RU2293788C2 - Corrosion-resistant steel having low hydrogen permeability for in-vessel thermonuclear reactor systems - Google Patents

Abstract

FIELD: ferrous metallurgy and nuclear engineering.

SUBSTANCE: invention relates to metallurgy of structural steels and alloys containing, as basis, iron with specified proportions of alloying and impurity elements, which are designed for use in nuclear, thermonuclear, and hydrogen power engineering in manufacture of equipment, gas holders, and other elements of in-vessel systems of reactor installations. Technical result of this invention is creation of novel high-technology hydrogen-resistant steel with improved complex of principal mechanical, technological, and function properties as compared to known materials, which provides increase in working capacity and reliability of reactor equipment in thermonuclear and hydrogen power engineering. Proposed steel is composed of, wt %: carbon 0.005-0.02, silicon 0.2-0. 5, manganese 0.1-0.5, chromium 17.00-19.00, nickel 12.0-14.0, titanium 0.08-0.3, aluminum 0.1-0.5, yttrium 0.05-0.1, calcium 0.001-0.005, nitrogen 0.005-0.01, sulfur 0.005-0.015, phosphorus 0.005-0.03, and iron - the rest, summary content of aluminum and silicon not having to exceed 0.8%, summary content of carbon and nitrogen not having to exceed 0.025%, and summary content of sulfur and phosphorus not having to exceed 0.04%.

EFFECT: improved performance characteristics of steel.

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Description

The invention relates to the metallurgy of structural steels and alloys containing iron as a basis with a predetermined ratio of alloying and impurity elements, and is intended for use in nuclear, thermonuclear and hydrogen energy in the production of equipment, gas tanks and other elements of reactor vessel internal systems.

Known metal structural materials used in engineering industries (for example, stainless steel grades 08X18H10T, OZX16H15MZ, OZX18H12), as well as other analogues mentioned in the scientific, technical and patent literature [1-5]. However, the known steels 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 internal components, pipelines and gas tanks of the technological systems of the reactor equipment under conditions of prolonged interaction with corrosive hydrogen-containing working fluids.

Closest to the claimed composition according to the purpose and composition of the components is austenitic chromium-nickel steel of the OZX18N12 grade according to GOST 5632-72 [2], which contains alloying elements in the following ratio, wt.%:

carbon ≤0.03 silicon ≤0.04 manganese ≤0.04 chromium 17.0-19.0 nickel 11.5-13.0 titanium ≤0.005 sulfur ≤0.020 phosphorus ≤0,030 iron rest

It is recommended to use this steel grade in accordance with the requirements of the current regulatory and technical documentation in various industries and the national economy as a structural material in the production of serial equipment for general technical purposes. Moreover, the known steel is characterized by a very low hydrogen resistance at operating temperatures of the reactor equipment and increased sensitivity of the welded metal to stress corrosion and hydrogen cracking. At the same time, the well-known composition is characterized by a wide spread and instability of the main physical, mechanical, technological and service properties, which does not meet the requirements that determine the specified working capacity and operational reliability of the material in the conditions of long-term operation of internal equipment when exposed to corrosive hydrogen-containing environments. According to the requirements of the current state and industry standards [1-3], the content in the analog steels of a number of alloying and impurity elements, which largely determine the required structural state of the metal and the level of its most important service characteristics, is not controlled and is in a very wide concentration range.

The technical result of the present invention is the creation of high-tech steel with an improved set of basic physical and mechanical properties, a lower tendency to hydrogen embrittlement and brittle fracture, as well as a low level of hydrogen permeability in comparison with known materials, which improves the operational reliability and overall life of the reactor vessel equipment installations of thermonuclear and hydrogen energy.

The technical result is achieved due to the fact that the composition of the known steel containing carbon, silicon, manganese, chromium, nickel, titanium, sulfur, phosphorus and iron, additionally introduced aluminum, yttrium, calcium and nitrogen in the following ratio of components, wt.%:

carbon 0.005-0.02 silicon 0.2-0.5 manganese 0.1-0.5 chromium 17.0-19.0 nickel 12.0-14.0 titanium 0.08-0.3 aluminum 0.1-0.5 yttrium 0.05-0.1 calcium 0.001-0.005 nitrogen 0.005-0.01 sulfur 0.005-0.015 phosphorus 0.005-0.03 iron rest

At the same time, a restriction on the total content of elements was introduced, the excess of which negatively affects the formation of the most optimal structural state and significantly reduces the specified level of the basic strength and deformation characteristics of the material, in particular:

- the total content of aluminum and silicon should not exceed 0.8%;

- the total content of carbon and nitrogen should not exceed 0.025%;

- the total content of sulfur and phosphorus should not exceed 0.04%.

The ratio of these alloying and impurity elements is chosen so that the claimed composition provides the required level and stability of the most important structurally sensitive characteristics of the material, which in many respects determine the high performance and operational reliability of the internal systems of fusion and hydrogen power reactor plants.

The introduction into the inventive steel microalloying and modifying additives of aluminum, yttrium and calcium, as elements with high thermodynamic and special physicochemical properties, in the specified ratio with other alloying elements, and primarily chromium, nickel and silicon improves its structural stability during working temperatures and, as a consequence, the whole range of basic physical, mechanical and service properties that positively affect the decrease in the diffusion mobility of hydrogen atoms in the auste crystal lattice itnoy steel, and also enhances the nucleation of dislocation and development work and brittle intergranular cracking in the corrosion cracking and hydrogen under conditions of static and dynamic loadings. At the same time, as our studies have shown [4, 5], a more uniform distribution of alloying elements and non-metallic inclusions occurs over the entire cross section of the ingot, large forgings and slabs, the metal is more effectively cleaned of harmful impurities and gases, grain boundaries become thinner and cleaner, strength increases intergranular bonding, which generally provides a significant reduction in the hydrogen permeability of both the base metal and welded joints. The tendency of steel to structural anisotropy is reduced and its manufacturability at the stage of metallurgical redistribution is significantly improved, which increases the yield of industrial sheets and tubes, as well as other semi-finished products for the manufacture of complex gas tanks and vessels. The introduction of aluminum, yttrium and calcium in combination with other elements 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 material’s performance under conditions of simultaneous exposure to tensile stresses and a corrosive environment.

Modification of steel with nitrogen in the indicated ratio with carbon and titanium significantly improves the structural stability of the weld metal and HAZ, contributes to the formation of a fine amount of finely dispersed carbide and nitride phases thermodynamically stable at temperatures of technological and welding heating, which ensures a decrease in structural heterogeneity in the metal and increases the activation energy of diffusion processes of hydrogen atoms, i.e. reduces its thermodynamic activity in γ-iron. At the same time, the required level of hydrogen permeability and the basic physical and mechanical characteristics of steel under long-term exposure to operating temperatures and corrosive hydrogen-containing media are achieved by forming a stable dislocation structure that determines the optimal density of active slip densities under the influence of operational loads and reflects the important contribution of dislocation inelasticity to processes of internal friction. At the same time, it should be noted that the introduction of nitrogen in the indicated ratio with carbon and titanium promotes the formation of highly dispersed titanium carbonitrides and increases the tempering resistance of the weld metal and the heat affected zone while maintaining the necessary corrosion and mechanical strength of steel with high ductility and viscosity.

Fractographic analysis of the surface of the fractures of the samples by scanning electron microscopy [4] showed that in the inventive steel the proportion of the viscous component in the fracture zone after hydrogenation of the metal significantly increases compared with the known composition. An increase in the total carbon and nitrogen content above the limit specified in the claims reduces the dispersion of the formed interstitial phases and makes it difficult to evenly distribute them over the grain volume, which weakens the mechanism of fixation of dislocations during subsequent technological heating and negatively affects the deformation ability and hydrogen permeability of the metal during long-term operation.

The obtained higher level of physicomechanical, welding-technological and service characteristics of steel is ensured by complex alloying 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 - sulfur and phosphorus.

In TsNII KM "Prometey", together with other industry enterprises, in accordance with the plan of ongoing research and government tasks [6-8], the necessary set of laboratory, design and experimental-industrial work was carried out on the smelting, plastic and heat treatment of the steel grade being created. The metal was smelted in a vacuum plasma-arc furnace with a capacity of 5 tons, followed by pressure treatment on industrial forging and rolling 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 entire complex of the most important properties and characteristics, are presented in Tables 1 and 2.

The expected technical and economic effect of the application of the developed steel grade in industry and the national economy will be expressed in increasing the working capacity and operational characteristics, as well as the environmental safety of the use of internal systems, thin-walled pipelines and gas tanks of fusion and hydrogen power reactor plants.

Table 1 The chemical composition of the investigated materials Structure Conventional composition number The content of elements, wt.% FROM Si Mn Cr Ni Ti Al Y Ca N S P Al + Si C + n S + p Fe The claimed one 0.005 0.2 0.1 17.0 12.0 0.08 0.5 0.05 0.001 0.01 0.005 0.02 0.7 0.015 0,025 rest 2 0.01 0.4 0.3 18.0 13.0 0.2 0.1 0.08 0.003 0.008 0.010 0,03 0.5 0.018 0.04 rest 3 0.02 0.5 0.5 19.0 14.0 0.3 0.3 0.1 0.005 0.005 0.015 0.005 0.8 0,025 0.02 rest Famous four 0,03 0.35 0.4 17.5 13.0 0.005 - - - - 0,020 0,030 - - 0.05 rest

table 2 The main physical, mechanical, technological and service properties of the studied steels Structure Conventional composition No. Tensile properties Properties of steel after hydrogenation Hydrogen permeability P, cm ³ · mm / cm ² · sec · atm ^0.5 Yield in the production of sheet roll products,% σ _in σ _0.2 δ ψ σ _in δ Fatigue limit σ-1 logarithmic decrement of oscillations MPa % MPa % MPa % The claimed one 510 190 fifty 75 480 thirty 230 8 3 · 10 ⁷ 85 2 530 200 45 75 490 25 235 6 2 · 10 ⁷ 85 3 550 220 46 70 500 23 250 5 2 · 10 ⁷ 90 Famous four 450 180 40 65 360 fifteen 210 3 6 · 10 ⁷ 78 Note. 1. The results of mechanical tests are averaged over 3 samples per point.
2. The samples were hydrogenated in autoclaves at a hydrogen pressure of 10 atm, a temperature of 350 ° C, and a duration of 500 hours.
3. The fatigue strength of the samples was determined under conditions of alternating cyclic loading on the basis of 5 · 10 ⁷ cycles.
4. The measurement of internal friction characterizing the structural state of the metal was carried out on a D-6M installation of the Institute of Strength Problems of the Academy of Sciences of Ukraine.
5. The hydrogen permeability steels investigated samples was determined on Detection Products Installation HP-8, operating on the principle of space-metric method of measuring the steady flow of hydrogen (T _App. = 350 ° C).

LITERATURE

1. V.N.

2. GOST 5632-72 "High-alloy steels and corrosion-resistant, heat-resistant and heat-resistant alloys" (grades and technical requirements), Moscow, Standard publishing house, 1977, pp. 13-20, 30-40 - prototype.

3. A.M. Parshin, I. A. Povyshev, and others. The current state and development prospects of corrosion-resistant steels with special physical properties. - Materials of the VIIth scientific and technical conference of the CIS countries on the problem of "Radiation damage and performance of structural materials", Belgorod, 1997, p. 68-70.

4. V.V. Rybin, I. A. Povyshev, “Physicochemical Foundations of the Creation of Hydrogen-Resistant Steels” - Materials of the 16th Mendeleev Congress on General and Applied Chemistry, vol. 2, Moscow, 1998, p. 461.

5. VVVasiliev, Yu.I. Zvezdin, I.A. Povyshev "The penetration of hydrogen through austenitic corrosion-resistant materials." - Collection of scientific works "Issues of shipbuilding", ser. "Metallurgy", No. 26, Leningrad, 1978, S. 55-56.

6. Federal target scientific and technical program "Development and research of structural materials for thermonuclear reactors (ITER, experimental modules of ITER, DEMO, etc.), as well as tritium-reproducing materials and tritium technology of TNR (1997-2006)."

7. Decree of the Government of the Russian Federation of March 18, 1992 No. 178 "On the agreement between the European Atomic Energy Community, the Government of the Russian Federation, the Government of the United States of America and the Government of Japan on cooperation in the development of the technical design of the International Thermonuclear Experimental Reactor."

8. Decree of the Government of the Russian Federation of September 19, 1996 No. 1119 on the approval of the federal target scientific and technical program "The ITER International Thermonuclear Reactor and research and development work in its support for 1996-1998."

Claims (1)

Corrosion-resistant steel with low hydrogen permeability for fusion reactor internal systems containing carbon, silicon, manganese, chromium, nickel, titanium, sulfur, phosphorus, iron, characterized in that it additionally contains aluminum, yttrium, calcium and nitrogen in the following ratio of components , wt.%: Carbon 0.005-0.02 Silicon 0.2-0.5 Manganese 0.1-0.5 Chromium 17.0-19.0 Nickel 12.0-14.0 Titanium 0.08-0.3 Aluminum 0.1-0.5 Yttrium 0.05-0.1 Calcium 0.001-0.005 Nitrogen 0.005-0.01 Sulfur 0.005-0.015 Phosphorus 0.005-0.03 Iron Rest while the total content of aluminum and silicon should not exceed 0.8%; the total content of carbon, nitrogen should not exceed 0.025%; the total content of sulfur and phosphorus should not exceed 0.04%.