US1975113A - Heat treatment of copperberyllium alloys - Google Patents

Description

Patented Oct 2, 1934 UNITED STATES PATENT OFFKZE HEAT TREATMENT OF COPPER- BERYLLIUM ALLOYS Georg MaaingfBerlin, and Otto Dali], Berlin- Oharlottenburg, Germany No Drawing. Application mm 22, 1931,

Serial No. 1926 570,504. In Germany May 21,

11 Claims. (01. lie-:12)

This invention relates to improvements in heat 0 said method comprising heating such a copperberyllium alloy to temperatures somewhat above a transition point lying at about 580 to 600 C., quenching and thereafter heating at temperatures below the-said transition point, say at temperatures from 150 to 500 C. for a time; said heating operations being sometimes used individually and sometimes in the succession given, the choice depending on the specific alloy treated and the particular results desired; all as more 0 fully hereinafter set forth and as claimed.

In a prior and copending application, Serial No. 191,263, filed May 13, 1927, of which the present application is a continuation in part, we have described methods for heat treating copperberyllium alloys and the properties of various alloys of this type; the alloys being specifically described and claimed. In a. prior patent No. 1,685,570, we have described and claimed processes for heat treating beryllium-nickel alloys in which nickel predominates. The present application is directed to copper-beryllium alloys of the type in which copper predominates and relates particularly to methods for heat treating such alloys.

While various alloys of beryllium have been mentioned in the art, but little has been published concerning their properties. And it has been found that certain of these alloys have properties which makethem particularly adapted for certain technical uses. Beryllium is one of the lightest metals employed technically and it is a good hardening agent in alloys. The hardness imparted to an alloy by the introduction of small proportions of beryllium is characteristic. Cop per hardened by alloying withberyllium is a particularly useful material for technical purposes. By methods hereinafter-described certain properties of copper-beryllium alloys may be varied at will. For example the hardness may be increased to that of hardened steel or reduced to a point at which the alloy may be readily worked.

The copper-beryllium alloys with which the present invention is most particularly concerned have a beryllium content ranging from about 0.3 up to 12 per cent; the residue. being copperor mainly copper. These alloys can be roughly divided into two ranges, according to their characteristics, (1) alloys from which a so-called beta modification separates from a melt and (2) alloys where the beta modification does'not separate from a melt. It may be said that the beta modification separates upon solidification of alloys having, roughly, a beryllium content of from 5 to 12 per cent, while alloys having a lower content do not show such separation. The lower limit of the existence of the beta modification, however, is altered by the presence of other alloying materials. Thus, in some instances, the beta modification has been found to exist at compositions representing a beryllium content of as low as 3 per cent, when other materials were present. 7 We have found that these copper-beryllium alloys may be hardened in a two-step process comprising heating at an elevated temperature for some time, followed by quenching and thereafter by age-hardening or tempering at a lower temperature for a time suflicient to improve their properties. But each step of this process can also be employed alone to produce advantageous repoint and 'the melting point, that is advantageously somewhat above 600 0., followed by cooling. Small pieces cool withsufiicient rapidity in the air while large pieces should be quenched. This process is followed by a prolonged heating at temperatures below the transition point, such as from 150 to 500 C. This heating is continued for a time sufficient to improve the properties of the alloys. At .the. lower temperatures several days may be required for this treatment, while at 300," 0. two hours is suflicient. In a specific example of such a heat'treatment, an alloy of 97 per cent. copper and 3 per cent beryllium, having an initial hardness of about 125 Brinell, was foundto have, 9. 817111811. f

Throughout the range of the existence of the beta modification the heat treatment required to produce the maximum hardness comprises merely the first step of the above described process,

namelyfa heating to temperatures above the final hardness of about 360 m5 transition point followed by quenching. The sec-- ond step, namely heating below the transition point may be advantageously employed to obtain the. alloy in agrelatively soft and mechanically workable condition. In one case a copperberyllium alloy containing 6.7 per cent of beryllium was found to have a hardness of 490 in the chilled casting. This hardness was increased to 730 by heat treatment above 580' 0., followed by quenching.

Upon a subsequent prolonged heat treatment at temperatures below 580 C. the hardness of the above mentioned alloy was reduced to about 240 Brinell. This latter treatment increases the duetility and toughness of the alloy. However, it may be worked readily while in this condition.

The above described heat treatments can be applied to both cast and to mechanically worked alloys. In the case of cast alloys the heat treatment at the higher temperatures may usually be obviated, the cooling in the casting taking the place of this treatment. A chilled casting may be merely reheated between 150 and 300 C.

For the production of alloys having intermediate properties between the extremely hard and the workable types there are two methods available. The first method consists'in a heat treatment at intermediate temperatures, for example between 450 and 800 C. Thesecond method consists of a prolonged heat treatment'at somewhat lower temperatures. This latter procedure is somewhat 'similar'to the final step of the usual two-step process. A preliminary mechanical.

working operation is frequently advantageous before the-heating step. i

The first efieet of a prolonged heating at temperatures below the transition point is to harden the alloy, but this is followed by the production of high ductility and toughness as well as a high tensile strength. Since the heating may be interrupted at any point, it is possible in this way to produce alloys having, within'wide limits, almost any desired properties. Definite values of hardness, ductility, toughness and strength may be produced. Somewhat similar results to the above may be obtained by heating the alloy above 600 C. followed by a slow cooling. This method is not as conveniently controlled, however.

In one particular example of the above heat treatment a copper-beryllium alloy, with a beryllium content of 2.5 per cent was heated at 500 C. for some time. The alloy was then found to possess a notched bar toughness of about 15 meterkilograms per square centimeter and a tensile strength of kilograms per square millimeter. This same alloy, after being treated by the twostepprocess, namely by heating above 600 C. and then at. temperatures in the neighborhood of 450 0., gave a notched bar test toughness of only 1 meter-kilogram per square centimeter and was found to have a tensile strength of 140 kilograms per square millimeter. -It has been found that advantageous results with'the above described single heating at the lower temperatures are only obtained when theberyllium content of the alloy amounts to at least 1 per cent. a q

The effect of added bodies upon the'properties of the alloys and upon the heat. treatments required is very striking. The addition of up to 1 percent of phosphorus. has been foundto produce a considerable reduction in the amount of beryllium metal required to produce certain improved, characteristics. The time for aluminum and magnesium may be present simultaneously in the alloy with the production of improved properties.

A typical heat hardening process, as carried out with-an 'alloy'containing 0.25 percent er phosphorus and about 1.5 per cent of beryllium, may be carried out as follows: The alloy is heated above the previously mentioned transition point,

say at 800 C., and then quickly cooled. After cooling the hardness of one particular sample was found to be..only Brinell. .By subsequently tempering the alloy by heating for an hour at 350 0., the hardness was increased to 210 Brinell.

- In comparison with the above, when a copperberyllium alloy of the same beryllium content but free from phosphorus was treated in the same manner, the hardness, on cooling from 800 C.. was found to be 74 Brineli and, upon heating for as long as 7 hours .at 350 0., the hardness increased only 20 Brinell. The beneficial eilects of the phosphorus addition is evident.

The beryllium content can be reduced without detrimentwhen addition metals, such as aluminum, tin, silver and magnesium, are present in the alloy. Alloys of this type contain up to about 2.5 per cerit b1 beryllium; a somewhat larger per beryllium. Since beryllium is by far the most expensive of the metallic constituents, a reduction in the quantity required is advantageous. For

example, when copper only is alloyed with the beryllium at least 1 per cent of beryllium must be present in order to give an alloy with a high degree of hardness. But, upon theaddition of from 5 to 25 per cent ofone oi the other metals mentioned, the beryllium content may be reduced to about 0.3 per cent to obtain the same degree of hardness.

The heat treatment required for these multimetal alloys is similar to that described previously. The two-step process is advantageous.

The properties of the above described copperberyllium alloys, including within this term alloys which may contain one or more additional metals, fit them for many special technical uses. The alloys are especially suited for making metallic springs, whether of leaf, helical or spiral form. The use of such springs in instruments of precision is highly advantageous due to their high resistance to corrosion and permanent characteristics. The use of the described alloys in electrical instruments is desirable, especially where there is frictional contact, for example in knife switches, commutators, slip rings, bearings, sliding contact points, etc.

By the terms remainder substantially copper" and "balance substantially copper, occurring in the claims, we mean that the alloys called for may also contain small amounts of addition metals acting to reinforce the hardening eflect of the beryllium, these metals, including phosphorus, tin, zinc, iron, cobalt and aluminum occurring in amounts insuiilcient to substantially alter the characteristic properties or the said alloys.

What we claim is:

1. In the heat treatment of copper-beryllium alloys containing from about 0.3 to 12 per cent by weight of beryllium with the remainder substantially copper, the process which comprises heating such an alloy at temperatures above a transition point, which lies in the neighborhood of 580 to 600 C., but below its melting point, quenching and age-hardening by prolonged heating at temperatures above about 150 C. but below said transition point.

2. In the heat treatment of copper-beryllium alloys containing from about 0.3 to 12 per cent by weight of beryllium with the remainder substantially copper, the steps which comprise heating such an alloy at temperatures below its melting point but above about 580 C. and subsequently quenching.

3. In the heat treatment of copper-beryllium alloys containing from about 0.3 to 12 per cent by weight of beryllium with the remainder substantially copper, the step which comprises tempering such an alloy by a prolonged heating at temperatures below about 580 to 600 C. but above about 150 C.

4. The process of heat treating copper-beryllium alloys having a beryllium content above about 0.3 per cent but below percentages at which the beta-modification separates upon solidification, ranging from about 3 to 5 per cent by weight, with a balance substantially copper, which comprises heating such an alloy at temperatures below its melting point but above about 600 C., and age-hardening by heating at temperatures ranging from about 150 to 500 C. until its physical properties have been improved.

5. In the heat treatment of copper-beryllium alloys containing suflicient beryllium to cause separation of the beta-modification upon solidification, ranging from about 3 per cent to 12 per cent by weight, with a balance substantially copper, the process which comprises heating such an alloy at temperatures below its melting point but above about 600 C.- and quenching.

6. The process of claim 5 in which the alloy is further heated at temperatures between 150 to 500 C. in order to produce workable properties.

7. In the heat treatment of copper-beryllium alloys containing from 0.3 to 12 per cent by weight of beryllium, with a balance substantially copper, the process which comprises heating such an alloy for a prolonged interval at temperatures between about 150-600 C. to produce high ductility and toughness.

8. The process of claim '7 wherein the heating step is preceded with a mechanical working operation.

9. The process of claim 3 in which the temperature of the tempering step lies between 150 and 500 C.

10. In the heat treatment of copper-beryllium alloys containing from about 0.3 to 12 per cent by weight of beryllium with a balance substantially copper, the process which comprises chillcasting such an alloy and reheating to temperatures between 150 and 500 C. untilthe physical properties have been improved.

11. The process of claim 1 wherein the copperberyllium alloy also contains from about 0.1 to 1 per cent of phosphorus.

12. The process of claim 2 wherein the copper-beryllium alloy also contains from about 0.1 to 1 per cent of phosphorus.

13. The process of claim 3 wherein the copperberyllium alloy also contains from about 0.1 to' 1 per cent of phosphorus.

14. The process of claim 4 wherein the copper-beryllium alloy also contains from about 0.1 to 1 per cent of phosphorus.

15. The process of claim 5 wherein the copperno beryllium alloy also contains from about 0.1 to 1 per cent of phosphorus.

16. The process of claim 7 wherein the copperberyllium alloy also contains from about 0.1 to 1 per cent of phosphorus. 115

17. The process of claim 10 wherein the copper-beryllium alloy also contains from about 0.1

to 1 per cent of phosphorus.

GEORG MASING. OTTO DAHL.