At a recent meeting of the Chemical Society, London, a paper was read
entitled "Notes on the Condition in which Carbon exists in Steel," by
Sir F.A. Abel, C.B., and W.H. Deering.
Two series of experiments were made. In the first series disks of steel
2.5 inches in diameter and 0.01 inch thick were employed. They were all
cut from the same strip of metal, but some were "cold-rolled," some
"annealed," and some "hardened." The total carbon was found to be:
"cold-rolled," 1.108 per cent.; hardened, 1.128 per cent.; and annealed,
0.924 and 0.860 per cent. Some of the disks were submitted to the action
of an oxidizing solution consisting of a cold saturated solution of
potassium bichromate with 5 per cent. by volume of pure concentrated
sulphuric acid. In all cases a blackish magnetic residue was left
undissolved. These residues, calculated upon 100 parts of the disks
employed, had the following compositions: "Cold-rolled" carbon, 1.039
per cent.; iron, 5.871. Annealed, C, 0.83 per cent.; Fe, 4.74 per cent.
Hardened, C, 0.178 per cent.; Fe, 0.70 per cent. So that by treatment
with chromic acid in the cold nearly the whole of the carbon remains
undissolved with the cold-rolled and annealed disks, but only about
one-sixth of the total carbon is left undissolved in the case of the
hardened disk. The authors then give a _resume_ of previous work on the
subject. In the second part they have investigated the action of
bichromate solutions of various strengths on thin sheet-steel, about
0.098 inch thick, which was cold-rolled and contained: Carbon, 1.144 per
cent.; silica, 0.166 per cent.; manganese, 0.104 per cent. Four
solutions were used. The first contained about 10 per cent. of
bichromate and 9 per cent. of H_{2}SO_{4} by weight; the second was
eight-tenths as strong, the third about half as strong, the fourth about
one and a half times as strong. In all cases the amount of solution
employed was considerably in excess of the amount required to dissolve
the steel used. A residue was obtained as before. With solution 1, the
residue contained, C, 1.021; sol. 2, C, 0.969; sol. 3, C 1.049 the
atomic ratio of iron to carbon was Fe 2.694: C, 1; Fe, 2.65: C, 1; Fe),
2.867 C, 1): sol. 4. C, 0.266 per 100 of steel. The authors conclude
that the carbon in cold rolled steel exists not simply diffused
mechanically through the mass of steel but in the form of an iron
carbide, Fe_{3}C, a definite product, capable of resisting the action of
an oxidizing solution (if the latter is not too strong), which exerts a
rapid solvent action upon the iron through which the carbide is
distributed.
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