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Standard Analysis
The selection of a standard analysis by the manufacturer is t...

Judging The Heat Of Steel
While the use of a pyrometer is of course the only way to hav...

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

Gas Consumption For Carburizing
Although the advantages offered by the gas-fired furnace for ...

The Effect
The heating at 1,600 deg.F. gives the first heat treatment w...

Calibration Of Pyrometer With Common Salt
An easy and convenient method for standardization and one whi...

Heat-treating Department
The heat-treating department occupies an L-shaped building. ...

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

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

Nickel
Nickel may be considered as the toughest among the non-rare a...

Machineability
Reheating for machine ability was done at 100 deg. less than ...

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

Impact Tests
Impact tests are of considerable importance as an indication ...

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

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

Fatigue Tests
It has been known for fifty years that a beam or rod would fa...

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

Carbon Tool Steel
Heat to a bright red, about 1,500 to 1,550 deg.F. Do not ham...

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



The Effect Of Tempering On Water-quenched Gages






Category: HARDENING CARBON STEEL FOR TOOLS

The following information has been supplied by Automatic and Electric
Furnaces, Ltd., 6, Queenstreet, London, S. W.:

Two gages of 3/4 in. diameter, 12 threads per inch, were heated
in a Wild-Barfield furnace, using the pyroscopic detector, and
were quenched in cold water. They were subsequently tempered in a
salt bath at various increasing temperatures, the effective diameter
of each thread and the scleroscope hardness being measured at each
stage. The figures are in 10,000ths of an inch, and indicate the
change + or - with reference to the original effective diameter
of the gages. The results for the two gages have been averaged.

TABLE 24.--CHANGES DUE TO QUENCHING
----------------------------------------------------------------
After Tempering temperature, degrees Centigrade
Thread quenching-----------------------------------------
220 260 300 340 380 420
---------------------------------------------------------
1 +25 +19 +17 +15 +13 +11 +11
2 +18 +12 +11 + 9 + 6 + 5 + 5
3 +12 + 6 + 5 + 3 0 0 0
4 +10 + 4 + 4 + 2 ... 0 - 1
5 + 9 + 4 + 4 + 2 0 0 0
6 + 9 + 4 + 3 + 2 0 0 0
7 +10 + 5 + 5 + 3 + 2 + 1 + 2
8 + 8 + 4 + 3 + 2 0 0 + 1
9 + 9 + 4 + 3 + 2 + 1 + 1 + 1
10 + 9 + 5 + 5 + 3 + 2 + 2 + 2
11 + 7 + 4 + 4 + 2 + 1 + 1 + 1
12 + 9 + 5 + 5 + 5 + 4 + 4 + 3

Scleroscope 80 70 70 62 56 53 52
----------------------------------------------------------------

Had these gages been formed with a plain cylindrical end projecting
in front of the screw, the first two threads would have been prevented
from increasing more than the rest. The gages would then have been
fairly easily corrected by lapping after tempering at 220 deg.C. Practically
no lapping would be required if they were tempered at 340 deg.C. There
seems to be no advantage in going to a higher temperature than
this. The same degree of hardness could have been obtained with
considerably less distortion by quenching directly in fused salt. It
is interesting to note that when the swelling after water quenching
does not exceed 0.0012 in., practically the whole of it may be
recovered by tempering at a sufficiently high temperature, but when
the swelling exceeds this amount the steel assumes a permanently
strained condition, and at the most only 0.0014 in. can be recovered
by tempering.





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