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High Speed Steel
For centuries the secret art of making tool steel was handed ...

Robert Mushet
Robert (Forester) Mushet (1811-1891), born in the Forest of D...

Testing And Inspection Of Heat Treatment
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Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

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

Silicon
Silicon prevents, to a large extent, defects such as gas bubb...

Care In Annealing
Not only will benefits in machining be found by careful anne...

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

Steel For Chisels And Punches
The highest grades of carbon or tempering steels are to be re...

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

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

Cutting-off Steel From Bar
To cut a piece from an annealed bar, cut off with a hack saw,...

Crankshaft
The crankshaft was the most highly stressed part of the entir...

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

The Forging Of Steel
So much depends upon the forging of steel that this operation...

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...

Heating
Although it is possible to work steels cold, to an extent de...

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



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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