The elasticity, extensibility, and tensile strength of iron and steel

There is no subject of greater importance to Civil and Mechanical Engineers than the properties of Iron and Steel, which fit them for application to useful purposes; and there is no subject of the kind which more deeply concerns the general public. The lives of the many thousand daily travellers by railway are in no inconsiderable degree at the mercy, so to speak, of Iron and Steel; and the same may also be said of voyagers in ships made of those materials. Architects, moreover, have in recent years largely employed Iron both in private houses and in public buildings; and upon the strength of the girders and columns introduced, the safety of the inmates depends.

Notwithstanding the numerous experimental investigations, which have been conducted in this and other countries, concerning the tensile strength of Iron and Steel, including Cast Iron, much yet remains to be done in that direction. Such problems, for example, as the relation between tensile strength and composition, previous mechanical treatment, and temperature, are at present but very imperfectly solved. Yet, obviously, they are problems of the highest practical value. It is certain that the mechanical properties of a metal may be affected by contamination with certain foreign matters in some cases when present only in extremely minute proportion. All Iron and Steel, manufactured as articles of commerce, contain invariably more or less foreign matter, usually sulphur or phosphorus or both. The carbon in Steel or Cast Iron is not to be regarded as foreign matter, as it is essential to the existence of Steel and Cast Iron; nor should it be so regarded when existing in small quantity in Malleable Iron.

All workers in metals know how strikingly the properties of malleability, ductility, and hardness are influenced by previous mechanical treatment, such as hammering, rolling, or wire-drawing; and the properties of elasticity as well as tensile strength are also affected by the same cause.

The tensile strength of a metal, it has been well established, varies notably with temperatures between such extremes as occur in habitable climates. A few years ago numerous accidents from breakage of Iron happened on railways in England, during the prevalence of a severe frosty and it was concluded that they were due to the diminished tensile strength of Iron at low temperatures.

Although information, on these problems, may be found scattered through various books and scientific journals, yet they have not hitherto been so systematically investigated as by the Author of this Treatise, M. Styffe, who has devoted some years of patient labour in attempting their solution; and by a life-long training in experimental science, no man could be named better qualified for the task. M. Styffe is Director of the Technological Institution at Stockholm, and I had the pleasure of becoming personally acquainted with him as a colleague on the Jury for Mining and Metallurgical Products of the International Exhibition, 1862. From the high position, which, I know, he occupies in the estimation of scientific men in Sweden, a country which has done so much towards the advancement of every branch of science in Europe, perfect confidence may be placed in the accuracy of his results, though his conclusions may not in every case be accepted.

A detailed account is given of the apparatus employed in determining tensile strength at common and other temperatures, and of the mode of conducting the experiments. The results are recorded in tables, and for the convenience of the reader the general conclusions are clearly and succinctly stated. The investigation was undertaken by a Commission appointed by His Majesty the King of Sweden, chiefly with the view of determining the relative values of different kinds of Iron and Steel applicable to railway purposes. Of that Commission the Author was a member, and to him was entrusted the carrying out of the necessary experiments. Amongst the numerous samples examined were some, it is alleged, from certain districts in England, which undoubtedly do not represent even the average quality of the Iron there manufactured.

The observations on the "Influence of Phosphorus and Slag on Iron" deserve careful consideration; and a novel doctrine is propounded as to the beneficial influence of the diffusion of slag, through Iron containing phosphorus in sensible quantity, in order to counteract its injurious effect. With regard to the influence of phosphorus in certain proportions upon the tenacity of Iron, the results of the Author agree pretty closely with those of Karsten. The tensile strength of Iron, the Author asserts, is not sensibly impaired by the presence even of 0,2 or 0,3 per cent, of phosphorus, provided the metal has not been strongly heated, after having undergone the operation of rolling or extension by other manipulation. But, what is important, the facility of extension, or, as it is termed, the extensibility of Iron is lessened by phosphorus. It is maintained that the presence of even a considerable quantity of slag or cinder in Iron impregnated with phosphorus, is beneficial by preventing the largely crystalline structure, which otherwise would result from the presence of that element.

There is a statement to the effect that “of the different brands of English Iron examined, only that from Lowmoor was fit for smiths' work.” Now, however well adapted for smiths' work Lowmoor Iron may be, it is certain that there are other brands of English Iron which are equally good for the purpose; and it is therefore desirable to note that, of this class of Irons, only that of Lowmoor was submitted to trial.

With respect to the cause of frequent fracture of certain articles of Iron in severe cold, the Author advances views, which will certainly be combated by many engineers in this country; and which, indeed, are strongly opposed by the Translator, M. Sandberg, from the results of experiments, on a large scale, which, at his suggestion, have been made and mostly conducted by himself at Stockholm during the winter. The results thus arrived at seem to be of much value, and practically to settle the question against the Author. They will be found recorded in extenso in an Appendix by the Translator.

The Author pronounces a decided opinion on the injurious influence of phosphorus on Steel, and few men in Europe are entitled, from long and accurate observation, to speak with greater authority on the subject. The Author says he "knows no authenticated instance in which the proportion of phosphorus has been higher than 0,04 per cent, in what has been considered a good Steel." Yet it is only fair to add his opinion, that “with regard to the influence of phosphorus on Steel, our knowledge is at present more imperfect than it is with reference to the effect of that element on Iron.”

The volume is illustrated with numerous working drawings and tables, and amongst the latter are some which particularly merit careful study. I allude to those in which the connection between composition and tensile strength is graphically shown; and assuredly, one of the most striking and interesting is that tabulated by the Translator (Plate IX.), in which the relative values of Iron and Steel are displayed side by side.