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Publication numberUS3852063 A
Publication typeGrant
Publication dateDec 3, 1974
Filing dateOct 4, 1972
Priority dateOct 4, 1971
Publication numberUS 3852063 A, US 3852063A, US-A-3852063, US3852063 A, US3852063A
InventorsKaneko Y, Katori Y, Niimi I, Noguchi M, Uchida T
Original AssigneeToyota Motor Co Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Heat resistant, anti-corrosive alloys for high temperature service
US 3852063 A
Abstract
The present invention relates to a heat resistant anticorrosive alloy characterized by good resistance to corrosion at high temperatures and high strength at high temperatures which is suitable as material for re-combustion-type emission gas purifiers such as thermal reactors, after-burners, more specifically to a metal alloy substantially composed of ferrite phase, its major components being:
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Description  (OCR text may contain errors)

ite te 11 1 Niimi et a1.

[111 3,852,063 Dec. 3, 1974 HEAT RESISTANT, ANTI-CORROSIVE ALLOYS FOR HIGH TEMPERATURE SERVICE [75] Inventors: ltaru Niimi, Nagoya; Yasuhisa Kaneko, Toyota; Masamitu Noguchi, Toyota; Tsuneo Uchida, Toyota; Youhei Katori, Toyota, all of Japan [73] Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha, Aichi-ken, Japan 221 Filed: Oct. 4, 1972 21 Appl. No.: 294,981

Primary Examiner-Hyland Bizot Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT The present invention relates to a heat resistant anticorrosive alloy characterized by good resistance to corrosion at high temperatures and high strength at high temperatures which is suitable as material for recombustion-type emission gas purifiers such as thermal reactors, after-burners, more specifically to a metal alloy substantially composed of ferrite phase, its major components being:

carbon... below 0.15% at least one of niobium and Tan1alumn.O.053.O/1

Titanium...0.051i0/( Silicon...below 2.071

chrome...l2-28% molybdenum..1O.2-3.07: aluminum...0.3-6t0% vanadium...0.13.0% b0ron...0.000 l-0.0050% zirconium...0.0 l -l .07: iron...balance and, if necessary with adequate additions of the following elements:

One or more than two from among rare earth elements such as yttrium, cerium lanthanum, calcium ...0.01-1.5%;

tungsten 0.2-3.0 percent; beryllium 0.0l-2.0%.

4 Claims, 5 Drawing Figures (ti)(b)(c)(d)(e)(f1(g)(h)(j)(q)(t)(w)(,i) A B C D E F G H PATENTEL 3 74 I saw 10F 4 A 68 x oem:

L IL FL PATENTELnac 31974 SHEET 2 OF 4 A :mm x 0 00M:

I w m 0 Q m E31:31:EIBCIBGI IQIB N O m O v6 PATENTh 553 31974 SHEET 30F 4 26 x o oom:

I o h. m a o m 2: 1:3::2132132 132: c:

PATENTEL DEC 31974 FIG.4

BACKGROUND OF THE INVENTION Both abroad and at home, the control of auto emission gases has come to be enforced with increasing stringency year after year. To accomplish such control effectively, it is necessary to equip the conventional internal combustion gasoline engine with new devices for emission gas purification such as thermal reactors, after burners, catalyst muffers or E.G.R. (exhaust gas recirculation) or to try engine modifications.

In the re-combustion type emission gas purifier which has to work at a maximum temperature of 1,200C, its component members, which are exposed to high temperature combustion gases, must be able to satisfactorily withstand the oxidation due to CO H and residual 0 contained in these gases and the high temperature corrosion due to PbO, S, S0 or P contained in them. Besides, to assure ample durability of the apparatus itself, its members have to be strong enough at high temperatures.

As materials for thermal reactors and after burners, Fe-Cr-Al alloys conventionally employed in furnace heaters or various heat-resistant stainless alloys are conceivable. The conventional Fe-Cr-Al alloys excel in high temperature corrosion resistance, but they have the drawbacks that they are liable to become brittle in high temperature service through coarsening of crystals and they lack high temperature strength. Meanwhile, austenitic stainless alloys and nickel base heat-resistant alloys, characterized by excellence high temperature strength, lack in high temperature corrosion resistance and accordingly they need surface treatment; or they are so expensive that they are found unfit for mass production.

The present inventors, setting an eye on the excellence of Fe-Cr-Al alloys in their high temperature corrosion resistance, investigated how to improve these alloys in the coarsening of their crystals and consequently from their investigation have successfully perfected the present invention of an alloy with remarkably better characteristics of high temperature corrosion resistance than that of the conventional austenitic stainless alloy or nickel base heat-resistant alloy, and better characteristics of high temperature strength, crystal coarsening and moldability than those of the conventional Fe-Cr-Al alloys.

SUMMARY OF THE INVENTION The object of the present invention is to provide an alloy suitable as material for component members of a re-combustion-type emission gas purifier which is characterized by excellence in high temperature corrosion resistance, high temperature strength, crystal coarsening characteristics and moldability, the major alloying elements to constitute this alloy to attain this object bemg:

carbon below 0.l5% zirconium 0.0l-l.0% chrome 12-2 8% iron balance molybdenum 0.2-3.0% at least one of niobiam and tantalum ODS-3.0% I

titanium 0.05- l .0%

silicon below 2.0%

aluminum 03-60% vanadium 0. l 3 0% boron 0.000l-0.0050% and, if necessary, the following elements being adequately added:

One or more than two from among rare earth elements such as yttrium, cerium, lunthanum, calcitungsten 0.2-3.0 percent; beryllium 0.- 01-20%.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the results of comparison in anti-oxidization characteristics between the invented alloy and various conventional heat-resistant anticorrosive alloys,

FIG. 2 is a diagram showing the results of comparison in corrosion resistance in a hot atmosphere of lead oxide between the invented alloy and various conventional heat-resistant anti-corrosive alloys,

FIG. 3 is a diagram showing the results of comparison in corrosion resistance in a hot atmosphere of sulphur between the invented alloy and various conventional heat-resistant anti-corrosive alloys,

FIG. 4 is a micrograph showing an intercrystalline corrosion recognized in an austenitic alloy (SUS 41) which has been etched by hot sulphur,

FIG. 5 schematically illustrates a specimen used in a Charpy test of the invented alloy.

DETAILED ACCOUNT OF THE INVENTION The present invention relates to an alloy characterized by excellence in high temperature oxidation resistance, high temperature corrosion resistance in an at mosphere of lead oxide or sulphur and high temperature strength which can be applied as material for heatresistant members in various re-combustion-type emission gas purifiers and for vessels in a catalyst muffler, for engine parts exposed to hot emission gases, for components of gas turbinecombustion chambers and for furnace heaters.

The invention alloy is substantially constituted by a ferrite phase, its chemical composition being broadly as follows carbon below 0.15% silicon below 2.0% chrome l228% aluminum 03-60% molybdenum 0.23.0% vanadium 0.l-3.0%

at least one of niobium and tantalum ODS-3.0% boron 0.000l0.0050% titanium ODS-1.0% zirconium 0.01-1 .0%.

iron balance O.23.0 percent; beryllium markedly reduced by addition of Si or excessive addition of B. Addition of Y greatly improves the impact withstanding characteristics. Addition of Cr, A1, Y is effective for improving the anti-oxidation, anti-lead oxide, and anti-sulphur characteristics, but excessive addition of B is harmful.

TABLE 1 Effects of various additives in the invented alloy on various characteristics.

TABLE 1.EFFECTS ()F YARN) US ADIHIIVES IN THE INYENTEI) ALLOY ()N YA 1110118 ("11A RAU'II", 111S'l1( 1 Elements Characteristics (1 Si Cr A1 Mo Tu N1) 'li Zr ll 111 Y High temperature strength... O A O Q GD m. ((1) [1 3 (1 1 A Crystal coarsening E1 E1 13 G (O [.1 D O O 1 Roomtemperatureelongation A X A A El 151 A [.1 [J ill 11 Impact strength A A A A O A U [3 O [L1 1 1 rtntioxidotion A O to (g) 13 :1 u U A L1 {A u Anti-load oxide" A A to 1:1 0 A o u u {1.1 Anti-snlphur A O 13 111 [1 C1 5 L] 1.1 (J

N0'rE. 1\Iark means that the relevant characteristic has been vastly improved. O means that the ellt-et, though nnl ennspicuous, is positive. [1 means that the l-tluct is insignificant or practically Zero. A means that. the elleet 15 rather negative. X means that the effect is markedly negative.

TABLE 2 Chemical compositions of alloys tested.

Chemical elements C Si Mn P S Cr Al Ni Others Remarks Specimen codes a(conventiona1 alloy 0.06 0.57 0.46 16.51 (SUS24) b( do. 0.05 0.82 1.09 18.29 9.20 (SUS27) c( do. 0.07 0.72 1.40 22.40 12.85 (SUS41) d( do. 0.06 1.05 1.68 24.74 19.89 (SUS42) e( do. 0.07 0.67 0.95 19.90 32.45 (1nco11oy800) f( do. 0.05 0.56 0.62 21.39 45.10 Fe (Hastelloy X) g( do. 0.02 0.46 0.53 15.70 Bal 8.48 (1nconc1l600) Fe h( do. 0.05 0.25 0.94 04959 19.80 8:11 0.63 (Nimonick 75) Ti Zr i( do. 0.06 0.44 0.82 0.032 0.008 19.65 3.72 0.06 0.34 0.11 (FCH j(tentative 0.01 0.08 0.l 0.007 0.012 16.23 1.92 0.08 (Conventional alloy) alloy) k( do. 0.01 0.05 do. 0.006 .006 16.60 1.77 0.01 0.16

Zr 1( do. 0.01 0.05 do. 0.005 0.012 15.60 2.48 0.03 0.11

. Ti m( do. 0.01 0.06 do. 0.007 0.011 16.08 2.29 0.04 0.93 n(tentative alloy) 0.01 1.36 do. 0.005 0.015 16.32 2.03 0.1

B o( do. 0.01 0.71 do. 0.005 0.011 16.24 2.55 do. 0.0014

Ti Y p( do. 0.01 1.01 do. 0.006 0.009 16.23 2.28 do. 0.20 0.18 q( do. 0.01 0.06 0.1 0.007 0.012 15.47 4.60 g0] (conventional Ti alloy) r( do. 0.01 0.02 do. 0.003 0.012 16.49 4.32 do. 0.14

V s( do. )0.01 0.03 do. 0.003 0.012 16.53 4.17 do. 1.29 t( do. 0.01 0.09 do. 0.006 0.015 20.86 1.91 do. (conventional) Mo alloy) u( do. 0.01 0.02 do. 0.007 0.012 20.56 2.08 do. 1.00

Nb v( do. 0.01 0.04 do. 0.004 0.016 20.11 1.74 do. 1.44 w( do. 0.01 1.30 do. 0.005 0.014 21.10 4.22 do. (conventional B alloy) x( do. 0.01 0.66 do. 0004 0.012 20.81 4.27 do. 0.12

B y( do. 0.01 0.06 do. 0.005 0.014 21.09 4.12 do. 0.37

Ti B z( do. 0.01 0.09 do. 0.003 0.011 21.13 4.31 do. 0.05 0.70

TABLE 2 Continued Chemical compositions of alloys tested.

Chemical elements C S| Mn P S Cr Al Ni Others Remarks Specimen codes A(lnvented Mo V Ti Zr Nb+Ta Y alloy) 0.06 0.38 0.55 0.014 0.011 17.33 2.82 0.24 1.00 0.57 0.41 0.17 0.12 0.03

Mo V Ti Zr Nb-l-Ta Y B( do. 0.05 0.43 0.68 0.009 0.006 16.75 2.76 0.19 1.06 0.52 0.36 0.16 0.52 0.04

Mo V Ti Zr Nb+Ta Y C( do. 0.07 0.36 0.63 0.013 0.008 16.98 3.13 0.23 1.00 0.58 0.39 0.18 0.12 0.37

Mo V Ti Zr Nb+Ta B D( do. 0.06 0.29 0.62 0.014 0.014 20.08 3.00 0.20 0.50 0.56 0.37 0.16 0.49 0.0009

Mo V Ti Zr Nb-l-Ta B E( do. 0.06 0.31 0.62 0.014 0.014 20.21 2.90 0.20 1.00 0.56 0.41 0.17 0.50 0.001

' Mo V Ti Zr Nb+Ta B F( do. 0.06 0.29 0.66 0.014 0.018 19.99 2.72 0.26 0.51 1.10 0.41 0.14 0.48 0.0009

- Mo V Ti Zr Nb-l-Ta B G( do. 0.06 0.27 0.62 0.014 0.016 19.99 3.05 0.29 1.11 1.08 0.40 0.16 0.51 0.0007

. Mo V, Ti Zr Nb+Ta B Be l-1( do. 0.06 0.32 0.64 0.013 0.014 3.07 0.20 0.53 0.54 0.38 0.16 0.47 0.0006 0.07

In the following, the features of the invented alloy will be described in examples of testing.

Table 2 is a list of chemical compositions of speci- 1n FIGS. l-3 and Table 3, the characteristics of the.

invented alloy and various specimens are compared.

'FIG. 1 shows the etched depths of various alloys as measured after being submitted to 200 hours of oxida-' tion in an alumina boat in an atmospheric furnace pr'eliminarily heated to 1,200C; these .depths' represent the high temperature oxidation characteristic of these alloys. It is evident from FIG. 1 that some of the commercial heat-resistant stainless alloys, for instance, the specimens (g) (h) exhibit considerably good antioxidation characteristic, but even compared with them, the invented alloy as well as the known Fe-Cr-Al alloys is far superior in this characteristic. It should be noted, however, that in the case of Fe-Cr-Al alloys the contents of Cr and Al affect the anti-oxidation characteris tic to a certain extent, but the invented alloys (A)-(C) and the tentative alloys (K) and (P), which contain Y and are added with relatively little Cr and Al, exhibit a remarkableexcellence in his characteristic which is a striking feature when it is recalled that in the case of Fe-Cr-Al alloys, reduced contents of Cr and Al vastly improve the moldability.

FIG. 2 shows the etched depths of various alloys which represent their corrosion resistance in a hot atmosphere of P O, as measured after these alloys had been washed, degreased, coated with a slurry mixture of Pb 0 powder and waterglass solution(water: water glass 4:1 in volume ratio of 1:3; placed in an alumina boat; and then held for hours in a furnace preliminarily heated to 1200C.

In nearly the same way as in the results of antioxidation test, all Fe-Cr-Al alloys including the known ones and the invented one are superior in corrosion resistance in a hot atmosphere of Pb O to any of the conventional commercial heat-resistant stainless alloys.

Similarly, FIG. 3 shows the etched depths of the specimens which represent their corrosion resistance in a hot atmosphere of sulphur, as measured after the specimens were coated with a slurry'mixture of powder sulphur and waterglass solution (water: waterglass 1:1) in volume ratio of 1:3; placed in an alumina boat; and held for 6 hours in a furnace preliminarily heated to 1,200C.

These results, just as those of oxidation tests and hot Pb O corrosion tests, point to the superiority in corrosion resistance in a hot atmosphere of sulphur of Fe- Cr-Al alloys including the known ones and the invented one to any of the conventional commercial stainless alloys or heat-resistant alloys; and these Fe-Cr-Al alloys are found free from any intercrystalline corrosion in FIG. 4 which is recognized in a sulphur-etched austenitic alloy or nickel base alloy.

Table 3 summarizes the characteristics of the conventional Fe-Cr-Al alloys and the invented Fe-Cr-Al alloy, such as strength at room temperature and at high temperature; elongation at room temperature; impact strength; and crystal coarsening. As seen from this Table, the invented alloys (A)(H) are remarkably better in high temperature strength characteristic than any Fe-Cr-Al alloy in the prior art; particularly the alloy (H) is about two times superior to any one of the conventional (j), (q), (t), (w) and (i).

This is probably due to the great effects of B, Be, Mo, Ta, Nb and V, as testified by the performances of the tentative alloys (0), (r), (s), (u), (v), (x), (y) and (z); to be more specific they are mainly the effect of solid solution by invasion in the case of B, that of solid solution by substitution in the case of the other elements; and partly that of precipitation of carbides.

Concerning the room temperature elongation characteristic, the contents of Cr, Al and particularly that of A1 are supposed to made great contributions; in this characteristic, the invented alloys are generally superior to the known (i), (j), (q), (t) and (w). This is, as suggested by the performances of the tentative alloys (r), (n), (o), (s), presumably due to the addition of Ta being small and those of B, Si and V being well controlled.

The impact strength mentioned in the Table is ex pressed by the energy absorption needed to break a specimen of a special shape indicated in FIG. 5, using a kg-m small size Charpy impact tester, as divided by the original cross-sectional area of the specimen.

The contributions of Cr, and Al particularly the latter to this impact strength are supposedly immense; the invented alloys are in general superior in this strength to any of the known (i), (j), (g), (t) and (w) which contain the same amounts of Cr and Al as the invented alloys. As suggested by the performances of tentative alloys, this seems to be due to additions of Y and Mo and restrictions of Si, B and V contents. It is noteworthy, as suggested by the performances of the tentative alloy (k) and the invented ones (A) (B) and (C), that the alloys added with Y are markedly improved in impact strength.

The crystal coarsening characteristic in Table 3 is expressed in terms of temperatures at which the ferrite crystal size becomes less than 1 when each alloy specimen has been held for 25 hours in the range of 800-l,200C at intervals of 50C and then observed for coarsening of crystals as the results of heating. An increase in the contents of Cr and Al is apt to be accompanied by a slight rise in the coarsening tempera- TABLE 3 Comparison of various properties among different Fe-Cr-Al alloys (known, tentative and invented) Room temperature elongation High temperature tensile strength Kg/mm lmpact Strength Specimen Kglmlcol codes Crystal coarsening temperature (C) service as a thermal reactor, the invented alloy receives less thermal strain due to heating and cooling and accordingly suffers less thermal fatigue.

Carbon as a solid solution constitutes a part of the alloy and strengthens it. As combined with elements such as Mo, V, Nb, it forms carbides, which contribute to the strengthening of the alloy, but its content should be limited to less than 0.15 percent, because too much carbon is likely to cause intercrystalline and intracrystalline precipitations of carbides (or nitrides) heated in the process, after permeating the carbon into the texture in the form of a solid solution; and thus, corrosion resistance is reduced through lack of Cr in the vicinity of the precipitates and with this, the moldability too becomes poor.

Si is effective for improving anti-oxidation, antisulphur and anti-PbO characteristics, but Si not as effective as Cr or Al. Meanwhile Si is likely to cause heavy deterioration in the moldability at room temperature and impact strength if used in large quantities. Thus, it is advisable to limit its content to less than 2 percent.

Cr as a solid solution in the texture is indispensable for giving heat resistance and anti-oxidation characteristics to the alloy and securing its ferrite structure.

Thus, its content should be more than 12 percent, but should not exceed 28 percent, because its excess deteriorates the moldability or weldability and is likely to cause 475C brittleness and cr-phase precipitation.

The favorable effect of Al on anti-oxidation, antisulphur and anti-PbO characteristics is prominent and its effect on high temperature strength, though insignificant, is also recognized. its effects, however, are not so great when its content is to little. Thus, 0.3 percent is the lower content limit on the contrary if 6 percent is (i)known (j)tentative (k) do.

(A)invehted 1200 up 1200 up 1200 up 1200 up 7 1200 up 1200 up 1200 up 1200 up 1200 up 1200 up 1200 up exceeded, the moldability and weldability are adversely affected to a great degree.

Mo, partly as a solid solution in the texture and partly as a carbide, is found useful for strengthening the alloy and preventing the coarsening of its crystals.

Too much Mo, however, results in deterioration of the anti-oxidation characteristic and corrosion resistance at high'temperatures. The appropriate content of Mo would, be 0.240 percent. W exhibits a similar effect as Mo, so a partial or whole content of Mo may be substituted by W.

V, similarly to M0, serves to strengthen the alloy partly through, its effect as a solid solution in the texture and partly through its effect as a carbide. Too much V,

however, willresult in reduction of its elongation at room temperature, its impact strength and its corrosion resistance at high temperatures such as its antioxidation characteristic. Thus, the recommendable content of V should be 0.12.0 percent.

Ta, when added to Fe-Cr-Al alloys, behaves uniquely; thereby a small amount of Ta can improve the high temperature strength, the crystal-coarsening characteristic and the room temperature elongation; but its excessive addition will heavily reduce the impact strength of the alloy. Thus, the right addition of Ta should be 0.05-3.0 percent. The effect of Nb is nearly the same as that of Ta. Besides, it would be so difficult to make separate use of Nb and Ta that a part of Ta addition might be substituted by Nb.

8 as a very small addition, can make'a remarkable improvement on the high temperature strength, but too much addition of B will result in heavy deterioration. Theroom temperature elongation, anti-oxidation, antisulphur and anti-Pb O characteristics. The appropriate addition of B should be 0.00010.0050 percent.

Y as a very small addition can improve the bonding of a protective film at high temperature heating and vastly enhance the high temperature anti-oxidation and anti-Pb characteristics. Whereas in Fe-Cr-Al alloys when they contain relatively low amounts of Cr and Al (Cr Al 3% they develop local and accelerated corrosion due to imperfectness of the protective film of d-Al O which should bring about a high corrosion resistance at high temperatures, in the case of the invented alloy with a Y-content, this film can be compact and can adhere well to the base metal, thereby compensating for the imperfectness of the film and exhibiting an excellent characteristic of high temperature corrosion resistance. Y is an expensive metal; its addition exceeding 1.5 percent will not be so effective as might be expected and thus, 0.01-1.5 percent will be the limits of its addition. Meanwhile, rare earth elements other than Y, i.e., Ce, La, Ca are practically as effective as Y and accordingly, a partial or whole addition of Y may be substituted by rare earth elements such as Ce, La, Ca.

7 Ti is an elementwhich is added to the conventional Fe-Cr-Al alloys, too;-it is foundeffective through formation of TiC for, fixation of solid-solution carbon or prevention of crystal coarsening. Since too much Ti is likely to deteriorate the anti-oxidation characteristic and impact strength of the alloy, it has been limited to 005-1 .0 percent.

Zr, just like Ti, is an element added to the conventional Fe-Cr-Al alloys, too. For the purpose of preventing the crystal coarsening its addition should be more than 0.01 percent, but it is an expensive metal; moreover, its excessive addition is likely to result in poor elongation at room temperature and lower impact strength. Thus, its appropriate addition should be from 0.011.0 percent.

Be is also known as an element which as a verysmall addition can vastly enhance the high temperature strength and can serve to prevent the coarsening of crystals. Accordingly, it constitutes one of the essential elements for the invented alloy, but it is extremely costly; besides, too much Be will deteriorate the room temperature elongation and the impact strength. Thus, the optimum addition of it should be 0.01-2.0 percent.

What is claimed is:

1. A heat-resistant, anti-corrosive alloy for high tem-' perature service, said alloy consisting essentially of:

less than 0.07 percent by weight carbon,

less than 0.5 percent by weight silicon,

15 to 21 percent by weight chromium;

2.5 to 4.0 percent by weight aluminum,

0.5 to 1.2 percent by weight molybdenum,

0.5 to 1.1 percent by weight vanadium,

less than 0.45 percent by weight titanium,

less than 0.18 percent by weight zirconium,

0.1 to 0.5 percent by weight of an element selected from the group'consisting of niobium and tantalum,

at least one element selected from the group consisting of: yttrium in an amount less than 1.5 percent by weight, beryllium in an amount less than 2.0 percent by weight, and boron in an amount less than 0.0050% by weight; and the balance of iron and inevitable impurities. 2. The alloy of claim 1, wherein yttrium is present in an amount in the range of 0.03-0.4 percent by weight.

3. The alloy of claim 1, wherein beryllium is present in an amount in the range of 00006-0001 percent by weight.

4. The alloy of claim 1, wherein at least one element selected from the group consisting of boron and beryllium is present in an amount less than 0.008 percent by weight.

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Classifications
U.S. Classification420/40, 420/64, 420/69, 420/68
International ClassificationC22C38/00, C22C38/22, C22C38/24, C22C38/32
Cooperative ClassificationC22C38/24, C22C38/22, C22C38/32
European ClassificationC22C38/24, C22C38/22, C22C38/32