Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

3 DMS > Stainless Steel and Wrought Alloys > Flashcards

Stainless Steel and Wrought Alloys Flashcards

1
Q

What are wrought alloys?

A

An alloy that can be manipulated or shaped by cold working and drawn into wire

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are common uses of wrought alloys?

A

Orthodontic wires
Partial denture clasps

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the composition of steel?

A

> 98% iron
<2% carbon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the other constituents of steel?

A

Chromium - 0.5-1% - improves tarnish resistance
Manganese - sulfur scavenger
Molybdenum
Silicon
Nickel
Cobalt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the dental uses of steel?

A

Cutting instruments - >0.8% C
Forceps - <0.8% C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does allotropic mean?

A

Undergoes two solid state phase changes with temperature so can exist in 1 of 2 crystalline structures
eg - iron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe the structure of iron >1400C

A

Body centred cubic (BCC) lattice structure - low carbon solubility (0.05%)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe the structure of iron between 900 and 1400C

A

Face centred cubic (FCC) lattice - higher carbon solubility (2%)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the structure of iron below 900C

A

BCC lattice structure - low carbon solubility (0.05%)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What different solutions are seen on the Fe-C phase diagram?

A

Austenite
Ferrite
Cementite
Pearlite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is an alloy?

A

Two metals that form a common lattice structure, are soluble in one another and so form a solid solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the different types of solid solution?

A

Substitutional - random or ordered
Interstitial - atoms markedly different in size

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What grain structure is found on the Fe-C phase diagram on rapid cooling?

A

Austenite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

When are ferrite and cementite found on the Fe-C phase diagram?

A

If molten alloy is cooled slowly - gives bad mechanical properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What happens when steel is quenched?

A

It actually gives martensite, not austenite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe martensite

A

Forms a distorted lattice as carbon is unable to diffuse normally within the iron atoms in each grain
Makes a hard, brittle material - we don’t want this

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What happens on cooling of austenite?

A

Slow cooling gives pearlite, ferrite or cementite
Fast cooling gives martensite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What happens when martensite is tempered?

A

It gives pearlite, ferrite or cementite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Describe tempering of martensite

A

Heating to 450C followed by quenching
Temperature and duration can cause conversion to ferrite (soft and ductile) or cementite (hard and brittle)
Control over heat treatment allows control over mechanical properties

20
Q

What are the main components of stainless steel?

A

Iron
Carbon
Chromium
Nickel

21
Q

Describe the role chromium plays in stainless steel

A

Must have at least 12% Cr to be stainless steel
Lowers austenite to martensite temperature
Lowers austenite to martensite rate
Causes corrosion resistance due to chromium oxide layer
Can be attacked by chlorides

22
Q

Describe the role Nickel plays in stainless steel

A

Lowers austenite to martensite transition temperature
Improves ultimate tensile strength
Improves corrosion resistance

23
Q

What are the two types of stainless steel?

A

Martensitic
Austenitic

24
Q

Describe martensitic stainless steel

A

12-13% chromium and little carbon
Heat hardenable (tempering process)
Can be tempered to produce dental hand instruments

25
Q

Describe austenitic stainless steel

A

Contains sufficient chromium and nickel to suppress the austenite to martensite transition
eg - 18% Cr and 8% Ni or 12% Cr and 12% Ni

26
Q

What are the uses of austenitic stainless steel?

A

Dental equiptment and instruments - not cutting edge
Orthodontic wires
Sheet forms for denture bases

27
Q

What is the composition of 18-8 stainless steel?

A

18% chromium
8% nickel
0.1% carbon
74% iron

28
Q

Describe 18-8 stainless steel

A

Does not heat harden
Soft and malleable when cast
Work hardens rapidly - can’t be repeatedly manipulated to form desired shape

29
Q

What is cold working?

A

Work done on a metal/alloy at low temperature eg - bending, rolling swaging
Causes slip - dislocations collect at grain boundaries
Makes a stronger, harder material

30
Q

What are the uses of 18-8 stainless steel wires?

A

Orthodontic appliances - springs and clasps
Partial dentures - clasp arms, wrought rests

31
Q

What are the grades of 18-8 stainless steel wires and what do they depend on?

A

Soft
Half hard
Hard
Spring temper
Depends on the degree of bending required

32
Q

What are the different type of alloy wires?

A

Stainless steel
Cobalt chromium
Gold
Nickel titanium
β-titanium

33
Q

What is the composition of cobalt chrome wires?

A

Co - 40%
Cr - 20%
Ni - 15%
Fe - 16%

34
Q

What is the composition of gold wires?

A

Au - 60%
Ag - 15%
CU - 15%
Pt/Pd - 10%

35
Q

What is the composition of Ni-Ti wires?

A

Ni - 55%
Tn - 45%
Some cobalt

36
Q

What is the composition of β-Ti wires?

A

Titanium
Some molybdenum

37
Q

What is springiness?

A

EL/YM
The ability of a material to undergo large deflections (form an arc) without permanent deformation

38
Q

What are the requirements of wires?

A

High springiness
Stiffness
High ductility
Easily joined
Corrosion resistant

39
Q

What can be used for soldering stainless steel wires?

A

Gold solder
Silver solder

40
Q

How are stainless steel wires soldered?

A

Temperature rise is close to stainless steel melting point
Quenched rapidly to maintain UTS

41
Q

What is wild decay?

A

A risk of soldering
Occurs between 500-900C
Chromium carbides precipitate at grain boundaries
Allow becomes brittle and more susceptible to corrosion

42
Q

How is wild decay minimised?

A

Low carbon content steels - expensive
Stainless steel with small quantities of titanium or niobium

43
Q

Describe stress relief annealing in stainless steel

A

Temperature of stainless steel at 450C for 1-2 minutes
Ensures configuration of metal atoms in grains settles into an equilibrium

44
Q

Describe swaging of stainless steel to make a denture base

A

A stainless steel sheet is placed between a die and counter-die
Pressure is applied and the sheet takes the shape of the counter-die as a denture base

45
Q

What are the advantages of stainless steel denture bases?

A

Thin
Light
Fracture resistant
Corrosion resistant
High polish obtainable
High thermal conductivity
High impact strength
High abrasion resistance

46
Q

What are the disadvantages of stainless steel denture bases?

A

Possible dimensional inaccuracy
Elastic recovery of steel may make it innacurate
Damage of die under hydraulic pressure during swaging
Loss of fine detail during many stages
Difficult to ensure uniform thickness
Uneven pressure on die and counter-die during swaging causes wrinkling of steel

3 DMS (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions