RU2351671C2 - Titanium alloy for pipelines and pipe systems of heat-exchange equipment for nuclear power - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy of titanium alloys, containing in the capacity of basis titanium with defined relation of alloying and impurity elements, and provided for using in ship and power machine building while production of pipelines and welded pipe systems, satisfying a requirement of commercial operation and radiation-ecological safety of up-to-date marine and reactor equipment. Invention is directed to creation of high-tech welded alloy, allowing improved complex of main physical-mechanical and service properties, low corrosion-fatigue cracking, and also higher deformation capacity in comparison with well-known materials in conditions of reactor irradiation and long-term exposure of corrosion-active mediums. Alloy contains, wt %: aluminium 1.8-2.5; zirconium 2.0-3.0; silicon 0.05-0.12; iron 0.15-0.25; oxygen 0.03-0.10; carbon 0.03-0.08; nitrogen 0.01-0.04; hydrogen 0.001-0.006; tin 0.005-0.01; cerium 0.003-0.008; titanium - the rest. Additionally total content of carbon and nitrogen shouldn't exceed 0.10 wt %, and relation of Zr/(C+N) must be no less than 30.

EFFECT: increasing of maintainability and total service life of pipe systems of direct-flow steam generator and ganged capacitor steam-raising unit of stationary and transport atomic power plant.

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Description

The invention relates to the metallurgy of titanium alloys containing titanium with a predetermined ratio of alloying and impurity elements, and is intended for use in ship and power engineering in the production of pipelines and welded pipe systems that meet the requirements of industrial operation and radiation and environmental safety of modern ship and reactor equipment.

Known structural titanium materials used in engineering industries (for example, titanium alloys such as VT, OT and PT, as well as other analogues), specified in state and industry standards, as well as in the scientific and technical literature [1-8]. However, in some cases, well-known alloys do not provide the required level and stability of the basic physical, mechanical and service characteristics, which reduces the operability and operational reliability of the heat exchange equipment used and does not meet the requirements for nuclear power facilities for their safe operation for a given service life.

Closest to the claimed composition in terms of its basic composition and functional purpose is the PT-7M titanium alloy according to GOST 19807 [1], which contains alloying and impurity elements in the following ratio, in wt.%:

aluminum 1.8-2.5 zirconium 2.0-3.0 silicon ≤0.12 iron ≤0.25 oxygen ≤0.15 carbon ≤0.10 nitrogen ≤0.04 hydrogen ≤0.006 titanium the basis

The well-known titanium alloy is characterized by increased sensitivity to corrosion-fatigue fracture and pitting formation under the conditions of pipe systems of the steam generator of ship installations with a high content of chlorides in water and aqueous solutions.

However, the known alloy has reduced plastic properties after neutron irradiation.

The technical result of the present invention is the creation of a titanium alloy having a higher resistance to corrosion-fatigue destruction and pitting, as well as having higher ductility after neutron irradiation.

The technical result is achieved due to the fact that the composition of the known alloy containing aluminum, zirconium, silicon, iron, oxygen, carbon, nitrogen, hydrogen and titanium, additionally introduced tin and cerium in the following ratio of components, in wt.%:

aluminum 1.8-2.5 zirconium 2.0-3.0 silicon 0.05-0.12 iron 0.15-0.25 oxygen 0.03-0.10 carbon 0.03-0.08 nitrogen 0.01-0.04 hydrogen 0.001-0.006 tin 0.005-0.01 cerium 0.003-0.008 titanium rest

In this case, the total carbon and nitrogen content should not exceed 0.10%, and the Zr / (C + N) ratio should be at least 30.

The ratio of these alloying and impurity elements is chosen so that the claimed composition ensures the formation of the most optimal structural state, the required level and stability of the most important structurally sensitive characteristics of the material, which largely determine the corrosion-mechanical strength and specified performance, as well as the operational reliability of the heat exchange equipment of the reactor installation.

The introduction of the inventive alloy of microalloying and modifying additives of tin and cerium in the indicated ratio with other alloying elements and, first of all, with aluminum and zirconium improves its structural stability and, as a result, the whole complex of basic physical, mechanical and service properties that positively affect a decrease in the sensitivity of the base metal, weld metal, and the heat affected zone of thin-walled pipe products to corrosion-fatigue failure during long-term operation, as well as yshaet job generation and development of intergranular cracks under static and cyclic loading. Moreover, as the research results showed, a more uniform distribution of alloying elements and excess phases occurs over the entire cross section of semi-finished products and pipe billets, the metal is more effectively cleaned of harmful impurities and gases, the formation of a fine-grained structure with an equiaxed grain shape is more active, the boundaries become thinner and cleaner grain, the intercrystalline bond strength increases, which in general provides a significant increase in the ductility and viscosity of both the base metal and welded joints. The tendency of the alloy to structural anisotropy is noticeably reduced and its manufacturability at the metallurgical redistribution stage is significantly improved, which increases the yield of industrial sheet metal and pipe products, as well as other thin-walled semi-finished products with a complex profile. The introduction of tin and cerium outside the limits specified in the claims reduces the effectiveness of their positive influence and does not lead to a noticeable improvement in these structurally sensitive characteristics of the working capacity of the material during the long-term operation of heat-exchange reactor equipment of a steam generating plant.

Quantitative modification of the alloy by the ratio of zirconium as an active carbide and nitrode forming element to the total content (C + N) improves the structural stability of the weld metal and the heat-affected zone, promotes the formation of fine carbide and nitride phases that are thermodynamically stable at temperatures under appropriate heat treatment technological and welding heatings, which increases the resistance of the base metal and welded joints to brittle fracture in difficult conditions amicheskogo impact loading and corrosive environments. At the same time, a higher level of plastic characteristics and deformation ability of the alloy than in the prototype is achieved by forming stable dislocation structures, which largely determine the optimal density of active slip planes during plastic deformation. As already noted, the limitation of the Zr / (C + N) ratio promotes the formation of a balanced content of highly dispersed zirconium carbonitrides and increases the tempering resistance of the weld metal and the heat affected zone while maintaining the required level of strength and plastic characteristics of the alloy.

Fractographic analysis of the surface of the fractures of the samples by scanning electron microscopy showed that in the inventive alloy the proportion of the viscous component in the fracture zone of the metal after corrosion-fatigue fracture in hydrogen-containing media significantly increases compared with the known composition. Failure to observe the ratio of zirconium to interstitial impurities indicated in the claims reduces the dispersion of the interstitial phases formed and complicates the uniformity of their distribution over the grain volume, which changes and weakens the dislocation fixing mechanism during subsequent technological heating of long and pipe products and negatively affects the deformation ability of the metal during long operation.

The obtained higher level of physicomechanical, welding-technological and service characteristics of the alloy is ensured by complex modification of the claimed composition in the indicated ratio with other elements, balanced chemical and phase composition, normalized content of introduced microalloying and modifying additives, as well as control of metal purity by residual harmful impurities .

In CRI KM “Prometey”, together with other industry enterprises, in accordance with the plan of ongoing research and development within the framework of the federal target program “National Technological Base”, the necessary set of laboratory, design and experimental-industrial work on smelting, plastic and heat treatment of the created brand has been performed alloy. The metal was smelted in vacuum skull ovens with a magnetically controlled arc, followed by processing on forge-and-press equipment to obtain semi-finished products of the required range.

The chemical composition of the materials studied, as well as the results of determining the most important physical and mechanical properties and characteristics, are presented in Tables 1 and 2.

The expected technical and economic effect of the use of the developed titanium alloy in machine-building industries and the national economy will be expressed in increasing the overall service life and operational reliability, as well as the environmental safety of using thin-walled pipelines and pipe systems of a wide range of heat transfer equipment of modern nuclear power reactor plants by reducing the propensity of the alloy to corrosion-fatigue fracture, pitting and higher plastic properties after neutron irradiation in comparison with the prototype.

Table 1
CHEMICAL COMPOSITION OF RESEARCHED MATERIALS Structure Conventional composition number The content of elements, wt.% Al Zr Si Fe ABOUT FROM N N Sn Xie (C + N) Zr / (C + N) The claimed one 1.8 2.0 0.05 0.15 0,07 0,03 0.01 0.001 0.005 0.003 0.04 50,0 2 2.2 2.7 0.08 0.20 0,03 0.05 0.04 0.004 0.008 0.005 0.09 30,0 3 2.5 3.0 0.12 0.25 0.10 0.08 0.02 0.006 0.01 0.008 0.10 30,0 Famous four 2.5 3.0 0.10 0.25 0.15 0.10 0.04 0.006 - - 0.14 21,4 Note. The rest is titanium

LITERATURE

1. GOST 19807 Titanium and wrought titanium alloys (grades) - prototype, p.2-4.

2. GOST 22897 cold-deformed bisch pipes from titanium-based alloys. Technical conditions

3. OST 1.92077 Titanium alloys (grades).

4. B. B. Chechulin, S. S. Ushkov and others. Titanium alloys in mechanical engineering, Publishing House "Engineering", L., 1977.

5. W. Zwicker. Titanium and its alloys. Publishing house "Metallurgy", M., 1979.

6. I.V. Gorynin, V.V. Rybin, S. S. Ushkov and others. Titanium alloys as a promising reactor material. Sat Art. “Radiation materials science and structural strength of reactor materials”, Publishing House of the Central Research Institute of CM “Prometey”, St. Petersburg, 2002.

7. S. S. Ushkov, V. A. Mezhonov, O. A. Kozhevnikov and others. The use of titanium alloys for pressurized-water reactor vessels of promising nuclear power plants. - Materials of the 7th International Scientific and Technical. conf. “Problems of materials science in the design, manufacture and operation of nuclear power plant equipment”, St. Petersburg, 2002.

8. VV Rybin, OA Kozhevnikov and others. Mechanical properties, fine structure and micromechanisms of destruction of neutron-irradiated titanium alpha-alloys, - MiTOM, No. 9, 1999, pp. 47-51.

Claims (1)

A titanium alloy for pipelines and pipe systems of nuclear power heat exchange equipment containing aluminum, zirconium, silicon, iron, oxygen, carbon, nitrogen, hydrogen and titanium, characterized in that it additionally contains tin and cerium in the following ratio, wt.%:
aluminum 1.8-2.5 zirconium 2.0-3.0 silicon 0.05-0.12 iron 0.15-0.25 oxygen 0.03-0.10 carbon 0.03-0.08 nitrogen 0.01-0.04 hydrogen 0.001-0.006 tin 0.005-0.01 cerium 0.003-0.008 titanium rest
the total carbon and nitrogen content does not exceed 0.10 wt.%, and the ratio Zr / (C + N) is not less than 30.