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rorging-Stamping- Hoat Treating
TABLE I.
Proportional
Limit,
ll». per sq. in.
Yield
Point,
DA. per sq. in.
Tensile
Strength,
lb. per sq. h
Elongation
in 2 in.,
per cent
August, 1925
Reduction
of Aren,
per cent
0.15 per cent Carbon Steel (Annealed), 30 870 32 000 49 400 41.0 69.1
0.37 per cent Carbon Steel (Annealed) 39 000 42 000 80 500 28.1 42.0
0.68 per cent Chromium. 2.93 per cent Nickel Steel 100 000 113 000 133 700 18.4 49.7
084 per cent Chromium, 3.33 per cent Nickel Steel 92 000 97 000 119 000 24.5 59.4
Manganese Bronze 52 SOO 79 500 105 500 8.0 17.0
0.15 per cent Carbon Steel (Annealed)
0.37 per cent Carbon Steel (Annealed)
0.68 per cent Chromium, 2.93 per cent Nickel Steel.
0.84 per cent Chromium, 3.33 per cent Nickel Steel.
Forged Manganese Bronze
In Table II are given the endurance limits obtained
for these various materials in direct stress. For the
purpose of comparison, fatigue tests were made on the
same material under cycles of flexural stress. These
endurance limits are also given in Table 11. The third
column of the table gives the ratio of the endurance
limit under direct stress to the endurance limit under
flexural stress and shows this ratio to be approximately
unity.
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Cycles of Stress
FIG. 8—Endurance test curve for nickel-chrome steel
The fourth column gives the ratio of endurance
limit to strength in tension—the steels agreeing closely
in this respect. It will be observed that in this
ratio the non-ferrous metal varies markedly from the
ferrous.
Conclusions.
—o—
fix/at.
From these considerations, it is concluded that a
satisfactory attachment has been designed, for direct
stress testing, which makes possible the speedy insertion
of test specimens and their removal without injury
to the surface of the fracture. Furthermore, a
new method of calibration has been devised in conjunction
with a new design of high-speed extensometer
which gives accuracy in calibration and which
may have other applications.
:
—l >
TABLE II
Endurance Limits
Direct
Stress
Flexural
Stress
Ih. per sq. in. per sq. in.
24 500
33 000
56 200
58 200
17 500
25 500
30 000
55 000
61 500
16 000
Ratios
Direct Direct
~ T Tensile
Hexural strength
0.96
1.10
1.02
0.95
1.09
0.50
0.41
0.42
0.49
0.17
A result of more importance to the designer, however,
lies in the comparative data which shows (for
all cases examined) that the endurance limit obtained
bv direct stress is the same as that obtained by flexural
stress.
Acknowledgement.
The author wishes to thank the Westinghouse
Electric & Manufacturing Company in whose research
laboratory this work has been executed for permission
to publish these results, and Mr. J. M. Lessells and
Dr. S. Timoshenko for valuable criticism and assistance
in the preparation of the manuscript.
German Alloy of Diamond Hardness
.\n interesting material which is claimed- to replace
the diamond in core-drilling and stone-curtrhg has recently
been developed in German}'. It is being offered
by the Roechling Steel Works, Wetzler, Germany,
under the name "Thoran" The company states that
the high cost of carbons used in diamond core drilling
and the necessity of great skill in their setting the bits
led it to undertake the task of developing a substance
to take their place.
Thoran is claimed to have approximately the. hardness
of the diamond. It has a melting point of 5,400
deg. F. (3000 deg. C.) ; it does not soften or fuse at any
lower temperatures and therefore connot be forged.
It has a minute crystalline body and is said to consist
of a mixture of tungsten carbides and tungsten. According
to the mineral scale it possesses a hardness
between 9.8 and 9.9, the diamond being 10.
Its structure is described as metallic and consequently
it has much greater strength and durability
for mechanical operations than the diamond. In spite
of its extraordinary hardness it has adequate tenacity,
contrary to the natural diamond. The mechanical
strength of Thoran is reported as about equal to that
of superior quality high-speed steel. Because it cannot
be forged its cutting edges must be obtained
through grinding. Because Thoran is harder than
emery wheels, special grinding equipment, similar to
that used for grinding diamonds, is required. Victor
F Halbarth, 50 Church Street. Xew York, is the
American representative of the German company producing
this new product.