FRANGIBLE TUNGSTEN PENETRATOR

Abstract: A material consisting essentially of tungsten having from about 5 to about 20 grains per square millimeter and a hardness on the Rockwell C scale from about 31, to about 35 is suited for armor penetration.

Description: The invention relates to a penetrator for armour and, in particular, to a specific tungsten material having the proper degree of frangibility and hardness to enable it to be used in armour penetrators. Penetrators for armour piercing applications have in the past been prepared from materials that have the desired strength and density to penetrate armour. From US-A-3,791,881 there is known a penetrator for armour piercing applications which have a fore-part (portion that actually strikes the target) which is hard and strong and which has a casing which follows the fore-part which is formed of material which breaks up into relatively large fragments in order that the fragments have some armour piercing capability themselves. The subject matter of the afore-mentioned US patent specification is a method for treating a steel warhead casing to cause said casing to produce fragments having a desirable average weight, said method comprising the steps of austenitizing said casing; oil-quenching said casing and then air-cooling to room temperature; reheating said casing and again air-cooling same to room temperature. The afore-mentioned US Patent refers, however, to a steel casing only and does not disclose any materials of suitable frangibility and hardness to be used in armour penetrators. It is, therefore, an object of the present invention to provide a penetrator for armour which essentially does not consist of iron and steel. Furthermore, the present invention intends to provide a process for the producing of the inventive penetrator. According to the present invention, the penetrator consists of a body of tungsten having from 5 to 20 grains per square millimeter and a hardness of from 31 to 35 on the Rockwell C hardness scale. The inventive process for producing the frangible tungsten penetrator of the invention is indicated in claim 3. A suitable material for armour piercing applications should not be too strong in order to avoid that either no particles or merely a small number of particles will be formed, thus creating only local damage. If, however, the material breaks into very fine particles, the resulting particles will not penetrate and do little or no damage. Some materials in the past have been tungsten alloys with minor amounts of iron, nickel or copper. While these materials have the strength and density to allow penetration of armour when fired from a conventional weapon such as an antitank gun, they do not possess the desired frangibility characteristics to enable them to break apart upon impact to form particles in the desired size range. For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above description of some of the aspects of the invention. The above desirable properties are achieved in one aspect of this invention which consists of a tungsten material having from 5 to 20 grains per square millimeter of cross-section area and a hardness, as measured on the Rockwell C hardness scale, of from 31 to 35. These materials are prepared by a process wherein conventional tungsten metal powder is pressed into a bar of a predetermined size using conventional power metallurgy procedures. The bar is presintered at a temperature of from 1100°C to 1300°C for about 10 minutes and thereafter sintered at a temperature of from 2700°C to 2900°C for a time sufficient to achieve a density of from 17.3 g/cm³ to 18.1 g/cm³. Usually about 1 hour is sufficient to achieve the desired density. After the foregoing density is achieved the bar is elongated sufficiently to achieve from about 30% to about 40% reduction in cross section. Conventional swaging is the preferred method of elongation. A typical bar prior to elongation has a length of about 90 cm and a cross-sectional area of 650 mm². The material is machined to the desired penetrator shape. After machining the material is annealed at a temperature of from 1700°C to 1900°C to achieve a material containing from 5 to 20 grains per square millimeter and a hardness measured on the Rockwell C scale from 30 to 35. In some armour penetrators it is desired to have a tracer cavity in a rear portion of the penetrator. If the portion containing the cavity for the tracer is annealed and recrystallized there can be premature cracking. In the instance where the cavity is desired, the annealing can be done on the body and nose portion while leaving the rear portion unannealed and unrecrystallized thus enabling the cavity for the tracer to be machined into the rear portion. Induction heating is the preferred method of annealing in such instances. In most instances the unannealed portion will extend from 10% to 35% of the total length, with from about 15% to 25% of the total length being preferred. The following detailed examples are presented to show the effectiveness of the present invention. Example I An ingot produced from conventional tungsten powder having near theoretical density is swaged to a rod having a diameter of about 18.4 mm and a penetrator is machined from the rod. The material has a fine grain structure having over 1000 grains per square millimeter. The hardness on a Rockwell C hardness ranges from about 35 to about 43 depending upon the point of measurement. The penetrator did not have the degree of frangibility desired and would not break apart into small particles. Example II A conventional M25 tungsten powder with 0.25% nickel addition is pressed into a blank. The blank is sintered at about 1550°C to achieve a density of about 94% of theoretical. The Rockwell C hardnees ranged from about 24.8 to about 30.6 depending upon the point of measurement. The penetrator machined from the blank failed before it got out of the barrel because of its extreme brittleness. Example III A penetrator prepared as in Example I is annealed at about 1800°C for about 10 hours to give a recrystallized structure containing from about 5 to about 20 grains per square millimeter of cross section. The Rockwell C hardness ranges from about 30 to about 34 depending upon the point of measurement. Excellent results are obtained when fired against a 28.6 cm aluminum plate. Penetration is achieved and the penetrator breaks into individual grains. Example IV The procedure given in Example III is followed except the rear portion constituting about 20% of the total length is not annealed and left in an uncrystallized state. The small tracer cavity is machined into the rear portion of the penetrator. Substantially similar results to those obtained with the penetrator of Example III are achieved.

Claims: 1. A penetrator for armour consisting of a body of tungsten having from 5 to 20 grains per square millimeter and a hardness of from 31 to 35 on the Rockwell C hardness scale. 2. A penetrator according to Claim 1 wherein a rear portion constituting from 10% to 35% of the total length is in an unannealed and unrecrystallized state. 3. A process for producing a penetrator for armour as defined in Claim 1 comprising: a) pressing tungsten powder having an average grain size of from 1 to 25 microns to form a bar of a predetermined cross-sectional area, b) sintering said bar in a non-oxidizing atmosphere at a temperature of from 2700°C to 2900°C for a sufficient time to attain a density in said bar of from 17.3 g/cm³ to 18.1 g/cm³, c) elongating said bar to achieve 30% to 40% reduction in cross-sectional area, d) machining the resulting bar to form penetrators of predetermined shape, and e) annealing at least a portion of said penetrator at a temperature of from 1700°C to 1900°C for a sufficient time to achieve a material having from 5 to 20 grains per square millimeter, and a hardness measuring from 31 to 35 on the Rockwell C hardness scale. 4. A process according to Claim 3 wherein all of said penetrator is annealed. 5. A process according to Claim 3 wherein a rear portion of the armour penetrator constituting from 10% to 35% of the armour penetrator's total length remains unannealed.

Inventors: KEGEL, ANDREW JOHN, MULLENDORE, JAMES ALAN, REIMAN, SCOTT KENWORTHY
Applicants: GTE PRODUCTS CORPORATION
Application year: 1982
Main classification: F42B12
IPC codes: C22F1, B22F3, F42B12, C22C1