STEEL 



709 



charcoal, and so on, up to within 6 inches from the 

 top. Then old 'cement powder' Le. charcoal 

 already nsed, and grinders' waste is moistened and 

 plastered over this, and the whole covered with 

 clay or moistened sand to exclude the air. All is 

 now closed in excepting the ends of some extra 

 long ' tasting bars,' which are allowed to protrude 

 from the ' tasting ' or testing holes. A glowing 

 red heat is maintained for eight or ten days, 

 when a tasting-bar is withdrawn to ascertain 

 whether the carbon has penetrated sufficiently. 

 \\~lien this is the case the furnace is allowed to 

 cool slowly during another week or thereabouts. 

 When the bars are withdrawn they are found to be 

 coated with a sort of dark skin which is raised in 

 Misters over a large part of their surface. It is by 

 the appearance of these and by fracture that the 

 quantity of carbon taken in and the depth of its 

 penetration is ascertained. This transfusion or 

 penetration of solid carbon into solid iron is a 

 mystery, the theory of which has been much dis- 

 cussed, too much so for exposition here. An 

 important practical fact is, however, connected 

 with it viz. that the distribution of the carbon 

 is very unequal. Its quantity is greatest on the 

 surface, and gradually decreases towards the in- 

 terior. Therefore the steel in this state, 'blister 

 steel," is of little value on account of its irregularity 

 of composition and consequent irregularity of hard- 

 ness, &c. To remedy this the outsides and insules 

 of the bars have to be stirred up and mixed together 

 so as to give uniformity of composition to the 

 whole. 



The most obvious mode of doing this is to melt 

 the whole and stir the fluid. This is done in 

 making the very best quality of steel ' cast-steel ' 

 or ' pot-steel,' as it is called in Sheffield. The bars 

 are cut into small pieces, melted in crucibles, and 

 then poured from these into ingot moulds. Oxide 

 of manganese and ferrocyanide of potassium are 

 added in small quantities to the melted metal in 

 the crucibles. The theory of the action of these 

 additions has been much debated, and its discussion 

 would occupy too much space for this article. The 

 consumption of fuel, the labour, and the destruc- 

 tion of crucibles renders this melting an expensive 

 process and the result correspondingly dear. A 

 cheaper mode of mixing is adopted in the produc- 

 tion of what is called 'shear-steel.' The blistered 

 bars are cut or ' sheared ' into short lengths ; these 

 are bound together into bundles or ' faggots," raised 

 to a welding heat i.e. heated until they become 

 sufficiently soft to be plastic, then placed under a 



Fig. 2. 



tilt hammer, "shown in fig. 2. The tail of this 

 hammer is struck by the cams of the revolving 

 wheel, whereby the head is lifted, and falls again 

 before the next cam comes into action. In this 

 manner the faggot receives 300 to 400 heavy blows 

 per minute, the rapidity of percussion fully main- 

 taining the heat of the faggot, while its constituent 

 pieces are welded into one coherent mass. This is 



then rolled out into a long bar which is resheared 

 into small pieces to form another faggot to be 

 similarly treated. The reshearing, &c., may be 

 repeated as often as demanded, and thus we have 

 ' single shear, ' ' double shear, ' &c. None of these 

 are so homogeneous as crucible steel, and they are 

 therefore inferior in this respect. 



A very important development of the manu- 

 facture of steel has followed the introduction of the 

 ' Bessemer process,' by means of which a low 

 carbon or mild cast-steel of inferior quality can be 

 produced at about one-tenth of the cost of crucible 

 steel. It is used for rails, for the tires of the 

 wheels of railway carriages, for ship-plates, boiler- 

 plates, for shafting, and a multitude of construc- 

 tional and other purposes to which only wrought- 

 iron was formerly applied, besides many for which 

 no metal at all was used. 



This process was originally based on the theory 

 then generally accepted that steel is ' iron car- 

 bonised in degrees intermediate between malleable 

 and cast iron;' and, as carbon is readily oxidised at 

 a high temperature and thus converted into gaseous 

 compounds, nothing further was supposed to be 

 necessary' for the conversion of cast-iron into steel 

 than to blow through the melted cast or pig iron a 

 sufficient quantity of air to burn out the redundant 

 carbon and leave behind the proportion required for 

 the production of steel. A large number of patents 

 were secured, including various devices for doing 

 this, and all failed. A sort of steel was produced, 

 but it was unworkable. When hammered, either hot 

 or cold, it either crumbled to pieces or split at its 

 edges when flattened down. The sources of failure 

 were twofold. The first was that ordinary pig or 

 cast iron contains other impurities than carbon, 

 notably silicon, sulphur, and phosphorus. The 

 carbon was readily removed by oxidation, and 

 gradually, as demanded by the theory ; the silicon 

 was also oxidised even more readily than the carbon, 

 but the sulphur and phosphorus remained obstin- 

 ately, even after nearly all the carbon was oxidised 

 and the iron itself began to burn. The other diffi- 

 culty was that of regulating the quantity of carbon, 

 by stopping when the required quantity was removed 

 by oxidation. This difficulty was overcome by Mr 

 Robert Mushet, who used a compound of iron and 

 much carbon of known composition ( spiegeleisen ), 

 and added this in the quantity necessary to give to 

 the whole the proportion of carbon required. Thus, 

 if the spiegeleisen contained 5 per cent, of carbon, 

 and 1 per cent, was required in the steel to be 

 produced, spiegeleisen was added to the decar- 

 buretted iron in the proportion of 1 to 4. 



After considerable struggles the first difficulty 

 was partially overcome by using only special kinds 

 of pig-iron, those made from haematite ores which 

 contain very little phosphorus. Mr Mushet's 

 'triple compound," the spiegeleisen, also assisted 

 here, as it contains a considerable amount of man 

 ganese, which exerts a purifying influence on steel. 

 The rationale of this purification has been much 

 debated ; the experiments of the writer indicate 

 that manganese acts by removing the last vestiges 

 of silicon and particles of oxide of iron in the 

 Bessemer converter. Its practical usefulness, how- 

 ever, is unquestionable. But the Bessemer steel 

 even thus produced is far inferior to the crucible 

 steel or shear-steel. There is still sufficient phos- 

 phorus in it to render it unfit for making tools with 

 acute edges, or for files, saws, &c. If highly car- 

 buretted its hardness is accompanied with brittle- 

 ness that causes cutting-tools to notch, and toothed- 

 tools, like saws and files, to strip. Phosphorus 

 -gives hardness of a glassy character. 



The Bessemer 'Converter' is shown diagram- 

 matically in section in fig. 3. It is a strong iron 

 vessel lined with refractory material. The bottom. 



