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TRANSCRIPT
.,SERIAL NO. SSC-61
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Fifth
~~PROGRESS REPORT
(Proiect SR-99)
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THE FUNDAMENTAL FACTORS INFLUENCINGTHE
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BEHAVIOR OF WELDED STRUCTURES:
The Effect of Subcritical Heat Treatment-
on the Transition Temperature of a
Low ‘Carbon Ship Plate Steel I,,
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by
E. B. Evahs and D. J. Garibotti
CASE INSTITUTE OF TECHNOLOGY
I
Transmitted through
NA710NAL ‘RESEARCHC10UNCIL’5
COMMITTEEON SHIP STEEL
Advisory to
SHIP STRUCTURE COMMITTEE
,!,,
l“Division of Engineering and lnd”stri~l Re~earCh
Na!ional‘Academy of Sciences -I National Research Council.1
Washington, D. C. ,,
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October 30, 1953
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SHIP STRUCTURE COMMITTEE
MEMBER AGENCIES: ADDRESS CORRESPONDENCE TO:
BUREAU OF SHIPS, D.CPT. DP NAVY SECRETARY
MILITARY SEA TRANSPORTATION SERVICE. Dcrr. gF NAVY SHIP STRUCTURE COMMI’fTEE
UNITED STATES COAST GUARD. TUEASURY DEPT. U. S. COAST GUARD HEADQUARTERS
MARITIME ADMINISTRATION. DEPT. OF COMMCRCK WASHINGTON 2s. D. C.
AMERICAN BUREAU OF SHIPmNa
October 30, 1953
Dear Sir:
As part of its research program rej.atedto theimprovement of hull structures of suips, the Skip Struc-ture Committee is sponsoring an investigation on %PheFundamental Factors Influencing the Behavior of WeldedStructures under Conditions of Multiaxial Stress andVariations of Temperature” at the Case Institute ofTechnology. Herewith is a copy of the Fifth ProgressReport, SSC-61, of the investigation, entitled ‘TheFundamental Factors Influencing the Behavior of Weldedstructures: The Effect of Subcritical Heat Treatmenton the TransitIon Temperature of a Low Carbon Ship PlateSteel” by E. B. Evans and D. J. Garibotti.
The project is being conducted with the advisoryassistance of the Committee on Ship Steel of the NationalAcademy of Sciences-National Research Council.
Any questions, comments, criticism or other matterspertaining to the Report should be addressed to the Secre-tary, Ship Structure Committee.
This Report is being distributed to those individualsand agencies associated with and interested in the work ofthe Ship Structure Committee.
Yours sincerely,
—
K“.K. C~WART 1Rear Admiral, U. S. Coast GuardChairman, Ship Structure Committee
FIFTHProgress Report(Froject HL99]
The Fmdament,al Factors Influencingthe Behavior of Welded Structures:
The Effect of Subcritical Eeat Treatmenton the Transition Temperature of a Low Carbon Ship Plate Steel
-by
E. B. lW~KWD. J. (+aribotti
CASE INSTITUTE OF TECHNOLOGY
under
Department of the NazBureau of Sips HQBS-4 70
BuShips Project No. NS-011-078’
for
SHIP STRUCTUFU3COMMITTEE——
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Impact Tests ,
Iiicmstru.elmres
Discussion, . . . . ,
Conclusions . , . . .
Future work o . . 0 0
BibliOgi-aphy . . , .
‘TABLE
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LIST OF FIGURES
20
3.
4-0
5-.
6.
7.
80
110
Effect of Various Aging Times and Temperatu~es ontileHardness of ‘UCqlSteel after liaterQuenchingfromljcO~F. . . . . . 0 . 0 . 0 . . 0 , . a . . ~
CkkarpyV-Notch Transition Curves for As-Recsived‘~C’iSteelo . . . . . . . . . . . .0 . , . . .0 9
C&LarpyV-Notch Transition Curves for ~’Cf~SteelSubcritically Eeatet!at 1300~F Tor 15Minutes and Air Cooled. . . . . . . . . . . . . . 9
C$harpyV-Notched Transition Curves for ‘“G’fSteelSubcritically Heated at 1300°F for 15]linu-tesand W-aterQuenched. Aged at RocqjTemperature for Times Indicated . . . . . . . . . 11
Charpy V-Notcl~ed.Transition Curves for ltCtiSteelSubcritically Heated at 1300°F for 15Minutes and Water Quenched. Aged at 125QFfor Times Inciica,ted. . . . . , . . . . . . . . . ,12
Charpy V-Notched Transition Curves for ‘~C~OSteelSubcritically E&ted. at 1300°F for 15Minutes tii~dWater Quenched. . . . . . . , . . . . 1.2
Charpy V-Notched Transition Curves for 9’C”SteelSubcritically Heated at l~OO°F for 15Flinutesand WatEr Quenched. Aged at 600QFfor Times Indicated . 0 . . . 0 . ~ . . , . . . . 13
Sumaiyj Curves Siilowingfiff~ctof Various &inSTemperatures antiTimes on the TransitionTe~p~rature and Eardness of ‘UC*USteel.Specimens Mater Quenched from 1300°F beforeAging.. . . . . . .0 . .0 . . . .0 . . .0 . 13
Microstructure of As-Received and Various&uench-Ages Conditions. . . , . . . . . , . . . . 16
Effect of Room Temperature Agin~ Time on theTransition Temperature and Hardness or ‘iCT’Steel af’terWater Quenching from TemperaturesIndicated . . . . . . . . , . . . . . . . 0 . . . 18
Solution and Room Temperature Aging Effects onthe Hardness and Impact Properties of ‘t(l’iSteel. . .0 . .0 . . . . . . . . . . .OO . . 20
—
ABSTRACT
An investigation was made to determine the impact transi-
“iim temperature and hardness changes att~ndant to the quench-
aging of Project Steel ~lC~ta semi-killed ship plate steel.
Aging temperatures;~xtendedover the range{:from35~ to llOO°F
after water quenching from 1300°F.
Both impact and hardness tests revealed that this steel
can be severely embrittled by the quench-aging ~ech~dsmi. with
aging temperatures ~p to.. -
Were obtained? i.e.a the
3500F9 characteristic aging curves
peak embrittlement and the time to
attain this peak degreased with increasi~~ ~ging
Far mom temperature aging this peak amounted to
in transition temperature and 25 points increase
temperature.
a 90°F increase
in Rockwell )5
hardness above that of a series air cooled from 1300~ (unembrit-
tied condition). Specimens aged above 350°F ‘overagedv so rap-
idly that no peak in the aging curve could be detected.
Metallographic
2000X showed that a
examination of quench-aged specinens at
two-stage precipitation reaction was
operative. At low aging temperatures the precipitate was
detected as a mottling of the ferrite grains; at higher aging
temperatures where an ‘overaged~ condition was rapidly reached$
the precipitate had grown so as to be resolvable.
It is believed that the quench-aging phenomenon is re-
sponsible for the ~$ittle zone previo-usl~m$oundin the sub-
critically heated region in weldrnentsof this and similar ship
iii
plate steels. This study suggest&that a law temperature post-
heat at 650*F (the solution temperature below which quench-
aging effects are absent) would lead to ra’pidoveraging in the
brittle zone of ship plate weldments and thus largely eliminate
the embrittlement.
IJSTRODUCTION
**weldments
temperature
investigate
of steel by
-2-
in a region not heated above the lower critical
(115 It was consider~d advisable toat any time
the maximum embrittlement possible in this grade
quench-aging and how to minimize or eliminate it.
TO this end, Charpy V-notch impact specimens wex=esolution heat
treated at the maximum subcritical temperature (1300°F)Y water
quenched7 and then aged for various periods of time in the ~~”
to llOO°F range. T& embrittlement was ey~luatei by transi=~
tim temperature and hardness changes7 supplemented by
microscopic examination
MATERIAL
The semi-killed? ship plate steel (C St~el) used in tkw
present work was the same 3/4-in. thick7 as-rolled plate
(Plate II) which supplied specimens for the earlier work on
subcritical heat treatment. The properties reported for this
(!5)steel are as fallows:
TABLE I
PROPERTIES OF C STEEL PLATE—-— —
Chemical AnalysisCarbon 0.24 copperManganese 0.&8 ChromiumPhosphorous 00012 MolybdenumSulfur 0.026 TinSilicon 0.05 NitrogenAluminum 0,016 VanadiumNickel 0002 Arsenic
Mechanical Properties
0.030.03(3.0050.0030.0090.020.01
**At least for weldmmts made or A and C steels$ the twoproject steels investigated.
>,,.
“3-
mommlus
blanks (C).&207tsquare) were cut from the as=
after quenehingo In following the progress of agingy specimens
were removed from the aging baths for a time only long enough
for the hardness tests to be made.
With the hardness checks as a guideq series of Charpy
V-notch impact blanks were taken from thE plate in the same
manner% quenched from 1~00%9 and
room temperature E’5°9 ~~Oo9 and
series was air cooled from 13000F
col-lditiono**
aged for various times at
600°F. In addition$ one
to give the unembrittled
*The composition of the neutral chloride salt was asfollowss13MI12 55$ mm 22$KCI 22$ l?Di@$ l?
**TIM Transition Temperature of this se;ies was approximatelythe same as that of the as-received material. In addition~hardness checks of broken specimens showed NO change withtime at room temperature.
-4--
After aging, the specimens were immediately grQund to
size and the notch cut perpendicular to the surface of the
plate9 with each series being machined and tested within
seven hours after aging. The impact testing procedure was
the same as given previously(Il. JLS pointed out in the
earlier work, the possibility exists that accelerat~d aging
can accur in the testing bath. In establishing the transi-
tion curves, it was necessary to test as high as 350°F
(specimens were held 10 minutes in the bath to assure tempera-
ture uniformity)? and thus7 accelerated aging in the test
bath may occur in those specimens prmioudy aged at room
temperature and 125°F. Hardness checks made on specimens
from these series before and after breaking indicated that the
hardness was unaffected up to testing temperatures of 17.5°F0
In view of the fact that the 15 ft~lb transition temperatur~
is to be used as the criterion of’em’brittlementand in no case
did this exceed 175°F5 the results WOU~U appear to be uIIaffecte~o
RESULTS
Hardness Tests
The Rockwell B harnesses obtained after aging in the 35°
to llOO°F range are shown as a function of the aging time in
Fig. 10
From an as-quenched hardness
specimen aged at roon temperature
for about one hour then gradually
of RB877 the hardness of the
(800Fl remained unchanged
increased7 reaching a maximum
:m: 85
c?o= 75
70
65
x
~——— 900 “F— Iioo”r- ALL SPECIMENS AIR COOLED
T\ — FROM AGING TEMPERATURE —
I ‘AS- RECEIVED
‘~ AIR COOLED
FROM 1300° F
3’ 0.1 I 10. 100 1000 10,000LOG AGING TIME-HOURS
FIG. I : EFFECT OF VARIOUS AGING TIMES AND TEMPERATURES ON THE
HARDNESS OF “C” STEEL AFTER WATER QUENCHING FROM 1300° F.
level of RB96 after five days. Aging at a lower temperatur~
(35QF) resulted in a slower rate of increase and a longer
tiu.e(about 50 days) to reach a slightly higher peak level
%9of “ 70
With increasing aging temperatures above room temperature
to 250°F$ the hardness increased at an ever increasing rate;
but the peak hardness reached and the time to reach this peak
decreased. Once the peak had been attained,
time caused a decrease in hardness at a rate
with aging temperature.
further aging
which Increased
At 350~F and higher the hardness dtd not rise above that
of the as-quenched specimen but fell off at a rate which again
increased with temperature.
A summary of the maximum hardness reached and the time
to reach this maximum for the various aging temperatures
employed are given in Table 11.
EFFECT GF AGING TEMPERATUXL ON TliEPEAKHARDNESS REACHED AND THE TIME TCIATTAIN
THI~ PEAK
$gingemnerature. oF
Peak HardnessReacheda RR
Time to ReachPeak Hardness
23 97 50 days96 5 days
125 95 23 hours200 91 2 hours250 88 15 minutes350 Not higher than as-quenched hardness of 11~87600 !1
900 #l
1100 11
Note: All specimens water quenched.aging. Hardness of specimenwas RE 70..
from 13000F prior toair cooled from 1300°F
“7-
These resultsshow that by aging the hardness can be raised
a maximxm Qf about 10 points above that of the as-quenched hard-
ness @#). In turn the as-quenched hardness was 17 points
Rockwell B above that of the air cooled hardness (RB70). The
maximum cumulative hardness increase due to solution and aging
then amounts to about 27 points RB.
h~act Tests
The impact transition temperatures by three criteria
obtained of the (1) as-received*g (2) air ccded~ and (3] the
various quench-aged conditions are swarized in Table 111.
The individual transition curves for each condition are plotted
in Figs. 2--7 with both the energy absorbed and the per cent
fibrous fracture plotted as the ordinate.
In the following sections of the report? the effects of
the various subcritical heat treatments are evaluated with the
15 ft-lb transition temperature as the criterion of enbrittle-
ment and with the properties of the air cooled series reflecting
the unembrittled state. The choice of either of the other two
criteria listed would revea,lthe same general effects.
In comparing the impact properties of the as-received
plate$ Fig. 2$ with those of the air cooled series, Fig. 3?
it is evident that there is little difference in properties
other than about a five ft-lb higher upper level for the air
cooled series.
The transition curves after aging for various times at
*Previous~y reported(l)
-ti -
?7
‘wCwLFm Y-Mm C%
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FIBROUS FRACTURE XPERCENT
n —FIBROUS FRACTURE XPERCENT
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+
-+ 07+mITr0H--
0
0
EE-P000
-P
I-vo -P
o00
IMPACT ENZRGY-FT.-LBS, IMPAGT E114ERGY~FT. -L8S.
___
Io l---~amam I I I I I I I 50
20
L
AGED 7 HOU
40 JJ
+—AL +-++1 ‘o
ii ‘Od-+l+4i+o.TO+-i~o!
30
I!i=ii‘-’J+k-
,0-●4* I ‘ I\; I I i3
& 100m. o 0
L(C)
‘wI* 0*0
d
ji~-~ 50 =20AGED 5 DAYS ‘~ —m 0\. : &-** I i 40
40
.,&”i I ! I 3060
-EIO o 00
TEST
FIG. 4.( A-E ) : CHARPY
FOR *’C” STEEL
1300” F FOR 15
AGED AT ROOM
INDICATED.
160 240 320 400
TEMPERATURE = ‘F
V-NOTCHED TRANSITION CURVES
SLIBCRITiCALLY HEATED AT
MINUTES AND WATER QUENCHED
TEMPERATURE FOR TIMES
‘m-”r”-!-ohl. ‘ ‘ ‘ ‘ I 150
t
r I .- 1 I!- 20 AGED 32 DAYS Iz
\i
KEIH3EPk-
1 “%U-.
●=p*40“o 1 #*1
30;,
20
mmm++’20
-eo o 80 !60 240 360 400
TEST TEhlPERATUREN*F
FIG. 4: 130 NT[MUED ,
Lt-’I
–80 o 80 160 240 320 400
TEST TEMPERATURE x“F
or ‘‘ ‘-y
0+ 50
(A]
20 AGEO 15 MIN. $Q ---- ---- ~-.iJO,.&!
I40 -– _“;- :_________ ;;
60 –– ?L:- q$:i
%$i{ ---/--,0
11 .,1
‘?
TEST TEMPERATURE +-F
FIG. 6: (A-C) CHARPY V-NOTCHED TRANSITION CIJRVES
FOR “C” STEEL SUBCRITICALLY HEATED AT 1300” F
FOR 15 MINUTES AND WATER QUENCHED, AGEDAT 350” F FOR TIMES INDICATED,
FIG. 5: (A-D) CHARPY V-NOTCHED TRANSITION CURVES
FOR “C” 5TEEL SUBCRITICALLY HEATED AT 1300°F
FOR 15 MINUTES AND WATER QUENCHED. AGED
AT 125°F FOR TIMES INDICATED ,
d3-
--..—.. .,
ILo
<’L –- -------J—---—-T--——--—
11
O-J-0co
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“-iEo—1-
wILILI&l
(n
1
mu
1
0m—
ss3r4aw4
Ln IL
ou
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om
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---–~ -—I
.34.
The transition temperature--aging time relationship for
125°F aging--shows that the transition temperature starts to
increase at much shorter times? reaching a peak (168%) atter
about 20 hours and renaining at this value at least up to
three days aging time.
For 350°1?aging it appears that a slight peak may be
present at an aging time less than 15 minutesq but it probably
would not be much greater than the 115°F transition temP~ra-
ture obtained after 1~ minutes aging because the hardness was
unchanged during this time interval. Aging beyond 15 minutes
results in a deerwasing embrittlement with tiime.
Aging at 600°F for two and ten minufiesare~pectivelyz
effects a considerable improvement in t“heimpact properties.
For both cases the transition temperature indicated an embrit-
tlement of but 10°F.
From the general trend of These aging curves? it is to
be expected that at aging temperatures higher than 6000F the
impact properties would approach those of the unembrittled
state very rapidly. However~ as will be pointed out in the
Discussion? this conclusion only holds for specimens cooled
relatively slowly from the aging temperature; a fast cool from
aging temperatures above about 650° can introduce another
quench-aging cycle.
Microstructure~
In order to detect any microstructural changes due to
quench-aging, a number os specimens representing various quench-
aged conditions were examined at 2000X.
‘Thestructure of the as-received condition is shown in Fig.
9(a). No difference in structure was noted in the air cooled
condition; howeverl immediately after quenching~ a mottled
ferrite was evident which did not appear to change with time
at room temperature. Fig. 9(b) shows the structure after one
month at room temperature. No change in this mottled structure
was revealed after aging at 125°F$ even after 23 days at tkcls
temperature, Fig. 9(c).
After aging 15 minutes at 350°Fq the mottled ferrite was
still in evidence; after 21 hours at 3500FY Fig. 9(d), the
mottled structure appeared to be more intense.
Upon aging at 600°F for two minutes, a precipitate, evenly
distributed throughout the mottled ferrite grains, was
resolvable. An increase in aging time to ten minutes, Fig. 9(e)~
resulted in better definition QT the precipitated particles
which appeared to be platelets and an increase in their size.
After aging ten minutes at llOO°F~ Fig. 9(f), the precip-
itate is no longer evenly distributed throughout the ferrite
grains but appears to have coalesced along the grain boundaries
as spheroids.
DISCUSSION
On the evidence of the hardness properties~ Fig. 19 aging
curves were obtained which were characteristic of quench-aging
-.—
-,.
-. >--,
(b) Aged30Daysat Fkmm (c) Aged2? Daysat 125*F.Temperature
L
(d) Aged21 Hoursat 3S0°F (e) Aged10
u Fig. ~: MICROSTRUCTH OF AS-RECEIVEDANDVARIOUSby a waterquenchfrom1300°F. 2000X. 3%
Minutesat 600*F (f)
QUENCH-AGEDCONDITIONS. AllNITAL●
Aged10 Mimutes atllOO°F
agingtreatmentspreceded
systems$ i.eo~ the maximum hardness attained a,ndthe time to
reach this maximum decreased with increasing aging temperature
The similar changes observed with the impact transition
temperature? Fig. 8? are believed to be new experimental data.
The only information found on the impact transition temperature
changes due to quench-aging in a similar grade of steel was
‘6] and was restricted to the room tempera-in the work by Low
ture aging effects. In this paper it was shown that after
quenching from 700°C <1290°F] the transition temperature in-
creased continually over the aging interval of three years.
The total increase amounted to a 110~ rise in Charpy keytiole
transition temperature (10 ft-lb value)$ with the greatest in-
crease occurring in the first ten days aging. This work was
done with a l/2-inch hot rolled semi-killed plate containing
0.17ficarbon.
In conjunction with the earlier work under this project,
it is now possible to show, Fig. 107 the effect of solution
temperature on the magnitude of the peak transition tempera-
ture and hardness reached by room temperature aging. As is
evident, increasing the solution temperature in the 1100° to
13000F range results in a greater initial (fas-quenchedt]
hardness and, apparently a greater initial transition tempera-
ture. Upon subsequent room temperature aging, the magnitude
of the peak also increases with increasing solution temperature.
This is to be expected in line with other quench-aging systems
—!
200
190
180
I70
160
150
140
I30
120
110
IOc
90
80
i’-
H
9-
-
-L8-
GHARPY
+rLL-
‘--- AS RECEIVED
100
90
0
‘ “--”””-l”-”----fi--+----”
t
80 --------------- —. ..
75x~.-– AS RECEIVED
I95 - 1300°F--
>i
‘o~o, o0-
1
❑ u~
1200” F’ –--””-u-”--–-—-
r’
.D-u ❑ .-”~-
m--<
70
k“-- ‘“
—. —————
65
600 “v 0.I I
....____. –-\---- _>.. , ,~o OF
-—— -——---— --- --- —..-
10 100 1000 10,000
LOG AGING TIME “-’ HOURS
FIG. 10: EFFECT OF ROOM TEMPERATURE AGING TIME
ON THE TRANSITION TEMPERATURE AND HARDNESS
OF “C” STEEL AFTER WATER QUENCHING FROM
TEMPERATURES INDICATED.
—
which show that a greater change in properties can be expected
with i.nereasingsolution temperature (greater degree of super-
saturation].
To obtain a quantitative measure of the solid solution
and the aging effects as a function of solution temperature
from room temperature to l~OOoF, Fig. 11 has been prepared.
Here for each property three heat treated conditions are under
mnsideration: (1) air cooled~ (2) as-quenched, and (3) quenched
and aged one month at room temperature. The air cooled data
sets the base line for evaluating the two effects because in this
condition it is assumed that the solid solution and aging effects
are absent*. The difference between thetas-quenched~ proper’~ies
and the base line then yields the effect due to solid solution~
whereas the difference between the ‘as-q-uenched9and ~quench-
agedi properties gives the effect due to aging. The aging ef--
fect may be altered for aging times greater than one vonth~
but it is believed that the change would be slight? if any~ and
therefore the effect shown may be considered a maximum.
This figure also shows that below a solutian temperature
of about 650°F the solid solution and aging effects are nil but
that above this temperature both effects increase with increasing
solution temperature. It is interesting to note that the hard-
ness is affected to a greater extent than the transition tempera-
ture by the solid solution effect, whereas the reverse is true
*Hardness checks showed no change with time at roomtemperature.
-
100
95
90
85
80
75
70
65
190
180
170
160
150
140
130
I20
110
100
90
80
AS RELEIVED
L_+_o—
——
——— .—
—o—
HARD
I x AIR COOLED I
<:( tAs QUENCHED (WATER)
QUENCHED AND AGED AT
ROOM TEMPERATURE
--IFI I
MONTH.
1
AS RECEIVED
/
I I I I I
o 200
——
400 600
:CT [
4.
7
/—
a
I I I I I
800 1000 1200
SOLUTION TEMPERATURE x “F
1400
FIG. 11: SOLUTION AND ROOM TEMPERATURE AGING
EFFECTS ON THE HARDNESS AND IMPACT
PROPERTIES OF “C” STEEL.
--
-21-
with aging. In any case the two effects are interrelated and
governed by the solution temperature which in turn controls
the amount of carbon available for the precipitation reaction.
With cooling rates intermediate to an air cool and water
quench? it is to be expected that these two effects will be
minimized due to the lower degree of supersaturatian~ i0@05 less
carbon is retained in solution on the quench.
From the rnetallographicchanges occurring during aging$
it would appear that a two-stage precipitation reaction is
operative. The first stage (evident as a mottling of the fer-
rite) was responsible for the greater degree of embrittlement~
while the second stage, in which a resolvable precipitate was
detected$ was associated with an improvement in properties
corresponding to a rapid ‘overaged~conditiong Although 110
attempt was made at identification? the sequence of micro-
structural changes observed appear to be the same as reported
recently (7)0 In this paper the metallographic changes occurring
during the quench-aging of an ingot iron {0.026~ carbon} were
followed by means of the optical and electron microscopes and
the identification of the two-stage precipitate made with
electron diffraction technique. The first stage was identified
as the hexagonal &-iron carbide after 15 hours at 200°C (390°F).
The second
lattice to
30 minutes
stage was associated with a change in the crystal
cementite~ (orthorhombicFe3C]9 observed after aging
at 300°C (570°F).
=22-
It can now be speculated that in the aging of C steel the
formation of the transition lattice (E-iron carbide) is associ-
ated with a high degree of ernbrittlement,while subsequent
formation of the equilibrium phase
a large improvement in properties
~overaged~ condition.
(cementite) brings about
corresponding to the rapid
Insofar as microstructural changes are concerueda the
brittle zone previously found in the subcritically heated
region in ship plate weldments has not been identified with a
precipitation reaction*O Howeve~~ due ho the cc]mplexityof
the temperature time at ternperatureyand cooling rate condi-
tions in multiple pass weldmentst it is difficult to determine
the exact quench-aging cycle experienced. It has been shown
previously (1] that the cooling rate in the subcritlcally heated
region** is such that the ferrite is not supersaturated to the
maximum possible as in water quenehed test specimns. Conse-
quently? less carbon is available fer the subsequent precipita-
tion reactions and the resultant precipitate may not be detected***.
In regard to the changes in hardness and transition tem,pera-
ture~ the results of this investigation givs the maximm possible——
*It shoL1ldbe recalled that the de~onstrated beneficial ef.fects of increasing preheat (decreasing ccoling rate) andpostheating (Qoveragingf certainly point to the quench-aging mechanism.
**The cooling rate at the critical zone was found to beintermediate to water quenched and air cocled impact testspecimens.
***It is not expect~d that the electron microscope would beable to detect any precipitation. In the reference citedin the Discussion (7)9 the only advantage of the electronover the light microscope was inprecipitate once it had formed.
better-resolution of the
-23-
embrittlement
ment designed
be applicable
of
to
to
C steel by quench-aging, Fi&. 11. Any treat-
remove these effects in the base plate should
weldments made of this and.similar grades of
steel. As was shown in Figs. 1 and 8B ‘overagingfitreatments
served to minimize the embrittlement, with the degree of em-
brittlement decreasing with increasing aging temperature
However, this finding must be qualified.in view of the fact
that the results were based on specimens aircooled from th~
aging tenperaturesa A consideration of Fig. 11 shaws that
if aging temperatures above 6500F were used, then the pos-
sibility exists that another quench-aging cycle could be
initiated
different
fore, the
should be
if a fast cool were employed. (Lowf6J~ using a
approacha arrived at the same condusion]o There.-.
postheating of weldments susceptible to quench-aging
restricted to a maximum of about 650°F when this
danger exists. As this investigation showed? aging in this
neighborhood (6000F) effected a rapid and considerable improve-
ment in the ductility by ‘overaging~.
CONCLUSIONS
In conjunction with previous work(11 on the subcritical
heat treatment of a low carbon ship plate steel (C steel)q the
following conclusions seem justified%
1. The quench-aging mechanisn was responsible for the loss inductility and-the increase in hardness.
-.
2.
3.
b o
5.
pa>g severity Of the embrittlement imer~a~ed “~’~ith~n~reasingsolution temperature from 6J00 to 1300 F; m embrittlementwas present when employing solution ter,peratvresless than650°F’O
On the evidence of impact transition temperature and hardn-ess changes? characteristic aging curves were obtained$i.e.$ the peak transition temperature and hardness reachedand the time to attain this peak decreased with increasingaging temperature.
Metallographic examination showed that a two-stage precipita-tion reaction was operative.
A low temperature postheat at about 650°F would do rrILIch “k
eliminate by overaging the zone of minimum ductilitypreviously fm.md in.the subcriticallyheated region of weld-ments Of this and similar grades of steel. ;Si,gherpostheattemperatures rufithe danger of introduci+~ another agingcycle if a fast cool is employed.
FUTURE WORK
This report concludes the experimental work done under this
contract. A final report will be prepared summarizing all the
work done on (1] the distributim of relative ductility in ship
plate weldments and (2) the subcritical beat treatment of base
‘plate o
.—
-25-
BIBLIOGRAPHY
1. E. B. Evans$ and L. J. JQinglerj ~iTheEffect of fibcritica~Heat Treatment on the Transition Temperature of a Low CarbonShip Plate Steel’~a Fourth Progress Report, Ship StructureCommittee Serial No. SSC-603 October 30, 1953.
2. G. Sachs5 L. J. Eberta and A. W. Da~7 Jrg? ‘tTheFundarLenta~Factors Influencing the Behavior of Welded Structures UnderConditions of Multiaxial Stress and Variations of Tempera-ture, Stress Concentration~ and Rates of Strain”9 NavyDepartmenta Bureau of Ships9 Contract NObs-45k70~ SerialNoe SSC-2k, May 10~ 1949*
30 Lo J, KLinglera L. J. Ebert and W. M. Baldwin, Jr.~ Ibid.$2, Serial NO. SSC-3k$ November 28? 1(3490
~. E. B. Evans and.L. J. Klingler~ Ibid 27 Serial No. SSC-~3October 143 19520
~. Technical Frogress Report of the ShiP St~u~ture Cammi~t~e~Welding Jouma15 Vol. 13 (July 1948)9 pPo 37?s-38~s0
6. Jo R. LOW, Jroa ‘tTheEffect of Quenc’h-Agingon the NotchSensitivity of SteelU’qWelding Research Supplement$ Vol.17 (my 1952)9 PO 253s-256s0
7. Anna L. T’soutJ. Nutting, and J. “W.Menterl ‘tThe@ench-Aging of Iron:f~Journal of the Iron and.Steel Institute$ Vol.1722 part 2, october, 1952$ pp. I63-I71O