Robert Forester Mushet

Robert Forester Mushet (1811–1891), an English metallurgist,

1811 April 8th. Born at Coleford, Gloucestershire. He was the youngest son of Agnes Wilson and David Mushet, an ironmaster.

Robert spent his formative years studying metallurgy with his father, formerly of the Clyde, Alfreton and Whitclift Ironworks.

In 1856 Mushet found an inexpensive way to make high quality steel by adding ferro-manganese, or spiegeleisen brought from Rhennish Prussia. He explained that "during the summer of 1848 Mr. Henry Burgess, editor of The Bankers' Circular, brought me a lump of white crystallized metal which he said was found in Rhenish Prussia, where, he was told, a mountain of it existed. He had merely confounded iron with iron ore, an error often committed. Being familiar with alloys of iron and manganese," says Mr. Mushet, "I at once recognized this lump of metal as an alloy of these two metals and, as such, of great value in the making of steel. Later, I found that the white metallic alloy was the product of steel ore, called also spathose iron ore, being, in fact, a double carbonate of iron and manganese found in the Rhenish mountains, and that it was most carefully selected and smelted in small blast furnaces, charcoal fuel alone being employed and the only flux used being lime. The metal was run from the furnace into shallow iron troughs similar to the old refiners' boxes, and the cakes thus formed, when cold and broken up, showed large and beautifully bright facets and crystals specked with minute spots of uncombined carbon. It was called, from its brightness, 'spiegel glanz' or spiegel eisen, i.e., looking-glass iron. Practically its analysis was: Iron, 86…25; manganese, 8…50; and carbon, 5…25; making a total of 100…00."

This improved the steel's malleability – its ability to withstand rolling and forging at high temperatures – without which the Bessemer process for making steel would not have been an economic success. Bessemer's method had only produced "burnt" wrought iron, lacking strength, but Mushet's innovation restored the quality of the steel.

1857 Mushet was the first to make durable rails of steel rather than cast iron, providing the basis for the development of rail transportation throughout the world in the late Nineteenth century. The first of Mushet's steel rails was delivered to Derby Railway Station, where it was laid down early in 1857 at a heavily trafficked part of the line where the iron rails had to be renewed every six months, and occasionally every three." Six years later, in 1863, the rail seemed as perfect as ever, although some 700 trains had passed over it daily.

1857 In a second key advance in metallurgy, under a patent he applied for in 1857, Mushet produced the first commercial steel alloy in 1868 by adding a small amount (8%) of tungsten to the molten steel in the crucible. The steel hardened in the air, whereas previously the only way to make steel hard enough for machine tools had been to quench it, by rapid cooling in water. Self-hardening (or tungsten) steel machine tools could run much faster and were able to cut harder metals than had been possible previously. This resulted in a revolution in the design of machine tools and in the progress of industrial metalworking. High strength tool steels could be precision machined for the production of rifles, cutlery, surgical and other instruments.

Although Mushet filed many valid patents for his inventions, unreliable business partners allowed them to lapse. Mushet was rescued from insolvency and supported by Henry Bessemer, who had benefited by the free use of Mushet's lapsed patents.

1865 During the year there is a mass of correspondence from Robert Mushet on the Bessemer process in 'The Engineer'

1869 'SOMETHING NEW IN STEEL.
It has long been a disputed point where steel leaves off and wrought iron begins; but it is generally received that the difference between steel and cast iron is so great that no doubt can exist as to which is which. Within the week we have proved to our own satisfaction that it is just as difficult to distinguish bewteeen iron and steel as it is to define those characteristics in which steel differs from wrought iron. There is, indeed, at this moment, a soc-called steel in the market, which possesses such extraordinary attributes, that the metallurgist may well feel in doubt under what head it shuld be classed. To all intents and purposes, it is a new material, and it claims the attention our readers.

'For some time past Mr. Mushet has advertised a "special tool steel", warranted to last — we are afraid to say how much longer than any other steel, worked in the same way, and in the same shape. Our readers may have seen advertisements, and passed them over as legitimate trade puffs. In this they were wrong. Ths material may be steel, cast iron, or some alloy — is, in reality, one of the most singular substances we have ever met with, and it possesses qualities which deserve the attention, not only of engineers, but of analytical metallurgists. We propose to put our readers in possession of all that we know about it, leaving them to draw their own conclusions, and trusting that Mushet will supply more information to the scientific public in general than he has hitherto thought proper to furnish to purchasers.

'A few days since we visited what we shall term the Etna works. Chatting with the manager about things in general, and engineering in particular, the subject of tool steel turned up, and we then learned that a couple of tyre turning tools, made of Mr Mushet's tool steel, were in use at the moment, which we were assured possessed such qualities that manager, foreman, smiths, and turner, were alike at a loss to comprehend the nature of the material with which they had to do. Our curiosity was excited, and every facility was courteously afforded us for testing the steel. Mr. Mushet issues with each bar printed instructions as to the system to be adopted in working it. In the first place we are told that, after forging or otherwise working the tool steel, it is to be suffered to cool slowly, and under no circumstances to be quenched and tempered. Now, it is well known that the hardest ordinary cast-steel may be softened so much by heating to bright red and suffering it to cool slowly, then it will not retain a sharp edge for two minutes. In other words, its temper may be drawn. We proved, on the other hand, that the temper of Mr. Mushet's " tool steel" cannot be drawn. After being heated red-hot and suffered to cool slowly, it still remained harder than any ordinary cast-steel tempered at straw colour. The proof of this lies in the fact that a tool of the best ordinary cast steel required to be ground three times in planing a given area of hard cast iron, whereas a tool of Mr. Mushet's steel not only planed a similar area without re-grinding, but remained to all intents and purpoes nearly as sharp as when it began. It is rather more brittle than ordinary steel, in so far that a different angle, slightly more than that commonly employed, must be given to turning tools, but it certainly is not objectionably brittle. In the shape of chisels, we have no experience of its qualities whatever.

'Having satisfied ourselves of its good qualities in the shape a tool, we next proceeded to investigate its properties as displayed under the hammer. We then learned that no smith at the Etna Works had forged it, and that the tools we saw had been supplied by Mr. Mushet ready made to shape, and requiring only be ground before being set to work. A short time before we saw them an attempt had been made to cut a piece off a tool, to test its forging qualities; but although heated only to a dull red, about 3in. broke off at the first touch of the "set." The character of the irregular fracture was totally unlike that of any steel or cast-iron with which we are acquainted. It would be impossible to describe it.

'Our good friend, the manager af the Etna Works, asked us if we would like to see the piece broken off the tool forged. We need scarcely say that our answer was in the affirmative. The fragment was about 4in. long, and 1 1/2in. square, externally resembling ordinary cast steel in every respect. It was heated to a cherry red by an experienced smith, placed on the anvil, and struck with a sledge striker. The striker produced no effect on the lump of any kind; forged on an ordinary anvil in this way, it was evident it could not be. It was then decided that we should test it under a small steam hammer. It was once more heated to dull red, and struck lightly by a 5 cwt. hammer. In about one minute the block of steel fell into a handful of fragments, totally different in the character of the fracture from either steel or cast iron. It is difficult, if not impossible, to convey an accurate idea of the appearance of the fragments. The real pieces lie before us, and resemnle nothing in the world so much as bits of vitreous slag from a blast furnace. They are not like any metal in the slightest degree, but on filing the surface assumes the character of polished steel. All the pieces manifested the same conchoidal fracture. In a second experiment with another piece a far higher temperature was imparted to the metal and it was then drawn with little difficulty about a quarter of an inch square. It was hardened in the usual way, and did not fly, so that it is possible that in small masses it will bear hardening. The little piece is so intensely hard that no file will touch it. A lump of the same steel, an inch and a quarter square, cracked in all directions when heated and quenched.

'What is this material? Is it steel, or cast iron ? Under the hammer it behaves more like cast iron then anything else ; as tool it behaves neither as cast iron or steel ever behaved before. To all intents and purposes it is a new metal. Mr. Mushet has not patented its mode of production, which he reserves as a secret. That it contains an enormous quantity of carbon is, in a sense, proved by its hardness. Why does not this carbon render it brittle as cast iron? Is the carbon combined or graphitic? Is the "steel" simply an alloy of iron with some other metal? What is the proper method of forging it in ordinary smith's fires? These and some other questions present themselves for solution. The only conclusion we can arrive at, and we confess we do not believe it to be the correct solution of an interesting problem, is that Mr. Mushet first forges his tools or bars from a hard cast steel of the ordinary kind, and then, by some process such as re-cementation, imparts additional hardness to them, which, although it makes the tools as such invaluable, renders the bar from which tools should be made as such useless in the hands of all but first rate smiths.— The Engineer'

In fact Mushet's tool steel, known as "self-hardening steel" was carbon steel alloyed with large percentage of tungsten. When cooled from yellow heat in a draught of air, was not only sufficiently hardened, but was thermally considerably more stable than that of plain carbon steel. The tools could take bigger cuts and work at higher speeds. Later, about 1880. Mushet still further improved his tools steel by the addition of relatively small percentages of chromium. By between 1880 and 1900, “self” or “air-hardening” steels were produced many steel manufacturers in considerable variety.

Mushet died January 19, 1891 in Cheltenham.

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1891 Obituary

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Sources of Information

• Wikipedia