"Of all the elements that are commonly found in steel, phosphorus stands pre-eminent as the most undesirable. It is objectionable in the rolling mill, for it tends to produce coarse crystallization, and hence lowers the temperature to which it is safe to heat the steel, and for this reason phosphoritic metal should be finished at a lower temperature than pure steel, in order to prevent the formation of a crystalline structure during the cooling."

"Aside from these considerations, its influence is not felt in a marked degree in the rolling mill, for it has no disastrous effect upon the toughness of red-hot metal when the content does not exceed 0.15 per cent."

"The action of phosphorus upon the finished material may not be dismissed in so few words. Mr. Howe 2 has gathered together the observations of different investigators, and the evidence seems to prove that the tensile strength is increased by each increment of phosphorus up to a content of 0.12 per cent., but that beyond this point the metal is weakened. Whether this last observation be correct or not is of little practical importance, for it would be criminal to use a metal for structural purposes that contained as much as an average of 0.12 per cent, phosphorus."

1 "Alloys of Iron and Silicon." Journal 1. and S. 1., vol. ii., 1889.

2 "The Metallurgy of Steel."

"Below this point it is absolutely certain that phosphorus strengthens low steels, both acid and basic. . . . The same certainty does not pertain to any other effect of this metalloid. Mr. Howe has ably discussed the whole matter, and I herewith make quotations from the Metallurgy of Steel, and place them in the form of a summary.

"(1) The effect of phosphorus on the elastic ratio, as on elongation and contraction, is very capricious.

"(2) Phosphoric steels are liable to break under very slight tensile stress if suddenly or vibratorily applied.

"(3) Phosphorus diminishes the ductility of steel under a gradually applied load as measured by its elongation, contraction, and elastic ratio when ruptured in an ordinary testing machine, but it diminishes its toughness under shock to a still greater degree, and this it is that unfits phosphoric steels for most purposes.

"(4) The effect of phosphorus on static ductility appears to be very capricious, for we find many cases of highly phosphoric steel which show excellent elongation, contraction, and even fair elastic ratio, while side by side with them are others produced under apparently identical conditions but statically brittle.

"(5) If any relation between composition and physical properties is established by experience, it is that of phosphorus in making steel brittle under shock; and it appears reasonably certain, though exact data sufficing to demonstrate it are not at hand, that phosphoric steels are liable to be very brittle under shock, even though they may be tolerably ductile statically.

"The effects of phosphorus on shock-resisting power, though probably more constant than its effects on static ductility, are still decidedly capricious. . . ."

"It is true that numerous cases can be cited of rails, plates, etc., containing from 0.10 to 0.35 per cent, of phosphorus, which have withstood a long lifetime of wear and adversity; but in the general use of such metal there has been such a large percentage of mysterious breakages that it seems quite well proven that the phosphorus and the mystery are the same."

On the subject of phosphorus, another authority1 remarks as follows: -

"In the case of what may be called the treacherousness of phosphoric steel, it is difficult to fix a definite limit for the maximum content of phosphorus which can be safely allowed, but there can be no doubt that the lower this is, the safer the material, and for structural purposes 0.06 per cent. is quite as much as can be accepted with a feeling of security. In steel rails 0.08 per cent. of phosphorus may be permitted with safety."

1 F. W. Harbord, "The Metallurgy of Steel," 1904.