MatSE 259 Exam 2 Review Session

1
MatSE 259 Exam 2 Review Session

1. Exam structure same as Exam 1
2. Please write your student I.D. on the answer
   sheet
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 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 Ficks 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

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

Ms
Mf
8
T-T-T Curves

• Textbook Example 10.18

9
Stainless Steels (Cr gt 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