The Behaviour of Some Cast High Tensile Beta Brasses Under Tensile Stress in Air and 3 Per Cent Sodium Chloride Solution

44 Pages·4.505 MB·English

by  Bailey, A. R

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D issertation fo r ■ - I MLEX, B#Se*
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Ann Arbor, Ml 48106- 1346
January 1951*
V.C.TBS- BEHAVIOUR OF ;SOMB: OASf ffidH flW aiLE BETA BRASSES " ■
v m m m is x L i -stress b ia ir k ro 3- p ir ca irr sodito ' chloride
' ^ SOLUTION" -v-
D issertation fo r M»Sc*(Bng*) Submitted by A,B* .BAILEY* B»So» ,
WM ’ART _ . ,W ,., ,,,!-
I t was known that cast 50-ton beta “brass { containing
about 5 per cent aluminium and 1-2 per cent each o f Iro n and
.manganese) was © specially susceptible to in te r crysta l lin e
fa ilu re under te n sile stress w hile In contact w ith sea?water
or 3 per cent sodium chloride solution* . ,.N The prim ary object
of the present research was to determine the influence o f ;
aluminium on the In te r crysta l lin e weakness*
A rang© o f sand cast 40-ton beta brasses, containing v ^
from n il to 4 per cent aluminium, was tested* fh© a llo ys
o f low aluminium content contained additions o f Iron and
manganese, and In a few eases, o f n icke l and tin , in order
to give the desired te n sile strength* A binary beta a llo y
and the 50-ton m aterial were included In the tests*
Although in sp e cific cases the re su lts were inconsistent,
rapid In te r cry sta llin © fa ilu re in s a lt solution under sustained
stress, o f the order.of the 0*1 per cent proof stress or
higher, occurred only In the a llo ys containing 3*4 and 4 per
2*
cent aluminium and the 50*ton brass w ith 5 p e r, cent aluminium*
In ter crysta l lin e fa ilu re s also occurred in the susceptible
alloys a t high sustained stresses in a ir* The 4 per cent
aluminium brass was most susceptible to in te r crysta l lin e
cracking in a ir, there being lit t le difference from behaviour
in s a lt so lu tio n , and cracking was not proven ted by immersing
the specimen in liq u id p a ra ffin or 'xmchine o il, o r by coating
w ith p la s tic * The weakness in the high alum iniua a llo ys
was indicated by low re su lts and in te r crystal lin e fra ctu re s
in ordinary tensile tests w ith the specimens immersed in
-.salt solution • - V*’ ' k7.,:,;'-. "7~: 7.,'7. ’
I t was concluded th a t aluminium was responsible fo r the
in te r c ry s ta llin e weakness, causing a condition o f b rittle n e ss
subject to aggravation by corrosion, although micro*examination
gave no inform ation to explain the b rittle n e s s i /There was
evidence th a t co*pres©nee o f Iron and manganese opposed the
weakness* 71 ^777 77,’7 7 \7 :'f-7..
January 1951#
' —THE :Bim iO UE^0FrS01B' CA5T HIGH: TfglSIXil Bgm'BimSSEB ' "
PTOBB feKSILE VSTitES3 j l - AIR AMD V FBH OBIT SODIUM CHLOEIDB
SOLUTION '
D issertation fo r M.3c.(Eng#) .Submitted by A.B* BAILEY, B.Sc.
XHTaOBHCTXOI and O B J E C T S "4;p
f-" 'Binary beta brass;is scarcely a h "In d u stria l m aterial,
b u tth e ' cosm ercial: h igh te n sile brasses, "although m ainly "
o f the alpha-beta v a rie ty , do include some a llo ys1 composed
of the beta phase# - The. high, te n sile brasses"'(or manganese "
bronzes) were developed to me®t the "demand fo r -u non-ferrous
a llo y w ith the sam e'density and strength as m ild steel ye t
possessing a "greater resistance to corrosion. ' 'They' contain,
.in- addition to copper'"and ■ sine,'" u su a lly two' or more of "the -
follow ings alum inium ,: Iro n , manganese, tin , lead and’ some*
times n icke l and s ilic o n . These elements improve 'the' "
strength o f the a llo ys, or in the case o f lead the machin-
a b illty .
ji- '"7 These special brasses' were'"the S ubject o f'a ' B ritish";"'
Patent as e a rly as 1876 and' numerous compositions have been
developed, such that, there is a need fo r some standardisation
A number "of" w rite rs 'have described the e ffe cts o f "the "extra '
elements* gives a general account and a tas©Jlil , ^
bibliography# As pointed out by M ille r, u ltim a te te n sile ^
s tresses s lig h tly "exceeding.;- 50 tons per sq* in . ©an. b©;: J;
obtained In the cast ecm ditlon, although a llo ys giving
figures o f about 40 tons per sq * in * or lower ar© preferred
because- .they--‘are more d u ctile • brasses are ..used; in
both cast and wrought condition* although more often in the , ?
form erj castings range in size up to 50 tons or more# , :-.-fhe
applications are varied! in p a rtic u la r, marine purposes,
such as p ro p e lle rs, rudders, gun mountings and non-magnetie
- moun tings fo r compass©s , may.-: be.men tio n @d#. . v w
^ I t M s been known In =, the Indus try , fo r considerable , ^
time that certain .high te n sile brasses are prone to fa ilu re ,
often in te r c ry s ta llin e , under stress when in contact w ith
molten ra ta ls or in corrosive o environment Instances have
been reported in the l it e r a t u r e f * although apparently
no system atic work was carried out# About ten years ago
the B ritis h Ifon-Ferrous Metals Research Association sta rte d
an Ingrestigation on the In te r© rysta llin e fa ilu re o f brasses,
© specially those containing aluminium, in various media#
The re su lts of th is work are described in Association reports
and In 'a summarised form In the technical press#***
Prelim inary experiments by ¥oee on the e ffe c t o f sea w ater,
carried out on extruded binary and aluminium bearing alpha, ,
alpha-be ta and beta alloys gave In d ica tio n o f In te r c ry s ta llin e
weakness in sea water under sustained te n sile stress in beta
a llo ys containing aluminium, but In none o f the other alloys#
During this work inform ation from In d u s tria l sources Indicated,
that in te rc ry s ta llin e ■'■failure in sea water was p a rtic u la rly
prevalent..' in the eoromercial cas t b© ta .bras 3©s containing
about 6 per cent aluminium and l-B per cent each o f Iron and
manganese and which have an ultim ate te n sile stress of about
50 tons per sq# in • - Tests were made by Voca on such m aterial
w ith varying e ffe ctive zinc content a and o f both laboratory
and in d u s tria l preparetion, side by side, w ith comparative
tests on. binary-beta,.;braas.#.:*.;^Voce®* showed th a t the sand
cast high te n sile a llo y was prone to ,ra p id fa ilu re o f In te r­
c ry s ta llin e inception a t sustained te n sile stresses approxi­
mating to the Q«1 per cent proof , stress when In contact w ith
sea water, 5 per cent sodium chloride solution and other
chloride solutions, although In certain conditions the wrought
m aterial was apparently Immune# On the other hand s tra ig h t
beta brasses, whether cast or wrought and Irrespective of
zinc content, showed no rapid in te rc ry s ta llin e fa ilu re a t
comparable stresses# The p a rtic u la r weakness o f the 50-ton
a llo y was also revealed by simple bend tests and ordinary
tensile tests w ith the specimens in contact w ith chloride
.solution#
Th© .prim ary,object'..of;.-.the;■-.next; stage, of the research ■
was to investigate, the .Influence' of. aluminium on the weakness
^ The use o f th is so lu tio n , made from ♦Analarf sodium
chloride and d is tille d w ater, was adopted fo r convenience
in subsequent work as experiments flowed th a t its e ffe c t
was s im ila r to th a t o f sea water*
Of the high te n s ile : a llo y * y,;--Por,:this purpose, - a:, range o f .
. sand/cast/high,; tensile': beta ;:brass©3,-,'containing'from" n il' .//--y.:
. to-; 4 ,per. - cent ■ aluminium and.,having1 e sse n tia lly' similar;/-,-
/ tensile^ strength.*'-'was t tested*.:,::.':, The 50- ton a llo y - and: binary y
be ta were >-■ a 1 so / include d, in th©y tea ts * /; ■/ y; y ;;
, c;/ y:;- Thisw orky(apart from /any/©hemlcaX:. analysis) was carried
...ont.::by;;th#icandIdate'v:in.-/the':/Assbciationt-s. laboratories;/
^during?the?period-.October; 1944 ^toyJ\ily':1046*;- yyfbo?restilts
0 * 5
have been- published:.- in.; re p o rts • aM/summary . * form* -The....
follow ing is ■ a,-somewhat expanded/and m odified account•
'MATURE OF TSS TESTS#,
In the m in tests a sustained te n sile stress was applied
to the specimen w hile com pletely Immersed in 3 per cent
sodium chloride solution, and p a ra lle l tests were carried
out in a ir* O rdinary te n sile tests (a t a slow rat© o f
stra in in g ) in 5 per cent sodium chloride solution and in a ir
were performed to d© termlne who ther shor t- time te a ts would
glv© any in d ica tio n of s u s c e p tib ility to fa ilu re under sus­
tained stress#
ExmnximmAh procedure.
Preparation of the A lloys fo r Test* .
Although 1& most cases suitable data is not available
on/ the': complex equiIIfor 1 a - InvoIve d lu M gh tonsil© brasses, zy/
and' ih ; any has©vwould'b©;vd lffic u lt vto-r©pr©sent- and- in te rp re t
alloy" compos!ticns?can^ be worked-out/to? give a p a rtic u la r ■
struciijr© -by?using-;C M ille tf s -o rig in a l 'c o e ffic ie n ts , /’possibly
w ith the; a id o f - a:-f©w? tr ia l - experiments The s©: co e fficie n ts
express' roughly -'the -zinc- replacement ’-capacity 'of /-■ the other' -
allo yin g elements, thus enabling■ a fig u re fo r the to ta l zinc
equivalence.-to b© . calculated:* "/? By re fe rrin g th is :figar© .-/i
to the binary copper-zinc phase diagram/th© -lik e ly -basic .
structure is "indicated* :/ d u ille t* s 'co e fficie n ts fo r/ the /
usual "additions; to "brass are "given below;
: ; ■ /' Flement // -■/'/y/y Equivalent' Value' - ”//- y.;
’'-Silicon:■■'■/■■■y /y y y - i. 10: /-//-.■ //-/ /-.»
: ; Aluminium © :
■ / / Tin ' / . /// ////--/; 2 /- , -
/' ""/ :y ' ■ h e a d . / / " / / I //// ;/--//;: /-■,
. "Iro n ;%y -€U9"'-/ ■///■
y '" Manganese ; ^ ?/-/■ 0*5 . - '^/y.
Fh J T i V M y -1. 2 / /-z/
Thus 1 per cant o f s ilic o n has sim ila r e ffe c t to 10 per cent
o f zin c, and 1 par cent o f aluminium is equivalent to 6 per
cent zin c, whereas 1 per cent of n icke l approximates to 1*2
per cent copper* I t w ill bo appreciated that in order to
6*
fin d the sine 'equivalence in a; complex- alloy,- the equivalence
o f ,-1h©-'extra,-elements is 'added::to--ibe^pereentag© o f actual
zln c| if:-tM s ; total::figune is x ■then^tiie-eqiiivalent -sine-^
percentage,,of,:-the.- a llo y is'.-equal to XOOx-divided by .thesum ;
of'f;x1.»nd- the ^ percentage of coppen*;:J; ':A l^io u ^i"it is ©greed
.that equivalents;-: o ffe r only a^noughnguid©; 'to ;:b©.:tis©d:w ith ’’ • •
care , w i th in : the/ usual:- range v of,-©ddi tions surprIs in g ly
accurate forecasts, can of ten be made • In add! tio n to ''"their
e ffe c t on;> the:basic ;,struettir© isomer o f the.: extras-alloying ;
additions! in tro.duee : a -new -pha se ■■ in-the > brass * ' fbua - lead * ?.
is . insoluble,; andrthe^m ajority ;of : iron: appears'-in--compound w
f o r m * f u r t h e r t h e ; presence: o f rtinm aycause- the - occurrence
of -©"-phase s im ila r. in appearance : to th© delta ’phase :o f "the
copper-tin system*
w, por the "present work,"-f^om in fo rm tio n /;contained;; in ’ the
literature--seven:com positions were- selected, ''a ll "having :©n
equivalent-2Ine co n te n t,;based on G u ille t*g c o e ffic ie n ts ,.
o f approxim ately • 48 per cent, and aluminium varying from n il
to : 4 per - ce nt ♦ A & dlti on s of .-manga n© say - iro n , ' n i ckel -and1 .
tin were adjusted to give an estim ated te n sile strength o f
40 tons per sq* in * in each case, but these additions were
varied as littl© as-possible, from' alloys to a llo y * -■ ; fh®:1 >FV
. com positions-obtained ©r© given in:-’!feble';I | they ©re