Stainless steel final /certified fixed orthodontic courses by Indian dental academy

STAINLESS STEEL
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


STAINLESS STEEL
Introduction
Carbon

steel

History
Structure
Composition
Classification
Properties
Hyper

& Hypo Eutectoid steels
Duplex stainless steel
Manufacture of stainless steel
Corrosion
Sensitization
Functions of alloying elements
Heat Treatment
Types of stainless steel arch wires
Merits of stainless steel wire alloys
A.J. Wilcock Wire

Stainless Steel

Introduction
Orthodontic wires, which generate the
biomechanical
forces
communicated
through brackets for tooth movement are
central to the practice of the profession.


CARBON STEEL


The American Iron and Steel Institute (AISI)
defines carbon steel as follows:



Steel is considered to be carbon steel when no
minimum content is specified or required for
chromium, cobalt, columbium [niobium],
molybdenum, nickel, titanium, tungsten,
vanadium or zirconium, or any other element to
be added to obtain a desired alloying effect.







Carbon steel can be classified, according to various
deoxidation practices, as rimmed, capped, semi-killed, or
killed steel.
Deoxidation practice and the steelmaking process will have
an effect on the properties of the steel. However, variations
in carbon have the greatest effect on mechanical properties,
with increasing carbon content leading to increased hardness
and strength.
As such, carbon steels are generally categorized according to
their carbon content. Generally speaking, carbon steels
contain up to 2% total alloying elements and can be
subdivided into low-carbon steels, medium-carbon steels,
high-carbon steels, and ultrahigh-carbon steels

Low-carbon steels contain up to
0.30% C. The largest category of this
class of steel is flat-rolled products
(sheet or strip), usually in the coldrolled and annealed condition.
The carbon content for these highformability steels is very low, less than
0.10% C, with up to 0.4% Mn. Typical
uses are in automobile body panels, tin
plate, and wire products.



Medium-carbon steels are similar to lowcarbon steels except that the carbon ranges from
0.30 to 0.60% and the manganese from 0.60 to
1.65%. Increasing the carbon content to
approximately 0.5% with an accompanying
increase in manganese allows medium carbon
steels to be used in the quenched and tempered
condition.





High-carbon steels contain from 0.60 to 1.00% C with
manganese contents ranging from 0.30 to 0.90%. Highcarbon steels are used for spring materials and highstrength wires.
Ultrahigh-carbon steels are experimental alloys
containing 1.25 to 2.0% C. These steels are thermo
mechanically processed to produce microstructures that
consist of ultra fine grains of spherical, discontinuous
proeutectoid carbide particles.






Carbon steels are steels whose alloying elements do
not exceed the following limits:
Element Max weight

Element

Max weight %

C

1.00

Cu

0.60

Mn

1.65

P

0.40

Si
S

0.60

0.05


Disadvantages of carbon steel.







The hardenability is low.
The physical properties (Loss of strength and brittle)
are decreased by both high and low temps
Subject to corrosion in most environments
Toughness and formability are quite low.
Not recommended for welding


These properties of carbon steel lead to the
development of stainless steel by alloying with
chromium and less than 1-2 % carbon.

STAINLESS STEEL


Extensively used in dentistry.
Used for almost all components of fixed appliance and
removable appliance



HISTORY



Discovered in England by Sheffield metallurgist during
early first world war.
Introduced for the construction of orthodontic appliances
in Ireland by Friel (1933)
By 1950, Stainless Steel alloys were used for most
orthodontic wires.








STRUCTURE





Steel are iron based alloys, that
contain less than 1-2% carbon.
The different classes of steel
evolve from possible lattice
arrangement of Iron (Fe)
Pure Iron at room temperature
has a body-centered cubic.
(BCC) Structure and is referred
to as “FERRITE”

This phase is stable up to 912oC
(1674F). The spaces between
atoms in the BCC structure are
small and oblate, hence “C” has
a very low solubility in ferrite.


At temperature between 912oC & 1394oC
stable form of iron is a Facecentered cubic (FCC) structure
called Austenite. The interstices in
the FCC lattice are larger than those
in the BCC. However the size of the
“C” atom is such that the lattice
strain still limits the maximum
carbon solubility to 2.11 wt%.


When austenite is cooled slowly from high
temperature, the excess “C” not soluble in ferrite
form FeC3. This hard brittle phase adds strength to
the relatively soft and ductile ferritic and austenitic
forms of Fe. However this transformation requires,
Diffusion and a defined period of time. If the
austenite is cooled very rapidly (Quenched) it
transformation to a Tetragonal structure called
martensite. This lattice is highly distorted and
strained resulting in a very hard, strong, brittle
alloy.

Composition
When chromium (12-30%) is added to steel the alloy is called stainless
steel. Other Constituents of stainless steel are.
 Chromium
 Nickel
 Carbon
 Silicon
 Phosphorus
 Sulphur
 Manganese
 Tantalum
 Niobium


COMPOSITION.
IRON

73-74%

CHROMIUM

18%

NICKEL

8%

CARBON

0-0.2%

Classification
The classification is based on the previously described
crystal structure.
 Ferritic
 Martensitic
 Austenitic


Composition in %
Type of lattice cr

ni

c

Ferritic(bcc)

11.5-27

0

0.2max

Austentic(fcc)

16-26

7-22

0.25max

Matensitic(bct)

11.5-17

0-2.5

0.15-1.20


FERRITIC STAINLESS STEEL







AISI series No 400 (American Iron & Steel Institute)
Good corrosion resistance
Higher strength cannot be applied
Not readily work hardenable
Lower cost
Not hardenable by heat treatment as temperature changes
induce no phase change in solid state.


MARTENSITIC STAINLESS STEEL










AISI series 400
Can be heat treated
High Strength and hardness
Corrosion resistance is less than other 2 types
Ductility is less
Yield strength may range from 492 mpa in the
annealed condition up to 1696 mpa in the hardened
(quenched & tempered) state.
BHN range – 230 to 600
Used for surgical and cutting instruments

AUSTENITIC STAINLESS STEEL









Most Corrosion resistant
2 types - AISI 302
 AISI 304
AISI 302 is the basic type, containing 18%,
Chromium, 8% Nickel and 0.15% Carbon.
AISI 304 has “C” content limited to 0.08%
Both may be designated as 18-8 stainless steel
Used by orthodontist to form bands & wires
Type 316L (0.03%C) is used for implants.

PROPERTIES
Greater ductility and ability to undergo more cold
work without breaking
Greater ease of welding
substantial strengthening during cold working
Readily overcomes sensitization
less critical grain growth
Comparative ease in forming
reasonable cost.

MECHANICAL PROPERTIES
ADA (American Dental Association) Specification No 32,
for orthodontic wires not containing precious metals.
Type I (Low resiliency)
Type II (High resiliency)
Tensile strength of 2100 mpa
Yield strength of 1400 mpa
KHN 600


TYPES OF STAINLESS STEEL ARCH
WIRES
1.

Rectangular arch wire

2.

0.16x0.22 inches
0.17x0.25 inches
0.19x0.25 inches

3.
4.

2.Round wires
3.Square Wires
0.16x0.16inches

2.

CO-AXIAL WIRES
Consist of varying no. of wires wrapped around a single core
wire which is stronger and resilient
Excellent initial arch wire.


3. BRAIDED & TWISTED WIRES
Small separate strands
interwined to form round or
rectangular shaped wires
.
Can sustain large elastic
deflections in bending
Better resilience
They apply a low force for a
given deflection compared to
solid stainless steel wires
Server as a transitional wire
from round to rectangular

EFFECTS OF COOLING
AUSTENITE

Slow
Cooling

Pearlite
Ferrite + Cementilte

Fast
Cooling

Tempering


Martensite



At a “C” concentration of 0.08% the alloy shows a
transformation from the single phase austenite to
a two structure consisting of “Ferrite” &
“Cementite”. This solid transformation is
defined as a eutectoid.



Steels with a “C” content of greater that 0.08%
are hypereutectoid steels.



If “C” content of lesser that 0.08% then it is hypo
eutectoid steels.

DUPLEX STAINLESS STEEL
Refers to steel having a 2 phase structure of almost equal properties
of austenite & ferrite.
High resistance to stress corrosion cracking
Higher tensile strength than austenite or ferrite
Weldable
Increased resistance to chloride ion attack.

MANUFACTURING OF STAINLESS
STEEL WIRES
An ingot of appropriate composition is cast.
Ingot is then subjected to a series of mechanical reduction,
operations till the cross sections is enough for wire
drawing.
Drawing is performed in a series of steps as work
hardening occurs in each step
.
Square and rectangular wires are made from round wires
using “Turks head apparatus” having 2 pairs of rollers at
right angle. This results in some inevitable rounding of
corners.

CORROSION RESISTANCE
Stainless Steel resist tarnish and corrosion
primarily because of the passivating effect of
chromium.
A very thin, transparent but tough & impervious
oxide layer forms on the surface of the alloy when
it is subjected to an oxidizing atmosphere as
mild as clean air.
This protective oxide layer prevents further
tarnish and corrosion.

SENSITIZATION
The 18-8 Stainless Steel may lose its resistance to corrosion
if heated between 400o & 900oC, the exact temperature
depending on its “C” content.
The reason is the precipitation of chromium carbon at the
grain at high temperature. The small rapidly diffusing “C”
atom migrate to the grain boundaries from all parts of the
crystal to combine with the large, slowly diffusing
chromium atoms at the periphery of the grain, where the
energy is highest the formation of Cr3C is most rapid at
650oC; Below it, the diffusion rate is less, whereas above it a
composition of Cr3C begins.


When chromium combines with “C” in this
manner, its passivating qualities are lost.
This condition can be minimized by reducing
the “C” content of steel to such an extend that
such carbide precipitations cannot occur.


FUNCTIONS OF ALLOYING
ELEMENTS
Chromium

-

Passivating Effect

Molybdenum

-

Increase resistance to pitting corrosion

Nickel

-

Helps reduce corrosion & Increases
strength

Cobalt

-

Decreases hardness

Manganese

-

Acts as scavenger and increases
hardness during quenching

Silicon

-

Acts as deoxidizer

Titanium

-

Inhibits precipitation of
chromium carbide

STABILIZATION
It is a process of protecting the chromium
– carbide precipitate at the grain
boundaries, when steel is subjected to high
temperature in case of soldering & welding
Titanium is added.


STRESS RELIEF HEAT TREATMENT


Heat treatment of stainless steel wire (b/w 370 – 480C) is recommended to
eliminate residual stress from wire manufacture



Prevents breakage of complex appliances during assembly



Stabilize shape of appliances.
18/8 stainless steel after heat treatment effects are :Slight increase in modulus of elasticity
Greater increase in yield strength
Considerable increase in modulus of resistance
Resistance in failure due to corrosion

.
Increase of stabilized austenitic stainless steel, stress relief treatment is done at
370C. Heat treatment above 650 C results in :Recrystallization of microstructure
Compositional changes
Formation of chromium carbide

RELATIVE MERITS OF STAINLESS
STEEL WIRE ALLOYS

High force delivery
Low spring back
Excellent formability
Orthodontist can fabricate arch wire or segments with complicated
loop configuration
High stiffness
Good resilience
Adequate ductility
Low cost
Can be soldered and welded easily.

A.J. WILCOCK WIRES


Late A.J. Wilcock founded
A.J. Wilcock Scientific &
Engineering Pvt. Ltd in 1946



Initially
involved
in
manufacture of metallurgical
research eg. Lagter led to the
dev. Of high tensile stainless
steel wires.



Today A.J. Wilcock Australian wire is an international house
hold name in orthodontics & sets the standard against all
other stainless steel wires.



Strain aged processing ensures extra ordinary St. Steel wire
products.



A.J. Wilcock St. Steel rectangular wires are manufactured
using a unique ageing process giving the wire unmatched
resistency and energy storage.



Wilcock wires are well known for their ability to withstand
masticatory forces as well as being able to maintain their
shape even when auxiliaries and elastics are used.



There is no other wire which opens the bite as effectively as
wilcock wires

WIRE GRADES

Regular Grade

Regular Plus Grade

Special Grade

Special Plus Grade

Premium Grade

Premium Plus Grade

Supreme Grade.
TYPES

Hard drawn S.S. Wires

Pulse Straightened

Rectangular Wire

Australian Wire up righting springs

AVAILABLE IN 8 GRADES:

REGULAR GRADE

White label lowest grade and easiest to bend. Used for
practice bending or forming auxiliaries. It can be
used as arch wire when distortion and bite opening
is not a problem.


REGULAR PLUS GRADE:

Green label relatively easy to form yet more resilient
than regular grade. Used for auxiliaries when more
pressure and resistance to deformation is required.



SPECIAL GRADE:
Black label highly resilient yet can be formed into intricate
shapes with little danger of breakage



SPECIAL PLUS GRADE:
Orange label - hardness and resiliency of the wire are
excellent for Supporting anchorage and reducing deep
overbite.
PREMIUM GRADE
More difficult to bend—occasional breakage to be expected
PREMIUM PLUS GRADE
Extremely resilient, not suitable for sharp bends
SUPREME GRADE
Highest degree of resiliency, not suitable for sharp bends.








Till 1980wires were straightened by what is called as spinner
straightening process. Spinner straightening is a mechanical process of
straightening, usually in the cold hard drawn conditions.



The wire is pulled through high speed rotating bronze rollers which
torsionally twist the wire into a straightened condition. This can result in
permanent deformation.


The Mollenhauer bending pliers is strongly
recommended for bending Wilcock
wire as it helps to minimize breakage.
The tips are tungsten carbide for
durability with rounded & highly
polished edges.
BENDING RECOMMENDATIONS
Sharp bends not recommended in
grades above special
carbide tip pliers will cause wire
fracture in all grades
Always grasp wire lightly with
instruments to avoid nicking wire
surface
Grip the wire with thumb &
forefinger 1- 1.5” from pliers contact
point.
While holding the pliers steady,
slowly rotate the wire around the
instrument using thumb pressure.


PULSE STRAIGHTENED WIRES
One of the most popular products especially when time is a factor.
Convenient to use
Easy to store
Unmatched resiliency & smoothness
Available only in Special Plus, Premium, Premium plus & Supreme
Available 30 pieces / tube
Stiffness of the wire by 300%
Improved martensitic response & smooth surface characteristic for reduced frictions
Larger diameter are ideal for application
Small diameter best used for forming auxiliaries and early treatment alignment.

REFERENCES
1.

Phillips
Science of Dental Materials

2.

William R. Profit
Contemporary Orthodontics

3.

William A. Brantley
Orthodontic Materials

4.

Craig RG
Dental Materials 10th ed. St. Louis

5.

www. ADA Specifications. com
Orthodontic wires not containing precious metals

6.

WWW. A j Wilcock. com




7. Am j orthod 1981; 80: 1-16



8. www.AISI. Com



9. Angle orthod 1981; 51: 319-24



10.Am j orthod 1984; 86: 396-402



11. Angle orthod 1997; 67: 197-208



12. Am j orthod 1998; 113: 91-5



13.Am j orthod 1990; 98: 300-312


 THANK YOU


Stainless steel final /certified fixed orthodontic courses by Indian dental academy

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Andere mochten auch

Andere mochten auch (20)

Ähnlich wie Stainless steel final /certified fixed orthodontic courses by Indian dental academy

Ähnlich wie Stainless steel final /certified fixed orthodontic courses by Indian dental academy (20)

Mehr von Indian dental academy

Mehr von Indian dental academy (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

Stainless steel final /certified fixed orthodontic courses by Indian dental academy