XV. On the difference in the magnetic properties of hot-rolled and cold-rolled malleable iron, as regards the power of receiving and retaining induced magnetism of subpermanent character

Abstract

In reflecting on the differences exhibited by different iron-built ships in the change of their subpermanent magnetism, it has often occurred to me as a subject worthy of experimental investigation, whether a portion of this difference might not depend on the temperature at which the plates of iron are passed through the rollers in the last stage of their manufacture. No favourable opportunity of making these experiments presented itself until, in the course of the last winter, I became aware that Mr. Fairbairn had been engaged in experiments on the difference of the strength of plates of malleable iron, according as they had been rolled at a high or at a low temperature. I immediately requested Mr. Fairbairn’s kind offices for procuring for me bars adapted to magnetic experiment, divided into the four classes of—1. Hot-Rolled, with the length of the bars parallel to the direction in which the rolling had lengthened the iron, or parallel to the direction of fibre; 2. Hot-Rolled, with the length of the bars transverse to the direction of fibre; 3. Cold-Rolled, with the length of the bars parallel to the direction of fibre; 4. Cold-Rolled, with the length of the bars transverse to the direction of fibre (which classes will hereafter be described by the words, 1. Hot-Rolled Longitudinal; 2. Hot-Rolled Transversal; 3. Cold-Rolled Longitudinal; 4. Cold-Rolled Transversal). Upon Mr. Fairbairn’s application, the bars which I requested were promptly and gratuitously furnished by Richard Smith, Esq., Superintendent of Lord Dudley’s Iron Works at the Round Oak Works near Dudley. The number of bars was 24, namely, 6 in each of the four classes above described. Each bar was 16 inches long, 4 inches broad, and about ¼ inch thick: the aggregate weight of the bars in each class was, —1st, 28 lbs. 8 oz.; 2nd, 28 lbs. 10 oz.; 3rd, 27 lbs. 10 oz.; 4th, 27 lbs. 8 oz. The manufacture of the bars is described to me in substance as follows:—The hot-rolled and cold-rolled bars were all manufactured in the same way up to the stage of producing sheets of iron of the desired thickness; the last rollings having commenced with large bars at a welding heat, and having terminated with the bars (now converted into sheets) at a dull red heat. Then the sheets to be cold-rolled were allowed to cool to a perfectly cold state, and in that state were rolled afresh between other rollers. After this, the experimental bars were cut out of the sheets. Each set of six bars was packed in one box, with the maker’s inscription on every bar reading forward in the same direction in all.