1. MatSE 259 Exam 2 Review Session
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

2. Diffusion Requirements: Empty adjacent site Sufficient energy Types:
Interdiffusion or Impurity diffusion and Self diffusion
Vacancy diffusion and Interstitial diffusion
Steady-state diffusion: Fick’s first law

3. 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

4. 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.
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

5. Fe-C (Fe-Fe3C) Phase Diagram (contd.)
Textbook Example 9.65
HYPOEUTECTOID U V T
HYPEREUTECTOID U V

6. 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.

7. T-T-T curves
Textbook Example 10.15
(a)
(b)
(c) Ms Mf

8. T-T-T Curves
Textbook Example 10.18
(d)
(a)
(c)
(b)

9. 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