US2059556A - Copper-base alloys - Google Patents

Description

alente Nov. 3, 1936 2,059,556 4 @UlPPlER-BASE ALLoys Michael G. Carson, New York, N. Y., assignor to Union lUarbide and Carbon Research Laboratories, l[nc., a corporation of New York No Drawing. Application April 25, 1935,

Serial No. 18,163

3 Claims. (G11. -154) various known processes for working metals in However, it has heretofore been diiiicult to hot work tin bronzes containing above about 3% tin. For instance, in order to form the cold state.

wire or sheets from the so-called phosphor bronze, it has been necessary first to heat the cast ingot to a high temperature of not less than 700 0., hold it at this high temperature for many hours for the purpose of homogenizing the ingot by diffusion, break the ingot down cold, anneal it, roll it down cold to 'a certain extent, again anneal it, and to repeat the alternate cold working and annealing steps until themetal has attained the desired size and shape. At nostage has hot working been used, because the metal cannot withstand the application of a forging hammer or hot rolls without cracking and breaking to pieces.

I have discovered that copper-tin alloys can be made forgeable and rollable at elevated ternperatures by introducing into the alloys certain additional elements which are only slightly s01- uble in the crystals of solid copper and of solid alpha tin bronze, and which in addition have a much higher melting point than the bronze. Such additional elements are'the first constituents to crystallize out of the molten .mass on coolingand thus effect favorable distribution of crystal nuclei and influence the atoms of copper and tin to crystallize in a more constant prop0rti on than is the case with normal binary tin bronzes and with ternary tin bronzes in .which the third elementforms a component of the alpha solid solution.

,Suitable additional elements are chromium and vanadium and, to a lesser degree, iron and cobalt. Vanadium is the most effective of these elements but it is dificult and expensive to introduce into molten copper or molten bronzes. For this reason chromium is preferred, this element being eflective as-soon as about 0.5% is added. If iron or cobalt alone were to be used, at least 4% would be necessary to produce the desired effect of'improving the hot workability of the bronze.

According to the present invention, hot-work ability. is imparted to copper-tin alloys containing about 3% to about 10% tin by the addition of efi'ective amounts of one or both of the eleheated. In fact, the bearings of hot rolling mills ments chromium and vanadium and the further addition ,of substantial amounts of iron or cobalt. If desired, the chromium or vanadium, or both, may be added in the form of ferro alloys, for instance, a commercial low carbon ferro-chromium containing about 50% to 95% chromium, or a low carbon ferrovanadium containing about 30% to 90% vanadium, or a farm alloy containing both vanadium and chromium.

When both iron and chromium or vanadium j are added, the iron crystallizes chiefly with the chromium or vanadium so that a tin bronze containing say 2% of ferrochromium containing about 50% chromium appears, under the microscope, morelike an alloy containing 1.75% to 2% chromium than like one containing 1% of chromium/as would have been the case had the iron gone into solid solution in the alpha tin bronze.

- Tin bronzes made according to the present invention and containing 3% to 10% tin, 0.5% to 2% chromium or 0.2% to 1% vanadium and up to about 2% iron may be taken from the ingot mold as soon as they are sufiiciently cold to hansdle, reheated to 700 to 800 (3., forged to about one-half of the area of the original cross-section, and finished into the desired shape by hot rolling.

Vanadium is somewhat difl'icult to introduce and in addition quite expensive, for which reasons the use of an amount exceeding that which is necessary for the development of the capacity for hot work (about 1%) is not usually desirable. ,The situation in the caseof'chromium is different: it can be introduced into'molten bronze It is well known for instance, that the usual bearing bronzes, working without a lining of a low melting antifriction alloy and containingtin in amounts sufficient to produce as a second constituent the delta eutectoid or bronzite, do not work well if the bearing happens to become overas used in steel making cannot be madeat all of suchduplex" (alpha plus delta) bronzes. The latter fail rapidly when their temperature approaches 500 C.

To cope with this handicap special bronzes have been introduced containing less than 8% tin and therefore containing no delta phase. In place of the delta phase a hard constituent, quite stable at high temperatures, is introduced into the structure of such bronzes by adding up to 0.3% of phosphorus and up to 3% nickel, the latter producing to some extent at least, fine grains of nickel phosphide of the supposed formula NiaP.

I have 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 deflnite intermetallic compound, must be considerably higher. Therefore, the probability of scratching the journals of the rolling mill is far less in the case of a chromium containing bronze.

The amount of chromium present in such a tin bronze may be as high as 10%, but not more than 4 or 5% is desirable. Likewise, the amount of iron or cobalt may be as high as The method of making such chromium or vanadium containing bronzes may vary to a great extent, as to raw materials, type of furnace, material of the crucible, etc. The only essential thing is that the metal should be properly deoxidized before the introduction of the chromium 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 flux 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 ing'ots 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 one-eighth inch in thickness in the molten state. I add just enough phosphor copper to make the melt quite fluid, usually not more than 0.05% phosphorus. Then I add chromium metal or ferrochrome or ferrovanadium or ferrochrome-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.

fluoride soaked sand forms, and it can be easily kept from flowing down into the mold.

The final casting proceeds 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 mold.

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, and. iron 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 improvement effects in other re-- spects. Small amounts of the usual deoxidizers, such as phosphorus, magnesium, and the like may also be present.

I claim:

3%,to 5% chromium; a substantial amount not over about 5% iron; and the remainder substantially all copper. 3. Copper-base alloy which can be forged and rolled at elevated temperatures and which has substantially the composition; 5% to 8% tin; 0.5% to 1.5% chromium; a substantial amount not over about 5% iron; and the remainder substantially all copper.

' MICHAEL G. CORSON.