Stainless Steel and Wrought Alloys

Question 1

how are wrought alloys shaped

Answer 1

by cold working

Question 2

what are uses of wrought alloys

Answer 2

wires (orthodontic) and partial denture clasps

Question 3

what is the composition of steel

Answer 3

iron - 98%
carbon - 2%
chromium
manganese

Question 4

what is the function of chromium in steel

Answer 4

improves tarnish resistance

Question 5

how many solid state changes does iron go through with temperature

Answer 5

2
this is known as allotropic

Question 6

what happens to iron at temperatures over 1400 degrees

Answer 6

BCC lattice structure, low carbon solubility

Question 7

what happens to iron at temperatures between 900 and 1400

Answer 7

FCC lattice - higher carbon solubility

Question 8

what happens to iron at temperatures under 900 degrees

Answer 8

BCC lattice structure - low carbon solubility

Question 9

what is austenite and when does it exist

Answer 9

it is the initial solid solution which exists at high temperature

Question 10

what is ferrite and when does it exist

Answer 10

it’s a very dilute solid solution
exists at a low temperature

Question 11

when does cemenite exist

Answer 11

low temperatures

Question 12

what is pearlite

Answer 12

eutectoid mixture of ferrite and cemenite

Question 13

what is the definition of an alloy

Answer 13

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

Question 14

why is marsenite not a desired product

Answer 14

it is hard and brittle

Question 15

what does fast cooling of austenite result in

Answer 15

pearlite

Question 16

what does fast cooling of austenite result in

Answer 16

martensite

Question 17

what does tempering of martensite, a distorted lattice thats hard and brittle, give

Answer 17

pearlite

Question 18

how is martensite tempered

Answer 18

heated to 450 then quenched

Question 19

what are the four constituents of stainless steel

Answer 19

iron
carbon
chromium
nickel

Question 20

what level of chromium is required to regard steel as stainless

Answer 20

at least 12%

Question 21

what causes stainless steel to be corrosion resistant

Answer 21

chromium oxide layer

Question 22

what can stainless steel be attacked by that is very important to remember

Answer 22

chlorides

Question 23

what are the benefits of nickel

Answer 23

improves fracture strength
improves corrosion resistance
lowers austenite to martensite transition temperature

Question 24

what two forms does stainless steel come in

Answer 24

autentic
martensitic

Question 25

what is the martensitic stainless steel used for

Answer 25

dental instruments

Question 26

how does autentic stainless steel prevent from converting to martensite

Answer 26

contains sufficient chromium and nickel

Question 27

what is autentic stainless steel used for

Answer 27

dental equipment that isn't cutting edge orthodontic wires sheet forms for denture bases

Question 28

does stainless steel heat harden

Answer 28

no

Question 29

how is the presentation of stainless steel when cast

Answer 29

soft/ malleable

Question 30

why can stainless steel NOT be manipulated repeatedly

Answer 30

due to rapid work hardening

Question 31

what is cold working

Answer 31

work done on metal/ alloy at a low temperature below the recrystallisation temperature and causes slip

Question 32

what is slip

Answer 32

dislocations collect at grain boundaries which results in a stronger/ harder material

Question 33

what are wrought alloys used for

Answer 33

wires and RPD clasps

Question 34

what are 18 chromium -8 nickel stainless steel wires used for

Answer 34

ortho appliances (springs and clasps) partial dentures (clasp arms)

Question 35

what are the grades of 18-8 stainless steel

Answer 35

soft half hard hard spring temper

Question 36

when does weld decay occur

Answer 36

between 500 and 900 degrees celsius

Question 37

what causes weld decay

Answer 37

chromium carbides precipitate at grain boundaries and the alloy becomes brittle which limits manipulation of the wire - less chromium in the centre of the solid solution makes it more susceptible to corrosion

Question 38

how do you minimise weld decay

Answer 38

low carbon content steel stabilised stainless steel

Question 39

what does stabilised stainless steel consist of

Answer 39

contain small amounts of titanium or niobium forms carbides preferentially not at grain boundaries

Question 40

advantages of using stainless steel as denture base

Answer 40

fracture resistant corrosion resistant high polish attainable high thermal conductivity high impact strength

Question 41

what are disadvantages of stainless steel as a denture base

Answer 41

possible dimensional inaccuracy loss of fine detail during many stages difficulty to ensure uniform thickness