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BDS3 Dental Materials Sciences > Stainless steel and wrought alloys > Flashcards

Stainless steel and wrought alloys Flashcards

1
Q

What are wrought alloys?

A

Alloys which have been shaped by cold working

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2
Q

give 2 uses for wrought alloys

A
  • orthodontic wires
  • partial denture clasps
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3
Q

What is the composition of steel?

A

> 98% iron, <2% carbon

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4
Q

what is an alloy?

A

2 metals that form a common lattice structure that:
- are soluble in one another
- form a solid solution

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5
Q

What are the components of stainless steel?

A
  • iron
  • chromium >12%
  • nickel
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6
Q

Why is stainless steel corrosion resistant?

A

it has a chromium oxide layer

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7
Q

Why is nickel added to stainless steel?

A
  • improves fracture strength
  • improves corrosion resistance
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7
Q

Why is nickel added to stainless steel?

A
  • improves fracture strength
  • improves corrosion resistance
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8
Q

What is cold working?

A
  • 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
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9
Q

What are the types of stainless steel?

A
  • martensitic
  • austenitic
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10
Q

describe the cementite phase

A

Fe3C - exists at low temperature

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11
Q

define the pearlite phase

A

eutectoid mix of ferrite and cementite

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12
Q

briefly outline the properties and use of martensitic stainless steel

A
  • 12-13%
  • can be hardened by heat
  • used in dental instruments
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13
Q

list the uses of austenitic stainless steel

A
  • dental equipment and instruments to be sterilised (not cutting edge)
  • orthodontic wires
  • sheet forms for denture bases
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14
Q

What is the composition of 18-8 stainless steel?

A
  • 18% chromium
  • 8% nickel
  • 0.1% carbon
  • 74% iron
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15
Q

What are the properties of 18-8 stainless steel?

A
  • does not heat harden
  • malleable when cast
  • work hardens rapidly
16
Q

List the ideal properties of wires

A
  • high springiness (YM/Elastic limit)
  • high ductility
  • easily joined without impairing properties e.g. soldering
  • corrosion resistant
17
Q

What is the Young’s modulus or elastic limit of a material?

A

The maximum force that can be applied without causing permanent deformation

18
Q

What are the advantages of a stainless steel denture base?

A
  • thinner than acrylic
  • light
  • fracture resistant
  • corrosion resistant
  • high polish attainable
  • high thermal conductivity
  • high impact strength
  • high abrasion resistance

BDS3 Dental Materials Sciences (10 decks)

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