US2059555A - Alloys - Google Patents

Description

Patented Nov. 3, 1936 UNITED STATES ALLOYS Michael George Corson, New York, N. Y., assignor to Union Carbide and Carbon Research Laboratories, Inc., a corporation of New York No Drawing.

3 Claims.

Copper-tin alloys with or without other ele-- ments like phosphorus, zinc, manganese, nickel,

etc. are well known to the art and are formed both as cast and as wrought into various shapes 5 by the known processes of working metals in the cold state. However, so far it has been quite impossible to apply to tin bronzes containing above 3% ,tin any of the processes of working in the hot state. To obtain, for instance, the so called phosphor bronze wire or sheets it has been necessary until now to heat the cast ingot to' a high temperature of not less than 700 C. and let it remain at this temperature for many hours for the purpose of homogenizing the ingot by a process of diffusion. After that the ingot was broken down cold, annealed, rolled down cold to a certain extent, again annealed etc. At no stage has hot working been used,the metal being unable to withstand the application of a forging hammer or the hot rolls without cracking profusely and breaking to pieces.

I have discovered that copper-tin alloys can be made directly hot forgeable and hot rollable, provided a certain additional element is introduced, which possesses the property of being only slightly, if at all, soluble in the crystals of solid copper and of solid. alpha tin bronze, and which in addition has a much higher melting point. For these reasons it is the flrst constituent to crystallize out of the molten mass on cooling and thus effects a distribution of crystal nuclei as well as influencing the atoms of copper and tin to crystallize together in a more constant proportion, than is the case with normal binary tin bronzes and their ternary derivatives in which the third element forms only a component of the alpha solid solution.

Such additional elements are specifically chromium and vanadium and to a lesser degree iron and cobalt. Of the first, vanadium is most potent, but it is difiicult and expensive to introduce into molten copper or molten bronzes. Chromium comes next, being potent in the direction above outlined as soon as more. than 0.5% of it is present. With iron and cobalt at least four percent must be present to produce the desirable efiect of enhancing the workability in the hot state.

To make the costs of so improving tin bronzes less high, ferro-alloys may be used in the place of technically pure chromium and technically pure vanadium. One may use for instance a low carbon ferro-chromium with 50-95% Cr or a low carbon ferro-vanadium with 30-90% vanadium, I or a ternary ferro alloy containing both vana- Application November 6, 1933, Serial No. 696,918

dium and chromium. When ferro-alloys are used instead of the pure metals, the excessive iron crystallizes largely with the chromium or vanadium, so that a tin bronze containing 2% of 50% ferrochromium under the-microscope looks far more like an alloy containing two or at least 1.75% chromium, than like one containing one per cent of chromium and one per cent iron, as would have been the case, had this one percent of iron gone into solid solution in the alpha tin bronze.

It is to be understood that the copper-base alloys of the present invention may contain, in addition to tin and one or more of the elements chromium, vanadium, iron and cobalt in proportions within the limits specified herein, one or more of the elements nickel, manganese, and aluminum in proportions up to say 10%. These elements do not contribute to the workability of the alloy in the hot state, but may be added for their known improving effects in other respects. Small amounts of the usual deoxidizers, such as phosphorus, magnesium, and the like may also be present.

Tin bronzes made according to the present invention and containing, for instance, 5-10% of tin, (LS-2.0% Cr or 0.2-1.0% V, plus 0-2% nickel, 0-2% manganese, 0-2% aluminium can be taken from the ingot mould as soon as sufficiently cold to handle, reheated to ZOO-800 C. forged down to about one half of the area of the original cross-section and finished into the desired shape by hot rolling. I

Vanadium is somewhat difficult to introduce and in addition quite expensive for which reasons its presence in the amount exceeding that which is necessary for the development of the capacity for hot work (about 1%) is not desirable. The situation in the case of chromium is quite difierent. It can be introduced into molten bronze easily enough, and its excess above the really necessary amount of 1.5% remains harmless for the capacity to be hot worked, and develops in addition interesting and industrially desirable antifriction haracteristics.

It is well known, for instance, that the usual bearing bronzes working without a lining of a low melting antifriction alloy, and containing tin in amounts suflicient to produce the second constituent, the delta eutectoid or bronzite, do not work well if the bearing happens to become overheated. In fact the bearings of hot rolling mills as used in steel making can not be made at all of such duplex, alpha plus delta, bronzes. These terial of the crucible etc.

latter fail rapidly, when their temperature approaches 500 C.

To cope with this handicap special bronzes were introduced, containing no delta phase because of their low tin content-not exceeding 8%. In its place a hard constituent, quite stable at high temperatures was introduced into the structure of such bronzes by adding up to 0.3 per cent of phosphorus and up to 3% nickel, the latter producing, partly at least, fine grainlets of nickel phosphide of the supposed formula Ni3P.

Ihave found, however, that by increasing the amount of chromium added to the copper-tin base bronze, the phosphide can be replaced by a far larger and far more efficient amount of chromium, which crystallizes in the shape of irregular single crystals or their star-like aggregates. While the actual hardness of these chromium crystals is not well known, it can be safely assumed to be in the neighborhood of 200 Brinell, while the hardness of nickel-phosphide, a definite intermetallic compound must be considerably higher. Therefore the probability of scratching the journals of the rolling mill is far less pronounced in the case of a chromium containing bronze.

The amount of chromium present in such a tin bronze, may be as high up as 10%, but not more than 4-5% is really necessary.

The method of making such chromium or vanadium containing bronzes may vary to a great extent, as to raw materials, type of furnace, ma-

The only essential thing is that the metal should be properly dexidized before the introduction of the chroium and protected from further oxidation by a layer of a liquid flux. For the latter I prefer a mixture of fluorides of sodium and calcium, to which other fluorides may be added. I may employ a fiux of commercially pure fused boric acid, and borax and its mixtures with glass also may be used, but with less convenience.

To illustrate a way of preparing such alloys, I shall state the following:

I take commercial bronze ingots and melt them in the usual graphite-clay crucibles. I add to them enough copper to bring the content of tin down to the desired level. I cover the molten alloy with a layer of fluorides about in thickness in. the molten state. I add just enough phosphor copper to make the melt quite fluid, usually, not more than 0.05% P. Then I add chromium metal or ferrochrome or ferrovanadium or ferro-chrome vanadium in pieces large enough to be produced conveniently and without much expense and small enough to allow them to be fully covered by the liquid fluoride in those parts which protrude above the level of the molten bronze due to the difference in the specific weights.

Next, I raise the temperature in the metal either by feeding more fuel and air to the furnace, or increasing its current input until it comes to about 1250 C. At this point chromium dissolves rapidly, as does ferro-vanadium. From time to time the pieces of the metal or of the ferro-alloy are pushed down under the surface of the molten bronze and the latter stirred to check the super-saturation of the top-layers with dissolved chromium or vanadium.

The liquid flux is next removed, by adding dry sand to it. In this manner a pasty mass of fluoride soaked sand forms, and it can be easily kept from flowing down into the mold.

The final casting proceeds then as usual, whether it is the manufacture of sand castings, ingots for forging, or castings in permanent moulds. In the latter case about 0.2% aluminum may be added to inhibit the welding of the molten metal to the metal of the permanent mould.

Having so described my invention, I claim:

1. A hot workable copper-base alloy containing from 3 to 10% tin, from .5 to 10% chromium, the remainder substantially all copper.

2. A hot workable copper-base alloy containing from 5 to 10% tin, from 3 to 5% chromium, the remainder substantially all copper.

3. A hot workable copperbase alloy containing from 5 to 8% tin, about 0.5% to 1.5% chromium, the remainder substantially all copper.

MICHAEL GEORGE CORSON.