Patent Number: 048141364
Section: summary

CROSS-REFERENCE TO RELATED APPLICATIONS Application Ser. No. 780,342, filed Sept. 26, 1985, describes a process for producing zirconium or hafnium utilizing a precharge of molten salt during reduction of zirconium tetrachloride to metal. The process uses a combination reduction-distillation vessel. The precharge of salt prevents reduction of metal outside the liner, facilitating removal of the liner after the reduction-distillation is completed. Copending application Ser. No. 780,343, filed Sept. 26, 1985, describes a high purity material having 500-1000 ppm of total impurities. Such material might be produced, for example, by the aforementioned process in Ser. No. 780,342 in a combined reduction-distillation vessel. A related process is described in copending application Ser. No. 871,182, Filed June 5, 1986. That related application also produces high purity material, utilizing an electron beam melting step following prebaking of the material and produces a low iron (50-300 ppm) low oxygen (250-350 ppm) for use as a liner material for reactor fuel element cladding. A related process is described in copending application Ser. No. 871,183, filed June 5, 1986, which also produces high purity material for the same uses as the preceding copending application and also uses essentially the same electron beam melting step (broadly at 1-20, but typically at about 4-16 inches per hour), but rather than requiring prebaking, utilizes a vacuum arc melting step after the EB melting to homogenize the material. A related process is describe in copending application No. 030,007, filed Mar. 23, 1987, which produces zirconium with a low iron content, that application utilizes a modified, somewhat lower temperature distillation step (the distillation step, which is after reduction, but prior to melting, removes magnesium chloride and magnesium from the zirconium sponge produced by the reduction). A method for the reduction of the oxygen content in magnesium (which low oxygen content magnesium may in be used in producing low oxygen zirconium), is described in copending application Ser. No. 017,301, filed Feb. 20, 1987. In that application, magnesium, in a molten state is contacted by a solid particulate metal such as zirconium or titanium. When the molten magnesium is separated from the particulate metal, the oxygen content of the magnesium metal has been substantially reduced. In addition, nickel, iron, chromium, and aluminum content of the magnesium may also be reduced. Copending application Ser. No. 111,230 filed 10/22/87 provides an ultra EB melting for liner material, Copending application Ser. No. 111,231 filed 10/22/87 provides an ultra pure alloy of tin and zirconium which provides a ductile, but reliably fabricatible liner material having somewhat better corrosion resistance than unalloyed zirconium, and also believed to give better crack propagation resistance at a reliably fabricatible hardness than any other material. The following copending applications describe various zirconium alloys; Ser. No. 057,715, filed June 1, 1987 as a continuation of now abandoned Ser. No. 709,852, which was filed Mar. 8, 1985 (typically containing 0.1-0.3% Sn, 0.05-0.40% Nb, 0.05-0.20% Fe, 300-1200 ppm oxygen, 0.03-0.1% Ni plus Cr, less than 0.25% Fe plus Cr, with the balance essentially Zr); Ser. No. 589,300, filed Mar. 14, 1984 (typically containing 0.1-0.6% Sn, 0.07-0.24% Fe, 0.05-0.15% Cr, less than 0.05% Ni, with the balance essentially Zr); Ser. No. 709,865, filed Mar. 8, 1985 (typically containing 0.19-0.60% Sn, 0.19-0.50% Fe, 0-0.3% Ni, 100-700 ppm oxygen, with the balance essentially Zr); and Ser. No. 071,588, filed Mar. 8, 1987 (typically containing 0.4-0.6% Sn, 0.5-1.4% Fe, 100-700 ppm oxygen, with the balance essentially Zr). The preceding copending applications are all assigned to the same assignee and are all hereby incorporated by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to zirconium and zirconium alloys, and in particular relates to processes for making purified zirconium for use in liner for reactor cladding. 2. Description of the Related Art In the commercial production of zirconium and hafnium metal, the ore is generally initially subject to a chlorination step which produces a relatively impure, hafnium containing, zirconium tetrachloride and by-product silicon tetrachloride (which by-product is relatively easily separated). The zirconium and hafnium containing material is then subjected to a number of purifying operations and also a complex hafnium separation operation. These operations result in purified oxides of zirconium and hafnium which, of course, are maintained separately. The purified oxides are then separately chlorinated. Zirconium and hafnium are commonly reduced from the chloride by means of a reducing metal (generally magnesium). Excess reducing metal and by-product salt, (e.g. magnesium and magnesium chloride) are removed from the so-called zirconium "sponge" by a distillation step. The zirconium metal is then generally double or triple vacuum arc melted to produce an ingot, which is then further processed (e.g. into zircaloy tubing for reactor fuel element cladding). Ultrapure zirconium has been proposed for a liner for the inside surface of Zircaloy tubing for use as a cladding for reactor fuel, as described in, for example, U.S. Pat. No. 4,372,817 to Armijo et al. on Feb. 8, 1983. A similar use, but with moderate purity material, is proposed in U.S. Pat. No. 4,200,492 to Armijo et al. on Apr. 29, 1980. Ultrapure zirconium has been produced in iodide cells by the so-called "crystal bar" process, (a very expensive process) as discussed, for example, in U.S. Pat. No. 4,368,072 issued to Siddall on Jan. 11, 1983. Material for lining cladding for reactor fuel elements by electron beam (EB) melting is disclosed in Japanese Patent Application No. 1979-144,789 by Kawakita et al., published June 8, 1981. That application discloses utilizing electron beam melting as the final melting, in a quite small laboratory (rather than commercial EB furnace. Commercial reactors generally use either Zircaloy-2 or Zircaloy-4. The history of the development of Zircaloy-2 and Zircaloy-4 is summarized in: Kass, "The Development of the Zircaloys", ASTM Special Technical Publication No. 368 (1964), pages 3-27. Also of interest with respect to Zircaloy development are U.S. Pat. Nos. 2,772,964; 3,097,094; and 3,148,055. Zircaloy-2 is a zirconium alloy having about 1.2-1.7 weight percent (all percentages herein are in weight percent) tin, 0.07-0.20 percent iron, about 0.05-0.15 percent chromium, and about 0.03-0.08 percent nickel. Zircaloy-4 generally contains about 1.2-1.7 percent tin, about 0.18-0.24 percent iron, and about 0.07-0.13 percent chromium. U.S. Pat. No. 4,675,153 is a cladding with a zirconium alloy liner having generally less alloying agent content than its conventional zirconium alloy outer layer (typically 0.2-0.6 Sn, 0.03-0.11 Fe, less than 0.02 Cr, less than 350 ppm oxygen, with the balance essentially Zr) and U.S. Pat. No. 4,613,479 is an example of a niobium zirconium alloy with less than 59% Zr (these two U.S. patents are hereby incorporated by reference). EB (electron beam) melting of materials, including zirconium, has been discussed in a number of patents. EB melting has been used to consolidate crushed particles or chips in so-called hearth furnaces and to separate impurities by either overflowing floating inclusions (U.S. Pat. No. 4,190,404 to Drs et al. on Feb. 26, 1980) or to produce an electrode for arc melting (U.S. Pat. No. 4,108,644 to Walberg et al. on Aug. 22, 1978). A number of U.S. patents have used EB melting of powders or granules, often producing an ingot in a chilled mold. These powder melting EB patents include U.S. Pat. Nos. 2,942,098 to Smith on June 21, 1960; 2,960,331 to Hanks on Nov. 15, 1960; 0 to Hanks et al. on Dec. 6, 1960; 2,997,760 to Hanks et al. on Aug. 29, 1961; 2,935,395 to Smith on May 3, 1960; and 4,482,376 to Tarasescu et al. on Nov. 13, 1984. Electron beam zone refining using multiple passes is described in U.S. Pat. No. 3,615,345 to King on Oct. 26, 1971. EB melting using a consumable feed "electrode" to produce an ingot collected in a chilled mold has also been discussed in a number of patents, including U.S. Pat. Nos. 3,087,211 to Howe on Apr. 30, 1963; 3,226,223 to Bussard et al. on Dec. 28, 1965; 2,880,483 to Hanks et al. on Apr. 7, 1959; and 4,130,416 to Zaboronok et al. on Dec. 19, 1978. U.S. Pat. No. 3,219,435 to Gruber et al. on Nov. 23, 1965 shows a commercial type EB furnace utilizing multiple beams. Typically the beams are directed to the surface of the molten pool and are continually swept across the pool surface to avoid overheating of any single portion of the pool surface. U.S. Pat. No. 3,091,525 to D'A. Hunt on May 28, 1963 describes adding a small amount of zirconium, for example, to hafnium, for example and melting in an EB furnace to deoxidize the hafnium. SUMMARY OF THE INVENTION This is a process for making an alloyed liner material for reactor fuel element cladding. This invention provides for significant reduction of metallic impurity content and produces a more consistent product due to reduced solid solution strengthening and second phase formation. The alloyed liner has significantly improved corrosion resistance, but with higher ductility than other zirconium alloys. The process utilizes electron beam melting of sponge zirconium, to reduce metallic impurities (especially aluminum, and in some cases iron) and is apparently the first EB melting of an alloy liner. The electron beam melted zirconium is then alloyed in a vacuum arc furnace by means of an alloying charge. The alloying charge comprises 0.1-2.0 weight percent of at least one alloying element selected from the group consisting of tin and iron. In some embodiments, the alloying charge also contains 0.02-1.0 weight percent of an additional alloying agent or element selected from the group consisting of niobium, chromium, molybdenum, copper and combinations thereof. Thus generally the alloying charge consists of 0.1-2.0 percent tin and/or iron and 0.02-1.0 percent of niobium, chromium, molybdenum and/or copper.