MT 348 ‐ Outline No. 1 ‐‐ 2009  MECHANICAL PROPERTIES    I. Introduction  

advertisement

MT   348  ‐  Outline   No.

  1  ‐‐  2009  

MECHANICAL   PROPERTIES  

 

I.

  Introduction   

A.

  Stresses   and   Strains,   Normal   and   Shear   Loading   

B.

  Elastic   Behavior  

 

II.

  Stresses   and   Metal   Failure   

A.

 ʺ Principal   Stress ʺ  Concept   

B.

  Plastic   Yield   Criteria   

C.

  Elastic   Fracture   Criteria   

D.

  Examples:   Uniaxial   Tension,   Torsion   

 

III.

  Tensile   Properties  

A.

  Engineering   Stress   and   Strain   

B.

  Strength   Characteristics   

 

1.

  Young ʹ s   modulus   

2.

  proportional   limit   (upper   yield   point   or   yield   point)   

3.

  yield   strength   

4.

  ultimate   tensile   strength   

C.

  Ductility   

1.

  elongation   at   fracture   

2.

  reduction   of   area   at   fracture   

D.

  Example   Calculations  

 

IV.

  Additional   Mechanical   Properties   

A.

  Creep   

1.

  creep   strength   

2.

  rupture   life   

B.

  Fatigue   (S/N   Curves   Only)   

1.

  endurance   limit   

2.

  fatigue   strength   

C.

  Fracture   

1.

  impact   strength   

2.

  fracture   toughness   

MT   348  ‐  Outline   No.

  2  ‐  2009  

DISLOCATIONS   AND   SLIP   PHENOMENA  

 

  I.

  Introduction   

A.

 

τ theoretical

  vs.

τ observed

  

B.

  Observation   of   Dislocations   

1.

  electron   microscopy   

2.

  etch   pitting   

3.

  slip   lines  

 

  II.

  Dislocation   Configurations   

A.

  Edge   Dislocations   (b

  t)   

1.

  definitions:   burger ʹ s   vector,   burger ʹ s   circuit,   and   tangent   vector   

2.

  slip   plane   

B.

  Screw   Dislocations   (b   //   t)   

1.

  ease   of   changing   slip   planes   

C.

  Mixed   Dislocations   

1.

  glide   loop   

D.

  Dislocation   Sources   

 

III.

  Slip   Phenomena   

A.

  Introduction   

1.

slip   system   as   a   close ‐ packed   direction   in   a   close ‐ packed   (or   closest ‐ packed)    plane   

2.

   changing   slip   planes    a.

  cross ‐ slip   (screw   dislocation)    b.

  climb   (edge   dislocation)   

B.

  Slip   Systems   in   Metallic   Crystals   

C.

  Resolved   Shear   Stress   and   Critical   Resolved   Shear   Stress   

1.

  resolved   shear   stress   

2.

 

τ

CRSS

  

3.

  factors   that   affect  

τ

CRSS

   

4.

  calculate   resolved   shear   stress   by   vector   algebra   

D.

  Deformation   in   Single   Crystals   

 

MT   348  ‐  Outline   No.

  3  ‐  2009  

ELEMENTS   OF   GRAIN   BOUNDARIES  

 

  I.

  Introduction   [6.1]   

A.

  Low   Angle   Boundaries   [6.2]   

B.

  High   Angle   Boundaries   [6.5,   6.8]  

 

II.

  Boundary   Energy   

A.

  Grain   Boundaries   [6.5]   

B.

  Interphase   Boundaries   [6.9]   

1.

  force   balance   

2.

  2 nd

  phase   morphology   (example:   hot   shortness)   

 

III.

  Grain   Size   [6.10]   

A.

  Measurement   

1.

  linear   intercept   method   

2.

  ASTM   grain   size   number   

B.

  Mechanical   Property   Effects   [6.11]   

1.

  strengthening   (Hall ‐ Petch   Equation)   

2.

  fabricability   

MT   348  ‐  Outline   No.

  4  ‐  2009  

VACANCIES   AND   DIFFUSION  

 

I.

  Introduction   

A.

  Temperature   Sensitive   Processes   

B.

  Free   Energy   Decrease   as  ʺ Driving   Force ʺ  

1.

  internal   energy   and   enthalpy   

2.

  configurational   entropy  

 

II.

  Vacancy   Formation   

A.

  Setting   up  

Δ

G   

B.

  Calculating  

k

ln

P

B

P

A

  

C.

  Minimizing  

Δ

G

dn v

=

0

 

D.

  The   Result:   

 

 

 

 

 

 

n v n v

=

Γ =

e

Q r

RT

III.

  Vacancy   Motion   

A.

  Setting   Up   Calculation   

B.

  The   Result:   

 

Ae

Q m

RT

 

 

IV.

  Solid ‐ State   Diffusion   

A.

  Vacancy   Mechanism   (

Q f  

+   Q m

)   

B.

  Interstitial   Mechanism   (

Q m

  only)   

 

 

MT   348  ‐  Outline   No.

  5  ‐  2009  

RECRYSTALLIZATION   AND   GRAIN   GROWTH

 

 

I.

  Introduction   

A.

  Cold   Work   /   Stored   Energy   

B.

  Release   of   Cold   Work   (Stages   of   Annealing)  

 

II.

  Recovery   

A.

  Subtle   Microstructural   Changes   

1.

  dislocation   annihilation   

2.

  polygonization   

3.

  sub ‐ boundary   coalescence   

 

III.

  Recrystallization   

A.

  Time   and   Temperature   Dependence   

1.

  observations   

2.

  apparent   activation   energy,  

Q r

 

 

3.

 ʺ recrystallization   temperature ʺ  

B.

  Effect   of   Prior   Strain   on   Recrystallization   Rate   

C.

  Nucleation   and   Growth   in   Recrystallization   

1.

 

ε

,   T   effects   on   nucleation   

2.

 

ε

,   T   effects   on   growth   

D.

  Recrystallized   Grain   Size   

1.

  effect   of   prior   strain   

2.

  effect   of   metal   purity   

3.

  effect   of   initial   grain   size   

E.

  Dynamic   Recrystallization   (Hot   Working)   

 

IV.

  Controlling   Strength   and   Ductility   by   Working   and   Annealing   Processes   

A.

  Forming   Parameters   

B.

  Example   Problems  

 

V.

  Grain   Growth   

A.

  Driving   Force   

B.

  Ideal   Grain   Growth   Law   (

D

2

=

D o

2

=

kt

)   

C.

  Factors   Affecting   Grain   Growth   

1.

  temperature   

2.

  impurities   or   solute   additions  

3.

  second   phase   particles   

MT   348  ‐  Outline   No.

  6   –2009  

SOLID   SOLUTIONS  

 

I.

  Introduction   

A.

  Types   of   Solutions   

1.

  substitutional   

2.

  interstitial   

B.

  Intermediate   Phases   

1.

  solid   solution   

2.

  intermetallic   compound  

 

II.

  Solubility   Criteria   

A.

  Interstitial   

1.

  size   considerations   

2.

  transition   metal   effect   

3.

  examples   

B.

  Substitutional   

1.

  size   

2.

  chemical   similarity   

3.

  additional   criteria   

4.

  examples   

 

III.

  Solid ‐ Solution   Strengthening ‐ Solute/Dislocation   Interactions   

A.

  Dislocation   Stress   Fields   

1.

  screw   dislocation   (shear   stresses   only)   

2.

  edge   dislocation   (shear   and   normal   stresses)   

B.

  Solute   Atom   Stress   Fields   

1.

  substitutional   solute   

2.

  interstitial   solute   

C.

  Stress   Field   Interactions   

1.

  edge   dislocations/all   solute   atoms   

2.

  screw   dislocations/interstitial   solute   only   

3.

  solute   atmospheres  

 

IV.

  Solute   Atmospheres   and   Mechanical   Effects   

A.

  Yield   Points   in   Low ‐ Carbon   Steel   

B.

  Luders   Bands   and   Stretcher   Strains   

MT   348  ‐  Outline   No.

  7  ‐  2009  

SOLIDIFICATION   OF   METALS  

 

 

I.

  Introduction   

A.

  The   Liquid   Phase  

B.

  Nucleation   

C.

  Metallic   Glass  

II.

  Crystal   Growth   from   the   Liquid   Phase   

A.

  Heat   of   Fusion   

B.

  Heat   of   Vaporization   

C.

  Liquid ‐ Solid   Interface   

 

III.

  Liquid ‐ Solid   Interface   Instability   

A.

  Continuous   Growth   

B.

  Lateral   Growth   

C.

  Cellular   Structure   

D.

  Dendritic   Structure   

 

IV.

  Freezing   in   Alloys   

A.

  Scheil   Equation  

B.

  Segregation  

C.

  Homogenization  

  

 

MT   348  ‐  Outline   No.

  8  ‐  2009  

PRECIPITATION   HARDENED   IN   ALLOYS  

 

I.

  Introduction   

A.

  Importance   of   Strengthening   Technique   

B.

  Relative   Effectiveness   

C.

  Basis   of   Technique  

II.

  Nucleation   and   Growth   Theory   

A.

  Homogeneous   Nucleation   

1.

  critical   radius   (r*)   

2.

  activation   energy   for   nucleation   (

Δ

G*)   

3.

  nucleation   rate   (

N

B.

  Heterogeneous   Nucleation   

)   

C.

  Growth   Rate   (

G

)   

D.

  Transformation   Rate   

 

1.

  microstructural   result   of   high  

 

III.

  The   Strengthening   Mechanism   of   Precipitates   

A.

  Observations   

B.

  The   Orowan   Bowing   Equation   

C.

  Coherency   Effects   

D.

  Overaging   

1.

  loss   of   coherency   

  vs.

  low

2.

  particle   coarsening   ( ʺ Ostwald   ripening ʺ )   

E.

  Additional   Factors   

1.

  transition   phases   

2.

  equilibrium   phases   and   annealing   

    

 

MT   348  ‐  Outline   No.

  9  ‐  2009  

METALLURGY   OF   STEELS  

I.

  The   Iron ‐ Carbon   Phase   Diagram   (pp.

  562 ‐ 566)   

A.

  Equilibrium   Phases   

1.

  austenite   

2.

  ferrite   

3.

  cementite   (metastable)   

B.

  Eutectoid   Decomposition   (pp.

  566 ‐ 574)   

1.

  the   eutectoid   reaction   and   pearlite   

2.

  pearlite   growth   

3.

  hypoeutectoid   compositions   (<   0.8%   C)   

4.

  hypereutectoid   compositions   (>   0.8%   C)   

C.

  Ferritic  ‐ Pearlitic   Steels   

1.

  characteristics   

2.

  effect,   carbon   content   

3.

  effect,   cooling   rate   

4.

  effect,   alloying   

5.

  AISI   and   SAE   designations   

D.

  Isothermal   Transformations   Diagrams   (pp.

  583 ‐ 584,   591 ‐ 600)   

1.

  experimental   determination   

2.

  examples   (eutectoid,   hypoeutectoid,   hypereutectoid)   

E.

  Martensite   Transformation   (pp.

  537 ‐ 540)   

1.

  mechanism   

2.

  microstructure   and   properties   

3.

  appearance   on   IT   diagram   

F.

  Tempered   Martensite   (a   misnomer)   (pp.

  639 ‐ 641)   

1.

  microstructure   and   properties   

G.

  Bainite   Transformation   (pp.

  584 ‐ 591)   

1.

  mechanism   and   characteristics   

2.

  microstructure   and   properties    a.

  high   magnification   (similarity   to   tempered   martensite)    b.

  low   magnification   

3.

  austempering   (isothermal   transformation   to   bainite)   

H.

  Review   and   Practice   

1.

  steel   transformations   as   nucleation   and   growth   

2.

  relation   of   IT   diagram   to   phase   diagram   

3.

  IT   diagram,   hypoeutectoid   steel   (Figure   18.37)   

4.

  hardenability   

5.

  IT   diagram,   hypoeutectoid   low   alloy   steel   (Figure   19.10)   

 

I.

  Continuous   Cooling   Diagrams   

MT   348   –Outline   No.

  10   –   2009  

THE   HARDENING   OF   STEEL

 

A.

  CCT   vs.

  IT   Diagrams   

B.

  Characteristic   Features   of   CCT   Diagrams   

1)

2) transformation absence   of  

  suppressed bainite   in  

  in   temperature transformation   of  

  and plain  

  time, carbon  

   steels,   

3)

4)

 

II.

  Hardenability    critical   cooling   rate,    bainite   curves   in   low   alloy   steels  

A.

  Introduction   of   Concept   

B.

  Measurement   and   Use   of   Hardenability   

1.

  critical   diameter,   D,   and   ideal   critical   diameter,   DI   .

  

2.

  severity   of   quench,   H   

3.

  Jominy   end   quench   test   

C.

  Hardenability   Variables   

1.

  prior  

γ

  grain   size   

2.

  carbon   content   effect   

3.

  alloying   effect   

D.

  Hardenability   and   Applications   

1.

  applications   for   high   hardenability   

2.

  applications   for   low   hardenability   

 

III.

  The   Martensite   Transformation   

A.

  Mechanism   /   Displacive   Transformation   

B.

  Additional   Factors   

1.

tetragonality   and   mechanical   properties,   

 

 

2.

3.

4.

5.

6.

irreversibility   of   M   reaction,    carbon   effect    significance   of   retained  

γ

,    alloying   effect,    martensite   hardness,   

7.

lath   and   plate   M   

C.

  Dimensional   Changes   and   Quench   Cracking   

1.

2.

3.

positive   transformation differential   thermal   contraction,   3)   preventing   quench   cracking   (small  

Δ

T,   martempering,   reducing   hardenability)   

  strain   and   stress,     quenching   stress   vs  

Δ

T,   

 

IV.

  Tempering   of   Steel   

A.

  Basic   Phenomena   ( ʺ Stages ʺ )   

B.

  Microstructure   and   Properties   

C.

  Time   and   Temperature   in   Tempering   

D.

  Secondary   Hardening   

Download