,;•'•
The Effect of Heat-treatment
--
--
---Upon the Physical Properties
Of
W
rought Iron
A
T H
·
E S
1
S
May, 1916Submitted
byf
,
j'
t~
~
'.l..J 1l <o5.
T, T ~ ~ '- 't (Q ).ie wish to expres s our sin-erei' apirc ciation
for the kind assistance and very valuable
sug-gestions given to us in this work by Professor Henry Fay. We also wish to thank Mr.Cowdrey for giving us much help in preparing the test
I N D EX P a rt I* p Introduction 1 Reference Notes 2-10 P a rt I I Experimental Prodedure:
Construction of electric furnace 12-14
Calibration of pyrometer 15916
Program pf heat-treatment 17
Tensile and Impact testing 18
Method of Polishing specimens 19
Method of etching polished specimens 20
Microscopic examination and
photo-micrography 21
Study of recrystallization of
deformed specimens 21-22
P a rt I I I
Test data and plots 23-24
Discussion of results 25-38
The Effect of Heat-treatment upon the
Physical Properties of Wr ht
Iron,-The introduction with its rapid decrease in cost of
Bessemer and Open-hearth steel has crowded wrought iton from many fields and made it fall in rank among materials
of engineering construction. However, wrought iron is
still popularly used as a material for general forging c.
pperations, particularly where welding is involved, as
rolled-rods and bars, as wire, as welded pipe, and as a metal for roofs and sides of buildings and for tanks.
According to Professor A. P. Mills of Cornell University,
wrought iron will hold indefinitely an important place among materials of construction.
Useful and important as wrought iron is, the effect upon its physical properties by heat-treatment has only
been slightly touched upon. It is therefore our object in
this thesis to investigate this subject as far as we can. Werhave studied the effect of heat-treatment upon its
ten-sile strength, its resistance to impact, and its
crys-taline growth. We have also to a limited extent
atteipt-ed to examine its recrystalization after deformation and subsequent heat-treatment.
To biAink our investigation we tried to find infornia-tion upo4 the subject from the journals and books
2
regarding the heat-treatment of wrought iron from these books and journals, we decided to see what we
could find about low carbon steel, which might suggest to
the behavior of wrought iron, since- the structural consti-tution and microstructure of low carbon steel are very similar to those of wrought iron as can be seen from the
following
comparison:-Name Total C. Ferrite Cementite na
Wrot. Irn .05-.3076 99-93.6% .75-.45% .12-2.00%
Microstructure: Crystaline. Large mass of grains of
ferrite with isolated patches of
pearl-Ite between grains of ferrite.
Streaks of slag in direction of rolling.
Name Total C. Ferrite Cementite Sla
L.C.Steel .05-.30% 99v3-99.5% .75-.45% Nearly zero
Microstructure: Crystaline. Large mass of grains of ferrite wIth isolated particles of pearlite at junctions of ferrite
and also since their physical properties are practically the same, both being soft, malleable, ductile, tough and forgeable, except that wrought iron does not harden
materially when suddenly cooled while the steel does har-den slightly.
As a result of our search into the works on low carbon
steel, we found the following facts many 6f them, as can
I. Formation of crystals and granules
1. There is a definite distinction between a
crystal and a granule. A granule is built up of crys-tals; its external form is not crystaline as it takes
its shape from its surroundings. It is an
allotimor-phic crystal or simply a grain. (Stead)
2. Grains formed in the solidification of liquid
metals are large or small, according to whether the freez-ing is rapid or slow, and they take their form vfrom sur-roundings, and this is most irregular owing to natural
interference. The size of the grains is also dependent
upon the temperature from which the metal cools; upon the length it is maintained at that temperature; upon the amount of mechanical work to which it is subjected during cooling; and upon the temperature at which working is dis-continued.
3. The prevailing crystaline forms of "gamma"
iron are octahedrons; of Aand ociron are cubes.(Sauvuer)
4. Upon the solidification of iron and steel crystals are found. The centre of each dtndriia-tlin growth
is called the centre of attraction, towards which the separate particles of cubic crystals are drawn to form a
granule. Sometimes during this crystalline growth, the
grains are so oriented that the component crystals are
sometimes group themselves in such a way that they are symmetrical with each other with respect to a plane be-tween them called the cleavage plane (Stead and Sauveur)
5. There is a distinct relation between the size
of grain and tensile stength. The specimen having the greatest breaking strength has the finer grain. This is
also true of the elastic limit. "The smaller and finer
the grain, the safer and stronger is the structure." (Stead)
II. Effect of heat-treatment on
micro-structure:-Fay and Badlom found that with low carbon steel
(.07%c) when annealed with subsequent slow cooling: 1. The size of the grain is apparently constant or increases b~ut slowlj at temperaturesbeloit 8500 C. A& 8000 the grain is suddenly refined, and the structure becomes close and porcelain like. From temperatures above
this, annealing seems to cause a gradual increase in Bite
slowly up to 11250C and rapidly from that point on.
2. Above 11000C a new type of structure appears which seems to con*lat of parallel bands and striations sometimes crossing the grain junctions.
3. Above 10000C, the banded structure appears to
increase the strength and also somewhat retard the grain development, but at 11250C. the latter takes the ascen-dency.
4. The banded structure when accompanied by large
III. Effect of heat-treatment upon the physical properties
1. Annealing at 8500 with subsequent slow
cobl-ing has little effect upon the strength of low and medium
carbon steels. The ductility is increased slightly.
(Brinnell)
2. Annealing at 7500C. has little effect upon
the strength of low and medium carbon steel. The
ductil-ity is increased considerably.
3. Annealing at 8500C has little effect on sti
strength but increases ductility considerably.
4. Annealing at 10000C. has practically no effect
upon strength, but the ductility especially of the low
car-bon steel increased about 15% to 30%.
5. Water quenching at 7500C increases the
strength of low carbon steel greatly. Ductility is
de-creased greatly.
6. Reheating to 5500C after water quenching at
7500C. restores the steel to practically its original
strength. The ductility is very much greater than that
obtained after quenching but is only slightly greater than that obtained with steel in its original condition.
7. Water quenching at 8500C increases the strengLh
of low carbon steel very greatly. The ductility is
6
8. Reheating at 5500C. after water quenching at
8500C, largely mullifiessthe gain in strength in low car-bon steel. The.,ductility is restored to practically its
original value before quenching.
9. Oil quenching at 75000 followed by reheating
to 5500C. has little effect upon the strength but
increas-es the ductility (oil temp.z860c)
10. Oil quenching at 8500C followed by reheating
to 5500C increases the sttength but the ductility is not
much affected.
11. Hardening in lead (lead temp. 55000) is the same
as hardening in water with subsequent annealing at 5500C, only it is less effective than water.
12. Fay and Badlom found that annealing low carbon
(.07%c) steel with subsequent slow
coolingi-(a) There is a fair degree of constancy in the
tenacity of bars heated to below 8500 with possibly a slight falling off between 8000 and 8500.
(b) At 8900 there is a sudden rise in the
ten-sile strength from 56,800 #/sq.in to 59,100#/sq. in.
(c) Beginning at 9000 there is a slLight falling
off reaching a minimum of 50,700 #/sq. in. at 10000 C
from which paint it rises again.
(d) At 11250 C. the strength a second maximum
7
(e) From 11430C there is a very decided falling
opf in strength reaching 53,300#/sq. in. at 12470C. (f) The elastic limits vary in the same manner as the tensile strgegths at the various temperatures.
(g) Annealed at 6500 C the elongation is 31%;
>-from here on to 80000 it is fairly constant. At 80000
it decreases to 29%. From 8000C on to 9000C. it is about
constant. At 90000 there is a sudden increase to 33%.
At 10000C there is a sudden drop to 29%. From here on to 12470C it gradually increases to 31%.
(h) The rqpidly coaled specimens show a tensile
strength quite uniformly from 2000#/sq. in. to 2500#/sq. in. higher than the corresponding slowly cooled specimens.
13. The impact stress for steel varying from
.09% C, to.25% carbon is between 403 and 209n-meter-kilo-grams per square centimeter of cross-section for annealed and slowly cooled steel and-between 504 and 290
meter-kilograms for quenched and reheated steel. These values
were obtained when the atmospheric temperature is 300C. Values obtained when the tetperature is -280C are much lower, being 141 to 123 meter-kilograms for unhardened steel and between 226 and 229 meter-kilograms for hard-ened steel.
.
IV. Effect of heat-treatment upon Re-crystallization
of Deformed Iron.
1. In practically carbonless pure irons and steels
of fine grain produced by forging or certain heat treat-ment the grains increase slowly in size at 5000C and more
rapidly between 6000C and 7500C and it is possible by
heat-ing for a few hours at about 70000 to develop granular
mas-ses of exceeding coarseness. When pure iron made coarsely
granular by long heating at a dull red heat is heated be-tween 7500C and 8700C as a rule the structure is not al-tered to any material extent, but as soon as the temper-ature rises above 9000C. the granules again become small; at heating to 120000 apparently do not change them.(Stead)
2. The size of granules increases with the
temper-sture, the coarsest being obtained by heating to the
high-est temperature, and the structure remains comsie whether
the metal is quenched or cooled slowly from that tempera-ture.
5. Elongated ferrite crystals, produced by severe
cold deformation, usually split up on recrystallization into smaller crystals, whose diameter in each direction approximately corresponds to the breadth of the original elongated ones.
4. The ferrite in cold drawn iron or steel
C4
the elongated ferrite crystals become replaced by crystals
of normal allotrimorphic shape. (Goerens)
5. Local deformation such as by a Brinell impression
resulted on annealing in the development of abnormall$r
large crystals, but only in certain parts of the deformed
areas (Charpy)
6. Plastic strain in practically every degree
pro-duces recrystallization on annealing below A3. (Chappel)
7. The process of recrystallization is one of
re-finement followed by growth. The extent to which
refine-ment takes place increases proportionally with the degree
of plastic deformation. The ultimate crystal size after
annealing the deformed iron may be regarded as the result-ant of these two opposing tendencies, and increases regu-larly with delcrease in the degree of deformation.
8. The temperature of recrystallization becomes
low-er with increase in the degree of deformation.
9. Given sufficient length of time the major part
ot the recrystallization-is coppjote tt7000C and 7500C,
and inAits incipient stages may commence as low as 3500C. 10. Plastic deformation of practically carbonless
iron results at all temperatures up to 90000 in recrys-tallization on annealing and the development of large cr, crystals.
10
11. The presence of carbon reduces the size of the
gross crystals produced, and also necessitates a higher stress for the production of crystal growth.
ii
Construction of Electric Furnace
Having obtained the results of investigation by prom-inent metalographists, whieh were presented in Part 1 bf this Thesis, we were ready to begin our experimental work.
For our heat-treatment we built an electric furnace. A
fur-nace which would be ideal for our purpose should have the
following qualities. First, it should have uniform
temper-ature throughout its length when heated. Second, it s)ould
have a large enough resistance in its resistance coil to transform heat ehergy at a rate such as to bring up high
temperature promptly. Third, it should have thick enpugh
insulation to prevent excessive radiation. To satisfy
the first specification a relatively long furnace iv
re-quired. According to Professor Norton of the Institute,
a furnace 19"-20" long, can hardly maintain a uniform
tem-perature at the middle portion of more than 4" length.
Since our furnace was only about 8" in length (a longer
tube was not available at the time)it would not give more
than 2" of uniform temperature. When we constructed our
furnace this defect was not thought of, consequently a uniform resistance and insulation was given the furnace.
Having thus constructed it, we foundthat the temperature
falls gradually from the center out towards the ends.In order to counterbalance this defect either more
resist-ance or more insulation must be added to the ends. As it would mean the tearing up and the
13
reconstruction of the whole furnace, if we were to add more resistance to the ends, we preferred to add on
insu-lation. So a gradual increase in thickness of insulation
was put on the furnace from the center out toward the ends.
(see kaltbng) Having so corrected it, we found that it
gave a fairly uniform temperature of about 5" in length. This was good enough for our purpose as our specimens were only 4" long.
The second specification.- to have a large enough re-sistance to transform heat energy at a rate to bring up
high temperature promptly, was satisfied by winding
bi-chrome wire into a long helical coil of about
"
diam-eter and then winding it around the allundumrinube
heli-cally.
The third specification, to have enough insulation to prevent excessive radiation, was easily answered by simply putting on enough insulating material around the furnace.
The prodedure of the construction of the furnace is as
follows: (see ftateng) First the resistance coil of
ft-chrome wire was made by holding Dne end of the wire and that of a long steel rod of about 1/8" in diameter,
togeth-er with a chuck set in the head stock of a lathe. By
thVS
turning the lathe, the long steel rod, and by holding tight the free end of the wire, it was wound on the rod
14
the rod was pulled off, and the resistance coil was made. This coil was then wound around the allundum tube in the
form of a helix at " apart. The ends of the coil were
firmly fixed to the ends of the tube through two holes and
then led out as leads. A layer of allundum cement was
pasted over the surface of the tube and the coil and al-lowed to harden, thus preventing any movement of the coil
and avoiding short circuiting. '.I Oae. end of the tube
was closed by fitting a piece of fire brick to the mouth. An envelope of asbestos dough was pasted around the tube
leaving one end open. When this envelope became dried, a
second and then a third layer was put on. Finally to keep
it firm and solid, the whole furnace was put into an as-bestos cement tube with opening provided for the leads to
come out. After having found that the furnace gave varying
temperatures at different portions, a varying thickness of asbestos fiber and magnesium oxide was pasted around it and then the whole thing was put into a wooden box which merely serves as a means to keep this outer layer of
insu-lation from falling off. A cover of asbestos and fire
brick was made to fit the open end of the furnace. A hole
through the cover was provided for the insertion of the hot junction of the pyrometer.
:lTr I -I . I . I - I I I I I I Oecf/ O .P-kl Poe/ 00-11 100// 00a/ VOC 00,0 .001 - 0,09 110-P 00+ Or 002, VO/ - 0 - --- -- - I-..-- -- -.- --.- -- -.-- - .1 l.---.--- -- - .---....-.-- t- -..-. --.-- -.- --- .-- - . I ... .... - ----. ---- --..- 0 --- 71 ---- 77. -- 7 --- -'---'-- I -7-- l -. . :1 -7- ;, j'.- I I i -.. 'I . . I ;.. I - .;: '-_ - I I I . : I ' ! I , " I, . ..-, It ' - " : ! i -1 - .. . 1 I -'' I - I - , - -':'--; -, . I I I - i I i I _;, - ) ; ' , .- - - . -i , '4 '- .' ' I !-- 7 t , - I I : . : I . I I I I : ! . ' - I, .1 +-,-!.. , 4 , i , . 4, , ; .. I- , -j , -I . . -' .- I -:'. I ! " ; - - -- . - -,-; ! .- .- ; t'. i I . - I i ., '- -' I , -- , ":.-..- 1, i. z i. . I.- 1 4- .. , , , ; I -, . , , I I I . I I -1 - - - i- -4 * ' ! I ' . - -. t-, . - I .-- '' IWI 1 hj,414 P a v S V I I I ";-".- 1. 1- -; -1.1 -1 - 'l , I i7- -w- t ,,, 4 1: I I i. ' - . 1. I " . - I ; '.; I I -. f i -J I . __-_ z - -- , --, --+. --4- .- --i -,,-,4--, i---- I -I -14PP-40 w u : ,11f; , I -j- - .11 . I I '---- 07- I . I , i I 11 ---- -1F 7,--+77 -T--'---'-- '!'- -: : 1-7 .,: -','- --i--- ---- -4,- - -i.-.-- - , ___-,- --- :74 T" --7. - - I --' -. _ ; ' I I i I.. --- '! -L - -- .- 1 4- , T ! li I . 1 , - , ; : - . 1., " '' I -1 1 ' -I-I . ! , ! : ' ' i '- " 4 -' -1 -1-1 ' -i : , i I L, ...- ' -I I I -.- -'. : !.. -.- I I '.; -7. I -- I .-& . - -11- ' '' -!, - i I ,: I - - Ill' I fo , It . . 4 ' i 4 11 ! . I 11 :- _1 i i-'-Ii . . ... .; A- ' -, p " -: : . :;,. -'' i .. I I . . . . I . . -i .1 'i.- -I I , j -t --L '; ; ' .- -I ... 4 1* I I., I : --- l -'. t. -j I I I " . 4 4 ; "I'll" t i-- .-.. .. I -.1 --+-t---I-- -- --. , -- -.- - ..---e-- , --. lw- A.l - ----7-- -- '-- 4 - . -1 I i I . / -. --- ' . -- --- ; -' ' 7 , ; . . , : . . ., !- I I --- ---.. L---i-- I -I , ; , . . 4 , I I I T , 1 : ' ' , , . . . I I -11 i - I I . . . m I ! I I . 4, , -; . 1 , , , , . , . -I : i . : . I t I ; I- . _ , - 4 4 I I" ;--, -, . I I , I -, I -4 -, : , 1 4 '. . - , , - . . , . I . . - I ' . . I I . . , " - -o , : ' . ! . , , : I I , - I . I -I , i, I ': i . , I' . I , 4 a, .1 I . . . , I . 7 I ; -! , -I I ; I : -, : .' ! . , , i- , , 1 j . I ! . I . , : _ 2 i _I i . - , I ; i I 4 : . , . I . i . i I I I . , . t -. , : 4 1 1 : .. I I i.- ' .-I. : . ' I I . . ; ' I ; -; : - 1 , - I -r- I I 1 1 ! - I I .. '- --. i---, _. ._ -- - . . I . . . - . ; I . -. 1. t I . I I . I - . i - it - I- - -- = .7 . I- --1 , , , -I : . -! . . . ; , 1 i , , .i I -: i ---, . - " . . I t - - - 1 -- -- -;- -I I I- I : ,,-.,, , I . , I -I I a -1- . -- 1- . . . . . - -- - -- 4- - . -- - - -- , - 1. . - - ---. , --- -- -- --. .-_- -- '- I :- : I I I I ,,, --- 1 ... .... -1 -'. t . -.- --- --t- . -i-- -" -. . . : , -' i 1 , -; - . , .,-- .-.. -- --71- , i ; , . . ; : I . i I , I , I ; ; -L I . f '[ , I 11 - . L' '4 1 ' --11, ... -4 -' I -, 4 -1 i , , ! ' ' I ' . - . j - -' f , . . , . I I -- -' * "! .' I , . . I . -- . I -; : I I : , I . i 4 . . I .; ; i ;. .. .-- -I , 1 -! l -i -. " -1, . -1. -' ., -i-4 -- --' . .I : . --.-- I -11 -. i ; T I j , , . ! ' . . , . . ; . - t-' - - - I ' I l i -. I ' ' I . I . . , i t . I I i ; 1 4 I I . , j 4 . ! , j -. j-! , 1 : 1, -. , -I .- ' -I -:x I , -1, -i -. -; L . I . I I -. -11 ' . : I ! I . , , . ; - I I . I I ; L-- - : . . I . . . .. 11 i I i j i I I -; , i I i ; ! , : 1, ... I I , ! !' -f -'; , , I ' I f I ; . ; . , , : i 7 4 ! I I I . ; . . . 1 1 . . , . : , , -. I - .-11 -4- -11 I . , I -.' I I I I --- I .--- T- I- -.-l 1 --- -.- -. -- ..--- .. -.- _: i .--- -.-- I t-- --- - ----I.- I -- I --- .4. ., -.- ---- --. I I . I I ... . I ' ---- .'...-- -... -, -.t.. .1- - "---.- . . -4-- --- . I I ' ' , * ' . I . . -, I I . ' ' ' ' . . , -' --: --- r I I . 4 -'. ;.! I i 1 t ; - J.- -- 4 : I-L i- , " t '' ' - : . ; . I I . . : . ; . , . -' -' 11 i ; -. 2 t -. -. -. ; , . . 1. -- + I I . , t 7 ' - ' I ' I I . . . . I , I . : -, : , i I . ! 1: ; : . i -! -, ; j ; ; .- x:_'I , I , i , . . ; . : I . i I I I . -I -I . -I . ! . : 1 , I ; , , ! I , 1 4, 1 -,- . I : -, -I ! , -, , I 7 . i ' ' ' , , : I 4' -- I I I . . . I - t--1 I . '. i : , I I I ! ; _ , I -i I J -: I -.4- :' " I ; 4 , -I I ; : 1 : , . , !! : : . I , I -. . . . . . . . , . ! f ' t 1 I - i , ' - . A I . i I :" - L I , , j ' . . i . : : , --- -1 --t-- L . " . L : --.- -- -- L I - _ _1_ - . -,. j - - I - I .I,. ': -, I ; , -" --- I . , -,---- ... I -- ! ; i I I . --- , I -- --- , , -- I- ,- --- -- -L-] . --- I -- - - I - . I , i I I - I.-i- - 11 . ... --:--.- --,-;- '- - -.--. -. - . -- - :LL,41 I ' :, . . I - : 1 , - - ., I - .4 ... , - , I - I . ' 1- -- ---- .-. -- -; -!-4- -1 1- 7 1 -!- .-; . *' . . I -' -I :.. .. , .- -' I.. .. . .1 - , I . i I --- -, . -li I .i 4 -I L- -l ,, , 1 i i --! ''I " 1, -: , . ; . , I !-I-,--: ; : i I I 14 ! 1 , ! -j i- , I'l . . 1 - . . . ; i -I ,-:,.,.t -- i t]- i , I 11 -: , ;''' I f., _ . it, i4 : I -' -: !, -1 1 . I ' , . , i z I I : I I . . ' ' ! ; I " ; ! ; - ] - - ' . : , ' '! - I - : t -I I I ' ; -, 1 -. I -. -. -. I ; -. 1- , ! -. -. - , , , , - ! -. -. t I -i- -. I I I -. I ,--,-, , ll-l-'; - P -i-." 4-i': i - -1 11 -- - + . 1 i !
i . . -..; L .1 . - . ;.-; 1, " - - . . i-''I I I [P- :1 1-: -- . ;- -i , i --1.; i-! "'., 1 , -.' ''; I " .' 1. . I . -- -, --.--. ,-, --- -6 . --- - - - -...- I'- - -- '- -- I -4- --- I -I "I ... ''I'll . ,-.-. --- 7...'.----l- -'.--t-.-..-.l ----..- ..---.- . - ,- .---..-- -- t--- --- 4-..- -.- - -_ -- di ..- , , t : c -- . I I -i : I 11 I . . . . I . b - . i , ' ' ' -I -'- : , ; , --L-1 "-i- L -. I ! I -. . . . I I -! -! i- -I I I I -, I I I . I I" I : * I -'r -I . i. I - , ; I . - : i : , . ; : . " -1 , : 1 , . : I . -'- -" i d.j ; + -1-A- . -; I i , 4 , , , . . , , -I , 1 . . ; I , , -, -, , . I . ; ; : , I . ; : . . . . . . . I . . I 1 - - I 'b ;. -1 I - r I . I . . -1 1, ! I b . . . . I . . i - , I : , . I ! i .- A 1 . ; -; ' - : - - .4 I 4 I i ; ' L - I . . , . , 4 , I I I ; , , -.- 1 -, '-. -. - - " - I -. I -. I : -. I I ,; -! , ..i . - I I . . -., I . i I -. i . , , ' ' --."- ---- , -, --- --,.I -J. i I i , I -: ' -1 I J- --4 1 -I--- -- . . -4,-! , -1 -' ' ' . -I .- - - -I - - - - -1-- -I -I"- ; -- - -- -- --- I - - I . - . . - - : . ., - ;- , , 4 -- % I i ."- L" --. 1 -i. ; -4 , ---L . --, -, , --:- -1 . -. . --.- .- --".- -.:- .. ' . . I I I i I I -- i-i . I I I I I I , . : . -. ,-;- b , , . , . . . . I I I . i , . - . - ... . ; - - i - I I -I -I 11 4-r' -41 . I 11 . --! t '- 1 ! : : I : -: 11- : " _ 1 , -, -, I . . ! I i : : I , 1 4 4 1 --- I , -' ;. ---. -. I I -I -;-- . ; . I " i- V" , -I : . . . I . i I - - i - . ; , I -: , I 1 I , -'- - ! i , I 1 . -. I -. d-,j , ,-., - i- - ll I I E I I , -. I- - ; / 1 " --. i , ; I : , - - 1-1 " : - - ' 4 + - ' ! - - I . ; I , : ! -. I , . i - i - I I , + -7 -4 4 -1 ' 11 .. .. -1 : , . j , . . -; -. j -i ; I t i i I i . I + 4 , , -: . . . I -1 , -L- -1 .1 I . , I I I I 7 I I -, I - ,--.. I - .- I . - ."- - .- I - 1-1- -- .4- - '--+- 4-' : ,-., - .--- -- ..-- ---..-1-
. - 1! -; - - ! , . ;-i I i - -; 1 4 -1 "I i , , , L 4 . I I . - "I
-- , _ , ----.---- --- .- *1 f L I 4 i . I --1 .,---".. --- .. ---+ '--- --- ----4 7. -I.- --. .--." -'6 -I . . I , I - . I " --- --L-: -b I i. : . i . , I -. I -. . . 1 . . -_ -_1 I- 4 1 -:7: I -- . I .;I r T 7 I 1.1 i -,_I_. .. '. -t ,,, -44, , - --11 r ,I ' +-1;;;; .. , : 1:: .-l' -' j: -; -.1 !: I I: 1. , , . - I, I ': -- - - - _4 ... - ; I:. . ,- ; , i -+ ,I -; ":. , 4 , ' I , - , I I -I -- ' -- : " 4 . -. -. . 1 4 + ' 1-i !-Ii I - - - -. I I -. i : 1 - I- I -. I- -t -"- " " -, I : : : ! ' ' : 1 1 ' .-f i 1 . I . ; -- -- , . I . I ;!: I I t 1, t -L , ; I -- il - I -L-i.: I t :: ' : _ '-F - 4 ' j. . I . i . I b . , . I . I I I I' 1 1, I I I"' -.- -''- - I-- I I i I I I ' ' i- ; . . . , , . I 4 : I . I -1. 4 i , . -, I b . ' I - - ': - - - - -, - '---. - -, -"4-- i - -' . - - I - .. . - - I .--. . -' .--- -- - . -1 - . ... . -1 1 -i 4- -' :4. , -. . I- -I .- , ..- .1 , ---+- .-I --f --- -- - - i -+--- - I - ;- -.. l- -l- -_I- I -1 -. I -j' 4 -L : . -I --!- --t-I -, I . I I -. I t ' , t i -I I . . I , 4 1 . I . I , . . -, . , I I I -.- .1. . . .. b- L I , A ' i -, , . , , i - ' , - I . I i : f I - --I , . . ; . . : , . . , " : . - . , - , I ' . , : I ! -: , '! . -, -+ 4 I I -, I -I - .1 I . i r ' I I -. -.; I -. -1 I , -I -! I . r i t .1 -, -. ! , -I- -7 -, . I -. . , : i ; ! 11 , ; I -; , , ; I I I . . ; i : I I I .: : .. , " . , : I I I I ; , . : ! - . . . I + . I , ' - - 1 f . ' . , ! ; L I 1. -t I If - -l . . . . I : . : I I . . . + ! " . i I I -* 1 1 -tfi+ : I : : I . '' :..' .. -' . i -: _ I t . -- ! , I . , I . I I , , I I *1 . I f I , I .. . -- - -- .- - ' : f- , t--L I . ., -T 4 - .. 1 : - : bb I . . . 1 ' ' --" -.b . , . ..- 1- '- . -- . --T --- ---': -.- , ,-,--- b -'. --lb- I -I --- -... -11-1 - -I.-.. -I I i -- -, -1-b--- -I .-t-- -..--.---.-. ?' , -- , . --- ---- j , . .. -- 7---'t . -- .-- I . , I I -- s -.- - . -, , , . + . I I ; q, 7 -. ! , 1, .- -- .1 -11 , I ' -'Ii --.-I.N ' .i -1 ... :: : I I . :ft -I - i ! I I I i I . . . . I ; . -. I I . . 1. , -. ,It --- I I z t . I . I I , : . . : i , : I . 1 ; I I . -,'- i-"- -- I ; I , 4 , . I . -I I - : ' . . ; 1 t - . - . b . ! j I ' 11 ' ! I :i ::: . - . I t , -; - - I - . I I : I i . . I . . I I : . I . ' ' ' . t . -, i -- -,: 1 -4 ! * , --. , - - - - -11 -fl 4 . -;-, .+ I I t . -I I. ! .1 7 - . --1 -' -: - -- , ' -- __-- ! , ; - - - -,-- - i . l .-- -- +- . .. . I - . I . t - -- I . I . -- t] -'. , : , - : - . : - i -- _; --- ---- -:- - , - 44. -.i-. - , ' I -- - - -- --- . 0 -4 . ---- - -- - . .-- -- . , - - - - + : f, - I --- -.. - ; - . --.. , : I -; I -,--t4 i-4 I ; , , "I ' -i , , I I -i I . . b + I : . I - I -., . , z I i- ' ' 1 t , 1 .!4 -I J- -1 1. . I 1 -, I I I I 1 . I I ! I .. , -i ' ; ': : .. , ! : . . .; I I i : . , . : , , : I ; : - i 4 .. ' -1 4- -. . I 1- -1-1 -; 4 1 - I - -.- - -I I - I .- - i I -1 . -. -I , I . I . I ; . . - J. : 1 4 ; I - ,-:- -- I : I mw-v/ I I : -i : ! .1 I ! , . I . 11 -; , i -I T -' ; ' I 1 , - "--, : , ; + . I . , I . . --1 I ; . -I I :::: -i -I -' : : I a ,? -of & .0 , . -, I : - : ' I - I , I I ' .' ! ' l - I .- ---' --- I--- - I L il , T -. ,-. - . ----. - ,-,- ..- : 9 . . I . . -1 - - -" --- , - -- - +- .. ---.- ,-..-; , - t . - --- -, - +.t- -'.'.-ll-;- ---. - .. - i.++-" --- - I . . I- - . - --- 7 1 1 - ---- - i - - -- - I - - - -+ --- r-- --- -4 I I . -" I ; b.--.-+. .- , i ... -4---- ' ' ' --' 1; , 4 , ; I -f . -: 4 ' , . -. -I I I t . I I I . . . . - . . I ! -- . - ; . i - . . I : :_ , q . - b I I - - I , . ! -j-" , I - 11 -4 - . , "I - , , j : - , , I . . I I . p . I 7 - . . b -I . -' . I I . I . . , i -! -, , j - - I . I ' . I I - i . . I I ' ' I - . . - i , i "I , I i 1. i -- -, b . i I -'.:: , : ' ' : : , . : I : ' -I -. -1 t I . -L I I i , . : I , . 11 I ' i . I I i ! .' ; , i i - I I , -I- I i ! -11 : . -! '- : l I- -11-1 , , , . -1 --- I- -i I I ! I . . . p I - . I -1 ; . . I I - . . ; , J ! ! . . - .. -! I I 11 -. . , ' , , , : . f - I ' - I ' I I : I I - - -- . i -. , . I-,-- - --- - I - - . :_ --;-:- .. , , , , -I ' i i -.- '-.. -+ --I---- -- -A n( i U qlj w -P O : - , ---- , -- ,- I - -- -1-b ' ; ' - I -- - ---- ,-- . , , . I -- I I ; -- . ;.. -j . '+ I 7 T .-'- t +' 't '' , . I . , I . -" .1. 9 1 ; I + I : t I ' --.- -- ' -1 , 6 + i . , 11 I -. I L ; ; ; : , t -f -I '/O ; -I -I i - . -I i + . I . I -t 1 . 4 1 , 11 1 41 I -. :t- -i .-i- : i ; ' I ; -. . . 1 , , : . 4 1 ; - , : . I . . . ' ' ' I I . + ' - I . ; . , 'I ---I--;, .'' 1 ;.!. !- ' 4 -.1 ,,, F, -.. I '. -: , b : I -i . -I 7 , , . j , : -I ; , I . . I I b b : ; - - , - ' - I , . I . . . . . . ! 4 , , . - I . * I I , , , I . . I I i ' . - . b , . I .- if --- . '. ' -: ... --I ... . ... 11 -11. . --. 1 -J- -- -I - --I-- -, - -.-j -.-.- --T-..-. -l.-l-. -..-. l--.. --- ---,--. .! -... --.. '--- -.. ,-- . -.-- -- -.-.--..-.-;- , - - - -- '.- --- j-- - - - - .. - - - --- , i,-.- ---- . - . I -- '. - I --- - : .4 11 il -7 : T -I T ... -.. -- " 7 -7 -i ; 4 i I -. . I . . I : ! !-.- . ; . -1 I i , 1 - - ; -. - t I, i- i 4-i ; : . . . ) , '.. " I . .1 :F I - -IV) '- - - ; - I I I b I . .. I I I I 4 - . . I - : , ' , 7 - t - I-- J- . I . I I I ., I -, .: -; 1 -; -i t 1 I . -I : - - -I , - - -I -I ' - ' - . . I- -, -i- . , . 1 -. -.-- . . I I ; . . . . . I I ; . , . . . . ; . I . . i- 1 , 1--;- .' 4 .. , . I -. . ; -L . . -; -i I b . - - , 4 - , r- - I ; 1-' I : I ; 1 J . I . . . I , _. ; . ; . ' . - I I I I . . : I I 7 I I L I : I ; - I - I I- I I i - - I - - I , .-....-.-. -,.. --- --L--- -..- . - ,-- ! , , - , 4 -1 - - - - . ,---+4---, 1 - 4 --. , : - : 7 . . . - T -. - . - - --- - '.- It -- -- '.. -- I I- " -4 . . -t - -i-i - . ;J -f 4 -. - .. . - - -' - -:- --- I . . .--- - --- , -A -I.- . --. . I I . . . QQ I- . i i I : i I ; , . - I I I I I . - ; . . . ; . ,- 1 z - , 4- - . . . '- - . L-1 I- ' -- - I 1; f . I . l: I I : : : . I . , I - - , : - i '. -: - - ; I , - !-i -- ! I , I . I --1 1 t 4 , ; -11 -I . . I . 1-4 I . . . . 1 - . I . , - , , I -- -1 . . . . 1 -1 j - +. '_1 , -I -i- : , -1 I , -j -. ;' i , - i-, ! i -, i-.F -I : I .I I . I . . I -.- . I -..-,-, 0 . I I -+ -. -. Zt *:i 1-. L- I ! -. -. 11 -. : -1 -. I t I I i ; ; ' I ; l -- i I . 1-1 I . I .- ; , . t . .1 I , I . . . ; I , I : - - ' 1 -4 - ' : i l i ... i ; I -1 -- I I -I . , -!.-. , - , ;- I , : I !- i . T -' . . I . . ; i i - I b -. I --- .-- l.. --.- -- . 11 --f .. I --- _ _t_ _ --;_ -11 -1-1-1 --- - ---4'4t-l -- - --, -,- -I- I . --.- .- . -4--.--l-.L.---. - -. ...- . * Ir 7- -- - - --- " -- - - - , -7- '" "' --- b 1 1 ,-- 4-'-- " - - - ! ' "' ' ' . - ,- -A -- I--- - --- . : I - I 14i 'It, 77 I . I , . ! ' i ' : -- ' ' - , I I- - -! I 11 . : ; , : , I -' -I + I ' ; . . I I - - 4 . I - i . . . . . , 'T t i : _-' -I I I ... . . . I . I . I . . . . i I 1% . 1 . i , -I , -f I I . -.1 I --!- , -'- . 1 , ! , ; * I ; -. I I I -- :, - . , : . 1 :' -, , ! , 4 I- . . i I . , I I . , : I . I . , . , -. 1 , t I 4 -' - . , - I - , , , -1 - , - - i- , F ' . . I . I ' : ' , '. - i - , - , - -- ) : --i -i L, - - i , - . I I ' - -.. ---- -- -. -. -. --. +--.. 1.4 -! -;-- :- i, - ---- I -:1 , :. -'I w -L'. ,--' I i -I-- -- '-.- _LL!'_1 L, --' -1-11. -!-- ': i .: I : . i - - -l . - - --- .r __ .1 , I . -f , , ; ' - i 7 .11 '' .i , - '. 4- I- L., . - . - - - . I - :_ . I . . , , I I ; ; . -, i i- .- -.- , , i , 1, I i- . i -7-1 ; I t - - . - - -; I - . - ' . 1 -, I... .-i - I . . ' ' . -- " ' . ;'--T 1 1 L ' ' ! ! 1 .: ,-! , ! l ' ; I I , -1 1 4 I ' - :_' - I ; -' . . . : . I I I I I - - .;- Il ! :-, ! , , : f,- 1 . I. , - . ;. . . I I - , - .- I . I I I . I . . 11 ' 1. !: .1'. I ... . 1! I i I. I . I- - - - - I , t . - . 1-: i I -A I . : ' : ! . - . : .1 ' . - 1 - : - i., I j " +- " I - . 1- . 1 1 . . . I I . I '-" I .- , , , i ' I . ' . : - . ! L---.-..; ----. -11-1 .I - .I . I I ! I ! , , _ j ! 1 1 .. 4- I -. 1- .. --.- ---..-..- --,---.-.- -- -- -- -- I I--' . -- ,.---- ".. - - !
-U , -Lt IIIEMIME3Ifl!!!!fEME iiijpm. Ut
ItI
I+44
m
4--4
mI
-na -.. flg44-au r.4mum ma -I ... m ... iUm Am4mu4m== a aam m4am+a
;4
I.T
.im-4 H-mn t-.. ..-....- ... 4- ; .... 4.. . t. --. .--~ ~ m -i -. -EEIE ai i-*.I MM iIIE IEEIIN __4l 4iBHEi T 71gg inagggg1a 1usngg 1~ T lunian~~~~~~~~ T45=-.ai~=ii n~eHB.!E naaas-e-a-mee.mesees-~messmmssmmnesasesemane.:::::mesesenesaas smeses -a ees..==Calibration of Pyrometer
For measuring the temperatures in the furnace we used a platimum and platinum iradium thermp-couple connected
to a Siemens and THalske millivoltmeter. In order to be
able to read the temperatures directly from the
milli-voltmeter it was necessary to calibrate it. The method
of calibration is as follows:- The hot junction %* a s
standard thermo-couple was tied together with that of our
Viermo-couple, keeping the ends of these
junctions
as neareach other as possible so that they would receive the same degree of heating, and then they were inserted into a steel
tube so as to insure uniform heating. These junctions
thus kept together were put into an electric furnace. The standard thermo-couple was connected with a portable thermo-couple :pbtentiometer which had previously been
calibrated. Its cold junction was kept in ice water at
00C. The cold junction of our thermo-couple was placed
in a glass bottle kept at room temperature. This glass
bottle was insulated with cork so as to keep the
temper-ature in it as near constant as possible. Heating the
fur-nace up to various temperatures between 2000 centigrade and 12000 centigrade, readings of the millivolmeter and of the :1pbtentiometer at each stage were taken simulta-neously, temperatures corresponding to the pottetiometer readlngs being obtained from its calibration plot. Then
16
the current was turned off and the furnace allowed to
cool down.. Readings at exactly the same stages when the
furnace was heating up were taken. The average readings
of each stage were obtained and knowing the corresponding temperatures, which as mentioned above were read off the
potentiometer calibration plots, a calibration plot with
temperatures as ordinates and the E. M. 1. at the Junction
in millivolts as abscissae was made for onr millivoltmeter.
with this plot we were able to read the temperature from the millivoltmeter.
Having the furnace properly connected to a 220 volt main (see drawing) and the pyrometer arranged, we were
ready to begin our experiment proper. One-inch "Burden"
ir on r ods ( c .o*%;t
=.2SK;
p - 59%jn 0,25%; s 1 0 D5%)slag -.16%
were cut into 4" long specimens each of which was
syste-matically numbered. The program of heat-treating these
follows:-Duration of specimen held at Annealing Temp. Annealing Method of Impact test Spec. No. Tensile test Spec. No. Reheating Temp. Method of cool-ing of Reheated specimens 1/2 hour It " 28 29 a 7 43 30 42 31 33 41 32 34 40 35 36 44 37 38 45 39 46 Temp. Cooling 7000 7000 7000 7500 7500 7500 8990 8000 8000 8500 8500 8500 9000 9001D 9000 9500 9500 950o air cooled
oil quenched(Reheating in oil air
(bath at 30000 for furnace coole# 15 min.
air cooled Furnace oil quenched ' air cooled Furnace oil quenched " air cooled Furnace oil quenched-air cooled Furnace o8l1nquenched air cooled Furnace oil quenched I t1 17 5 4 3 2 12 1 11 18 10 14 16 15 21 22 20 27 Raw Material cooled U I-s
18
After the heat-treatment the pieces intended for the
tensile tests were turned into 2" A. S. T. M. standard
specimens (see Plat6-;g) and those intended for impact teste were turned down to size according to the specifi-cations given by the authorities of the WateZltpnn
Arse-nal. The tensile tests were made at the Institute
employ-ing the 109,000 # Olsen machine (se. ctc ). The
loads at which the scale beam of the machine dropped sud-denly were taken as the yield point of the specimens, and the loads at which fracture occurred were taken as the
ul-timate strengths.
The method employed to obtain the total elongation in two inches was to measure, after fracture had occurred, by hold-ing the fractured ends together, the distance between two points punched on the specimen before testing at two inches
apart. The difference between the new distance between
these two points and the one before testing (2") gave the
total elongation. The contracted diameters of the broken
specimenswere obtained by simply measuring with a pair of
e-ordinary calipers.
The impact tests were made with a Charpy machine at the
Watertown Arsenal by the Arsenal authorities, as outsid-ers were not permitted to enter this Government munition works.
19
physical qualities were picked out for microscopic
exami-nation, in order to see tieiiMicrostructure. Portions
of the specimens near the fracture were not used for this purpose as the crystals there were subjected to the ten-.
sile stress and would not show the real condition of the
original structure. Consequently portions near the
thread-ed ends where no sttain was apparent were cut and polishthread-ed
for use. Considerable care and patience were exercised in
polishing the specimens. First the surface to be examined
was ground flat, using an ordinary grinding wheel. Then
it was rubbed over with the finest grade of emery cloth. After this it was polished on a very fine alundum stone, rubbing always in the same direction so that the scratches
would be parallel to each other. Then it was ptt on a high
speed alundum wheel, placing the surface on the face of the wheel in such a way so that the new scratches formed would be perpendicular to those obtained in the predeedi
ing process, and polishing this way until all the
scratch-es has disappeared. The specimen was then polished on
the rouge wheel, taking away whatever scratches that were
left and giving it a final touch. During all these
pro-cesses of grinding and polishing, the surface was kept wet all the time and precaution was taken not to press the surface on the polishing medium too hard so as to bur-nishniit.
