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Патент USA US3038807

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nited States atent
3,030,707
1C6
Patented June 12, 1962
2
1
met in a nickel, molybdenum, vanadium steel containing
less than .40% manganese, between 3.50 and 4.25%
3,038,797
ALLOY STEEL FOR FORGINGS
nickel, and between .18 and .40% vanadium. Not only
Samuel J. Manganelio, Wilkins Township, Allegheny
does such steel have an 0.02% offset yield strength in
County’ and 501.“! E‘ Steiner’ Churchill Borough’ Pa" 5 the range of 94,000 to 98,000 p.s.i. but such increase in
2:25:03‘; ggegniiigpystates Steel Corporation’ a corpo~
7 '
N0 Drawmg' 4%iggmlgovkélswlggfl’2ss? No. 852,596
.
yield strength is accompanied by a decreekllse irsiofrapcture
a
earance transition tem erature to lesst an
°
.
pThe fracture appearancg transition temperature is de
I
termined by using V-notch Charpy specimens. The frac
This invention relates to improvements in magnetic 10 mm app?§ifance tYPPSiiiOYI @Qmperamre di?el's from the
alloy steels for forgings and more particularly to alloy
more familiar ductility transition temperature. The frac
steels providing high yield strength combined with good
‘El-1T8 eppeafanfle transmqn temperature {8 detel‘ml?ed by
notch toughness for large generator rotor fol-gings,
breaking specimens at different temperatures and deter
In the electric power industry, there is a need for a
mmms from the appearanee of the fraetures at what
strong, tough, and magnetic steel suitable for large gen- 15 tsmpefatllre lb? Steel f?ll?d 111 3 50704116016, 50%43T1tt1e
erator rotor iorgings that serve as the rotating ?eld com010M161‘- Dllcille ffacturf’is appeal‘ gray and ?brous, bl1_t
ponents of large steam-turbine generators. These large
011mg ffictllfes aPP@3Y_$11VeTy afld granular; P)’ cflmpfil‘
rotor forgings range in diameter from 12 to 70 inches
mg the lfactllfed 5136911116113 'Wlth a Chan, Lil? lelatlve
and in length from 15 to 35 feet. The steel rotors should
ductlllty 01‘ bl‘lt?eiless of the frafitjlfe 031110815113! be (1':
be free of internal defects so they can withstand high 20 tarmlPed- I11 Fo?imst, the ductllliy ifansltion tempera
operating stresses. They must be tough (nonbrittle) to
mm 15 fieiermmefi usually by measllrmg tile energy ab"
resist the propagation of any internal or external cracks
Sorbed 111 ?acfm‘mg speclmens at dl?erem temperatures
or defects present or incurred in service. Propagation of
and determmmg at What ‘temperature the amount of
these cracks or defects results in sudden failure in servenergy absorbed sudden1y_ {ncreases or decmases; The
ice. In addition, these ?eld rotor forgings should exhibit 25 fracture F‘Ppeamme “2111510011 @mljerafuw ?lmlshes a
a high magnetic permeability (B/H or slope of the mag
more reliable and reproducible indication of the ‘notch
netization curve) to minimize the current necessary to
tqj‘ghness of "forging .i‘egls' Iierea?i; th: {1cm} tran'
generate the required magnetic field.
illgsénartfgégetrrgglsriiiogviemgelfiireto m ‘can’ “6 ractum
It Is accorihngly an obiectpf this mvfa'linonip prelude 30 Our investigations have demonstrated that the desired
alloy genera‘or rotor forgmgs ccmlimmg h1gh_ yleld
properties may be obtained with the following compo~
strength’ good notch toughness and hlgh magnenc Per‘
nents within the following ranges (percent by weight).
meability-
It is preferable that rotor-forging ingots of the steel be
It is another object to provide a readily forgeable alloy
steel providing the foregoing properties.
f
vacuum cast
35
The type of steel commonly used for rotor orgings
for high speed generator units is a nickel, molybdenum,
vanadium steel containing 0.18/ 0.33% carbon, 0.4‘0/
0
_
S‘
Mn
Ni
Gr
v
V
M0
A1‘
_
0.70%
nickel, 0.20/0.70%
manganese, 0.15/0.40%
molybdenum,silicon,
0.03/0.12%
2.50% vanadium,
minimum 40
0'1‘
“~26 0'20
040 0'15
0'40
and sometimes up to 0.75% chromium if higher strength
350
4‘25 ‘150U
_
'
0'20
(1-50 0'18
0-40
_ I
_
is desired. Such steel usually exhibits an 0.02% offset
yield strength of about ‘65,000 to 90,000 p.s.i., a fracture
Fjffflfgollrlféllfnd usuallmpmmesm Common amounts
The preferred range of componcnts is as follows_
appearance transition temperature (based on 50% shear
'
fracture appearance) of 60 to 200° F., and a magnetizing 45
force (H) of 600 to 1300 ampere-turns per inch to pro-
0
Mn
Si
N1
Cr
M0
V
All
0 0-20 0-18
(1)118;
duce a ?ux density (B) of 130,000 lines per square inch.
This steel falls far short of properties desired by the
‘118 ‘12° 9-15 3-70
steam-turbine
0.24
generator manufacturers
for
generator 50
0.35
0. 40
4.00
0.30
0.30
0. 30
'
rotors, i.e. 90,000 p.s.i. yield strength (0.02% offset),
50" F. maximum fracture appearance transition tem-
‘Acid-soluble
Peramre (50% Shear), and 725 ampere-011115 Per inch,
Atypical composition of our new steel is:
0
Mn
P
s
Si
Ni
Cr
M0
V
All
0. 22
0. 30
0.012
0.012
0.25
3.75
0.25
0.30
0. 22
0. 010
Fe
Remainder
and Im
purities
1 Acid-soluble.
maximum, to produce a ?ux density of 130 kilolines per
square inch.
We have discovered that the desired objectives can be
Steel
1 Acid-soluble.
_ Test steels of the following compositions are illustra
tive of the unusual combination of properties resulting
from the composition of our invention:
0
Mn
P
0.32
0. 31
0. 30
0.31
0.011
0.012
0.009
0.010
S
0. 015
0.013
0.013
0.013
' Si I N1
0. 32
0. 24
0.24
0.23
2. 97
3. 65
2.97
3.72
Cr M0 , V I A11
0.28 0.26
0. 27 0.32
0.26 i 0.28
0.28 0.31
0. 00
0.10
0.22
0.22
0. 045
0. 054
0.006
0.069
3,039,797
3
and tested at room temperature. The following results
Steel A is similar to the rotor forging steel mentioned
hereinabove as being in common use in the industry; it
were obtained:
differs from that rotor forging steel only in that it con
tains less manganese. Steel B is similar to Steel A except
for a higher nickel content; Steel C is similar to Steel A
with higher vanadium content. The results with these
steels show that the desired properties cannot be obtained
without increasing both nickel and vanadium. When
both nickel and vanadium are increased the required
amount and the manganese is low (Steel D), the desired
properties are obtained.
Forged bars of these four steels were homogenized
2 hours at 1700° F., air cooled at room temperature,
austenitized 4 hours at 1500° F., cooled at about 120° F.
per hour to 600° F. (approximately the cooling rate that
prevails at a location a few inches below the surface of
a normalized 45-inch-diameter rotor forging), and free
furnace cooled to room temperature. This constitutes
the normalizing treatment, to which all specimens were
subjected. With air-cast steels, it is necessary to hold ~
between 450‘ and 625° F. to prevent cracking or ?aking.
However our steel, if vacuum cast, may be air cooled to
room temperature without harmful effects and in fact it
has a bene?cial effect on notch toughness without lower
Ampere-Turns per
Inch for 130 Kilolines
per Square Inch
Steel
1,160u F.+ 1,110° F. +
l,l20° F.
l,070° F.
747' __________ ._
626
__________ _.
788
727
7l8
707
After normalizing and tempering, the steels of our in
vention have a microstructure consisting essentially of
ferrite and bainite.
The results given above show that the desired 0.02%
offset yield strength (90,000 p.s.i.) is not obtained in
Steel A but is obtained in Steel B tempered at 1070° F.
Furthermore, the magnetic properties of Steel B are very
good (magnetizing force of 626 ampere-turns per inch).
However, the transition temperature of Steel B, though
good, is still rather high (60° to 75° F.). By increasing
ing the yield strength.
the vanadium content from 0.10 to 0.22%, however, a
marked improvement in the transition temperature was
The tensile specimen blanks were tempered 24 hours
obtained (Steels C and D). Steel C, which contains
at either 1140 or 1070° F. and air cooled. Tempering
only 2.97% nickel, exhibits a low transition temperature
in the range of 1060 to 1080° F. is preferred. Tensile
(10° F.) but also exhibits a low yield strength (79,000
specimens (0.505-inch-diameter) were machined from
the blanks and tested at room temperature. The follow 30 p.s.i.) like Steel A. This indicates that 2.97% nickel
mg results were obtained:
or 0.22% vanadium, by itself, will not give an 0.02%
Table l
Steel
Tempering
Yield Point,
p.s.i.
Yield Strength,
p.s.i.
Temp ,
F.
Tensile
Strength,
p.s.i.
Upper Lower 0.02%
O?set
1, 140
1, 070
1, 140
1, 070
1, 140
1, 140
1, 070
Elongation Reduction
in 2",
of Area,
Percent
Percent
0.2%
Offset
98,200
103, 1100
109, 000
115, 300
90, 300
104, 200
112, 500
24. 5
24. 5
19. 5
22. 0
27. 5
24. 6
23. 0
66. 0
64. 0
64. 4
65. 9
67.6
67. 2
65. 7
After normalizing, the impact-specimen blanks were
offset yield strength of 90,000 p.s.i. By increasing the
tempered 24 hours at either 1140 or 1070” F., then either
nickel content from 2.97% to above 3.50% and the
brine-quenched or slowly cooled (about 7° F. per hour
vanadium content to above .'18%, however, the desired
combination of high strength, good notch toughness, and
ture). Charpy V-notch impact specimens were then ma 50 high magnetic permeability (relatively low magnetizing
force value) was obtained (Steel D). Moreover, Steel D
chined from the blanks and tested at temperatures in the
was only slightly susceptible to temper embrittlement, as
range —100° F. to +80° F. The following results were
shown by the increase of only 20° F. in the transition
obtained:
temperature of the specimens slowly cooled from tem- ~
Table II
55 poring over the transition temperature of those brine
quenched from tempering. It is believed that the low
Transition Temp, °F.
manganese content of Steel D contributed greatly toward
Tempering
its relative insensitivity to temper embrittlement.
Steel
TemperaSlowly
Brine
ture, ° F.
Cooled
Quenehed
The mechanisms by which increases in nickel and, to
From
From
Temperlng Tampering 60 a lesser degree, vanadium improve the strength of the
nickel, molybdenum, vanadium steel are not fully under
stood, but it is believed that nickel strengthens the ferrite
1,140
60
35
to 750° F., then free-furnace cooled to room tempera
1,070
1,140
1,070
1,140
1,140
1,070
60
75
60
10
—20
0
35
55
55
—10
~40 65
—20
and that vanadium forms carbides that also serve to
strengthen the steel. Vanadium, above about 0.18%,
improves the notch toughness of nickel, molybdenum,
vanadium steel by one or more of the following mecha
msms:
After normalizing, some of the magnetic-test speci
(1) Re?ning the austenitic and ferritic grain size. (The
austenite grain size of the steels containing 0.22% vana
furnace cooled, tempered 24 hours at 1120" F., and again 70 dium was ASTM No. 7 or ?ner, and the ferrite grain
size was 81/2 or ?ner. An austenite grain size of ASTM
free~furnace cooled (both coolings at about 150° F. per
No. 4 or ?ner is desirable, as such ?neness of grain
hour). Other magnetic-test specimen blanks were tem
is necessary for satisfactory ultrasonic testing.)
pered at 1070° F. and were similarly cooled. Magnetic
(2) Combining with and hence lowering the amount of
test specimens (13716 inches wide by 1A inch thick by
12 inches long) were machined from the tempered blanks 75 carbon in solution.
men blanks were tempered for 24 hours at 1160“ R, free
spar-3,797
5
6
(3) Decreasing, perhaps, the susceptibility of nickel,
3. A steel characterized ‘by an 0.02% offset yield
strength in excess of 90,000 p.s.i., a transition tempera
ture below 50° F., a high magnetic permeability, as in
dicated by a magnetizing force of below 725 ampere-turns
molybdenum, vanadium steel to temper embrittlement.
The low manganese content is believed to make the
steel less susceptible to temper embrittlement.
per inch to produce a ?ux density of 130 kilolines per
square inch and substantial freedom from temper em
This application is a continuation-in-part of our co
pending application Serial No. 803,829, ?led April 3,
brittlement, said steel containing by weight
1959, now abandoned.
While we have shown and described several speci?c
embodiments of our invention, it will be understood that
these embodiments are merely for the purpose of illustra
tion and description and that various other forms may
be devised Within the scope of our invention, as de?ned
.18 to .24% carbon
.20 to .35 % manganese
.15 to .40% silicon
3.70 to 4.00% nickel
Up to 30% chromium
.20 to .30% molybdenum
in the appended claims.
We claim:
.18 to 30% vanadium
1. A steel characterized by an 0.02% oifset yield 15
.05 % max. acid soluble aluminum
strength in excess of 90,000 p.s.i., a transition tempera
balance iron and residual impurities.
ture below 50° F., a high magnetic permeability, as in
dicated by a magnetizing force of below 725 ampere
4. A generator rotor forging characterized by an
turns per inch to produce a ?ux density of 130 kilolines
0.02% offset yield strength in excess of 90,000 p.s.i., a
per square inch and substantial freedom from temper 20 transition temperature below 50° F ., a high magnetic per
embrittlement, said steel containing by weight
meability, as indicated by a magnetizing force of below
725 ampere-turns per inch to produce a flux density of
.17 to .26% carbon
130 kilolines per square inch, a ferritic-bainitic micro
.20 to .40% manganese
structure and substantial freedom from temper embrittle
.15 to .40% silicon
25
ment, said steel containing by weight
3.50 to 4.25% nickel
.20 to .50% molybdenum
.18 to .24% carbon
.18 to .40% vanadium
.20 to .35 % manganese
Up to 50% chromium
.10% max. acid soluble aluminum
.15 to .40% silicon
30
3.70 to 4.00% nickel
balance iron and residual impurities.
Up to .30% chromium
‘2. A generator rotor forging characterized by an
.20 to .30% molybdenum
0.02% offset yield strength in excess of 90,000 p.s.i., a
.18 to 30% vanadium
transition temperature below 50° F., a high magnetic
.05% max. acid soluble aluminum
permeability, as indicated by a magnetizing force of be 35
low 725 ampere-turns per inch to produce a ?ux density
balance iron and residual impurities.
of 130 kilolines per square inch, a ferritic~bainitic micro
structure and substantial freedom from temper embrit
References Cited in the ?le of this patent
tlement, said steel containing by weight
UNITED STATES PATENTS
40
.17 to .26% carbon
.20 to .40% manganese
.15 to .40% silicon
3.50 to 4.25 % nickel
.20 to .50% molybdenum
.18 to .40% vanadium
Up to 50% chromium
.10% max. acid soluble aluminum
balance iron and residual impurities.
45
934,697
1,261,742
2,206,370
Schneider ____________ .. Sept, 21, 1909
Churchward __________ __ Apr. 2, 1918
Scherer ______________ __ July 2, 1940
2,845,345
Bauscher et a1. ______ .. July 29, 1958
OTHER REFERENCES
Hall: Nickel in Iron and Steel, 1954, page 168. Pub
lished by John Wiley and Sons, Inc., New York, NY.
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