Patent Application
20100003162
Process for the production of forged steel for weapons subject to heavy stresses, barrel blanks and a weapon equipped therewith
The invention relates to a process for the production of gun barrel blanks for machine guns in the caliber. range, in particular, of 25-50 mm.
Standard materials for machine guns subject to such heavy loading are heat-resistant CrMoV-alloyed heat-treated steels, such as the steel 32 CrMoV 12-10, material No. 1.7765 in accordance with “Stahl-Eisen-Liste” (Steel/iron list) (Verlag Stahleisen, Dusseldorf) for 30 mm machine guns, which has been customary to date. This material satisfies the demands for high yield strength (min. 950 N/mm2) together with a high heat resistance up to 4500 (min. 550 N/mm2) to achieve a sufficiently long service life of the barrels.
In the context of improving performance, improving quality and increasing the standard of safety, even more stringent demands are being placed on the material and on the quality of the forged blank. These result from the features of development such as increased gas pressure loading by new munitions concepts, the inducing of residual stresses by hydraulically expanding the inner wall of the barrel in order to increase the fatigue strength, more stringent demands on the aiming accuracy as a result of increased muzzle velocities of the new munitions, the ability of the chromium layer to be readily chromium-plated and to be durable during firing, and an increased potential to protect against brittle fracture in the temperature range of −50 to +80° C.
Although the steel used, grade 32 CrMoV 12-10, has a sufficient potential for satisfying the demands regarding strength which are made, for example, on a new 30 mm machine gun, it fails to achieve the targets regarding the required degree of toughness. Further inadequacies of the conventional material include the low degree of purity in the case of open melting and the pronounced tendency of the barrel to distort owing to directional loading during firing.
DE 101 11 304 C2 discloses a process for the production of barrels for heavy cannons. The heat-treated steel produced in different compositions is hardened and tempered, subsequently bored and then finished. The result of this is that a maximum degree of straightness is achieved, and the quality of the barrels produced in this way is superior to that of conventionally straightened barrels. It is known, however, that different demands are placed on large caliber blanks than on medium caliber blanks. Medium caliber weapons are exposed to a higher firing rate than large caliber weapons.
On the basis of this process, the object of the invention is to specify a process for the production of barrels in the medium caliber range with a relatively high firing rate and also a corresponding barrel which satisfies even the latest demands.
This object is achieved by the features of claims 1, 7 and 10. Advantageous refinements are specified in the dependent claims.
The invention is based on the concept, in a manner similar to the barrels in the large caliber range, of providing a change of the barrel material as well as its constituent proportions and also a production process which is already known from the large caliber barrel but is specially adapted to medium caliber barrels. Although it must be taken into account that a barrel for medium caliber use is exposed to higher permanent loading during functional use than is known for large caliber use, an additional requirement in further considerations of these medium caliber weapons is that the so-called opening shot of a medium caliber or rapid-fire weapon should, in practice, produce the required hit accuracy. When selecting the barrel material, it should therefore also be taken into account that the weapon barrel is to be designed both for single rounds and for a high firing rate. It is correspondingly proposed that the novel material concept coming into effect should be developed on the basis of an electroslag remelted NiCrMoV steel which has been heat treated in a suspending/rotating manner, which therefore even largely corresponds to the steel 35NiCrMoV 12-5, material No. 1.6959 which is known for large caliber weapons. To date, this steel has not been used for high-firing rate machine guns owing, in particular, to the stringent demands regarding heat resistance which are placed on the barrel.
In practice, it has also been shown that this steel, in modified form, corresponds to the required degrees of heat resistance in conjunction with increased resistance to heat treatment. At the same time, the martensitic microstructure of this novel NiCrMoV steel means that it has a considerably increased toughness potential compared to the bainitic CrMoV steel. The safety requirements demanded can be met down to temperatures as low as −50° C. owing to the high degree of toughness.
The barrel produced by the novel process is distinguished in that a higher yield strength is achieved (approx. 1050 N/mm2). Furthermore, the barrel has a sufficiently high notched impact strength and fracture toughness down to −50° C. and has a sufficiently high heat resistance up to +50° C. The high degree of purity (K0 value max. approx. 12) is a further advantage. The production of the gun barrel blank takes place without residual straightening stresses, i.e. the heat treatment takes place without subsequent straightening operation.
A process for the production of gun barrel blanks for machine guns in the preferred caliber range of between 25-50 mm is distinguished by the following composition:
max. 0.60% silicon
max. 1.00% manganese
max. 0.010% phosphorus
max. 0.010% sulfur
1.00-1.40% chromium
2.00-4.00% nickel
0.30-0.70% molybdenum
0.10-0.30% vanadium
max. 0.05% aluminum and
remainder iron and conventional (unavoidable) impurities,
wherein the blanks are produced from remelted steel or from steel which is melted in the open and has a high degree of purity.
The following composition of the heat-treated steel has proved to be preferred:
0.30-0.35% carbon
max. 0.40% silicon
0.4-0.70% manganese
max. 0.005% phosphorus
max. 0.005% sulfur
1.00-1.40% chromium
2.50-3.3% nickel
0.50-0.60% molybdenum
0.10-0.20% vanadium
max. 0.03% aluminum and
remainder iron and conventional impurities.
In order to ensure that the high demands placed on the degree of purity are met, the steel is preferably remelted in the cast state using the ESR (electroslag remelting) process. The high homogeneity of the microstructure which is associated therewith (as a result of improved segregation) is the basis for the low-distortion heat treatment which is carried out in the vertical dipping direction by means of oil or water cooling. The blanks which are forged as a bar are tempered in this process by means of the vertical liquid heat-treating process to yield strengths of >1000 N/mm2. During the heat treatment, the bars permanently rotate about their axis or are permanently turned mechanically about their axis. Machining takes place without prior straightening operation.
In addition, the novel steel for a medium caliber barrel makes it possible to achieve improved autofrettage (the barrel becomes more heat-resistant—up to 500° C.). The barrel itself is thereby able to more efficiently absorb residual stresses, which means that the ability of the barrel to absorb pressure is increased.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 025 241.1 | May 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/004443 | 5/18/2007 | WO | 00 | 12/1/2008 |
