18mty en 5 special steels and non-ferrous alloysmech.fd.cvut.cz/education/bachelor/18mty-en/... ·...
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18MTY – EN 5Special steels and non-ferrous alloys
Alloying elements in steelElement
Hardness
Increase
Mechanism
Tendency to
form hard
Carbides
Major / Minor Functions
Manganese
Mn
Moderate
increase
Powerful
solution
strengthener
Middle
1. Takes care of Sulphur (S).
2. Makes special steels in high concentrations
3. Cheap increase of hardenability.
Silicon
Si
Hardens,
but reduces
ductility
Moderate
increase
None
1. Deoxidation ("killing") of liquid steel.
2. Increases electrical resistivity (important for transformer
cores).
3. Improves oxidation resistance.
Aluminum
Al
Small
Grain size
hardening
No carbides but
nitride.
1. Deoxidation ("killing") of liquid steel.
2. Improves oxidation resistance.
Chromium
Cr
Moderate
increase
(Secondary)
prec. hardening
Strong
1. Corrosion resistance.
2. Strength + oxidation resistance at high T.
3. Abrasion resistance (needs high C, too).
Red = stabilizes austenite, black = stabilizes ferrite
Alloying elements in steel
ElementHardness Increase
Mechanism
Tendency
to form
hard
Carbides
Major / Minor Functions
Titanium
Ti
Strong increase;
Prec. hardening
Grain size
hardening
Extremely
strong
1. Oxygen, nitrogen and sulphur scavenger.
2. Forms hard carbides. prevents grain growth.
3. Prevents local depletion of carbon in stainless steels due to Cr-
carbide formation
Vanadium
V
Very strong
increase
Prec. hardening
Grain size
hardening
Moderate solid
solution hardening
Very
strong
1. Restricts grain coarsening of austenite.
2. Increases hardenability.
3. Delays softening during tempering.
Nickel
NiMild increase None
1. Enables austenitic steels
2. Enables Invar steel
Molybdenum
Mo
Strong increase
Prec. hardening
Grain size
hardening
Very
strong
1. Improves corrosion resistance of stainless steels.
2. Prevents embrittlement of certain Ni/Cr steels.
3. Keeps strength at higher T.
4. Provides high abrasion resistance.
Red = stabilizes austenite, black = stabilizes ferrite
Stainless steel
Passivation layer in stainless steel
Powder metallurgy - steps
Powder mettalurgy
Steels - summary „banana curve“
DP (dual phase steel)
TRIP (transformation induced plasticity) steek
TWIP (twinning induced plasticity) steel
Non-ferrous metals and alloys
Ferromagnetic alloys
Classification of non-ferrous metals
• Noble metals (Au, Ag, Pt, Pd, Rh, Ir)
• Radioactive metals (U, Pu, Th)
• Semiconductors (Si, Ge)
Strength of pure metals and their alloys
Alloys for castingMalleable alloys
Melting temperature of alloys
Soldering, refractories
Density of metals
5 g/cm3
Copper (Cu)
• Conduction of electricity and heat
• Density 9g/cm3
• Alloys – brass (Cu+Zn) and bronze (Cu+another metal - mainly Sn, Be (bearing), Pb,
Ni (alpaca 14%Ni))
can
no
n
bel
l
Ternary diagram Au-Ag-Cu - color
Thermal expansion coefficient
Nickel (Ni)• FCC lattice
• Corrosion resistance
• Cryogenic touhghness
• superalloýs
• Nimonic 20Cr2.5Ti20Co
• Invar Fe36Ni vs bimetal
Tungsten (W)
• Very high density19.3 g/cm3
• Very hard, high melting point (3422°C)
• Steel alloying, cutting tools - WC
• Fibres in incadescent bulbs
• Armor-piercing ammunition
Aluminium (Al)• Soft, high conductivity, malleability (Al-foil)
• Passivation layer =
corrosion resistance
• Al alloys• Dural AlCu4Mg1
• Precipitation, aging
Zeppelin, Junkers
Precipitaionhardening
1
2
3
PrecipitationhardeningNO-hardening
Titan (Ti)
• TiO2 Rutil, titanium white
• Complex production, after WW2, Kroll process
• High strength, low density of steel (4.4 g/cm3)
• Ti-6Al-4V main two-phase alloy up to 400°C.
• Density 4420 kg/m3, Young modulus 115 GPa, Strength1000 MPa
• Aerospace, military
• Biocompatible - medicinebcc
hcp
Magnesium (Mg)
• Lowest density (1.7g/cm3)
• Hexagonal lattice less malleable, casting
• Reactive (magnesiun flash)
• Elektron: Alloy Mg 90%, Al 9%, rest 1%
Metallic foam
• Decrease of density
• Elements of passive safety – deformation zone
Car body parts
Metallic foams- cont.
Stress-strain diagram of a metallic foam
Metallic glass
• Extreme rate of cooling 103-106K/s
• Critical cooling rate depends on alloy complexity
• Amorphous structure• No lattice• No dislocations• No plasticity• Elastic behavior till fracture• Strong and hard• Non-magnetic
• Metglas, Vitreloy
Metallic glass
Glassy alloys
Shape memory materials
Nitinol
Shape memory materials
Shape memory effect
Temperature
Co
mp
ress
ion
Stre
ssTe
nsi
on
Shape memory materials