US 3780465 A
A wear resistant gun barrel and method of producing it is disclosed. The barrel has hardened zones or lands which penetrate into the barrel material between rifling grooves and which are highly resistant to wear from repeated projectile firings. The hardened zones or lands are produced by heating a narrow zone on the outside of the gun barrel with a high intensity heat source, allowing any desired pattern to be melted into the steel. The molten zones, when cool, produce areas having increased hardness. The final step is to machine the gun barrel to the proper inner diameter and engrave rifling grooves between the hardened zones. In the case of large caliber gun barrels the hardened zones are provided in an inner liner which is then shrunk fit into the outer cylinder before the machining step is performed.
Description (OCR text may contain errors)
United States Patent [191 Polcha Dec. 25, 1973 WEAR RESISTANT GUN BARREL AND METHOD OF MAKING THE SAME  Inventor: Raymond J. Polcha, Fredericksburg,
 Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.
 Filed: June 1, 1972  Appl. No.: 258,622
 US. Cl. 42/76 A, 29/].1, 42/76 R, 42/78, 148/152  Int. Cl. F4lc 21/02, B23p 13/00, C21d 1/06  Field of Search 29/].1; 148/152; 42/76 R, 76 A, 78; 89/14 R, 16
 5 References Cited UNITED STATES PATENTS 2,968,723 1/1961 Steigerwald 148/152 Primary Examiner-Benjamin A. Borchelt Assistant Examiner-C. T. Jordan Attorney-R. S. Sciascia et a1.
[ 57] ABSTRACT A wear resistant gun barrel and method of producing it is disclosed. The barrel has hardened zones or lands which penetrate into the barrel material between rifling grooves and which are highly resistant to wear from repeated projectile firings. The hardened zones or lands are produced by heating a narrow zone on the outside of the gun barrel with a high intensity heat source, allowing any desired pattern to be melted into the steel. The molten zones, when cool, produce areas having increased hardness, The final step is to machine the gun barrel to the proper inner diameter and engrave rifling grooves between the hardened zones. In the case of large caliber gun barrels the hardened zones are provided in an inner liner which is then shrunk fit into the outer cylinder before the machining step is performed.
8 Claims, 5 Drawing Figures BACKGROUND OF THE INVENTION The invention relates generally to gun barrels and more specifically to the design and manufacture of gun barrels which have hardened zones penetrating into the barrel material between rifling grooves and which are highly resistant to wear from repeated projectile firings as a result of said zones. Gun barrels of all sizes exhibit wear after several firings. The greater the working pressures of the gun and the higher the muzzle velocity, the greater the wear will be for each projectile rifling. The complete wear phenomenon is not well understood, and many parameters enter into any attempt to characterize it. One fact is clear, however, that in general the harder a surface is, the more it is resistant to wear. While there are certainly instances where making a surface harder may increase its wear rate (under impacts for instance) it is believed that in a gun barrel a harder inside surface is desirable.
To this end, chrome plating is an obvious solution. However, such a solution has disadvantages. Harder materials such as chrome generally have a modulus of elasticity different than that of steel; therefore, as their surface is stressed, strain will occur. The stresses upon firing can become very high and the material may yield and flow plastically.
In addition to chrome plating the prior art has employed both mechanical and electrolytic methods to form rifling in gun barrels. However, these methods of manufacture do not necessarily result in a barrel which has better wear characteristics but are directed generally at the problems associated with the actual methods of manufacture.
SUMMARY OF THE INVENTION The instant invention not only provides a novel method of manufacture but also results in a barrel that is highly resistant to wear from repeated projectile firings. In the method a steel gun tube is mounted on a fixture which will allow a beam of a high energy heat source, such as an electron beam welder, to impinge upon its outer surface at an angle. The fixture allows for simultaneous rotation and translation of the barrel to allow any desired pattern to be melted into the steel as the beam impinges upon it. The heat causes molten zones to form along the barrel surface which from contact with cooler adjacent material results in the formation of a fusion zone. The fusion zone has some iron carbide formation and is harder than the original material. The inside of the barrel is then machined to final diameter size and grooves between the fusion zones are formed either mechanically or by a chemical milling process. Gun barrels fabricated in this manner will have superior wear characteristics to barrels in which the lands are the same strength and hardness as the rest of the tube.
OBJECTS OF THE INVENTION An object of the present invention is the provision of a gun barrel having rifling therein which has superior wear characteristics.
Another object is to provide a gun barrel which has rifling lands that are composed of a harder material than the remainder of the barrel.
A further object of the invention is the provision of a novel method for making such a gun barrel.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a gun tube mounted on an indexing fixture of an electron beam welder;
FIGS. 2, 3 and 4 show a cross-section of the gun tube at various stages during the process of manufacture; and
FIG. 5 shows an alternative use of the gun tube as a liner.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 there is shown a gun tube 10 mounted on an electron beam welding apparatus. The electron beam welder is comprised of an indexing support fixture generally indicated at 14 and an electron beam gun 16. As the gun tube is bombarded with the electron beam energy the zone 12 beneath the beam becomes liquid. The indexing support fixture 14 is comprised of a movable bed 13 and rotatable support 11. The path, which the electron beam is to trace, is determined by moving the indexing support fixture. The support fixture provides translational as well as rotational motion to trace a predetermined path by the electron beam gun 16. The gun tube 10 is moved to achieve a molten zone depth of at least percent of the wall thickness. Upon removal of the beam the liquid zone solidifies becoming cooler as the adjoining regions become warmer. This immediate quenching results in the formation of iron carbide.
A cross-section of the gun tube is shown in FIG. 2, after several passes of the heat source have been made. In general, the thickness of the gun tube 10 will depend upon the working pressure of the gun or, in the case of it being a liner, on the smallest thickness that can be worked with or two to three times the usual rifling tube depth, whichever is larger. The zones deepest tip should be within a few percent of the thickness from the inside wall. The number of zones and the desired thickness after final machining depends on the nature of the projectile and its obturation technique.
The next step of the fabrication consists of machining the inside diameter of the gun tube to a value between 5 and 10 percent smaller than the final intended inner diameter of the barrel. This step will result in a structure as shown in FIG. 3. The gun tube may then be autofrettaged, i.e., pressurized internally until the inner surface yields somewhat and takes on a permanent set, relieved and then honed or ground between zones to achieve a configuration as shown in FIG. 4. Alternatively, if the tube is a liner it may be shrunk fit into the outer cylinder 22 as shown in FIG. 5. In either instance the gun tube will now have compressive stresses at its inner surface. The last step is a final sizing by grinding, reaming, or firing some abrasive projectile through the completed barrel.
It should be pointed out that when more than one or two zones are placed into a thin gun tube, the tube should be allowed to cool down to nearly ambient or room temperature between each successive zone induction. In other instances all zones may be applied simultaneously employing several sources.
The gun tube material should be a high quality steel with a reasonable quantity of carbon to render heat treatment feasible and be easily forged, such as an AlSl 4130 class. Such material has a Rockwell C hardness of 20-30. The application of the instant process to such material produces lands having a Rockwell C hardness of 40-60. It is further pointed out that the internal milling, grinding, or machining would be most readily accomplished with a chemical-milling process to which iron carbide is less sensitive than the normal iron carbon mixture. Additionally, a laser might be substituted for the electron beam welder.
Furthermore, the fusion zones may have other new materials introduced into them while they are molten. Addition of such materials as molybdenum, cobalt or other materials can be easily added in a wire form. This process is accomplished by simply feeding the wire 17 off of a spool (not shown) and allowing it to touch the gun tube at the point where the high energy heat source is melting the tube. The heat source will melt both the new material and the gun tube and mixing will occur naturally, provided that the new material type and quantity is soluble in the steel. From one to three percent by volume molybdenum is soluble in pure gamma iron. Thus, the amount will vary depending upon the initial tube material alloy.
Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.
What is claimed is:
l. A method of producing a gun barrel having hardened zones penetrating into the barrel material between rifling grooves comprising:
applying heat with a high energy heat source to produce a predetermined narrow molten zone on a metal tube; allowing the molten zone to cool and form a fusion zone; and forming rifling grooves between fusion zones. 2. The method of claim 1 wherein the step of applying heat comprises:
attaching the metal tube to a movable indexing support fixture of an electron beam welder; and heating the metal tube with an electron beam gun along the path determined by the indexing support fixture. 3. The method of claim 2 further comprising: moving the metal tube at a speed sufiicient to achieve a molten zone depth of approximately percent of the wall thickness of the tube. 4. The method of claim 1 wherein the step of forming rifling grooves between fusion zones comprises:
machining the inside diameter of the tube to a value 5-10 percent smaller than the final desired inner diameter of the gun tube; pressurizing the tube internally until the inner surface yields and takes on a permanent set; and removing material between fusion zones. 5. The method of claim 4 wherein the step of removing material between fusion zones comprises:
chemically milling the material between fusion zones. 6. The method of claim 2 further comprising: shrink fitting said tube into an outer cylinder before forming said rifling grooves. 7. The method of claim 6 wherein the step of forming rifling grooves between said fusion zones compries:
machining the inside diameter of the tube and chemically milling out the material between fusion zones. 8. The method of claim 1 wherein the step of applying heat further comprises feeding wire composed of a different material than said metal tube into said molten zone at the point where the high energy heat source is melting the tube.