Stainless steel and wrought alloys Flashcards
What are wrought alloys?
Alloys which have been shaped by cold working
give 2 uses for wrought alloys
- orthodontic wires
- partial denture clasps
What is the composition of steel?
> 98% iron, <2% carbon
what is an alloy?
2 metals that form a common lattice structure that:
- are soluble in one another
- form a solid solution
What are the components of stainless steel?
- iron
- chromium >12%
- nickel
Why is stainless steel corrosion resistant?
it has a chromium oxide layer
Why is nickel added to stainless steel?
- improves fracture strength
- improves corrosion resistance
Why is nickel added to stainless steel?
- improves fracture strength
- improves corrosion resistance
What is cold working?
- work done on a metal or alloy at low temperature (below recrystallisation temperature
- causes slip - dislocations collect at grain boundaries
- results in stronger, harder material
What are the types of stainless steel?
- martensitic
- austenitic
describe the cementite phase
Fe3C - exists at low temperature
define the pearlite phase
eutectoid mix of ferrite and cementite
briefly outline the properties and use of martensitic stainless steel
- 12-13%
- can be hardened by heat
- used in dental instruments
list the uses of austenitic stainless steel
- dental equipment and instruments to be sterilised (not cutting edge)
- orthodontic wires
- sheet forms for denture bases
What is the composition of 18-8 stainless steel?
- 18% chromium
- 8% nickel
- 0.1% carbon
- 74% iron
What are the properties of 18-8 stainless steel?
- does not heat harden
- malleable when cast
- work hardens rapidly
List the ideal properties of wires
- high springiness (YM/Elastic limit)
- high ductility
- easily joined without impairing properties e.g. soldering
- corrosion resistant
What is the Young’s modulus or elastic limit of a material?
The maximum force that can be applied without causing permanent deformation
What are the advantages of a stainless steel denture base?
- thinner than acrylic
- light
- fracture resistant
- corrosion resistant
- high polish attainable
- high thermal conductivity
- high impact strength
- high abrasion resistance