The genesis of the bessemer process

It will, perhaps, assist the non-technical reader to understand what follows if I explain, in a few words, the forms in which iron and steel existed at the time when I commenced the experiments which resulted in the creation of the Bessemer process. At that date there was no steel suitable for structural purposes. Ships, bridges, railway rails, tyres and axles were constructed of wrought iron, while the use of steel was confined to cutlery, tools, springs, and the smaller parts of machinery. This steel was manufactured by heating bars of Swedish wrought iron for a period of some six weeks in contact with charcoal, during which period a part of the carbon was transferred to the iron. The bars were then broken into small pieces, and melted in crucibles holding not more than 60 lb. each. The process was long and costly, and the maximum size of ingot which could be produced was determined by the number of crucibles a given works could deal with simultaneously. Such steel when rolled into bars was sold at £50 to £60 a ton. The wrought iron bars from which the steel was made were manufactured from pig-iron, as was all wrought iron, by the process known as "puddling." Naturally, such a process was costly; puddling demands great strength and endurance on the part of the workmen, combined with much skill.

Practically, all objects in iron, except such as were simply castings, were at that time made from wrought iron manufactured by puddling. The object I set before myself was to produce a metal having characteristics comparable with those of wrought iron or steel, and yet capable of being run into a mould or ingot in a fluid condition. I was aware that Fairbairn and others had sought to improve cast iron by the fusion of some malleable scrap, along with the pig iron, in the cupola furnace. This fusion of scrap-iron, intermixed with a mass of coke, was found to convert the malleable iron into white cast iron, which was at the same time much contaminated with sulphur. Therefore, to a great extent, this system had failed in its object. In my experiments I avoided the difficulties inseparable from Fairbairn's method, by employing a reverberatory furnace in which the pig-iron was fused. Into the bath so formed I put broken-up bars of blister-steel, made from Swedish or other charcoal-iron, its fusion taking place without its being further carburised by contact with the solid fuel, or contaminated by the absorption of sulphur. The high temperature necessary for the fusion of a large proportion of steel in the bath was obtained by constructing the fire-grate much wider than the bath, by contracting the width of the furnace considerably at the bridge, and also by continuing to taper slightly the furnace all the way from the fore-bridge to the downcast flue, which was connected with a tall chimney-shaft. Many alterations and modifications of this furnace were made from time to time, but it was found that the large volume of flame sweeping over the open hearth of the furnace was mixed with a considerable quantity of combustible gas. To consume this gas a hollow fire-bridge was employed, having numerous perforations made in the clay lumps of which it was composed, and so arranged as to allow jets of hot atmospheric air to mingle with these combustible gases, and produce an intense heat close down to the surface of the bath. It was also found that this admission of hot air all along the back of the fire-bridge produced a decarbonising action on the bath; hence the state of carburation of the metal might be altered by regulating the admission of air. This passage of air through the hollow fire-bridge served also to keep down the temperature of the latter and render it more durable.

Some of the samples of metal which I produced were, when annealed, of an extremely fine grain, and of great strength. At this stage of my experiments I cast a small model gun, which in the lathe gave shavings slightly curled, and closely resembling the turnings from a steel ingot; the metal, when polished, also looked white and close-grained like steel. I was so well pleased with this little model gun that I took it over to Paris, obtained an audience with, and showed it to, the Emperor, who had encouraged this attempt to improve the iron employed in founding heavy ordnance. His Majesty, who had desired me to report progress, accepted this experimental gun, remarking that some day it might have an historical interest. It was in recognition of this circumstance that His Majesty, later on, intimated, through Colonel Belleville, his desire to confer on me the decoration of the Legion of Honour, provided I could obtain permission to wear it, a privilege which our Ambassador twice refused. His Majesty also sanctioned the erection of my furnace at the Government Cannon Foundry at Ruelle, near Angouleme, to which place I went with proper introductions for the purpose of arranging all the necessary details. I also sent over from England several thousand special firebricks, etc., for the erection of the furnaces.