Test 3. Chapter 11 Flashcards
give percent carbon for low carbon, med carbon, high carbon
low carbon
as you go to low carbon to med carbon to high carbon, what happens to strength cost and ductility?
strength increases, increase cost, and decrease ductility
“cast iron”
Ferrous alloys with >2.1 wt are much _________ than steels
-more common ____ wt% carbon
higher
3- 4.5 wt %C
it usually has low melting (also brittle) so easiest to cast
what are two types of cast iron and give descriptions for each
Gray iron= graphite flakes weak & brittle under tension stronger under compression excellent vibrational dampening wear resistant
Ductile iron=
add Mg or Ce
graphite in NODULES not flakes
matrix often pearlite - better ductility
White iron=
<1wt% Si so harder but brittle
more cementite
Malleable iron=
Heating white iron at 800-900ºC
graphite in rosettes
more ductile
what are the limitations of ferrous alloys?
Relatively high density
Relatively low conductivity
Poor corrosion resistance (Exception?)
how can we fabricate metals?
Blacksmith - hammer (forged)
Molding - cast
Compare hot working to cold working
hot working=
T high enough for recrystallization
larger deformations
cold working=
well below TR
work hardening
smaller deformations
what are the different fabrication methods?
forming, casting and joining
forging
hammering, stamping
drawing
(rods, wire, tubing)
extrusion
(rods/tubings
rolling
(hot or cold rolling)
what are some different methods in forming?
forging, rolling, drawing, extrusion
what is casting?
Casting- mold is filled with metal
- metal melted in furnace, perhaps alloying elements added. Then cast in a mold
- most common, cheapest method
- gives good production of shapes
- weaker products, internal defects
- good option for brittle materials
Name different types of casting?
sand casting
investment casting
die
continuous casting
define sand casting
its cheap and easy to mold, use of sand.
pack sand around form (pattern) of desired shape
define investment casting
low volume and you can do complex shapes such as jewelry, turbine blades
- pattern is made from was, mold made by encasing in plaster of paris
- melt the wax and the hollow mold is left
- pour in metal
define die
(high volume, low T alloys)
define continuous casting
(simple slab shapes)
what are some methods for joining?
powder metallurgy, welding
what is powder metallurgy
used with materials w/low ductility
what is welding
used when one large part is impractical
define the heat affected zone
region in which the microstructure has been changed
what are some thermal processing of metals
stress relief
process anneal
spheroidize
full anneal
normalize
How to anneal?
heat to T anneal, then slowly cool
Stress relief: reduced stress caused by :?
plastic deformation
nonuniform cooling
phase transformation
name three different types of heat treatments
annealing
quenching
tempered martensite
“effect of geometry”
when surface-to-volume ration increases what happens?
cooling rate increases
hardness increases
why does hardness change with position?
the cooling rate varies with position
Steels: increase TS, hardness (and cost) by adding?
- C (low alloy steels)
- Cr,V,Ni,Mo,W (high alloy steels)
- ductility usually decreases with additions
non ferrous:
cu,Al,Ti,Mg, refractory, and noble metals
what are some fabrication techniques?
forming, casting, joining
define hardenability
changes with positions
