This section is from the book "Notes On Construction In Mild Steel", by Henry Fidler. Also available from Amazon: Notes On Construction In Mild Steel.
"Nothing is better established than the fact that sulphur injures the rolling qualities of steel, causing it to crack and tear, and lessening its capacity to weld. This tendency can be overcome in some measure by the use of manganese and by care in heating, but this does not in the least disprove that the sulphur is at work, but simply shows that it is overpowered.
"The critical content at which the metal ceases to be malleable and weldable varies with every steel. It is lower with each associated increment of copper, it is higher with each unit of manganese, and it is lower in steel which has been cast too hot.
"In the making of common steel for simple shapes, a content of 0.10 per cent, is possible, and may even be exceeded if great care be taken in the heating; but for rails and other shapes having thin flanges, it is advantageous to have less than 0.08 per cent., while every decrease below this point is seen in a reduced number of defective bars.
"It is impossible to pick out two steels with different contents of sulphur and say that the influence of a certain minute quantity can be detected, but it is none the less true that the effect of an increase or decrease of 0'01 per cent, will show itself in the long run, while each 0.03 per cent, will write its history so that he who runs may read.
"The effect of sulphur upon the cold properties of steel has not been accurately determined, but it is quite certain that it is unimportant. In common practice the content varies from 0.02 to 0.10 per cent., and within these limits it seems to have no appreciable influence upon the elastic ratio, the elongation, or the reduction of area. It is more difficult to say that it does not alter the tensile strength, for a change of 1000 lbs. per square inch can be caused by so many things that it is a bold venture to ascribe it to one variable.
"In rivets, eyebars, and fire-box steel, the presence of sulphur is objectionable, for it will tend to create a coarse crystallization when the metal is heated to a high temperature, and reduce the strength and toughness of the steel.
"In other forms of structural material the effect of this element is probably of little importance."
Another authority1 states, "the real danger of using a high sulphur steel for structural purposes, even when it has not in any way to be worked hot, lies in the fact that, during rolling, numerous cracks are likely to develop, which close up and are quite imperceptible in the finished material. Nevertheless, these remain as flaws, and may form starting-points for rupture when the material is subjected to any sudden stress. . . . Probably material of this description is one of the most dangerous that can be employed by the engineer, the more so that the tensile strength and elasticity, as evidenced by elongation and reduction of area, will give no indications in the majority of cases that the material is in any way untrustworthy."
"Starting with fairly good materials, with careful treatment manufacturers should have no difficulty in producing regularly a steel with about 0.06 per cent., and certainly 0.08 per cent, is the very maximum that should be allowed in any steel, either for rails or structural purposes."