The first known steel was possibly produced accidentally by the primitive method which smelted wrought iron direct from the ore. The increase of the degree of heat in the primitive smelting furnace caused the iron to become hot enough to absorb in a combined form that quantity of carbon which gave it a new property. It was found that, although this newly discovered grade of metal had to a greater or less degree the malleability of wrought iron when cooled slowly, it further had the property of becoming hard and brittle when cooled suddenly from a red heat.

The uses of steel made in this primitive way must have been very limited because of the uncertain means of producing it.

Not until the cementation process of steel making was discovered and developed, about 1770, did steel become a fairly dependable and practical product, although its uses remained confined for a long time, by the limitations of this process, to the making of cutlery, edged tools, and special parts of machinery. The cementation process could not supply steel for a wider field of use because

(1) the product in large quantities lacked uniform composition;

(2) it could not always be depended upon when strength was of first importance, and (3) its production was expensive.

The need for a steel of uniform quality, dependable strength, and low cost in large quantities, led to investigations along other lines of possibility in steel production. The puddling process, as used in wrought-iron making, was tried for steel making, with the idea that the burning out of carbon should be stopped when enough remained in the charge to give the grade of steel desired, but this was not satisfactory because the stopping of the oxidizing process at the point to retain the necessary amount of carbon left too much of the other impurities in the metal.

Finally, in 1856, Sir Henry Bessemer made public the process which bears his name. In 1868 Sir Wm. Siemens in England and Messrs. Martin in France perfected the Siemens and the Siemens-Martin processes (almost identical) which are developed from the puddling process for wrought iron. These processes have revolutionized the manufacture of steel, and have so extended its limits in regard to its carbon content, that a new definition of the product became necessary, particularly as mild steel cannot be hardened by sudden cooling.

It was early discovered, in the use of these processes, that a reliable steel could not be made from pig iron containing more phosphorus or sulphur that the steel should contain, because these impurities do not remain oxidized in a furnace or converter with a silica lining, as then used, and therefore could not be disposed of with the slag. Silicious materials are acid materials, and they reduce oxidized phosphorus and sulphur as soon as it is formed, causing these impurities to re-enter the steel. The use of silica linings in the furnace and converter classed these processes as acid processes of making steel. This limitation of the newly discovered processes restricted them to the use of pig iron low in phosphorus and sulphur, and this restriction caused investigators to seek and develop the basic method of steel making. This method differs from the acid process primarily in having a lining of basic material for the furnace and converter. Such a lining permits the use of a lime flux, which will remove phosphorus and surphur, while a silica lining will not permit the use of a lime flux, because chemical action between lime and silica would soon disintegrate the furnace or converter lining.