Stainless steel (2) /certified fixed orthodontic courses by Indian dental academy

Stainless steelStainless steel
soldering & weldingsoldering & welding
INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in continuing dental educationLeader in continuing dental education
www.indiandentalacademy.comwww.indiandentalacademy.com

IntroductionIntroduction
 Stainless steel because o its high strengthStainless steel because o its high strength
& shiny surface & resistance to corossion& shiny surface & resistance to corossion
has done wonders in technology.has done wonders in technology.
 It is being used from our daily req.utensilsIt is being used from our daily req.utensils
to big machineries used in industries.to big machineries used in industries.
 It has become the basic need in dentistry.It has become the basic need in dentistry.
 It has revolutionised the world.It has revolutionised the world.

HistoryHistory
 stainless steel is an alloy of iron.it was discoveredstainless steel is an alloy of iron.it was discovered
accidently by shiffield metallurgist Harry Bearly duringaccidently by shiffield metallurgist Harry Bearly during
world war 1 daysworld war 1 days
 it entered dentistry in 1919 introduced at krupps dentalit entered dentistry in 1919 introduced at krupps dental
polyclinic in germany by F.Hemptmeyer who 1polyclinic in germany by F.Hemptmeyer who 1stst
use it touse it to
mak a prosthesis called WIPLA(wie means like platinum)mak a prosthesis called WIPLA(wie means like platinum)
 Apllication of s.s in the fabrication of of appliances wasApllication of s.s in the fabrication of of appliances was
credited to a Belgian Lucien de Coster.research studiescredited to a Belgian Lucien de Coster.research studies
was done by R M Williams.was done by R M Williams.
 Earlier orthodontist use gold to make bands & wires.butEarlier orthodontist use gold to make bands & wires.but
nowdays because of strength & cost ss has overcome it.nowdays because of strength & cost ss has overcome it.

SteelsSteels
 Steels are iron based alloys containing less thanSteels are iron based alloys containing less than
1.2% carbon.1.2% carbon.
 Polymorphism-it crystalises into more than onePolymorphism-it crystalises into more than one
structure such as ferritic martensitic & austeniticstructure such as ferritic martensitic & austenitic
property called as Allotrophy.property called as Allotrophy.
 At room temp pure iron is bcc structure refferedAt room temp pure iron is bcc structure reffered
as ferrite(alfa form).this is stable till 912 *C.as ferrite(alfa form).this is stable till 912 *C.
 At temp.betn 912-1394*C stable form isAt temp.betn 912-1394*C stable form is
austenite.(gamma form0 having fcc structureaustenite.(gamma form0 having fcc structure

AusteniteAustenite
Ferrite + cementite(FeC3) martensite
quenchedCooled slowly
annealed
Martensite is extremely hard & brittle alloy
Tempering- Heat treament to reduce the hardness & to increase the toughness is
called TEMPERING

Stainless steelStainless steel
 It’s a compound of Fe,C & Cr where % of Cr isIt’s a compound of Fe,C & Cr where % of Cr is
not less than 11%. Other elements present arenot less than 11%. Other elements present are
Ni,Co,Mn,S,Ti etc.Ni,Co,Mn,S,Ti etc.
 Functions of these are-Functions of these are-
1.1. Cr- tarnish & corossion resistanceCr- tarnish & corossion resistance
2.2. Ni – tarnish & corossion resistance & stengthNi – tarnish & corossion resistance & stength
3.3. Co- hardnessCo- hardness
4.4. Si-acts as deoxidizer & scavangerSi-acts as deoxidizer & scavanger
5.5. Mn-acts as scavanger & increase hardnessMn-acts as scavanger & increase hardness
6.6. Ti-inhibits ppt. Of chronium carbideTi-inhibits ppt. Of chronium carbide
7.7. S-helps in easy machining of wrought partsS-helps in easy machining of wrought partswww.indiandentalacademy.comwww.indiandentalacademy.com

ClassificationClassification
 Acc. To american iron & steel instituteAcc. To american iron & steel institute
(AISI)numbers from 300-502 are given(AISI)numbers from 300-502 are given
for s.s.depending upon the physicalfor s.s.depending upon the physical
properties.this is in parallel with theproperties.this is in parallel with the
unified number system (UNS) &unified number system (UNS) &
German Standards.This includes-German Standards.This includes-
 Ferritic -400Ferritic -400
 Auatenitic -302,304,316Auatenitic -302,304,316
 Martensitic -400Martensitic -400

 According to Crystal lattice S.S is classifiedAccording to Crystal lattice S.S is classified
as-as-
sp lattice compositionsp lattice composition
Cr Ni CCr Ni C
 Ferritic BCC 11.5-27% 0% 0.2%Ferritic BCC 11.5-27% 0% 0.2%
 Austenitic FCC 16-26% 7-22% 0.25%Austenitic FCC 16-26% 7-22% 0.25%
 Martensitic BCT 11.5-17% 0-2.5% 0.15-Martensitic BCT 11.5-17% 0-2.5% 0.15-
-1.2%-1.2%

 Stainless steel wire classification acc. ToStainless steel wire classification acc. To
hardness-hardness-
Very soft or fullyannealedVery soft or fullyannealed
HardHard
Extra hard or high tensile or spring hard orExtra hard or high tensile or spring hard or
super hard.super hard.

Comparison betn diff. S SComparison betn diff. S S
 Ferritic-Ferritic-
Mechanical properties are inferior to others.Mechanical properties are inferior to others.
Good corrosion resistanceGood corrosion resistance
Cannot be heat treatedCannot be heat treated
Cannot be work hardenedCannot be work hardened
CheapCheap
 Application-for making instruments &Application-for making instruments &
equipments provided strength is notequipments provided strength is not
requiredrequired

 Martensitic s s-Martensitic s s-
Can be heat treatedCan be heat treated
Have high yield strengthHave high yield strength
High hardnessHigh hardness
Poor corrosion resistancePoor corrosion resistance
More brittleMore brittle
 Application-for making cutting & grindingApplication-for making cutting & grinding
instruments due to high hardness &instruments due to high hardness &
strengthstrength

 Composition-Cr-18%Composition-Cr-18%
Ni-8%Ni-8%
C-0.15%C-0.15%
 Austenitic ss or 188 ss or AISI-302.Austenitic ss or 188 ss or AISI-302.
High % of Ni stabilises the austenite phase at room temp.High % of Ni stabilises the austenite phase at room temp.
-high corrosion resistance-high corrosion resistance
-can be cold worked-can be cold worked
-easy to weld & shape-easy to weld & shape
-easy to overcome sensitization-easy to overcome sensitization
-high strength-high strength
-less critical grain growth-less critical grain growth
Application-orthodontics as wires bands & bracketsApplication-orthodontics as wires bands & brackets
-endodontic instruments-endodontic instruments
-implants-implants www.indiandentalacademy.comwww.indiandentalacademy.com

Passivation ,sensitizationPassivation ,sensitization
&stabilization&stabilization
 Passivation-Cr is added to steel as passivatingPassivation-Cr is added to steel as passivating
agent.it reacts to the atmspheric oxygen to formagent.it reacts to the atmspheric oxygen to form
its oxides thus preventing corrosion.its oxides thus preventing corrosion.
 Sensitization-it’s the loss of corrosion resistanceSensitization-it’s the loss of corrosion resistance
of 188 sswhen heated to high temp.due toof 188 sswhen heated to high temp.due to
formation of Cr carbides.hence its not availableformation of Cr carbides.hence its not available
to react with oxygen.to react with oxygen.
 Cause-high temp used in soldering 7 weldingCause-high temp used in soldering 7 welding
 Prevention-use low fusing flux & less timePrevention-use low fusing flux & less time

 Stabilization-done to preventStabilization-done to prevent
sensitization.here titanium is added to 6sensitization.here titanium is added to 6
times that of carbon in ss.Ti has moretimes that of carbon in ss.Ti has more
affinity to form carbides than Cr making Craffinity to form carbides than Cr making Cr
free to react with oxygen.Such ss arefree to react with oxygen.Such ss are
called stabilized ss.called stabilized ss.

Heat treatment of stainless steelHeat treatment of stainless steel
 Def-it’s the process of subjecting a metal toDef-it’s the process of subjecting a metal to
given controlled heat followed by sudden orgiven controlled heat followed by sudden or
gradual cooling to develop desired qualities ingradual cooling to develop desired qualities in
metal.are of 2 types-metal.are of 2 types-
 Softening heat treatment-annealingSoftening heat treatment-annealing
 Hardening heat treatment –temperingHardening heat treatment –tempering
 Annealing-effect of cold working like low ductilityAnnealing-effect of cold working like low ductility
& distorted grains can be revearsed by heat& distorted grains can be revearsed by heat
treatment called annealingtreatment called annealing

 It consists of 3 stages –recoveryIt consists of 3 stages –recovery
-recrystalization-recrystalization
-grain growth-grain growth
1.1. Recovery-in this stage cold wok propertiesRecovery-in this stage cold wok properties
begins to disappear.Slight decrease inbegins to disappear.Slight decrease in
tensile strength & no change in ductility istensile strength & no change in ductility is
seen.Internal stresses incorperated in coldseen.Internal stresses incorperated in cold
working are releaved but no change inworking are releaved but no change in
microstructure is seenCold workedmicrostructure is seenCold worked
orthodontic appliances are subjected to thisorthodontic appliances are subjected to this
stage treatment ot reduce warpage &stage treatment ot reduce warpage &
distortion called as STRESS RELEAFdistortion called as STRESS RELEAF
ANNEALING.ANNEALING.

PROCEDURE-PROCEDURE-
 by Backfen & Gale-heat app.at 260*C for 20by Backfen & Gale-heat app.at 260*C for 20
min or at 399*C for 10 min in oven.min or at 399*C for 10 min in oven.
Arch wire by electric current-3-4 VArch wire by electric current-3-4 V
For finer arch wire 2.5VFor finer arch wire 2.5V
For springs & clasps 399*C for 10 min inFor springs & clasps 399*C for 10 min in
electric oven.electric oven.

 Recrystalization-here old set f distortedRecrystalization-here old set f distorted
grains are replaced by new set of distortgrains are replaced by new set of distort
free grains.material attains original ductilitfree grains.material attains original ductilit
& strength.& strength.
 Grain-growth-here grains startGrain-growth-here grains start
growing.bigger the grains poorer thegrowing.bigger the grains poorer the
properties.properties.
 TEMPERING-heat treatment of steel toTEMPERING-heat treatment of steel to
reduce the hardness but it isreduce the hardness but it is
counterbalanced by an increase thecounterbalanced by an increase the
toughness is called tempering.it is heatedtoughness is called tempering.it is heated
450*C for one min.450*C for one min.www.indiandentalacademy.comwww.indiandentalacademy.com

Corrosion o stainless steelCorrosion o stainless steel
 Defined as distruction or deteriration ofDefined as distruction or deteriration of
material by a chemical ormaterial by a chemical or
electrochemical reaction.electrochemical reaction.
 Causes-Causes-
1.1. If surface inhomogenity is present itIf surface inhomogenity is present it
allows corossion cells to form inallows corossion cells to form in
presence of saliva.presence of saliva.
 Surface should be polished.Surface should be polished.

 If bits of carbon steel s incorporated onIf bits of carbon steel s incorporated on
the metal surface as in manupulation ofthe metal surface as in manupulation of
stainless steel wirewith carbonsteel plierstainless steel wirewith carbonsteel plier
then electric couple may form causingthen electric couple may form causing
corrosioncorrosion
 Separate ss & cs instruments.Separate ss & cs instruments.
 Dip carbon-steel instrument in rust inhibitingDip carbon-steel instrument in rust inhibiting
solution.solution.
 Rust-it’s the formation of iron oxide whenRust-it’s the formation of iron oxide when
iron & steel alloy corrodes.it may beiron & steel alloy corrodes.it may be
brown,black or reddish in color.can takebrown,black or reddish in color.can take
form of pits and blisters .form of pits and blisters .
 Prevent direct contact of iron with oxygenPrevent direct contact of iron with oxygen

 Catastrophic corrosion-when ss is sensitised as in brazingCatastrophic corrosion-when ss is sensitised as in brazing
welding & than exposed to chemical agents then Cr depletedwelding & than exposed to chemical agents then Cr depleted
boundaries are readily atached by oxygen phenomenonboundaries are readily atached by oxygen phenomenon
catastrophic corrosion.catastrophic corrosion.
 MIC-microbiologically influenced corrosion-microorganismsMIC-microbiologically influenced corrosion-microorganisms
such as sulphate reducing Bacteroid corrodens & acidsuch as sulphate reducing Bacteroid corrodens & acid
producing step mutans are known to attach stainless steel &producing step mutans are known to attach stainless steel &
other alloys in mouth.other alloys in mouth.
 Chlorides into our diet can penetrate & destroy passivityChlorides into our diet can penetrate & destroy passivity
which is responsible for corrosionwhich is responsible for corrosion

Important termsImportant terms
 Stress & strainStress & strain
Stress- it is the internal resistance offered by the material to theStress- it is the internal resistance offered by the material to the
external force.it is measured as force per unit curved surface area.external force.it is measured as force per unit curved surface area.
Strain-it’s the deformity produced by strain.it can be –elastic-reversibleStrain-it’s the deformity produced by strain.it can be –elastic-reversible
-plastic-irreversible or-plastic-irreversible or
-combination-combination
Stress-is of 3 types-tensileStress-is of 3 types-tensile
- compressive.in both force acts at right angles- compressive.in both force acts at right angles
- shear here force acts parallel to tooth surface.- shear here force acts parallel to tooth surface.
Elastic limit-it is the greatest stess that may be produced in a materialElastic limit-it is the greatest stess that may be produced in a material
such that it will return to its original dimension when the forces aresuch that it will return to its original dimension when the forces are
released.released.
Proportional limit-greatest stress that may be produced in a materialProportional limit-greatest stress that may be produced in a material
that the stess is directly proportional to strain.that the stess is directly proportional to strain.

 Modulus of elasticity (youngs mod or elasticModulus of elasticity (youngs mod or elastic
mod)-ratio of stess to Yield strength-stressmod)-ratio of stess to Yield strength-stress
req.to produce plastic deformation is defined asreq.to produce plastic deformation is defined as
y.s.Usually taken as 0.1 -0.2 deformity.y.s.Usually taken as 0.1 -0.2 deformity.
 strain within elastic limit is calledstrain within elastic limit is called moe.its the
slope of the curve.its the measure of rigidity &
flexibility.steeper the slope more moe more rigid
is the material.in wires light continues force is
req so moe should be less.
 ULTIMATE TENSILE STRENGTH-def as max
stress that a mat can withstand before failure.

 Cold working-or strength hardening-Cold working-or strength hardening-
subjecting metals to processes like rolingsubjecting metals to processes like roling
drawing hammering etc. increasesdrawing hammering etc. increases
hardness & reduce resistance to corrosionhardness & reduce resistance to corrosion
, resiliency& ductility., resiliency& ductility.
 Joinability-ability to attach auxillaries toJoinability-ability to attach auxillaries to
orthodontic wires by welding & solderingorthodontic wires by welding & soldering
to provide additional advantages whento provide additional advantages when
incorporating modification to theincorporating modification to the
appliancesappliances

 Formability-ability of wire to bend into desiredFormability-ability of wire to bend into desired
configurations such as loops coils etc without #configurations such as loops coils etc without #
the wire.the wire.
 Thermoelasticity- thermal analogue ofThermoelasticity- thermal analogue of
pseudoelasticity in which the martensitic phasepseudoelasticity in which the martensitic phase
is transformed to austenitic as temp isis transformed to austenitic as temp is
decresed.it is reversed by increasing thedecresed.it is reversed by increasing the
temperature.temperature.
 Pseudoelasticity-mechanical analogue of th.el.Pseudoelasticity-mechanical analogue of th.el.
In which at constant temp austenite toIn which at constant temp austenite to
martensite phase transformation occurs withmartensite phase transformation occurs with
increase in applied force.as forces are removedincrease in applied force.as forces are removed
reverse occurs.reverse occurs.

 Resilency- it is the energy absorbed by the material ehenResilency- it is the energy absorbed by the material ehen
it is stressed to its proportional limit.it shows theit is stressed to its proportional limit.it shows the
springiness of the material&is the area under the elasticspringiness of the material&is the area under the elastic
portion of stress strain curve.for wires high resiliancy isportion of stress strain curve.for wires high resiliancy is
req.for continuous force.req.for continuous force.
 Toughness-it is the amount of energy that a matrrialToughness-it is the amount of energy that a matrrial
canabsorb before it fractures .its area under stress staincanabsorb before it fractures .its area under stress stain
curve till breaking point.curve till breaking point.
 Brittleness-its opp of toughness.material tends toBrittleness-its opp of toughness.material tends to
fracture near their prop.limit.fracture near their prop.limit.
 Fatigue-when a material is subjected to cycles of loadingFatigue-when a material is subjected to cycles of loading
& unloading as during mastication it may # due to& unloading as during mastication it may # due to
fatigue.fatigue.

 Endurance limit- it is the amount of stress to which aEndurance limit- it is the amount of stress to which a
material can be subjected for an infinite no. of cyclesmaterial can be subjected for an infinite no. of cycles
without #without #
 Ductility-ability of a material to withstand rupture underDuctility-ability of a material to withstand rupture under
tensile load or its ability to withdrawn into wires.tensile load or its ability to withdrawn into wires.
 Malleability-ability of material to withstand rupture underMalleability-ability of material to withstand rupture under
compression or its ability to beat into sheetscompression or its ability to beat into sheets
 Poisons Ratio –whentensile force is applied matPoisons Ratio –whentensile force is applied mat
undergoes both axial &lateral strain within elastic limitsundergoes both axial &lateral strain within elastic limits
than the ratio of stress to strain is called Poisons ratiothan the ratio of stress to strain is called Poisons ratio

Other steels includeOther steels include
 Duplex steels-is an assembly of bothDuplex steels-is an assembly of both
austenite & ferritic grains.includesaustenite & ferritic grains.includes
properties of bothlike high yield strengthproperties of bothlike high yield strength
inc.toughness & ductility.when improperlyinc.toughness & ductility.when improperly
heat treated there is a tendency to form aheat treated there is a tendency to form a
brittle phase with very poor coosionbrittle phase with very poor coosion
resistance(sigma phase).it is used forresistance(sigma phase).it is used for
manufacturing of one piece brackets.egmanufacturing of one piece brackets.eg
bioline.bioline.

 Precipitation hardenable steels(ph steel)-it canPrecipitation hardenable steels(ph steel)-it can
be hardened by heat treatment.it has got highbe hardened by heat treatment.it has got high
tensile strength & thus widely used in minitensile strength & thus widely used in mini
brackets & edgelock brackets.brackets & edgelock brackets.
 Mangenese containing steels .mn is called asMangenese containing steels .mn is called as
austenising element as it solubilises the reallyaustenising element as it solubilises the really
austenising element nitrogen thus replacingaustenising element nitrogen thus replacing
nickle.nickle.
 Soft stain less steel-it is the thoroughly annealedSoft stain less steel-it is the thoroughly annealed
steel to remove all the streesses incorporatedsteel to remove all the streesses incorporated
during cold working.these are commonly usedduring cold working.these are commonly used
as ligature wires.as ligature wires.

bracketsbrackets
 Steel remains the standered material forSteel remains the standered material for
many years to to be usedfor brackets.butmany years to to be usedfor brackets.but
now resently titanium brackets have beennow resently titanium brackets have been
introduced. These are made by casting orintroduced. These are made by casting or
metal strips stamped to shape.castingmetal strips stamped to shape.casting
ones are more precise & accurateones are more precise & accurate
 There is mesh at the back of the bracketThere is mesh at the back of the bracket
which is used for bonding.howeverwhich is used for bonding.however
corossion is a problem.corossion is a problem.

Bands & tubesBands & tubes
 Bands-Also prepared from stainlessBands-Also prepared from stainless
steel.band is a ss strip that encircle thesteel.band is a ss strip that encircle the
crown.brackets are welded to bands.crown.brackets are welded to bands.
 Tubes-allows the wire to slide through it .itTubes-allows the wire to slide through it .it
may be rounded to square.it may bemay be rounded to square.it may be
single or combination of severalsingle or combination of several
tubessingle double or trippletubessingle double or tripple

Power pins.Power pins.
 Is a traction hook that can be fited in theIs a traction hook that can be fited in the
vertical slot from gingival side.it is retainedvertical slot from gingival side.it is retained
in the bracket slot by bending thein the bracket slot by bending the
occlusally projecting end by 90*.occlusally projecting end by 90*.

archwiresarchwires
 St.st & Co-Cr has replaced preciousSt.st & Co-Cr has replaced precious
metals because of better properties likmetals because of better properties lik
strength springiness & equivalentstrength springiness & equivalent
corrosion resistance.can be softened bycorrosion resistance.can be softened by
annealing and hardened by cold working.annealing and hardened by cold working.
 Fully annealed wires are used ligatureFully annealed wires are used ligature
wires.wires.
 Special type of ss arch wire has beenSpecial type of ss arch wire has been
prepared by A J Wilcock called australianprepared by A J Wilcock called australian
arch wire.arch wire.

Australian archwireAustralian archwire
Thank youThank you
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Stainless steel (2) /certified fixed orthodontic courses by Indian dental academy

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