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Steel Making

Air-hardening Steels
These steels are recommended for boring, turning and planing...

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

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

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

Carbon-steel Forgings
Low-stressed, carbon-steel forgings include such parts as car...

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

Knowing What Takes Place
How are we to know if we have given a piece of steel the ver...

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

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

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

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

Heat-treating Equipment And Methods For Mass Production
The heat-treating department of the Brown-Lipe-Chapin Company...

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

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

Heat Treatment Of Milling Cutters Drills Reamers Etc
THE FIRE.--Gas and electric furnaces designed for high heats ...

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

Tempering Round Dies
A number of circular dies of carbon tool steel for use in too...

Crucible Steel
Crucible steel is still made by melting material in a clay or...

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

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



Hardness Testing






Category: ALLOYS AND THEIR EFFECT UPON STEEL

The word hardness is used to express various properties of metals,
and is measured in as many different ways.

Scratch hardness is used by the geologist, who has constructed
Moh's scale as follows:

Talc has a hardness of 1
Rock Salt has a hardness of 2
Calcite has a hardness of 3
Fluorite has a hardness of 4
Apatite has a hardness of 5
Feldspar has a hardness of 6
Quartz has a hardness of 7
Topaz has a hardness of 8
Corundum has a hardness of 9
Diamond has a hardness of 10

A mineral will scratch all those above it in the series, and will
be scratched by those below. A weighted diamond cone drawn slowly
over a surface will leave a path the width of which (measured by
a microscope) varies inversely as the scratch hardness.

Cutting hardness is measured by a standardized drilling machine,
and has a limited application in machine-shop practice.

Rebounding hardness is commonly measured by the Shore scleroscope,
illustrated in Fig. 11. A small steel hammer, 1/4 in. in diameter,
3/4 in. in length, and weighing about 1/12 oz. is dropped a distance
of 10 in. upon the test piece. The height of rebound in arbitrary
units represents the hardness numeral.



Should the hammer have a hard flat surface and drop on steel so hard
that no impression were made, it would rebound about 90 per cent
of the fall. The point, however, consists of a slightly spherical,
blunt diamond nose 0.02 in. in diameter, which will indent the steel
to a certain extent. The work required to make the indentation
is taken from the energy of the falling body; the rebound will
absorb the balance, and the hammer will now rise from the same
steel a distance equal to about 75 per cent of the fall. A permanent
impression is left upon the test piece because the impact will
develop a force of several hundred thousand pounds per square inch
under the tiny diamond-pointed hammer head, stressing the test
piece at this point of contact much beyond its ultimate strength.
The rebound is thus dependent upon the indentation hardness, for
the reason that the less the indentation, the more energy will
reappear in the rebound; also, the less the indentation, the harder
the material. Consequently, the harder the material, the more the
rebound.

Indentation hardness is a measure of a material's resistance
to penetration and deformation. The standard testing machine is
the Brinell, Fig. 12. A hardened steel ball, 10 mm. in diameter,
is forced into the test piece with a pressure of 3,000 kg. (3-1/3
tons). The resulting indentation is then measured.



While under load, the steel ball in a Brinell machine naturally
flattens somewhat. The indentation left behind in the test piece is
a duplicate of the surface which made it, and is usually regarded
as being the segment of a sphere of somewhat larger radius than
the ball. The radius of curvature of this spherical indentation
will vary slightly with the load and the depth of indentation.
The Brinell hardness numeral is the quotient found by dividing the
test pressure in kilograms by the spherical area of the indentation.
The denominator, as before, will vary according to the size of the
sphere, the hardness of the sphere and the load. These items have
been standardized, and the following table has been constructed
so that if the diameter of the identation produced by a load of
3,000 kg. be measured the hardness numeral is found directly.

TABLE FOR BRINELL BALL TEST
------------------------------------------------------------------------
Diameter of Ball Hardness Number Diameter of Ball Hardness Number
Impression, mm. for a Load of Impression, mm. for a Load of
3,000 kg. 3,000 kg.
---------------------------------------------------------------------
2.0 946 4.5 179
2.1 857 4.6 170
2.2 782 4 7 163
2.3 713 4.8 156
2.4 652 4.9 149
2.5 600 5.0 143

2.6 555 5.1 137
2.7 512 5.2 131
2.8 477 5.3 126
2.9 444 5.4 121
3.0 418 5.5 116

3.1 387 5.6 112
3.2 364 5.7 107
3.3 340 5.8 103
3.4 321 5.9 99
3.5 302 6.0 95

3.6 286 6.1 92
3.7 269 6.2 89
3.8 255 6.3 86
3.9 241 6.4 83
4.0 228 6.5 80

4.1 217 6.6 77
4.2 207 6.7 74
4.3 196 6.8 71.5
4.4 187 6.9 69
------------------------------------------------------------------------





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Previous: Fatigue Tests



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