An iron alloy is provided which exhibits strength and toughness characteristics at cryogenic temperatures. The alloy consists essentially of about 10 to 16 percent by weight nickel, about 0.1 to 1.0 percent by weight aluminum, and 0 to about 3 percent by weight copper, with the balance being essentially iron. The iron alloy is produced by a process which includes cold rolling at room temperature and subsequent heat treatment

Stephens, J. R.

Witzke, W. R.

English

NASA Technical Reports Server

United States Patent [19] 
Stephens et al. 
1541 HIGH TOUGHNESS-HIGH STRENGTH 
IRON ALLOY 
[75] Inventors: Joseph R. Stephens, Berea; Walter R. 
I731 Assignee: The United States of America as 
Witzke, Seven Hills, both of Ohio 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 7,083 
[22] Filed: Jan. 25, 1979 
Related U.S. Application Data 
[63] Continuation-in-part of Ser. No. 803,822, Jun. 6, 1977, 
abandoned. 
[Sl] Int. C l . 2  .............................................. C22C 39/02 
1581 Field of Search ..................... 75/124, 125; 148/31 
[561 References Cited 
[52] U.S. C1. ...................................................... 75/124 
U.S. PATENT DOCUMENTS 
2,683,677 7/1954 Walters, Jr. et al. .................. 75/124 
3,132,938 5/1964 Decker et al. ....................... 148/142 
3,262,777 7/1966 Sadowski ............................. 148/142 
3,284,191 11/1966 Hadrean et al. ....................... 75/124 
4,214,902 
[45] Jul. 29, 1980 
3,348,981 10/1967 Godu et al. .......................... 148/142 
3,388,988 6/1968 Nagashima et al. ................. 148/142 
3,475,164 10/1969 Hadrean ................................. 75/124 
3,514,284 5/1970 Eiselstein et al. .................... 148/142 
3,836,407 9/1974 Partier et al. ........................ 148/142 
FOREIGN PATENT DOCUMENTS 
1073784 6/1967 United Kingdam ...................... 75/125 
Primary Examiner-M. J. Andrews 
Attorney, Agent, or Firm-N. T. Musial; J. R. Manning; 
G. E. Shook 
1571 ABSTRACT 
An iron alloy is provided which exhibits excellent 
strength and toughness characteristics at cryogenic 
temperatures. The alloy consists essentially of about 10 
to 16 percent by weight nickel, about 0.1 to 1.0 percent 
by weight aluminum, and 0 to about 3 percent by 
weight copper, with the balance being essentially iron. 
The iron alloy is produced by a process which includes 
using cold rolling at room temperature and subsequent 
heat treatment at temperatures ranging from 400" to 
650" C., and possesses a fracture toughness ranging 
from 200 to 230 ksi vin.  and yield strengths up to 230 
ksi. 
9 Claims, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=19800023976 2020-03-21T03:32:46+00:00Z
4,2 14,902 
1 2 
posed of 9.5 to 13.5% Ni, 2.5 to 8 Cr, 1.9 to 4.2% Mo, 
up to 0.75% Al, Ti, Ni and other elements in small 
amounts. It will be understood that the patents dis- 
cussed above are exemplary only and that this listing is 
5 in no way represented to be exhaustive. 
SUMMARY OF THE INVENTION 
In accordance with the invention, m~ improved high 
strength, high toughness iron alloy is provided which is 
10 particularly adapted for use at cryogenic temperatures. 
The iron alloy of the invention consists essentially of 
about 10 to 16 percent by weight nickel, about 0.1 to 1.0 
percent by weight aluminum, and 0 to about 3 percent 
by weight copper, with the balance essentially iron. 
Is Two embodiments of the invention which possess par- 
ticularly good characteristics have the compositions 
Fe-12Ni-0.25Al and Fe-12Ni-0.25A1-2.0 Cu. These al- 
loys exhibit fracture toughness up to 230 ksi in and yield 
strengths of about 230 ksi. 
The alloys of the invention are preferably produced 
by a process which comprises heating the alloy compo- BACKGROUND OF THE INVENTION 
Cryogenic Pressure vessels and Pipes for storing and sition to produce a cast ingot, hot rolling the ingot to 
transporting liquified gases must have high Strength and produce a sheet, subjecting the sheet to a second rolling 
toughness to be able to withstand both thermal and operation at a temperature ranging from the tempera- 
me@hanical shocks* Further, alloys with high strength 25 ture of the first hot rolling to room temperature, and 
and toughness are also desirable for use in extra-terre- annealing the sheet at ranging from 400" 
strial applications since the sheet thickness required is C.  to 900" c., followed by water quenching. Height- 
both weight and 'pace* It ened toughness and strength characteristics are ob- 
HIGH TOUGHNESS-HIGH STRENGTH IRON 
ALLOY 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the United States Government and may be manu- 
factured or used by or for the Government without the 
payment of any royalties thereon or therefor. 
STATEMENT OF COPENDENCY 
This application is a continuation-in-part of applica- 
tion Ser. No. 803,822 which was filed June 6, 1977 and 
is now abandoned. 
FIELD OF THE INVENTION 
This invention relates to an improved iron alloy 
hich exhibits both high toughness and high strength at 
ogenic temperatures. 
*O 
thereby 
& noted that data pe~aining to the strength and tained when the second rolling operation is made at 
Of at does not 30 room temperatures, followed by annealing at tempera- 
sarily indicate the toughness behavior at lower tempera- 
tures and alloys which exhibit high strength characteris- 
toughness. 
high strength, high toughness steel alloy capable of use 
at cryogenic temperatures. A number of examples of 
such attempts can be found in the patented art. For 
discloses AS discussed hereinabove, the present invention con- 
a Fe-12Nia.sTi alloy which is mid to be suitable for 40 cerns an Fe-Nk-A1 alloy which pssesses high strength 
cryogenic use a d  to exhibit a Chqy V-Notch tough- and high toughness characteristics at cryogenic temper- 
atures. Such very low temperatures are encountered by 
of about 150 h i .  Moreover, further attempts at produc- systems wherein the iron alloys are exposed to liquefied 
ing high strength steel alloys for cryogenic use are dis- g- Or an extra-terrestrial or space environment. 
closed in U.S. Pat. Nos. 3,132,938 (Decker et al) and 45 AS also was discussed, the alloy composition consists 
3,514,284 (Eiselstein). The former discloses a steel com- essentially of about 10 to 16 Percent by weight nickel, 
prising 17 to 19% Ni, 8 to 9% Co, 2.8 to 3.5% Mo, 0.05 about 0.1 to 1.0 percent by weight aluminum and 0 to 
to 0.15% A1 as well as other elements in small amounts, about 3 Percent bY Weight Copper, With the balance 
m e  latter discloses a nickel-iron alloy which comprises being essentially iron. Preferred compositions Of the 
36 to 42% Ni, Nb and Ta and UP to 0.015% AI, with the 50 invention are Fe-12-Ni-0.25Al and Fe-12Ni-0.25A1-2.0 
remainder being Fe and small amounts of other ele- CU which Possess exceptional Strength and toughness 
ments. Other patents of interest include U.S. Pat. Nos. characteristics at CWgenic temperatures. 
3,348,981 (Goda et al) and 3,388,988 (Nagashima et al). The Fe-Ni-Al alloy of the invention is preferably 
The former discloses an alloy which is said to possess prepared by the process to be described. The process 
good strength characteristics at low temperatures and 55 begins with melting high purity starting materials to 
which comprises 0.04% to 0.17% A together with Mn. produce an ingot. To adequately homogenize the ingot, 
Cr, and C. The alloy disclosed in the Nagashima et al the alloy is given a minimum of four melts. The ingot i s  
patent is also said to be tough at low temperatures. This hot rolled at 1 loo' C. after annealing for one-half hour 
alloy comprises 4.5 to 7.5% Ni, together with AI, Mn, at that temperature. Final rolling can be accomplished 
Cr, W, M o  and other elements. Also, U.S. Pat, No. 60 over the temperature range from that of the initial hot 
3,338,709 (Baker et al) discloses a high strength steel rolling operation to room temperature. The alloy is then 
said to have good toughness which comprises 8 to 10% subjected to heating treatment in an argon atmosphere 
Ni, 3 to 5% Co, 0.5 to 2.5% Mo, 0.1% A1 and other for two hours at temperatures ranging from 400' C. to 
elements. A final patent of interest in US. Pat. No. 900" C. followed by water quenching. 
3,262,777 (Sadowski) which relates to maraging steels 65 Certain steps in the process described above are ex- 
using high levels of chromium and molybdenum. The tremely important in producing an alloy having opti- 
steels disclosed are said to be of high strength and ultra mum properties. In accordance with a preferred em- 
tough. In an example of interest, the steel alloy is com- bodiment of the process includes, final rolling at room 
tures in the range of 400' c. to 650" c. 
Other features and advantages of the invention will 
tics do not posses correspndingly high be set forth in, or from, the detailed descrip- 
Attempts have been made in the prior art to produce 35 tion of a preferred embodiment found hereinbelow. 
DETAILED DESCRIPTION OF THE 
PREFERRED EMBODIMENTS 
U.S. pat. N ~ .  3,836,407 (parker et 
,,due up to about 170 ksi din. and a yield 
4.214,902 
3 
temperature (cold rolling) followed by heat treatment at 
temperatures ranging from 400" to 650" C. 
The microstructure of the alloy of the invention is 
dependent upon the annealing conditions and the 
amount of the reactive metal aluminum and the addi- 
tional element copper which are present. For example, 
toughness in the Fe-12Ni-0.25A1-2.0 Cu composition 
referred to above is achieved by the additions of nickel 
and the reactive element aluminum, the aluminum re- 
acting with the interstitial impurities normally con- 
tained in iron alloys, while strengthening is achieved by 
the copper rich precipitates developed in this alloy 
which range in size from about 100 to 400 Angstroms in 
diameter. 
Microstructural differences can be controlled by the 
various heat treatments used in the process of this in- 
vention. For example, the hot rolling step of the process 
occurs in the austentite region producing a face-cen- 
tered-cubic VCC) arrangement. On cooling this FCC 
structure transforms to a bodycentered-cubic (BCC) 
structure. The air cooling utilized should be sufficiently 
slow to produce a microstructure consisting mainly of 
ferrites with some austenite present. The various an- 
nealing temperatures, and the water quenching step 
which follows, will determine how much of the ferrite 
structure is transformed to martensite. A higher anneal- 
ing temperature produces a greater amount of trans- 
formed structure. 
Measurements have been made to determine the 
toughness of the iron alloy using the following slow- 
bend precracked Charpy method. Specimens were ori- 
ented longitudinally in the sheet bar with a 45" notch 
across the thickness. After annealing, each specimen 
was fatigue cracked to an initial crack length to speci- 
men width ratio of approximately 0.4. Testing was con- 
ducted in a three-point bending apparatus immersed in a 
liquid nitrogen bath or at room temperatures. The speci- 
men was positioned between a 6.35-mm-diameter center 
roller and two similar rollers that provide a support 
span of 38.1 mm. A crosshead speed of 1.3 millimeters 
per minute was used. A load/deflection curve was gen- 
5 
10 
15 
20 
25 
30 
35 
40 
4 
men crack depth, B is the specimen thickness, f(a/w) is 
the value of the power series for the initial crack length 
to specimen width ratio (a/w), P represents any point 
on the linear portions of the load/deflection curve, S is 
the span for the three-point bending, and W is the speci- 
men width. 
The methods used herein for measuring toughness 
and strength of the iron alloy of the invention are stan- 
dard procedures and should be well known to those 
skilled in the art. 
Specific properties exhibited by the iron alloys of this 
invention are shown in Table 1 below. The table pro- 
vides a comparison with a Fe-12Ni-O.5Ti composition 
as that disclosed in U.S. Pat. No. 3,836,407 (Parker et al) 
discussed hereinabove. It will be understood that al- 
though the process used for the production of the Fe- 
12Ni-0.5 Ti alloy of the Parker et al patent is different 
from that of the present invention, a comparison can be 
made between the elemental composition and the 
toughness and strength characteristics of the different 
alloys can be determined. 
Table 1 demonstrates the enhanced toughness and 
strengths of the alloys of this invention, particularly as 
provided by the preferred embodiments of Fe- 12Ni- 
0.25A1 and Fe-12Ni-0.25Al-2 Cu. It should be noted 
that the Fe-12Ni-0.25Al alloy has also exhibited good 
weldability. In this regard, a gas-tungsten arc weld was 
employed to weld this alloy using the same composition 
as the filler metal. Following a post weld anneal at 550" 
C., the fracture toughness and strength properties of the 
weld metal and the heateffected-zone were equivalent 
to the base alloy which was heat treated at 550" C., but 
contained no welds. As can be seen from Table I, the 
preferred compositions provide yield strengths of up to 
230 ksi and fracture toughness in the range of 200 to 230 
ksi in. In contrast, the prior art composition exhibits 
toughness and strength values approaching 172 ksivm. 
and 150 ksi, respectively. 
As is also evident from Table I, the temperatures at 
which the alloy is annealed is very important in produc- 
ing a high strength, high toughness product. 
TABLE I 
FRACTURE TOUGHNESS AND YlELD STRENGTHS OF VARIOUS Fe-12Ni ALLOYS 
Testing Temperature - 196" C. 25' c. 
Annealing Temperature 550' C. 685" C. 820' C. 550" C. 685' C. 820' C.  
Y.S.' K.2 Y.S. K. Y.S. K. Y.S. K. Y.S. K. Y.S. K. 
Fe-12Ni-OSAl 129 287 128 86 139 57 85 297 86 148 89 134 
Fe-12Ni-O.25AI 130 258 160 216 151 199 88 291 129 171 101 I 6 4  
Fe-12Ni-O. 12AI 120 227 134 157 126 117 86 325 106 130 99 111 
Fe-12Ni-O.25A1-2.OCu 230. 200' 178 201 155 136 140 - 128 - 106 - 
Fe- 12Ni-O.42Ti I50 55 129 162 117 172 I15 171 96 154 97 161 
'Annealing temperatures of 450' C. 
'Yield strength in ksi 
2Fracture toughness in ksi in 
erated on an X-Y plotter from the outputs of a load cell 
which supported the bend apparatus and a double canti- 
lever clip-in displacement gage. The gage caused the 
deflection by means of the vertical movement of a ce- 
ramic rod riding on the bend bar. The fracture tough- 
ness parameter, K was determined from the load/de- 60 
flection curve using the relation: 
SP UAllAl J(o/w) 
B W 3/2 65 K =  
where A1 is the area under the curve to the maximum 
load, A2 is the area under tRe curve to P, a is the speci- 
A preferred range for producing optimum results lies 
between about 400" C. and 650" C., with alloys annealed 
in this range exhibiting high toughness values corre- 
sponding to that given for the 550" C. annealed condi- 
tion. Testing has also shown that high strength, high 
toughness characteristics of iron alloys can be tempera- 
ture dependent, in that the high values exhibited at 
room temperature may not be retained under cryogenic 
conditions. This is particularly evident in the Fe-12Ni- 
0.5Ti alloy annealed at 550" C. where the fracture 
toughness at 25" C. is 1.71 ksi in. but drops to 55 ksiqin. 
at -196" C. 
5 
4,214,902 
6 
Although the invention has been described relative to 
exemplary embodiments thereof, it will be understood 
that other variations and modifications can be effected 
in these embodiments without departing from the scope 
and spirit of the invention. 
What is claimed is: 
1. An iron alloy possessing high strength and high 
toughness characteristics at cryogenic temperatures 
consisting of 
about 10 to 16 percent by weight nickel, 
about 0.1 to 1.0 percent by weight aluminum, 
about 0.5 to about 3 percent by weight copper 
the balance being essentially iron. 
2. The alloy according to claim 1 wherein the nickel 
is present in an amount of about 12 to 15 percent. 
3. The alloy according to claim 2 wherein the nickel 
is present in an amount of about 12.5 to 13.5 percent. 
4. The alloy according to claim 3 wherein the alumi- 
num is present in an amount of about 0.25 percent. 
5. The alloy according to claim 4 wherein the copper 
is present in an amount of about 2 percent. 
6. The alloy according to claim 3 wherein the copper 
is present in an amount of about 1.8 to 2.2 percent. 
7. The alloy according to claim 1 wherein the alumi- 
10 num is present in an amount of about 0.2 to 0.5 percent. 
8. The alloy according to claim 7 wherein the alumi- 
num is present in an amount of about 0.25 percent. 
9. The alloy according to claim 1 wherein the copper 
is present in an amount of about 1.8 to 2.2 percent. 
5 
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High toughness-high strength iron alloy

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