1. An article should never be thrown into the bath.
corresponding to various colors are given in table 6-1;
By permitting it to lie on the bottom of the bath, it is apt
however, the accuracy with which temperatures may be
to cool faster on the top side than on the bottom side,
judged by colors depends on the experience of the
thus causing it to warp or crack.
worker and on the light in which the work is being done.
2. The article should be slightly agitated in the
QUENCHING PROCEDURE.--A number of
bath to destroy the coating of vapor, which might
liquids may be used for quenching steel. Both the
prevent it from cooling rapidly.
media and the form of the bath depend largely on the
nature of the work to be cooled. It is important that a
3. An article should be quenched in such a
sufficient quantity of the media be provided to allow the
manner that all parts will be cooled uniformly and with
metal to be quenched without causing an appreciable
the least possible distortion.
change in the temperature of the bath. This is
4. Irregularly shaped sections should be
particularly important where many articles are to be
immersed in such a manner that the area with the
quenched in succession.
biggest section enters the bath first.
The tendency of steel to warp and crack during the
Quenching Media.--In certain cases water is used
quenching process is difficult to overcome because
in the quenching of steel during the hardening process.
certain parts of the article cool more rapidly than
The water bath temperature is normally held at 18C
others. Whenever the transformation of temperature is
(65F). For specific applications, other bath
not uniform, internal strains are set up in the metal that
result in warping or cracking, depending on the severity
temperatures may be used; however, cold water may
of the strains. Irregularly shaped parts are particularly
warp or crack the part, and hot water may not produce
susceptible to these conditions, although parts of an
the required hardness.
even section are often affected in a similar manner.
A 10-percent salt brine solution is used when
Operations such as forging and machining may set up
higher cooling rates are desired. A 10-percent salt brine
internal strains in steel parts; therefore, it is advisable to
solution is made by dissolving .89 pounds of salt per
normalize articles before attempting the hardening
gallon of water.
process. The following recommendations will greatly
reduce the warping tendency and should be carefully
Oil is much slower in action than water, and the
observed:
tendency of heated steel to warp or crack when
Table 6-1.--Color Chart for Steel at Various Temperatures
COLOR
METAL TEMPERATURE
Degrees C
Degrees F
Faint red
482
900
Blood red
566
1,050
Dark cherry
579.5
1,075
Medium cherry
677
1,250
Cherry or full red
746
1,375
Bright red
843
1,550
Salmon
899
1,650
Orange
940.5
1,725
Lemon
996
1,825
Light lemon
1,079.5
1,975
White
1,204
2,200
Dazzling white
1,288
2,350
6-40
