By Mr. L. TETMAJER.
This memoir is the first of a series upon the unification of nomenclature
and classification of building materials, undertaken by the author at the
request of the Swiss Engineers' and Architects' Union. For its
preparation numerous mechanical tests have been made upon steel rails,
both good and bad, taken from the Swiss railways, while the corresponding
chemical analyses have been made by Dr. Treadwell in the Polytechnic
Laboratory, at Zurich. The results are given for twenty-two examples,
about one-half of which have stood well, while the remainder have either
broken, split, or suffered considerable abrasion in wear; but in many
instances the mechanical test of tensile strength, elongation, and
contraction, and the figures of quality (Wohler's sum and Tetmajer's
coefficient) deduced from these have varied very considerably for the
results obtained in practice.
The best wearing rails, which often give contradictory results with the
tensile test, were comparatively pure manganese steels, low in silicon,
only exceptionally up to 0.2 per cent., but generally below 0.1 per
cent., and with less than 0.1 per cent. of phosphorus and sulphur. On the
other hand, rails with a tendency to break or split are low in carbon,
with variable proportions of manganese, but contain much silicon, 0.3 to
0.9 per cent., and often above 0.1 per cent. of phosphorus. Another
series of experiments upon rails for the Finland lines made by the author
in 1879-80 shows the high quality of manganese steel. These are
essentially highly carburized (0.3-0.4 per cent. carbon) with 0.7 to 1.4
per cent. manganese, and have stood three and a half years' wear without
a single one being broken; while those of silicon steel with 0.106-0.144
per cent. carbon, 0.592-0.828 manganese, and 0.423-0.435 silicon have
failed in many cases, showing a great tendency to split. In both of the
latter instances, however, the figures deduced from tensile tests of both
good and bad specimens were substantially the same.
The causes of the difference between the two kinds of steel the author
attributes to differences in the structure of the ingot due to the agent
used in "chemical consolidation," which may be either manganese or
silicon, which structures are illustrated by photographs of ingot
fractures. When silicon is used there is a tendency to unsoundness about
the exterior of the ingot, which is surrounded by a honeycomb-like
cellular casing of greater or less depth; while with manganese the
vesicular cavities are more or less dispersed through the whole
substance, or concentrated toward the interior of the ingot. Rails made
from the former are, therefore, more likely to contain unsound portions
near the outer wearing surface, and to give unsatisfactory results in
wear, than those from the latter; but as the test pieces are usually cut
from the center of the railhead, the tensile resistance of the interior
may be equal to or surpass that of the superior material. In summing up
his observations the author concludes that the method of tensile testing
is mainly of value in determining the quality of the material, but that
for the finished product properly arranged falling weight tests are
necessary. He also considers that the test pieces should be flat bars of
2.5 to 3.5 centimeters in area, cut as near as possible to the outer
surface of both head and foot of the rail. He reprobates especially the
research for microscopic imperfections (mikrobensücherei) upon the
fractured surfaces, as an annoyance to the producer, and perfectly
useless to the consumer.--_Stahl und Eisen_, vol. iv., page 608; through
_Proc. Inst. Civ. Eng_.
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