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These steels are recommended for boring, turning and planing...

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As noted above, steel can be worked cold, as in the case of ...

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Such portable flame shields as the one illustrated in Fig. 1...

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Do not hesitate to ask for information from the maker as to t...

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

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...

Typical Oil-fired Furnaces
Several types of standard oil-fired furnaces are shown herew...

Preventing Decarbonization Of Tool Steel
It is especially important to prevent decarbonization in such...

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

William Kelly's Air-boiling Process
An account of Bessemer's address to the British Association w...

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

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...

Hardening
The forgings can be hardened by cooling in still air or quen...

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

Sulphur
SULPHUR is another element (symbol S) which is always found i...

For Milling Cutters And Formed Tools
FORGING.--Forge as before.--ANNEALING.--Place the steel in a ...

Quality And Structure
The quality of high-speed steel is dependent to a very great ...



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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