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

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...

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Knowing What Takes Place
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Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

Hardening High-speed Steels
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Drop Forging Dies
The kind of steel used in the die of course influences the he...

Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

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

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

Chromium
Chromium when alloyed with steel, has the characteristic func...

Shrinking And Enlarging Work
Steel can be shrunk or enlarged by proper heating and cooling...

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

Hardening
Steel is hardened by quenching from above the upper critical....

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

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

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

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

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

A Chromium-cobalt Steel
The Latrobe Steel Company make a high-speed steel without tun...



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.





Next: Tempering Colors On Carbon Steels

Previous: Tempering Round Dies



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