US2256492A - Method of treating copper and product thereof - Google Patents

Description

Patented. Sept. 23, 1941 METHOD or TREATING corrEn AND rnonuo'r 'rnnnrzor Albert J. Phillips, Piainiield, Albert A. Smith, Jr.. Metuchen, and John 8. Smart, In, Orange, N. J., assignors to American smelting and Refining Company, New York, N, Y., a corporation of New Jersey No Drawing. Application August 17, 1939, Serial No. 290,628

6 Claims.

The present invention provides for improvements in commercial copper, wherein the recrystallization temperature of themetal has been,

raised to such an extent that there is no tendency of the copper to become detrimentally soft at such elevated temperatures as are encountered in soldering operations of the character employed for example in the soldering of radiators for internal combustion engines. 1

The copper usually employed in the production of such radiators contains the relatively high silver content of from 6 to 8 oz./ton of silver. The softening temperature of the copper is raised sufiiciently by the addition of silver in'the abovementioned amounts to enable it to withstand the temperature of the soldering operations without softening to a detrimental extent.

In view of the cost of adding silver to copper, various attempts have been made to produce a copper which is comparable in its properties, including resistance to softening, to silver-bearing copper. Among such attempts have been various efforts to substitute an antimony-bearing copper for silver-bearing copper, wherein commercial copper has been alloyed with antimony, but all of these attempts have been commercially unsuccessful, the results of such attempts being highly erratic. These failures have been due, apparentto a lack of understanding of the equilibrium relationship between antimony and antimony oxide in the copper.

The present invention is based upon cert discoveries which the inventors have made in connection with this equilibrium, and in connection withthe behavior of copper when subjected to certain heat treating, operations.

One object of the present invention is to provide an improved and simplified procedure for producing a copper which will have a softening temperature substantially above the temperature employed in soldering operations, such as, for example, the soldering employed in radiator manufacture.

other commercial forms which are to be subjected to fabricating operations, are characterized by a tendency to become soft at relatively low temperatures, so that fabricated shapes produced from such copper, such as the flns of internal combustion engine radiators, are easily distorted after heating to such temperatures. This soften- Further objects and advantages of the present invention will become apparent as the description proceeds, and the features of novelty are pointed out in "particularity in the appended claims.

Usual commercial copper, such as that used ing is due to recrystallization of the metal.

In accordance with the present invention, it has been found that commercial copper, such as, for instance, electrolytic tough pitch copper, when heated to a temperature within a definite range and quenched. retainsits hardness at temperatures substantially above those which produce softening in the untreated copper. That is to say, by heating commercial copper to a temperature of from approximately 700 C.-1000 C. and

then quenching the copper in water or in a pickling solution at room temperatures, the resulting copper remains hardat temperatures at which softening of the untreated copper appears.

In case of commercial coppers, this hardening effect disappears if. the copper is annealed during working. However, this hardening is found to be permanent if small additions of antimony be made to the copper prior to its original heating to the above mentioned temperatures, this effect being found to be due to the antimony being held in solid solution after the quenching. The amount of antimony found to be eflective, while maintaining the conductivity prescribed by A. S. T. M. standards for electrolytic wire bar coppers ranges from approximately .003% as the minimum to approximately 0.02% as the maximum. This conductivity value is. of consequence in that it is demanded by fabricators, since the thermal conductivity of the metal approximately follows the electrical conductivity thereof.

The present improvements are found in prac tice, to apply particularly well to the copper known to the trade as tough-pitch" copper, which is used customarily for the production of cast copper cakes and wire-bars, which copper "contains usually from about 0.025% to about mercial oxygen-bearing copper in the manner inin the production of copper cakes, wire bars, and dicated above.

In the case of oxygen-bearing copper, a reaction between antimony and oxygen takes place in the temperature range 500 to 700 C., this reaction, however, resulting in the precipitation of antimony from solid solution as an insoluble oxide, and the loss of its eifectiveness in raising the softening temperature. This precipitation apparently takes place in accordance with the reversible reaction The equilibrium characteristics of this reaction are such that the formation of antimony oxide, SbaOs, approaches completion at 500 C., and practically all of the antimony may be precipitated at this temperature if sufllcient time is allowed for the reaction to take place. As the temperature increases, the amount of $1320: that can exist progressively decreases, until at approximately 850 C. practically all of the antimony is present in solid solution. During the hot rolling process, precipitation of SbaOz occurs as the copper cools from the temperature of the heating furnace. Further precipitation takes place in subsequent annealing between 400 and 100 C.

It is apparent from the equation given above that increases in the amouhts of either antimony or CuzO present in the copper will increase the amount of SbzOa formed. The rate of precipitation also increases with increasing amounts of antimony. Additions of antimony to copper for the purpose of raising the softening temperature therefore lose much of their effectiveness after the normal commercial hot rolling and annealing treatments have been carried out.

Since equilibrium conditions in the above equation depend on the temperature, it has been found possible to preserve the antimony in solid solution by heating preferably to approximately 850 C., where SbaOa cannot exist in appreciable quantities, and then quenching. Carried out on hot rolled material, this process restores the precipitated antimony to its effective form of solid solution, and permits final cold finishing to supply a product having a high softening temperature.

While antimony has been used as an example, and has a large effect on the softening temperature of copper if preserved in solid solution by this heat treatment, the process has also been found to apply to other impurities present in coppers of commercial purity, as has beenindicated abpve. Thus, commercial coppers, both oxygen-bearing and oxygen-free, to which no antimony has been added show a decided increase in softening temperature when heated to 850 C. and quenched, after hot rolling, this eifect being obtainable, however, over a range of 700- 1000 C. This is due to the fact that the solid solubilities of certain of these impurities are higher at this temperature; that they are retained in this form of solid solution by the quenching operation, and are therefore rendered effective in raising the softening temperature. This effect is permanent if the metal is not reheated; but the additions of antimony enable the metal to be heated to annealing temperatures during the fabrication process without losing the effect.

Where oxygen-free copper is used, obviously there is no great dimculty in retaining the antimony in solid solution, since the reversible reaction indicated above cannot take place, but nevertheless, an increase of softening temperature is. obtained by the heat treatment due to the increaesd solubility of other impurities which are present. Quenching is usually done in a pickling solution containing 10% sulphuric acid, and the period of heating necessary to effect the solution is found to be about 20 minutes at 850 C.

As an illustrative example of the results obtained by the present invention a rod of electrolytic copper containing 0.0068% of antimony was annealed for 20 minutes at 850 C. and quenched, after which the rod was cold drawn to a diameter of 0.162", whereupon it was annealed for one hour at 850 C. and quenched, and cold drawn to 0.081" diameter. It was found that this copper had a softening temperature of 296 C., with a resistivity of .15267' ohm per metergram at 20 C. when annealed for 20 min. at 500 C., whereas silver-bearing copper containing 7.5 oz./ton of silver showed a softening temperature of 295 C. and a resistivity of .15176 ohm per metergram at 20 C. when annealed in the same manner.

The term softening temperature as used herein refers to a temperature determined by the following procedure: Samples of the wires are annealed at various temperatures for a period of one hour in an oil bath equipped with automatic temperature control. The tensile strength of the samplesis then determined for the hard drawn condition, after anneals at various temperatures in the oil bath, and in the-completely annealed condition caused by a one hour anneal at 500 C. Tensile strength is then plotted against annealing temperature, and the point representing 50% of the total drop in tensile strength from the hard drawn to the fully annealed condition is determined, and the temperature corresponding to this point is taken'as the softening temperature.

The following table shows .comparatlve'softening temperatures after indicated heat treatment.

The types of heat treatment indicated in the above table are as follows:

Type A: rod annealed for 20 minutes at 850 C. and quenched. Cold drawn to 0.162" diameter and annealed for lhour at 850 C. and quenched, then cold drawn to 0.081" diameter.

' Type B: rod annealed for 20 minutes at 850 C. and quenched. 'Cold drawn to 0.162" diameter and annealed for 30, minutes at 400 C. and quenched, then cold drawn to 0.081" diameter.

Type 0: rod annealed for 20 minutes at 850 C. and quenched. Cold drawn to 0.162" diameter and annealed for 15 hours at 500 C. and quenched, then cold drawn to 0.081" diameter.

Type D: same as type B, except annealed for 1 hour at 400 C. at 0.162" diameter.

Copper containing 7.5 oz./ton of silver when annealed for 15 hours at 500 C. and quenched ,before drawing showed a softening temperature of approximately 265 0.; when annealed for 1 hour at 850 C. and quenched before drawing. it

showed a softening temperature of 295 C., the softening temperature of the silver bearing' copper being increased, therefore 30 C. when subjected to the treatment of the present invention.

When commercial wire bar copper was annealed for 15 hours at 500 C. and quenched before drawing, it showed a softening temperature of 191 C.; and when annealed 1 hour at 850 C. and quenched before drawing, it showed a softening temperature of 269 ,C., or an increase of 78 in its softening temperature when subjected to the present process.

Upon the addition of 0.0068% antimony to the above wire bar copper, and the material annealed for '15 hours at 500 C. and quenched before drawing, it showed a softening temperature of 215 C.; but when the same copper ,was annealed for 1 hour at 850 C. and quenched before drawing, it showed a softeningtemperature of 296 C., or an increase of 81 C. in the softening temperature. It will be seen thatthe softening temperature of this copper when annealed at 850 C. and quenched before drawing is substantially the same as that of the copper containing 7.5 oz./ton of silver when subjected to the same annealing and quenching treatments.

From the foregoing considerations, it will be seen that the present procedure raises thevsoftening temperature of even silver-bearing copper. The increase in its softening temperature apparently is independent of the silver content, which in theamounts present is completely soluble at both 500 C. and 850 C. The noted rise in softening temperature is believed to be due t increases in the solubilities of other impurities in the copper at 850 C. 1

In the case of electrolytic wire bar, which showed an increase of 78 C. when subjected to the treatment of the present invention, it is believed that the change is due also to increased solubility of impurities at 850 C. Likewise, the electrolytic copper to which a small amount of antimony was added also has a low softening temperature if precipitation is allowed to occur at 500 C. Its response to the process of this invention is the largest, it increasing 81 C. in softening temperature.

It is evident from the above data that the softening temperature of each of these grades of copper is dependent not only on chemical composition but also on the heat treatment employed during fabrication. Thus, an addition of 0.0068% antimony to electrolytic wire bar copper is in effective in raising the softening temperature sufliciently to compare with silver-bearing copper if these coppers are annealed at 500 C. for hours. If the same coppers are annealed for 1 hour at 850 C. and quenched during the fabri cation process, and no subsequent anneals are employed during cold fabrication, the softening temperatures are raised to different extents and the electrolytic copper containing 0.0068% antimony is equal in softening temperature to the silver-bearing copper. The softening temperature of electrolytic copper can also be raised substantially by this treatment. It appears that the heating to 850 C. increases the solubilities of the impurities present in these coppers, and quenching from this temperature after solution has occurred retains the impurities in thisdissolved condition.

The following table shows comparative ductility of. these coppers:

Heat treatment A.-Wire annealed at 0.162 diameter for 15 hours at 500 C., drawn to 0.081" wire and annealed for 1 hour at 500 C.

Heat treatment B..-Wire annealed at 0.162" diameter for 1 .hour at 850 C}. and uenched. Drawn to 0.081," wire and annealed for 1 our at 850 C. and quenched.

The following table shows the electrical resistivity of electrolytic copper containing antimony, which resistivity was measured -in each instance on wires that were annealed for l'hour at 850 C. and quenched, and then annealed for 20 minutes at 500 C; as prescribed by the A. S. T. M. standards for resistivity measurement.

Restivityohms per nietergram at 20 0.

Percent antimony It will be seen, therefore, that the inclusion of a small amount of antimony in accordance with the present invention'does not effect deleteriously the ductility of the resulting copper. Also, that the electrical resistivtiy of the copper containing 0.008% antimony and 0.0068% antimony does not exceed the A. S. T. M, maximum resistivity for high conductivity electrolytic copper wire bars, which is .15436 ohm per metergram, whereas the resistivity of the copper containing 0.020% antimony -is but slightly above such standard.

It will be seen from the foregoing description that the scope of this invention includes the obtaining of large increases in the softening temperature of copper by increasing the effective-- ness of small amounts of impurities, e. g. antimony, the invention imparting to the copper a softening temperature of above250 C.

Where high conductivity is of minor importance, such as where the copper is to be used for engraving plates, for example, the antimony content of the copper may be increased to 0.1%.

As it has been indicated in the foregoing, impurities other than antimony have a similar effect. Thus, in determining the effect of impurities varying amounts of sulphur were added both to oxygen-free and to oxygen-bearing copper, the former being very pure copper,-and the latter pure except for the oxygen content. The results obtained are tabulated as follows:

Sol ning tem- Softening tem- Percent. perature when perature when 3 Percent O heated 2 hrs. at heated 1 hr. at

600 C. and 850 C. and quenched quenched I C. C. 136 136 163 190 162 174 219 176 206 176 226 181 234 e. the cop er contained solid solut on of oxygen It will also be noted from the foregoing'that the process of quenching from 850 C. when applied to pure copper to which .0015% sulphur has been added, raises the softening temperature 90 C. as compared to pure copper containing no sulphur. The same copper heated to 600 C. and quenched, showed but a 40 C. increase in softening temperature. It will also be seen that the pure' copper being free from detectable amounts of all impurities is entirely unaffected by quenching from 850 C. This will be apparent from the previous description of the process, which requires the presence of impurities in order that they may be converted into solid solution within the temperature range of 700-1000 C. before they are retained in this condition by the quenching operation.

In addition, it will be seen from the data that the addition of oxygen to the coppers containing various amounts of sulphur had no effect on the results of the quenching treatment from 850 C. which produced substantial increases in the softening temperatures of the various coppers, irrespective of the presence or absence of oxygen as described'previously herein.

What is claimed is:

1. The process of treating copper containing from 0.025% to 0.05% oxygen for increasing the softening temperature thereof, which comprises including antimony therein in. effective amounts but not exceeding substantially 0.02% thereof, heating the said copper to within a temperature range of from approximately 700 C. to approximately 1000 C., maintaining the said copper within such temperature range until the antimony is converted substantially completely into solid solution in the copper, and quenching the resulting copper from the said temperature to maintain the antimony in solid solution.

2. The process of treating commercial oxygenbearing copper containing 0.025% to 0.05% oxygen for increasing its softening temperature,

which comprises alloying with the said copper from approximately 0.003% to approximately 0.02% of antimony, heating the resulting copper to a temperature not less than substantially 850 C., maintaining the said temperature until substantially all of the antimony' has been converted into solid solution in the copper, and quenching the resulting heat-treated copper. from the said temperature to maintain the antimony in solid commercial tough-pitch copper containing antimony but not more than approximately 0.02% thereof, the antimony being substantially entirely in solid solution in of from 0.025% to 0.05% copper.

5. A new metallurgical product composed of commercial oxygen-bearing copper containing from approximately 0.025% to approximately 0.05% oxygen, and from approximately 0.003%, to approximately-0.02% of antimony which is present at least substantially entirely in solid solution.

6. As a new metallurgical product, heat-treated oxygen contained in the copper having impurities including antimony present substantially completely as solid solution in the copper, the said copper having a composition corresponding substantially to commercial tough-pitch copper but having a softening temperature substantially above 250 C.

' ALBERT J. PHILLIPS. ALBERT A. SMITH, JR. JOHN S. SMART, JR.

the copper in the presencev