Full resolution (JPEG) - On this page / på denna sida - Second part - IX. Mining Industry and Metal Production - 2. The Iron and Steel Industry. By the late Prof. J. G. Wiborgh - Ingot iron (Steel)
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742-
ix. mining industry and metal production op sweden.
1 %, the steel actually falls to pieces when an attempt is made to work it under
the hammer. The higher the percentage of carbon in the steel, the lower is the
temperature at which it will become burnt. This test is always combined with
a tempering test, the percentage of carbon being estimated by the brittleness of
the steel and the appearance of the fracture after the tempering.
For this test the steel is forged into dimensions of 15x4 millimeters, after
which it is heated to yellow heat and then broken off. Now the amount of carbon,
if above 0"5o % is judged of by the brittleness of the steel after tempering, i. e.,
the more or less heavy strokes of the hammer which are required to break it off,
in connection with the appearance of the fracture.
Already at an amount of carbon of O’so %, the steel breaks off without
bending if it is laid on the ed^e of an anvil and given heavy blows with the hammer,
the fracture being light coloured and coarse grained, but the higher the percentage
of carbon, the easier the steel breaks off and the finer grained and darker the
fracture appears. If the carbon be lower than 0\v the steel will bend slightly
before breaking, and the lower the percentage of carbon, the more the steel will
stand bending, so that the soft iron with a percentage of carbon of 0’15 can be
completely doubled up without any cracks occurring.
Percentages of carbon below 0-5o are therefore always estimated according
to the degree to which the hardened steel can be bent in a cold state withoat
cracking in the bend, instead of by the appearance of the fracture and the
proneness of the steel to get burnt.
The accuracy with which it is possible to judge of the carbon percentage of
soft steel and iron is best shown by the above photographic reproduction of
bending tests with steels of different percentages of carbon, of which N:o 1 has
0-15 N:o 2 0’25 •», N:o 3 0"3o and N:o 4 0 35 % of carbon.
In connection with these tests of the hardness of the steel, tests are also
made with respect to its red shortness. For carbons above O-so, this is done
by bending the steel forged out at red heat to 15x4 millimeters to and fro
The bending-test.
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