[619] Vide Slocum, Chem. Eng. 1911, 13, 257.
Whilst it is very generally agreed that the addition of titanium results in the production of much stronger and more durable products, the question of the precise effect obtained is by no means definitely settled. The experimental work, whilst pointing on the whole to the superiority of titanium-treated steel, is by no means conclusive; in some cases, indeed, it is conflicting. Thus the micro-photographs obtained by von Maltitz[620] and Venator[621] show that the titanium-treated steel has a far cleaner fracture and far more homogeneous structure than steels not so treated; on the other hand, the micro-photographs of Treuheit[622] show practically no improvement in structure for the titanium steel. The exhaustive tests of the first two authors, again, and the experiments of numerous railways in the use of titanium steel rails,[623] demonstrate clearly that the treatment results in improvement in strength and durability of the product; but the work of Otto[624] proves equally clearly that his products did not differ markedly, whether titanium-treated or not, and he is of opinion that the rail tests were not sufficiently prolonged or searching to be considered conclusive. It is nevertheless to be considered certain that the use of titanium does cause a marked improvement in the quality of the steels obtained, and especially in the durability of rails. The negative results obtained by some authors may be explained, firstly, on the ground that no tests are conclusive unless carried out with steel from the one bath, one half of which has been treated with titanium, and the other half not so treated; secondly, that the ferro-titanium must be incorporated with the metal, and must not be suffered to be taken up by the slag, and so lost; and thirdly, that the bath must be allowed to remain for some minutes after treatment, in order that the reaction may be complete, and the titanium-bearing slag allowed to rise to the surface. When these conditions are carefully observed, experiment shows that marked improvement in the quality of the steels produced is effected.
[620] Stahl Eisen, 1910, 29, 1593.
[621] Ibid. 1910, 30, 650.
[622] Ibid. 1910, 30, 1192.
[623] Vide Dudley, J. Ind. Eng. Chem. 1910, 2, 299; also Cass. Mag. 1911, 40, 483.
[624] Vide abstract in Stahl Eisen, 1912, 32, 1497.
As to the actual nature of the effect produced, it is generally believed that titanium acts merely as a cleansing agent, freeing the metal from occluded or combined gases, and removing blow-holes, so producing a denser and more homogeneous structure, with consequent improvement in properties. The added titanium is usually found entirely in the slag, so that it appears certain that it does not alloy, but merely purifies. It certainly acts as a powerful and rapid deoxidiser, removing the last traces of the gas which have escaped the action of the manganese, silicon, etc., with which steels are now generally treated. Many authorities, on the ground of analyses, and of the known affinity of titanium for nitrogen, believe that it very largely reduces the nitrogen-content,[625] which is so harmful; this, however, is still an open question.[626] It is stated that if excess of titanium is used, so that small quantities—0·05-0·20 per cent.—remain in the finished steel, the toughness and durability are further increased;[627] but as a rule, manufacturers prefer to work with smaller quantities, so that no free titanium remains in the product.
[625] Vide von Maltitz, loc. cit.
[626] Vide Venator, loc. cit.