MATSE 259 EXAM 3 REVIEW SESSION
1. Exam Structure: Multiple choice (same as previous
exams) ,
hours , 25 questions
2. Please write your student I.D. on the answer sheet (NOT
SSN)
3. Please mark your answers clearly
4. Do not leave a question unanswered – there is no negative
marking
5. Hand in both question and answer sheets at the end of
the exam – the questions will be posted on the website
after the last conflict exam
TOPICS
CASE HARDENING
JOMINY TEST (HARDENABILITY)
CAST IRONS
 CORROSION
 POLYMERS
CASE HARDENING
 Steel alloy is exposed to a carbonaceous (usually CO) or
nitrogenous (usually NH3) atmosphere at elevated
temperature so that the “case” becomes carbon or
nitrogen rich.
- In nitriding, Fe2N forms which is very hard. In
carburizing, the alloy is then quenched and tempered to
get a hard casing.
 In induction hardening, a high frequency AC is used to
heat the alloy surface past its austenitizing temperature
and the alloy is then quenched and tempered.
JOMINY TEST
 hardenability: ability to form martensite! (not hardness)
 specimen is fully austenitized
 max. cooling at the quench end, decreases with distance
from quenched end.
 hardness is measured as a function of distance from
quenched end.
JOMINY TEST
Cooling rate, “severity of quench”, is dependent on:
 quenching medium:
» Water --- most severe
» Oil
» Air --- least severe
 specimen size and geometry:
» as surface area / mass increases, more rapid cooling rates
are achieved
(rounded shapes)
JOMINY TEST
Hardness at the center of a 2” diameter bar quenched in
water with a little agitation for 1040, 3140 and 4340 steels?
CAST IRONS
 Ferrous alloys with 2.5 < % wt C < 5.5 and other alloying
elements.
 For slow cooling rates,
 Fe-C (as opposed to Fe-Fe3C) phase diagram:
1153
g + GRAPHITE
a + GRAPHITE
740
CAST IRONS
Types:
» Gray cast iron  graphite flakes in an a or P
matrix, depending on the cooling rate and % Si
- Weak and brittle in tension, stronger and more
ductile under compression
- Effective in damping vibrations
- High fluidity at casting temperature, low
casting shrinkage
CAST IRONS
» Nodular (ductile) cast iron
- flakes become spheres, with addition of small amounts
of Mg and/or Ce before casting
- Several times stronger than gray cast irons
- High ductility: % EL up to 40
» White cast iron
- almost all C is as CM in P matrix
- Extremely hard: wear resistant
- Very brittle: unmachinable
» Heating white cast irons to ~850 C for ~30 hrs gives
Malleable Cast Irons
- Graphite clusters in an a or P matrix
- Mechanical properties: Relatively high strength and
malleability
CAST IRONS
Gray cast iron
White cast iron
Nodular (ductile) cast iron
Malleable cast iron
CORROSION
 Requirements:
»
»
»
»
• Anode: oxidation  CORROSION
• Cathode: reduction
Anode
Cathode
Electrolyte
Electrical connection
CORROSION
Classes of electro-chemical corrosion:
- Uniform attack
- Crevice corrosion
- Intergranular corrosion
- Erosion-corrosion
- Galvanic corrosion
- Pitting
- Selective leaching
- Stress corrosion
CORROSION
 MACRO
~ Dissimilar metals
- (Galvanic series); A galvanic series determines
which metal will act as the anode – the lower the
metal in the series, the more anodic it is.
~ Same metal in different electrolytes
- Crevice / pitting corrosion
~ Deformation
- Non-homogeneous residual stress
~ non-passivated vs. passivated metal couple
CORROSION
MICRO (single material)
~ grain boundary – anodic wrt bulk (high
energy regions)
~ orientation difference in grains
~ presence of different phases
~ segregation
CORROSION
 WELDING
CORROSION
 Remedies:
~ Environmental alteration
~ Protective coating
- anodizing (Al coating)
- galvanizing (Zn coating)
~ Material selection (i.e. passivated material usage)
~ Design (i.e. keep the ratio [anode area / cathode area] large
~ Cathodic protection:
-Electrically connect the metal to be protected to another metal
(sacrificial anode) that is more reactive in the particular environment.
Ex: Zn, Mg.
- Connect the negative terminal of an external DC source to the
metal to be protected and the positive terminal to an inert anode like
graphite.
POLYMERS

Polymers: long chains of covalently bonded small,
successively repeating units called monomers.
 Classification of polymers:
- Based on monomer/s: homopolymer, copolymer, blend.
CH2 CH2
O
O
||
||
-NH-(CH2)6-NH-C-(CH2)4-C-
Polyethylene
Nylon (6,6)
Copolymers: random, alternating, block, graft.
–A–A–B–A–B–B–B–A–
–A–A–A–A–B–B–B–B–B–B–B–B–A–A–A–A–A–
–A–B–A–B–A–B–A–B–
–A–A–A–A–A–A–A–A–A–A–A–A–A–A–A–A–A–A
|
|
B
B
|
|
B
B
|
|
B
B
POLYMERS
- Based on molecular structure: linear polymer, branched
polymer, crosslinked polymer, network polymer.
CH3
CH3
CH3
CH CH2 CH CH2 CH CH2
CH3
|
CH3
|
CH3
CH3
CH3
|
|
|
– C – CH2 – CH – CH2 – CH – CH2 –
|
CH3 – CH
|
CH2
|
CH3
|
– C – CH2 – CH – CH2 – CH – CH2 –
|
– C – CH2 – CH – CH2 – CH – CH2 –
|
|
|
CH3
CH3
CH3
Polyethylene
POLYMERS
- Based on tacticity: isotactic, syndiotactic, atactic.
CH3
CH3
CH3
CH3
CH3
CH CH2 CH CH2 CH CH2 CH CH2
CH3
CH CH2 CH CH2 CH CH2 CH CH2
CH3
CH3
CH3
CH3
CH3
CH3
CH CH2 CH CH2 CH CH2 CH CH2 CH CH2 CH CH2 CH CH2
CH3
CH3
Polypropylene
CH3
- Based on monomer geometry: cis-polymer, trans-polymer.
H CH3
| |
– CH2 – C = C – CH2 –
H
|
– CH2 – C = C – CH2 –
|
CH3
Polyisoprene
- Based on properties: thermoplasts, thermosets.
POLYMERS
 The molecular weight of polymers is determined in
two ways:
- Number-average molecular weight
- Weight-average molecular weight
 Degree of polymerization: