portion in which the concentration of the a stabilizer
element(s) and/or the neutral element(s) is higher is set to the thickness of the
melted-resolidified layer. Note that, in the case where the melted-resolidified layer
is larger than the measurement range of SEM/EPMA, the measurements are
10 performed several times in the thickness direction, and the results are combined to
measure the thickness of the melted-resolidified layer.
15
[0026]
[Method of measuring element concentrations in molten portion and base metal
portion]
The concentrations in the melted-resolidified layer and the base metal
portion are determined by cutting out test pieces for analytical use from a part at
which the concentration is increased and a central part of the material and perfom1ing
ICP emission spectroscopic analysis on the test pieces. Regarding measurement of
the concentrations, analysis samples may be collected from within 1 mm of the
20 surface layer of any multiple sites (for example, 10 sites) of the rolling surface of a
titanium cast product, ICP emission spectroscopic analysis may be performed on the
analysis samples, and the average value thereof may be set as the concentration in the
melted-resolidified layer. Further, by way of comparison, analysis samples may be
collected from within 20 mm of the surface layer of any multiple sites (for example,
25 3 sites) of the rolling surface of the titanium cast product before remelting the surface
layer of the titanium cast product, the ICP emission spectroscopic analysis may be
performed in the same manner, and the average value thereof may be set as the
concentration in the base metal portion.
(0027]
30 [Addition method]
In the present invention, in order to concentrate one or more elements out of
13/25
a stabilizer elements or neutral elements in the surface layer portion of the ingot, a
technique is used that the ingot surface layer portion is molten together with a
material made of one or more elements out of those elements. In this way, the
concentration of those elements in the surface layer portion of the ingot can be
5 increased. Further, a titanium alloy containing those elements may be used. In
this way, a ~ stabilizer element may also be contained easily together with those
elements. As a material, powder, chips, a wire, a thin film, and swarf can be used
individually or in combination.
[0028]
10 [Method of melting surface layer]
The present invention is characterized in that the titanium material surface
layer portion is heated together with a material made of one or more elements out of
a stabilizer elements or neutral elements, and is molten and resolidified. As the
methods of heating the surface layer portion, there may be used electron beam
15 heating, induction heating, arc heating, plasma heating, and laser heating may
individually or in combination. In the case where the above methods are used in
combination, for example, the surface layer may be preheated by induction heating,
and then may be molten by laser heating. The method to be employed may be
selected by taking into account conditions such as cost, the size of the titanium
20 material, and treatment time. In the present invention, the titanium material surface
layer portion is preferably heated in a vacuum or an inert gas atmosphere. Since
titanium is an extremely active metal, a large amount of oxygen and nitrogen is
mixed in the melted-resolidified portion if the treatment is performed in the
atmosphere, resulting in change in the quality. Therefore, when the treatment is
25 performed in a container under a vacuum or an inert atmosphere, a satisfactory result
can be obtained. Note that inert gases according to the present invention represent
argon and helium, and do not include nitrogen which reacts with titanium. The
degree of vacuum in the case where the treatment is performed in a vacuum container,
the degree of vacuum is desirably approximately higher than or equal to Sx 10·5 Torr.
30 [0029]
The present invention provides a titanium material for hot rolling including
14/25
a melted-resolidified layer in which one or more elements out of a stabilizer
elements or neutral elements are concentrated in the above-mentioned range on an
surface layer in a range of more than or equal to 1 mm in depth, and the other portion
of the material is an as-cast structure or a structure obtained by perfonning casting,
5 then performing heating to higher than or equal to the ~ transformation temperature,
and thereafter performing quenching. Using this material, even when a slabing step
is omitted, a titanium material having the same surface quality as the case of
undergoing an ordinary slabing step can be obtained.
[Examples]
10 [0030]
Hereinafter, the present invention will be described in detail by way of
examples. Nos. 1 to 19 shown in Table 1 are each an example in which a sheet
material is used, and Nos. 20 to 26 are each an example in which a wire material is
used.
15 [0031]
[Table 1]
• H h h 1 1 1 1 1 1 l 1 j. j 1 1 l 1 1 1 u I· t· l 1 l 1 z 8! ,! ~ 0
j ~ ~ ~ ~ ~ ] ! ! ] ] ~ ~ ~ l ~ ] ] ~ l ~ 1 ~ ~ ~ l l
l , r
n~. j ' • ~ ~ -~ !!t ' ' .i ~ ~ .i ~ ~ 1 ! ! ! ! ! ! ! ! . , I ! ~ ! l ~ _g' j H ~j > > ' > . ' Hl .j;,J
)U
' ' I I i l ' ' j j ! 1 l 1 l 1 l ! y' y' y' I • • ' I ' ' ' ' ' y • n I ~ • • ! ~ • • • c0 • • • ~ • • ~ • • I ~ • • s ! ffi w ~I II I I I I I I I I I I I I I I I I I ll II ll I I I I
' i
I il I I I I I I I I I I I ~ ~ : ~ I I I I I I I I I I I d
'u".' H~ t ~q I 0 .0 ~ ! ~ ~ ! ' § ~ ~ ~ 3 ~ ~ ~ ~ ; I I ~ ' ! ~ ~ l. i ' ' ' "
--
fl I I ' I I I I I I I I ' ' ~ " I I I ' :~J I I I I I I I
l o''•
j
IH I i i ~ ~ ~ ~ ! ~ ~ ~ ! ! ! ! ! 8 ! § § § ! ! 8 j §
j,, ' • • • • • ' •
fl
I! I I I I I I I I I I I ~ ' ' ~ I I I I I I I I I I I
1-- i' f'Jr I ~ " ! ! I ~ ~ ~ ~ ! ~ ! ~ ~ ! 8 8 i ~~1 " d ~ I I "' " ~ ~ ~ t 8! "
'
If • ~ ~ ~ ~ ~
I I < < < < < ' • ~ • < • < < I I < < < ' < •
j I ~ ,, ~ ' ~ " ~ , ~ "
, ~ : ,
'
, ~ ~ I ~ '' : ~ , :
-~rd' I I I I I I l ~ ~ l l ~ l l l l l l l I I I I I ! l
-·--
i I ~ ~ l l l l l l l ~ l l ~ ~ l ~ l l I l l ! ! l l
I .J l' H ll H H H ·jl' .i i li H Hl i li HH li I j li li!l !I 11 nn 1 1 ~i
--f-f--· --
1 I I I I I l I I I I I l I .I I I .I I .! I I I l I I I ; ; I
i ' ' '' ' ' ' ' ' ' ' '' '' ' ' ' ' ' ' ' ' i ' i ' i ' J ~ ! ! ! ! l l ! l ~ ! ! ! ! ~ ~ ! l j j ! ~ j l l 0 0 0 0 0 0
l - " . . . . . - - e = ' " e " e ' e e ' " " " ' ---'(;!~
16/25
[0032]
In each of Reference Example, Examples, and Comparative Examples
shown in Nos. 1 to 19 of Table 1, a titanium cast product was manufactured by the
electron beam remelting method, and was casted using a square-shaped mold. After
5 that, in the case where cutting mending of a casting surface was performed, the
cutting mending of an surface layer of the titanium cast product was performed, and
in the case where the cutting mending is not performed, the melting of the surface
layer was performed without performing the cutting mending of the surface layer.
Next, an ingot having a thickness of 250 mm, a width of 1000 mm, and a length of
10 4500 mm was hot rolled using a hot rolling plant for a steel material, and was
manufactured into a belt-shaped coil having a thickness of 4 mm. Note that an
evaluation of surface defects was performed by visually observing a sheet surface
layer after being subjected to pickling.
15
[0033]
In each of Reference Example, Examples, and Comparative Examples of
Nos. 1 to 6, after an ingot was manufactured, a casting surface of the ingot (cast
product) was cut and removed. On the other hand, in each of Examples of Nos. 6 to
31, after an ingot was manufactured, a casting surface was subjected to melting and
resolidification treatment.
20 [0034]
In "melting method" shown in Table 1, "EB" represents performing melting
and resolidification of the surface layer by an electron beam, "TIG" represents
perfonning melting and resolidification of the surface layer by TIG welding, and
"laser" represents performing melting and resolidification of the surface layer by
25 laser welding. For the melting of the surface layer using the electron beam, ·an
electron beam welding apparatus having a standard output of 30 kW was used. The
melting of the surface layer performed by the TIG welding was performed at 200 A
without using a filler material. For the melting of the surface layer perfom1ed by
the laser welding, a C02 laser was used.
30 [0035]
Reference Example of No. 1 describes a case where manufacturing was
5
17/25
performed by usmg an commercially pure titanium ingot and following a
conventional slabing step. Since the slabing step is performed, surface defects of
the manufactured sheet material were minor.
[0036]
In Comparative Example of No. 2, the ingot was subjected to cutting
mending, and then was subjected to surface layer melting treatment using EB without
adding an u stabilizer element or a neutral element. Therefore, the thickness of the
melted-resolidified layer was as deep as more than or equal to 1 mm, and although
the surface defects were minor, they occurred in some parts and were deteriorating.
10 [0037]
In Comparative Example of No. 3, the ingot was subjected to the cutting
mending, and then the surface of the ingot was subjected to the surface layer melting
treatment using EB together with AI powder. Although the content of AI in the
melted-resolidified portion was sufficiently high, which was higher by more than or
15 equal to 0.1% compared to the base metal portion, the thickness was as small as 0.5
mm, and hence, slightly coarse surface defects were observed in some parts.
[0038]
In Example of No. 4, the ingot was subjected to the cutting mending, after
that, the surface of the ingot was subjected to the surface layer melting treatment
20 using EB together with Al chips, the content of Al in the melted-resolidified layer
was sufficiently high, which was higher by more than or equal to 0.1% compared to
the base metal portion, and the thickness was as deep as more than or equal to 1 rnm,
and hence, the surface defects were minor, which was the same level as the case of
undergoing the slabing step.
25 [0039]
In Example of No. 5, the ingot was subjected to the cutting mending, after
that, the surface of the ingot was subjected to the surface layer melting treatment
using laser together with AI foil, the content of AI in the melted-resolidified layer
was sufficiently high, which was higher by more than or equal to 0.1% compared to
30 the base metal portion, and the thickness of the Al-concentrated layer was as deep as
more than or equal to 1 mm, and hence, the surface defects were minor, which was
18/25
the same level as the case of undergoing the slabing step.
[0040]
In Example of No. 6, the ingot was subjected to the cutting mending, after
that, the surface of the ingot was subjected to the surface layer melting treatment
5 using TIG together withAl foil, the content of Al in the melted-resolidified layer was
sufficiently high, which was higher by more than or equal to 0.1% compared to the
base metal portion, and the thickness was as deep as more than or equal to 1 mm, and
hence, the surface defects were minor, which was the same level as the case of
undergoing the slabing step.
10 [0041]
In Example of No. 7, the ingot was not subjected to cutting, the surface of
the ingot was subjected to the surface layer melting treatment using EB together with
Al powder, the content of Al in the melted-resolidified layer was sufficiently high,
which was higher by more than or equal to 0.1% compared to the base metal portion,
15 and the thickness was as deep as more than or equal to 1 mm, and hence, the
surface defects were minor, which was the same level as the case of undergoing the
slabing step.
[0042]
In Example of No. 8, the ingot was not subjected to cutting, the surface of
20 the ingot was subjected to the surface layer melting treatment using EB together with
Sn powder, the content of Sn in the melted-resolidified layer was sufficiently high,
which was higher by more than or equal to 0.1% compared to the base metal portton,
and the thickness was as deep as more than or equal to 1 mm, and hence, the
surface defects were minor, which was the same level as the case of undergoing the
25 slabing step.
[0043]
In Example of No. 9, the ingot was not subjected to cutting, the surface of
the ingot was subjected to the surface layer melting treatment using EB together with
Zr swarf, the content of Zr in the melted-resolidified layer was sufficiently high,
30 which was higher by more than or equal to 0.1% compared to the base metal portion,
and the thickness was as deep as more than or equal to 1 mm, and hence, the surface
19/25
defects were minor, which was the same level as the case of undergoing the slabing
step.
[0044]
In Example of No. 10, the ingot was not subjected to cutting, the surface of
5 the ingot was subjected to the surface layer melting treatment using TIG together
with powder of AI and Zr, the total content of AI and Zr in the melted-resolidified
layer was sufficiently high, which was higher by more than or equal to 0.1%
compared to the base metal portion, and the thickness was as deep as more than or
equal to 1 mm, and hence, the surface defects were minor, which was the same level
10 as the case of undergoing the slabing step.
[0045]
In Example of No. 11, the ingot was not subjected to cutting, the surface of
the ingot was subjected to the surface layer melting treatment using TIG together
with swarf of a titanium alloy containing Al and Sn, the total content of Al and Sn in
15 the melted-resolidified layer was sufficiently high, which was higher by more than or
equal to 0.1% compared to the base metal portion, and the thickness was as deep as
more than or equal to 1 mm, and hence, the surface defects were minor, which was
the same level as the case of undergoing the slabing step.
20
[0046]
In each of Examples of No. 12 to 15, the ingot was not subjected to cutting,
the surface of tl1e ingot was subjected to the surface layer melting treatment using
TIG together with swarf of a titanium alloy containing AI and a ~ stabilizer element,
the content of AI in the melted-resolidified layer was sufficiently high, which was
higher by more than or equal to 0.1% compared to the base metal portion, and the
25 content of the ~ stabilizer element was as low as less than or equal to 1.5%.
30
Further, the thickness was as deep as more than or equal to 1 mm, and hence, the
smface defects were minor, which was the same level as the case of undergoing the
slabing step.
[0047]
In Example of No. 16, the ingot was not subjected to cutting, the surface of
the ingot was subjected to the surface layer melting treatment using EB together with
20/25
AI chip, the content of AI in the melted-resolidified layer was sufficiently high,
which was higher by more than or equal to 0.1% compared to the base metal portion,
and the thickness was as deep as more than or equal to 1 mm, and hence, the surface
defects were minor, which was the same level as the case of undergoing the slabing
5 step.
[0048]
In Example of No. 17, the ingot was not subjected to cutting, the surface of
the ingot was subjected to the surface layer melting treatment using TIG together
with Sn powder, the content of Sn in the melted-resolidified layer was sufficiently
10 high, which was higher by more than or equal to 0.1% compared to the base metal
portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the
surface defects were minor, which was the same level as the case of undergoing the
slabing step.
15
[0049]
In Examples of Nos. 18 and 19, the ingots made of class 3 pure titanium and
class 4 pure titanium, respectively, were not subjected to cutting, the surface of each
ingot was subjected to the surface layer melting treatment using EB together with AI
powder, the content of AI in each melted-resolidified layer was sufficiently high,
which was higher by more than or equal to 0.1% compared to the base metal portion,
20 and the thickness was as deep as more than or equal to 1 mm, and hence, the surface
defects were minor, which was the same level as the case of undergoing the slabing
step.
[0050]
In each of Reference Example, Comparative Examples, and Examples
25 shown in Nos. 20 to 26 of Table 1, the class 2 commercially pure titanium was used,
and a titanium ingot was manufactured by the vacuum arc remelting method or the
electron beam remelting method. An ingot having a diameter of 170 mm and a
length of 12 m was hot rolled, and was manufactured into a wire material having a
diameter of 13 mm. Note that an evaluation of surface defects was performed by
30 visually observing a sheet surface layer after being subjected to pickling.
[0051]
21125
In each of Reference Example, Comparative Examples, and Examples of
Nos. 20 to 24, after an ingot was manufactured, a casting surface of the ingot was cut
and removed. On the other hand, in each of Examples of Nos. 25 and 26, after an
ingot was manufactured, a casting surface was subjected to melting and
5 resolidification treatment.
10
[0052]
Reference Example of No. 20 describes a case where manufacturing was
performed by following a conventional slabing step.
[0053]
In Comparative Example of No. 21, the ingot was subjected to cutting
mending, and then was subjected to surface layer melting treatment using EB without
adding an a stabilizer element or a neutral element. Therefore, the thickness of the
melted-resolidified portion was as deep as more than or equal to I mm, and although
the surface defects tend to be minor, they occurred in some parts and were
15 deteriorating.
[0054]
In Comparative Example of No. 22, the ingot was subjected to the cutting
mending, and then the surface of the ingot was subjected to the surface layer melting
treatment using EB together with AI foil. Although the content of A1 in the melted-
20 resolidified portion was sufficiently high, which was higher by more than or equal to
0.1% compared to the base metal portion, the thickness was as small as 0.5 mm, and
hence, slightly coarse surface defects were observed in some parts.
[0055]
In Example of No. 23, the ingot was subjected to the cutting mending, after
25 that, the surface of the ingot was subjected to the surface layer melting treatment
using EB together with AI foil, the content of AI in the melted-resolidified layer was
sufficiently high, which was higher by more than or equal to 0.1% compared to the
base metal po1tion, and the thickness was as deep as more than or equal to 1 mm, and
hence, the surface defects were minor, which was the same level as the case of
30 undergoing the slabing step.
[0056]
22125
In Example of No. 24, the ingot was subjected to the cutting mending, after
that, the surface of the ingot was subjected to the surface layer melting treatment
using TIG together with AI foil, the content of AI in the melted-resolidified layer was
sufficiently high, which was higher by more than or equal to 0.1 %, and the thickness
5 was as deep as more than or equal to I mm, and hence, the surface defects were
minor, which was the same level as the case of undergoing the slabing step.
[0057]
In Example of No. 25, the ingot was subjected to the cutting mending, after
that, the surface of the ingot was subjected to the surface layer melting treatment
10 using laser together with Sn powder, the content of Sn in the melted-resolidified
layer was sufficiently high, which was higher by more than or equal to 0.1%
compared to the base metal portion, and the thickness of the Sn-concentrated layer
was as deep as more than or equal to I mm, and hence, the surface defects were
minor, which was the same level as the case of undergoing the slabing step.
15 [0058]
In Example of No. 26, the ingot was subjected to the cutting mending, after
that, the surface of the ingot was subjected to the surface layer melting treatment
using EB together with AI foil, the content of AI in the melted-resolidified layer was
sufficiently high, which was higher by more than or equal to 0.1% compared to the
20 base metal portion, and the thickness of the Al-concentrated layer was as deep as
more than or equal to I mm, and hence, the surface defects were minor, which was
the same level as the case of undergoing the slabing step.

CLAIMS
Claim I
A titanium cast product made of commercially pure titanium, the titanium
cast product comprising:
a layer in a range of more than or equal to I mm in depth on a surface
serving as a rolling surface, the layer containing one or more elements out of any one
of or both of at least one u stabilizer element and at least one neutral element,
wherein a total concentration of the at least one u stabilizer element and the
at least one neutral element in the range of more than or equal to I mm in depth is
10 higher than a total concentration of the at least one u stabilizer element and the at
15
20
least one neutral element in a base metal by, in mass%, more than or equal to 0.1%
and less than 2.0%.
Claim2
The titanium cast product according to claim I,
wherein the at least one u stabilizer element and the at least one neutral
element each include AI, Sn, and Zr.
Claim 3
The titanium cast product according to claim I,
wherein the layer containing one or more elements out of any one of or both
of the at least one u stabilizer element and the at least one neutral element further
contains, in mass%, fess than or equal to 1.5% of one or more ~ stabilizer elements.
25 Claim 4
A method of manufacturing a titanium cast product, the method comprising:
melting a surface serving as a rolling surface of the titanium cast product
together with a material containing one or more elements out of any one of or both of
at least one u stabilizer element and at least one neutral element, and then solidifying
30 the surface,
wherein a total concentration of at least one u stabilizer element and at least
5
24/25
one neutral element in the range of more than or equal to 1 mm in depth is made
higher than a total concentration of at least one a stabilizer element and at least one
neutral element in a base metal by, in mass%, more than or equal to 0.1% and less
than2.0%.
Claim 5
The method of manufacturing a titanium cast product according to claim 4,
wherein the material containing one or more elements out of any one of or
both of at least one a stabilizer element and at least one neutral element includes one
10 or more of powder, chips, a wire, a thin film, and swarf.
Claim 6
The method of manufacturing a titanium cast product according to claim 4,
wherein the surface of the titanium cast product is molten by using one or
15 more of electron beam heating, arc heating, laser heating, plasma heating, and
induction heating.
20
Claim 7
The method of manufacturing a titanium cast product according to claim 4,
wherein the surface of the titanium cast product is molten in a vacuum
atmosphere or an inert gas atmosphere.