US3826649A - Nickel-chromium-iron alloy - Google Patents

Nickel-chromium-iron alloy Download PDF

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US3826649A
US3826649A US00313322A US31332272A US3826649A US 3826649 A US3826649 A US 3826649A US 00313322 A US00313322 A US 00313322A US 31332272 A US31332272 A US 31332272A US 3826649 A US3826649 A US 3826649A
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alloy
content
rupture strength
alloys
creep rupture
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R Soederberg
C Helmer
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Santrade Ltd
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Sandvik AB
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    • 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten

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  • the present invention relates to a Ni-Cr-Fe alloy for use at high temperatures.
  • Alloys of the type 20%. CR-30% Ni and the rest substantially Fe are used i.e. in the petrochemical and the hydrocarbon processing industries particularly in tubes and furnace details.
  • alloys with relatively high W contents and increased contents of mainly Ni and Co have been made, said alloys showing improved creep rupture strength compared to the prior 20 Cr-30 Ni base alloys.
  • the invention also includes a combination as an addition of W and an increase of the contents of C and Ti.
  • This variant of the new alloy can be used when a still higher creep rupture strength is needed and when some reduction in creep ductility can be tolerated.
  • the surprising property of this alloy is that the further increase of the creep rupture strength, obtained by increasing the contents of C and Ti, will not decrease at increased service times, contrary to the earlier known alloys which had an increased content of C and Ti but no addition of W.
  • the W addition prevented or at least reduced the rate of the overaging of the carbide particles.
  • the W addition in the high C+Ti grade thus increases the creep rupture strength in two ways, by solid solution hardening and by counteracting the overaging of the carbide particles.
  • the alloy according to the invention contains, in percent by weight, from traces up to 0.40% C, 20-35% Ni, 15-25% Cr, 2-4% W, 0.2-1.6%"Ti, 0.2-1.0% A1, at the most 1% Si, at the most 3% Mn, 0-0.1% B and the rest Fe besides normally present impurities.
  • the alloy is characterized by good ductility and absence of embrittling phases in any appreciable degree.
  • the optimum W content has been found to be about 3% for service temperatures around 900 C. At higher contents of W, an improved creep rupture strength will be obtained at short service times, but at prolonged service times the creep rupture strength will be reduced compared to the alloy containing 3% W because of precipitation of embrittling phases. At service-temperatures above 1000 C. the W content can be increased to about 4%. A lower W content than 3% will usually not give a complete solid solution hardening.
  • the C content is at the most 0.15% and at the lowest 0.05% which is in the same order as for ordinary Alloy 800.
  • the creep ductility will be approximately the same as for Alloy 800.
  • the solution heat treatment temperature should be around 1150 C., to give a complete resolution of the TiC particles.
  • the solution heat treatment temperature must be increased for the solution of the TiC to obtain maximum creep rupture strength.
  • the solution heat treatment temperature should be around 1250" C.
  • Ti should preferably be added in stoichiometric proportion to the C content, thus about 4X C, to obtain maximum creep rupture strength and ductility.
  • a corresponding effect regarding solution hardening and oxidation resistance may also be obtained by the addition of A1.
  • a particularly suitable content has been 03-08%.
  • Ni and Cr principally nickel contributes to a stable austenitic structure while chromium mainly gives the alloy good oxidation resistance and high resistance to carburization. Lower Ni contents than about 20% are generally not used because of risks of instability and formation of embrittling sigma phase. At moderate demands upon oxidation resistance, however, it has been found sufficient to have 2. Ni content of -25%. At the high demands normally present, a Ni content of at least must be used. The content of Cr must be well adjusted in consideration of the fact that an increased content gives unfavourable sigma phase formation. An optimum content, in regard of oxidation resistance as well as of sigma phase formation, has shown to be at the lowest 19% and preferably at the most 23% Cr.
  • Silicon and manganese may be present in contents normal for this kind of alloys. Particularly Si has shown a favourable effect Concerning the oxidation resistance.
  • Each alloying element should be present in contents of at the lowest 0.3%.
  • Mn should preferably be at the most 1.5%.
  • S and P may usually be present in contents of at the most each 0.015%.
  • the contents of other possible alloying elements should also be low and be regarded more as impurities.
  • Niobium has thus shown a less stabilizing effect than Ti and tendencies to form embrittling phases have been found.
  • a normal impurity content is max. 0.1% Nb.
  • Cobalt is of small interest as addition in alloys according to the invention and neither positive nor negative effects have been found. Because of the high costs of this alloying element the contents should thus be as low as possible.
  • a normal impurity content is max. 0.1% Co.
  • B in small amounts can improve the creep strength of alloys of actual type. Furthermore, it improves the ductility in the hot working range and influences the carbide precipitation favourably.
  • a suitable content has shown to be max. 0.005% B.
  • the alloy according to the invention is particularly useful for manufacturing plastically worked products as for instance tubing, bar, plate, forgings, etc.
  • the alloy according to the invention has here shown particularly superior properties at use in tubes for steam reforming of hydrocarbon, in which process hydrogen and carbon monoxide are formed.
  • the mateial has found similar use in so called pig tail tubes and as tubing in ethylene furnaces.
  • Characteristic for the alloy according to the invention has been the particularly high resistance to creep at temperatures above 700 C. and preferably also above 800 C. under heavy mechanical stress and very corrosive conditions. It has also been found that the alloy has the same good resistance to thermal fatigue and high ductility as the base alloys with 20 Cr- Ni, i.e. Alloy 800.
  • the following example shows the results obtained in creep testing alloys according to the invention.
  • the alloys (No. l and No. 2) were compared with the standard alloy, Alloy 800, on 20 Cr-3O Ni base.
  • the composition of the test material is evident from Table I.
  • Results from creep testing at 900 C. have been assorted in Table II.
  • the creep test results are also illustrated in diagram, see FIG. 1, showing the connection between the stress (a) in kp./mm. and the time to fracture (t) in hours.
  • the creep rupture strength (0 in kp./mm. at 900 C. at failure after 100,000 hours is given as a function of the tungsten content (W%).
  • the test materials were a 20 Cr-30 Ni base alloy with varying additions of W (x-marked points) and alloy No. 1 (o-marked point).
  • Nickel-chromium-iron alloy having excellent heat resistance and high creep rupture strength in combination with good ductility at long time use, said alloy consistin'g, in percent by weight, from traces up to 0.40% C, 20-35% Ni, 15-25% Cr, 24% W, 0.21.6% Ti, 0.2- 1.0% A1, 0.3-1.0% Si, 0.33.0% Mn, 00.01% B, and the balance Fe.

Abstract

A STAINLESS STEEL ADAPTED FOR USE AT HIGH TEMPERATURES CONTAINS FROM UP TO 4% BY WEIGHT OF TUNGSTEN, TOGETHER WITH TITANIUM AND ALUMINUM.

Description

July 30, 1974 sbp ETAL 3,826,649
NICKELCHROMIUM-IRON ALLOY Filed Dec. 8, 1972 Fig.7
"Allo 000" 0.5-
Fig.2
United States Patent 3,826,649 NICKEL-CHROMIUM-IRON ALLOY Rolf Harald Siiderberg and Clas Erik Helmer, Sandviken, Sweden, assignors to Sandvik Aktiebolag, Sandviken, Sweden Filed Dec. 8, 1972, Ser. No. 313,322 Claims priority, application Sweden, Dec. 21, 1971, 16,378/71 Int. Cl. C22c 37/10, 39/02 US. Cl. 75-124 9 Claims ABSTRACT OF THE DISCLOSURE A stainless steel adapted for use at high temperatures contains from up to 4% by weight of tungsten, together with titanium and aluminum.
The present invention relates to a Ni-Cr-Fe alloy for use at high temperatures.
Alloys of the type 20%. CR-30% Ni and the rest substantially Fe are used i.e. in the petrochemical and the hydrocarbon processing industries particularly in tubes and furnace details.
It has been tried to fulfill the always increased demands upon creep rupture strength and heat resistance of such alloys by i.e. additional alloy components or higher alloying additions.
Thus, it is earlier known that an addition of W by solution hardening increases the creep rupture strength in alloys of 20 Cr-30 Ni base. It was found among other things, by means of creep testing at relatively short times (up to about 1000 hours) that the creep rupture strength at 900 C. increased particularly much at contents above 4% W.
Based upon these results, alloys with relatively high W contents and increased contents of mainly Ni and Co have been made, said alloys showing improved creep rupture strength compared to the prior 20 Cr-30 Ni base alloys.
A disadvantage with these newer alloys has been, however, the relatively high costs because of the increased alloying contents and the relatively complicated manufacturing.
Another method which has been used to improve the creep rupture strength of the 20 Co-30 Ni base alloys has been to increase the C content, sometimes in combination with an increased Ti content. This method to improve the creep rupture strength is relatively cheap and gives a considerable increase in creep rupture strength for short service times. A disadvantage with this type of alloys, however, is that for prolonged service times the creep rupture strength will decrease rapidly, at least at the higher service temperatures which are normally of interest, because of overaging of the carbide particles. Thus, for the service times normally required there will only be an insignificant improvement in creep rupture strength.
According to the invention it has been found possible by adding only about 2-4% W to obtain at least the same creep rupture strength as for those alloys which, based upon solid solution hardening, contain higher contents of W, Ni and Co. The reason for this is probably that the higher contents of Ni and Co, added to improve the solubility of W will reduce the creep rupture strength by increasing the mobility of the dislocations. By adding at the most 3.5% and preferably at the lowest 2.5% W to the 20 Co-30 Ni base alloys it was also found that the creep rupture strength was improved but no reduction in creep ductility was observed.
The invention also includes a combination as an addition of W and an increase of the contents of C and Ti. This variant of the new alloy can be used when a still higher creep rupture strength is needed and when some reduction in creep ductility can be tolerated. The surprising property of this alloy is that the further increase of the creep rupture strength, obtained by increasing the contents of C and Ti, will not decrease at increased service times, contrary to the earlier known alloys which had an increased content of C and Ti but no addition of W. Obviously, by some mechanism the W addition prevented or at least reduced the rate of the overaging of the carbide particles. The W addition in the high C+Ti grade thus increases the creep rupture strength in two ways, by solid solution hardening and by counteracting the overaging of the carbide particles.
The alloy according to the invention contains, in percent by weight, from traces up to 0.40% C, 20-35% Ni, 15-25% Cr, 2-4% W, 0.2-1.6%"Ti, 0.2-1.0% A1, at the most 1% Si, at the most 3% Mn, 0-0.1% B and the rest Fe besides normally present impurities. In addition to good heat resistance and high creep rupture strength the alloy is characterized by good ductility and absence of embrittling phases in any appreciable degree.
The optimum W content has been found to be about 3% for service temperatures around 900 C. At higher contents of W, an improved creep rupture strength will be obtained at short service times, but at prolonged service times the creep rupture strength will be reduced compared to the alloy containing 3% W because of precipitation of embrittling phases. At service-temperatures above 1000 C. the W content can be increased to about 4%. A lower W content than 3% will usually not give a complete solid solution hardening.
In the low C grade of the new alloy the C content is at the most 0.15% and at the lowest 0.05% which is in the same order as for ordinary Alloy 800. At this carbon level the creep ductility will be approximately the same as for Alloy 800. At this carbon level the solution heat treatment temperature should be around 1150 C., to give a complete resolution of the TiC particles.
At higher C contents than about 0.15%, and preferably at C contents of at the most 0.35% and at the lowest 0.20%, the solution heat treatment temperature must be increased for the solution of the TiC to obtain maximum creep rupture strength. Thus, at a C content of about 0.2% the solution heat treatment temperature should be around 1250" C.
Ti should preferably be added in stoichiometric proportion to the C content, thus about 4X C, to obtain maximum creep rupture strength and ductility.
A corresponding effect regarding solution hardening and oxidation resistance may also be obtained by the addition of A1. A particularly suitable content has been 03-08%.
Concerning the main alloying elements Ni and Cr, principally nickel contributes to a stable austenitic structure while chromium mainly gives the alloy good oxidation resistance and high resistance to carburization. Lower Ni contents than about 20% are generally not used because of risks of instability and formation of embrittling sigma phase. At moderate demands upon oxidation resistance, however, it has been found sufficient to have 2. Ni content of -25%. At the high demands normally present, a Ni content of at least must be used. The content of Cr must be well adjusted in consideration of the fact that an increased content gives unfavourable sigma phase formation. An optimum content, in regard of oxidation resistance as well as of sigma phase formation, has shown to be at the lowest 19% and preferably at the most 23% Cr.
Silicon and manganese may be present in contents normal for this kind of alloys. Particularly Si has shown a favourable effect Concerning the oxidation resistance. Each alloying element should be present in contents of at the lowest 0.3%. Mn should preferably be at the most 1.5%.
Concerning normally occurring impurities, S and P may usually be present in contents of at the most each 0.015%. The contents of other possible alloying elements should also be low and be regarded more as impurities. Niobium has thus shown a less stabilizing effect than Ti and tendencies to form embrittling phases have been found. A normal impurity content is max. 0.1% Nb. Cobalt is of small interest as addition in alloys according to the invention and neither positive nor negative effects have been found. Because of the high costs of this alloying element the contents should thus be as low as possible. A normal impurity content is max. 0.1% Co.
It is per se known that B in small amounts can improve the creep strength of alloys of actual type. Furthermore, it improves the ductility in the hot working range and influences the carbide precipitation favourably. A suitable content has shown to be max. 0.005% B.
The alloy according to the invention is particularly useful for manufacturing plastically worked products as for instance tubing, bar, plate, forgings, etc.
As has been mentioned earlier the petrochemical and the hydrocarbon processing industries are important consumuers. The alloy according to the invention has here shown particularly superior properties at use in tubes for steam reforming of hydrocarbon, in which process hydrogen and carbon monoxide are formed. The mateial has found similar use in so called pig tail tubes and as tubing in ethylene furnaces.
Characteristic for the alloy according to the invention has been the particularly high resistance to creep at temperatures above 700 C. and preferably also above 800 C. under heavy mechanical stress and very corrosive conditions. It has also been found that the alloy has the same good resistance to thermal fatigue and high ductility as the base alloys with 20 Cr- Ni, i.e. Alloy 800.
The following example shows the results obtained in creep testing alloys according to the invention. The alloys (No. l and No. 2) were compared with the standard alloy, Alloy 800, on 20 Cr-3O Ni base. The composition of the test material is evident from Table I.
Results from creep testing at 900 C. have been assorted in Table II. The creep test results are also illustrated in diagram, see FIG. 1, showing the connection between the stress (a) in kp./mm. and the time to fracture (t) in hours.
TABLE II Results of creep testing at 900 0.
Percent Stress, Time to Alloy kp./ rupture, Area No. Heat treating mm. hrs. Elonga. reduction 1 Solution 1,150 0., 4. 0 255 39. 7 62 30 min. quenching, H20. 1 do 3. 0 1, 006 50. 3 57 l do 2. 5 2,125 26. 4 33 1 do 2.0 5, 616 45. 1 36 1 do 1. 5 1 Solution 1,250 0., 4 564 15.4 14
' 30 13in. quenching,
I 2 do 3 1, 754 20. 7 15 2 do 2. 5 9, 637 12.3 I. 8 2 do. 2 2 .do 1. 5
1 Still running.
In FIG. 2 the creep rupture strength (0 in kp./mm. at 900 C. at failure after 100,000 hours is given as a function of the tungsten content (W%). The test materials were a 20 Cr-30 Ni base alloy with varying additions of W (x-marked points) and alloy No. 1 (o-marked point).
From the results it is evident that an addition of only about 3% W at long times (above 10,000 h.) has given the highest creep rupture strength. It has thus been possible to obtain about higher creep rupture strength (for 100,000 h. at 900 C.) compared to the 20 Cr-30 Ni base alloy at a very moderate increase of the alloying content (i.e. the price). The low carbon alloy according to the invention (N0. 1) has shown about the same creep ruptpre strength as considerably more expensive and complicated alloys.
The results also show that the high carbon variant (No. 2) has obtained 45% higher creep rupture strength than the low carbon variant (No. l). The ductility of No.
2 is naturally lower, but quite acceptable. A necessary condition for sufficient ductility should be an addition of Ti in stoichiometric proportion.
We claim:
1. Nickel-chromium-iron alloy having excellent heat resistance and high creep rupture strength in combination with good ductility at long time use, said alloy consistin'g, in percent by weight, from traces up to 0.40% C, 20-35% Ni, 15-25% Cr, 24% W, 0.21.6% Ti, 0.2- 1.0% A1, 0.3-1.0% Si, 0.33.0% Mn, 00.01% B, and the balance Fe.
2. Alloy according to claim 1 wherein the Ti content is about 4 times the content of C.
3. Alloy according to claim 1 wherein the A1 content is 0.30.8%.
TABLE I.CHEMICAL ANALYSES OF TEST MATERIAL Alloy No. C Si Mn Cr Ni W Ti Al B Fe 1* 0. 11 0. 60 0. 55 20. 5 29. 9 2. 95 0. 45 0. 23 0. 005 Rest. 2* 0. 21 0. 58 0. 55 21. 7 30. 9 3. 14 0. 92 0. 28 0. 011 Do. Alloy 800** 0. 05 O. 55 0.55 21.0 31. 0 0. 35 0. 30 Do.
Alloys according to the invention (with low resp. high content of carbon).
"Reference material (nominal analysis).
4. Alloy according to claim 1, wherein the W content is 2.5-3.5
5. Alloy according to claim 1, wherein the C content is 0.05-0.15%.
6. Alloy according to claim 1, wherein the Ni content is 20-35%.
7. Alloy according to claim 1, wherein the Cr content iS 8. Alloy according to claim 1, wherein the Mn content is 0.31.5%.
5 6 9. Alloy according to claim 1, wherein the C content 3,212,884 10/1965 Soler 75-124 is 0.200.35%. 3,243,287 3/1966 Lillys 7S-l24 References Cited UNITED STATES PATENTS HYLAND BIZOT, Primary Examiner 2,143,423 1/1939 Remmers 7s 124 5 US. 01. m.
3,169,858 2/1965 Heydt 75-124 75-123 128 W
US00313322A 1971-12-21 1972-12-08 Nickel-chromium-iron alloy Expired - Lifetime US3826649A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4077801A (en) * 1977-05-04 1978-03-07 Abex Corporation Iron-chromium-nickel heat resistant castings
US4442068A (en) * 1981-10-12 1984-04-10 Kubota Ltd. Heat resistant cast iron-nickel-chromium alloy
US20080163963A1 (en) * 2007-01-08 2008-07-10 Ling Yang Heat Treatment Method and Components Treated According to the Method
US20100276041A1 (en) * 2007-01-08 2010-11-04 Ling Yang Heat Treatment Method and Components Treated According to the Method
US20110061394A1 (en) * 2009-09-15 2011-03-17 General Electric Company Method of heat treating a ni-based superalloy article and article made thereby

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IN149220B (en) * 1977-05-04 1981-10-10 Abex Corp

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4077801A (en) * 1977-05-04 1978-03-07 Abex Corporation Iron-chromium-nickel heat resistant castings
US4442068A (en) * 1981-10-12 1984-04-10 Kubota Ltd. Heat resistant cast iron-nickel-chromium alloy
US20080163963A1 (en) * 2007-01-08 2008-07-10 Ling Yang Heat Treatment Method and Components Treated According to the Method
US20100276041A1 (en) * 2007-01-08 2010-11-04 Ling Yang Heat Treatment Method and Components Treated According to the Method
US8663404B2 (en) 2007-01-08 2014-03-04 General Electric Company Heat treatment method and components treated according to the method
US8668790B2 (en) * 2007-01-08 2014-03-11 General Electric Company Heat treatment method and components treated according to the method
US20110061394A1 (en) * 2009-09-15 2011-03-17 General Electric Company Method of heat treating a ni-based superalloy article and article made thereby
US8313593B2 (en) 2009-09-15 2012-11-20 General Electric Company Method of heat treating a Ni-based superalloy article and article made thereby

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FR2170521A5 (en) 1973-09-14
GB1398010A (en) 1975-06-18
DE2262137A1 (en) 1973-07-05

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