The discovery of a cheap and simple, process for freeing cast iron from carbon has long been a subject of earnest inquiry on the part of scientific and practical men. Mr. John Heaton's process for making' wrought iron and steel seems to be pretty generally admitted to be a most expeditious and thorough method, but it is still an open question in the minds of many whether it is sufficiently economical. Our readers are already aware that the basis of the method is the conversion of the carbon by means of nitrates of soda or potash. He also claims the use of chlorates. The application of these oxidizing agents is to be made to the under surface of the molten iron, so that the oxygen may act from below upward through its mass. The nitrate or chlorate is to be placed in chambers within the receiver of the melted iron, winch is made to revolve, so that the chambers may come under the molten metal, and the nitrate or chlorate may act through it. The surface of the nitrate or chlorate is protected from a too rapid action of melted iron by means of an iron plate perforated with numerous holes. Mr. Heaton says, that if the cast iron contains about five per cent of carbon, one hundred weight and a quarter of nitrate or chlorate will be sufficient for each tun of iron, and that the effect will be produced in three minutes. The same process may also be used for the conversion of cast iron into steel. A hot dispute has arisen in regard to tlie relative merits of this process as compared with that of Bessemer, culminating in, two actions at law against the editor of Engineering, a leading scientific journal in England. This plan has taken a most decided position against the merits of the Heaton process. Indeed, looking upon the contest with entirely disinterested optics, it has seemed to us that its position was untenable on scientific grounds, and that it desired nothing so much as the failure of the new method. Its language has been that of deprecation, and its spirit, as evinced in the course of the discussion, seemed any thing but candid. The matter has, however, fallen into excellent hands, and has been investigated by Professor Miller, of world-wide reputation as a chemist, in connection with Dr. Mallet and Mr. Kirkaldy. Each of these gentlemen has made elaborate reports entirely favorable to the success. Prof. Miller's preliminary report describes Heaton's process thus: On the occasion of our (namely, his and Dr. Mallet's) visit to the works of Langley Mill, on the 10th of July, 1868, 6 cwts. of Clay Lane forge pig, No. 4, were charged into a hot cupola which contained no other iron; and immediately 6\ cwts. of Stan ton forge pig, No. 4 (produced from two-thirds of Northamptonshire brown ore, one-sixth of Chesterfield clay ore, and one-sixth of puddling cinder) were added, and the whole, when melted, was drawn off into a ladle, from which it was transferred to the converter. The converter is a wrought-iron pot, lined with fire-clay. In the bottom of it was introduced a mixture of 169 lbs. of crude nitrate of soda, 40 lbs. of silicious sand, and 20 lbs. of air-slaked lime; but these proportions in practice are varied considerably. On the top of this mixture a cast-iron perforated plate, weighing 95 lbs., was placed. The converter was then securely attached to the open mouth of a sheet-iron chimney, and the melted iron from the cupola (sample of this marked No. 4) was poured in. In about two minutes a reaction commenced ; at first a moderate quantity of brown nitrous fumes escaped, these were followed by copious blackish, then gray, then whitish fumes, produced by the escape of steam carrying with it, in suspension, a portion of the flux. After the lapse of five or six minutes, an intense deflagration occurred attended with a loud roaring noise, and a burst of a brilliant yellow flame from the top of the chimney. This lasted for about a minute and a half, and subsided as rapidly as it commenced. When all had become tranquil, the converter was detached from the chimney, and its contents were emptied upon the iron pavement of the foundery. The crude steel was in a pasty state and the slag fluid ; the cast-iron perforated plate had become melted up and incorporated with the charge of molten metal. The slag had a glassy, blebby appearance, and a black or dark green color in mass. A mass of crude steel from the converter was then subjected to the hammer (No. 7). About 4 cwts. of the crude steel were transferred to an empty, but hot reverberatory furnace, where, in about an hour's time, it was raised to a welding heat, and forged into four blooms under the steam hammer, then rolled into square billets, which were cut up, re-heated, and rolled into finished bars, varying in thickness from an inch to five-eighths of an inch (No. 8). Three or four cwts. of the crude steel from the converter were transferred to a re-heating furnace,'then hammered into flat cakes, which, when cold, were broken up and sorted by hand for the steel melter (No. 9). Two fire-clay pots, charged with a little clean sand, were heated, and into each 42 lbs. of the cake steel were charged. In about six hours the melted metal was cast into an ingot (10 B). Two other similar pots were charged with 35 lbs. of the same cake steel, 7 lbs. of scrap iron, and 1 oz. of oxide of manganese. These, also, were poured into ingots (10 C). The steel, 10 B and 10 C, was subsequently tilted, but was softer than was anticipated. These results, on the whole, are to be considered rather as experimental than as average working samples. I have, therefore, made an examination of the following samples only: No. 4. Crude cupola pig. No. 7. Hammered crude steel. No. 8. Rolled steely iron. No. 5. Slag from the converter. I shall first give the results of my analysis of the three samples of metal: Cupola Pig. Crude Steel. Steel Iron. (No. 4.) (7). (8). Carbon............ 2*830 .... 1-800 .... 0*993 Silicon with a little titanium......... 2'950 ___ 0266 ___ 0149 Sulphur........... 0-113 ___ 0-018 ___ traces. Phosphorus......... 1-455 ___ 0*298 ___ 0*292 Arsenic...___...... 0-041 ___ 0039 ___ 0*024 Manganese........ 0-318 ___ 0090 ___ 0*088 Calcium........... - - .... 0-319 .... 0*310 Sodium............ ___ 0*144 ___ traces' Iron (by difference).. 92*293 ___ 97*026 ___ 98.144 100-000 100-000 100-000 It will be obvious from a comparison of these results that the reaction with the nitrate of soda has removed a large proportion of the carbon, silicon, and phosphorus, as well as most of the sulphur. The quantity of phosphorus (0*298 per cent) retained by the sample of crude steel from the converter which I analyzed, is obviously not such as to injure the quality. The bar iron (No. 9) was, in our presence, subjected to many severe tests. It was bent and hammered sharply round without cracking. It was forged and subjected to a similar trial, both at a cherry red and at a clear yellow heat, without cracking ; it also welded satisfactorily. The removal of the silicon is, also, a marked [result of the action of the nitrate. It is obvious that the practical point to be attended to is to procure results which shall be uniform, so as to give steel of uniform quality whon pig of similar composition is subjected to the process. The experiments of Mr. Kirkaldy on the tensile strength of various specimens, afford strong evidence that such uniformity is attainable. I have not thought it necessary to make a complete analysis of the slag, but have determined the quantity of sand, silica, phosphoric and sulphuric acid, as well as the amount of iron it contains. It was less soluble in water than I had been led to expect, and it has not deliquesced; though left in a paper parcel. I found that of 100 parts of finely-powdered slag, 11*9 were soluble in water. The following was the result of my analysis: Sand, 47'3; silica in combination, 6*1; phosphoric acid, 6*8 ; sulphuric acid, 1*1; iron (a good deal of it as metal), 12*6; soda and lime, 26*1. Total, 100. The result shows that a large proportion of phosphorus is extracted by the oxidizing influence of the nitrate, and that a certain amount of the iron is mechanically diffused through the slag. The proportion of slag to the yield of crude steel was not ascertained by direct experiment, but, calculating from the materials employed, its maximum amount could not have exceeded 23 per cent of the weight of the charge of molten metal. Consequently the 12#6 per cent of iron in the slag could not be more than 3 per cent of the iron operated on. In conclnsion, I have no hesitation in stating that Heaton's process is based upon correct chemical principles. The mode of attaining the result is both simple and rapid. The nitric acid of the nitrate in this operation imparts oxygen to the impurities always present in cast iron, converting them into compounds which combine with the sodium, and these are removed with the sodium in the slag. This action of the sodium is one of the peculiar features of the process, and gives it an advantage- over the oxidizing methods in common use. We may hereafter allude to the reports of Dr. Mallet and Mr. Kirkaldy, both of which contain further matters of interest.
This article was originally published with the title "Conversion of Cast Iron Into Wrought Iron—The Heaton Process" in Scientific American 20, 14, 218 (April 1869)