US2058039A - Hardened malleable iron - Google Patents

Description

Patented Oct. 20, 1936 v UNITED STATES PATENT OFFICE.

2,058,039 HARDENED MALLEABLE IRON Harry A. Schwartz, Cleveland Heights, Ohio, assignor to National Malleable and Steel Castings Company, Cleveland, Ohio, a corporation of Ohio No Drawing.

31 Claims.

The principal object of the present invention is,

hence, to provide a malleable cast iron which satisfies these varied and conflicting requirements, or in other words, in which the hardness of the material is superior, while the other desired properties are not detrimentally affected, and even in some instances improved.

I have found that this may be accomplished by adding certain amounts of copper to the iron, for instance, to the usual run of malleable cast iron containing carbon, silicon, manganese, phosphorus, and sulphur, in-the quantities ordinarily present in malleable iron castings and particularly by subsequently heat treating the product, preferably at temperatures below the critical, or without recombination of carbon. I have found that the addition-of a small amount of copper to malleable cast iron imparts to the annealed product increased hardness, without the loss of other essential properties of the iron, and more particularly that the hardness may be still further increased by a subsequent heat treatment, especially of the character hereinafter in- .from 375% to 2%.

elongation than the other samples.

dicated. e

For example, I have taken a regular run of metal employed for making malleable cast iron and added thereto varying amounts of copper These samples were annealed as in regular commercial practice and found to have materially increased ultimate strength, no serious loss of elongation, and Brinell hardness of 140-150 as compared to a hardness of around 130 for similar iron but without copper, although the sample in which 2% copper was incorporated showed a somewhat lower ultimate strength and These samples were then heated to 700 C. (moderately below the critical temperature) and quenched in water from that temperature, and subsequent- Application December 14, 1931, Serial No. 580,940

ly heated at 500 C. for a period of several hours with the result shown in the following table:

Table I gg g Brinell Brinell hardness g to hardness of annealed metal ordiuar after the quenched from i, usual an-- 700 C. and heaton nealiug ed at 500 C 75 151 163 (heated hrs.) 1. 00 149 156 (heated 4 hrs.) 1. 50 147 179 (heated 4 hrs.) 2. 00 142 174 (heated 4 hrs.)

It will thus be seen that a rather remarkable result is achieved by the combination of adding copper to malleable iron and subsequently heat treating above about 700 C., for while small amounts of copper do harden malleable cast iron successive increases in the amount of copper above 375% and up to 2% produce successively taining copper is radically further increased, and

the metals containing relatively large amounts of copper are made even harder than those containing smaller amounts. While .75 to 2.00% of copper is thus indicated as preferred for present purposes, it will be understood that the invention is not limited to the particular proportions of copper used, as these may be varied considerably in accordance with the desired hardness of the product. However, it may be noted that the effect of the addition of copper begins to become app rent between .5 and .'75%, and increases rather rapidly around 1% and then considerably more slowly around 1.5%. In gen- .eral, it appears that the amount of copper used with a subsequent heat treatment. For instance, samples of annealed malleable cast iron containing 1% of copper have been heated to 725 C. and to 740 C., quenched in water from these temperatures, and then heated for about five hours at around 500 C. The results of such treatment are given in the following table:

It may be particularly noted that through the treatment indicated, the hardness of the metal is particularly increased by the combination of the quenching and heating in that order. Where the metal is merely quenched from temperatures above 700 C. without the heating operation, the hardness is substantially below what is produced by the combined treatment. In short, the quenching from above 700 C.without any heat treatment hardens the iron somewhat but does not produce the hardness required for many purposes.

Tests have showed that in some instances the quenching from the higher temperatures is not entirely necessary, but that cooling in air from such temperatures may be sufficient. For instance, if malleable cast iron which has been annealed, and which has a copper content of about 1%, is cooled in the air from around 700 C. the hardness of the metal is increased slightly, and this hardness does not appear to be improved by a subsequent heating of the character indicated. However, it appears that as the temperature from which the metal is cooled increases above 700 C. the effect of a heat treatment appears to become more and more effective, in combination with the heating to the temperature above 700 C. These principles may be further exemplified by the following table:

Table III It has further been found that if malleable cast iron containing copper in amounts indicated but subjected, after annealing, to a heat treatment of the character described, the hardness of the metal is increased over the hardness given in the second column of Table I, but that such increase is comparatively small unless the metal has first been cooled from' above 700. However, there is no intention in this last statement of disclaiming a process in which the cooling from above 700 is combined with the annealing cycle, particularly where the metal is rapidly cooled. While 700 C. is at present regarded as the lower practical limit for the quenching operation, insofar as the production of the hardest malleable cast irons is concerned, it will be understood that somewhat lower temperatures might be used, with, however, a sharp falling off in the hardness. It may also be mentioned that while the 'quenching and air cooling, both from above 700 C. in combination with the heat treatment give good results, the quenching is preferred over the air cooling.

While temperatures above 700 C. and below 760 C. are especially recommended, the metal may even be quenched from above the critical point (760 C.) with some recombination of carbon, though in this event there may be some loss of machinability, depending upon the amount of carbon which has been recombined. In this manner, an even harder malleable cast iron may be produced through the recombination of amounts of carbon. Furthermore, the quenching operation is apt to be more eifective when elements such as silicon are present in amounts greater than usual, because silicon raises the critical point of the iron, or in other words, permits it to be heated to a higher temperature before recombination of substantial amounts of carbon take place. On the other hand, manganese and nickel lower the critical point, and hence tend to reduce the hardness which is producible without recombination of carbon and consequent loss of machinability.

In other words, increase in silicon may be desirable, over that present in normal malleable cast iron, but increase in manganese or nickel is generally undesirable for present purposes. Hence, while a malleable cast iron having normal content of silicon, manganese and so forth, may be advantageously used in carrying out the present invention, other malleable irons in which such ingredients are present in different proportions, may be used, within the limitations indicated.

The figures given for the time and temperature of the heating must, of course, be taken as purely exemplar, and not as essential details, for they may be varied considerably between limits and good results still secured. For instance, it has been found that heating at 500 C. for less than an hour is scarcely advantageous, and that the continuation of the heat treatment beyond, say, four or five hours results in but little or no additional hardness, and the hardness may even be decreased.

In this manner, I have provided a malleable cast iron which is not only inexpensive but can be formed into shapes impossible with pressed steel, and which is much superior to the latter for certain purposes. For instance, my improved metal retains its shape better in brake drums or similar constructions than does pressed steel, and in addition is easier to machine than steel. Furthermore, my improved malleable cast iron is highly shock-resistant and can be readily cast in the desired thin sections while at the same time,

it possesses the necessary wear resistance for a brake drum, or other part subjected to shocks and friction. In short, the present invention provides for imparting to malleable cast iron the desired hardness while at the same time, maintaining all of the other essential properties of the metal.

While the improved metal according to the present invention has been spoken of as particulanly useful for brake drums it may also be used for combined brake drums and hub constructions, and for any other purpose for which machineable metal of this character is desired. In fact, the invention is not confined to any particular use for the metal.

In the production of regular malleable iron it is generally recognized that the relatively small variations in Brinell hardness which occurs in this product are accompanied by corresponding given no subsequent heat treatment.

variations in strength, the strength increasing with the increase in Brinell hardness. I have found that this same relationship holds true in my present invention and that the relatively great increase in hardness which I have attained is accompanied by corresponding increases in strength. I have found, for instance, that additions of copper and suitable heat treatments which produce a Brinell hardness of from 150 to 155, produce an increase of about 10,000 pounds per square inch in. strength over the same iron to which copper was not added and which was Thus my invention, in addition to providing for very substantial increase in hardness, also provides for material increase in strength, without sacrifice of other valuable properties.

The figures which have been given are not to be taken as absolutely accurate in every instance because they are based upon a few samples made in a particular shop, using amounts of copper which are calculated to produce the amounts stated in the products, allowance being made for possible losses from various causes. In this way, errors may have crept in to the general results indicated in specific instances. However, the general trend of the results is not affected by any deviation in a single instance. For instance, particular attention is called to the figure 156 in the third column of Table I which seems to be somewhat out of line with the other figures, which may have resulted from some discrepancies such as those stated.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention in the use of such terms of excluding any equivalents of the matter described but recognize that various modifications are possible within the scope of the invention.

I claim:

1. A brake drum formed of malleable cast iron containing about .75 to 2% of copper, heat treated,below thecritical temperature to increase its hardness.

2. A unitary brake drum and hub formed of malleable cast iron containing about .75 to 2% of copper, heat treated below the critical temperature to increase its hardness.

3. Method of making malleable cast iron of the character described which comprises adding copper in an amount more than .5% and up to about 2% to the ingredients of ordinary malleable cast iron, annealing to cause graphitization. and subsequently heating over a substantial period of time at a temperature below the critical.

4. Method of making malleable cast iron of the character described which comprises adding copper in an amount more than .5% and up to about 2% to theingredients of ordinary malleable cast idly irom between about 700 C. and .the critical temperature, andsubsequently heating over a substantial period of time at a temperature below the critical.

5. Method of making malleable cast iron of the character described which comprises adding copper in an amount more than .5% and up to about 2% to the ingredients of ordinary malleable cast iron, annealing to cause graphitization, cooling rapidly from between about 700 C. and the critical temperature, and subsequently heating 6. Method of making malleable cast iron of the character described which comprises adding from .5 to 2% of copper to the ingredients of ordinary malleable cast iron, annealing to cause graphitization, heating the annealed iron to above 700 C. but not above the critical temperature, and quenching from such temperature.

7. Method of making malleable cast iron of the character described which comprises adding from about .75 to 2% of copper to the ingredients of a malleable cast iron, annealing to cause graphitization, quenching from a temperature in the order of 725 to 740 C., and heating for several hours at a temper-ature considerably below the critical.

8. A precipitation hardened ferrous alloy coritaining the ingredients of malleable cast iron in the proportions adapted to the production of malleable cast iron with the addition of from .5% to about 2% of copper and having a Brinell hardness in substantial excess of that of ordinary malleable iron.

9. Method of making a ferrous alloy which comprises adding from .5% to about 2% copper to ingredients adapted to form malleable cast iron, annealing to cause graphitization and subsequently heating substantially entirely below the critical temperature to increase the hardness of the ferrite.

10. A precipitation hardened ferrous alloy brake drum containing the ingredients of malleable cast iron in proportions capable of producing malleable cast iron with the addition of from .5% to about 2% of copper and without substantial combined carbon and having a Brinell hardness in substantial excess of that of ordinary malleable iron.

11. Precipitation hardened malleable cast iron of the character described including from about .75% to about 2% of copper and having a Brinell hardness of about 160-170. v

12. A brake drum formed of machineable, shock-resistant, precipitation hardened malleable cast iron containing from above about .5% to about 2% copper and having a Brinell hardness of above about 160-170.

13. Method of making malleable cast iron of increased hardness which comprises adding copper to the ingredients of ordinary malleable cast iron, said copper being present in the amount of above .5 to about 2%, annealing to cause graphitization, and rapidly cooling the alloy in air from between about 700 C. and the critical temperature.

14. Method of making malleable cast iron of annealed iron from a temperature above about 700 C., and subsequently subjecting the iron to i a sufiicient heat treatment at a temperature considerably below the critical temperature to effect precipitation hardening.

16: Method of making malleable cast iron of the character described which comprises adding from about .75 to 2% of copper to the ingredientsof a malleable cast iron, annealing to cause graphitization, quenching from a temperature in the order of 700 to 760 C., and heating for several hours at a temperature considerably below the critical.

17. Method of making malleable cast iron of the character described which comprises adding from .5% to about 2% of copper and more silicon than is customarily present in ordinary malleable cast iron to the other ingredients of ordinary cast iron, annealing to cause graphitization, and.

rapidly cooling the annealed iron from a temper-' ature above about 700 C. and heat treating to harden the ferrite by precipitation hardening.

18. A method for increasing the hardness of malleable cast iron comprising adding more than .5% and not more than about 2% of copper to the ingredients of malleable cast iron, heating the alloy to dissolve the copper and heat treating the alloy to precipitate copper and harden the alloy.

19. A method of preparing malleable cast iron of increased hardness comprising adding about .5 to 2% of copper to the ingredients of malleable cast iron, heating at a temperature above 700 C. to dissolve the copper, annealing to cause graphitization, cooling rapidly and maintaining the alloy at a temperature in which the copper will precipitate, sufficiently long to increase the hardness of the cast iron.

20. A method of preparing a malleable cast iron of increased hardness comprising heating a malleable cast iron containing more than .5% and not over 2% copper at a temperature above 700 C. to dissolve the copper, cooling rapidly and heating the alloy at a temperature of about 500 C. to precipitate the copper.

21. A method of making malleable cast iron of increased hardness comprising annealing a malleable cast iron containing about .5 to 2% of copper to cause graphitization, cooling it rapidly from between 700 and 760 C. and heating for 4 to 5 hours at a temperature of about 500 C.

22. A method of preparing malleable cast iron of increased hardness comprising adding about .5 to 2% of copper to the ingredients of malleable cast iron, heating at a temperature above 700 C. to dissolve the copper, annealing to cause graphitization, cooling rapidly and maintaining the alloy at a temperature in the neighborhood of 500 C. until a cast iron of maximum hardness is obtained.

23. A method for preparing malleable cast iron of increased hardness comprising adding about 1 to 1.5% of copper to the ingredients of malleable cast iron, annealing the alloy to cause graphitization, cooling rapidly from above 700 C. and heating at a temperature in the neighborhood of 500 C. for a sufiicient time to efiect precipitation hardening.

24. A malleable precipitation hardened cast iron containing about .75 to 2% of copper.

25. A malleable precipitation hardened cast iron containing about .75 to 2% of copper and more silicon than is normally present in malleable cast iron.

26. A malleable precipitation hardened cast iron containing about 1 to 1.5% of copper.

27. A malleabilized and precipitation hardened cast iron containing about .5 to 2% of copper.

28. A malleabilized and precipitation hardened cast iron containing about 1 to 1.5% of copper.

29. Method of making malleable cast iron which comprises adding from about .75 to 2% of copper to the ingredients of malleable cast iron, annealing the alloy and subjecting it to heat at temperatures below the critical temperature to increase the hardness of the ferrite.

30. A malleable graphitized ferrous casting containing copper precipitated from solid solution and comprising over 90% iron, together with small percentages of other elements commonly present in malleable cast iron and from above about 5% to about 2% copper, and having a Brinell hardness of above about 160.

31. A brake drum formed of a machinable shock resistant malleable graphitized ferrous casting containing copper precipitated from solid solution and comprising over 90% iron, together with small percentages of other elements commonly present in malleable cast iron and from above about .5% to about 2% copper, and having a Brinell hardness of above about 160.

HARRY A. SCHWARTZ.