In time-keeping invar is likely to be as valuable as in surveying. At the Bureau of Standards and the Naval Observatory at Washington, pendulums of invar have been adopted with gratifying results. In ordinary watches and clocks the alloy will banish the compensating devices now requisite, of brass and steel which expand with heat and shrink with cold. For chronometers of the highest grade it is desirable that invar be improved with respect to its stability, an improvement which appears to be highly probable.
One other discovery by M. Guillaume deserves a word. He has found a nickel-steel which when warmed has the same expansibility as glass, so that it may displace platinum wire in leading an electric current into an incandescent lamp, a Crookes’ tube or similar illuminator. More singular still is another of his nickel-steels which shrinks slightly when warmed, holding out the hope of finding an alloy which will neither shrink nor expand as its temperature rises. With such a substance, of trustworthy stability, the arts would have a working material of inestimable value for theodolites, frames for microscopes and telescopes, and cameras for exact picturing.
Manganese Steel.
The magnetic properties of steel, to-day of supreme importance, have for ages excited curiosity. As long ago as 1774, Rinman observed that steel alloyed with manganese is non-magnetic. Here was a material for time-pieces which would free them from magnetic derangement. In the hands of Mr. R. A. Hadfield, of the Hecla Works, Sheffield, England, manganese steel has been produced in remarkable varieties. As the proportion of manganese is increased, the alloys manifest singular changes in their properties. When the manganese is four to six per cent., and the carbon less than one-half per cent., the alloy is brittle enough to be readily powdered by a hand hammer. When the proportion of manganese is doubled, the alloy displays great strength, which reaches its maximum when the manganese is fourteen per cent. No other material approaches manganese steel in its ability to resist abrasion; it outwears ordinary steel four times, much reducing the need for repairs, renewals, or pauses in work while worn-out parts are being replaced. It gives equally good service as the pins and bushings of dredges of the bucket-ladder type, lifting gold-bearing gravels and sands. It is used for centrifugal pumps in dredging sandy harbors, slips, or ponds, where the grit borne in the water plays havoc with ordinary steel surfaces. In ore-crushing manganese steel is particularly effective; a pair of jaws built of it have crushed 21,000 tons of flinty ore and were still good for 4,000 to 6,000 tons more, while the best chilled iron plates failed to crush as little as 4,000 tons.
This alloy is so hard that it cannot be machined or drilled by ordinary means; it must be treated by emery or carborundum wheels. Yet it is so malleable that it can be used for rivets when headed cold. It is so tough that it may be bent and twisted at will without rupture, so that it forms railroad switches, frogs, and crossings of great durability.
High-Speed Tool Steels.
Until 1868, the steel tools used in lathes and drills, planers and so on, were limited to the moderate pace at which they remained cool enough to keep their temper. Beyond that quiet gait they became worthless, snapped apart, or melted as if wax. In 1868 Robert Forester Mushet, of the Titanic Steel and Iron Company, Coleford, England, discovered an alloy of steel, tungsten and manganese which took rough cuts at a depth and with a speed unknown before. This alloy, because hardened simply in air, was called “air-hardening” or “self-hardening.” Thirty years afterward at the Bethlehem Steel Works, Pennsylvania, a tool of this steel was heated to what was feared to be a ruinously high temperature; experiment proved that the tool could be used at a heat, and therefore at a speed, never attained before in the workshop. From that hour hundreds of investigators have proceeded to combine steel with tungsten in various percentages, adding manganese, molybdenum, chromium, silicon, and vanadium. Of these ingredients much the most important are tungsten and molybdenum. Particular pains must be taken thoroughly to anneal the alloy when worked into bars.
As to the gain introduced by high-speed tool steels let Mr. J. M. Gledhill testify from the experience of the Sir W. G. Armstrong, Whitworth & Company’s works at Manchester:—
“Formerly where forgings were first made and then machined with ordinary self-hardening steel, a production, from bars eighteen and one half by six and five eighth inches, of eight bolts in ten hours was usual. With the new steel forty similar bolts from the rolled bar are now turned out in the same time, further abolishing the cost of first rough forging the bolt to form. The speed is 160 feet a minute, the depth of cut three-quarter inch, of feed 1⁄32 inch, the weight removed from each bolt sixty-two pounds, or 2,480 pounds per day, the tool being ground only once in that time. This is a fairly typical case. Just as striking is the behavior of this steel in twist drills, which supersede the punching process by passing through stacks of thin steel plates quite as swiftly and economically as a punch, while avoiding the liability to distress which accompanies the action of a punch.”