All steel contains silicon, phosphorus, sulphur, oxygen, hydrogen, and nitrogen, none of which add any useful property to the material. It is admitted that, starting with very small quantities of silicon or phosphorus in mild steel, small additions of either element will increase the tensile strength of the steel perceptibly up to a given amount, and that then the addition of more of either one will cause a reduction of strength. The same increase of strength can be obtained by the addition of a little carbon, producing a much more reliable material. It is not known that even such slight apparent gain in strength can be made by using oxygen, nitrogen, or hydrogen.
Manganese is present in all steel as a necessary ingredient, it gives an increase in strength in the same way as phosphorus, and when increased beyond a small limit it causes brittleness. Hadfield’s manganese steel is a unique material, not to be considered in connection with the ordinary steel of commerce.
Webster’s experiments are perhaps the most complete of any that show the effects of small increases of silicon, phosphorus, sulphur, and manganese, but as these are not completed they are not quoted here, because Mr. Webster may reach additional and different results before these pages are printed.
The chief bad qualities of steel that are caused by these impurities are known as “red-shortness,” “cold-shortness,” and “hot-shortness.”
A steel is called red-short when it is brittle and friable at what is known commonly as a low red heat—“cherry red,” “orange red.”
Red-shortness is caused chiefly by sulphur or by oxygen; many other elements may produce the same effects; it seems probable that nitrogen may be one of these, but the real action of nitrogen is as yet obscure.
A red-short steel is difficult to work; it must be worked at a high heat—from bright orange up to near the heat of granulation—or it will crack. When hardened, it is almost certain to crack. When red-short steel is worked with care into a sound condition, it may when cold be reasonably strong, but hardly any engineer of experience would be willing to trust it.
Hot-short steel is that which cannot be worked at a high heat, say above a medium to light orange, but which is generally malleable and works soundly at medium orange down to dark orange, or almost black.
This is a characteristic of most of the so-called alloy steels, or steels containing considerable quantities of tungsten, manganese, or silicon. It is claimed that chrome steel may be worked at high heats and that it is less easily injured in the fire than carbon steel. This is not within the author’s experience. It is this property of hot-shortness that makes the alloy steels so expensive; the ingots cannot be heated hot enough nor worked heavily enough to close up porosities, and therefore, there is a heavy loss from seams.
The range of heat at which they can be worked is so small that many re-heatings are required, increasing greatly the cost of working.