Stainless Steel and Wrought Alloys Flashcards
how are wrought alloys manipulated
cold working
when are wrought alloys used
ortho wires
partial denture clasps
what is steel made of
iron
carbon
chromium
manganese
what does chromium do
improve tarnish resistance
what are the uses for steel
cutting instruments
forceps
what does it mean that iron is allotropic
it undergoes two solid state phase changes with temperature
where does ferrite exist
at low temperature
where does austenite exist
at high temperature
where does cementite exist
at low temperature
what is pearlite
mix of ferrite and cementite
what is an alloy
two metals which form a common lattice structure, are soluble in one another, and form a solid solution
what are the types of substitutional solid solution
random and ordered
what does the quenching of austenite produce
martensite
what are the properties of martensite
hard and brittle
what does slow cooling of austenite give
pearlite (mix of ferrite and cementite)
if fast cooling of austenite gives martensite how do we change that into pearlite
tempering
what is tempering of martensite
heating followed by quenching
what is the composition of stainless steel
iron
carbon
chromium
nickel
what does chromium do in stainless steel
lowers austenite to martensite temperature and rate
corrosion resistance
what does nickel do in stainless steel
improves fracture strength
improves corrosion resistance
what are the two types of stainless steel
martensitic
austenitic
why does austenitic stainless steel contain sufficient chromium and nickel
to supress austenite to martensite transition
what are the uses of austenitic stainless steel
dental equipment and instruments
ortho wires
denture bases
what are the properties of 18-8 stainless steel
does not heat harden
soft when cast
work hardens rapidly
what is cold working
work done on metal/alloy at low temperature below recrystallisation temperature
what does cold working cause
slip - dislocations at grain boundaries
what does cold working make a material
stronger and harder
what are the requirements of wires
high springiness
stiffness
high ductility
easily joined
corrosion resistant
what is springiness
ability of material to undergo large deflections without permanent deformation
at what temperature does weld decay occur
between 500-900 degrees
what happens if weld decay occurs
alloy becomes brittle
more susceptible to corrosion
how do you minimise weld decay
low carbon content steels
stabilised stainless steels
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
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
