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DeCarb
Free Tool Steel Plate
Technical
Notes
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Description
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- (a)
The temperature at which to start heat treating is given as a
range, the higher side of which should be used for large sections
and heavy or rapid reductions, and the lower side for smaller
sections and lighter reduction. As the alloy content of steel
increases, the time of soaking at forging temperature increases
proportionately. Likewise, as the alloy content increases, it
becomes necessary to cool slowly from the maximum heating temperature.
With very high alloy steels, such as high speed steels and air
hardening steels, this slow cooling is imperative in order to
prevent cracking and to leave the steel in semi-soft condition.
Either furnace cooling or burying in an insulating medium, such
as lime, mica, or silocel, is satisfactory.
- (b)
The length of time the steel is held, after being uniformly heated
through at the normalizing temperature, varies from about 15 minutes
for a small section to about 1 hour for large sizes. Cooling from
the normalizing temperature is done in still air. The purpose
of normalizing after forging is to refine the grain structure
and to produce a uniform structure throughout the forging. Normalizing
should not be confused with low temperature [about 1200°F (649°C)]
annealing used for the relief of residual stresses resulting from
heavy machining, bending, and forming.
- (c)
The annealing temperature is given as a range, the upper limit
of which should be used for large sections and the lower limit
for smaller sections. The length of time the steel is held, after
being uniformly heated through at the annealing temperature, varies
from about 1 hour for light sections and small furnace charges
of carbon or low alloy tool steel, to about 4 hours for heavy
sections and large furnace charges of high alloy steel.
- (d)
Normalizing, annealing and hardening temperatures of carbon tool
steels are given as ranges because they vary with carbon content.
The following temperatures are suggested:
- Normalizing
- 0.60
to 0.75% C: 1500°F (816°C)
- 0.75
to 0.90% C: 1450°F (788°C)
- 0.90
to 1.10% C: 1600°F (871°C)
- 1.10
to 1.40% C: 1600 to 1700°F (871 to 927°C)
- Annealing
- 0.60
to 0.90% C: 1360 to 1400°F (738 to 760°C)
- 0.90
to 1.40% C: 1400 to 1450°F (760 to 788°C)
- (e)
Varies with carbon content as follows:
- 0.60-0.80%
C: 1450-1550°F (788 to 843°C)
- 0.85-1.05%
C: 1425-1550°F (774 to 843°C)
- 1.10-1.40%
C: 1400-1525°F (760 to 829°C)
- (f)
Toughness decreases with increasing carbon content and depth of
hardening.
- (g)
For large tools and tools having intricate sections, preheating
at 1050-1200°F (566-649°C) is recommended.
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(h) When high temperature heating is carried out
in a salt bath, the range of temperatures should be about 25°F
(14°C) lower than that shown.
- (j)
Times shown apply to open furnace heat treatment. For pack hardening
a common rule is to heat for 1/2 hour per inch (25.4 mm) of cross
section of the pack.
- (k)
Double tempering suggested for not less than one hour at temperature
each temper.
- (i)
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O: Oil quench
- S:
Salt bath quench
- A:
Air Cool
- B:
Brine quench
- W:
Water quench
- (m)
Triple tempering suggested for not less than one hour at temperature
each temper.
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(n) When high carbon material is involved, lowering
of the hardening temperature an additional 25°F (14°C) is suggested.
This is in addition to the 25°F (14°C) reduction involving salt
bath hardening.
- (o)
Available in two silicon contents, nominally 0.33% and 0.55%.
When 0.55% silicon is used, the maximum suggested hardening temperature
is 2150°F (1177°C).
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