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Engineering Alloys
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!ngineering "lloys
#E.g. stainless steel, cast iron, aluminium alloy and etc.#Iron and its alloy (steel) account for 90% world production of
metals due to their mechanical properties (strength, toughness
and ductility).
# Ferrous alloys (based on Fe), nonferrous alloys (based onother
metals.
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ear teeth
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Production o iron and steel
#Iron e!tracted from ores in large furnace (Fig 9.").##o$e acts as reducing agent to reduce iron o!ide
#&he iron (pig iron), in li'uid form is transferred to a steelma$ing furnace.
teel ma$ing
#lain steel, up to ".*% carbon (ma+ority 0.-%)
#teel is made by o!idiing carbon and other impurities in pigiron until the re'uired le/el (o!ygen process).
#ig iron and up to 0% steel scrap are charged in the refractory
with o!ygen (Fig. 9.*)
* * COFeCOOFe ++
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Figure 9.1
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Figure 9.2
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Production o steel- Cont$
&hen,
#&he molten steel is then cast is stationary mould or
continuously cast in long slabs (91%). (fig 9.-b).
#2bout one3half of the raw steel are from recyle old steel (+un$
cars and appliances).
FeOOironpigFe *)( * +
COFesteelfromC +)(
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Figure 9.5b
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Iron-iron car%ide phase diagram
e/eral solid phase (Fig 9.1)#ferrite 4 an interstitial solid solution of # in 5##iron lattice
(low solubility of #).
#2ustenite () 3 an interstitial solid solution of # in F## iron
lattice (higher solubility of # as compared to ferrite).##ementite (Fe#) 4 intermetallic compound (1.16% # and
9.% Fe)
#ferrite 3 an interstitial solid solution of # in 5##iron lattice
with greater athan ferrite.
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Figure 9.6
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In&ariant reactions
Peritatic reaction:7i'uid (0.-% #) 8 (0.09% #) "9- o# (0."6% #)
Eutectic reaction:
7i'uid (.% #) "":o
# (*.0:% #) 8 Fe# (1.16% #)
Eutectoid reaction:
(0.:% #) 6* o# ferrite (0.0*% #) 8 Fe# (1.16% #)
C G C
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Plain Car%on steel '(.)* C+ !utectoid steel
Fig 9.6#If heated at 6-0 o#, held for sufficient time, structures becomes
austenite, (austenitiing process)#Further slow cooling to about eutectoid temperature or slightly
abo/e, the structure is still austenite ().#Further cooling to below eutectoid temperature, the structure ischanged to alternate plates of ferrite and cementite (Fe#) 4
pearlite structure.
C i ht Th M G Hill C i I P i i i d d ti di l
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Figure 9.7
C i ht Th M G Hill C i I P i i i d d ti di l
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Plain Carbon steel (< 0.8% C) hypoeutectoid steel
Fig 9.9
#2bo/e eutectoid temperature (900 o#), austenite structure#Further cooling, the structure $eep on changing until all structure
will change to ferrite and cementite.
Plain Carbon steel (> 0.8% C) hypereutectoid steelig .//0#or composition ha&ing 1(.) * car%on, a%o&e eutectoid
temperature '9-0 o#), austenite structure.#Further cooling, the structure $eep on changing until all structurewill change to ferrite and cementite
!.g. Pg 2
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Figure 9.9
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Figure 9.11
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Heat treatment o plain car%on steel
5y /arying the way plain carbon still is heated and cooled,different combinations of mechanical properties can be obtained
#Formation of Fe3# martensite steel in austenitic condition is
cooled rapidly to ;& by 'uenching with water, the structure
willchange to martensite.
3
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Figure 9.13
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Heat treatment o plain car%on steel Cont$
Isothermal decomposition procedure (Fig 9.*0), show that
microstructural change o/er the process (Fig 9.*").eating martensitic steel at a temperature below
eutectoid, to ma$e it softer and more ductile.3Martempering(mar'uenching) 4 to minimie the distortion
and crac$ing during une/en cooling.3Austempering4 to impro/e ductility, impact resistance and
decrease distortion.
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Figure 9.20
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py g p , q p p y
Figure 9.21
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py g p , q p p y
Figure 9.28
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py g p q p p y
3imitations o plain car%on steel
##annot be strengthened beyond "00,000 psi (190 ?a)
withoutloss in ductility and impact resistance.
#7arge section thic$nesss cannot be produced with martensite
structure.#7ow corrosion and o!idation resistance#oor impact resistance at low temperatures#?ust be 'uenched rapidly to obtain full martensitic structure
which lead to possible distortion and crac$ing.
&o o/ercome this, other types of alloy steels ha/e been
de/eloped to impro/e their properties.
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Figure EP9.3
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Classiication o plain- car%on steels
#igh3carbon steel ("0103"09-)
AISI - American Iron and steel Institute, SAE Society for automotive Engineers
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3ow "lloy 4teels#2lloy steel may contain up to -0% alloying elements and can
still considered alloy steels.
#7ow alloy steels contain "3 % alloying elements.#E!amples manganese, molybdenum, sulfur, chromium,
nic$el and silicon (refer to table 9.)
#2lloy steels in A are designated by digits
3 "sttwo digits 4 the principle alloying elements
3 7ast * digits 4 the hundredth of % # in steel#
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Figure 9.35
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"l i i "ll
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"luminium "lloys#&he hardening process that is used to increase many 2l and
other metal alloys is precipitation hardening
#rocess in/ol/ed 3 olution heat treatment (sample is heated to a certain
temperature, soa$ed there until uniform solid structure is
produced)
3 Duenching, rapid cooling to ;& using water
3 2ging, to form fine dispersed precipitate which pre/entdislocation mo/ement. Batural aging at ;&, artificial aging
at ele/ated temperature.
#2l has low density, good corrosion resistance, nonto!ic, good
electrical properties, relati/ely cheap, low strength but can be
alloyed up to 190 ?a.
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Figure 9.43
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"l i i "ll C t$
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"luminium "lloys Cont$#2l is produced from bau!ite (hydrated aluminum o!ide).
5au!ite is treated with BaC> (5ayer rocess)
bau!ite 8 BaC> sodium aluminate precipitatealuminium hydro!ide thic$ened calcine 2l*C
dissol/ed in cryolite (Ba2lF1)electrolysed, # as
cathode and anode metallic 2l forms in the li'uid state(99.-399.9% purity with Fe and silicon as ma+or impurities)
#2l is sent to refractory furnace for refining where
alloying elements can be added to the furnace followed by
casting into desired shapes (wrought 2l alloys or 2l casting
alloy).
#rought 2l alloy (sheet, plate, rod, wires) are calssifiedaccording to the ma+or alloying elements (&able 9.6)
#"stdigit indicate alloy group, *nddigit indicates modification
of the original alloy and the last * digits indentify the 2l alloy
or 2l purity
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"l i i "ll C t$
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"luminium "lloys Cont$
Non-Heat-Treatable wrought Al alloys #annot be
precipitation strengthened but can be cold wor$ed to increasestrength.
#&he main group are "!!!, !!! and -!!! groups
E.g. "!!! 4 min 99% 2l, Fe and silicon (alloying elements)
with 0."*% #u for e!tra strength. (refer to pg of the hand
out for the rest)#;efer to table 9.: (pg. - of handout) for the list of
compositions, mechanical properties and etc.
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"l i i "ll C t$
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"luminium "lloys Cont$
Heat-Treatable wrought Al alloys #an be precipitation
strengthened by heat treatment.#&he main group are *!!!, 1!!! and 6!!! groups
E.g. *!!! 4 &he principle alloying elements is #u. ?g is also
added. Cne of the most important is *0* (.-% #u, ".-%
?g, 0.1% ?n) 4 high strength and is used for aircraft
structural. (refer to pg. of the hand out for the rest).
#;efer to table 9.: (pg. - of handout) for the list of
compositions, mechanical properties and etc.
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"l i i "ll C t$
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"luminium "lloys Cont$
Al casting alloys
main process and casting4 small 'uantities of identical casting, comple!
casting, large casting and structural casting.
Permanent mould casting4 simple shape and small sie
mould. roduced finer grain structure and less shrin$age than
sand casting. !ie casting4 can be produced at high rates (high pressure),
smooth surfaces and process can be automated.
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"l i i "ll C t$
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"luminium "lloys Cont$
Al casting alloys are de/eloped casting 'ualities such fluidity,
feeding ability, strength, ductility and corrosion resistance.#
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Figure 9.44
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Copper "lloys
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Copper "lloys
##u metal can be used in the unalloyed condition (mainly used
in electrical industries as well as alloyed form.#In unalloyed form 4 high electrical and thermal conducti/ity,
good corrosion resistance, ease of fabrication, medium
strength and etc.
#2lloyed conditions in a series of brass and brone
##u is e!tracted from ores containing #u and iron sulfides(refer to pg. 1 of handout for detail e!planation). 2t the end of
the processes produce electrolytic tough pitch (E&) #u,
99.9-%.
#E& #u is used to produce wire, rod, plate and strip. #ontain0.0% o!ygen as impurity.
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Copper "lloys Cont$
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Copper "lloys Cont
#lassification of #u alloys
3 #"0"00 to #69900 refer to wrought alloys 3 #:0000 to #99900 refer to casting alloys
;efer to table 9."0 pg.1, for #u alloys classification
;efer to &able 9."" pg 6, for properties and application of #u
alloys.
3 E.g. #u3Gn brasses, -3 0% Gn. mall amount of lead isadded to impro/e machinability. (Fig. :.*-)
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Figure 8.25
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4tainless 4teels
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4tainless 4teels#&hese alloys is selected due to their e!cellent corrosion
resistance in many en/ironment (due to the presence of #r, at
least "*%).
# main types ferritic, martensitic, austenitic and precipitation
hardening.
3 Ferritic ("* 4 0% #r), relati/ely low cost
3 ?artensitic ("* 4 "6% #r, 0."-3".0% #)
3 2ustenitic ("1 4 *-% #r and 63*0% Bi). 5etter corrosion
resistance due to the presence of Bi.
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Figure 9.55
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Cast Iron
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Cast Iron#2 family of ferrous alloys. &hey are intended to be cast into
the desired shape. Anli$e steels ("% #), cast irons contain
*3% # and "3% silicon, other element may be present also.
#Easily melt and /ery fluid in li'uid state and ha/e wide range
of strengths and hardness, good wear resistance. >a/e
relati/ely low impact resistance and ductility.
# different common types which can be differentiated by the
distribution of carbon in their microstructures 3 White iron4 iron carbides in a pearlitic structure (when
fractured produce whiteor bright crystalline surface)
3 ray iron4 precipitates as graphite fla$e (when
fractured produce graysurface due to e!posed graphite 3!allea"le iron4 first cast as white iron, and then heated to
dissociate iron carbide to graphite and iron (temper carbon)
3#uctile iron4 combine the processing ad/antages of gray
cast iron with similar engineering properties as steel (high
strength, toughness, ductility and etc)
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5ther alloys
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5ther alloys#Mg alloys4 light metal, suitable for low3density application
(aerospace applications).7imited ad/antages due to /ery high
cost, difficult to cast (burns in air), low strength, poor
resistance to creep, fatigue and wear. rought alloys and
casting alloys
#Titanium alloys4 relati/ely light but has high strength,
superior corrosion resistance. It is e!pensi/e because /ery
difficult to e!tract from its compound.#Nic"el alloys4 E!ceptional resistance to corrosion and high
temperature o!idation. ;elati/ely e!pensi/e and high density
(limits its use).
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