MatSE 259 Exam 2 Review Session
1.
2.
3.
4.
5.
Exam structure – same as Exam 1
Please write your student I.D. on the answer
sheet
Please mark your answers clearly
Do not leave a question unanswered – there is
no negative marking
Hand in both question and answer sheets at
the end of the exam – the questions will be
posted on the website on Thursday after the
last conflict exam
Diffusion
•
1.
2.
Requirements:
Empty adjacent site
Sufficient energy
•
1.
2.
Types:
Interdiffusion or Impurity diffusion and Self diffusion
Vacancy diffusion and Interstitial diffusion
•
Steady-state diffusion: Fick’s first law
Solid Solutions
• A solid solution consists of at least two different atoms:
solute and solvent.
• The crystal structure of the solid solution is that of the
solvent, and the solute atoms occupy either interstitial or
substitutional positions.
• Solubility limit depends upon:
– Atomic Size
– Crystal Structure
– Electronegativity
– Valences
Fe-C (Fe-Fe3C) Phase Diagram
•
A phase diagram (equilibrium/constitutional diagram) shows the
relationship between temperature and the composition and
quantities of the phases of a system.
•
1.
2.
3.
The (Fe-Fe3C) phase diagram tells you:
The phases present
The composition of the phases present
The fractions (mass or volume) of the phases present
Eutectoid Reaction:
•
•
Hypo-eutectoid steels give pro-eutectoid a and pearlite
Hyper-eutectoid steels give pro-eutectoid CM and pearlite
Fe-C (Fe-Fe3C) Phase Diagram (contd.)
Textbook Example 9.65
HYPOEUTECTOID
HYPEREUTECTOID
UV
V
T
U
Martensite (MAR)
•
•
•
•
•
Transforms from AUS on quenching or rapid cooling via a
diffusionless shear process (CCP
BCT)
Very hard and strong
Hardenability of a steel: ability to make MAR (depth of
transformation to martensite)
Controlling the position of T-T-T plots:
- Changing C content
- Alloying
- Increasing AUS grain size
MAR tempering produces tempered martensite; the mstructure
of which consists of extremely small and uniformly dispersed
cementite particles in a continuous ferrite matrix. Tempered
Martensite is a lot tougher than MAR, depending on the
tempering temperature.
T-T-T curves
Textbook Example 10.15
Ms
Mf
(b)
(c)
(a)
T-T-T Curves
Textbook Example 10.18
(d)
(c)
(a) (b)
Stainless Steels (Cr > 11% wt)
Based on the predominant mconstituent, S.S. are classified
as:
1. Martensitic (heat treatable)
Medium Cr, Low Ni, Medium-High C
2. Ferritic (not heat treatable)
Medium Cr, Low Ni, Medium C
a ferrite is the predominant phase
3. Austenitic (not heat treatable)
High Cr, High Ni, Low C
g phase extended to room temperature
•