Stainless Steel and Wrought Alloys

Question 1

how are wrought alloys manipulated

Answer 1

cold working

Question 2

when are wrought alloys used

Answer 2

ortho wires
partial denture clasps

Question 3

what is steel made of

Answer 3

iron
carbon
chromium
manganese

Question 4

what does chromium do

Answer 4

improve tarnish resistance

Question 5

what are the uses for steel

Answer 5

cutting instruments
forceps

Question 6

what does it mean that iron is allotropic

Answer 6

it undergoes two solid state phase changes with temperature

Question 7

where does ferrite exist

Answer 7

at low temperature

Question 8

where does austenite exist

Answer 8

at high temperature

Question 9

where does cementite exist

Answer 9

at low temperature

Question 10

what is pearlite

Answer 10

mix of ferrite and cementite

Question 11

what is an alloy

Answer 11

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

Question 12

what are the types of substitutional solid solution

Answer 12

random and ordered

Question 13

what does the quenching of austenite produce

Answer 13

martensite

Question 14

what are the properties of martensite

Answer 14

hard and brittle

Question 15

what does slow cooling of austenite give

Answer 15

pearlite (mix of ferrite and cementite)

Question 16

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

Answer 16

tempering

Question 17

what is tempering of martensite

Answer 17

heating followed by quenching

Question 18

what is the composition of stainless steel

Answer 18

iron
carbon
chromium
nickel

Question 19

what does chromium do in stainless steel

Answer 19

lowers austenite to martensite temperature and rate
corrosion resistance

Question 20

what does nickel do in stainless steel

Answer 20

improves fracture strength
improves corrosion resistance

Question 21

what are the two types of stainless steel

Answer 21

martensitic
austenitic

Question 22

why does austenitic stainless steel contain sufficient chromium and nickel

Answer 22

to supress austenite to martensite transition

Question 23

what are the uses of austenitic stainless steel

Answer 23

dental equipment and instruments
ortho wires
denture bases

Question 24

what are the properties of 18-8 stainless steel

Answer 24

does not heat harden
soft when cast
work hardens rapidly

Question 25

what is cold working

Answer 25

work done on metal/alloy at low temperature below recrystallisation temperature

Question 26

what does cold working cause

Answer 26

slip - dislocations at grain boundaries

Question 27

what does cold working make a material

Answer 27

stronger and harder

Question 28

what are the requirements of wires

Answer 28

high springiness
stiffness
high ductility
easily joined
corrosion resistant

Question 29

what is springiness

Answer 29

ability of material to undergo large deflections without permanent deformation

Question 30

at what temperature does weld decay occur

Answer 30

between 500-900 degrees

Question 31

what happens if weld decay occurs

Answer 31

alloy becomes brittle
more susceptible to corrosion

Question 32

how do you minimise weld decay

Answer 32

low carbon content steels
stabilised stainless steels

Question 33

what are the advantages of having a stainless steel denture base

Answer 33

it is thin
light
fracture resistant
corrosion resistant
high polish
high thermal conductivity
high impact strength
high abrasion resistance

Question 34

what are the disadvantages of stainless steel denture base

Answer 34

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