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