Stainless Steel and Wrought Alloys Flashcards

1
Q

how are wrought alloys manipulated

A

cold working

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2
Q

when are wrought alloys used

A

ortho wires
partial denture clasps

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3
Q

what is steel made of

A

iron
carbon
chromium
manganese

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4
Q

what does chromium do

A

improve tarnish resistance

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5
Q

what are the uses for steel

A

cutting instruments
forceps

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6
Q

what does it mean that iron is allotropic

A

it undergoes two solid state phase changes with temperature

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7
Q

where does ferrite exist

A

at low temperature

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8
Q

where does austenite exist

A

at high temperature

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9
Q

where does cementite exist

A

at low temperature

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10
Q

what is pearlite

A

mix of ferrite and cementite

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11
Q

what is an alloy

A

two metals which form a common lattice structure, are soluble in one another, and form a solid solution

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12
Q

what are the types of substitutional solid solution

A

random and ordered

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13
Q

what does the quenching of austenite produce

A

martensite

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14
Q

what are the properties of martensite

A

hard and brittle

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15
Q

what does slow cooling of austenite give

A

pearlite (mix of ferrite and cementite)

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16
Q

if fast cooling of austenite gives martensite how do we change that into pearlite

17
Q

what is tempering of martensite

A

heating followed by quenching

18
Q

what is the composition of stainless steel

A

iron
carbon
chromium
nickel

19
Q

what does chromium do in stainless steel

A

lowers austenite to martensite temperature and rate
corrosion resistance

20
Q

what does nickel do in stainless steel

A

improves fracture strength
improves corrosion resistance

21
Q

what are the two types of stainless steel

A

martensitic
austenitic

22
Q

why does austenitic stainless steel contain sufficient chromium and nickel

A

to supress austenite to martensite transition

23
Q

what are the uses of austenitic stainless steel

A

dental equipment and instruments
ortho wires
denture bases

24
Q

what are the properties of 18-8 stainless steel

A

does not heat harden
soft when cast
work hardens rapidly

25
what is cold working
work done on metal/alloy at low temperature below recrystallisation temperature
26
what does cold working cause
slip - dislocations at grain boundaries
27
what does cold working make a material
stronger and harder
28
what are the requirements of wires
high springiness stiffness high ductility easily joined corrosion resistant
29
what is springiness
ability of material to undergo large deflections without permanent deformation
30
at what temperature does weld decay occur
between 500-900 degrees
31
what happens if weld decay occurs
alloy becomes brittle more susceptible to corrosion
32
how do you minimise weld decay
low carbon content steels stabilised stainless steels
33
what are the advantages of having a stainless steel denture base
it is thin light fracture resistant corrosion resistant high polish high thermal conductivity high impact strength high abrasion resistance
34
what are the disadvantages of stainless steel denture base
possible dimensional inaccuracy elastic recovery of steel = inaccurate damage of die under hydraulic pressure loss of fine detail during many stages difficult to ensure uniform thickness uneven pressure on die and counter die