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Hardness Testing
The word hardness is used to express various properties of me...

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

Heat Treatment Of Gear Blanks
This section is based on a paper read before the American Gea...

Corrosion
This steel like any other steel when distorted by cold worki...

Making Steel Balls
Steel balls are made from rods or coils according to size, st...

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...

The Modern Hardening Room
A hardening room of today means a very different place from ...

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Properties Of Steel
Steels are known by certain tests. Early tests were more or l...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

Tensile Properties
Strength of a metal is usually expressed in the number of pou...

Phosphorus
PHOSPHORUS is an element (symbol P) which enters the metal fr...

Case-hardening Treatments For Various Steels
Plain water, salt water and linseed oil are the three most co...

Annealing
There is no mystery or secret about the proper annealing of d...

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

Annealing Of High-speed Steel
For annealing high-speed steel, some makers recommend using g...

Annealing Method
Forgings which are too hard to machine are put in pots with ...

Temperature For Annealing
Theoretically, annealing should be accomplished at a tempera...



The Quenching Tank






Category: CASE-HARDENING OR SURFACE-CARBURIZING

The quenching tank is an important feature of apparatus in
case-hardening--possibly more so than in ordinary tempering. One
reason for this is because of the large quantities of pieces usually
dumped into the tank at a time. One cannot take time to separate
the articles themselves from the case-hardening mixture, and the
whole content of the box is droped into the bath in short order,
as exposure to air of the heated work is fatal to results. Unless
it is split up, it is likely to go to the bottom as a solid mass,
in which case very few of the pieces are properly hardened.



A combination cooling tank is shown in Fig. 38. Water inlet and
outlet pipes are shown and also a drain plug that enables the tank
to be emptied when it is desired to clean out the spent carburizing
material from the bottom. A wire-bottomed tray, framed with angle
iron, is arranged to slide into this tank from the top and rests
upon angle irons screwed to the tank sides. Its function is to
catch the pieces and prevent them from settling to the tank bottom,
and it also makes it easy to remove a batch of work. A bottomless
box of sheet steel is shown at C. This fits into the wire-bottomed
tray and has a number of rods or wires running across it, their
purpose being to break up the mass of material as it comes from
the carbonizing box.

Below the wire-bottomed tray is a perforated cross-pipe that is
connected with a compressed-air line. This is used when case-hardening
for colors. The shop that has no air compressor may rig up a
satisfactory equivalent in the shape of a low-pressure hand-operated
air pump and a receiver tank, for it is not necessary to use
high-pressure air for this purpose. When colors are desired on
case-hardened work, the treatment in quenching is exactly the same
as that previously described except that air is pumped through
this pipe and keeps the water agitated. The addition of a slight
amount of powdered cyanide of potassium to the packing material
used for carburizing will produce stronger colors, and where this is
the sole object, it is best to maintain the box at a dull-red heat.


is necessary.]

The old way of case-hardening was to dump the contents of the box
at the end of the carburizing heat. Later study in the structure
of steel thus treated has caused a change in this procedure, the
use of automobiles and alloy steels probably hastening this result.
The diagrams reproduced in Fig. 39 show why the heat treatment of
case-hardened work is necessary. Starting at A with a close-grained
and tough stock, such as ordinary machinery steel containing from 15
to 20 points of carbon, if such work is quenched on a carbonizing
heat the result will be as shown at B. This gives a core that is
coarse-grained and brittle and an outer case that is fine-grained
and hard, but is likely to flake off, owing to the great difference
in structure between it and the core. Reheating this work beyond
the critical temperature of the core refines this core, closes
the grain and makes it tough, but leaves the case very brittle;
in fact, more so than it was before.





Next: Refining The Grain

Previous: Quenching The Work



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