Stainless steel is an alloy of iron and chromium that is commonly used in orthodontic appliances. It exists in three forms - austenitic, martensitic, and ferritic - with austenitic stainless steel being the most corrosion resistant. Stainless steel was first developed accidentally in the early 1900s and introduced for dental and orthodontic use in the 1930s, where it is still widely used today for wires, brackets, and other components. While stainless steel has advantages like strength and cost-effectiveness, it has limitations such as lower springback than nickel-titanium alloys and needing more frequent activations during treatment.

1. TOPIC: STAINLESS STEEL
PRESENTED BY: Danish Hamid
3RD Prof.
ROLL NO. : 02

2. INTRODUCTION
• Steel is an alloy of iron and carbon. Carbon
content should not exceed 0.2% max.
• When it contains 12 to 13% chromium it is
called stainless steel.
• Steel exists in three forms; Austenitic,
Martensitic and Ferritic.

3. History
• First developed accidently by Harry Brearley in
Sheffield, England.
• Stainless steel was introduced in dentistry in 1919
by F. Haupt Meyer.
• In 1930, angle used it to make ligature wires.
• By 1937, the value of stainless steel as orthodontic
wire had been confirmed.
• Stainless steel now a days is used to make arch
wires, ligature wires, band material, brackets and
buccal tubes.

4. Composition
Types Chromium Nickel Carbon
Ferritic 11.5 – 27 % 0 0.2 % max.
Austenitic 16 – 26 % 7 – 22 % 0.25 %
Martensitic 11.5 – 27 % 0 – 2.5 % 0.15 – 1.2 %
• Silicon, Phosphorus, Sulphur, Manganese, Tantalum, Niobium
may be present in small amounts.

5. Function of constituent metals
• Chromium :
– A thin transparent, tough, impervious oxide layer of
Chromium oxide forms on the surface of the alloy when
subjected to room air - “passivating film effect”.
– Increases hardness, tensile strength and proportional limit.
• Nickel :
– Increases strength.
– Increases tarnish and corrosion resistance.
• Cobalt :
– Increases tarnish and corrosion resistance.
– Decreases hardness.

6. • Manganese:
–Scavenger for sulphur.
–Increases hardness during quenching.
• Silicon:
–Deoxidiser and scavenger.
• Titanium:
–Inhibits the precipitation of Chromium
carbide

7. Types Of Stainless Steel
FERRITIC (BCC) AISI-400
• Stable between room temperature and 912 C.
• Carbon has low solubility in this structure. Interstices in
BCC are very small.
• Good corrosion resistance at low cost provided increased
strength is not required.
• Temperature change does not induce phase change in
solid state.
• The alloy can’t be hardened by heat treatment.
• Little application in Dentistry.

8. AUSTENITIC (FCC) AISI-302,304
• Most corrosion resistant of all types of stainless steel.
Formed between 912 – 1394C
• 18-8 stainless steel – 18% Chromium, 8% Nickel and
0.15%(302) 0r 0.08%(304) Carbon – 18-8.
• Austenite is preferred to Ferritic because of greater ductility,
ability to undergo more cold work without fracture.
• Increased strength during cold working, ease of welding,
readily overcomes sensitisation, less critical grain growth and
ease of forming.
• When austenite is allowed to cool slowly to room temp. it
forms Fe3C and ferrite.
• The iron carbide compound is called Cementite and the solid
solution of ferrite along with cementite is called Pearlite.

9. MARTENSITIC (BCT) AISI-400
• If austenite is cooled rapidly (Quenched), it will undergo
spontaneous diffusion-less transformation to a Body
Centered Tetragonal.
• The lattice is highly distorted, strained resulting in a hard
strong brittle alloy.
• Martensite decomposes into ferrite and carbide.
• Decomposition is accelerated by appropriate heat
treatment to reduce hardness but this is counter
balanced by increased toughness – “Tempering”.
• Increased strength and hardness – used for surgical
and cutting instruments.

10. MARTENSITIC (BCT) AISI-400
• Yield strength of 492 MPa (annealed). Hardened –
1898 MPa
• Brinell’s hardness range- 230 – 600.
• Elongation – less than 2%.
• Reduced ductility.
• Corrosion resistance is the least. Reduced further
with Hardening heat treatment.

11. MECHANICAL PROPERTIES
• Modulus of Elasticity: This is a measure of stiffness of the
material. Gives the flexibility of the wire component. 179 GPa
• Strength: Capacity of a material to resist a deforming load without
exceeding the limits of plastic deformation. Strength is
proportional to the resiliency of the material.
• Yield strength: The stress at which increase in strain is
disproportionate to stress. 1579 MPa 0.2% plastic deformation.
• Ultimate strength: The strength at which the material fractures.
2117 MPa
• Tensile strength – 200 MPa
• Resilience: Total energy storage capacity. The amount of energy
absorbed by a structure when it is stressed within it’s
proportional limit.
• Knoop’s hardness number: 600

12. GENERAL PROPERTIES
SENSITISATION:
• When heated between 400 and 900 C Austenitic stainless
steel loses it’s resistance to tarnish and corrosion.
• Carbon atoms migrate to grain boundaries and combine
with chromium to form chromium carbide where the
energy is the highest.
• If the stainless steel is severely cold worked the carbide
precipitate along slip planes, as a result the areas
deficient in chromium are less localized and carbides are
more uniformly distributed.
• Corrosion resistance is reduced in regions adjacent to
grain boundaries in which the chromium level is depleted
below that necessary for protection ( approx. 12%)

13. STABILIZATION
• This is the process by which carbon is made
unavailable for the sensitizing reaction.
• This is done at the time the alloy is
manufactured by either keeping the carbon
content exceptionally low or by adding other
metals such as Titanium that precipitates as
carbide instead of chromium.

14.  ANNEALING
• The effect associated with cold working such as strain
hardening, low ductility and distorted grains can be
reversed by simply heating the metal.
• The greater the amount of cold working the more
rapidly the effects can be reserved by annealing.
• Stages of annealing:
– Recovery.
– Recrystallisation.
– Grain growth.

15. .
• Recovery
– Cold work properties begin to disappear. Slight decrease in
tensile strength and no change in ductility. All the residual
stress is relaxed.
• Recrystallisation
– Old grains disappear totally and are replaced with strain free
grains.
– Occurs mostly in regions where defects have accumulated. It
attains it’s soft and ductile condition at the end of this stage.
• Grain Growth
– The Grain size and number of the recrystallised structure
depends on the amount of prior cold working.
– On repeated annealing larger grains consume smaller grains.
At the end of annealing the number of grains decrease and
size increases.

16.  Cold Working
• Cold forming stainless steel is generally
different to plain carbon (mild) steels, primarily
because stainless steels are stronger, harder
and more ductile, work harden more rapidly
and must maintain their inherent corrosion
resistance.
• When stainless steel is cold worked , carbide is
precipitated along slip planes , so chromium is
dispersed throughout rather than conc. at the
boundaries.
• More protection from corrosion.

17. SOLDERING
• It is a process of joining two metals by the use of an intermediate alloy
which has a lower melting point.
• Soldering temperature – 620 to 665 C.
• Ideally silver solders are used- alloy of silver, copper, zinc to which tin
and indium are added to lower the fusion temperature and improve
solderability.
• Needle like non luminous gas air flame is used. Thinner the diameter of
the flame, less the metal surrounding the joint is annealed.
• The work is held 3mm beyond the tip of the blue cone in the reducing
zone of the flame.
• Soldering should be observed in shadow against a black background so
the temperature can be judged by the colour of the work. The colour
should not exceed dull red.
• If possible the parts should be tag welded to hold them together.

18. • The flux is applied and the heavier gauge is heated first.
• Flux should cover all the area and the metal should be
allowed to flow around the joint.
• The work should be immediately quenched in water.
• The flux used for soldering stainless steel contains fluoride to
dissolve the passivating film formed by the chromium. The
solder does not wet the metal when such a film is present.
•Potassium Fluoride is one of the active chemicals in this
respect.
Flux:
• Aids in removing the oxide coating so as to increase the flow.
• Dissolves any surface impurities.
• Reduces the melting point of the solder.

19. WELDING
• Joining of two or more metal pieces directly under
pressure without introduction of an intermediary or a
filler material.
• Spot welding is used to join various components in
orthodontics.
• A large current is allowed to pass through a limited area
on the overlapping metals to be welded.
• The resistance of the material to the flow of current
produces intense localized heating and fusion of metals.
• The welded area becomes susceptible to corrosion due
to Chromium carbide precipitation and loss of
passivation.
• Increased weld area increases the strength.

20. Factors to be taken into account during
soldering and welding
As the annealing temperature of stainless steel falls
within the soldering and welding temperature ranges,
these procedure can lead to loss of working range and
elasticity of the metal.
Precautions:
• By using low fusing solders.
• Using low diameter needle like flame.
• Reducing the number of welding procedures and
duration

21. CHARACTERISTICS OF CLINICAL RELEVENCE
• Spring back (maximum elastic deflection)
– The extent to which the range recovers upon deactivation of
an activated arch wire.
– A measure of how far a wire can be deformed without causing
permanent deformation or exceeding the limits of the
material.
– Higher the spring back, grater the working range and lesser
are the requirements of frequent activations.
– Stainless steel has a spring back lesser than Nickel-titanium or
beta titanium.
• Working range and flexibility
– The distance a wire will bend elastically before permanent
deformation occurs.
– Flexibility is the measure of the amount at which the wire can
be strained without undergoing plastic deformation.

22. • Load deflection rate
– For a given load the deflection observed within the elastic limit.
– The force magnitude delivered by an appliance and is proportional to
the modulus of elasticity.
– Low load deflection rate provides ability to apply low forces, a more
constant force over time while deactivation, greater ease and accuracy
in applying a given force.
• Stress relaxation
– When a wire has been deformed and held in a fixed position the stress
may diminish with time even though the total strain may remain
constant.
• Resilience
– The capacity of a material to absorb energy when the material is
elastically deformed.
– It is measured by the area under the stress strain curve.
• Stiffness
– Amount of force required to produce a specific amount of deformation.

23. ADVANTAGES
• High stiffness, High yield strength and High resilience
• Good formability & Good environmental stability
• Good jointability & Adequate springiness
• Biocompatible
• Corrosion resistant & Economical
DISADAVTAGES
• Soldering is demanding
• Lower springback than NiTi
• High modulus of elasticity
• More frequent activations are required
• Heating to temperatures b/w 400-900 degrees cause release of Ni
and Cr thereby decreasing corrosion resistance

24. SOURCES
• PHILIPS’ SCIENCE OF DENTAL MATERIALS 12TH
EDITION
• CONTEMPORARY ORTHODONTICS – W.R.
PROFFIT 5TH EDITION
• SLIDESHARE.NET