ch 14 carbonandalloysteels
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Chapter 14 – Carbon and Alloy
Steels
• All of these steels are alloys of Fe and C – Plain carbon steels (less than 2% carbon and
negligible amonts of other residal elements!
• "o# Carbon (less than $&% carbon!• 'ed Carbon ($&% to $%!
• )igh Carbon ($% to $*+%!
– "o# Alloy Steel
– )igh Alloy Steel
– Stainless Steels (Corrosion,-esistant Steels! – contain at least 1$+% Chromim
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AISI - SAE Classification System
AISI XXXX
American Iron and Steel Institute (AISI)
• classifies alloys by chemistry
• 4 digit number – 1st number is the major alloying element
– nd number designates the subgrou!alloying element "# the relati$e !ercent of!rimary alloying element%
– last t&o numbers a!!ro'imate amount ofcarbon (e'!resses in %1)
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./amples0
2&+$
2++$
414$
1$$
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Common Carbon and Alloy Steels0
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AISI - SAE Classification
System
• letter !refi' to designate the !rocess used to !roduce thesteel
– E * electric furnace
– X * indicates !ermissible $ariations
• If a letter is inserted bet&een the nd and +rd number
– , * boron has been added
– * lead has been added
• etter suffi' – . * &hen hardenability is a major re/uirement
• "ther designation organi0ations
– AS2 and 2I
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ASSA. most common3 also hae 5nified
6mbering System (56S! and AS7'
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3lain Carbon Steel
3lain Carbon Steel• o&est cost
• Should be considered first in
most a!!lication• + Classifications
• "o# Carbon (less than $&% carbon!
• 'ed Carbon ($&% to $%!• )igh Carbon ($% to $*+%!
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3lain Carbon Steel
• Again alloy of iron and carbon &ith carbon the
major strengthening element $ia solid solution
strengthening%
• If carbon le$el high enough (greater than %5)
can be /uench hardened (a6a7 dis!ersion
hardening through hardened heat treated
austeni0ed and /uenched etc%%)%
• Can come in .#S and C#S o!tions
• he most common C#S are 15 through 18
and 111 1119 and other free machining steels
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1 "o# Carbon (less than $&% carbon!
• "o# strength3 good formability• f #ear is a potential problem3 can be carbri8ed
(diffsion hardening!• 'ost stampings made from these steels• AS 1$$93 1$1$3 1$1+3 1$193 1$2$3 1$223 1$2+
2 'ed Carbon ($&% to $%!• )ae moderate to high strength #ith fairly good dctility• Can be sed in most machine elements• AS 1$&$3 1$4$3 1$+$3 1$$:
& )igh Carbon ($% to $*+%!• )ae high strength3 lo#er elongation• Can be ;ench hardened• 5sed in applications #here srface sb<ect to abrasion –
tools3 =nies3 chisels3 ag implements• AS 1$9$3 1$*+
3lain Carbon Steel
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7rends>
ncreasing carbon content
– tensile strengthincreases3 elongation
decreases
Carbon steels0 lo#3 med and hight
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3lain Carbon Steel
• 11:
– o& carbon ;ield strength 886si
• 148
–2edium carbon ;ield strength 96si• A+5
– o& carbon ;ield strength +56si
• 114
– o& carbon ;ield strength 96si• 1144
– 2edium carbon ;ield strength <86si
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)-S s C-S
• )-S
– A?A hot finishing – ingots
or continos cast shapes
rolled in the @)7B
condition to a smallershape
– Since hot3 grains
recrystalli8e #ithot
material getting harder
– Dislocations areannihilated (recall
dislocations impede slip
motion!
• )-S Characteri8ed by0
– ./tremely dctile (ie %
elongation 2$ to &$%!
– 'oderate strength (S
appro/ $ – E+ =si for1$2$!
– -ogh srface finish –
blac= scale left on srface
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)-S s C-S
• C-S – A?A cold finishing – coil of
)-S rolled throgh aseries of rolling mills A7-' 7.'P.-A75-.
– Since rolled at roomtemperatre3 get crystaldefects called dislocations#hich impede motion iaslip
– A?A #or= hardening
– "imit to ho# mch yo can#or= harden before toobrittle
– )o# reerse> Canrecrystalli8e by annealing
• C-S Characteri8ed by0 – "ess dctlie – almost brittle
(ie % elongation + to1$%!
– )igh strength (S appro/
12$ =si for 1$2$!
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Alloy Steel
• ther elements (besides carbon! can beadded to iron to improe mechanicalproperty3 manfactring3 or enironmental
property• ./ample0 slfr3 phosphoros3 or lead can
be added to improe machine ability
– enerally #ant to se for scre# machineparts or parts #ith high prodction rates
– ./amples0 11//3 12// and 12"//
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Alloy Steel
• Again3 elements added to steel can dissole in
iron (solid soltion strengthening!0
– ncrease strength3 hardenability3 toghness3 creep3
high temp resistance• Alloy steels groped into lo#3 med and high,alloy
steels
– )igh,alloy steels #old be the stainless steel grops
– 'ost alloy steels yoGll se fall nder the category of
lo# alloy
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Alloy Steel
• = 1%582n = %5 Si or =%5 Cu• 2ost common alloy elements7
– Chromium nic6el molybdenum $anadium tungstencobalt boron and co!!er%
• o& alloy7 Added in small !ercents (>8) – increase strength and hardenability
• .igh alloy7 Added in large !ercents (=) – i%e% = 1%8 Cr * stainless steel &here Cr im!ro$es
corrosion resistance and stability at high or lo& tem!s
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Alloying Elements used in
Steel
2anganese (2n)• combines &ith sulfur to !re$ent brittleness
• =1 – increases hardenability
• 11 to 14 – increases hardness
– good ductility
– high strain hardening ca!acity
– e'cellent &ear resistance
• Ideal for impact resisting tools
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Alloying Elements used
in Steel
Sulfur (S)
• Im!arts brittleness
• Im!ro$es machineability
• "6ay if combined &ith 2n
• Some free-machining steels contain
%: to %18 S• E'am!les of S alloys7
– 11'' ? sulfuri0ed (free-cutting)
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Alloying Elements used in Steel
@ic6el (@i)
• 3ro$ides strength stability and toughnessE'am!les of @i alloys7
– +'' ? @ic6el (%9) chromium (%9)
– +1'' ? @ic6el (1%8) chromium (%5)
– +'' ? @ic6el (1%98) chromium (1%) – ++XX ? @ic6el (+%8) chromium (1%8)
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Alloying Elements used in Steel
Chromium (Cr)• sually >
• increase hardenability and strength
• "ffers corrosion resistance by forming stable o'ide surface
• ty!ically used in combination &ith @i and 2o
– +XX ? @ic6el (%9) chromium (%9)
– 8''' ? chromium alloys – 5''' ? chromium-$anadium alloys
– 41''' ? chromium-molybdenum alloys
2olybdenum (2o)• sually > %+
• increase hardenability and strength
• 2o-carbides hel! increase cree! resistance at ele$ated tem!s – ty!ical a!!lication is hot &or6ing tools
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Alloying Elements used in Steel
Banadium (B)
• sually %+ to %8
• increase strength
– &ithout loss of ductility
ungsten ()
• hel!s to form stable carbides
• increases hot hardness
– used in tool steels
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Alloying Elements used in Steel
Co!!er (Cu)
• %1 to %8
• increase corrosion resistance
• #educed surface /uality and hot-&or6ing ability
• used in lo& carbon sheet steel and structuralsteels
Silicon (Si)• About
• increase strength &ithout loss of ductility
• enhances magnetic !ro!erties
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Alloying Elements used in Steel
,oron (,)
• for lo& carbon steels can drastically
increase hardenability
• im!ro$es machinablity and cold formingca!acity
Aluminum (Al)• deo'idi0er
• %<8 to 1%+
• !roduce Al-nitrides during nitriding
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Corrosion #esistant Steel
• Stainless Steels (Corrosion,-esistant Steels!
– contain at least 1$+% Chromim
– trade name
• AISI assigns a + digit number
– and + D Austenitic Stainless Steel
– 4 D erritic or 2artensitic Stainless Steel
– 8 D 2artensitic Stainless Steel
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ool Steel
•-efers to a ariety of carbon and alloy steels thatare particlarly #ell,sited to be made into tools
• Characteristics inclde high hardness3 resistance
to abrasion (e/cellent #ear!3 an ability to hold a
ctting edge3 resistance to deformation ateleated temperatres (red,hardness!
• 7ool steel are generally sed in a heat,treated
state
• )igh carbon content – ery brittle
l
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ool
Steel
AS,SA. tool steel gradesH1I
Defining property AS,SA. gradeSignificantcharacteristics
Jater,hardening J
Cold,#or=ing
il,hardening
A Air,hardeningKmedim alloy
D)igh carbonK high
chromim
Shoc= resisting S
)igh speed
7 7ngsten base
' 'olybdenm base
)ot,#or=ing )
)1,)1*0 chromimbase)2$,)&*0 tngstenbase)4$,)+*0molybdenm base
Plastic mold P
Special prpose" "o# alloy
F Carbon tngsten
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-eie# C.S
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-ecall3 tensile strength appro/imately +$$ L
M)6
F f f C 1+
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A Fuic6 #e$ie& of .eat reating 3rocesses from Cha!ter 1+7
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?no# 7hese Masic )7 Processes0
• Fll Annealing – )eat aboe the astenitetemperatre (or 5C! ntil the composition isniform Cool ery slo#ly (sally at roomtemperate otside the oen -eslt0 a soft3 lo#,strength steel3 free of significant internalstresses enerally done before Cold Formingprocess
• Stress relief annealing – )eat slightly belo#astenitic temperatre (or belo# "C! generallydone follo#ing #elding3 machining or coldforming to redce residal stress
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?no# 7hese Masic )7 Processes0
• 6ormali8ing0 Similar to annealing bt at
higher temperatre Again3 slo# cooling
-eslt0 niform internal strctre #ith
some#hat higher strength than theannealing process 'achinability and
toghness improed oer the as,rolled
condition
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?no# 7hese Masic )7 Processes0
• 7hrogh )ardening3 Nenching and
7empering (and then slo# cooling!0 – )eat
aboe the astenite temperatre (or 5C!
ntil the composition is niform Coolrapidly (Nench! -eslt0 strong bt brittle
martensite strctre So temper and slo#
cool to improe toghness at the e/penseof strength
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7ensile Strength and
.longation s
7empering
7emperatre
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S!heroidi0ing0 (mst hae carbon content of $% or
higher! Spheroidite forms #hen carbon steel is heated toappro/imately E$$ OC for oer &$ hors Spheroidite can
form at lo#er temperatres bt the time needed
drastically increases3 as this is a diffsion,controlled
process 7he reslt is a strctre of rods or spheres ofcementite #ithin primary strctre (ferrite or pearlite3
depending on #hich side of the etectoid yo are on!
7he prpose is to soften higher carbon steels and allo#
more formability 7his is the softest and most dctile
form of steel 7he image to the right sho#s #here
spheroidi8ing sally occrs
?no# 7hese Masic )7 Processes0
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)-S s C-S
s
Annealed>
)7>
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7ensile Strength and
.longation for
arios Alloy Steels
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