In favor of the Bessemer process we may say that when steel of from .06 to .10 per cent phosphorus is wanted it is a cheaper process than open-hearth, but low phosphorus Bessemer requires a very careful selection of raw materials. Phosphorus and sulphur must be lower in the raw materials than is desired in the steel. A disadvantage of the Bessemer process is that the steel cannot be tested dur ing the operation. Bessemer plants are suitable where tremendous tonnages of a rather cheap product are required. The open-hearth proc ess gives a good outlet for steel scrap, billet ends, old rails, etc. The product is more re liable than Bessemer, and the low phosphorus open-hearth steels are much cheaper than low phosphorus Bessemer. The process allo*s more latitude in the selection of raw materials. Low or high sulphur pig can be used and both phosphorus and sulphur can be reduced. The steel can be tested chemically and physically during the operation, and whereas in Bessemer it is customary to continue the blow until all the carbon of the pig is oxidized, in the open hearth process the decarbonization can be checked when it has gone far enough, or when the carbon desired in the product is reached.
As regards the quality of steels made by the various methods, it is undoubtedly true that even when the analyses are almost identical that crucible steel takes first place. Next in order comes open-hearth, and last place falls to Bessemer. As regards excellence of analy sis, they usually stand in the same order, crucible being finest, open-hearth next and Bessemer last. Acid open-hearth, if the proper materials are used, i.e., if virtually a crucible mixture is melted in an acid open hearth furnace, will be a most excellent ma terial, but as actually made, acid open-hearth is usually very high in sulphur and phosphorus and much of it resembles a Bessemer analysis. In general then basic open-hearth takes next rank to crucible because of its low phosphorus and sulphur contents. In general, of two steels of identical analysis, acid and basic open-hearth, the former will show much the higher tensile strength. Campbell has even constructed a formula for calculating tensile strength from the analysis, and in his formula it is assumed that each 1/100 per cent of car bon increases the tensile strength by 1,000 pounds in acid steel and only 770 pounds in basic. Each 1/100 per cent phosphorus exerts the same effect in either process and raises the tensile 1,000 pounds. One one-hundredth per cent manganese in low carbon acid steel raises the tensile 80 pounds and .130 pounds in basic, but the condition is reversed when the carbon is high and then the manganese raises the tensile by 400 pounds per 1/100 per cent in acid and only 250 pounds in basic. The effect of sulphur is very smalL As regards the tonnage production of steel we find that the most remarkable increase is in open-hearth steel. In 1917 the increased
production of open-hearth steel over 1907 was over 200 per cent; and the total reached the impressive figure of 34,148,893 tons, or three times the production of 10 years. ago.
The total production of open-hearth and Bessemer steel in 1896 was 5,250,000 tons, while in 1906 it was about 23,000,000, and in 1916 42,500,000 tons. In 1896 25 per cent of all steel produced was open-hearth and 75 per cent Bessemer, while in 1917 there was three and one-half times as much open-hearth steel made as there was Bessemer.
One must not imagine from these figures that the production of Bessemer is declining materially. The facts are that Bessemer pro duction is about at a standstill while the gain is in the making of open-hearth steel The basic open-hearth process has made much more rapid gains than the acid. In 1917 about one-sixteenth of the open-hearth steel was of acid manufacture. Nevertheless that was the biggest year by a considerable margin the country has ever had in the manufacture of acid steel.
Bessemer steel still holds its own to a con siderable extent for rails, although open hearth steel is making great progress in this direction and is more largely used than Besse mer for ordinary structural purposes. Of the Bessemer steel made in the United States every bit is acid. Of the acid open-hearth steel produced in the country the larger part is used in the form of castings, rather than in the manufacture of ingots for rolling.
Electric processes, which represent the latest development in the steel industry, 'are not an important factor yet, so far as tonnage is con cerned, but they have already outstripped the production of crucible steel, and in fact in 1917 the production of electric steel was more than double that of crucible.
The total production in the United States of steel ingots and castings by all processes in 1917 exceeded 45,000,000 gross tons which is almost exactly double the production of 10 years ago.
Bibliography.— Brough, 'The Early Use of Iron> (in Iron and Steel Magazine, Vol. XI, p. 417, 1906) • Campbell, H. H.,