US2378916A - Manganese alloys - Google Patents

Description

Patented .inne 26, 1345 MANGANESE ALLOYS Reginald S. Dean,

sait Las@ city, Utah., assigner to Chicago Development Company, Chicago, Ill., a corporation o1 Illinois 13 Claims.

My invention relates to the preparation and heat treatment o; alloys consisting essentially of manganese, iron and chromium, and is particularly concerned with the preparation of such alloys which are highly resistant to atmospheric corrosion, possess the ability to withstand great extension by cold work without the hardening which is characteristic of austenitic stainless steels and irons heretofore known in the art, and, in addition, have the properties of retaining workhardening at relatively high temperatures, oi

hardening and being rendered non-magnetic,

Without embrittlement, by heat treatment.

Alloys ofv manganese, chromium and iron have heretofore been suggested but, in all cases, those alloys whose properties have been investigated have contained asubstantial content of carbon,-

of the order of 1% or more, although suggestions have been made for alloys where the carbon content was allegedly zero. In such alloys ofthe prior Cri art, the manganese content always was lessthan that of the chromium. Such alloys are disclosed by the prior art to have a magnetic permeability not exceeding from 2 to 5% of that of cast iron. In other known alloys containing manganese, chromium and iron, present, the silicon and up to 8%.

The alloys of my invention are sharply distin guishable from those of the prior artl not only in composition but in physical characteristics and properties, including amenability to different types of heat treatment. Thus, for example, the alloys of my invention must be substantially free from the oxides of silicon and aluminum, carbon comprising in excess of 3% both carbon and silicon are is substantially,- and preferably entirely, absent,

and silicon should not exceed 1 and is preferably present in amounts less than 0.7% and particularly close to 0%. In connection with the matter of properties of the alloys of my invention, it may be pointed out, among other things, that their magnetic permeability, after quenching from high temperatures, is substantially that of cast iron, a property which distinguishesthem radically from numeroiis of the alloys of the prior art. As is well known and shown in Handbook for Electrical Engineers, by Harold Pender, first edition, published by John Wiley 8: Sons, Inc., New Y'ork City (page 901B),4 cast ironr at a eld strength of 100 ampere turns per inch has a permeability of from or from about 1.35, to ,1.5m The alloys of my es invention, therefore, have a permeability falling within this same general range.

Again, there is a denite and radical. dierence between the heat treatment proposed by the prior art as applied to alloys of manganese, chromium and iron and the heat treatments which I utilize. The heat treatment of the alloys of the present invention usually consists of a quenching, cold working and reheating procedure, the quenching taking place from a temperature higher than 1100 degrees C. and particularly about 1200 degrees C. The heat treatment described'in thev prior art with respect to manganese, iron, chromium alloys involves heating the cast alloy to 1000 degrees C. to 1100 degrees C. for several hours and then cool ing in the furnace. Such a heat treatment does not produce increased strength in the allo'ys of my invention. Here it has no substantial edect on the hardness or produces a softening, depending upon the rate at which the alloys were cooled in casting. Heating the alloys of my present invention to 1000 degrees C. causes softening without the reappearance oi magnetism, that is, they are not carried into the state from which they were quenched. This state is only attained at higher temperatures, usually above 1100 degrees C.

It will be seen, therefore, as hereinafter pointed out in detail. that, by a suitable selection of alloy composition and by heating of the alloys to a proximately 1200 degrees C and quenching, I may cold work the said alloys by rolling, swaging or by any other means to an extent, in many instances, of 90% or more reduction in area without excessive hardening. By excessive hardening, I refer to l any hardness labove about 25 as measured on the Rockwell C scale. I have found that the range of alloy composition in which this phase of my invention may be practicsed may be dened approximately as follows: If the said alloys contain at least 18% ganese is substantially entirely free of carbon and oxides of silicon and aluminum and egceeds the amount of chromium, a certain critical amount of chromium must be present to prevent excessive hardening of the alloys by cold working. This critical amount of chromium depends on the manganese content of the alloy. Between 18% and 30% manganese. where the manganese exceeds the chromium, the critical minimum percentage of chromium is 17.5% and-the upper percentage of chromium is about 19%. Above 30% manganese, the critical minimum percentage of chromium falls, being 12.5% when the manganese is 40%, the upper percentage of chromium in such case being about. 16%. In the range of 10% manganese, and wherein the mam.

Rlockglell O ar ess Pell-ent cold worked 75% reduc tion in area Per cent Per cent Mn Cr All of the alloys in the range of composition set out hereinabove, as previously indicated. have a magnetic permeability of the same order as that of cast iron.

The alloys within the composition range which I have set forth hereinabove, as previously stated, may be greatly hardened and strengthened by heat treatment after quenching from about 1200 degrees C.4 and c old working. I have found, for example, that alloys having at least 18% manganese and at least the critical amount of chromium necessary for great extension by cold work without undue hardening but containing less than the uppercritical-limit of chromium may be hardened without-embrittlement by heating to temperatures between about 400 degrees C. and about 800 degrees C. after quenching from approximately 1200 degreesC. and cold working. Within the percentage ranges set out hereinabove, the range or variation in the limiting percentage of chromium is` substantially linear. While the amount of hardening which is obtainable in the alloys of my invention varies somewhat with the temperature of heat treatment, the important factor is, however, that, by the practice of my invention, Yhardeningimay be obtained without embrittlement. This is in sharp contrast from the results obtained with alloys of iron, manganese and chromium heretofore known in the art, all of which, due to the presence of oxides of aluminum or silicon or to carbon or to the selection of relativeproportions of iron, manganese and chromium, become brittle at room temperatures after being heated to temperatures of about 600Hdegrees C. after quenching from'about 1200 degrees C. followed by cold working. For the purpose of illustrating this phase of myv invention, the

While there is a small amount of hardening Abelow the critical percentage of chromium, the

rangeV of hardening is,.however, materially less than above the critical percentageof chromium for best coldworking, accordingly, I prefer particularly to utilize those alloyshaving more than the critical amount of chromium in the practice of the preferred aspects of my invention. In ceriron become brittle by reheating at any temperal tain cases, some useful results may be obtained with not more than 2.5% less than the critical amount of chromium as hereinabove dened.

It should be understood that the hardness of the alloys, after reheating to about 600 degrees C., is not necessarily the maximum hardness which can be obtained. Haldening at this temperature is described for the purpose of illustrating the fact that the alloys of my present invention do not become brittle on heat treatment, since I have found that, if alloys of manganese, chromium and ture, they do so at about 600 degrees C. It is not uncommon, fo-r example, to obtain hardnesses as high as about Rockwell C 60 by heating at ternperatures somewhat below 600 degrees C. It should be understood that I consider an alloy brittle when it will not give a reading on the Rockwell C scale without chipping. I have found this to be a reliable indication of the extent of brittleness which renders an alloy useless or substantially so for at least most commercial purposes.

The alloys of my invention, while hardening less by cold work than austenitic alloys of iron, chromium and manganese; retain or enhance their hardness by heating to temperatures such as 800 degrees C., a treatment which softens the austenitic alloys of iron, chromium and manganese. This is illustrated by the following examples:

Illustrative alloy of present invention Austenitic alloy Mnl-25,; Cr-lS; Fe-57 Cold worked, 20 Rockwell C 650 C., 5l Rockwell C 800 C., 45 Rockwell C Mil-25; Cr-lO; Fe-65 Cold worked, 39 Rockwell C 650 C., 20 Rockwell C 800 C., 2 Rockwell C Alloys falling within the scope of my invention, if anealed, for example, at about 800 degrees C. or even as high as 1200 degrees C. and slow cooled, are' much harder and stronger and much less workable than austenitic iron, chromium.V and manganese alloys. When heated to temperatures from 1000 degrees C. to 1200 degrees C. and rapidlyv cooled, however, the forged or otherwise worked alloys of my invention are softened, and when quenched from 1200 degrees C. they have certain properties comparable to nickel silver and austenitic. iron, chromium, manganese. alloys in the annealed state. This is illustrated by the following examples:

Illustrative alloy of present invention [Mn-25; Cr-ls; Fe-:m

tained if it were allowed to cool in an ordinary y heat-treating furnace; in general,.by cooling at a rate such that at least six hours is required for the alloy to reach room temperature after the heat is turned off. It will be understood, of course, that the length of time required to bring the temperature of the heated alloy down to room temperature during the slow cooling process will depend, in part, upon the size and shape of the alloy element being treated. It will also be understood that the slow cooling may be carried out in airalthough, for best results, it' should be carried out in an inert atmosphere. The alloys which have this property contain from 22% to 30% manganese, from 15% to about 30% chromium, balance iron, the manganese not being less than the chromium and, particularly, exceeding the chromium.

As I have previously indicated, alloys of the present invention which contain from 22% to 30% manganese and more than 19% chromium cannot be hardened at 600 degrees C. after quenching from 1200 degrees C. without embrittlement. Hence, the alloys of myinvention which may be hardened without embrittlement by either 1) slow cooling or (2) by quenching and reheating are those containing approximately 25% manganese, approximately 18% chromium, and balance substantially all iron.

With respect tomagnetic properties, I have found that the alloys which are hardened after quenching and cold work without becoming brittle at 600 degrees C. lose a substantial proportion of their magnetism. They may, however, harden usefully without losing their magnetism.

I have found a wider range of alloy compositions which possess useful hardening characteristics below 600 degrees C. but which become brittle at that temperature. This group of alloys embraces all of those above the critical percentage of chromium necessary to prevent undue harden- [All alloys quenched from 1200 C. and cold worked] Per cent Per cent Per cent Hardness Hardness Mn Cr Fe cold worked 550 Q 25 23 52 24 s4 25 20, 55 43 25 25 5o 25 io In the practice of my invention, I prefer to employ electrolytic manganese having a purity of at least about 99.0% and preferably of 99.9%.

By virtue of their hardening by reheating after quenching, particularly with intermediate cold work, my alloys are particularly useful for various purposes as, for example, gears, bearings, armour plate, and for purposes, in general, where case-hardened nickel or nickel-chromium steels have heretofore been used. The alloys of my present invention, hardened as described herein, have a wide utility in articles of cutleryl ball and roller bearings, tools and dies, especially saws, and other tools which are necessarily exposed to corrosive iniluences. In the soft state, the alloys of :my present invention maybe employed for cooking utensils and other purposes where a relatively soft material of satisfactory working qualities and a high degree of stainlessness is desired. They may also be utilized in the aircraft andl automotive industries such as for the manufacture of thin sheets, of very high strength, for the fabrication of airplane wings or the like.

My presentapplication is a continuation-inpart of my copending applications Serial No. 219,501, led July 16, 1938, now Patent No. 2,286,-

199, issued June 16, 1942; and Serial No. 267,706,

cent up to 25 per cent manganese and from 12 per cent to 15 per cent at 40 per cent manganese with intermediate chromium percentages at intermediate contents of manganese in said alloys, the manganese being not less than the chromium, the balance being substantially all iron, said alloys being severely cold worked and having magnetic permeability of about 1.35,:1. to 1.57/1 Vat a v eld strength of 100 ampere turns'per inch and being capable of retaining or enhancing their hardness when heated toV temperatures from about 800 degrees C. to about 1200 degrees C, and slow cooled and of softening by heating to temperatures between 1000 degrees C. to 1200 degrees C, followed by rapid cooling.

2. Alloys consisting of substantially only iron,

l manganese and chromium, substantially free from' carbon and from oxides of silicon and alu..

mium, said alloys being cold Worked to a high degree after quenching from about 12:00 degrees C., said alloys having a magnetic permeability of about 1.35# to 1.571 at a field strength of 100 ampere turns per inch, said alloys containing morethan 18 per cent and less than 45 per cent manganese and a percentage of chromium from ploy electrolytic iron, electrolytic chromium and electrolytic manganese of high purity so as not to introduce deleterious constituents into the alloys. I have found, for example, that the presence of oxides of aluminum and silicon, such as are present in silica-thermic or aluminothermic manganese or ferro-manganese prevents the effective practice of my invention. While the mnatmese whiieI employ may/be produced by a vacuum 17 per cent to 32 per cent where the manganese content of said alloys is up to 25 per cent, and

r from 12 per cent to 15 per cent chromium at 40 Der cent manganese, with intermediate percentages of chromium at intermediate contents ofY l manganese, the manganese being always in excess of the chromium, the balance being substantially all iron. l

3. Hardened alloys consisting of substantially only iron, manganese and chromium, substantially free from carbon and from oxides of siliheating the same to a temperature of about 400 distinction process, I prefer, particularly. to em- ,76 decrees C. toabout 800 degrees C. after quenchcent to per cent chromium at 40 per cent manganese, with intermediate percentages of chroinium at intermediate contents of manganese, the manganese being always in excess of the chromium, the balance being substantially all iron.

4. Alloys consisting substantially onlyof iron,

vmanganese and chromium. substantially free from carbon and from oxides of aluminum and silicon, said alloys having more than 18 per cent and less than 45 per cent manganese and a percentage of chromium from 17 percent to 32 per cent up to 25 per cent manganese and from 12 to 15 per cent at 40 per cent manganese with intermediate chromium percentages at intermediate contents of manganese in said alloys, the manganese being not less than the chromium, the balance being substantially all iron, said alloys being severely cold worked and having magnetic permeability of about 1.35# to 1.57# at a field strength of 100 ampere turns per inch, said alloys being in a softened condition by reason of being heated to temperatures between about 1000 degrees C. and about 1200 degrees C followed by rapid cooling.

5. Alloys consisting of substantially only iron, manganese and chromium, substantially free from carbon and from oxides of silicon and aluminum, said alloys being worked to a high degree after quenching from about 1200 degrees C.,

said alloys having a magnetic permeability of about 1.35a to 1.57/1 at a eld strength of 100 ampere turns per inch, said alloys containing more than 18 per cent and less than 45 per cent manganese and a percentage of chromium from 17 per cent to 24 per cent where the manganese content is up to 25 per cent, and varying substantially linearly to about 15y per cent chromium at 40 per cent manganese, the manganese being always not less than the chromium, the balance being substantially all iron, said alloys having the property of not becoming brittle atroom temperature after heating to any temperature belowl their melting points followed by slow cooling.

6. Alloys consisting substantially only of iro'n, manganese and chromium, substantially free from carbon and from oxides ofaluminum and silicon, said alloys having more than 18 per cent and less than 45 per cent manganese and a percentage of chromium from 17 per cent to 24 per cent where the manganese content is up to 25 per cent and varying substantially linearly to about 15 per cent chromium at 40 per cent manganese, the manganese being always not less than the chromium, the balance being substantially all iron, said alloys having magnetic permeability of about 1.35/1 t0 1.571. at a eld strength of 100 ampere turns per inch and being hardened by reason of having been quenched from about 1200 degrees C. followed by cold working and reheating to temperatures between about 400 degrees C. and about 800 degrees C.

7. An alloy consisting essentially of approximately 25 per cent manganese, approximately 18 per cent chromium and the balance substantially all iron, said alloy being substantially free from the oxides of aluminum vand silicon, said alloy being hardened without embrittlement by quenching from approximately 1200 degrees C., cold working and reheating to a temperature between about 400 degrees and about 800 degrees C.

8. An alloy containing approximately 25 per cent manganese, approximately 18 per cent chromium and the balance substantially all iron, said alloy being substantially free from the oxides of aluminum and silicon, said alloy being hardened by slow cooling from approximately 1200 degrees C.

9. An alloy containing approximately 37 per cent manganese, approximately 14.5 per cent chromium and the balance substantially all iron, said alloy being substantially free from the oxides of aluminum and silicon, said alloy being hardened without embrittlement by quenching from approximately 1200 degrees C., cold working, and reheating to a temperature between about 400 degrees C. and about 800 degrees C.

10. vA .magnetic alloy capable of being cold worked to a high degree without exceeding Rockwell C 25, of being hardened without embrittling,

having the property of suffering loss of magnetism either by slow cooling from 1200 degrees C. or by quenching from 1200 degrees C. and reheating to 650 degrees C., and having a composition from 23 to 28 per cent manganese, from 17 to 19 per cent chromium, balance being substantially all iron.

11. A hardened non-brittle alloy resulting from I slow cooling of said alloy fromA temperatures of about 1200 degrees C., said alloy containing 22 to 30 per cent manganese, 15 to 30 per cent chromium, the manganese not being less than the chromium, balance substantially all iron.

1.2. Stainless alloys hardenable without cracking by heating, cooling, and reheating to a. lower temperature, said stainless alloys which are ductile as cast consisting essentially of chromium,

manganese, and iron in the following proportions: 14% to 16% chromium, 36% to 39% manganese, and the balance iron, with the exception of such small amounts of impurities as will not affect the properties of the alloys.

the alloys.

REGINALD S. DEAN.

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