Stainless steel

STAINLESS STEEL,
SOLDERING AND
WELDING
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STRUCTURE OF MATTER
 Study of dental materials and its
properties particularily of solids.
 Basic materials used in the field of
Dentistry.
 Collective reaction of these atoms,
whether physical or chemical determine
the effectiveness of an material.

INTER ATOMIC BONDS
 PRIMARY BONDS
Ionic bonds Covalent bonds
Metallic bonds

 SECONDARY BONDS
(Vander waals force)

EQUILIBRIUM INTER ATOMIC
DISTANCE
 Limiting factor for the atoms & molecules
from approaching each other too closely.
 Boundaries & volumes of an atom are not
discrete instead they are vague determined
by their electrostatic fields.

 Forces of
attraction versus
forces of repulsion
dictating the
equilibrium
position of the
atoms.

CRYSTAL STRUCTURE
 UnitCell-smallest
repeating unit that is
contained in a crystal.
 SpaceLattice-any
arrangement of atoms
in space such that
every atom is situated
similarly to every
other atom.

BCC FCC HCP

CRYSTAL IMPERFECTIONS
 Point defects
Impurities
vacancies

 Line defects (dislocations)

 Planar defects (grain boundaries in
metals)
Orientation of space lattice of each grain.
Structure of grain proper & grain
boundaries are they same?
Grain boundaries a region of transition.
Non crystalline.
High energy.
Tendency towards amorphism.

SURFACE ENERGY
 The increase in the energy per unit area of
surface is referred as the surface energy
or surface tension.
 Surface energy of a solid is greater than
its interior.

 Factors affecting the surface energy
Available functional groups.
Type of crystal plane of a space lattice
present at the surface.

Adhesion & Bonding
 Adhesive force - like molecules.
 Cohesive force - unlike molecules.
 Adhesive.
 Adherend.
 Chemisorption.

BASIC METALLURGICAL TERMS
 What is a metal?
Any chemical element that ionises (+vely )
in solution is known as metal.
 What is an alloy?
A solid mixture of two or more metals.

 What is an cast
metal?
Solidification of pure
metal.
 What is an wrought
metal?
Wires are made from
castings by drawing
a cast metal through
die.
certain metallurgical
characteristics not
associated with cast
structure.

HISTORY OF STAINLESS STEEL
 In the year 1740 Beryamin Huntsman.
 In the year 1913,a break through came
when Brearly of Shiffield.
 Introduction of chromium steel to the field
of orthodontics by Friel of Ireland in 1933.
 Steel is an iron based alloy that contains
carbon less than 1.2%.
 When chromium is added to steel the alloy
is called stainless steel(12%-30%).

CLASSIFICATION
 Based on lattice arrangements
Ferritic (bcc)
Austenitic (fcc)
Martenistic (bct)
 Based on carbon content(0.8%)
Hypo-eutectoid
Hyper-eutectoid

 Acc to American iron and steel institute
300 – 502
 Acc to Andereson
Soft
Half-hard
Hard
 ANSI/ADA specification no 32
Type 1 (low-resilience)
Type 2 (high-resilience)

PROPERTIES BASED ON
LATTICE ARRANGEMENTS
 Ferritic (AISI-400)
Good corrosion
resistance.
Not hardenable by
heat treatment.
Not readily work
hardenable.
Finds little application
in dentistry.
 Martensitic(AISI-400)
Can be heat treated.
High strength &
hardness.
Used in surgical &
cutting instruments.

Austenitic(AISI-302),18-8 stainless steel.
 Type 304(0.08%),Type 316L(0.03%).
 Greater ductility and ability.
 Substantial strengthening.
 Ease of welding
 Readily over comes sensitization
 Less critical grain growth
 Ease in forming

SENSITIZATION (weld decay)
 When 18-8 stainless steel is heated to
4000
-9000
c.
 Formation of chromium carbide at grain
boundaries highest at 6500
c.
 An inter- granular corrosion occurs and a
partial disintegration of the metal may
occur.

STABILIZATION
 Theoretical stand point reduce the carbon
content such that carbide precipitation
does not occur.
 The method most commonly employed is
introduction of titanium approximately 6
times the carbon content.

DEFORMATION OF METALS
 From the physical properties of the metals
two types of deformation may exist.
Stresses below the proportional limit.
Stresses above the proportional limit.

COLD WORKING
 Also known as strain hardening/work hardening.
 In a poly crystalline material.
 Over a period of time greater stress is required
to produce the further slip.
 Metal becomes stronger and harder.
 As a result surface hardness, strength &
proportional limit are increased, where as the
ductility & resistance to corrosion are decreased.
 Elastic modulus remains the same.

ANNEALING
 Effects associated with cold working can
be reversed by heating the metal.
 Severe the cold working ,more readily
does annealing occur.
 In general comprises of three stages
recovery, recrystallisation and grain
growth.
 Higher the melting point of the metal
higher is the temp needed for annealing.

MANUFACTURING OF
ORTHODONTIC WIRES

DESIRABLE PROPERTIES
 Wires should have good modulus of
elasticity.
 low constant forces.
 Large elastic deflections.
 Ease of joining.
 Good tarnish & corrosion resistance.
 Good formability.

MECHANICAL PROPPERTIES
Stress and strain.
 The internal force divided by the area over which
it acts within the body is the resultant stress.
 The deformation is called strain.
 Depending on their direction they are classified
into three types,
Tensile stress
Compressive stress
Shear stress
Complex stress

 Elastic limit
 Proportional limit
 Yield strength

MODULUS OF ELASTICITY :
YOUNGS MODULUS(ELASTIC
MODULE)
 Ratio of stress to strain.
 The slope of this ratio indicates the
relative stiffness and the springiness of a
wire.
 Wire with low modulus of elasticity has
increased flexibility as compared to a wire
of high modulus of elasticity.

 Flexibility
 Resilience
 Spring back (range of
action)
 Formability

 Hardness
Property used to predict the wear
resistance of a material.
 Toughness
Property of being difficult to break.
 Brittleness
Opposite of toughness, indicates the
material is apt to fracture at or near its
proportional limit.

 Stress relaxation
Change in the stress over a period of time.
 Zero stress relaxation
In a deflected wire ,if the stress does not
reduce and wire still exists a constant
force.

Ductility
 Ability to with stand
under a tensile load.
 The relative ease in
which a metal can be
drawn into wire.
 Dependent on tensile
strength.
Malleability
 Ability to with stand
under compression.
 Increases with
increase in temp.
 The relative ease in
which a metal can be
drawn into sheet.

HEAT TREATMENT OF ALLOYS
Softening.
 Electric furnace for 10
mins at 7000
c &
quenched in water.
 Indicated for
structures that are to
be ground, shaped or
cold worked.
Hardening.
 Heated for 15-30
mins.
 Temp depends upon
the alloy composition.
 Generally ranges
from 2000
c-4500
c.

METAL JOINING OPERATIONS
 Soldering.
 Brazing.
 welding.

PARAMETERS GOVERING THE
PROCEDURE
 Parent metal.
 Flux.
 Brazing filler metal.
 Heat source.
 Methods of soldering.

FLUX
 Latin word means to flow.
 Purpose is to remove any oxide layer on
the parent metal.
 Based on their action
Protective
Reducing
Solvent
 Type1 (low temp glass)
 Type 2(reducing)

 Anti-flux .
Graphite, rouge (iron oxide) or whiting
(calcium carbonate)

TYPES OF SOLDERS
Soft
 Lead-tin alloys.
 Low melting point.
 Lack corrosion
resistance.
Hard
 Silver, copper, zinc,
cadmium.
 High melting point.
 Gold & silver solders.
 Have good tarnish &
corrosion resistance.

PROPERTIES OF A SOLDER
 Appropriate flow temperature.
 Ability to wet the parent metal.
 Sufficient fluidity.
 Good contrast.

HEAT SOURCE
 A gas-air or gas-oxygen torch.
 Gases commonly used,
Hydrogen.
Natural gas.
Propane.
Acetylene.

OVEN(FURNACE BRAZING)
 Provides an heated surroundings.
 Less heat is lost as compared to torch
brazing.
 Transmission of heat from the heating
elements to the working area.
 Convection.
 Conduction.
 Radiant heat.

METHODS OF SOLDERING
 Free hand soldering.
 Investment soldering.
 Infra red soldering.
1000 watt tungsten filament quartz iodine
bulb.
Mounted at the primary focal point of a
gold plated elliptical reflector.www.indiandentalacademy.com

WELDING
 A portion of metal being joined is melted &
flowed together.
 Joining of flat structures.
 A nugget of re-solidified cast structure.
 Strength of the joint depends on the area
of weld.
 Pioneer work in this field was done by
Friel1933&McKeag1939.

PARTS OF A TYPICAL WELDER
Heat generated=KI2
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Stainless steel

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