Valve

There is disclosed a valve comprising one valve seat ring, of a disc or a body, having a surface composed of a Cr-Mn-Fe system or a Cr-Ni-Fe system Fe-based precipitation hardening type alloy, and another valve seat ring thereof having a surface composed of a Cr-Ni system Ni-based alloy having a hardness Hv of 400 or more. The valves of this invention can have excellent wear resistance, cavitation erosion resistance and galling resistance, and since emitting no cobalt, the valves of this invention are suitable for various plants such as chemical plants, particularly nuclear power plants.

BACKGROUND OF THE INVENTION 
This invention relates to a valve excellent in galling-resistant and 
cavitation erosion-resistant properties. 
Heretofore, seat rings of valves used in various plants such as chemical 
plants and nuclear power plants are welded with a Co-based Cr-W-C-Co alloy 
which is generally called a Stellite in order to provide them with 
galling-resistant and cavitation erosion-resistant properties. 
However, from the viewpoints of the prevention of exhaustion of cobalt 
resources and the improvement of safety in the nuclear power plants, 
researches have been conducted into valve seat rings on which an Ni-based 
or Fe-based cavitation erosion-resistant and wear-resistant alloy is 
employed instead of the above-mentioned Stellite, with the intention of 
inhibiting the emission of cobalt (see D. Ellis and R. L. Squires, "Weld 
Deposition and Properties of Nickel Based Hardfacing Alloys", Metal 
Construction, 15 (7) 388-393). 
The known Ni-based and Fe-based alloys are, however, poorer in cavitation 
erosion-resistant and galling-resistant properties as compared with the 
Co-based Stellite. 
SUMMARY OF THE INVENTION 
This invention has now been completed to eliminate the above-mentioned 
problem, and its object is to provide a valve from which neither cobalt 
particles nor cobalt ions are released essentially in any plant and which 
has excellent cavitation erosion-resistant and galling-resistant 
properties. 
The present inventors have researched into how the cavitation 
erosion-resistant and the galling-resistant properties equivalent to or 
superior to those of the Stellite can be given to the valve seat rings 
without using any cobalt. It is apparent that when the surfaces of the 
valve seat ring which will be brought into contact with and will slide on 
each other are made of similar and ductile materials, a wear loss will be 
large and a galling phenomenon will tend to occur. Therefore, it can be 
presumed that the employment of the pair of valve seat rings made of 
specific different materials will lead to functional effects equivalent to 
the Stellite even without relying on the latter, and from this 
presumption, this invention has been created. 
That is to say, this invention is directed to a valve which comprises one 
valve seat ring, of a disc or a body, having a surface composed of a 
Cr-Mn-Fe system or a Cr-Ni-Fe system Fe-based precipitation hardening type 
alloy, and another valve seat ring thereof having a surface composed of a 
Cr-Ni system Ni-based alloy having a hardness Hv of 400 or more such as a 
Cr-Mo-Nb-Ni system and a Cr-Si-B-Ni system Ni-based alloy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to this invention, there can be provided a valve excellent in 
galling-resistant properties by the combination of a Cr-Mn-Fe system or a 
Cr-Ni-Fe system Fe-based precipitation hardening type alloy having good 
corrosion resistance and hardness, and the above-mentioned Ni-based alloy 
having good corrosion resistance and hardness. 
Examples of the Cr-Mn-Fe system Fe-based precipitation hardening type 
alloys used in this invention include alloys comprising, for example, 10 
to 30% by weight of chromium, 10 to 30% by weight of manganese, 0.5 to 
3.0% by weight vanadium, 0 to 0.3% by weight of carbon, 0.2 to 1.0% by 
weight of nitrogen and a residue of iron. 
The contents of the aforesaid components are limited for the following 
reasons: 
Cr (chromium) is an essential element for improving corrosion resistance 
and strength, and its necessary content is at least 10% by weight. 
However, its upper limit is put on a level of 30% by weight, since when 
the content of Cr is too high, toughness will deteriorate. More 
preferably, 12 to 25% by weight. 
A content of Mn (manganese) is required to be 10% by weight or more to 
heighten strength, work-hardening properties and resistance to cavitation 
erosion, but since its excessive addition impairs workability, the content 
is limited to 30% by weight and is preferably within the range of 15 to 
25% by weight. 
With regard to V (vanadium), its content of at least 0.5% by weight is 
necessary to obtain precipitates and to improve strength and resistance to 
cavitation erosion. Its suitable content is 1.0% by weight or more, but 
the upper limit is regulated to 3.0% by weight, since the addition of much 
vanadium will bring about the deterioration of workability. 
C (carbon) is an element effective to obtain precipitates in cooperation 
with V and to enhance strength and resistance to cavitation erosion, but 
the addition of much carbon will impair corrosion resistance remarkably. 
Therefore, the content of C preferably is 0.2% by weight or less, though 
the upper limit of 0.3 % by weight has been given hereinbefore. 
N (nitrogen) is an element necessary to obtain precipitates in cooperation 
with V and to enhance strength and resistance to cavitation erosion, and 
its required content is at least 0.2% by weight. The content of 0.3% by 
weight or more is suitable, but when it is too much, pin-holes and 
blow-holes will occur and melting will become difficult. Thus, the upper 
limit is regulated to 1.0% by weight. Preferably, the content of N is 
within the range of 0.3 to 0.6% by weight. 
Examples of the Cr-Ni-Fe system Fe-based precipitation hardening type 
alloys used in this invention include SUS 630, SUS 631 and maraging 
steels. 
Above all, the Fe-based precipitation hardening type alloy having a 
composition of 7 to 14% by weight of Cr, 6 to 10% by weight of Ni, 0.5 to 
2.0% by weight of Al, 1.5 to 3% by weight of Mo, 0.1% by weight or less of 
C and a residue of Fe is particularly suitable for this invention, because 
of excellent hardness and corrosion resistance. 
With regard to Cr, its content is required to be 7% by weight or more for 
the improvement of corrosion resistance. However, much chromium will 
accelerate the formation of a ferrite and will deteriorate hardness. 
Therefore, the content of Cr is 14% by weight or less and ranges 
preferably from 11.5 to 13.5% by weight. 
In order to perform the functions of bringing about a precipitation 
hardening phenomenon and impeding the formaiton of a ferrite, Ni should be 
added in an amount of 6 % by weight or more. However, when its content is 
too high, the formation of an austenite will be accelerated and strength 
will be poor. For these reasons, its upper limit is regulated to 10% by 
weight, and thus the content of Ni preferably ranges from 7.0 to 9.0% by 
weight. 
As for the element Al, its addition of 0.5% by weight or more is necessary 
in order to allow precipitation hardening and too much aluminum will 
impair workability, and thus the content of Al is regulated to 2% by 
weight or less and ranges preferably from 0.7 to 1.5% by weight. 
A content of Mo is required to be 1.5% by weight or more so as to improve 
corrosion resistance and strength. However, since much Mo will accelerate 
the formation of a ferrite, the content of Mo is 3% by weight or less and 
ranges preferably from 1.7 to 2.5% by weight. 
Carbon is a component for improving strength and inhibiting the formation 
of a ferrite, but when its content is too high, this element will hurt 
corrosion resistance and ductility. Therefore, the content of carbon is 
regulated to 0.1% by weight or less, preferably 0.05% by weight or less. 
With regard to the Cr-Mo-Nb-Ni system alloy used for another valve seat 
ring of this invention, there may be mentioned, for example, an alloy 
consisting essentially of 15 to 45% by weight of chromium, 3 to 15% by 
weight niobium, 0 to 20% by weight of molybdenum, 0 to 20% by weight of 
iron and a residue of nickel. In the following, the reasons why contents 
of these components are limited to the aforesaid ranges are explained. 
First, chromium is a component effective to improve corrosion resistance 
and necessary to heighten oxidation resistance at high temperatures and 
hardness, but when its composition ratio is less than 15% by weight, 
functional effects will be insufficient; when it is more than 45% by 
weight, coarse primary phase will deposit excessively and desired 
properties will deteriorate. Therefore, the content of chromium is 
preferably within the range of 20 to 35% by weight. 
Niobium can be combined with chromium and nickel to produce an 
intermetallic compound such as Cr.sub.2 Nb, and to thereby heighten 
strength, and it is a component necessary for wear resistance and 
cavitation erosion resistance. When a composition ratio of niobium is less 
than 3% by weight, the effects will be insufficient; when it is more than 
15% by weight, toughness will become poor and mechanical strength will 
also be impaired. In consequence, the content of niobium is preferably 
within the range of 7 to 15% by weight. 
Molybdenum is a component necessary for the improvement of corrosion 
resistance and for the improvement of hardness, wear resistance and 
cavitation erosion resistance by strengthening a solid solution. When its 
composition ratio is in excess of 20% by weight, effects will reach a 
maximum level and toughness will fail. This is the reason why the 
limitation of molybdenum has been made as given above. Moreover, the 
composition range of molybdenum is preferably within the range of 5 to 15% 
by weight. 
In this Ni-based alloy, a part of niobium may be replaced with tantalum. 
Further, a part of molybdenum may be replaced with tungsten. The Ni-based 
alloy may contain manganese and silicon which will be added at the melting 
step as a deoxidizer and a desulfurizer. 
The further addition of 20 % by weight or less of iron to the 
above-mentioned alloy contributes to the improvement of strength and 
toughness of the alloy material. A small amount of iron can give some 
effect to the alloy material, but its content preferably is 3% by weight 
or more. When the content of iron is more than 20% by weight, the strength 
of the alloy material will fall and the mechanical strength of the alloy 
will be impaired. Accordingly, it is preferably within the range of 3 to 
12% by weight. 
As the Cr-Si-B-Ni system alloy to be used in this invention, there may be 
mentioned, for example, an alloy comprising 0.3 to 1.5% by weight of 
carbon, 5 to 25 % by weight of chromium, 0.5 to 6.0% by weight of boron, 
0.5 to 6.0 % by weight of silicon, 10% by weight or less of iron and a 
residue which is substantially nickel. 
Carbon is an element effective to heighten wear resistance and hardness, 
and when its content is less than 0.3% by weight, wear resistance and 
hardness will be poor; when it is more than 1.5% by weight, toughness will 
drop. Therefore, the content of carbon is within the range of 0.3 to 1.5 % 
by weight, preferably the range of 0.4 to 1.0 % by weight. 
Silicon and boron are elements effective to enhance wear resistance and 
strength due to the formation of a silicide and a boride, and when a 
content of each element is less than 0.5% by weight, effects will be 
insufficient; when they are present in large quantities, the coarse 
silicide and boride will be produced and toughness will fall. Therefore, 
the content of each element is regulated to 6% by weight or less, and it 
is preferred that the content of boron is within the range of 0.5 to 5.0% 
by weight and the content of silicon is within the range of 2.5 to 6.0% by 
weight. 
Iron contributes to the reinforcement of the matrix and the improvement of 
thermal shock resistance, and when its content is in excess of 10% by 
weight, the strength of the matrix will drop and mechanical strength will 
be impaired. The preferable content of iron is within the range of 1 to 6% 
by weight. 
Further, chromium is a component necessary to improve corrosion resistance 
and to reinforce the matrix, and when its content is less than 5% by 
weight, effects will not be satisfactory; when it is more than 25% by 
weight, toughness will fall. Therefore, the content of chromium is 
regulated to the range of 5 to 25% by weight, preferably the range of 10 
to 20% by weight. 
The Ni-based alloy used in this invention has a hardness Hv of 400 or more, 
preferably 450 or more, and the combination of this Ni-based alloy with 
the above-mentioned Fe-based precipitation hardening type alloy can lead 
to good resistance to galling. 
The Cr-Mn-Fe system or the Cr-Ni-Fe system Fe-based precipitation hardening 
type alloy and the Cr-Mo-Nb-Ni system or the Cr-Si-B-Ni system Ni-based 
alloy which have been just described may be used in manners of, for 
example, pad welding on the surfaces of a valve seat ring, brazing, 
diffusion bonding, joining by screw or the like. In short, it is necessary 
that the sliding surfaces of valve seat rings are constituted with the 
above-mentioned alloys. 
Now, this invention will be described in detail with reference to Examples. 
EXAMPLES 
Table 1 shows chemical compositions of alloys for the test. Sample Nos. 1 
to 5 and 11 were vacuum induction melted and subjected to a hot forging 
treatment and then a solid solution treatment at 950.degree. to 
1150.degree. C. for about 1 to 2 hours and an aging treatment at 
500.degree. to 700.degree. C. for about 1 to 10 hours were performed and 
specimens were taken from the thus treated samples. Sample Nos 6 to 10 and 
12 were taken from cast materials which were obtained using the 
high-frequency vacuum induction melting furnace. 
A cavitation erosion test was carried out under conditions of an amplitude 
of 90 .mu.m, a frequency of 6.5 KHz and a test time of 180 minutes in 
accordance with an ultrasonic vibration method prescribed by 19th 
Corrosion Prevention Forum, Cavitation Section, 98th Committee (1972) in 
order to measure a cavitation erosion loss of each sample. The results are 
set forth in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Hard- 
Weight 
Sample 
Chemical composition (wt %) ness 
loss 
No. C B N Si Mn Cr Mo Nb Fe Ni Others 
(Hv) 
(mg) 
__________________________________________________________________________ 
1 0.11 
-- 0.61 
0.13 
24.6 
18.3 
-- -- Remainder 
-- V 1.39 
401 0.4 
2 0.12 
-- 0.49 
0.14 
20.2 
16.8 
-- -- Remainder 
-- V 1.21 
392 0.7 
3 0.05 
-- -- -- -- 17.2 
-- 0.30 
Remainder 
4.32 Cu 4.21 
422 5.1 
4 0.06 
-- -- -- -- 17.0 
-- -- Remainder 
7.13 Al 1.21 
410 4.5 
5 0.03 
-- -- -- -- 13.2 
2.14 
-- Remainder 
8.07 Al 1.26 
495 4.2 
6 -- -- -- 0.21 
-- 24.6 
9.6 
9.4 
-- Remainder 
-- 494 3.2 
7 -- -- -- 0.19 
-- 25.0 
11.1 
10.3 
6.3 Remainder 
-- 476 3.0 
8 0.37 
2.42 
-- 2.71 
-- 10.7 
-- -- 3.51 Remainder 
-- 462 19.8 
9 0.59 
2.98 
-- 4.20 
-- 13.6 
-- -- 3.73 Remainder 
-- 620 9.5 
10 -- -- -- 0.18 
-- 15.6 
8.6 
2.4 
-- Remainder 
-- 272 40.1 
11 0.08 
-- 0.11 
0.19 
5.93 
7.21 
-- -- Remainder 
-- V 1.02 
243 51.4 
12 1.0 
-- -- -- -- 28.0 
-- -- 3.0 Co W 4.0 
478 3.6 
Remainder 
__________________________________________________________________________ 
As is clear from Table 1, Sample Nos. 1 to 9 which were the Cr-Mn-Fe system 
and the Cr-Ni-Fe system iron-based precipitation hardening type alloys and 
the Ni-based alloys were equivalent, in a cavitation erosion loss, to the 
cobalt-based alloy of Sample No. 12 which had heretofore been used as 
wear-resistant parts such as the valve seats, and it was also confirmed 
that they were excellent in cavitation erosion resistances. 
Next, sluice valves, one example of which was shown in FIG. 1 and each of 
which had a nominal diameter of 100 mm, were manufactured by combining the 
above alloys with each other as shown in Table 2, and a leakage of each 
sluice valve was tested after repeated opening and closing operations 
thereof. In the FIG. 1, reference numeral 1 is a body, 2 is a body seat 
ring, 3 is a disc, 4 is a disc seat ring, 5 is a stem, 6 is a bonnet and 7 
is a handwheel. For comparison, sluice valves each having the same 
structure were manufactured by combining the alloys of Sample Nos. 5, 8 
and 10 to 12 with each other as shown in Table 2, and the test was 
accomplished under the same conditions. The results are exhibited together 
in Table 2. 
The aforesaid opening and closing operations were carried out 100 times 
under load conditions of a surface pressure of 2 Kg/mm.sup.2, and the leak 
test was accomplished by causing high-pressure water to pass through the 
sluice valve and measuring a flow rate of leaked water on the outlet side 
thereof. 
TABLE 2 
______________________________________ 
Combination of Flow rate of 
valve seats leaked water 
Body seat ring 
Disc seat ring 
(cc/min) 
______________________________________ 
Example 1 
Sample No. 6 
Sample No. 1 
0 
Example 2 
Sample No. 2 
Sample No. 8 
0 
Example 3 
Sample No. 7 
Sample No. 5 
0 
Example 4 
Sample No. 3 
Sample No. 6 
0 
Comparative 
Sample No. 5 
Sample No. 5 
Galling occured 
example 1 at 23nd opera- 
tion 10.4 
Comparative 
Sample No. 8 
Sample No. 8 
Galling occured 
example 2 at 30th opera- 
tion 6.9 
Comparative 
Sample No. 10 
Sample No. 11 
Galling occured 
example 3 at 2nd opera- 
tion 8.6 
Comparative 
Sample No. 12 
Sample No. 12 
0 
example 4 
______________________________________ 
As is apparent from Table 2, the sluice valves regarding this invention 
were excellent in galling resistance similarly to the sluice valve made of 
the cobalt-based alloy of Comparative example 4 which had heretofore been 
used for the valve seats, and it has also confirmed that they had good 
wear resistance. 
Next, by the use of welding rods of Sample Nos. 13 to 15 shown in Table 3, 
pad welding was carried out on the seat ring. 
TABLE 3 
______________________________________ 
Sample 
Chemical composition (%) 
No. C B Si Cr Mo Nb Fe Ni 
______________________________________ 
13 -- -- 0.17 26.3 10.7 11.0 3.2 Remainder 
14 -- -- 0.18 25.1 10.2 10.8 6.2 Remainder 
15 0.45 2.36 2.65 10.5 -- -- 3.0 Remainder 
______________________________________ 
A test was accomplished in the same manner as described above, and the 
results are shown in Table 4. 
TABLE 4 
______________________________________ 
Combination of Flow rate of 
valve seats leaked water 
Body seat ring 
Disc seat ring 
(cc/min) 
______________________________________ 
Example 5 
Sample No. 13 
Sample No. 1 
0 
Example 6 
Sample No. 5 
Sample No. 14 
0 
Example 7 
Sample No. 15 
Sample No. 5 
0 
Comparative 
Sample No. 15 
Sample No. 15 
Galling occured 
example 5 at 25th opera- 
tion 8.5 
______________________________________ 
As is apparent from Table 4, the sluice valves regarding this invention 
were excellent in galling resistance similarly to the sluice valve made of 
the cobalt-based alloy which had heretofore been used for the valve seats, 
and it was also confirmed that they had good wear resistance. 
The aforementioned results indicate that in the valves regarding this 
invention, the Ni-based alloys and the Cr-Mn-Fe system and the Cr-Ni-Fe 
system Fe-based precipitation hardening type alloys are high in cavitation 
erosion resistance, and the combinations of both the alloys excellent in 
resistance to galling. Therefore, it is fair to say that the valves of 
this invention can have excellent wear resistance, cavitation erosion 
resistance and galling resistance, since emitting no cobalt, the valves of 
this invention are suitable for various plants such as chemical plants, 
particularly nuclear power plants.