US3552950A - High temperature corrosion resistant fe-g-ni-mn alloy - Google Patents

Abstract

AGE HARDENABLE, AUSTENITIC ALLOY CHARACTERIZED BY HIGH ELEVATED AND AMBIENT TEMPERATURE HARDNESS, STRENGTH AND CORROSION RESISTANCE, PARTICULARLY ADAPTED FOR INTERNAL COMBUSTION ENGINE VALVES, AND CONSISTING ESSENTIALLY OF ABOUT; 20-70% NICKEL, 4-20% MAGANESE, 12-40% CHROMIUM, UP TO 0.5% CARBON, UP TO 0.3% NITROGEN, UP TO 0.6% SILICON, UP TO 5% MOLYBDENUM, UP TO 6% TITANIUM, UP

TO 4% EACH OF ALUMINUM AND COPPER, UP TO 0.2% BORON, BALANCE SUBSTANTIALLY IRON.

Description

. Jan. 5, 1971 UN ETAL 3,552,950

HIGH TEMPERATURE CORROSION RESISTANT FeG-NiMn ALLOY Filed June 14, 1967 Sheets-Sheet 1 Tiii..-

I00 H\GH sxucow ALLovs w I g 50 Cr R Z U J C: I!

Z I0 9 I 5 I m LOW 61. 0 C7 O 0: Low si-2o% Cr a: 5 (mmcm'zo BY O u N ICKEL CONTENT CORROSION RQTES OF SIMPLE.

FECR"'N\ HLLOVS RS R FUNCTION OF NBCR AND 8!.

INVENTORS GENE F2. RUNDELL ALVIN E. NEHRENBEEG HTTORNEVS Jan. 5, 1971 Filed June 14 1967 5:. U LL! '5: (X

Z 9 l0 (/3 O DA 5 U 5 G. R. RUNDE L ET AL 3,552,950

HIGH TEMPERATURE CORROSION RESISTANT FeGNiMn ALLOY 5 Sheets-Sheet 2 IIIII 0 U l 30 Cr lllll I l I l N\CKEL CONTENT,

CORROSKDN RATES OF LOW suJcoN va-cse-m ALLOYS coN'mmmG TrmmuM AND GLUNHNUM INVENTORS GENE R. RUNDELL Aw: E. NEHRENBERG WW1, Myra twin/mm,

QTTORNEYS N g 50- O v} Z U m E [X 2 I0 9 0 Z g I (1 5 20 Cr, {2 Mn, LOW Si, 8 PLUS Ti. AND n1 Jan. 5, 1971 R R ETAL 3,552,950

HIGH TEMPERATURE CORROSION RESISTANT F -G-Ni-Mn ALLOY Filed June 14, 19,67 5 Sheets-Sheet 3 20 Cr, L0w M'n, LOW st PLUS TL AND Q1 1 l I I so 5o 70 N\CKEL CONTENT,

EFFECT OF l2 MN ON CRFFICQL NKLKEL CONTENT OF Nl-F'E-C.R HLLOYS HARDENED WITH T HND Q1 INVENTORS GENE R RUNDELL. QLVIN E NEHRENBERG Jan. 5, 1971 HIGH TEMPERATURE CORROSION RESISTANT Fe-G-Ni-Mn ALLOY Filed June 14, 1967 SILICON CONTENT, 7

. e. R. RUNDELL ET AL 3,552,950

5 Sheets-Sheet 4 CORROSION 2 RQTE 55 GRHMS GMS/DM 2 RATE \5 GRAMg X X o x x o r 1 1 l I I5 25 :55

CHROMIUM comm-r,

RELATIONSHIP OF CHROMIUM AND SILICON CONTENTS ON CORROSION BEHHV\OR OF FE.N\CRMN ALLOYS CONTFHNG TITANIUM FIND ALUMINUM.

' INVENTORS GENE R RUNDELL Q3LYVIN E. NEHRENBERG HTTORNEYS STRESS, IOOO PSI Jan. 5, 1971 R RUNDELL ETAL 3,552,950

HIGH TEMPERATURE CORROSION RESISTANT Fe-G-N1-Mn ALLOY Filed June 14, 1967 5 Sheets-Sheet 5 II I I IIIIII NOTE ALL ALLOYS HNNEQLED AT 2100' F PmoR TO name HT 1300 F 5 lIIIIIII-l I I-llllll I0 I00 I000 RUPTURE LIFE, HOURS CQEEP-RUPTURE cuevas 0F l2 MN, 20 CE, 40 NI, 2 TI, IRL ALLOYS QT I350 F INVENTORS GENE R. RUNDELL Pilaf/IN E NEHRENBERG Wand MeZQn Wk z/m/nmm,

QT ORNEVS United States Patent O 3,552,950 HIGH TEMPERATURE CORROSION RESISTANT Fe-G-Ni-Mn ALLOY Gene R. Rundell and Alvin E. Nehrenberg, Lockport,

N.Y., assignors to Simonds Saw and Steel Company,

Fitchburg, Mass., a corporation of Massachusetts Filed June 14, 1967, Ser. No. 646,130 Int. Cl. C22c 19/00, 39/02 US. Cl. 75--122 5 Claims This invention pertains to high temperature, corrosion resistant, age hardenable, austenitic alloys,'and moref'particularly to an essentially medium tolow carbon, low silicon, nickel-manganese-chromium-iron alloy .of this type, preferably containing aluminum and titanium as age hardening elements, and wherein manganese is present in substantial amount along with nickel in critically restricted amount for imparting high elevated temperature corrosion resistance to the combustion products of leaded gasoline fuels. 7 V For a'number of years past, an alloy steel commonly known as 2l-4N has been widely used for automotive exhaust valves. This steel nominally containsabout 21% chromium, 10% manganese, 4% nickel, 05% carbon, 0.4% nitrogen, and the balance substantially iron. The steel is hardened by the precipitation of carbides and nitrides, and is characterized by unusually high tensile strengthand hardness for 'an austenitic alloyaIn-addition it has good resistance to corrosion in the combustion products of leaded gasoline fuels.

It is an object of the present invention to provide an alloy which is an improvement over the 21-4N. steelwas regards corrosion resistance to the combustion products 3 0f leaded fuels and which in other respects. possesses properties comparable thereto. V t I H There are a number of requirements to. be met by an alloy or alloy steelto render it suitable for use in internal combustion engine valves and valve partsrSuch-analloy should be austenitic for reasons of strength at valve operating' temperatures on the order of 1200-1600 F. Also the austenitic alloy should be hardenable by precipitation of a stable phase such as carbides or intermetallic compounds to provide resistance to wear and to indentation. Also the alloy must have adequate corrosion resistance to the combustion products of leadedengine, fuels.

Inconel .750 has a corrosion rate in molten .lead oxide of less than 3.0 gram per sq. decimeter, but its cost is several times that of 21-4N steel which has a corrosion rate of about 20.0 gms./dm. As shown below the alloy of the present invention has a corrosion rate in molten lead oxide of about 10.0 gms./dm. which places it between the iron-base alloy, 21-4N, and the nickel-base alloy, 750.

The addition of tetraethyl lead to increase the octane rating of gasoline fuels has magnified the problems of hot corrosion to the extent that the usefulness of valve alloys is judged by the corrosion resistancein pure lead oxide. A technique for testing alloys in this regard has 3,552,950 Patented Jan. 5, 1971 ice been carefully specified in recent years, including the grade and manufacture of the lead oxide and the crucible in which such tests are conducted, specimen preparation, method of testing, and also the procedure for removing the corrosion products and calculating the corrosion rates. In practice, a specimen blank about /2 inch long is cut from .444 inch centerless ground bar. The blank is surface ground on both ends to a length of .444 inch, and is finished by hand grinding on dry 240 grit paper over the complete surface. The specimen is measured, degreased in methanol, and weighed to the nearest tenth of a milligram. It is then placed in a small magnesia crucible, covered with 40 grams of lead oxide, heated to a temperature of 1675 F., and held for an hour. After cooling to room temperature the specimen is broken out of the lead oxide, scraped to remove the loose lead oxide, and immersed in a molten solution of caustic soda and soda ash (1075 to 1100 F.) for several minutes. The

sample is then cleaned by wire brushing and reweighed to determine the weight loss. This is divided by the original sample area to obtain the corrosion rate. Al-

though the test is arbitrary, it has been found that corrosion rates correlate well with laboratory and field engine tests.

In reviewing the published literature, it is well to keep onerfact clearly in mind. Many of the lead oxide corrosion test results of the published literature, *were conducted in clay crucibles rather than magnesia crucibles. Tests conducted in clay crucibles result in corrosion rates which are about one fifth those for tests conducted in magnesia crucibles. All of the corrosion tests, the results of which are presented below in this application, were conducted in magnesia crucibles.

- In the accompanying drawings:

FIG. 1 is a graphical showing of the corrosion rate in molten lead oxide of the various'iron-chromium-nickel alloys, with both high and low silicon contents.

FIG. 2 is a similar graphical showing of other ironchromium-nickel alloys containing titanium and aluminum as age hardening elements.

FIG. 3 is a similar graphical showing of other ironnickel-chromium alloys which also contain manganese as well as titanium and aluminum in varying amounts.

FIG. 4 is a similar graphical showingof various ironnickel-chromium-manganese alloys which contain titanium and aluminum.

FIG. 5 is a graphical showing of the elevated temperature, creep-rupture properties of an alloyaccording to the invention and of the analysis set forth therein.

1 In the course of the research resulting in the present invention, a large number of experimental alloys were melted and tested as identified and discussed below. These experimental alloys were tested for corrosion resistance in the cast or in the wrought condition, as hereinafter indicated. Those alloys tested in the wrought condition were solution annealed at 2100 F. and aged at 1300 F. prior to testing. Those in the cast condition were given an age hardening treatmentat 1300 F. if they contained hard ening elements, and were tested with no heat treatment if they did not contain hardening elements.

" One objective of the research program resulting in this invention was to survey the corrosion behavior of simple Fe-Cr-Ni alloys which were treated essentially as ternary alloys, in order to determine a suitable base composition for further work.

Alloys were made with nickel contents in the range 20 to and chromium contents in the range 5 to 30%. Both elements were varied independently of the other except that combinations of nickel and chromium were avoided that did not produce fully austenitic alloys. Silicon and manganese contents consistent with normal steelmaking practice (.2 to 3% and .3 t o .4%,respectively) were OORROSION RATES OF SIMPLE Fe-Cr-Ni CAST ALLOYS (O 0.05% MAX., RESIDUALS NIL) [Corrosion rate, gms./drn. at indicated nickel and chromium contents] Cr content, percent Nickel content, percent:

The corrosion rates of the 5 Cr and 20 Cr alloys are plotted as a function of nickel content in the upper two curves of FIG. 1, and serve to indicate the potent effect of nickel on corrosion resistance.

One unsettling aspect of the above data is the high corrosion rates for low nickel-high chromium alloys. The rates were considerably higher than would be anticipated from the corrosion rate of commercial alloys, such as 2l-4N. Since it appeared that the silicon content of the above alloys was responsible for the high corrosion rates, a series of 5% and 20% chromium alloys at various nickel contents containing low silicon, less than 0.1%, were melted and tested for corrosion resistance as above for comparison with high silicon alloys. Theresults are given in the following Table II, wherein all alloys were tested in the cast condition. These data also also shown graphically in FIG. 1. 1

TABLE II.--EFFECT OF SILICON ON CORROSION RATES 4 (O 0.05%; Mn 0.30.4%; RESIDUALS NIL) As shown in the tabulation, all of the alloys with less than .1% silicon have lower corrosion rates than their higher silicon counterparts. It is also evident that nickel overshadows the effects of chromium and silicon on cor.-

rosion resistance as shown in FIG. 1, wherein it is further seen that an increase in chromium from 5 to 20% displaces the curves to the left (to lower nickel) by about 5%. An increase in silicon from about .1 to .25 has an opposite and greater eifect.

Finally, it may be noted that low-silicon alloys do not exhibit increasing corrosion rates with decreasing nickel below about 40%. This appears to be fundamental to alloys of low silicon, and is indicated by the horizontal extension of the low silicon graphs to-the left in FIG. v1 below the 40% Ni level, which implies a maximum corrosion rate of about 16 to 22 grams for Fe-base, Fe-Cr-Ni alloys. According to this figure, the only way'of achieving lower corrosion rates is' to increase the nickel content above 40%. h As pointed out above, one of the requirements for a suitable alloy for internal combustion engine valve "applications is that it be hardenable'by the precipitation of a stable phase, such as carbides or intermetallic com pounds. Obviously, the addition of elements to promote hardening could affect the corrosion behavior of the simple alloys having corrosion resistant properties as above described.

Accordingly a series of alloys was made with a carbon content of "about /2 each, very low silicon, under 0.1%, and with a chromium content of 20%. The nickel was varied from '30 to 70% The corrosion rates ofth ese 20% chromium-high carbon alloys fall very close to thosefor similar alloys containing low carbon, as shown in Table III below:

TABLE III.-GORROSION RATES OgHIGH AND LOW OAR BON ALLOY Nominal comp., percent Corrosion rate, 0 Ni Cr gmsJdm.

The data for these high carbon alloys are included in the plot of 20 Cr-low Si alloys of FIG. 1. These data show that carbon is not detrimental in alloys containing 20% chromium. In addition, the corrosion data of these jalloys lendssupport to the previous observation that ironbase alloys containing less than 40% nickel exhibit a characteristic corrosion rate in the range 16 to 22 grams per square decimeter. This level of corrosion resistance is no better thanjexists in conventional stainless steels, such as 2l4N. v i A seriesfof alloys containing titanium" and aluminum for hardening was prepared'for corrosion tests. These elements combine with nickel to form 'an' interinetallic, compound, Ni (TiAl), which can be precipitated by heat treatrnent to increase hardness and strength. These alloys were tested in the wrought .condition, with resultsas given below in Table IV.

TABLE IV.CORROSION RATES OF e-Cr-Ni ALLOYSCON- a ,TAINING Ti AND Al- Nominal comp.,

percent Corrosion rate,

Ni Or Al-l-Ti gms./d rn.

20 2. s V 62. 5 20 3. 5 58. 6 20 3. 5 56. 6 20 V 3. 9 59. 9 20 3. 4 y -3. 6 20 3. 5 1. 9 20 3. 0 t 65. 1 10 2. 7 I 58. 0 10 3. 7 75. 0 10 V 3. 4 l4. 1 30 2. 8 49. 6

The effect of nickel is shown in the first group of this series; 'thatof chromium and hardener content, in the last group. When these data are plotted as in FIG. 2, it is readily apparent that nickel exerts the most potent effect onfcorrosion behavior/An increase in hardener content from 2.7 to 3.7% for alloys 86 and 87 has a moderate detrimental efi ect'A chromiumincrease of 10% was found 'to shift the curves slightly to the left i n'FIG Z to lower nickel. One ofthe striking aspects of these data is '1 the abrupt decrease in corrosion rate between and nickel. The corrosion rates are not affected once the nickel content is reduced below 55%. This isevident' as the flat portion of 'the' curve near the upper left 'cornerbfFIQ. 2. Also," the effect of nickel is, only slightly beneficial above pic er contentsof'abo'nt 65%. I J Acorn'par'ison ofFIGS l and 2' indicates the effect of addinttitaniumand aluminum to low-silicon Fe-Cr-Ni alloys is to. shift the steep portion of the curve to the right (to higher nickel contents); to make the transition from high to low corrosion rates more abrupt; and to raise the position of the flat portion of the curve to higher corrosion rates. a

.It is also evident from FIGS. 1 and 2 that nickel exerts the most influence on the corrosion resistance of these alloys, and it is useful to consider the. effect of other elements in terms of the nickel content required for a given corrosion.rate..For purposes of this invention, the term critical nickel content will be used to denote the nickel content required for a corrosion rate of less than grams per square decimeter. For low silicon alloys the effect of adding titanium and aluminum is to increase the nickel content from 45 to about 60% v I FIG. 2 also indicates that the objective ofdeveloping an alloy of lower cost than Inconel 750,. cannot be realized in Fe-Cr-Ni alloys containing titanium and aluminum, since a reduction in nickel from about 75% for Inconel 750 to 60% is not sufficient to affect the cost appreciably.

The most significant discovery leading to the development of a completely new alloy according to this invention, is the effect of manganese in lowering the critical nickel content from about 60 to 34% for alloys hardened with titanium and aluminum, as shown by the following.

A series of alloys all containing essentially constant chromium contents of 20%, with about 12% Mn, less than .06% Si, and between 3 and 4 /2 titanium plus aluminum were melted and corrosion tested. The corrosion rates are plotted as a function of nickel content in Graph A of FIG. 3. The critical nickel content of this series is shown about 34%, compared to 60% for a similar series without manganese, the latter as shown by Graph B of FIG. 3, copied from the 20% Cr graph of FIG. 2.'

Two additional series of Mn-containing alloys were] prepared with varying manganese contents. The purpose was to establish a relationship between manganese level and corrosion rate and to determine whether 12% manganese is necessary to provide the desired low level of corrosion. These data are tabulated below in Table V for alloys containing 36% nickel, low' silicon, and combined titanium and aluminum in excess of 2.3%.

TABLE v [Efiect of manganese variation at 20% Cr, 36% Ni] Manganese Corrosion content, r e. percent gins/rim.

These data show that the minimum manganese content required for the necessary low level of corrosion is much lower than 12%. In the 36% vNi-25% Cr low Si alloys, as

little as about 5% Mn is adequate. There is no further TABLE VI.-EFFECT OF SILICON AT VARIOUS CHROMIUM CONTENTS IN 36% NICKEL ALLOYS These data again confirm that silicon has a detrimental effect on corrosion resistance. For example, an increase in silicon from .12 to .16% for 20% Cr alloys increases the corrosion rate by a factor of six. A similar effect occurs for 25% Cr alloys at somewhat higher silicon; It is also shown from thelow corrosion rates of all of the 30% Cr alloys, that chromium increases the amount of silicon that can be tolerated.

This is shown graphically depicted by plotting data points of high corrosion resistant and low corrosion resistant alloys as a function of silicon and chromium contents in the manner illustrated in FIG. 4. The alloys represented by the letter x have corrosion rates in excess of 55 grams/dmF; those by open circles have rates less than 15.

The inter-relation of chromium, silicon, and corrosion behavior may be expressed in terms of the following 1 equation:

If the chromium equals or exceeds the amount calculated from this equation, the corrosion rate will be less than 15 gms./dm If the chromium is less than the amount indicated the corrosion rate will exceed 55 gms./dm

Equation 1 is written with silicon as the independent variable. However, if chromium is to be considered as an independent variable, Equationl may be transposed in accordance with Equation 2 below: 1

( 1 Percent Cr 16 Percent S1 T It is obvious that the silicon must be less than this amount for good corrosion resistance. r

In considering how generally the above relationship may be applied, reference may be had to the corrosion behavior of some of the other alloys melted and tested in the course of the present investigation. For example, alloys VS 54 and VS 55 containing. Ni, 10% Cr, 0.3O.34% Si and about 2.83.6% Ti and Al, did not have a chromium content equal to that calculated from Equation 1, yet the corrosion resistance was very good. This serves to illustrate that chromium and silicon variations do not affect corrosion resistance independently of nickel. An alloy similar to VS 54 and 55, except for the absence of chromium, was found to have poor corrosion resistance. .It is thus concluded that chromium is necessary in 70% nickel alloys hardened with titanium and aluminum. However, the amount of chromium required can be considerably lower for the 70% nickel alloys than for alloys containing less than about 40% nickel. Since the objective in practicing this invention is to provide good corrosion resistance at low cost, primary concern is with the effects of chromium and silicon at intermediate nickel contents where Equation 1 is valid.'

.By way of summary, it has been shown above that Fe-Cr-Ni alloys, containing substantial manganese in addition to titanium and aluminum for hardening, have useful Percent Crz16+43.5% Si corrosion resistance at much lower. nickel contents than low manganese alloys. Our investigations have shown that good corrosion resistance is obtained at nickel conof. 12% manganese alloys. The amount of silicon thatcan be tolerated increases with increasing chromium and can be predicted in the manner shown above. The. test results presented above have shown that nickel, chromium and manganese are beneficial to corrosion resistance, while silicon, titanium and aluminum are detrimental. Other elements which have been included and which do not appear to influence corrosion behavior are copper and carbon.

In order to show the mechanical properties of the alloys of'the invention, typical compositionsaccording to Table VII below were wrought,- solutionannealed at 2100 F. andage hardened 'at1300 F. for'22 01"32 hoursfThe aging times were sele'cted'to produce the maximum hardness obtainable at a temperature of 1300 F.' The carbon contents of all"alloys were 0.1% max. The alloys were found to resist rapid over-aging at this temperature, and aging times of 22. or 32 hours gave essentially equal results.

strengthening effect of 2% molybdenum."This addition of molybdenum'alsoha's' a beneficial effect on-creep rup tu're'd'uctilityat 1350 and'lSOO F.-' I V In the alloy's'of the invention, the amoun'tof jnickel that may be replaced is about six times the manganese (both have about equal atomic weight); Only about half of the nickel otherwise required maybe thus replaced. The alloys containing or more'of manganese and 33 %1 or more "ofnick'el show"characteristically higher corrosion rates than nickel-base, lowr'nanganese alloys,

as shown by'FIG. 3. However, the higher corrosion rates of manganese'modified alloys is well within a valueof 12, thought to be necessary for a new alloy.

Manganese has a completely difiYerent function in the alloys of this invention than in known types of iron-base austeniticstainless' steels, such as those containing low nickel, high manganese, carbon, and nitrogen. The func tion of manganese in such alloys 'is to stabilize the aus tenitic structure in the absence of'suflicient nickel. From a consideration of the similar corrosion resistance of high manganese stainless steels such as'-21'4N. and'ordinary stainless steels such' as Type 304, it is evident that manganese is not required to impart corrosion resistance thereto. The alloys of this invention on' the other hand, contain TABLE VIL-TENSILE PROPERTIES OF HIGH MANGANESE Fe-Or-Ni ALLOYS HARDENED WITH Ti AND Al Strength, 1,000

p.s.1. Ductility, Nominal 0011111., percent percent Alloy Code Hard. .2% Vs i Cr Mn M0 011 Ti+Al Re Ult. yield El. vILA.

It is apparent from the above data that aged hardness far more nickel than necessary to result in an austenitic varies with the hardener content (Ti+Al), the higher alloy. Manganese is added for its effect on corrosion recontents yielding the highest hardness. The yield strength sistance alone. The amount .of manganese required for varies in a similar manner. Tensile ductility tends to good corrosion resistance is substantially less than that vary inversely with the hardener content. The manganese required to stabilize the austenitic structure of low-nickel, contents of 5 and 12 percent do not significantly affect chromium stainless steels. the mechanical properties. A lower limit of Ti and Al It has been shown in accordance with this invention that for the alloys of this invention is dictated by the require the addition of manganese in critical amount of about ments of hardness and strength. Conversely, an upper 4'5 4-5% to an alloy containing about 36 nickel, 25%

- limit is dictated by tensile ductility which drops off sharply chromium, 2% Ti, 1% Al, markedly improves the corrowith hardener contents in excess of about 4%. sion resistance thereof.

Typical creep rupture properties for the alloys of the The prior literature indicates that increasing silicon invention are given below in Table VIII for the alloys content in chromium-nickel or in chromium-nickel-manin wrought form as annealed at 2100 F. and age hardened ganese stainless steels adversely affects corrosion resistat 1300 F. V ance. In contrast it has been shown herein as evidenced TABLE VIHFFCREEP' RUPTURE STRENGTH F by the data of FIG. 4 that the amount of silicon which o F HIGH MANGANESE Fe-Cr-Ni ALLOYS CONTAINING can be tolerated increases with increasing chromium con- T1 AND M tent. The importanceof this relationship rests on the fact 100 hour that the important raw materials used in the manufacture ,5132%? of alloysaccording to the invention generally contain Alloy Code Ni Cr Mn Cu Mo Ti+A1 psisubstantial amounts of silicon, such that it is difficult to 41 21 3.3 29, 500 maintain silicon contents below about .2 percent for high 33 3g 1 S88 chromium alloys. If 10W silicon raw materials, such as 34 23 1 1 5 60. electrolytic chromium are used, the cost of the alloy be- 34 23 3.1 38.000 comes prohibitive. From a knowledge"of'the information given in FIG. 4, one mayselect chromium and silicon Creep-rupture strength increases with higher solution contents consistent with good corrosion resistance and annealing temperatures (up to 2100 F.) although hard also'with economical meltingpractice; r l ness, tensile strength, and ductility are reduced somewhat. Addition of certainelements which are soluble-in aus- The significant variant of the first three alloys in the tenite, and which are known to'promote solution strengthabove table is copper. 'As shown, each addition of copper ening,'-'are to be considered within the scope of this invenresults in a substantial loss of high temperature strength; tion, since hardness, strength, and corrosion resistance are The last two alloys contain5% manganese rather than 12 required. Elements such as Mo, W, and Vtall into this percent, and last of these also contains two percent group- Of these elements, M0 is regarded as one of the molybdenum. Alloy VS 138, containing 5% manganese, most promising, as evidenced by the creep-rupture strength has slightly lower strength than its high manganese counat 1350" F. Addition of such elements is permissible in terpart, VS 84B. This slightly lower strength is probably total amount up'to about 5%. due to the lower hardener content of V8 138. A compa'ri- Although the alloys of this invention have been devel- Son of VS 138 and VS I39 demonstrates the'potent' oped for their resistance tocatastrophic oxidation inthe" presence of lead oxide, their oxidation resistance in other environments renders them suitable for applications other then exhaust valves.

Broad and preferred range for alloys according to the invention are as follows:

Weight percent Broad range Preferred 1 Substantially Fe.

What is claimed is:

1. An age hardenable alloy characterized in having a corrosion rate in molten lead oxide as measured in a magnesia crucible of less than about 15 grams per square decirneter, said alloy consisting essentially of up to 0.5% carbon, up to 0.3% nitrogen, up to 0.6% silicon, up to 5% in total amount of at least one metal of the group MO, W and V and combinations thereof, up to 4% copper, up to 0.2% boron, 1.5 to 3% titanium, 0.8 to 1.5% aluminum, 12 to chromium with the chromium content at least equal to 16+43.5 percent silicon, 34 to nickel, 4 to 20% manganese, the nickel content being selected relative to the manganese content to provide said corrosion rate, and the balance substantially iron.

2. An age hardenable alloy as set forth in claim 1 wherein the carbon content is up to 0.1%, the nitrogen content is 0.03 to 0.1%, the silicon content is less than 0.45%, the content of metal of said group is up to 3%, the copper content is up to 0.5%, the boron content is up to 0.1%, the chromium content is 20 to 36%, the nickel content is 34 to 40% and the manganese content is 5 to 8%.

3. An article for use at elevated temperature under corrosive conditions made of an alloy according to claim 1.

4. An internal combustion engine valve made of an alloy according to claim 1.

5. An internal combustion engine valve part made of an alloy according to claim 1.

References Cited UNITED STATES PATENTS 3,495,977 2/1970 Denhard et a1 128 RICHARD O. DEAN, Primary Examiner US. Cl. X.R.

patent 552,950 Dated January 5 1971 Gene R. Rundell et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the drawings and printed specification title of invention, "HIGH TEMPERATURE CORROSION RESISTANT Fe-G-NiMn ALLOY", each occurrence, should read HIGH TEMPERATURE CORROSION RESISTANT Fe-Cr-Ni-Mn ALLOY Column 7 TABLE VI II, lines 52 to 62 inc. in the column headings designated "Alloy Code", "Cu" should read M0 and "Mo" should read Cu Signed and sealed this 29th day of June 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents Enclnniuntn l1n-Rtl\ uer'nuu-nr arr-17s

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