Alloy Steels and their Characteristics.
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As stated by our Sheffield correspondent, chrome-vanadium steel and similar high-grade alloys are claiming a large share of attention in motor works throughout the Kingdom, and, as many of our readers may not have had ample and suitable opportunities for the making of observations of the mechanical and physical properties of such steels, it may not be out of place to give a few notes relating to the characteristics of a few of the moreextensively-used alloys produced in modern steel works. In motor-vehicle construction, the various parts must be made from the best and mostsuitable materials which can be procured, and such materials should combine a high factor of safety with the least possible weight. High tensile strength in itself is not sufficient: the material must also combine other qualities. For instance, it must have a high limit of elasticity, so that it may stand up to heavy stresses without permanent deformation, and, also, it must be tough yet ductile, in order that it will not easily suffer breakage as the result of suddenly-applied loads or shocks. Motor mane
facturers now have at their command a number of high-class steels which, if treated in an intelligent and suitable manner, will give test results that would have been considered impossible of attainment fifteen or twenty years ago. Take as an example the test figures for two pieces of nickel-chrome steel, taken from the same bar, which figures were brought to our notice recently. One of these pieces, which was tested in its natural state—as it left the rolls in the steel mills, held up to a pull of 70 tons per square inch of section before the yield point was reached, and that with an elongation of five per cent., and a contraction of area equal to 91 per cent. The second test piece, after being oil-tempered and annealed, showed that, while the yield point remained practically unchanged, the elongation had been increased from five to '20 per cent., and the contraction of area from 91 to 50 per cent. The operations of annealing and oil tempering had converted an otherwise-brittle material, but which. however, possessed a high yield point, into a perfectly-trustworthy and dintile steel with an almost-equally high yield point. This is but one of the characteristics of high-grade steels.
Chrome-vanadium Steel.
The shock-resisting properties of chrome-vanadium steel were first brought prominently before engineers by Captain Iliall Sankey, who, in conjunction with Mr. Kent Smith. read a paper, before the Institution of NIRehanien1 Engineers, on the 16th December, 1904, on the subject of the heat treatment. of these high-grade and, necessarily, highpriced alloys. For a considerable period, ehrome-vanadium steel was made only by Wilkins and Robinson, Ltd., of Rugby and Queensferry S.O., but is now also being manufactured in other makers' works. Such alloys are best when produced in the crucible or electric furnace, although satisfactory results have been obtained from steel which was produced by the openhearth process. This class of steel is made in several grades, some of which contain from 0.43 to 0.6 per cent, of carbon, whilst others contain only about 0.2 per cent, of carbon. The high-carbon varieties are intended for the manufacture of oil-hardened parts, whilst those griules which are low in carbon are more suitable for details which are to be rase-hardened. Chrome-vanadium alloys are said to represent the " high watermark " in the art of steel making. The addition to the steel of suitable quantities of chromium and vanadium insures the possession by the metal of static qualities equal to the best results given by nickel-steel and similar alloys, and, in addition, shock resistim, and antifatigue properties which excel those of most other alloys. Steels of this class may more easily be forged and machined than nickel-chrome steels
having the same carbon content, but, like all other high-grade steels, they should only be used in the natural state for parts which are to be highly stressed. The operations of rolling, hammering, or stamping set up internal strains in the material that necessitate the most careful handling of the material both before and during machining operations.
Nickel-chrome Steel.
The special features of nickelchrome steel are its exceptionally high elastic limit and tensile strength. and its great toughness. This class of
steel is also made in two grades—of high-carbon and low-carbon content rs.speetively. The former grade hasabout 0.3 per cent, of carbon, whilst the latter class contains only about half that amount. The percentage of nickel varies from two to 3, per cent., with from one to 1 cent, cent. of chromium added. Its heat treatment is a matter which requires considerable skill and judgment, and, for that reason, nickel-steel or chrome-vanadium steel is preferred by many engineers. Another reason for this preference is that results equal to those given by nickel-chrome steel may often be obtained with nickel or chromevanadium alloy at a. lower first cost— taking info account the difficulties of machining, heat-treatment, etc.
Nickel-steel.
Perhaps the most-extensively used of all the alloy steels is a nickel-steel which contains approximately three per cent, of nickel. 0.2 per cent. to 0.25 per cent. of carbon, 0.6 to 0.9 per cent. of manganese, and not more than 0.04 per cent.. of sulphur and phosphorus. Nickel-steel for parts which are to be case-hardened should contain rather less carbon, whilst, for crankshafts, and other parts where, in addition to great tensile strength, a hardwearing surface is required without case-hardening, the percentage of carbon may, with advantage, be slightly increased. This class of steel is generally accredited with being the first, for forging and tooling, among all the steel alloys, but it should not be forged at too high a temperature, and, therefore, it is not suitable for every form of stamping. Such parts as gear wheels, etc., may often be produced from blanks, which blanks are cut from a hammered or rolled bar and are subsequently machined in a high-speed lathe or semi-automatic machine, at is cost comparable with that of pieces which are finished from (hop forgings, whilst the shock-resisting qualities of parts made from the bar generally excel drop-forged articles.