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Patent 2010174 Summary

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(12) Patent: (11) CA 2010174
(54) English Title: HEAT-RESISTANT AUSTENITIC STAINLESS STEEL
(54) French Title: ACIER INOXYDABLE AUSTENITIQUE RESISTANT A LA CHALEUR
Status: Deemed expired
Bibliographic Data
(52) Canadian Patent Classification (CPC):
  • 75/120
(51) International Patent Classification (IPC):
  • C22C 38/44 (2006.01)
  • C22C 38/58 (2006.01)
(72) Inventors :
  • UEMATSU, YOSHIHIRO (Japan)
  • SHIMIZU, ISAMI (Japan)
  • HIRAMATSU, NAOTO (Japan)
(73) Owners :
  • NISSHIN STEEL COMPANY, LTD. (Japan)
(71) Applicants :
(74) Agent: RICHES, MCKENZIE & HERBERT LLP
(74) Associate agent:
(45) Issued: 2000-09-12
(22) Filed Date: 1990-02-15
(41) Open to Public Inspection: 1991-06-20
Examination requested: 1996-10-29
Availability of licence: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): No

(30) Application Priority Data:
Application No. Country/Territory Date
330128/89 Japan 1989-12-20

Abstracts

English Abstract




A heat-resistant austenitic stainless steel is
disclosed. This steel essentially consists of: not more
than 0.06% C, 1 - 4% Si, 0.5 - 4% Mn, not more than 0.035%
P, not more than 0.005% S, 10 - 17% Ni, 14 - 20% Cr, 1 - 4%
Mo, 0.01 - 0.5% A8, not more than 0.035% N, and balance
essentially Fe, and may further contain small amounts of
any of Cu, REM and B and the composition thereof is
adjusted so that a limited amout of .delta. -ferrite appears in
solidification. The steel has excellent hot salt corrosion
resistance, weldability, salt errosion resistance of the
weld and hot-workability.


Claims

Note: Claims are shown in the official language in which they were submitted.




We claim:

1. A heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1 - 4%
Mn: 0.5-4%
P: not more than 0.035%,
S: not more than 0.005%,
Ni: 10 - 17%
Cr: 14 - 20%
Mo : 1 - 4%
A~: 0.01 - 0.5%
N: not more than 0.035%
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) below is
7 - 11, said steel having excellent hot salt corrosive
resistance, weldability, salt corrosion resistance of weld and
hot-workability.
(Si% + Mo%) ~ 3% . . . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) ~ 11% . . . . . . . . . . . . . . . (2)
D = (Cr% + 1.5Si% + Mo% + 3A~%) - (Ni% + 30C% + 30N% +
0.5Mn%)
........................(3)

2. A heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1 - 4%
Mn: 0.5 - 4%
P: not more than 0.035%,
S: not more than 0.005%,
Ni: 10 - 17%
Cr: 14 - 20%



-19-
- 19 -



Mo: 1 - 4%
A~: 0.01 - 0.5%
Cu: 0.5 - 2.5%
N: not more than 0.035%
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) below is
7 - 11, said steel having excellent hot salt corrosive
resistance, weldability, salt corrosion resistance of weld and
hot-workability.

(Si% + Mo%) ~ 3% . . . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) ~ 11% . . . . . . . . . . . . . . . (2)
D = (Cr% + 1.5Si% + Mo% + 3A~%) - (Ni% + 30C% + 30N% +
2Cu% + 0.5Mn%)
........................(3)

3. A heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1 - 4%
Mn: 0.5-4%
P: not more than 0.035%,
S: not more than 0.005%,
Ni: 10 - 17%
Cr: 14 - 20%
Mo: 1 - 4%
A~: 0.01 - 0.5%
N: not more than 0.035%
0.005 - 0.1% of one or more of REM
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) below is
6 - 11, said steel having excellent hot salt corrosive



-20-


resistance, weldability, salt corrosion resistance of weld and
hot-workability.
(Si% + Mo%) ~ 3% ~ . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) ~ 11% . . . . . . . . . . . . (2)
D = (Cr% + 1.5Si% + Mo% + 3A~%)- (Ni% + 30C% + 30N% +
0.5Mn%)
................ (3)

4. A heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1 - 4%
Mn: 0.5 - 4%
P: not more than 0.035%,
S: not more than 0.005%,
Ni: 10 - 17%
Cr: 14 - 20%
Mo: 1 - 4%
A2: 0.01 - 0.5%
N: not more than 0.035%
One or more of Nb, Ti and V: 0.05 - 0.5% in total.
and/or
B: 0.05 - 0.02%
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) is
6 - 11, when the steel contains B and is 7 - 11 when the steel
does not contain B, said steel having excellent hot salt
corrosion resistance, weldability, salt corrosion resistance
of weld and hot-workability.
(Si% + Mo%) ~ 3% . . . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) ~ 11% . . . . . . . . . . . . . . . (2)
D = (Cr% + 1.5Si% + Mo% + 3A~% + 2.6Ti% + 0.5Nb% + 0.5V%)
- (Ni% + 30C% + 30N% + 0.5Mn%)
. . . . . . . . . . . . . . . . (3)


-21-



5. A heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1 - 4%
Mn: 0.5- 4%
P: not more than 0.035%,
S: not more than 0.005%,
Ni: 10 - 17%
Cr: 14 - 20%
Mo: 1 - 4%
A~: 0.01 - 0.5%
N: not more than 0.035%
Cu: 0.5 - 2.5%
One or more of Nb, Ti and V: 0.05 - 0.5% in total.
and/or
B: 0.05 - 0.02%
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) is
6 - 11, when the steel contains B and is 7 - 11 when the steel
does not contain B, said steel having excellent hot salt
corrosion resistance, weldability, salt corrosion resistance
of weld and hot-workability. ~
(Si% + Mo%) ~ 3% . . . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) = 11% . . . . . . . . . . . . . . . (2)
D = (Cr% + 1.5Si% + Mo% + 3A~% + 2.6Ti% + 0.5Nb% + 0.5V%)
- (Ni% + 30C% + 30N% + 2Cu% + 0.5Mn%)
. . . . . . . . . . . . . . . . (3)
6. A heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1-4%
Mn: 0.5 - 4%


-22-



P: not more than 0.035%,
S: not more than 0.005%,
Ni: 10 - 17%
Cr: 14 - 20%
Mo: 1 - 40
A~: 0.01 - 0.5%
N: not more than 0.035%
0.005 - 0.1% of one or more of REM
One or more of Nb, Ti and V: 0.05 - 0.5% in total.
and/or
B: 0.05 - 0.02%
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) is
6 - 11, when the steel contains B and is 7 - 11 when the steel
does not contain B, said steel having excellent hot salt
corrosion resistance, weldability, salt corrosion resistance
of weld and hot-workability.
(Si% + Mo%) ~ 3% . . . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) ~ 11% . . . . . . . . . . . . . . (2)
D + (Cr% + 1.5Si% + Mo% + 3A~% + 2.6Ti% + 0.5Nb% + 0.5V%)
- (Ni% + 30C% + 30N% + 0.5Mn%)
. . . . . . . . . . . . . . . . (3)

7. A heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1 - 4%
Mn: 0.5 - 4%
P: not more than 0.035%,
S: not more than 0.005%,
Ni: 10 - 17%
Cr: 14 - 20%
Mo: 1 - 4%

-23-



A~: 0.01 - 0.5%
Cu: 0.5 - 2.5%
N: not more than 0.035%
0.0005 - 0.1 of one or more of REM
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) below is
6 - 11, said steel having excellent hot salt corrosive
resistance, weldability, salt corrosion resistance of weld and
hot-workability.
(Si% + Mo%) ~ 3% . . . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) ~ 11% . . . . . . . . . . . . . . . (2)
D + (Cr% + 1.5Si% + Mo% + 3A~%) - (Ni% + 30C% + 30N% +
2Cu% + 0.5Mn%)
. . . . . . . . . . . . . . . . (3)

8. A heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1 - 4%
Mn: 0.5 - 4%
P: not more than 0.035%,
S: not more than 0.005%,
Ni: 10 - 17%
Cr: 14 - 20%
Mo: 1 - 4%
A~: 0.01 - 0.5%
N: not more than 0.035%
Cu: 0.5 - 2.5%
0.005 - 0.1 of one or more of REM
One or more of Nb, Ti and V: 0.05- 0.5% in total.
and/or
B: 0.05 - 0.02%

-24-



the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) is
6 - 11, when the steel contains B and is 7 - 11 when the steel
does not contain B, said steel having excellent hot salt
corrosion resistance, weldability, salt corrosion resistance
of weld and hot-workability.
(Si% + Mo%) ~ 3% . . . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) ~ 11% . . . . . . . . . . . . . . . (2)

D + (Cr% + 1.5Si% + Mo% + 3A~% + 2.6Ti% + 0.5Nb% + 0.5V%)
- (Ni% + 30C% + 30N% + 2Cu% + 0.5Mn%)
. . . . . . . . . . . . . . . . (3)

9. The steel as claimed in any one of claims 1 to 8, wherein
the C content is 0.03 - 0.060%,
the Si content is 2 - 3%,
the Mn content is 0.5 - 1%,
the P content is not more than 0.03%,
the S content is not more than 0.005%,
the Ni content is 12 - 16%,
the Cr content is 16 - 18%,
the Mo content is 2 - 3.2%,
the A~ content is 0.01 - 0.03%, and,
the N content is not more than 0.03%.

10. The steel as claimed in any one of claims 1 to 9, wherein
the C content is 0.03 - 0.05%,
the Si content is 2 - 2.8%,
the Mn content is 0.5 - 1%,
the P content is not more than 0.03%,
the S content is not more than 0.005%,
the Ni content is 12 - 14%,
the Cr content is 16 - 18%,


-25-



the Mo content is 2 - 2.8%,
the A~ content is 0.01 - 0.03%
the N content is not more than 0.03%, and
the balance being Fe and unavoidable impurities.


-26-

Description

Note: Descriptions are shown in the official language in which they were submitted.





20101"4
SPECIFICATION
Title of the Invention
Heat-Resistant Austenitic Stainless Steel
Field of the Invention
This invention relates to a heat-resistant austenitic
stainless steel which has excellent high temperature salt
corrosion resistance as well as hot salt corrosion
resistance of welds in addition to weld hot cracking
I0 resistance, hot-workability and weldability, and is
usable in hot-corrosive environments, especially under
conditions that the steel is subjected to repeated heating
and cooling in environments in which corrosion by salt,
including corrosion by molten salt, may occur.
Background of the Invention
Heat-resistant steels are employed far uses under
severely corrosive conditions such as automobile exhaust
emission control systems, parts of furnaces, parts of
heat-exchangers, electric appliances for cooking such as
electric range and grill. Such steels are required to be
provided with hot gas corrosion resistance under burning
conditions, hot corrosion resistance in environments
containing various oxides such as PbO, VZOS, etc.,
chlorides such as PbCQz, NaCB, MgCQ2, KCQ, etc., and
resistance to hot corrosion by molten salt in addition to
general high temperature characteristics such as high
temperature strength, high temperature oxidation
resistance, adherence of scale, etc. Further, these
steels must be resistive to wet corrosion by condensed
water at low temperatures. Under these severely corrosive
environments, carbon steel sheets which are surface-treated
for heat resistance cannot stand, and, therefore, heat-
resistant austenitic stainless steels are used.
It is known and is a problem to be solved that
incinerators for treating a large quantity of waste
materials, tuyere burners of blast furnaces, heavy oil
burners, exhaust gas pipes of internal combustion engines,
etc. and parts of apparatus which are used in environments
- 1 -




;~~so~~4
~_
in which adhesion of salt or ash occurs such as in the
cold districts where antifreezing agents are sprinkled on
the roads, often suffer remarkable high temperature
coarosion. Investigations of cases of this kind of
corrosion have revealed that accelerated oxidation of
intergranular corrosion type is observed in common in all
the cases. This is a corrosion by adhering salt or molten
salt and the corrosion with chlorides is marked.
For this kind of corrosion, known heat resistant
stainless stee.Is such as SUS304, SUS321, SUS310S, etc.
are not satisfactory.
Generally, high degree addition of Si and Mo is
effective for improvement of corrosion resistance.
However, such high alloying deteriorates hot workability,
reduces production yields, roughens the surface of steel
in manufacturing, and makes difficult pipe-making and
welding in application. Also it has been revealed that
welds are often selectively and remarkably corroded by
hot salt although the parent metal is sound when a fresh
material is subjected to high temperatures in environments
where the material comes into contact with a high concent-
ration salt solution.
Japanese Laid-Open Patent Publication No. 63-213643
(1988) discloses a stainless steel having excellent high
temperature corrosion resistance in the presence of
chlorides, said steel comprising not more than 0.03 C,
10 - 20~ Cr, 10 - 30~ Ni, not more than 2~ Mn, 1 - 6~ Si,
0.5 - 5~ Mo and 0.02 - 0.4~ N, wherein the D value
defined as
24.4 Cr + 28 Ni + 6.7 Mn - 48.8 Si - 56.9 Mo - 148.0 Nb
is not more than 500. The steel may contain 0.1 - 1~ in
total of at least one of Ti, Zr, Nb and Ta. However,
improvement in weld hot cracking resistance is not
considered in this steel.
Therefore, there is a demand for a heat-resistant
anstenitic stainless steel which is provided with both
excellent weld hot crocking resistance and excellent hot
workability in addition to hot salt corrosion resistance.
- 2 -




2~ 101,'4
We made an intensive research in order to improve hot
salt corrosion resistance, weld hot cracking resistance
and hot-workability of the heat-resistant austenitic
stainless steel simultaneously and have found that these
properties can be improved by adding limited amounts of
Si and Mo for the purpose of improvement of hot salt
corrosion resistance; adding a limited amount of Cu from
the viewpoint of stress corrosion cracking resistance or
weatherability, if desired; adding limited amounts of Nb,
Ti or V for the improvement of resistance to intergranular
attack hot corrosion and intergranular corrosion by
combination attack in the cool state, high temperature
strength as well as hot workability; and adding limited
amounts of H and REM for the improvement of hot workability
and weld hot cracking susceptibility.
Summary of the Invention
The above-described purpose is achieved by providing a
heat-resistant austenitic stainless steel basically comp-
rising:
c: not more than 0.06
Si: 1 - 4~
Mn: 0.5 - 4%
P: not more than 0.035
S: not more than 0.005$
Ni: 10 - 17~
Cr: 14 - 20~
Mo: 1 - 4~
AR: 0.01 - 0.5~
N: not more than 0.03
which, if desired, may contain:
Cu: 0.5 - 2.5~,
further
at least one of Nb, Ti and V: 0.05 - 0.5~ in total
and/or
H: 0.0005 - 0.02,
and further
one or more of REM: 0.005 - 0.1~,
the balance being Fe and unavoidable impurities, wherein
- 3 -




~. 2~1.0~.'~4
the value of (Si% + Mo%) (Formula (1} below) is not less
than 3, the value % (2.5 Si% + Mo%) (Formula (2) below)
is not more than 11 and the D value represented by
Formula (3} below is not less than 6 and not more than
11, when the steel contains REM or H from the viewpoint
of weldability, and is not less than 7 and not more than
11 when the steel does not contain these elements.
(Si% + Mo%) ~ 3 ......................... (1)
(2.5 Si% + Mo%) ~ 11 .................... (2)
D = (Cr% + l.5Si% + Mo% + 3AB% + 2.6Ti% + 0.5Nb%
+ 0.5V%) - (Ni% + 30C% + 30N% + 0.5Mn% + 2Cu%)
.................... (3)
The D values as defined above of all the steels of the
working examples described in the above-mentioned Japanese
Laid-Open Patent Publication No. 63-213643 are less than-
4. We have found that the weld hot cracking resistance of
austenitic stainless steels containing high-Mo high-Si is
improved by adjusting the composition so that said D value
is more than 6 or 7.
The preferred steels of the present invention have the
composition: C: 0.03 - 0.06%, Si: 2 - 3%, Mn: 0.5 - 1%,
P: not more than 0.03%, S: not more than 0.005%, Ni: 12 -
16%, Cr: I6 - 18%, Mo: 2 - 3.2%, Ap: 0.01 - 0.03$, N: not
more than 0.03% and the balance being Fe and unavoidable
impurities.
The more preferred steels of the present invention
have the composition: C: 0.03 - 0.05, Si: 2 - 2.5, Mn:
0.5 - 1%, P: not mroe than 0.03, S: not more than 0.005%,
Ni: 12 - 14, Cr: I6 - 18%, Mo: 2 - 2.8, AQ: 0.01 - 0.03%,
N: not more than 0.03% and the balance being Fe and unavoid-
able impurities.
The reasons why the composition is defined above is as
follows.
C: This element that is unavoidable is a strong
austenite former and an important necessary component for
the steel of the present invention from the viewpoint of
the composition balance. Carbon is also useful for saving
expensive nickel. Further C is an interstitial solute and
- 4 -




2~ ~.0~.'~4
effective for enhancing the high temperature strength.
However, the addition of an excessive amount of C makes
the steel brittle and deteriorates workability. From such
consideration, the upper limit of the content is defined
as 0.06. On the other hand, the reduction of the C
content lengthens the refining time and thus invites
increase of the manufacturing cost and at least 0.03 of
C is required for the desired high temperature strength.
Si: This element is one of the most important compo-
nents that improve oxidation resistance and high
temperature salt corrosion. At least 1$ and preferably
2~ of this element is required to achieve the satisfactory
effect thereof. On the other hand, Si induces precipita-
tion of the a -phase, which deteriorates toughness of the
steel. Also, this element deteriorates hot workability,
weldability and formability. From the consideration of
these facts the upper limit content of this element is
defined as 4~, preferably, 3~.
Mn: This element is effective for fixing and excluding
the deleterious S as MnS. If the Mn content is not
sufficient, MnS deposits as a film at the granular inter-
faces and promotes deterioration of the intergranular
strength. Hut MnS globurizes and reduces its effect for
deteriorating intergranular strength when Mn is contained
in higher concentration. At least 0.5~ Mn is required
but its effect saturates at around 4~. Thus the Mn
content is defined as 0.5 - 4~. When the D value is
considered, however, the Mn content is preferably not more
than 1~.
P: This element is deleterious for weld hot cracking
resistance like S. Therefore, the lower, the better.
However, it invites increase in the manufacturing cost to
reduce the P content excessively. The allowable limit is
0.035.
S: As mentioned above with respect to P, this element
is deleterious for weld hot cracking, and thus the lower,
the better. However, reduction of the S content invites
increase in the manufacturing cost. The allowable upper
- 5 -




~,~ ~"~~~:~
limit is 0.005$.
Ni: This element is one of the fundamental elements of
austenitic stainless steels. From the viewpoint of the
weld hot cracking resistance, the lower limit of the
content thereof is defined as 10~, because 8 -ferrite
must be formed in the weld. The upper limit is defined as
17~ from the consideration of the balance of the composi-
tion and the manufacturing cost. When the D value is
considered, however, the preferred content of Ni is 12 -
16~.
Cr: This is the most fundamental element of stainless
steels for achieving oxidation resistance and corrosion
resistance. With less than 14~, the steel cannot be even
provided with the mere high temperature oxidation
resistance in hot corrosive environments. If the content
exceeds 20$, however, the adjustment of the composition
becomes difficult, and the formation of b -ferrite
increases, which invites difficulty in working. Therefore,
the upper limit is defined as 20~. If the D value is
considered, however, 16 - 18~ is preferred.
Mo: This element is effective for achieving corrosion
resistance in high temperature corrosive environments and
high temperature salt-corrosive environments and thus
must be positively added. The lower limit of the content
thereof is defined as l~, since the effect thereof cannot
be well exhibited with less than 1~. However, Mo is an
expensive element and promotes deposition of the a -phase
and thus invites deterioration of toughness of the steel.
With addition of over 4~, hot workability of the steel
is impaired. Therefore, the Mo content should be not
higher than 4~. When the D value is considered, 2 - 3.2~
is preferred.
A~: This is a most effective element for improvement
of oxidation resistance and effective for improving the
cleanness of the steel. It is desired that AQ is contained
in an amount of at least 0.01. However, AB is a strong
ferrite former and thus the upper limit is restricted to
0.5$ from the viewpoint of the composition balance as
- 6 -




2~~.~1~~4
well as of the toughness of the product. When the D value
is considered, the preferred range is 0.01 - 0.03.
H: This element is effective for enhancing inter
granular strength and improving hot workability and weld
hot cracking resistance. With less than 0.0005, however,
the effect is not remarkable. With more than about 0.02,
borides are formed, which degrade the intergranular
strength. Therefore, the B content is defined as 0.0005 -
0.02$.
Nb, Ti and V: These elements combine with C and N
to form minute precipitate and thus are effective for
corrosion resistance as well as high temperature strength,
especially for improvement of creep strength. These effects
are manifested at the content of 0.05 or higher. However,
as the content increases, workability and toughness are
deteriorated. Therefore, the upper limit is defined as
0.5~ in total. The preferred range is 0.05 - 0.4b.
REM: These elements fix deleterious S as high melting
point compounds at the early stage of solidification and
thus improve cracking susceptibility. Also, they are
effective for enhancing the resistance to pealing off of
the oxide scales which result from heating-cooling cycles.
These effects are manifested at the content of 0.005 or
higher. And this deteriorate intergranular strength at
high temperatures, which spoils the improvement in the
hot cracking susceptibility. On the contrary, when REM
are contained in too high concentrations, large amounts
of REM oxides deposit at the grain boundaries. Therefore,
the upper limit is restricted to 0.1~ or less.
Cu: This element is effective for improvement of
stress corrosion cracking resistance and weatherability,
for which at least 0.5$ is required. On the other hand,
when a large amount of Cu is contained, it is segregated
in the grain boundaries and remarkably degrade hot
workability. Therefore, the upper limit is defined as
2.5$. When the D value is considered, the preferred
content range is 1 - 1.3~.
N: This element is effective for improvement of high
-


CA 02010174 2000-03-27
temperature strength. However, excessive addition of N
impairs workability and thus the upper limit is defined as
0.03% or less.
Further, the total amount of Si and Mo is regulated by
formulas (1) and (2). The lower limit value (Sio + Mo%) must
be 3 or more for better hot molten salt corrosion resistance.
The upper limit value (2.5 Si% + Moo) must be 11 or less in
order to minimize degradation in hot workability, weld hot
cracking resistance, 6 -brittleness resistance and formability.
The reason why the D value is defined as above in as follows.
Steels containing high Si or high Mo are very susceptible to
weld hot cracking. The D value is an index for precipitation
of ferrite. The D value must be 6 or more when REM or B is
contained and 7 or more when they are not contained.
Appearance of a larger amount of 8 -ferrite causes hot work
cracking and deteriorates maufacturability.
Considering these facts, the upper limit of the D value
is defined as 11.
Accordingly, in one aspect the present invention resides
in a heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1 - 4%
Mn: 0.5-4a


P: not more than 0.0350,


S: not more than 0.005%,


Ni: 10 - 170


Cr: 14 - 200


Mo 1 - 4 0
:


A2: 0.01 - 0.5%


N: not more than 0.035%
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) below is
7 - 11, said steel having excellent hot salt corrosive
resistance, weldability, salt corrosion resistance of weld and
hot-workability.
_ g _

CA 02010174 2000-03-27
0
(Si% + Mo%) > 3° . . . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) < 11% . . . . . , . , , . , , , . . (2)
D = (Cr% + l.5Si% + Mo% + 3A~%) - (Ni% + 30C% + 30N% +
0.5Mn%)
........................(3)
In another aspect, the present invention resides in a
heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06x,
Si: 1 - 40
Mn: 0.5-4%
P: not more than 0.035%,
S: not more than 0.0050,
Ni: 10 - 170
Cr: 14 - 20%
Mo: 1 - 4%
A~': 0.01 - 0.5%
Cu: 0.5 - 2.5%
N: not more than 0.035%
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) below is
7 - 11, said steel having excellent hot salt corrosive
resistance, weldability, salt corrosion resistance of weld and
hot-workability.
(Si% + Mo%) > 3°- . . . , . , , , ,
° . . . . . . . (1)
(2.5 Si% + Mo%) < 11% . . . . . , . , . . , . . . , (2)
D = (Cr% + l.SSi% + Mo% + 3AP%) - (Ni% + 30C% + 30N% +
2Cu% + 0.5Mn%)
........................(3)
In a further aspect, the present invention resides in A
heat-resistant austenitic stainless steel essentially
consisting of:
C: not more than 0.06%,
Si: 1 - 4%
- 8a -


CA 02010174 2000-03-27
Mn:0.5 - 4%


P: not more than0.035%,


S: not more than0.005%,


Ni:10 - 17%


Cr:14 - 20%


Mo:1 - 4a


A~:0.01 - 0. 5%


N: not more than0.0350


Oneor more Nb, Ti and V: 0.05 - 0.5o in total.
of


and/or
B: 0.05 - 0.02%
the balance being Fe and unavoidable impurities, wherein the
total content of Si and Mo satisfies the formula (1) and (2)
below, and the D value as defined by the formula (3) is 6 -
11, when the steel contains B and is 7 - 11 when the steel
does not contain B, said steel having excellent hot salt
corrosion resistance, weldability, salt corrosion resistance
of weld and hot-workability.
0
(Sio + Moo) = 3% . . . . . . . . . . . . . . . . (1)
(2.5 Si% + Mo%) ; 11% . . . . . . . . . . . . . , . (2)
D = (Cr% + l.SSio + Mo% + 3A~o + 2.6Tio + 0.5Nb% + 0.5Vo)
- (Nio + 30C% + 30N% + 0.5Mn%)
. . . . . . . . . . . . . . . . (3)
Brief Description of the Attached Drawings
Fig. 1 is a graph showing the relation between the
corrosion weight loss (mg/cm2) and the (Si + Mo)o value with
respect to the steels of the present invention.
Fig. 2 is a graph showing the relation between the null
point and the 2.5(Si + Mo)% value with respect to the steels
of the present invention. Fig. 3 is a graph showing the
relation between the critical strain s ~ (%) and the D value of
the steel. Figs. 4 - 6 are microphotographs (x about 70) of
TIG welding welds which were subjected to repeated heating in
the presence of NaC~ of SUS304 steel, SUSXM15J1 steel and a
steel of the present invention respectively.
- 8b -


CA 02010174 2000-03-27
Specific Disclosure of the Invention
Now the invention will be described specifically
in detail. In a fundamental experiment, steels the
compositions of which are shown in Table 1 were prepared
by vacuum melting and specimens thereof were subjected to
the high temperature tensile tests and the high temperature
- 8c -




salt corrosion test. For the high temperature tensile
test, 20 x 20 x 110 mm pieces were prepared from ingots,
the pieces were heat-treated at 1200°C for 2 hours and
they were worked into rod specimens having a diameter of
10 mm. For the high temperature salt corrosion test,
ingots were forged into 30 mm thick plates, which were
held at 1200°C and thereafter hot-rolled to 5 mm in
thickness and further reduced to 2 mm by ordinary cold
rolling and the glates were finally annealed. They were
finally made into 25 x 35 mm specimens, the surface of
which was polished to #400. The high temperature salt
corrosion test was carried out by immersing the specimens
in a saturated aqueous salt solution at 20°C for 5 minutes,
held at 650°C for 2 hours and air-cooled for 5 minutes,
and repeating the above cycle 10 times. After the test,
the specimens were descaled and the corrosion resistance
was evaluated by corrosion weight loss> The results are
indicated in Table 1. From the results, it is apparent
that the weight loss of SUS302H and SUSXM15J1 containing
high Si is remarkably smaller in comparison with SUS304
and SUS321. The weight loss is further reduced in E33 -
F96 which contains both Si and Mo. Fig. 1 shows the
effect of the (Si + Mo) content to the high temperature
salt corrosion resistance of the invention steels of
which the D value is ? - 11. From this figure, it is
apparent that the corrosion weight loss of the steels of
which the (Si + Mo) amount is not less than 3~ is remark-
ably small, i.e., addition of not less than 3~ of (Si + Mo)
is very effective for the high temperature salt corrosion
resistance. Generally, excellent heat resistance of
austenitic stainless steels is brought about by the Crz03
film formed on the surface of the steels. Although this
film exhibits excellent protective effect against atmos-
pheric oxidation, it is not satisfactory
in high temperature salt corrosion environments in which
the steels of the present invention are to be used, and
it is markedly corroded_ It is considered that addition
of not less 3~ of (Si + Mo) makes the steel form an
- g -




c



~~ CON N C~JL L :~ :~~ '~ ~ L c~ ~ ~ r. ~,x
: . :


N .-r ...r
ra ~ x Lr_c :~ : N :wi V
c: ~


w.


3


c ~ ~ 0 0 00 _ ~ c c c~ 0 0


N ( C ~ N ~~.N N :"~ O ~ N C O
._.


O C O O I ~ ~ C . . ,
.C C .~ O O O O C O
~



~ r~~ ~ ~ .v.,~ ~ . .
~ ~1 ' ~ .
~~


Z Z Z Z Z ~ ...
:- j .,,


Cr


C.N _ N ~,.r _ ~.r-.r_..~~J :V:V ~V .~r-.r


O O C. C O C O C .~~O O O ."~O G' O O O
. . . . . .


. . . . . . . . . .
O G C C ~ O C O O C O O O ~ O O C O


N N C'~.-~ N N N N :V


r G sr O :r v ".~.~rCi .,~~,,~v O v


y . . . . . .


.
v ~ v ~ G CrO ~r'J 'iCr'~r Cr~


c :r;~ .rc c'o o .-.:.,
O


O N .- N C O O L"~L-L: L: C O
I


. .
N N ~~ N N ':N N .~'~N
~


N ~ f'--~.--~,~ G N :~i~ L' Cue-('L7
' -
-


C C V ~ 'C'~~ . C: "~~.L~ --N '~N .--iC~O
~-


1 . 1 . 1 . .
v, x x r- c:.v c~c: :~: c c~:~ :'r- ;~c- ~ c ~
:


.-..-,.-~-~.-,~ ,.-~~..-~..-, --._. .-,_



(


-~N ~ ~~ r..~.rr L: ~ C:T N ~ .-~,..rN
~'W . .w.~ _-;C ~. C~ --w.:.x N ~ p ~ N


~t . . . . .


. . .
Z x .~ p ~7L~ C~~ L: C~ c ~' N L'~C'C: N :~.:V
~ -, .-...r_



x L. C.~.~ 'W .-~_ ~ _ .-_:


W _ o ~ ~ G y r ~ fir W
r


C w p G . .
C O C O ~.G ....O .~O C C


o o v:r~~r O O C v "Wr ~ o .:w~r O G v


Ice-I1 C~ L~_........~ L~ ~,~~C t~ LDC~ r:L~ L~ N N
N N ' :


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C


G C ~ ~rvr ~r~ v O G ~r v~r'~ ~~..~~.r~..~r
. . .


O ~.~iO ~ O O O '~. 'J o O O O O C. .."~.C '.


o c~ c L~c c o :~ N c~o c~c L~o .-~N o


C N CO L~ cCx 00oC x x c~.r- r-x c-x x


~ o o c o o ~ o o .~o ~ 0 0 0


~ ~ W '' J .~.I' C'JC'~ L'7C O l.~L"7~ ~
:


c C._ ._,.
...t . . C .--~C:rJ L~ l~L~ ~;L C:JlC7lC':....
f' . . ~ C'~
.
.


. , ,
O V N :"'Li N ~~ vJ :: :~N N ~~ ~~~,~,N ~V :V:\7


-~~':--~c .-~o c c~ r- :~c c M: L~- -,
C:~ ~~


. L a L~L ~ c c c :~:~~N . c ~ c c :-~
c ~ --


J o o o .~.... o o ~ 0 0 o c o 0 0
-~



O O G' O v~'J ~ C o O 0 0 O 0 0 0 C


L~:


C'--iN -.


O N O


C'7:'~C'~Y --.M I L. '~ IC~C~ 000 C'~V~.~~ N C"~


'~ ;r:-~ r c ~- W r:m ~ L~:c~c;
co


:n;r;-onccnW =~W W :~;:=7=:7W _, W W~ ~ ~


,
.



- 10 -




excellent protective film resistant to high temperature
salt corrosion environments.
On the other hand, as the contents of Si and Mo
increase, deterioration of hot workability, weld hot
cracking resistance and toughness is caused. Therefore,
excessive amounts of Si and Mo cannot be contained. Fig.
2 shows the relation between the null point and the (Si +
Mo)~ value. The null point is the temperature at which
the rupture reduction value (the value of cross-sectional
reduction at rupture), is 0 when the steel specimens Were
subjected to a high speed high temperature tensile test
at 800 - 1400°C and the rupture reduction value in ~ were
measured. From these results, it is apparent that the
null point is lowered as the contents of Si and Mo ~.
increase, and, especially, the effect of Si is 2.5 times
that of Mo. This is because liquation cracking owing to
intergranular melting is promoted when the contents of Si
and Mo increase. Therefore, addition of large amounts of
Si and Mo is not allowed and it is desirable that (2.5 Si +
Mo) is not more than 11.
As shown in the drawing, when H is added, there is
remarkable rise of the null point in comparison with the
steels containing (si + Mo) of the same level. This is
because B enhances intergranular strength and addition of
H is effective for improvement of the materials which are
poor in hot-workability.
For the above-described reason, addition of Si and Mo
is regulated by the total amount thereof. The lower limit
is determined from the viewpoint of hot salt corrosion
resistance and the upper limit is determined from the
viewpoint of hot-workability, weld hot cracking and c -
brittleness. When the hot-workability of the steel is not
sufficient even if the upper limit amount of the content of
Si and Mo, B is added. That is, B, which enhances inter-
granular strength, is effective for improvement of hot-
workability.
In hat salt corrosion environments, welds are often
severely corroded in preference to mother metal. Figs.
- 11 -




2~3.~1'~~4
4, 5 and 6 are photomicrographs (x Ca. 70) of welds of
repsectively of SUS304, SUSXM15J1 and the E57 steel
specimens which underwent the following test. That is,
the steels were made into plates the thickness of which
is 0.3 mm or less by the ordinary hot and cold rolling and
annealing. After the steel specimens were subjected to
TIG welding. They were wetted with a 5 ~ NaCE solution of
60°C for 1 hour, dried at 60°C for 3 days and held at
350°C for 4 hours, and this cycle was repeated 10 times.
As seen there, the weld of SUS304 steel was corroded
along the 5 -ferrite phase and corrosion is so remarkable
at the bonds that the specimen was broken there. The weld
of the SUSXM1531 steel, which contains Si, did not suffer
so serious corrosion as to be broken at the bond as SUS304,
but the b -ferrite phase was considerably selectively
corroded. In contrast to these two steels, E57 steel
remained completely uncorroded.
It is thought that in SUS304 and SUSRM1531, the 8
ferrite phase is baser than the matrix and thus the bond
is electrochemically corroded severely, while in E57, the
b -ferrite phase per se is more resistant to corrosion
because of Si and Mo, which are effective for hot salt
corrosion resistance. That is to say, addition of Si and
Mo is desirable for improving the corrosion resistance of
not only the mother metal but also the weld. It is one
of the characteristics of the present invention that the
austenitic stainless steel has acquired corrosion
resistance against severe corrosion environments as
described above, which was not achieved by addition of Si
alone.
For automobile exhaust emission control apparatuses,
parts of incinerators, parts of heat exchangers, etc.
fabrication of which requires welding, materials having
high weld hot cracking susceptibility is fatally defective.
Especially, steels containing high-Si and high-Mo have
high weld hot cracking susceptibility and, therefore, are
difficult to use them therefor. For weld hot cracking, the
d -ferrite, which is formed in the course of solidification,
- 12 -




:~lfl~'~~4
plays a deleterious role. In austenite single phase
steels, the initial crystals comprise austenite phase
only. Therefore, impurities are concentrated at the
primary grain boundaries of the austenite phase and weaken
the intergranular strength causing hot cracking. If 8 -
ferrite is present, the b -ferrite in the initial crystals
transforms into austenite in the course of solidication,
accompanied by change of grain boundaries. Therefore, in
such a steel, the amount of the intergranular impurities
is smaller than in austenite single phase steels, and
thus weld hot cracking resistance is improved. Using
steels, the compositions of which are indicated in Table
2, which form b -ferrite, we carried out evaluation of
cracking susceptibility by the weld hot cracking test and
obtained the results represented by Fig. 3. Ingots of the
steels of Table 2 were prepared by vacuum melting and
made into 30 mm thick slabs by forging, the slabs were
held at 1200°C and thereafter, they were hot-rolled to 5 mm
thick plates and further cold-rolled to 1.5 mm thick
plates, which were finally annealed. The plates were
worked into 40 x 200 mm specimens. The weld hot cracking
test was carried out by holding the two ends of a specimen
by the chucks and subjecting the specimen to TIG welding
under a longitudinal tensile load applied. Five to ten
welded samples were obtained with tensile load varied.
After welding, the strain was measured from the marking
lines scratched beforehand. Also, cracks in the weld
generated during solidification was observed and the
relation between the minimum strain at which cracking
occurred (called "critical strain") and the D value, which
is an index of the amount of b -ferrite, is shown in Fig.
3. From this test, it is apparent that hot cracking
resistance of the high-Si and high-Mo steel is improved by
adjusting the composition thereof so that a proper amount
of b -ferrite be formed in the weld, and it is proper to
adjust the D value within the range of 7 - 11 for that
purpose when the steel does not contain B or REM. As
seen in Fig. 3, when B or REM is contained in the basic
- 13 -




~....
.n,
_



~r:
I


c~ I ca Lm n .-i N o
c~


c ~ . . . . . . .-r


b o0 00 C7 N C" n ~a Ca CO


3 0



O O


ft t O


O


O


..



C


.--a.--aN ~ I , N N N
'V N


0 0 0 0 0 0 0 o I o
c



o c o G I G o c ~ G
o o


M ,M C' I:~ N C"~ M M M


oZ O O O ~ ~ O O O O O
O O



O O ~ O I O O O O C
O O
'


I
-i N :11 Q ~ ~
(


O O O O C' O O L'~ M C
-



t': N ~N ~N -, N N ~N N N


I ~


C"~ u~ -.r .--a I .-, C
~ (~..
~


G'7 C O C" G'~ 00 M ~ N
I O
~.~.


:., w . . . . . . .
.


U :~ L~. t~ c'
a t~ O ~ x N



I



o , o .-, c~ o N .-.
~ W ~ ~
.c:


..-~ ~~~ M - C:~ G'7 O N Ice-L'~
. . i i
O.
.
~


. . .
Z M :~~ N N L(~ La"~N L7 LC:
N I


( I


N .--.e:V N N N N .-r


O ~ O O O O O O V

~


.


O O O G O O O O O O
I


N O O G'~ C C7 O~ N M
I I


G 0.~ x~ c0 t'~ b L~ tI~ t~ 00 00



C O O O O O ~ O C C


i
O G'~ ..-,C~ M N O N O
x


~i ~' Q' L L~- Lf LI7 O~ C'~ C.J
~ N ~



N N N N N N N N N
~
N


L7 C -r C~ N LCD C7 - O M


:~ M ~ M C~ ~ M c--~ c c


U o o ~ 0 0 0 0 0 0 0


.
c o 0 0 o o c o 0 0
~


N :'~ ~ ~~ CJ L~ b ~ o


::..L. .,....r..-..~~, ~- (.:.,..~ ~ L,,
..... ._.


- 14 -




2~ 1fl1'~4
composition, the cracking susceptibility abates and results
better than the steels having D value of the same level
but containing no D or REM are obtained. That is, a D
value range of 6 - lI will do.
As described above, we studied the composition of
the heat resistant austenitic stainless steel from the
viewpoints of hot salt cracking resistance, hot-workability
and weld hot cracking resistance and now provide a heat
resistant high-Si and high-Mo austenitic stainless steel
provided with the above-mentioned properties of high level.
Working Examples
Now the invention will be illustrated by way of
working examples and comparative examples.
Steels the compositions of which are shown in Table
3 were prepared and made into the specimens as described
above and they were tested in the same manner. The
results of the tests, i.e., corrosion weight loss in the
hot salt corrosion test, critical strain obtained in the
weld hot cracking test and the null point from the high
temperature tensile test, are summarised in Table 3. The
specimens and the methods employed were entirely the same
as those employed in the tests relating to Figs. 1, 2 and
3. From this table, the following facts are apparent.
Comparative Still E74, which is outside of the claimed
composition in that it does not positively contain Mo and
the Si content is low, exhibits a very large weight
loss. Steel E75, which does not positively contain Mo,
suffers high degree corrosion and the null point thereof
is low because of high content of Si. Although the D
value was adjusted to 8.8 so that some amount of 8 -
ferrite was formed, the critical strain is very low because
of high content of Si. Steel E76, which contains high
degrees of Si and Mo, has a low null point and a very low
critical strain. Steel F6, the composition of which
falls in the general composition range of the present
invention but out of the claimed scope in that the D
value thereof is as low as 4.5, exhibited an extremely
low critical strain. Steel E77, the composition of which
- 15 -




...w
2~~t.~~:'~~
C alt. Crit. ull
lue loss Pt


(m8/ca~ strain (C)
(%)



F1 0.035 5 20 15 1360


E57 0.034 ;,5 20 16 1360


E60 0. ;, 25 17 1360
033 g


E61 0.047 ;,5 23 15 1325


E62 0.040 :,5 23 I9 1350


Fg 0040 ~.2 28 12 1360


E63 0.042 :,0 28 17 1360


r
E64 0.03 ,, 26 . 19 1350
5


E65 0.0x0 .,g 20 18 1360


o E66 0.042 ;, 19 15 1360
0


FIO 0. :, 25 11 1350
043 0


E67 0.038 ,1 2a 15 1350


H
E68 0.042 ;4 2 1~ I350


E69 0.040 ;g 28 17 1360


E70 0.041 ,0 25 17 1360


E71 0.046 ,2 26 15 1350


E72 0.042 ,g 25 17 1360


E73 0.045 ,8 24 15 1360


E 74 0 . . 100 z20 13 i
038 0 5


.' E 75 0. ~, 3g 5 1300
047 g


E76 0.055 ~,0 I6 5 . 1300


F6 0.045 ,5 29 0.2 1360


v E77 0.038 ,1 4~ 8 1325


SLS304 0.06 ,4 08 z20 1375
~~


o SUS302B 0.08 ,I ~2 20 1360


c
St;SW15J10.05 , 48 18 1325
g






~~~~.~'~~
falls in the general composition range of the present
invention but out of the claimed scope in that the D
value is too high, was corroded along the b -ferrite
grains and exhibited a large corrosion weight loss. The
known Steel SUS304 markedly suffered corrosion. The
known Steels SUS302H and SUSXM15J1 positively containing
Si exhibited less corrosion weight losses than SUS304 but
the weight losses were significantly larger in comparison
with the steels of the present invention, because the
former steels do not contain Mo.
In contrast with the above described known and com-
parative steels, Steels F1 and E57 of the present invention
contain Si and Mo, which are effective for hot salt
corrosion resistance, exhibited small corrosion weight
losses, high critical strains and high null points ,
because the D value is adjusted to 8.5. Steel E60
contains Si and Mo, which are effective for hot salt
corrosion resistance, as well as Cu, which is effective
for stress corrosion cracking resistance, recorded a
small corrosion weight loss, a high critical strain and a
high null point like Fl and E57. Steels E61 - E66 and F9
positively contain Si and Mo like the above-described
steels, and, therefore, their corrosion weight losses are
small. Of these steels, E61 contains Nb and Ti which are
especially effective for improvement of creep strength,
E62 contains V from the same consideration, and E64 contain
Cu, Nb and V and their D values were adjusted to 6.2 - 8.5,
which is a range proper for prevention of weld hot
cracking. These steels exhibited high critical strain
values. Steels F9, E63, E65 and E66 contain H, which is
effective for improving hot workability, and in addition
to Cu, Nb or Ti or V. Therefore, they exhibited high
null points.
Steels F10 and E67 - E73 positively contain Si and
Mo, which are effective for hot salt cracking resistance,
like the above-described steels and, therefore, their
corrosion weight losses are small. They also contain
REM, which are effective for improvement of weld hot
- 17 -




23.~1'~~4
cracking and, resistance therefore, they recorded high
critical strain values although their D values are
relatively low. Of these, E67 further contains Cu, E68
contains Nb and E71 contains Cu and Nb, but their null
points are high. E69, E70, E72 and E73 contains H in
addition to REM or Nb, etc., and, therefore, their null
points are high. As has been described above, the steels
of the present invention, are provided with excellent hot
salt corrosion resistance, excellent weld hot cracking
resistance as well as excellent hot-workability.
20
30
- 18 -

Representative Drawing

Sorry, the representative drawing for patent document number 2010174 was not found.

Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date 2000-09-12
(22) Filed 1990-02-15
(41) Open to Public Inspection 1991-06-20
Examination Requested 1996-10-29
(45) Issued 2000-09-12
Deemed Expired 2004-02-16

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Application Fee $0.00 1990-02-15
Registration of a document - section 124 $0.00 1990-12-12
Maintenance Fee - Application - New Act 2 1992-02-17 $100.00 1991-12-02
Maintenance Fee - Application - New Act 3 1993-02-15 $100.00 1992-10-28
Maintenance Fee - Application - New Act 4 1994-02-15 $100.00 1993-11-08
Maintenance Fee - Application - New Act 5 1995-02-15 $150.00 1994-12-21
Maintenance Fee - Application - New Act 6 1996-02-15 $150.00 1995-12-14
Request for Examination $400.00 1996-10-29
Maintenance Fee - Application - New Act 7 1997-02-17 $150.00 1996-12-17
Maintenance Fee - Application - New Act 8 1998-02-16 $150.00 1998-01-14
Maintenance Fee - Application - New Act 9 1999-02-15 $150.00 1999-01-13
Maintenance Fee - Application - New Act 10 2000-02-15 $200.00 1999-12-20
Final Fee $300.00 2000-06-06
Maintenance Fee - Patent - New Act 11 2001-02-15 $200.00 2001-01-18
Maintenance Fee - Patent - New Act 12 2002-02-15 $200.00 2002-01-17
Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
NISSHIN STEEL COMPANY, LTD.
Past Owners on Record
HIRAMATSU, NAOTO
SHIMIZU, ISAMI
UEMATSU, YOSHIHIRO
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
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Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Abstract 1994-01-21 1 18
Drawings 1994-01-21 4 153
Description 1994-01-21 18 1,163
Claims 2000-03-27 8 194
Description 2000-03-27 21 972
Cover Page 2000-09-05 1 26
Cover Page 1994-01-21 1 48
Claims 1994-01-21 3 113
Fees 1999-12-20 1 36
Assignment 1990-02-15 8 285
Prosecution-Amendment 1996-10-29 2 97
Correspondence 1990-08-23 2 67
Prosecution-Amendment 1999-09-27 2 3
Prosecution-Amendment 1999-01-18 2 54
Prosecution-Amendment 2000-03-27 15 380
Correspondence 2000-06-06 1 38
Fees 1998-01-14 1 43
Fees 1999-01-13 1 41
Fees 1996-12-17 1 45
Fees 1995-12-14 1 44
Fees 1994-12-21 1 48
Fees 1993-11-08 1 34
Fees 1992-10-28 1 35
Fees 1991-12-02 1 37