High boron alloy steel fragmentation munition
United States Patent 1 Riffin et a1.  
 1 1 Apr. 29, 1975 1 1 HIGH BORON ALLOY STEEL FRAGMENTATION MUNITION [75] Inventors: Paul V. Rii&#39;fin, Lexington; Ernest N.  
 Kinas, Newton. both of Mass.  
 {22] Filed: Dec. 19, 1973 [21} Appl. No.: 426,265  
 [52] US. Cl 102/67; 75/123 B; 75/123 D; 75/123 L; 75/123 N [51] Int. Cl F421) 13/48; C22c 39/54 [58] Field of Search 75/123 B. 123 D. 123 L. 75/123 N; 102/67 [56] References Cited UNITED STATES PATENTS 2.280.283 4/1942 Crafts. 75/123 B 2.388.215 10/1945 Murph)- 75/123 8 2.390.594 12/1945 Krause 75/123 8 2.521731 10/1950 llacqua i 75/123 8 3.791.818 2/1974 Watmough 102/67 X Primary Examiner-L. Dewayne Rutledge Assisum! Examiner-Arthur J Steiner Attorney, Agent. or Firm-Robert P. Gibson; Nathan Edelberg; Frank .1. Dynda [5 7] ABSTRACT An alloy steel for high explosive fragmentation munitions, having a high boron content. and wherein the alloying elements are:  
 Weight &#39;74. about:  
 carbon .3 to .7 boron .05 to v5 manganese 1.25 In 2 ,0 phosphorus (l to 2 silicon (1 to 2.5 iron and incidental impurities remainder 4 Claims, No Drawings HIGH BORON ALLOY STEEL FRAGMENTATION MUNITION STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government for govern mental purposes without the payment to us of any royalty thereon.  
 BACKGROUND OF THE INVENTION The anti-personnel and anti-materiel effects of high explosive fragmentation steel munitions, such as artillery shells and mortar shells, rifle grenades, are maximized by the use of a steel alloy in the form of a hollow body, that upon detonation by means of a high explosive, produces a large number of small fragments. Great progress has been made by ordnance metallurgists over the years in the formulation of fragmentation steels, but there is still room for considerable improvement.  
  A vexing problem that the ordnance metallurgist must face is the striking of a compromise, in the formulation of an alloy steel for high explosive fragmentation ammunition. between the antithetical properties of fragmentability on the one hand to achieve the desired fragmentation, and of forgeability and machineability on the other hand to produce a munition component of the desired shape. Forged steel is the traditional material largely used for that purpose; e.g. SAE Xl340 during World War II.  
  It is accordingly a principal object of our invention to provide an alloy steel for high explosive fragmentation ammunition, that is a substantial improvement over traditional shell steel alloys, as regards fragmentation characteristics, while possessing the necessary forgeability and machineability for munition manufacturing purposes.  
  A further object of our invention is a family of special alloy steels that can be industrially produced with available steel making equipment.  
  Other objects and advantages will readily become apparent to those skilled in the art from the following description of our invention and of several ways of carrying the same into practice.  
 SUMMARY OF THE INVENTION In essence. we have found that a family of alloy steels having the improved fragmentation characteristics and the necessary machineability for high explosive fragmentation munition can be obtained by the use of a controlled high amount of boron, about 0.05 to 0.5%8, in a low or medium carbon steel, about 0.3 to 0.7%C, which also contains a substantial amount of manganese, about 1.25 to 2% Mn. Silicon may be added in a proportion of about 0.3 to 2.5%, preferably about I to 2.5%, but may be omitted. Phosphorus may be present as an incidental impurity, or may be added, if desired, in significant amounts between about 0.05 to 0.2%.  
  Thus, the composition of our novel alloy for high explosive fragmentation munition is:  
 -Continued Weight it, about:  
 phosphorus 0 to .2 silicon 0 to 2.5 iron and incidental impurities remainder In a preferred form of our invention, boron is present in a proportion of about 0.05 to 0.1 weight and silicon in a proportion of about 1 to 2.5%. Phosphorus may be present, if desired, in a proportion of about 0.05 to 0.2 weight We are, of course, aware that the addition of boron to carbonmanganese steels in various proportions is not broadly new. However, we have discovered, unexpectedly, that by adhering to the proportionate ranges of boron and other alloying ingredients in accordance with the teachings of our invention, a series of alloy steel high explosive munitions can be produced that upon detonation produces a great number of effective anti-personnel and anti-materiel fragments of smaller average fragment weight than fragmentation munitions made of alloy steels. Our special boron alloy steels possess the desired degree of machineability and other good mechanical qualities to assure the production of reliable ammunition that is safe to manufacture, handle and fire, while inflicting great damage on enemy personnel and materiel upon detonation.  
  We have further found that by varying the amounts of boron, carbon and/or manganese additives within the range limits here disclosed by us, or by varying the conditions of the heat-treatment in the course of producing the alloy steel, or by varying both, the fragmentation characteristics of the ammunition can be varied so as to achieve optimum effect in different types of high explosive ammunition.  
  Metallurgical treatments well known to those skilled in the art of alloy steel making, such as austerizing, quenching, tempering, may be advantageously used for the practice of our invention.  
  As regards fragmentation characteristics of general purpose high-explosive ammunition, it may be stated generally that the production of a few large fragments, upon detonation, is not desirable, as the damage radius from the point of impact is relatively small. For practical results in terms of antipersonnel and antimateriel damage, a high explosive shell or other munition should break up into many jagged fragments; thus, indicators of effectiveness are, average fragment weight (usually in grains), and number of fragments over one-half grains (per one detonated test item of predetermined mass). Generally speaking, the larger the number of fragments above one-half grain and the smaller the average fragment weight, the better are the fragmentation characteristics of the tested item.  
  Fragmentability of a munition steel alloy should not be confused with brittleness. A conventional brittle steel isunsuitable for that purpose, as a shell made from it may prematurely break up in or near the gun, resulting in death or injury to the gun crew and destruction of or serious damage to the weapon.  
 DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION We now illustrate the practice of our invention by means of several examples, but wish it to be understood that they are illustrative and do not limit the scope of our invention to the specific details shown.  
  In Examples l to 7. set forth in the following table. forged [V2 inches bar steel alloy stock was produced from melts to which boron and other eo-alloying elet vention as hereinafter claimed.  
 TABLE Composition Fragmentatwcight 7r; remainder. YS TS EL RA RC Charp tion l Treat- Fe and incidental (.l.r&#39; d 71 (RT) dia. cylinder) ment: (see impurities) KSI KSI ft. lb. M NV; footnotes) C Mn St P B Example I .5 I3 ll] .1 l5 (I7 K4 I37 :0 3s 24 3 ll .4 750 Example 2 .5 lb 2.1 08 8o I42 10 37 3 4 .6 525 2 Example 3 .5 l h 2.] (I8 78 I34 20 4I 23 3.7 .5 685 3 Example 4 .5 It: l2 (l8 lhb I84 l0 I3 38 L8 .3 7H) Example 5 .5 I3 1.0 l .(I7 90 I43 IU 39 29 4.2 .7 610 5 Example (1 .5 l3 1.0 .l (l7 Ill] l5ll ll 38 23 5.7 .4 830 Example 7 .5 l 3 1.0 .1 I5 .07 83 I34 It] 3) 22 3.0 .6 675 7 M merage fragment weight in grains; N /z number of fragments over a grain Footnotes Example l Heat Treatment lo()(t&#34;ltor 1 hours. an cool Example 2 Heat Treatment lfitttPF for I&#39;m hours. air cool Eoimple 1 Heat Ireatmcnt t-IMIF for l hour. air cool &#39;Eutmple -I Heat Treatment l50ttF for I hour. oil quench. temper I 50? for l hour. air cool Example 5 Heat Treatment litll|F for l hour: oil quench. temper l IUUF for l hour. air cool Example 6 Heat Treatment l50llF for l hour. oil quench. temper ll50F for l hour. air cool Emrnple 7 Heat Treatment l5(tll&#34;F for l hour: cool to HIST. hold for l hour; air cool ments had been added to the molten iron. The steels We claim:  
 were produced by heating and cooling treatments in the manner indicated in the footnotes to the Table. Test samples for standard metallurgical tests were machined from the bar stock. to determine yield strength (Y.S. and tensile strength (TS) in 1000 lbs./in.=( KSI elongation (EL), area reduction (RA Rockwell scale C hardness (Re). and impact strength (Charpy). The observed values showed that each numbered example possesses the requisite machineability and safety re quired for making high explosive fragmentation munition.  
  Fragmentability of the steel alloys of Examples l to 7 was determined by an objective testing procedure used at US. Army Picatinny Arsenal. Lengths of bar stock were machined into hollow cylinders of 2 inch lengths, l inch diameter. and one-eighth inch wall thickness. Each cylinder was filled with 20 grams of a standard high explosive pentaerythritol tetranitrate (PETN) in rolled sheet form, and an additional 5 grams protruding from one end of the cylinder. After detonation of each cylinder in a recovery tank. the fragments were collected. weighed, automatically counted with an electronic counter. and sieved to segregate the fragments weighing over one-half grain. The results were tabulated in terms of average fragment weight in grains (PI) and number of fragments over one-half grain (N one-half). An N one-half fragmentation value of 400 in this type of test is considered good. The observed N one-half values of Examples l to 7. ranging from 525 (Example 2) to 830 (Example 6) thus range from good to excellent. We ascribe the excellent fragmentation performance of the alloy of Example 6 to the combined effects of a judicious selection of alloying ingredients within the parameters of our invention and the employ- I. In a high explosive fragmentation munition the improvement. comprising a fragmentable shell body made of an alloy steel consisting essentially of the following elements:  
 Weight 71. about:  
 carbon .3 to .7 boron .05 to .5 manganese L25 to 2.0 phosphorus .05 to .2 silicon 0 to 2.5 iron and incidental impurities remainder.  
 Weight 71. about:  
 carbon .3 to .7 boron .05 to .l manganese 1.25 to 2.0 phosphorus .05 to .2 silicon 1.0 to 2.5 iron and incidental impurities remainder.