Appendix J.

METHOD OF PRODUCING SOUND INGOTS.

Introduction by W. C. CUSHING, Chief Engineer Maintenance of Way, South West System, Pennsylvania Lines West.

"In general terms, welding may be described as the crystallizing into union of two solid metallic surfaces when they are brought together under suitable conditions. That such is the case is proved by microscopic examination, for on polishing and etching sections of the united metals, the crystals along the junction are found to be common to each of the original pieces of metal. In perfect welding, there is no visible joint, for the line or plane of junction is occupied by crystals, portions of which belong to one piece of metal and portions of the same crystals to the other. When the boundaries of the crystals are coincident with the juxtaposed plane surfaces, it is evidence of non-welding, which is equivalent to saying that unless the crystals become common to the two pieces there is no welding. . .

"The conditions necessary for the welding of two metallic surfaces of

iron or steel are:

“(1) The surfaces must be clean and free from any foreign infusible substance, such as oxide of iron, slag, lime, etc.

"(2) The metallic surfaces must be in actual contact.”

The above quotation is taken from "Notes on the Welding Up of Blow Holes and Cavities in Steel Ingots," by J. E. Stead, D. Met., F.R.S. (then Vice-President of the Iron and Steel Institute), in "Journal of the Iron and Steel Institute," No. I for 1911.

Dr. Stead then describes several series of experiments which "prove conclusively that when two metallic surfaces quite free from oxide or any foreign matter such as slag, sulphide of manganese, alumina, etc., are brought together and are forged under the conditions given (in his tests) at temperatures about 1100° C., they do weld up completely."

In connection with the description of his experiments, Dr. Stead explains the difference between honeycombed ingots and piped ingots, and in speaking of blowholes he quotes Professor Howe, who has given the subject a great deal of study in the United States.

"It is well known... that if the steel has been in contact with more or less ferruginous slag previous to being poured, the metal is more Report No. 32, Oct. 1912.

or less highly charged with oxide of iron; and that if no metal or metalloid -such as aluminum, silicon or titanium-capable of reducing this oxide, is added to the liquid steel on cooling down . . . a chemical reaction is brought about by fall of temperature, or by passage from the liquid to the solid state."

The examination of the fractured and cut surfaces of honeycombed ingots, made by Dr. Stead, has yielded proof that the honeycombed cavities are lined with metal rich in sulphur and phosphorus.

Nevertheless, he has proved "that welding up of the blowhole cavities in ordinary practice, unless the cavities themselves contain foreign matter, is, as a rule, complete and perfect, has been proved by microscopic examination of a large number of specimens at the points where blowhole segregations indicated that small cavities had originally existed."

This is his explanation of piping in ingots:

"Piping in steel ingots is always coincident with the complete or partial absence of blowholes, or evolution of gas from the steel when it is in the plastic state. When gases are liberated in sufficient quantity, piping is impossible.

"All steel in cooling towards the point of solidification contracts, and as solidification proceeds from the cold sides of the moulds in an inward direction, and when no gases are evolved in the steel as it passes through the plastic state, the liquid contracts and sinks down the center, leaving a pipe or cavity, but if gas is evolved it causes the whole mass of plastic steel to expand, which more or less balances the contraction of the metal still remaining liquid, with the result that no pipe or very little pipe can form, or the volume of plastic steel and the gases together may increase and cause the metal to froth over the top of the mould. . .

"In cases where the cavities consist of central continuous pipes, long experience has shown that finished rails and forgings made from piped steel ingots are almost invariably unsound in the parts where the pipe existed, and that welding together of the walls of the pipe cannot be depended upon, and, as a result, it is usual to reject the parts of ingots in which there is a central cavity when the object is to obtain perfectly sound finished material."

Nevertheless, Dr. Stead has proved that it is possible to weld together the surfaces of a closed up pipe. When the conditions of temperature are right and no foreign material is present, he has "strong ground for the presumption, however, that if the faces of a closed up pipe are crystallized or welded together at several separate points only, and not completely, forging at relatively low temperatures, say at 750° or 850° C., tends to cause disruption of the primarily united portions, particularly in cases where the steel is rolled to small sections. The reason for this hypothesis is that juxtaposed faces probably do not always flow evenly when the steel is being forged or rolled, and that if one face flows in advance of the other, disruption of the parts united occurs, due to shearing effect.

"It is well known that even in quite sound material it is possible to produce internal disruption by a special rolling process, and if it can be

effected in sound steel, how much more readily must it occur in initially imperfectly welded material."

In the case of steel ingots, "the upper ends of the pipes are open to the gases of the heating furnace, and the walls of the cavities become coated with oxide scale, which effectually prevents the metallic surfaces from coming into contact." This fact makes it very doubtful whether or not pipe cavities in steel ingots can be readily welded. "It is a fact observed by Dr. Stead that the surfaces of the walls of the pipes in commercial ingots containing .06 per cent. or more sulphur are rich in manganese sulphide, and this must interfere with the perfect contact of the metallic surfaces, for from a practical point of view, manganese sulphide is equivalent to scoria or slag."

The final quotation from Dr. Stead's paper which the writer will give leads up to the real subject of this communication, and it is as follows:

"It is obvious that if the uppermost layers of steel in an ingot could be kept fluid across the whole area or section till the metal from the bottom to an inch below the surface had solidified, there would be no pipe, and if the steel were of a non-gaseous character there would be no blow

holes."

The writer has had these problems in mind for a long time, and finally turned to Sir Robert Hadfield, F.R.S., Past-President of the Iron and Steel Institute of Great Britain, and a manufacturer of famous steel at the Hecla Works in Sheffield, England, on account of his having been the author of many valuable works containing original researches in the problems of steel making, and he met with such a hearty and cordial response from Sir Robert that it resulted in his presentation of the two papers, "Method of Producing Sound Ingots," and "On a New Method of Revealing Segregation in Steel Ingots," which he had just written for the Iron and Steel Institute, to be read at its meeting on September 30th, 1912,

and his cabled permission to issue them in the Bulletin of the

American Railway Engineering Association.

The subjects of segregation, blowholes and piping are well explained by Sir Robert, and he has clearly shown that in tests and in practice it is possible to overcome those defects, so that "in many cases no less than 92 per cent. of the fluid steel in the mould is made utilizable, and this at expense. . . It is estimated that on a large output the saving by this method is about 8s to 12s per ton."

small

This is timely and cheerful news, as it shows that improvements in steel manufacture have already been made in the very direction in which

we

are most concerned, and that those improvements have resulted in a

saving of money to the manufacturer himself. After reading Sir Robert Hadfield's papers, there is no ground whatever to stand upon for demand

ing a manufacture of rails, such, for instance, as 25 per cent. The proper amount of discard is the amount of unsound metal, whether it be 8 per cent. or 50 per cent., and we believe the method of our specifications to be the proper one for bringing this about as nearly as possible.

fixed percentage of discard from the tops of ingots used for the

Sir Robert has read with interest Mr. Wickhorst's report on "Pipeless Ingots" in Appendix "D" (first printed in Bulletin No. 147, July, 1912), and makes the following comments on the difference between the method of the Standard Steel Works Company and of the method described in his papers:

"I have carefully read the description of these experiments. Whilst the method quoted represents a procedure better than current practice in rail ingots, I do not agree with the addition of carbon in the form of graphite, that is, added in this particular manner, as the steel on the upper surface of the ingot would be very liable to become contaminated, and help to increase segregation troubles.

"It is for this reason my process differs from all others to my knowledge, namely, in having an insulating layer of fluid slag interposing between the fluid steel of the ingot and the source of heat from above, which helps to feed the metal as it shrinks.

"My method differs therefore in this respect, and, I think, is much superior. Moreover the continuation of the heating process enables the feeding of the ingot from the top to take place naturally, and as it should

occur.

"The method described of the Standard Works would be liable to very serious irregularity; by my method every ingot can be made the same."

METHOD OF PRODUCING SOUND INGOTS.

BY SIR ROBERT HADFIELD, F. R. S. (PAST-PRESIDENT IRON
AND STEEL INSTITUTE).

(Reprinted from Journal Iron and Steel Institute by permission of Author.) INTRODUCTION.

Owing to the trouble which has been experienced by railroads, especially in countries where low temperatures prevail in winter time, it has become a necessity to look more carefully into the matter of obtaining sound rails, free from piping, blowholes and other defects. This in its turn means that the ingots from which the rails are made should also be quite sound and free from piping, segregation or other defects. The improved method is applicable to ingots for other purposes, whether of the ordinary square, oblong, round, or other form.

In view of the rapid production of the large quantities of steel ingots required for a modern rail mill, whilst the production of a "sound" ingot may not be so easy as it seems at first sight, yet attention may be drawn to the subject with advantage. Perhaps the question has not received as full investigation as should have been the case. Moreover, apart from the question of soundness, the waste experienced under the present condition of manufacture is very considerable. Therefore, any system which shows how to reduce the loss by waste and scrap is one of more than ordinary interest to the steel maker, as this means not only a better product, but a more economical one. Although some of the information now given has appeared elsewhere, it has been suggested to the author of this paper that the questions dealt with, being of considerable importance, might well be brought before the Institute.

The question of producing sound steel is as important a factor in meeting the requirements of the times as ever it was. By sound steel is generally meant material free from (a) segregation, (b) blowholes and (c) piping. Unless these requisites are fulfilled, trouble and breakdown of the rolled or forged material produced from the ingots may occur in some stage of its history. Fortunately, as a rule, the remedy which obviates or overcomes any one of the difficulties tends to improve all. For example, steel which is sound and free from blowholes is less liable to segregation or intermingled slag, and the ingots made therefrom, if properly fed, will have the defects under (c), that is, piping, largely reduced.

Many simple devices as well as complicated arrangements have been suggested and tried to overcome the difficulties in question-as, for example, fluid compression from the top, also from the bottom; feeding