CH 14 CarbonandAlloySteels

7/24/2019 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



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)



./amples0

2&+$

2++$

414$

1$$



Common Carbon and Alloy Steels0



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



ASSA. most common3 also hae 5nified

6mbering System (56S! and AS7'



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 $*+%!



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



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







7rends>

ncreasing carbon content

– tensile strengthincreases3 elongation

decreases

Carbon steels0 lo#3 med and hight



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



)-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



)-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$2$!







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"//



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



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



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



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)



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)




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




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




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




,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



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



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

http://en.wikipedia.org/wiki/Carbon

http://en.wikipedia.org/wiki/Carbon



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



-eie# C.S





-ecall3 tensile strength appro/imately +$$ L

M)6

F f f C 1+



A Fuic6 #e$ie& of .eat reating 3rocesses from Cha!ter 1+7



?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




• 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




• 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



7ensile Strength and

.longation s

7empering

7emperatre



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




)-S s C-S

s

Annealed>

)7>



7ensile Strength and

.longation for

arios Alloy Steels



Properties of Some

Strctral Steels –

All se AS7' call,

ots

Documents

CH 14 CarbonandAlloySteels