U.S. patent application number 14/394745 was filed with the patent office on 2015-05-07 for method for producing a plug for hot tube-making.
The applicant listed for this patent is NIPPON STEEL & SUMITOMO METAL CORPORATION. Invention is credited to Yasuyoshi Hidaka, Yasuto Higashida, Kazuhiro Shimoda.
Application Number | 20150125630 14/394745 |
Document ID | / |
Family ID | 49383280 |
Filed Date | 2015-05-07 |
United States Patent
Application |
20150125630 |
Kind Code |
A1 |
Hidaka; Yasuyoshi ; et
al. |
May 7, 2015 |
METHOD FOR PRODUCING A PLUG FOR HOT TUBE-MAKING
Abstract
A plug for hot tube-making having a sprayed coating resistant to
peeling is provided. A method for producing a plug for hot
tube-making according to the present embodiment includes a step of
preparing a plug whose surface includes a sprayed coating formed
thereon, the sprayed coating containing iron and an iron oxide; and
a heat treatment step during which the plug is kept at 400.degree.
C. to 550.degree. C. for 5 to 60 minutes.
Inventors: |
Hidaka; Yasuyoshi;
(Chiyoda-ku, JP) ; Higashida; Yasuto; (Chiyoda-ku,
JP) ; Shimoda; Kazuhiro; (Chiyoda-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON STEEL & SUMITOMO METAL CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
49383280 |
Appl. No.: |
14/394745 |
Filed: |
March 6, 2013 |
PCT Filed: |
March 6, 2013 |
PCT NO: |
PCT/JP2013/056063 |
371 Date: |
October 16, 2014 |
Current U.S.
Class: |
427/580 ;
427/383.1 |
Current CPC
Class: |
B21B 25/04 20130101;
C23C 4/18 20130101; B21B 19/04 20130101; B21B 25/00 20130101; C23C
4/06 20130101; C23C 4/131 20160101 |
Class at
Publication: |
427/580 ;
427/383.1 |
International
Class: |
C23C 4/06 20060101
C23C004/06; C23C 4/12 20060101 C23C004/12; C23C 4/18 20060101
C23C004/18; B21B 25/00 20060101 B21B025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 19, 2012 |
JP |
2012-095434 |
Claims
1. A method for producing a plug for hot tube-making, comprising a
step of preparing a plug whose surface includes a sprayed coating
formed thereon, the sprayed coating containing iron and an iron
oxide; and a heat treatment step during which the plug is kept at
400.degree. C. to 550.degree. C. for 5 to 60 minutes.
2. The method for producing a plug according to claim 1, wherein
the step of preparing the plug further comprises: a step of
preparing a plug body; and a step of forming the sprayed coating by
performing arc spraying with an iron wire rod onto a surface of the
plug body.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing a
plug for hot tube-making (hereafter simply referred to as a plug),
and more particularly to a method for producing a plug included in
a piercer and an elongator.
BACKGROUND ART
[0002] The Mannesmann tube-making process is widely adopted as the
method for producing seamless tubes. In the Mannesmann tube making
process, a round billet heated to around 1200.degree. C. is
piercing-rolled by a piercer. The piercer includes a pair of
inclined rolls and a plug. The plug is disposed between the
inclined rolls of the pair and on a pass line. The piercer presses
the round billet onto the plug while rotating the round billet in
the circumferential direction by means of the inclined rolls, to
piercing-roll the round billet into a hollow shell. Further, as
needed, the elongator elongates the hollow shell to expand the
diameter and reduce the thickness thereof. The elongator has a
similar configuration to that of the piercer, that is, a pair of
inclined rolls and a plug.
[0003] As so far described, since the plug is used for piercing,
and elongating a round billet of high temperature to expand the
diameter thereof, the plug is subject to high temperature and high
interfacial pressure from the round billet. As a result, the
surface of the plug is subject to wear and scoring. Such wear and
scoring will reduce the life of the plug.
[0004] To improve the life of the plug, a technique to form a
sprayed coating on the surface of the plug is proposed. For
example, in WO2009/057471 (Patent Document 1), arc spraying is
performed with iron wire rod onto the surface of the plug to form a
sprayed coating. Patent Document 1 describes that the sprayed
coating improves the scoring resistance of the plug thereby
increasing the life thereof.
DISCLOSURE OF THE INVENTION
[0005] However, the sprayed coating may have a poor adhesiveness to
the plug body. Poor adhesiveness will cause the sprayed coating to
peel off. If the sprayed coating peels off, inner surface flaws of
the hollow shell become more likely to occur. Moreover, the life of
the plug will also decline.
[0006] It is an object of the present invention to provide a method
for producing a plug having a sprayed coating which is resistant to
peeling.
[0007] A method for producing a plug for hot tube-making according
to the present embodiment includes a step of preparing a plug whose
surface includes a sprayed coating formed thereon, the sprayed
coating containing iron and an iron oxide; and a heat treatment
step during which the plug is kept at 400.degree. C. to 550.degree.
C. for 5 to 60 minutes.
[0008] The method for producing a plug according to the present
embodiment can produce a plug whose sprayed coating is less likely
to peel off.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a longitudinal sectional view of a plug according
to the present embodiment;
[0010] FIG. 2 is a diagram showing the relationship between the
heat treatment temperature and the proportions of iron and iron
oxide in the coating;
[0011] FIG. 3 is a cross sectional view of a specimen to be used
for a test to measure tensile residual stress in the sprayed
coating of the plug; and
[0012] FIG. 4 is a schematic diagram to explain the method of
measuring tensile residual stress by use of the specimen shown in
FIG. 3.
BEST MODE FOR CARRYING OUT THE INVENTION
[0013] Hereafter, referring to the drawings, an embodiment of the
present invention will be described in detail. The like or
corresponding parts in the drawings are given the like reference
characters, without repeating the description thereof.
[0014] The method for producing a plug according to the present
embodiment includes a step of preparing a plug whose surface
includes a sprayed coating formed thereon, the sprayed film
containing iron and an iron oxide; and a heat treatment step during
which the plug is kept at 400.degree. C. to 550.degree. C. for 5 to
60 minutes.
[0015] The iron oxide in the prepared sprayed coating of the plug
is composed dominantly of wustite (FeO). Wustite has a relatively
low adhesiveness. Retaining the plug, on which such sprayed coating
is formed, at 400.degree. C. to 550.degree. C. for 5 to 60 minutes
causes the wustite in the sprayed coating to transform into
magnetite (Fe.sub.2O.sub.3). Magnetite has a higher adhesiveness
than that of wustite. Therefore, the adhesiveness of the sprayed
coating to the plug body is improved, and the sprayed coating
becomes less likely to peel off.
[0016] Further, tensile residual stress remains in the sprayed
coating, which has been formed on the surface of the plug body by
spraying. If a plug in which tensile residual stress still remains
in the sprayed coating is used for piercing-rolling, the sprayed
coating becomes more likely to peel off due to the tensile residual
stress. In the present embodiment, the plug including a sprayed
coating formed thereon is subjected to a heat treatment at the
above described conditions (at 400.degree. C. to 550.degree. C. for
5 to 60 minutes). As a result, the tensile residual stress in the
sprayed coating is reduced, and the sprayed coating becomes less
likely to peel off.
[0017] Hereafter, the details of the method for producing a plug
according to the present embodiment will be described.
[Method for Producing a Plug]
[0018] The method for producing a plug according to the present
embodiment produces a plug for hot tube-making. The plug for hot
tube-making can be utilized for a piercer and an elongator. The
method for producing a plug of the present embodiment includes a
step (preparation step) of preparing a plug having a sprayed
coating, and a step (heat treatment step) of heat treating the
plug.
[Preparation Step]
[0019] In the preparation step, a plug 10 as shown in FIG. 1 is
prepared.
[0020] The plug 10 includes a plug body 11 and a sprayed coating
12. The plug body 11 has, for example, a well-known shape and
material.
[0021] The sprayed coating 12 contains iron (Fe) and an iron oxide.
Preferably, the sprayed coating 12 consists of iron, an iron oxide,
and impurities. The sprayed coating 12 consisting of iron, an iron
oxide, and impurities is formed by, for example, arc spraying as
follows. An iron wire rod which provides a spraying material, and
an arc spraying apparatus are prepared. The arc spraying apparatus
includes a spraying nozzle. The spraying nozzle blows out the
spraying material which is melted by arc, with compressed air or
nitrogen gas.
[0022] The iron wire rod is arc sprayed by the arc spraying
apparatus to form a sprayed coating 12 on the surface of the plug
body 11. By adjusting the distance (hereafter referred to as a
spraying distance) between the spraying nozzle of the arc spraying
apparatus and the plug body 11, it is possible to adjust the
content of the iron oxide in the sprayed coating. The spraying
distance is, for example, 200 to 1000 mm. The arc spraying
apparatus can adjust the position of the spraying nozzle. Note that
the sprayed coating 12 may be formed by other spraying processes
than the above described arc spraying.
[0023] Since the sprayed coating 12 contains iron, which provides
the matrix, and an iron oxide, it has wear resistance and thermal
insulation performance. Thereby, the wear and melting loss of the
plug body 11 are suppressed.
[0024] However, the iron oxide in the sprayed coating 12 formed by
spraying is mostly wustite (FeO). Wustite has poor adhesiveness to
the plug body 11. Therefore, the sprayed coating 12 may peel off
from the plug body 11. Further, since the sprayed coating 12 is
formed by spraying, tensile residual stress remains in the sprayed
coating 12 after it is cooled. The tensile residual stress reduces
the adhesiveness of the sprayed coating 12. Thereby, the tensile
residual stress makes the sprayed coating 12 more likely to peel
off from the plug body 11.
[0025] Accordingly, to further increase the adhesiveness of the
sprayed coating to the plug body 12, the following heat treatment
is conducted.
[Heat Treatment Step]
[0026] Heat treatment is conducted on the prepared plug 10, that
is, the plug 10 after the sprayed coating 12 is formed by spraying.
To be specific, the plug 10 is put into a heat treatment furnace.
The internal temperature of the heat treatment furnace is kept at
400.degree. C. to 550.degree. C. As a result, the temperature of
the plug 10 put into the heat treatment furnace will become
400.degree. C. to 550.degree. C. In the heat treatment furnace, the
temperature of the plug 10 is retained at 400.degree. C. to
550.degree. C. for 5 to 60 minutes. The plug 10 is taken out from
the heat treatment furnace after the retention time has passed.
[0027] In the sprayed coating 12 of the plug 10, which is produced
by the above described step, the transformation from wustite to
magnetite takes place, and the ratio of magnetite in the sprayed
coating 12 increases. Further, the tensile residual stress
decreases. Thereby, the adhesiveness of the sprayed coating 12 to
the plug body 11 increases, and the sprayed coating 12 becomes less
likely to peel off. Hereafter, such operation will be described in
detail.
[Transformation from Wustite to Magnetite]
[0028] The iron oxide includes wustite (FeO), magnetite
(Fe.sub.3O.sub.4), and hematite (Fe.sub.2O.sub.3). Among these,
since magnetite is more consistent with iron than wustite and
hematite are, magnetite has a highest adhesiveness with the plug
body 11. Further, the heat insulation performance of magnetite is
equal to those of wustite and hematite. Therefore, to increase the
adhesiveness of the sprayed coating of the plug 10, it is
preferable to increase the ratio of magnetite in the iron oxide of
the sprayed coating.
[0029] Employing a heat treatment temperature of 400.degree. C. to
550.degree. C. and a heat treatment time of 5 to 60 minutes will
make it possible to reduce the ratio of wustite and increase the
ratio of magnetite in the sprayed coating.
[0030] FIG. 2 is a diagram showing the relationship between the
heat treatment temperature and the proportions of iron, which is
the matrix, and each iron oxide (wustite, magnetite, and hematite)
in the coating. FIG. 2 was resulted from the following method.
[0031] A plurality of thick plate test specimens (each of which has
dimensions of 20 mm.times.50 mm.times.10 mm) were prepared. For
each test specimen, arc spraying was performed at the same
condition by using an iron wire rod having the same composition, to
form a sprayed coating of the same thickness (500 .mu.m) in each
test specimen.
[0032] After the sprayed coating was formed, the composition of the
sprayed coating of each test specimen was analyzed. To be specific,
by an X-ray diffraction method (XRD method), peak intensities of
iron and each oxide (wustite, magnetite, and hematite) in the
sprayed coating of each test specimen were determined. In the
present discussion, for the sake of convenience, the heights of
maximum peaks out of the obtained peak intensities were used as the
indices for the ratios of iron and each iron oxide in the sprayed
coating. The ratios of iron and each iron oxide in the sprayed
coating of each test specimen as sprayed were the same for every
test specimen.
[0033] Next, each test specimen was subjected to heat treatment.
The heat treatment temperature was 400.degree. C. to 650.degree.
C., and the heat treatment time was 60 minutes for every test
specimen. The ratios of iron and iron oxides in the sprayed coating
were analyzed by an XRD method on the sprayed coating of the test
specimens after heat treatment to obtain FIG. 2. The ordinate in
FIG. 2 indicates peak intensity ratios of iron and each iron oxide.
The peak intensity ratio was defined by the following formula.
Peak intensity ratio=Each maximum peak height of iron and iron
oxide/total of maximum peak heights of iron and each iron oxide
[0034] A higher peak height ratio means a larger ratio of the
content in the sprayed coating. With reference to FIG. 2, when the
heat treatment temperature is not less than 400.degree. C., the
peak intensity ratio of magnetite remarkably increased and also the
peak intensity ratio of iron (Fe) increased as the temperature
rose.
[0035] Here, the chemical reaction formula of the transformation
from wustite to magnetite is as follows.
4FeO.fwdarw.Fe+Fe.sub.3O.sub.4
[0036] Referring to the above described chemical reaction formula
and FIG. 2, when the heat treatment temperature is not less than
400.degree. C., the transformation from wustite to magnetite is
facilitated, and the iron ratio and magnetite ratio in the spray
coating increase. On the other hand, the wustite ratio
decreases.
[0037] Further, when the heat treatment temperature is higher than
550.degree. C., the iron ratio rapidly decreases and the hematite
ratio increases as the heat treatment temperature rises. The
decrease of the iron ratio is probably due to that the oxidation of
the sprayed coating itself has progressed causing the iron in the
sprayed coating to transform into hematite.
[0038] As so far described, if the heat treatment temperature is
400.degree. C. to 550.degree. C., the magnetite ratio and the iron
ratio, which increase the adhesiveness with the plug body 11, will
increase in the sprayed coating 12. As a result, the adhesiveness
of the sprayed coating 12 to the plug body 11 will increase.
[Reduction of Tensile Residual Stress]
[0039] Conducting heat treatment at 400.degree. C. to 550.degree.
C. will further reduce tensile residual stress in the sprayed
coating. Table 1 shows the level of tensile residual stress (a
deflection) when heat treatment is conducted at each condition
(heat treatment temperature and heat treatment time). Table 1 was
resulted from the following method.
TABLE-US-00001 TABLE 1 Heat treatment temperature Heat treatment
time (minutes) (.degree. C.) 5 20 40 60 70 400 0.3 0.25 0.2 0.1 0.1
450 0.35 0.3 0.22 0.12 0.12 500 0.3 0.3 0.2 0.16 0.16 550 0.3 0.25
0.22 0.2 0.15 600 0.25 0.25 0.2 0.15 0.15 650 0.3 0.2 0.15 0.1 0.1
Non-heat 0.55 treatment
[0040] A plurality of specimens 20 shown in FIG. 3 were prepared.
Each specimen 20 included a base 21, a base metal 22, a sprayed
coating 23, and a plurality of bolts 24. The base 21 had dimensions
of 20 mm width, 50 mm length, and 10 mm thickness. The base metal
22 was disposed on the upper face of the base 22. The base metal 22
had a shape of 20 mm width, 50 mm length, and 1 mm thickness. As
shown in FIG. 3, each end portion (opposite side portions) of the
base metal 22 was secured to the base 21 with a bolt 24. A sprayed
coating 23 was formed on the upper face of the base metal 22. The
sprayed coating 23 was formed by arc spraying, the condition of
which was the same as in FIG. 1, and the thickness thereof was 500
.mu.m.
[0041] Heat treatment was not conducted for one specimen 20, and
heat treatment was conducted at various heat treatment temperatures
(400 to 650.degree. C.) and heat treatment times (5 to 70 minutes)
shown in Table 1 for the other plurality of specimens 20. One of
the bolts 24, which were secured to both end portions of the
specimen 20 which was not subjected to heat treatment and the
specimen 20 subjected to heat treatment, was detached as shown in
FIG. 4. At this moment, as shown in FIG. 4, the base metal 22 and
the sprayed coating 23 were deflected due to tensile residual
stress. Then, as shown in FIG. 4, the distance from the upper face
of the base 21 to the edge of the lower face of the base metal 22
was defined as a deflection FL (mm). It was judged that the
deflection FL was an index of tensile residual stress, and the
larger the deflection, the larger the tensile residual stress.
[0042] Referring to Table 1, in the specimens 20 which were
subjected to heat treatment, the deflection FL was smaller than in
the specimen 20 which was not subjected to heat treatment, and thus
tensile residual stress was reduced. Further, in the specimens 20
subjected to heat treatment, the tensile residual stress decreased
as the heat treatment time increases.
[0043] As so far described, retaining the sprayed coating 12 at a
heat treatment temperature of 400.degree. C. to 550.degree. C. for
5 to 60 minutes will result in an increase in the magnetite ratio
in the sprayed coating 12, thereby increasing the adhesiveness of
the sprayed coating 12 to the plug body 11. Further, the tensile
residual stress of the sprayed coating 12 also decreases.
Therefore, in the plugs 10 subjected to heat treatment at the above
described condition, the sprayed coating 12 becomes less likely to
peel off from the plug body 11.
[0044] When the heat treatment time is too short, the
transformation from wustite to magnetite will not proceed so that
the adhesiveness of the sprayed coating 12 is not likely to
increase. On the other hand, when the heat treatment time is too
long, further oxidation will proceed in the sprayed coating 12 so
that the ratio of iron which is the matrix, declines and the ratio
of iron oxides such as hematite increases. Therefore, the
adhesiveness of the sprayed coating 12 to the plug body 11
decreases on the contrary. Accordingly, the heat treatment time is
5 to 60 minutes. A preferable lower limit of the heat treatment
time will be 10 minutes, and more preferably 20 minutes.
[0045] The heat treatment temperature is preferably 500.degree.
C..+-.25.degree. C. (475.degree. C. to 525.degree. C.).
[0046] In the plugs 10 which are produced in the above described
steps (the preparation step and the heat treatment step), the
adhesiveness of the sprayed coating 12 to the plug body 11
increases. Therefore, the sprayed coating 12 is less likely to peel
off.
[0047] In the plugs 10 prepared in the above described preparation
step, the sprayed coating 12 contains iron and iron oxides.
However, the sprayed coating 12 may further contain other oxides.
For example, the sprayed coating 12 may contain W oxide (WO.sub.3)
along with iron oxides. For example, by arc spraying an iron wire
rod containing W, the sprayed coating 12 will contain iron, iron
oxides, and W oxide. Even with a plug on which such a sprayed
coating is formed, the result of conducting the above described
heat treatment step will be that the magnetite ratio in the sprayed
coating increases, and the tensile residual stress decreases.
Therefore, the sprayed coating is less likely to peel off.
Examples
[0048] Each plug having a sprayed coating was heat treated at
conditions of test numbers 1 to 20 shown in Table 2. An
anti-peeling property of the sprayed coating of the each plug
produced was evaluated.
TABLE-US-00002 TABLE 2 Heat Heat treatment treatment Peeling Test
temperature time rate number (.degree. C.) (minutes) (%) 1 350 20
40 2 350 40 40 3 400 10 30 4 400 20 20 5 400 40 20 6 400 60 20 7
400 80 50 8 500 10 30 9 500 20 10 10 500 40 15 11 500 60 10 12 500
80 50 13 550 10 30 14 550 20 20 15 550 40 20 16 550 60 20 17 550 80
40 18 600 20 50 19 600 40 50 20 -- -- 40
[Test Method]
[0049] Every plug of each test number had the shape shown in FIG.
1. A sprayed coating of a thickness of 600 .mu.m was formed on the
surface of each plug. The sprayed coating was formed by arc
spraying an iron wire rod. The conditions of arc spraying of each
plug were the same for all of them. Ten plugs were prepared for
each test number.
[0050] Heat treatment was conducted on 10 plugs for each test
number at the conditions (heat treatment temperature and heat
treatment time) shown in Table 2. Note that the plug of test number
20 was not subjected to the heat treatment.
[0051] After the heat treatment, the plugs of test numbers 1 to 20
were used to piercing-roll round billets. The round billets had a
chemical composition corresponding to SUS304 of the JIS Standard,
and each had the same diameter and length. Each plug of each test
number was used to piercing-roll three round billets. At this
moment, the heating conditions and the piercing-roll conditions of
each round billet were the same for every test number.
[0052] After piercing-rolling three round billets, the surface of
each plug was visually observed to judge the presence or absence of
the peeling of the sprayed coating. Then, a peeling rate (%) was
determined for each test number based on the following formula.
Peeling rate=number of plugs in which peeling is
confirmed/10.times.100
[0053] In short; out of the 10 plugs of each test number, the rate
of the plugs in which peeling is confirmed was defined as a peeling
rate (%).
[Test Results]
[0054] Referring to Table 2, in test numbers 3 to 6, 8 to 11, and
13 to 16, the heat treatment temperature was within a range of
400.degree. C. to 550.degree. C. and the heat treatment time was
within a range of 5 to 60 minutes for each test number. As a
result, the peeling rate was as low as not more than 30%.
[0055] On the other hand, in test numbers 1 and 2, the heat
treatment temperature was as low as 350.degree. C. Thereby, the
peeling rate was high.
[0056] In test numbers 7, 12, and 17, although the heat treatment
temperature was appropriate, the heat treatment time was as long as
80 minutes. Thereby, the peeling rate was high.
[0057] In test numbers 18 and 19, the heat treatment temperature
was as high as 600.degree. C. Thereby, the peeling rate was
high.
[0058] In test number 20, no heat treatment was conducted. Thereby,
the peeling rate was high.
[0059] Although an embodiment of the present invention have been
described so far, the above described embodiment is merely an
example for carrying out the present invention. Therefore, the
present invention will not be limited to the above described
embodiment, and can be carried out by appropriately varying the
above described embodiment within the range not departing from the
spirit of the present invention.
* * * * *