A method for manufacturing a zirconium alloy tubular product

Abstract

The present invention relates to a method for manufacturing a zirconium alloy tubular product that can be used as a water-cooled nuclear reactor housing product. A method for manufacturing a tubular product from a zirconium alloy, which contains a mass percentage of: niobium 0.9-1.7; iron 0.10-0.20; oxygen 0.10-0.20; silicon less than 0.02, carbon less than 0.02, and a basis of zirconium alloy. The method includes melting an ingot by repeated vacuum arc remelting, machining the ingot, heating, hot multi-stage forging to obtain a forging, and heat treating the forging. The method also includes subsequently machining the forging to obtain a tube blank and performing vacuum heat treatment, applying a protective coating to it and heating it to a hot pressing temperature, hot pressing, removing the protective coating, and vacuum heat treatment. The method also includes multiple cold rolling, each rolling with a total deformation of 58-74%, a tube coefficient Q=1.18-2.01, and performing intermediate vacuum heat treatment to produce a tubular product. The final vacuum heat treatment is performed at the final size, followed by a finishing operation. The technical result is improved processing properties of materials used to manufacture piping products at various stages of hot and cold press processing, as well as high corrosion resistance of piping products with stable mechanical properties and resistance to shape changes.

Description

Technical Field

[0001] The present invention relates to the field of nuclear engineering, and in particular to a method for manufacturing a pipe product from a zirconium alloy (used for a water-cooled nuclear reactor, in particular a shell tube and a channel tube of a VVER type reactor). Background Art

[0002] Zirconium alloys are used as materials for structural elements of power nuclear reactors due to their unique characteristics: small cross section for thermal neutron absorption, corrosion resistance in high temperature water and water vapor, resistance to oxidation and hydrogenation, small radiation growth and other physical and mechanical properties. The properties of the tubular product depend on the chemical composition and each process operation, starting from ingot melting and ending with finishing.

[0003] There is known a "Method for producing a tubular product from a zirconium alloy (variant)" (RU 2123065S1 publ. 12.03.1997, CL C22R / 1 / 18) which comprises cold rolling of a starting billet for a binary zirconium alloy, obtaining a tube billet, intermediate and final annealing of the tube billet.

[0004] The disadvantage of this method is that no protective coating is applied to the workpiece before hot extrusion, which leads to metal oxidation during the manufacturing process and reduces the manufacturability of the pipe product. In addition, there is no final finishing operation to remove the residual technical contamination on the surface of the pipe product, reduce the surface roughness, and thus reduce the corrosion resistance of the product.

[0005] In the technical field, a "method for producing products from zirconium alloys" is known (RU 2110600S1 publ. May 10, 1998, CL. C22F / 1 / 18). First, an initial blank is obtained from an ingot by hot forming. Then, using hot forming, an intermediate blank is obtained. Then there is quenched and tempered cut-to-size blanks, tempering before hot forming and cold rolling, cold rolling.

[0006] The disadvantage of this method is that the protective coating is not applied to the ingot before hot extrusion. This leads to metal oxidation during the extrusion process, which reduces the manufacturability of the pipe product. There is also no final finishing operation to remove residual technological contamination from the surface of the pipe product. Machining operations reduce surface roughness, thereby reducing the corrosion resistance of the product.

[0007] The closest method to the claimed protection is "Zirconium alloy with increased corrosion resistance for fuel rod shells and production method thereof" (US2016 / 0307651A1publ.20 / 10 / 2016, CL G21S3 / 07, B22D 21 / 00, B22D 7 / 00, S22S16 / 00, S22F 1 / 18). The method shows the composition of the corrosion-resistant zirconium alloy and the method of manufacturing fuel rod shells from it. The process includes melting steel ingots, coating the steel ingots with protective steel sleeves, heat treating the steel ingots with sleeves before hot rolling, hot rolling, removing the protective steel coating, heat treatment of hot rolled tube blanks, three cold rolling processes, intermediate heat treatment after each rolling, and finishing heat treatment.

[0008] The main disadvantage of this method is the small development of the cold-rolled material, with a total deformation of up to 60% per pass, which leads to an incomplete elimination of the inhomogeneous hot-rolled structure. In addition, the disadvantage of this method is the use of steel sleeves containing carbon, which interact with the zirconium alloy at hot rolling temperatures, possibly forming carbides. The degree of recrystallization of the material is an important factor determining the shape change resistance characteristics of zirconium alloys (resistance to heat, radiation-thermal creep and radiation growth).

[0009] Intermediate annealing at low temperatures (first pass from 570°C to 590°C, second pass from 560°C to 580°C, third pass from 560°C to 580°C) manufactured with the selected deformation scheme (30-40% deformation in the first and third stages, 50-60% in the second stage of cold deformation) is not enough to relax the residual stresses and complete the recrystallization process. This has a negative impact not only on the technological properties of the material, but also on its resistance to shape changes, including under the influence of radiation. The use of three levels of long-term finish annealing (first level from 460°C to 470°C, second level from 510°C to 520°C, third level from 580°C to 590°C) allows to increase the strength of the material. At the same time, the deterioration of the resistance to shape changes is mainly due to the incompleteness of the recrystallization process. This technical solution does not provide for finishing operations that enable the removal of residual technological contamination from the surface of the pipe product and reduce surface roughness, which reduces the corrosion resistance of the product. Summary of the invention

[0010] The object of the present invention is to develop a method for producing tubular products of various diameters from zirconium alloys for use as shell tubes in water-cooled nuclear reactors.

[0011] The technological result is an improvement in the technical characteristics of the material at all stages of hot and cold pressure treatment (used to manufacture pipe products). This creates highly corrosion resistant pipe products with stable mechanical properties and anti-forming characteristics.

[0012] The technical result is achieved as follows. A method for manufacturing pipe products from zirconium alloys (containing mass percentage %: niobium - 0.9-1.7 mass percent; iron - 0.10-0.20 mass percent; oxygen - 0.10-0.20 mass percent; silicon - less than 0.02 mass percent; carbon - less than 0.02 mass percent; zirconium - the rest). The method includes melting an ingot by repeated vacuum arc remelting, machining the ingot, heating, hot multi-stage forging to obtain a forging, and heat treating the forging. The method also includes subsequent machining of the forging, obtaining a tube blank and performing vacuum heat treatment, applying a protective coating to it and heating it to a hot pressing temperature, hot pressing, removing the protective coating, and vacuum heat treatment. It also allows multiple cold rolling, with a total deformation of 58-74% and a tube coefficient Q = 1.18-2.01, with intermediate vacuum heat treatment to produce a pipe product. The final vacuum heat treatment is carried out at the final size, followed by a finishing operation.

[0013] The hot multi-stage forging of the ingot is carried out at a temperature of 980°C to 700°C, with a total deformation degree of up to 93%, and the intermediate preheating is carried out at a temperature of 850°C to 800°C.

[0014] Heat treatment of forgings is carried out at a temperature of 1050°C to 1100°C, followed by cooling in water.

[0015] The tube blank is obtained by drilling, then the axial center hole is bored in the forging and cut to measured length.

[0016] Before hot pressing, the tube blank is vacuum heat treated at a temperature of 570°C to 600°C.

[0017] The hot pressing of the tube blank was carried out at a temperature ranging from 600°C to 620°C and an elongation ratio μ=8.9.

[0018] The tube blank after hot pressing is vacuum heat treated at a temperature of 565°C to 595°C.

[0019] The intermediate vacuum heat treatment of the pipe products is carried out at a temperature of 565°C to 595°C.

[0020] Vacuum heat treatment of tube billets and products is 1*10 -4 -1*10 -5 The residual pressure in the furnace was 1.5 mmHg.

[0021] When the pipe product reaches its final size, its surface is treated chemically and mechanically.

[0022] The selected proportions of alloying components in zirconium alloys provide technical properties, corrosion resistance, stable characteristics of mechanical properties and resistance to forming of pipe products.

[0023] The advantage of obtaining a tubular product according to the claimed method is that hot forging and hot pressing ensure uniform machining of the cast structure along the length and cross-section of the ingot. The use of a copper protective coating provides protection against gas saturation and eliminates diffusion interactions of the coating and the workpiece. Cold rolling with intermediate heat treatment provides a tubular product with a uniform recrystallized structure having high mechanical properties, as well as the desired anisotropic properties in the transverse and longitudinal directions. The finishing operation provides a roughness of less than Ka = 0.8 microns on the outer and inner surfaces, which increases the stability of the corrosion properties. The roughness of the inner surface makes it possible to improve the process flow of loading fuel particles into the pipe product. DETAILED DESCRIPTION

[0024] The method for implementing the present invention is as follows:

[0025] Example

[0026] According to the claimed technical solution, the technology of zirconium pipe products includes the following operations: the composition of the smelted alloy ingot is as follows: niobium - 1.00-1.03 mass percent, iron - 0.116-0.119 mass percent, oxygen - 0.120-0.125 mass percent, silicon - 0.002-0.003 mass percent, carbon - 0.003-0.005 mass percent, and the rest is zirconium.

[0027] The initial alloy components are mixed with zirconium magnetocaloric sponge and then formed into consumable electrodes, which are remelted by triple vacuum arc remelting. The ingot is machined. The ingot is heated to a temperature of 930°C to 980°C in a resistance furnace. Multi-stage forging of the heated ingot is carried out in a temperature range of 980°C to 700°C, with intermediate preheating in a resistance furnace in the temperature range of 850°C to 800°C. During the hot deformation treatment of the ingot, the total deformation rate is as high as 93%. Forging is heating to a temperature of 1050°C to 1100°C, followed by cooling in water.

[0028] The forgings are cut to measured lengths and machined to a diameter of 109x28.5mm, then the axial center hole is drilled and subsequently bored. This is how the tube blank is obtained.

[0029] Vacuum heat treatment is carried out at a temperature of 570°C to 600°C. The surface roughness of the workpiece does not exceed Ra = 2.5 microns. Next, a copper coating is applied to the tube to prevent gas saturation during the subsequent heating and hot pressing process. The heating of the tube for hot pressing is carried out in an induction furnace. The heating temperature of the tube before hot pressing ranges from 600°C to 620°C.

[0030] The pressing is carried out with an elongation ratio μ = 8.9. The copper coating is then removed and vacuum heat treatment is carried out at a temperature of 565°C to 595°C. The tube billet is rolled on a cold rolling mill for HPT, 2HPTS, KPW type pipes, 4 passes, with a total deformation ∑ε from 58 to 74%, while the pipe coefficient Q is in the range of 1.18-2.01. The intermediate heat treatment is carried out in a vacuum at a temperature range of 565°C to 595°C, and the residual pressure in the furnace is not higher than 1*10 -4 -1*10 -5 mm Hg.

[0031] After the final vacuum heat treatment at a temperature of 565°C to 595°C, the pipe products are subjected to intermittent or spray etching, inner surface grinding treatment, outer surface grinding and polishing.

[0032] Industrial Applicability A tube product made of a zirconium alloy, manufactured according to the claimed technical solution, is characterized by having the following properties (Table 1).

[0033] Therefore, the proposed pipe manufacturing method allows to obtain a highly corrosion-resistant pipe product with stable mechanical properties and resistance to shape changes.

[0034]

Claims

1. A method for manufacturing a tubular product from a zirconium alloy, wherein the weight percentages are: niobium - 0.9-1.7; iron - 0.10-0.20; oxygen - 0.10-0.20; silicon - less than 0.02, carbon - less than 0.02, and zirconium as the remainder, the method comprising: Multi-stage vacuum arc remelting ingot melting, Ingot machining, heating, Multi-stage forging to produce forgings, heat treatment of forgings; the method also includes Subsequent machining of forgings to produce tube blanks, Vacuum heat treatment, Applying copper coating on the tube to prevent gas saturation during heating and hot pressing, The tube blank is heated to a hot pressing temperature; the method also includes Heat pressing, Removal of copper coating, Vacuum heat treatment, Multiple cold rolling, total deformation degree is 58-74%, pipeline coefficient = 1.18-2.01, intermediate vacuum heat treatment produces pipeline products, and final vacuum heat treatment is carried out at the final size, followed by finishing operations.

2. The method according to claim 1, characterized in that: The multi-stage forging of the ingot is carried out at a temperature of 980°C to 700°C with a total deformation of up to 93%, and intermediate preheating at a temperature of 850°C to 800°C.

3. The method according to claim 1, characterized in that Heat treatment of forgings is carried out at a temperature of 1050°C to 1100°C, followed by cooling in water.

4. The method according to claim 1, characterized in that: The tube blank is cut to measured length, drilled, then bored and forged with an axial center hole.

5. The method according to claim 1, characterized in that The vacuum heat treatment of the tube blank before hot pressing is carried out at a temperature of 570°C to 600°C.

6. The method according to claim 1, characterized in that Hot pressing of the tube blank is performed at a temperature of 600° C. to 620° C., and an elongation μ=8.

9.

7. The method according to claim 1, characterized in that The vacuum heat treatment of the hot-pressed tube blank is carried out at a temperature of 565°C to 595°C.

8. The method according to claim 1, characterized in that: The intermediate vacuum heat treatment of the tube product between the multiple cold rolling processes and the final vacuum heat treatment is carried out at a temperature of 565°C to 595°C.

9. The method according to claim 5, 7 or 8, characterized in that: The residual pressure in the furnace is 1*10 -4 -1*10 -5 The tube blank and product are vacuum heat treated at 3700 mmHg.

10. The method according to claim 1, characterized in that When the pipe product reaches its final size, its surface is treated chemically and mechanically.

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