US2286064A - Ammunition - Google Patents

Description

2 Sheets-Sheet 2 AMMUNITION c. D. cox

Filed June l2, 1940 June 9, 1942.`

E z Aanv ST55: As Denn/Al INVENTOR TeA-'Afef BY d/ ATToRNEYs Corpse ALLOY 5755:

Ex reACr/au #were *t 'primers and/or powders unstable.

Patented June 9, 1942 AMMUNITION Charles D. Coxe, Bridgeport, Conn., assignor to Remington Arms'Company, Inc., a corporation of Delaware Application June 12, 1940, Serial No. 340,004 (c1. 14s- 12) 2 Claims.

This invention relates to the manufacture oi' ammunition components from steel and particularly from a steel that has a precipitation hardenable alloy therein. In the embodiment disclosed, the use of the steel is shown as applied to a cartridge case of the conventional rimflre.

type, but it lis to be distinctly understood that the invention may be applied to any type of cartridge case andfor other ammunition components, such as for example, shotshell heads and center fire cartridge primer cups.

Brass is in almost universal use as a cartridge ments in such use in regard to cost, shaping,

strength, corrosion resistance and extractibility after it `has been nreheated for four vhours at 450 C.

Fig. 5 is a graph showing the relation between Brinell hardness and time of reheating of a copper alloy steel which has previously been nor-y malized.

In Fig. 6 there appears a graph which shows the number of splits and extraction force required for various materials in various stages from the gun. Brass, however, has many dist advantages and much work and research have been expended in the search for a substitute which will still meet the desired requirements.

Brass is expensive and cannot be used in combination with certain very desirable primers and/or powders, as it will season crack, corrode, and will also cause reactions renderingV the The matter of expenseV is of particular importance in the manufacture of the conventional rimre cartridges. There have been many attempts to use steel or' an alloy thereof, but such has never proven feasible. The other` objects of the invention will appear from the following description and illustrations which, as stated before,

'are not intended to limit the use of the invention to the forms shown and described.

In the drawings:

Fig. 1 is a sectional view of a rimiire cartridge case ywith the ,clearance between the case and the chamber of the gun exaggerated, the bulging of the shell dueto 'firing pressures and a split being also'exaggerated.

Fig. 2 shows diagrammatically, by way of Fig. 4 is a graph showing the relation betweenv the relative elongation and the yield point and tensile strength of a copper bearing alloy which has been reduced in size by cold rolling. Two

- sets of curves appear in the graph, one for the metal as rolled after normalizing and the second of treatment,l including the conventional brass -oase and a copper alloy lsteel treated in accord- Y ance with the present invention.

The purpose of a cartridge case is to be a container or carrier for the powder and the priming mixture which initiates the `combustion of the powder. The projectile is placed in the mouth of the cartridge case and is propelled from the barrel when the primer of the cartridge is struck by the firing pin, thereby igniting the propellent powder. When in position in the gun, the s is located in the chamber thereof which is closely matched with the size of the shell, the shell being properly sized in the course of manufacture so that it will fit into the chamber. It is obvious, however, that a certain clearance will always be present between the outside of the case and the chamber. There is also a variation in the snugness'of the fit yoi! the case inthe' chamber and the relative roughness of the chambers in different guns, all of which affect the operation of the cartridge and extraction thereof.

Referring to Fig. 1, lin which a conventional rlmflre shell is depicted, I0 represents the bolt .of the gun which has been closed against the 1 head II of the case I2. 'I'he case I2 ts within the chamber I3 of the barrel I 4 (shown fragmentarily); An extractor I5 of the conventional type engages the rim of the shell as it is pushed into the chamber I I. A suitable striker or firing pin 22 is provided to strike the rim of the case I2 in which the priming mixture is placed. It is to be noted that Fig. 1 is a horizontal section and that the striker in the case of a rimre shell contacts the case at or near the edge of the rim. It is necessary that the material of the case have sufficient strength and a suillciently high yield point so that upon the combustion of the prop ellent charge and under the high pressure developed thereby, that it will not be forced a subenough so that it will spring outwardly and seal the chamber, and prevent the escape of gases from the chamber of the barrel. In the event that the pressure is such as to cause the yield point of the metal inthe shell to be exceeded thereby, allowing too great a permanent deformation to take place, it is obvious that the bulging portions of the shell will tightly engage the side of the chamber I3. This bulging of the shell will require an unusually high extraction force which in many instances causes the extractor I to pull through the rim or portion of the shell with which it engages as the bolt is moved backwardly, leaving the expended shell within the chamber and causing great inconvenience and dilcult operation. Even if the extractor does engage the shell and withdraw it, an excessive force is required to operate the gun, which obviously is undesirable. It is seen, therefore, that the yield point of the metal bears.` an important relationship to the extraction force necessary to withdraw the shell and also to the sealing of the powder gases and prevention of the escape thereof through the mechanism of the gun and into the face of the operator. Such leakage of gas. backwardly also detracts power from the propelling of the projectile through the barrel of the gun and is undesirable. In the high velocity rimre cartridges of the present day; the powder pressures at the initial time of firing are in the vicinity of 18,000 pounds per square inch, and of the standard rimre shells in thelvicinity of 14,000 pounds per square inch. The ductility of the metal of the case must also be such that upon the firing thereof it will not split, such as has been indicated at I1 of Fig. 1.

Brass shells also have the disadvantage of developing season cracks, which is attributed to the l dezincication of brass in the shell caused by eleparticular type of firearm, and it can also be seen 'that the test showed no splits for the brass.

In Fig. 2, A, B, C. D, E, five of the steps in the forming of the usual rimre shell are shown, it

being understood that any number of intermedi# ate operations may be used or any type of shell or case may be formed similarly.

A is a cross section through a circular disc of metal. It is usual to both form`the disc A from a strip of metal and at the same time pass it through a die byfmeans of a punch,A and cup it as shown in B of Fig. 2. vBy successive drawing operations, the shell and rimre case are shaped until they reach the iinal form shown in E.

In Fig. 3 is shown an enlarged view of a finished rimre shell in which, due to the drawing operations, the upper portion indicated at I8 has been reduced by about 41% through the working. The section at I9 has been reduced by about 35% and the section in the base 0%, or the base remains substantially the same thickness asl the original. vlit is obvious that these amounts vary in accordance with the dies and process used and are not limited to those shown. It has been found by the heat treating process, hereinafter described, that an alloy steel containing a precipitation hardenable material may be made 'that will have the proper tensile strength and ductility to satisfactorily operate in a gun, and tests have shown that it will have practically the samefperformance characteristics as the brass, as 'far as extraction force and splits are concerned, as can to make it impossible to use them. It has also been diflicult to suitably draw and'form the cartridge case from the strip of metal and still `have it so that it will function in the chamber of a gun. By the use of a copper bearing alloy steel, it has been found that it may be heat treated in the manner about to bedescribed, and ay successful cartridge case produced thereby.

In the heat treatment of ya steel, it is said to be normalized after 'it has been brought to a temperature around or above 700 C., and then allowed to cool in air. It might also be cooled by quenching to hasten the cooling, or be allowed to remain in the furnace for a length of time, either of which will result in a different grain structure of the metal than when it is cooled in air, depending upon the percent of carbon in the steel or other alloying elements. When copper or other alloy making the steel precipitation hardenable, such as columbium, beryllium or titanium, is added to the steel, the steel may be heated to r100 C., preferably 800 to 900 C., at which time the copper goes into solid solution in the iron; then,- upon cooling at a moderate rate such as in air, the copper stays in the solid solution. These temperatures are for copper as the precipitation hardenable element, and are-not necessarily for the others. 'I'his may be termed solution heat treating. If then the articlebe subjected to a heat of between 400 and 616 C. and held at that temperature for a period of from 16 hours to 10 minutes, respectively, as will be explained later, the copper which is in the solid solution will tend to precipitate out of the solution, whether or not this is complete not being known at present. However, it does have a very decided eiect upon the metal. The copper is thrown out of the solution into a critically dispersed frm, which may or may not be a precipitation, on reheating to a temperature that gives suiilicient atomic mobility to allow the change. There is a possibility thatsome recrystallization will occur at the higher temperatures, but such is immaterial. This last heat treatment is known as precipitation hardening. .The tensile and yield strengths of steels that have not been cold shaped before the precipitation .hardening are raised ysomewhat and the ductility decreased slightly.- The graphs of Figs. 4 and 5,

representing work of Cyril S. Smith and Earl W. Palmer, are copyrighted by the American Institute of Mining and Metallurgical Engineers and are used with the permissionof that Institute. As may be seen by referring to Fig. 4, theyield point is raised from approximately 48,000 pounds per square inch to 68,000 pounds per square inch in a copper alloy steel of the composition inditaken place.

cated when 0% reduction by cold rolling has The percentage elongation in 2 inches, whichis an indication of the ductility, is seen to fall from approximately 28% to 24%. However, if cold shaping or working takes place before the last heat treatment, such as occurs steel is increased to 108,000 pounds per square inch, and that the ductility is reduced to about 3%. Upon reheating the cold shaped'piece for 4 hours at 450 C., it is to, be noted that the yield point remains substantially the same, and yet the percentage elongation'is raised to about 121/2%.

This puts the formed steel case in condition such that it may be satisfactorily used in a lirearm because the yield strength has been increased to` such a point that permanent deformation will not take place-to any appreciable extent, 'thereby causing diiiicult extraction, nor will the shell split due to brittleness or lack oi' ductility thereof. The period of time which it is necessaryA to reheat for precipitation hardening the steel component depends upon the temperature and probably the degree of work hardening. In Fig. 5 it may be seen that if a temperature of 600 C. be used for a normalized copper alloy lsteel of the composition indicated, that the maxlmum Brinell hardness is reached in approxi-` mately 15 minutes, whereas if 450 C. be employed the maximum Brinell hardness is reached at some time between 16 and 64 hours, this Brinell hardness being slightly greater. l

It isl to be understood that the temperature used will depend upon the time the component is subjected thereto and should be a time ternperature cycle wherein no or little recrystallization takes place. It has been found that a shell may be placed into a heat treating furnace and, when the shell reaches 616 C. in a period of 10 minutes, that satisfactory results will be obtained. If 'higher temperatures are used, a much shorter time of treatment must be employed or substantial recrystallization will take place, and the results will not be satisfactory.

Referring to Fig. 3, it is seen' that in a conlventional rimiire cartridge there is a much larger reduction of the wall near the mouth than there is near the lower part, and that in the base there is substantially no reduction. In the exand characteristics is combined with a base having the desired properties.

During the cold shaping process of a rimre shell, such as shown in Fig. 3, considerable strain is set up at the bend portion of the rim, which I serves to work harden to a slight extent in this particular area. The heat treating temperature serves to relieve the stresses at this point, vwhich also assists the sensitivity characteristics of the shell because the priming mixture is contained in the rim.

Referring now to Fig. 6, various types of shells have been tested and a comparison indicated. For brass, extraction force was found to be in the neighborhood of 5 pounds and no splits were recorded. The copper alloy steel after normalizing and drawing gave about splits and 5 pounds extraction force. The same copper alloy steel upon the precipitation hardening treatment gave 0% splits and 5 pounds extraction force, which is substantially identical tothe brass. It is preferable to use an alloy steel that has carbon in a low amount, not over .50% and preferably v.10% or under. In order to strengthen or give desirable properties to the steel, any'of the following elements singly or in lcombination in the amounts indicated may be used.

Molybdenumnot over 1.00%, preferably less than 0.50%

Chromium-not over 5.00%, preferably 0% to 2.00% Vanadium-0% to 1.00%,

or other ,alloying elements in such proportion ample shown, this is 41% near the mouth, 35%l at the lower part of the wall, and 0% Vat the base. -By referring to Fig. 4, it is noted that -when the blank or cup is subjected, first, to a normalizing treatment, then is cold shaped, and

then is reheated for. the purpose of precipitation hardening, that at the mouth, the copper alloy steel as indicated in Fig. 4 will have a yield strength in the vicinity of 108,000 pounds i per square inch and that the elongation will be suilicient strength and ductility produced by the cold working and precipitation hardening to withstand the firing pressures. It is also to be noted that the base is suiiiciently soft so that the impact of the firing pin will be properly transmitted to the primer mixture, the strength rt this point beingimmaterial because it is backed up by the bolt and does not receive the same forces that the case does near the mouth and along the wall. The advantage of such a distribution of strength and ductility in a cartridge case is obvious from the foregoing in that a shell with a wall that is of the proper strength as will increase the strength of the steel without so lowering the ductility as to make it impossible to fabricate.` The phosphorus should be not over .50% and preferably under .25%. The copper in the steel should behot over 5.00% and preferably under 3.00%. As an example, the

following steels have been found to besatisfactory: l .'No. 1

Per cent Carbon. .08

Manganese .50

' Silicon .l0

Nickel 2.00

Phosphorus maximum-- .04

Sulphur do .04

Copper l 00 Per cent Carbon .08

Manganese .40

Nickel 1.00

.Copper 1.30

y Molybdenum .20

Phosphorus maximum .04

Sulphur do .04

It is to be understood, however, that the invention is not limited to these two alloys, but

that they are cited merely as examples of some stantially 50,000 pounds per squareinch or more in the normalized steel and which renders the tionI of the copper from solid solution.

splits.

steel capable of being precipitation hardened falls within the scope of the invention, the precipitation hardening serving to keep the yield strength of the cold shaped sections substantially constant and to increase the ductility so that the shell will function satisfactorily. It has been found that the best results are obtained with an alloy steel in which the copper is in excess of 0.5% and preferably between 1 and 2%. The shell is heated at some point, C or before of Fig. 2, to about 700 C. and preferably 800 to 900 C., and is maintained at this temperature for a suiiicient time to rmit the copper to go into solid solution in t e iron. The component is then allowed to cool at a moderate rate,

v such as in air or room temperature, this being fast enough to prevent any substantial precipita- The ishell is then worked into a form such ias in D of Fig. 2 so that the material of the walls of the shell receive cold working such as shown in Fig. 3, causing work hardening of the portions indicated. The shell in this condition, due to the increase in yield point, will probably have a low extraction force, as shown in Fig. 6 but, due tothe lackof ductility, a large percentage of splits will take place. At this ypoint or at D the shell Vis subjected to a temperature preferably between 400 and 616 C. and held there from between 16 hours to 10 minutes as indicated generally by Fig. 5, and preferably 450 to 500 C. for 4 hours. This gives the required ductility with only a slight change in theA yield point or elastic limit, because the simultfaneous precipitation hardening due to copper content will compensate forthe loss in yield strength which ordinarily accompanies the heating of cold worked steel. It is to be noted that' the graph of Fig. 5 is for illustrative .purposes only and' does not necessarily represent the preferred metal to be used. As a specific example, either steel' I or 2, composition of which is set forth above, after step B, Fig. 2, is annealed at 620 C. to facilitate the drawing operation of step C of Fig. 2. After step C, the shell is heated at 870 C. for 1/2 hour and then air cooled.l After step E, Fig. 2,l the shell is heatedto 450 C. for 4 hours and will then give the results substantially as shown in Fig. 6 in which the extraction force will be around 5 pounds and there will be no thereon.

It is to be understood that the annealing step is not essential nor is the normalizing or solutionl heat treating at 870 C., providing the steel can be properly drawn without cracking or undue wear and strain ofthe dies, and the normalizing is not necessary if, in the manufacture of the shell from which the component is cut, the sheet was so .processed as to place the copper in solid solution in the iron.

YIf desired, the steel may be plated with copper or other rust inhibiting material placed It is evident from the foregoing description that a method has been evolved and a novel ammunition component produced that is superior in many `ways to those in present day use. As

l. In the manufacture of a cartridge shell, themethod which comprises providing a disc of low carbon steel containing a precipitation hardenable element; cold shaping said disc into a head of substantially the thickness of said disc and a Ybody integral with said head which decreases in wall thicknesstoward the open end thereof;

andc precipitation hardening the shell thus formed, whereby issecured a maximum ductility in saidrhead and an increasing yield strength toward the mouth of said body. v

2. In' the manufacture of rimre cartridge shells, the method which comprises providing a disc of low carbon steel containing copper in a state of solid solution, cold working said disc to form therefrom a cartridge shell 'comprising a head of substantially the thickness of said disc and a body of lesser thickness joined to said headby an integral folded hollow rim, and subsequently precipitation hardening the shell thus formed to increase the ductility of the metal v without material decrease in the yield strength the scope of the appended

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