CA2084912A1 - Alloy and composite steel tube with erosion resistance for use in boilers - Google Patents
Alloy and composite steel tube with erosion resistance for use in boilersInfo
- Publication number
- CA2084912A1 CA2084912A1 CA 2084912 CA2084912A CA2084912A1 CA 2084912 A1 CA2084912 A1 CA 2084912A1 CA 2084912 CA2084912 CA 2084912 CA 2084912 A CA2084912 A CA 2084912A CA 2084912 A1 CA2084912 A1 CA 2084912A1
- Authority
- CA
- Canada
- Prior art keywords
- alloy
- boilers
- content
- erosion resistance
- erosion
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C30/00—Alloys containing less than 50% by weight of each constituent
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Preventing Corrosion Or Incrustation Of Metals (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An alloy with erosion resistance for use in boilers whose composition is specified in weight % as:
not more than 0.1% C, not more than 2.5% Si, not more than 1.0% Mn, not more than 0.03% P, not more than 0.005% S, 10 - 25% Co, 18 - 28% Cr, 10 - 50% Ni, either or both of 2 - 4% Mo, and not more than 8% W, and the balance of Fe and unavoidable impurities, wherein 0.5 Co + Ni + 1.5 Cr ? 75, and 1.2 ? (Ni + Cr)/(Co + Mo + 0.5 W) ? 2.8.
An alloy with erosion resistance for use in boilers whose composition is specified in weight % as:
not more than 0.1% C, not more than 2.5% Si, not more than 1.0% Mn, not more than 0.03% P, not more than 0.005% S, 10 - 25% Co, 18 - 28% Cr, 10 - 50% Ni, either or both of 2 - 4% Mo, and not more than 8% W, and the balance of Fe and unavoidable impurities, wherein 0.5 Co + Ni + 1.5 Cr ? 75, and 1.2 ? (Ni + Cr)/(Co + Mo + 0.5 W) ? 2.8.
Description
8~2 ALLOY AND COMPOSITE STEEL TUBE WITH EROSION
RESISTANCE FOR USE IN BOILERS
BACKGROUND OF THE INVENTION
Field of the Invention 5This invention relates to a steel tube for use in coal-fired boilers and more particularly to an alloy exhibiting excellent resistance to erosion by high-temperature particles.
Description of the Prior Art 10Reflecting recent energy resource circumstances, coal utilization technologies are receiving increasing attention in connection with high-temperature energy equipment such as fuel-fired boilers, fluid bed reactors, coal gasifiers and coal liquefiers. As regards fuel-fired 15boilers, for example, while use has conventionally been made mainly of oil, an awarenes~s of the current need to utilize alternative energy sources has led to a tendency toward increased use of coal.
Up to now, however, high-temperature energy 20equipment has been designed with oil utilization in mind and the problems encountered when coal is used have not been fully overcome. For instance, oal-fired boilers are fabricated using the same materiaIs as used in conventional oil-fired boilers. Differently from th~e oil-fired~boiler, 25however, the coal-fired boiler experiences severe high-temperature erosion damage owing to the falling of clinkers :
.
~ ' " ': ~
RESISTANCE FOR USE IN BOILERS
BACKGROUND OF THE INVENTION
Field of the Invention 5This invention relates to a steel tube for use in coal-fired boilers and more particularly to an alloy exhibiting excellent resistance to erosion by high-temperature particles.
Description of the Prior Art 10Reflecting recent energy resource circumstances, coal utilization technologies are receiving increasing attention in connection with high-temperature energy equipment such as fuel-fired boilers, fluid bed reactors, coal gasifiers and coal liquefiers. As regards fuel-fired 15boilers, for example, while use has conventionally been made mainly of oil, an awarenes~s of the current need to utilize alternative energy sources has led to a tendency toward increased use of coal.
Up to now, however, high-temperature energy 20equipment has been designed with oil utilization in mind and the problems encountered when coal is used have not been fully overcome. For instance, oal-fired boilers are fabricated using the same materiaIs as used in conventional oil-fired boilers. Differently from th~e oil-fired~boiler, 25however, the coal-fired boiler experiences severe high-temperature erosion damage owing to the falling of clinkers :
.
~ ' " ': ~
2~8~9l2 formed by the solid ash component in the boller and also to solid ash entrained by the combustion gas stream as flyash.
Although these problems are well known among those in the industry, measures for overcoming them have not been worked out. Hardly any measures are available from the point of material, and the response has been limited to design countermeasures based on experience, such as reduction of stream velocity and the installation of protectors. In actual practice, however, such efforts to cope with the problem through design are generally ineffective. Any attempt to limit flow velocity tends to produce local flow channels with higher-than-e~pected velocities, while the protectors installed are themselves rapidly damaged.
As regards boiler materials, on the other hand, the boiler tubes are made from SUS 304 steel, or from 18-8 austenitic stainless steels such as SUS 321, 347 and 316, or from alloys such as incoloy 800 and SUS 310. For the high-temperature members in general there are used various high-temperature austenitic stainless steels. However, all of these materials were adopted not for their resistance to high-temperature particle erosion but solely on the basis of experience with oil-fired boilers and the like.
Thus there are almost no measures available for preventing erosion damage by high-temperature particles through the selection of materials. The other side of this is that if it should become possible to overcome the aforesaid problems through material selection, this would ' . ,~ ' , - - ~ .
.- ' ..
' 2V8~912 provide the freedom in equipment designed needed for realizing more compact and higher efficiency equipment.
SUMMARY OF THE INVENTION
One object of this invention is to provide an alloy material with excellent resistance to erosion by hi~h-temperature particles such as is observed in coal-fired boilers. Another object of the invention is to provide an alloy material for coal-fired boilers which is excellent in hot workability and on-site workability and also exhibits strong resistance ~o molten salt corrosion.
Through their research toward the achievement of these objects, the inventors discovered that it is possible to obtain a steel alloy with both erosion resistance and hot workability by using as alloying elements a specific combination of Co, Cr, Ni, Mo and W. They accomplished this invention on the basis of this finding. They further learned that addition of Hf or Zr to the alloy is effective for improving its characteristics, that addition of a small amount of Al is highly effective for coping with an environment made corrosive by molten salt and that addition of Ca and reduction of S content enable improvement of the alloy workability.
Specifically, the aforesaid objeats are achieved by:
~1) An alloy with erosion resistance for use in~
boilers whose composition is specified in weight % as:
not more than 0.1% C, :
. ~
. .
., , . .. ~
-- ~ ,, : , :.
' ': , :, 2 ~ 2 not more than 2.5% Si, not more than 1.0% Mn, not more than 0.03% P, not more than 0.005% S, 10 - 25% Co, 18 - 28% Cr, 10 ~ 50% Ni, eithex or both of 2 - 4% Mo, and not more than 8% W, and the balance of Fe and unavoidable impurities, wherein 0.5 Co + Ni + 1.5 Cr < 75, and 1.2 < (Ni + Cr)/(Co + Mo + 0.5 W) ~ 2.8.
(2) An alloy with erosion resistance for use in boilers according to (1) above, further comprising either or both of not more than 0.2% Hf and not more than 0.2% Zr.
Although these problems are well known among those in the industry, measures for overcoming them have not been worked out. Hardly any measures are available from the point of material, and the response has been limited to design countermeasures based on experience, such as reduction of stream velocity and the installation of protectors. In actual practice, however, such efforts to cope with the problem through design are generally ineffective. Any attempt to limit flow velocity tends to produce local flow channels with higher-than-e~pected velocities, while the protectors installed are themselves rapidly damaged.
As regards boiler materials, on the other hand, the boiler tubes are made from SUS 304 steel, or from 18-8 austenitic stainless steels such as SUS 321, 347 and 316, or from alloys such as incoloy 800 and SUS 310. For the high-temperature members in general there are used various high-temperature austenitic stainless steels. However, all of these materials were adopted not for their resistance to high-temperature particle erosion but solely on the basis of experience with oil-fired boilers and the like.
Thus there are almost no measures available for preventing erosion damage by high-temperature particles through the selection of materials. The other side of this is that if it should become possible to overcome the aforesaid problems through material selection, this would ' . ,~ ' , - - ~ .
.- ' ..
' 2V8~912 provide the freedom in equipment designed needed for realizing more compact and higher efficiency equipment.
SUMMARY OF THE INVENTION
One object of this invention is to provide an alloy material with excellent resistance to erosion by hi~h-temperature particles such as is observed in coal-fired boilers. Another object of the invention is to provide an alloy material for coal-fired boilers which is excellent in hot workability and on-site workability and also exhibits strong resistance ~o molten salt corrosion.
Through their research toward the achievement of these objects, the inventors discovered that it is possible to obtain a steel alloy with both erosion resistance and hot workability by using as alloying elements a specific combination of Co, Cr, Ni, Mo and W. They accomplished this invention on the basis of this finding. They further learned that addition of Hf or Zr to the alloy is effective for improving its characteristics, that addition of a small amount of Al is highly effective for coping with an environment made corrosive by molten salt and that addition of Ca and reduction of S content enable improvement of the alloy workability.
Specifically, the aforesaid objeats are achieved by:
~1) An alloy with erosion resistance for use in~
boilers whose composition is specified in weight % as:
not more than 0.1% C, :
. ~
. .
., , . .. ~
-- ~ ,, : , :.
' ': , :, 2 ~ 2 not more than 2.5% Si, not more than 1.0% Mn, not more than 0.03% P, not more than 0.005% S, 10 - 25% Co, 18 - 28% Cr, 10 ~ 50% Ni, eithex or both of 2 - 4% Mo, and not more than 8% W, and the balance of Fe and unavoidable impurities, wherein 0.5 Co + Ni + 1.5 Cr < 75, and 1.2 < (Ni + Cr)/(Co + Mo + 0.5 W) ~ 2.8.
(2) An alloy with erosion resistance for use in boilers according to (1) above, further comprising either or both of not more than 0.2% Hf and not more than 0.2% Zr.
(3) An alloy with erosion resistance for use in boilers according to ~1) or (2) above, further comprising one or more of not more than 0.1% Y, not more than 0.1% La and not more than 0.1% Ce.
(4) An alloy with erosion resistance for use in boilers according to (1), (2) or (3) above, wherein the s content is not more than 0.0008%.
(5) An alloy with erosion resis~tance~for use in boilers according to (1), (2) or~ (3) above, :further comprising 0.01 - 0.03% Al.
:
2~8~912 (6) An alloy with erosion resistance for use in boilers according to (1), (2) or (3) above, further comprising 0.01 - 0.08% ca.
:
2~8~912 (6) An alloy with erosion resistance for use in boilers according to (1), (2) or (3) above, further comprising 0.01 - 0.08% ca.
(7) A composite steel tube for use in ~oilers whose outer tube is constituted of an alloy according to any of (l) - (6) above.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The reason for limiting the contents of the components of the invention alloy in the foregoing manner will be explained first.
The upper limit of the C content is set at 0.1%
because at higher content C degrades workability and increases the probability of intergranular corrosion cracking.
The upper limit of the Si content lS set at 2.5%
because, while Si is re~uired as-a deoxidi~ing component, it degrades hot workability at a higher content.
The upper limit of the Mn content is set at 1.0%
because, while it has a deoxidation effect sim1lar to Si, it leads to brittleness when present in excess.
The upper limit of the P content is set at 0.03%~
because when P, an unavoidable impurity, ~is~present at a~
higher content, pronounced intergranular segregation thereof occurs.
The upper limit of the S content~is set at 0.005%
because at higher~content S markedly~ degrade he hot workability of the steel. Moreover, since further reducing~
~ .
` , : -~ . ' ~:: ' . . : , `
.
2~84~12 the S content to not more than 0.0008% produces a quantum improvement in the hot workability, it is preferable to set the upper limit of the S content at 0.0008% so as to impart the alloy with excellent hot workability. The improvement in the elongation of the steel that can be obtained by reducing the S content increases sharply as the S content passes below 0.0008%.
Co is an element which improves erosion resistance property when co-present with Ni, Cr, Mo and W.
Its lower limit is set at 10% because, when present at lower content, it does not produce a pronounce effect and the desired erosion resistance can be realized only by increasing the amount of other alloying elementsj which is uneconomical. Its upper limit is set at 25% because it degrades workability at a higher content.
Ni works to improve corrosion resistance. Its lower limit is set to 10~ because, when present at lower content, it has no effect and the desired erosion resistance can be realized only by increasing the amount of other alloying elements, which is uneconomical. Its upper limit is set at 50% because the cost of lncreasing its content beyond this level is high for the effect obtained.
Cr is an element which markedly improves corrosion resistance when co-present with~ Ni~, Mo and W.
Its lower limit is set at 18% because it does not produce a pronounce effec;t when present at lower content~. Its upper limit is set at 28% because the~cost of increasing : :
; . . ~. .
:
2~912 its content beyond this level i5 high for the effect obtained.
Like Co, Mo also improves erosion resistance, particularly through its effect of increasing hardness.
Its content range is set at 2 - 4% because at a content l~wer than 2% the hardness is insufficient and at a content higher than 4% the hardness becomes so high as to degrade workability.
Like Mo, W also improves erosion resistance by increasing hardness. The upper limit of W content is set at 8% because adding it to hi~her content does not produce a proportional improvement in erosion resistancs, but only degrades workability.
Among the aforesaid alloying elements, Co, Ni, Cr, Mo and W are the ones which contribute to the improvement of erosion resistance property. This effect of these elements cannot be obtained, however, when they are added independently, and is obtained only when they are added in combination. Research conducted by the inventors for realizing an alloy exhibiting excellent erosion resistance property in a high-temperature (400 CC) boiler environment showed that the properties of the alloying eIements are manifested most effectively within the aforesaid content ranges when (1) The amounts of Co, Ni and Cr ~satisfy the relation~
0.5Co + Ni ~ 1.5Cr < 75 : ~
, :
: :
, :
' ~, .
2~8~
and (2) The amounts of Ni, Cr, Co, Mo and W satisfy the relation:
1.2 < (Ni + Cr)/(Co + Mo + 0.5W) < 2.8 Hf and Zr are preferably added since they improve high-temperature strength even when present in only small amounts. The upper limit of the content of these elements is set at 0.2% because addition beyond this level does not produce an effect commensurate with the addition.
Y, La and Ce work to improve the hot workability and are therefore added as required in cases where hot working is to be conducted under: severe conditions. The upper limit of the content of each of these elements is set at 0.1% because addition beyond this Ievel does not produce an effect commensurate with the addition and may~even have a degrading effect.
Al not only acts as a deoxidizer but also works to reduce damage from molten salt by forming Al203 on the : . ~
alloy surface. It is therefore prePerably added for~
increasing resistance to molten salt corrosion. Its lower limit is set at 0.01% because lt does not form an A1203 film at a lower content. Its upper limit ~lS ~set at 0.03%;~
because addltion to a higher content de~grades workability.
Ca acts as a deoxidizer and~,~ moreover,: since it , combines with S~present~as an impurlty to~form CaS which,~
in turn, forms~nuclei~that promote~ferrite transformation,~
its addi~ion~maKes it p -slb e~to obta_n -n alIoy~ ~-e~
:
208~12 g with relatively low hardness. It is therefore preferably added when on-site workability is required in addition to resistance to corrosion by molten salt and the like. Its lower limit is set at 0.01% because it does not form CaS at low content. Its upper limit is set at 0.08% because its effect saturates at this level.
The inventors produced alloys with different amounts of Co, Ni and Cr, casted them, and hot rolled each into a 7 mm-thick plate. Each plate was heat treated by first holding it at 1050 C for 30 min~ltes and then quenching it. A test specimen measuring 2 mm in thickness, 15 mm in width and ~0 mm in length was cut from the plate perpendicular to its rolling direction. The test specimen was subjected to an erosion test in which it was placed in a tester heated to 400 'C and blasted for 500 hours with coal particles sized to a diameter of 2 mm. The amount of erosion was observed before and after the test. The test results were scientifically analyzed. Analysis~ of the relationship between the molten salt corrosion property and the alloying elements showed that, in addition Ni and Cr, Co is also an element necessary for improving resistance to molten salt corrosion, and that it ~is effective to determine the amounts of these alloying elements using a molten salt corrosion resistance factor (factor A) of A = 0.5 Co + Ni + 1.5 Cr.
An analysis~of the results of an abraslon~ test conducted on alloys~with a Ni, Cr and Co base~added with , ~ :
,, ' ~ ~ - .::
:
:. . ~ ~ .
: ~ : , :
2~8~ 2 different amounts of one or both of Mo and w showed that Mo and W are effective for improving abrasion resistance, and that as a factor (factor B) for securing a preferable balance with the molten salt corrosion resistance it is important to consider B = (Ni ~ cr)/~co + Mo + 0.5W).
It was then ascertained that an alloy exhibiting excellent molten salt corrosion resistance and abrasion resistance can be obtained by setting A to be not more than 75 and B to be not less than 1.2 and not more than 2.8.
Examples one ton of each of the alloys of the compositions shown in Table 1 was melted in a vacuum induction heating furnace, cleaned by ESR (electro slag refining) treatment, cast into an ingot measuring 500 mm x 250 mm in section and hot rolled into a 7 mm-thick plate. The plate was heat treated by first holding it at 1050 C ~for 30 minutes and then ~uenching it. A test specimen measuring 2 mm in thickness, 15 mm in width and 20 mm in length was cut from the plate perpendicular to its rolling direction. The test specimen was subjected to an erosion test in which it was placed in a tester heated to ~00 C and blasted for 500 hours with coal particles sized to a~diameter of 2 mm. The amount of Prosion was observed before and after the test.
The results are shown in Table 1. In~ the "Abrasion in erosion test" column of Table 1, O indicàtes absence of surface pitting and X indicates conspicuous pitting.
.
208~9 1 2 Additional specimens of the same size were prepared, coated with NaCl-KCl molten salt, and subjected to a 500-hour test in a tester heated to 400 C. The amount of corrosion of the specimens was measured (in terms of weight loss (mg~ owing to corrosion) before and after the test. The results are shown in Table 1. In addition, test specimens meas~ring 2 mm in thickness, 15 mm in width, and 80 mm in length were bent double in the lengthwise direction, coated with the same molten salt and subjected to the same test. Workability was evaluated by visually observing the change in the appearanca of the test pieces following the test. The results are shown in Table 1. In the "Test piece workability" column of Table 1, O indicates absence of cracking and pucker, and X indicates crackin~ or pucker.
The results indicated in Table 1 clearly show that in contrast to the poor erosion exhibited by the comparison alloys, the alloys 1 - 37 according to the invention did not incur pitting, bending-induced pucker or pronounced corrosion, but exhibited excellent characteristics as regards erosion resistance, molten salt corrosion resistance, hot ~ workability and on-site~ ;
workability.
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208~912 In view of the excellent resistance to erosion and molten salt corrosion and the superb workability exhibited by the alloy according to the invention, it can be expected to make a very large contribution to the realization and wide-scale application of practical high-temperature energy equipment, which has become a focus of attention in recent years.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The reason for limiting the contents of the components of the invention alloy in the foregoing manner will be explained first.
The upper limit of the C content is set at 0.1%
because at higher content C degrades workability and increases the probability of intergranular corrosion cracking.
The upper limit of the Si content lS set at 2.5%
because, while Si is re~uired as-a deoxidi~ing component, it degrades hot workability at a higher content.
The upper limit of the Mn content is set at 1.0%
because, while it has a deoxidation effect sim1lar to Si, it leads to brittleness when present in excess.
The upper limit of the P content is set at 0.03%~
because when P, an unavoidable impurity, ~is~present at a~
higher content, pronounced intergranular segregation thereof occurs.
The upper limit of the S content~is set at 0.005%
because at higher~content S markedly~ degrade he hot workability of the steel. Moreover, since further reducing~
~ .
` , : -~ . ' ~:: ' . . : , `
.
2~84~12 the S content to not more than 0.0008% produces a quantum improvement in the hot workability, it is preferable to set the upper limit of the S content at 0.0008% so as to impart the alloy with excellent hot workability. The improvement in the elongation of the steel that can be obtained by reducing the S content increases sharply as the S content passes below 0.0008%.
Co is an element which improves erosion resistance property when co-present with Ni, Cr, Mo and W.
Its lower limit is set at 10% because, when present at lower content, it does not produce a pronounce effect and the desired erosion resistance can be realized only by increasing the amount of other alloying elementsj which is uneconomical. Its upper limit is set at 25% because it degrades workability at a higher content.
Ni works to improve corrosion resistance. Its lower limit is set to 10~ because, when present at lower content, it has no effect and the desired erosion resistance can be realized only by increasing the amount of other alloying elements, which is uneconomical. Its upper limit is set at 50% because the cost of lncreasing its content beyond this level is high for the effect obtained.
Cr is an element which markedly improves corrosion resistance when co-present with~ Ni~, Mo and W.
Its lower limit is set at 18% because it does not produce a pronounce effec;t when present at lower content~. Its upper limit is set at 28% because the~cost of increasing : :
; . . ~. .
:
2~912 its content beyond this level i5 high for the effect obtained.
Like Co, Mo also improves erosion resistance, particularly through its effect of increasing hardness.
Its content range is set at 2 - 4% because at a content l~wer than 2% the hardness is insufficient and at a content higher than 4% the hardness becomes so high as to degrade workability.
Like Mo, W also improves erosion resistance by increasing hardness. The upper limit of W content is set at 8% because adding it to hi~her content does not produce a proportional improvement in erosion resistancs, but only degrades workability.
Among the aforesaid alloying elements, Co, Ni, Cr, Mo and W are the ones which contribute to the improvement of erosion resistance property. This effect of these elements cannot be obtained, however, when they are added independently, and is obtained only when they are added in combination. Research conducted by the inventors for realizing an alloy exhibiting excellent erosion resistance property in a high-temperature (400 CC) boiler environment showed that the properties of the alloying eIements are manifested most effectively within the aforesaid content ranges when (1) The amounts of Co, Ni and Cr ~satisfy the relation~
0.5Co + Ni ~ 1.5Cr < 75 : ~
, :
: :
, :
' ~, .
2~8~
and (2) The amounts of Ni, Cr, Co, Mo and W satisfy the relation:
1.2 < (Ni + Cr)/(Co + Mo + 0.5W) < 2.8 Hf and Zr are preferably added since they improve high-temperature strength even when present in only small amounts. The upper limit of the content of these elements is set at 0.2% because addition beyond this level does not produce an effect commensurate with the addition.
Y, La and Ce work to improve the hot workability and are therefore added as required in cases where hot working is to be conducted under: severe conditions. The upper limit of the content of each of these elements is set at 0.1% because addition beyond this Ievel does not produce an effect commensurate with the addition and may~even have a degrading effect.
Al not only acts as a deoxidizer but also works to reduce damage from molten salt by forming Al203 on the : . ~
alloy surface. It is therefore prePerably added for~
increasing resistance to molten salt corrosion. Its lower limit is set at 0.01% because lt does not form an A1203 film at a lower content. Its upper limit ~lS ~set at 0.03%;~
because addltion to a higher content de~grades workability.
Ca acts as a deoxidizer and~,~ moreover,: since it , combines with S~present~as an impurlty to~form CaS which,~
in turn, forms~nuclei~that promote~ferrite transformation,~
its addi~ion~maKes it p -slb e~to obta_n -n alIoy~ ~-e~
:
208~12 g with relatively low hardness. It is therefore preferably added when on-site workability is required in addition to resistance to corrosion by molten salt and the like. Its lower limit is set at 0.01% because it does not form CaS at low content. Its upper limit is set at 0.08% because its effect saturates at this level.
The inventors produced alloys with different amounts of Co, Ni and Cr, casted them, and hot rolled each into a 7 mm-thick plate. Each plate was heat treated by first holding it at 1050 C for 30 min~ltes and then quenching it. A test specimen measuring 2 mm in thickness, 15 mm in width and ~0 mm in length was cut from the plate perpendicular to its rolling direction. The test specimen was subjected to an erosion test in which it was placed in a tester heated to 400 'C and blasted for 500 hours with coal particles sized to a diameter of 2 mm. The amount of erosion was observed before and after the test. The test results were scientifically analyzed. Analysis~ of the relationship between the molten salt corrosion property and the alloying elements showed that, in addition Ni and Cr, Co is also an element necessary for improving resistance to molten salt corrosion, and that it ~is effective to determine the amounts of these alloying elements using a molten salt corrosion resistance factor (factor A) of A = 0.5 Co + Ni + 1.5 Cr.
An analysis~of the results of an abraslon~ test conducted on alloys~with a Ni, Cr and Co base~added with , ~ :
,, ' ~ ~ - .::
:
:. . ~ ~ .
: ~ : , :
2~8~ 2 different amounts of one or both of Mo and w showed that Mo and W are effective for improving abrasion resistance, and that as a factor (factor B) for securing a preferable balance with the molten salt corrosion resistance it is important to consider B = (Ni ~ cr)/~co + Mo + 0.5W).
It was then ascertained that an alloy exhibiting excellent molten salt corrosion resistance and abrasion resistance can be obtained by setting A to be not more than 75 and B to be not less than 1.2 and not more than 2.8.
Examples one ton of each of the alloys of the compositions shown in Table 1 was melted in a vacuum induction heating furnace, cleaned by ESR (electro slag refining) treatment, cast into an ingot measuring 500 mm x 250 mm in section and hot rolled into a 7 mm-thick plate. The plate was heat treated by first holding it at 1050 C ~for 30 minutes and then ~uenching it. A test specimen measuring 2 mm in thickness, 15 mm in width and 20 mm in length was cut from the plate perpendicular to its rolling direction. The test specimen was subjected to an erosion test in which it was placed in a tester heated to ~00 C and blasted for 500 hours with coal particles sized to a~diameter of 2 mm. The amount of Prosion was observed before and after the test.
The results are shown in Table 1. In~ the "Abrasion in erosion test" column of Table 1, O indicàtes absence of surface pitting and X indicates conspicuous pitting.
.
208~9 1 2 Additional specimens of the same size were prepared, coated with NaCl-KCl molten salt, and subjected to a 500-hour test in a tester heated to 400 C. The amount of corrosion of the specimens was measured (in terms of weight loss (mg~ owing to corrosion) before and after the test. The results are shown in Table 1. In addition, test specimens meas~ring 2 mm in thickness, 15 mm in width, and 80 mm in length were bent double in the lengthwise direction, coated with the same molten salt and subjected to the same test. Workability was evaluated by visually observing the change in the appearanca of the test pieces following the test. The results are shown in Table 1. In the "Test piece workability" column of Table 1, O indicates absence of cracking and pucker, and X indicates crackin~ or pucker.
The results indicated in Table 1 clearly show that in contrast to the poor erosion exhibited by the comparison alloys, the alloys 1 - 37 according to the invention did not incur pitting, bending-induced pucker or pronounced corrosion, but exhibited excellent characteristics as regards erosion resistance, molten salt corrosion resistance, hot ~ workability and on-site~ ;
workability.
. .
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208~912 In view of the excellent resistance to erosion and molten salt corrosion and the superb workability exhibited by the alloy according to the invention, it can be expected to make a very large contribution to the realization and wide-scale application of practical high-temperature energy equipment, which has become a focus of attention in recent years.
Claims (7)
1. An alloy with erosion resistance for use in boilers whose composition is specified in weight % as:
not more than 0.1% C, not more than 2.5% Si, not more than 1.0% Mn, not more than 0.03% P, not more than 0.005% S, 10 - 25% Co, 18 - 28% Cr, 10 - 50% Ni, either or both of
not more than 0.1% C, not more than 2.5% Si, not more than 1.0% Mn, not more than 0.03% P, not more than 0.005% S, 10 - 25% Co, 18 - 28% Cr, 10 - 50% Ni, either or both of
2 - 4% Mo, and not more than 8% W, and the balance of Fe and unavoidable impurities, wherein 0.5 Co + Ni + 1.5 Cr ? 75, and 1.2 ? (Ni + Cr)/(Co + Mo + 0.5 W) ? 2.8.
2. An alloy with erosion resistance for use in boilers according to claim 1, further comprising either or both of not more than 0.2% Hf and not more than 0.2% Zr.
2. An alloy with erosion resistance for use in boilers according to claim 1, further comprising either or both of not more than 0.2% Hf and not more than 0.2% Zr.
3. An alloy with erosion resistance for use in boilers according to clalm 1 or 2, further comprising one or more of not more than 0.1% Y, not more than 0.1% La and not more than 0.1% Ce.
4. An alloy with erosion resistance for use in boilers according to any of claims 1 to 3, wherein the S
content is not more than 0.0008%.
content is not more than 0.0008%.
5. An alloy with erosion resistance for use in boilers according to any of claims 1 to 3, further comprising 0.01 - 0.03% A1.
6. An alloy with erosion resistance for use in boilers according to any of claims 1 to 3, further comprising 0.01 - 0.08% Ca.
7. A composite steel tube for use in boilers having an outer tube constituted of an alloy according to any of claims 1 to 6.
Applications Claiming Priority (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3-326206 | 1991-12-10 | ||
| JP3326206A JP2536802B2 (en) | 1991-12-10 | 1991-12-10 | Boiler alloy with excellent erosion resistance |
| JP7150892A JP2649627B2 (en) | 1992-03-27 | 1992-03-27 | Boiler alloy with excellent hot workability and erosion resistance |
| JP4-71508 | 1992-03-27 | ||
| JP8112392A JPH05279810A (en) | 1992-04-02 | 1992-04-02 | Boiler alloy excellent in molten salt corrosion resistance |
| JP4-81123 | 1992-04-02 | ||
| JP29620892A JPH06145909A (en) | 1992-11-05 | 1992-11-05 | Alloy for boiler excellent in field workability |
| JP4-296208 | 1992-11-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2084912A1 true CA2084912A1 (en) | 1993-06-11 |
Family
ID=27465375
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2084912 Abandoned CA2084912A1 (en) | 1991-12-10 | 1992-12-09 | Alloy and composite steel tube with erosion resistance for use in boilers |
Country Status (2)
| Country | Link |
|---|---|
| EP (1) | EP0546517A1 (en) |
| CA (1) | CA2084912A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6293311B1 (en) | 1998-05-22 | 2001-09-25 | Pmd Holdings Corp. | Multilayer composite pipe fluid conduit system using multilayer composite pipe and method of making the composite |
| CN101979687A (en) * | 2010-09-29 | 2011-02-23 | 山西太钢不锈钢股份有限公司 | Method for smelting nickel alloy in vacuum induction furnace |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1070103A (en) * | 1963-09-20 | 1967-05-24 | Nippon Yakin Kogyo Co Ltd | High strength precipitation hardening heat resisting alloys |
| US3834901A (en) * | 1969-04-23 | 1974-09-10 | Isuzu Motors Ltd | Alloy composed of iron,nickel,chromium and cobalt |
| US3811872A (en) * | 1971-04-21 | 1974-05-21 | Int Nickel Co | Corrosion resistant high strength alloy |
| US3816106A (en) * | 1972-08-25 | 1974-06-11 | Int Nickel Co | Strong, corrosion resistant alloy |
| FR2335611A1 (en) * | 1975-12-15 | 1977-07-15 | Kubota Ltd | Heat-resistant alloyed steel having high compressive strength - contg. chromium, silicon, manganese, nickel, cobalt, molybdenum, niobium and opt. tungsten |
-
1992
- 1992-12-09 EP EP92120983A patent/EP0546517A1/en not_active Withdrawn
- 1992-12-09 CA CA 2084912 patent/CA2084912A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| EP0546517A1 (en) | 1993-06-16 |
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