RU2669261C1 - Corrosive-resistant material with high boron content - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, namely to corrosion-resistant neutron-absorbing iron-based alloys used for the manufacture of compacted fuel storage racks. Alloy contains carbon, manganese, silicon, chromium, boron, titanium, zirconium and iron at the following component ratio, mass%: carbon – ≤0.05, manganese – 0.2–0.5, silicon – 0.1–0.4, chromium – 15.0–17.0, boron – 3.0–3.3, titanium – 4.0–6.0, zirconium – 4.0–6.0, iron – the rest.

EFFECT: increase in neutron-absorbing ability of a corrosion-resistant alloy and, as a consequence, in the possibility of storing a more enriched fuel while maintaining high process ductility under hot pressure treatment.

1 cl, 7 dwg, 3 ex

Description

The invention relates to the field of metallurgy, primarily to corrosion-resistant neutron-absorbing materials for the manufacture of shelves of compacted fuel storage.

Corrosion-resistant steels with a high boron content are currently almost the only structural material for the manufacture of compacted storage racks for nuclear fuel, due to the high ability of boron to absorb neutron radiation. In addition to the ability to absorb neutrons, the material must also have a good combination of anticorrosive, mechanical properties and manufacturability in pressure processing. However, due to the large amount of brittle borides in the structure, steel has a low level of ductility, both at room and at elevated temperatures. In this regard, the boron content in currently used steels is limited to 1.8 mass. % (steel ChS-82). This patent describes the composition of an alloy containing more than 3% boron, as well as additionally alloyed with chromium, titanium, zirconium, providing a high level of technological plasticity, corrosion resistance and mechanical properties.

GB 1199030 (publ. 12/19/1967) proposes an alloy for use as an absorbing material in a nuclear reactor. It is produced by incorporating austenitic chromium-nickel steel with a chromium content of at least 30% and boron up to 2%. The alloy can be obtained by vacuum melting austenitic steel with the addition of Ti and Al, and then boron. The alloy has the following composition: Cr 36-38%, Ni 6-8%, isotope B ¹⁰ 2%, C 0.05%, Al 0.2%, Fe - the rest. The disadvantage of this invention is the large amount of chromium and nickel and, as a consequence, the high cost and low technological ductility.

JPH 06192792 (publ. 07.12.1994) describes the production of stainless steel having a higher neutron absorption capacity than conventional boron-containing stainless steel, excellent corrosion resistance, good workability during hot rolling, and the possibility of use for neutron shielding. Boron-containing stainless steel has the following composition: by weight, ≤0.02% C, ≤0.5% Si, ≤2% Mn, 10-22%, Ni, 18-26% Cr, ≤3.0% B, ≤ 0.1% Mg, ≤0.5% Al, 0.05-1.0% Gd and / or 0.1-5%, individually or in combination, from one or more elements of Ti, Zr and Nb, ≤ 1% of each of one or more elements of Cd, Sm, Eu, and / or 0.1-5% individually or in combination of one or more elements of Mo, W and V, the rest is Fe. The disadvantage of this invention is the high concentration of expensive nickel, as well as its boron content of less than 3%, which limits its use for storing more enriched fuels.

JPH 0499806 (published March 31, 1992) discusses the production of boron-containing austenitic stainless steel for transporting and storing spent nuclear fuel from the powder of quickly hardened boron-containing austenitic stainless steel, as well as SUS304 or SUS316. Atomized powder (% by mass: 0.3-3.0% V, ≤0.08% C, 0.01-2.0% Si, ≤2.0% Mn, 16.0-20.0% Cr, 8.0-15.0 % Ni, ≤0.2% H, the rest Fe) is laid between the plates of SUS304 (L) or SUS316 (L) steels having a thickness of 2-50 mm for the manufacture of a steel slab by hot extrusion. This hot rolled and boron-containing austenitic stainless steel plate has excellent corrosion resistance and processability. The disadvantage of this invention is the complexity and high cost of production due to the presence of powder spraying procedures and subsequent extrusion.

GB 1244876 (publ. 09/02/1971) describes stainless steel that protects against nuclear radiation and has the following composition: by mass, C <0.1%, Cr 20-30%, Ni <5%, Mn <3% , Si <2%, B 0.5-6%, Fe - the rest. The disadvantage of the present invention is the low technological ductility of steel and the possibility of manufacturing from it only castings.

In the patent of the Russian Federation No. 1122009 (published on July 19, 1983), corrosion-resistant steel of the following composition is considered: C 0.02-0.10; Si 0.10-0.80; Mn 0.10-0.50; Cr 13.0-16.0; B 1.0-2.0; V 0.05-0.35; Ce 0.01-0.04; Al 0.15-0.8; Ti 2.0-4.0; Fe the rest. The disadvantage of this steel is the impossibility of ensuring safe storage of spent nuclear fuel with a U-235> 5% uranium content due to the low content of boron in its composition.

Closest to the proposed invention is steel of the following composition: C 0.021-0.10, Si 0.10-0.80, Mn 0.10-0.50, Cr 13.0-16.0, B 2.01-3 5, V 0.05-0.35, Ce 0.01-0.04, Al 0.15-0.8, Ti 4.02-10.0, Fe - the rest from patent RU 2399691 (publ. 20.09 .2010). Due to the increased boron content in steel, the neutron absorption capacity is increased and the possibility of its use in means of transportation and storage of fuel with nuclear safety in normal operation and in emergency situations is ensured. The difference of the invention is the presence in the composition of the zirconium alloy, which provides a higher level of technological plasticity during hot processing, as well as increased mechanical properties.

The technical result of this invention is to increase the neutron-absorbing ability of a corrosion-resistant alloy and, as a result, the ability to store more enriched fuel, while maintaining high technological plasticity during hot processing by pressure. The result is achieved due to the formation of a structure consisting of dispersed borides, due to the following chemical composition of the material (wt.%): C ≤0.05%, Mn 0.2-0.5%, Si 0.1-0.4%, Cr 15.0 -

 -17.0%, B 3.0-3.3%, Ti 4.0-6.0%, Zr 4.0-6.0%.

Description of the drawings.

FIG. 1 - Microstructure of alloy Fe-17% Cr-6% Ti-4% Zr-3.3% B-0.2% Mn-0.2% Si-0.03% C in molten state

FIG. 2 - Diffraction pattern of the alloy Fe-17% Cr-6% Ti-4% Zr-3.3% B-0.2% Mn-0.2% Si-0.03% C in the cast state

FIG. 3 - Microstructure of the alloy Fe-15% Cr-4% Ti-6% Zr-3% B-0.3% Mn-0.1% Si-0.05% C in molten state

FIG. 4 - X-ray diffraction pattern for Fe-15% Cr-4% Ti-6% Zr-3% B-0.3% Mn-0.1% Si-0.05% C alloy

FIG. 5 - Microstructure of the alloy Fe-15% Cr-8% Ti-2% Zr-3.1% B-0.3% Mn-0.2% Si-0.05% C in the molten state

FIG. 6 - Diffraction pattern of the alloy Fe-15% Cr-8% Ti-2% Zr-3.1% B-0.3% Mn-0.2% Si-0.05% C in the cast state

FIG. 7 - Destruction of an alloy sample Fe-15% Cr-8% Ti-2% Zr-3.1% B-0.3% Mn-0.2% Si-0.05% C during deformation by compression at a temperature of 1150 ° C and strain rate 1 s ^-1

The implementation of the invention.

The alloy of the following composition (wt.%): C 0-0.05%, Mn 0.2-0.5%, Si 0.1-0.4%, Cr 15.0-17.0%, B 3, 0-3.3%, Ti 4.0-6.0%, Zr 4.0-6.0%, obtained by alloying pure charge materials and master alloy ferroboron FB17 in an argon-arc furnace on a copper water-cooled hearth. The melt is cast by gravity casting into a massive copper mold. The study of the structure of the alloys is carried out using x-ray diffraction analysis on samples cut from the cross section of the castings, as well as by scanning electron microscopy. The plasticity determination during hot pressure processing is carried out on a physical modeling complex Gleeble 3800 at temperatures of 1050-1150 ° C and strain rates of 0.1-10 s ^-1 .

Example 1

The alloy composition Fe-17% Cr-6% Ti-4% Zr-3.3% B-0.2% Mn-0.2% Si-0.03% C was obtained as follows:

To prepare the alloy, pure metals were used: iron, chromium, zirconium, titanium with a purity of 99.9%, as well as ligature ferroboron FB17, containing 17 mass. % boron, as well as impurities of manganese, silicon and carbon. Melting was conducted in an argon-arc furnace on a copper water-cooled hearth. Casting was carried out in a massive copper mold with a diameter of 12.7 mm.

The structure of the alloy sample was investigated by scanning electron microscopy (Fig. 1) and X-ray diffraction analysis (Fig. 2). The alloy structure is a ferrite matrix with dispersed borides of titanium, zirconium and boride (Fe, Cr) ₂ B.

Analysis of the results of mechanical tests on a complex of physical modeling of thermomechanical processes, as well as the appearance of samples after testing, showed no signs of fracture at test temperatures of 1050, 1100 and 1150 ° C and strain rates of 0.1, 1 and 10 s ^-1 , and as a result, good technological plasticity in a wide range of temperatures and strain rates.

Example 2

The alloy composition Fe-15% Cr-4% Ti-6% Zr-3% B-0.3% Mn-0.1% Si-0.05% C was obtained as follows:

To prepare the alloy, pure metals were used: iron, chromium, zirconium, titanium with a purity of 99.9%, as well as ligature ferroboron FB17, containing 17 mass. % boron and impurities of manganese, silicon and carbon. Melting was carried out in an argon-arc furnace on a copper water-cooled hearth. The casting was carried out in a massive copper mold with a diameter of 12.7 mm.

The structure of the alloy sample was investigated by scanning electron microscopy (Fig. 3) and X-ray diffraction analysis (Fig. 4). The alloy structure is a ferrite matrix with dispersed borides of titanium, zirconium and boride (Fe, Cr) ₂ B.

Analysis of the results of mechanical tests on a complex of physical modeling of thermomechanical processes, as well as the appearance of samples after testing, showed no signs of fracture at test temperatures of 1050, 1100 and 1150 ° C and strain rates of 0.1, 1 and 10 s ^-1 , and as a result, good technological plasticity in a wide range of temperatures and strain rates.

Example 3

The alloy composition Fe-15% Cr-8% Ti-2% Zr-3.1% B-0.3% Mn-0.2% Si-0.05% C was obtained as follows:

To prepare the alloy, pure metals were used: iron, chromium, zirconium, titanium with a purity of 99.9%, as well as ligature ferroboron FB17, containing 17 mass. % boron and impurities of manganese, silicon, carbon. Melting was carried out in an argon-arc furnace on a copper water-cooled hearth. The casting was carried out in a massive copper mold with a diameter of 12.7 mm.

The structure of the alloy sample was investigated by scanning electron microscopy (Fig. 5) and X-ray diffraction analysis (Fig. 6). The alloy structure is a ferrite matrix with dispersed borides of titanium, zirconium and boride (Fe, Cr) ₂ B distributed in it. In addition, large needle-like primary crystals (Fe, Cr) ₂ B are also present in the structure (Fig. 5).

Analysis of the results of mechanical tests on a complex of physical modeling of thermomechanical processes, as well as the appearance of the samples after testing showed the presence of cracks in the samples (Fig. 7) after testing at test temperatures of 1050, 1100 and 1150 ° C and strain rates of 1 and 10 s ^-1 . The presence of signs of destruction indicates a low technological plasticity with a zirconium content in the alloy of less than 4 mass. % due to the formation of large needle-shaped primary crystals (Fe, Cr) ₂ B.

Claims (9)

A corrosion-resistant iron-based neutron-absorbing alloy containing carbon, manganese, silicon, chromium, boron, titanium and iron, characterized in that it additionally contains zirconium in the following ratio of components, wt.%: carbon ≤0.05; manganese 0.2-0.5; silicon 0.1-0.4; chrome 15.0-17.0; boron 3.0-3.3; titanium 4.0-6.0; zirconium 4.0-6.0; iron is the rest.

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