Metallic Materials

1
Metallic Materials

• Ferrous Alloys (iron and steels)
• Steels
• Plain carbon steels Fe-C alloys
• Alloy steels Fe-C alloying elements such as
  Cu, Ni, Cr, Mn, Mo, V, W etc
• Low-carbon steels
• C lt 0.30 wt
• a pearlite
• relatively soft
• good ductility and toughness
• easily manufactured
• inexpensive
• example applications car body parts, beams and
  sheets for construction

• Medium-carbon steels
• C 0.25-0.6 wt
• often tempered martensite
• stronger
• less ductile and less tough
• example applications railway wheels, gears,
  crankshafts

Table 11.2
Table 11.1
Yield strength 400-1800 MPa Ultimate tensile
strength 600-2100 MPa Elongation 30-10
Yield strength 200-400 MPa Ultimate tensile
strength 400-500 MPa Elongation 20-30
Reading 12.5-12.14 (5th ed), 11.1-11.3 (6th ed)
2
Metallic Materials

• High-carbon steels
• C 0.6-1.4 wt
• tempered martensite other carbides in alloy
  steels
• hard and strong
• not ductile
• example applications tools and dies

• Stainless steels
• Cr gt10 wt
• Ni and Mo often added
• martensite, ferrite or austenite
• a large range of strength and ductility depending
  on microstructure
• highly corrosion resistant
• example applications cutlery, pressure vessels,
  chemical processing equipment, surgical tools,
  furnace parts

Table 11.4
Table 11.3
HRC 60-70
3
Metallic Materials
C exists in most cast irons as graphite rather
than forming carbide usually as a result of Si
addition and slower cooling

• Cast irons (C 3-4.5 wt)

This is the Fe-C equilibrium phase diagram and
different from the Fe-Fe3C phase diagram which
contains the metastable phase Fe3C
1147C in Fe-Fe3C
4.3 in Fe-Fe3C
The Fe-rich part is similar with slightly
different eutectoid and eutectic compositions and
temperatures
727C in Fe-Fe3C
0.76 in Fe-Fe3C
4
Metallic Materials

• Grey cast iron
• C 2.5-4 Si 1-3
• flakes of graphite in a matrix of a or pearlite
• weak and brittle in tension
• high damping ability
• high wear resistance
• good castability
• cheap
• example applications base for machines, garden
  furniture, pistons, engine cylinders

Graphite
Ultimate tensile strength 150-250
MPa Elongation 0
5
Metallic Materials

• Nodular cast iron (ductile cast iron)
• grey iron Mg/Ce
• nodules of graphite in a matrix of a or pearlite
• stronger and more ductile comparable to low
  carbon steels
• example applications valves, gears, crankshafts

Graphite
Yield strength 300-500 MPa Ultimate tensile
strength 400-800 MPa Elongation up to 20
6
Metallic Materials
Family of cast irons
White irons contain less Si (lt 1) and Fe3C forms
upon casting instead of graphite. White irons are
very brittle and hard.
Malleable irons result from reheating white irons
to 700C for gt30 h, and consist of
rosette-shaped graphite in a matrix of either
pearlite or ferrite.
Table 11.5 lists the compositions, properties and
applications of some cast irons
7
Metallic Materials
Family of ferrous alloys
8
Metallic Materials

• Nonferrous Alloys
• Al alloys
• Attractive properties
• low density (2.7 g/cm3)
• high corrosion resistance
• high electrical and heat conductivity
• easy to form and manufacture
• Series of wrought Al alloys
• 1xxx (e.g. 1100, 1199) pure Al
• soft and very ductile
• good electric conductivity
• applications including electrical conductors,
  foil
• 2xxx (e.g. 2024, 2618) Al-Cu (Mg)
• precipitation hardenable
• high strength
• uses in aircraft structures

• 3xxx (e.g. 3003, 3004) Al-Mn (Mg)
• moderate strength with good ductility
• work hardened and solution strengthened
• uses in making beverage cans (body)
• 4xxx Al-Si alloys
• use as electrodes in welding and brazing
• 5xxx (e.g. 5005, 5182, 5454) Al-Mg
• solid solution and work hardened
• moderate strength
• weldable and good corrosion resistance
• for making petrol tanks,boats, beverage can (top)

9
Metallic Materials

• 6xxx (e.g. 6061, 6063) Al-Mg-Si
• age hardened
• medium strength
• weldable and good corrosion resistance
• good extrudability
• uses in window frames, cars
• 7xxx (e.g. 7075, 7475) Al-Zn-Mg
• age hardened
• very high strength
• used for structural applications in aircraft
• 8xxx Al-Li ( other elements)
• very light

Ti alloys Mg alloys Cu alloys Superalloys Ni,
Co Refractory metals Nb, Mo, W, Ta Noble metals
Au, Ag, Pt Intermetallics TiAl, NiAl, FeAl, etc.
Self study