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Precipitation Hardening
Solution Treatment
Age-Hardening
Age-Hardening
A quenched alloy increase its hardness with aging time
this is known as Age-Hardening (Precipitation
hardeni...
Continue…..
Removal of carbon from ferrite done in two ways;
1. The formation of new nuclei
2. Growth of previously formed...
 The speed at which precipitation occurs varies
with temperature this is shown qualitatively in
fig. At very low temperat...
Effect of free energy
In this cause the solution is only slightly over
saturated and the free-energy decrease resulting
f...
Precipitation of second phase
The most important effect of the precipitation of the
second phase (cementite) is that the ...
Effect of different temperatures
The curve mark T1 represents aging at too low a
temperature. In this cause, atomic motio...
Continue…
Temperature T2 corresponds to an optimum
temperature, a temperature at which maximum
hardening occurs within a ...
T2 ( 40.5o
C)
T1 ( 0 o
C )
T3 ( 99 o
C)
Effect of composition
Solubility at room temperature = 8.2 x 10 – 12
percent
Solution treatment (precipitation hardening)
Solution treatment (precipitation hardening)
Solution treatment (precipitation hardening)
Solution treatment (precipitation hardening)
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Solution treatment (precipitation hardening)

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Solution treatment (precipitation hardening)

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Solution treatment (precipitation hardening)

  1. 1. Precipitation Hardening
  2. 2. Solution Treatment Age-Hardening
  3. 3. Age-Hardening A quenched alloy increase its hardness with aging time this is known as Age-Hardening (Precipitation hardening) Steps for age- hardening The aging treatment accomplished by nucleation & growth process. Growth First we nucleate cementite crystals & cementite crystals grow in size due to the diffusion of carbon from surrounding ferrite.
  4. 4. Continue….. Removal of carbon from ferrite done in two ways; 1. The formation of new nuclei 2. Growth of previously formed nuclei Incubation Period Precipitation not begin immediately it require a (to ) before it detectable. Here we use Logarithmic units for time because spontaneous reaction of this nature start rapidly & finish slowly.
  5. 5.  The speed at which precipitation occurs varies with temperature this is shown qualitatively in fig. At very low temperatures, long times are required to complete the precipitation because the diffusion rate is very slow. Here the rate of reaction is controlled by the rate at which atoms can migrate.  The rate of precipitation is also very slow at temperatures just below the solvus line(point e fig).
  6. 6. Effect of free energy In this cause the solution is only slightly over saturated and the free-energy decrease resulting from precipitation is very small. Nucleation is, accordingly, slow, and precipitation is controlled by the rate at which nuclei can form. Conclusion The combination of moderates diffusions and nucleation rate makes precipitation rapid.
  7. 7. Precipitation of second phase The most important effect of the precipitation of the second phase (cementite) is that the matrix (ferrite) is hardened. Figure shows a typical hardening curve for a dilute iron-carbon alloy. Over aging Holding, the specimen for too long a period at a given temperatures causes them to lose their hardness. This effect is known as over aging.
  8. 8. Effect of different temperatures The curve mark T1 represents aging at too low a temperature. In this cause, atomic motion is so slow that no appreciable precipitation occurs and hardening occurs slowly. A further lowering of the aging temperature below T1 will effectively stop all precipitation and prevent hardening.
  9. 9. Continue… Temperature T2 corresponds to an optimum temperature, a temperature at which maximum hardening occurs within a reasonable length of time. At T3 hardening occurs quickly due to rapid diffusion. However, softening effects also are accelerated, resulting in a lower maximum hardness.
  10. 10. T2 ( 40.5o C) T1 ( 0 o C ) T3 ( 99 o C)
  11. 11. Effect of composition
  12. 12. Solubility at room temperature = 8.2 x 10 – 12 percent

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