|
Material
|
Purpose |
Process |
Comments |
| 0.30% to 0.60% Carbon |
Facilitate machining |
Full anneal: heat to 28 to 56°C
(50 to 100°F) above the upper critical limit and cool
slowly at a predetermined rate. |
Long cycle time, sometimes many hours. |
| Up to 0.25% Carbon |
Facilitate cold working |
Process anneal (sub-critical annealing or stress-relief
annealing): heat to a point just below the lower critical point, hold
for a prescribed time and cool. |
|
| 0.69% or higher Carbon |
Facilitate cold working or machining |
Spheroidizing: heat to just below the critical point
or to just above and slow cool (5.5°C or 10°F
per hour) through the critical point. |
|
| All |
|
Normalizing:1 heat to 55 to 85°C
(100 to 150°F) above the upper critical point and
slow cool. |
Ensures homogeneous austenitic grain size on reheating
for hardening, and improves toughness. |
| Thin sections or small parts |
|
Isothermal annealing (cycle annealing): heat to
above the upper critical point, cool rapidly to predetermined level,
hold, then cool to room temperature. |
Rapid cycle. |