Improved Steels for Motor Manufacture
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MOTOR manufacturers should be
interested I n some of the latest developments in metallurgy, both ferrous and non-ferrous. Reference has been made in earlier, issues to the nickel molybdenum steels. It is, however, important to note that a variation in composition has enabled certain steels of this type to be produced which, for the manufacture of case-hardened gears, are definitely superior to the plain nickel casehardening steels.
These steels have an analysis of approximately 1.75 per cent. nickel and 025 per cent. molybdenum, and, with their fineness of grain, they offer high resistance to grain growth. Furthermore, they need only a simple heattreatment after case-hardening (oil-, quenching, or tempering at about 150 degrees C.).
This means that a large number of heats and the warping that often re sults can be eliminated. The steel gears thus produced are tougher, whilst, from the point of view of the steel maker, there is no waste, owing to the fact that no losses of alloys occur in refining or in remelting the scrap.
A Steel for Gears.
For those gears which require oilhardening, nickel-molybdenum steel of the same analysis, with carbon percentage ranging from 0.4 to 0.5, has been substituted satisfactorily for the 5-per-cent.-nickel oil-hardening steels. Gears made from this steel are readily machinable and free from distortion during or after the hardening process.
Another important advance is the utilieation of chrome-molybdenum steel for rear-axle shafts, etc. This steel has approximately 1 per cent. chromium and 0.20 per cent, molybdenum, and is usually oil-quenched from about 830 degrees C.
Equally interesting are the manganese-molybdenum steels, containing 0.25 per cent. molybdenum. These steels have a higher impact value than have medium manganese steels, respond more readily to heat treatment, and are highly suitable for the less costly bearings and gears.
It is claimed that these steels will take a greater depth of carburizing, in a given period, than will the nickelmolybdenum material, but their impact strength is not so great as that of the latter, so far as the case is concerned. So long as the service for which they are required is not too severe, and where the load is uniform, gears made from these steels will be perfectly satisfactory.
Carbon-molybdenum steels are now being suggested. They have actually been embodied by one American motor manufacturer in the latest designs for helical springs for front-wheel suspension. There are drawbacks to the carbon-molybdenum steels, but it is argued that these are due to the fact that little first-rate metallurgical intelligence has in the past been applied to their study. Their increased use may be one of the developments of the future.
Devetopment of Vanadium Steels.
A great deal of valuable work has been done in connection with vanadium steels, especially in the production of intermediate alloy steels designed for medium-stressed parts of chassis and engines. For example, a steel with 0.35 per tent. chromium, 1.25 per cent. manganese, and 0.1 per cent, vanadium is being more and more used for such parts as axle shafts, steering arms, brackets, universal joints, bolts and the like, where cost has to be studied. Uniform performance, freedom from distortion, ready machining and absence of internal stresses are advantages claimed for these materials.
A steel with 0.25 per cent. carbon, 1.60 per cent. manganese, 0.25 per cent. silicon and 0.16 per cent. vanadium has been produced for piston rods, crank pins and similar parts. Another of the same type, but containing 0.35 per cent. carbon, 1.40 per cent. manganese and 0.10 per cent. vanadium, is used for castings, forgings and rolled plates and forms.
Competing with Aluminium.
In the non-ferrous region, an important competitor for aluminium, in the shape of magnesium, has entered the field. Magnesium castings are being used because they enable weight to be saved. When magnesium and magnesium-alloy plates and forms are employed, trailers for carrying completed motor vehicles weigh about fourfifths as much as aluminium structures of the same kind.
In the tool steels, greatest interest centres on the determined efforts being made in the United States to find a molybdenum high-speed steel which will satisfactorily replace the existing commercial tungsten high-speed steels. The reason why this problem is of such great importance for America is that it lacks adequate supplies of tungsten and, in the event of war, the country would find itself severely handicapped.
Hitherto, although claims have been made by one or two makers, no steel inwhich the tungsten content has been
completely replaced by molybdenum can be said to have given perfectly reliable results, although the Watertown Arsenal seems to have had a measure of success which calls for investigation. R e ceiatly, however, it has been found that by replacing four-fifths of the tungsten by molybdenum a molybdenum tungsten high-speed steel is obtained which gives performance results equal to those afforded by the standard high-speed steels. Further experiment is taking place and the result should be of great interest to metallurgists and steel users.
In the stainless steels, the already large range of analyses for different purposes has been enriched by the addition of a steel containing 16 per cent. chromium and 1 per cent. nickel. This material is not so greatly corrosionresistant as are the standard 18-8 stainless steels, but it is more readily machinable. and can be fabricated and heat-treated after fabrication.
This steel is of most interest to the aircraft maker, on account of its ability to retain toughness at temperatures below zero, combined with a high ultimate strength at those temperatures. The ordinary' stainless steels, although they preserve their toughness at low temperatures, have not so great an ultimate strength as that of the 16-1 material.
Stainless-steel Progress.
The uses of stainless steel in motor manufacture are also greatly extending. Hub caps are being produced from rustless-steel sheets, embossed and lacquered, and then bent over the edges of a thicker backing of mild steel. Stainless-steel headings, mouldings. window fitments, door handles and the like are beint increasingly employed in the motor industry.
A phenomenon of importance to the maker of steel sheets for deep forming is that known as ageing of steel. This occurs when a steel has satisfactorily passed its tests at the factory, but, when put into use at the purchaser's works, proves to have lost some of its ductility in the intervening period. andto give trouble under the forming dies. This phenomenon has been attributed to a form of precipitation hardening, and a good deal of work has been done by metallurgists in an attempt to discover both the cause and the remedy for the trouble. Whilst no definite facts announcing success have yet been produced, it is noteworthy that one manufacturer has placed on the market a steel for deep-drawing purposes, which is claimed to be non-ageing." The concern gives 110 details as to the method of manufacture, and judgment of the claim must, therefore, be deferred.