Neutron absorbing material blank for spent fuel storage and transport and method for producing the same

Abstract

The application discloses a kind of neutron absorption material blank preparation method for spent fuel storage and transportation, contain the following chemical elements with percentage as follows: C:0.03%~0.06%, Si:0.20%~0.50%, Mn:0.20%~0.50%, P:≤0.010%, S:≤0.003%, Cr:13.0%~16.0%, Ni:0.10%~0.50%, Ti:3.2%~4.0%, B:1.6%~1.8%, Mo:0.01%~0.06%, N:≤0.05%, the rest is Fe and inevitable impurities;Its preparation method includes the following steps: steel ingot preparation: raw material is smelted using vacuum induction smelting, so that the percentage of chemical elements in molten steel reaches the proportion of the above chemical elements, then steel ingot casting is carried out;Steel ingot annealing: when the steel ingot is heated to 700 DEG C with furnace, after holding for 4h-6h, it is cooled, and when the temperature is lower than 400 DEG C, it is discharged;Electroslag remelting: the annealed steel ingot is baked, the baking time is between 15min-25min;Baking melting rate is between 450kg / h~550kg / h, the baking temperature of slag is greater than or equal to 600 DEG C, and the baking holding time is greater than or equal to 4h. The method produces high boron element content and uniform distribution, and improves the material hot forming capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy steel manufacturing, in particular to a neutron absorbing material blank for spent fuel storage and a preparation method thereof. Background Art

[0002] Boron-containing stainless steel is a neutron-absorbing material formed by adding boron, an element with high thermal neutron absorption capacity, to stainless steel. It has high strength, excellent corrosion resistance and strong neutron absorption ability, and is widely used in nuclear fuel storage hangers, transportation and storage containers.

[0003] Because boron-added stainless steel solidifies in a eutectic form, its liquidus temperature decreases with increasing boron addition. Boron is an active element and can easily alter the properties of the continuous casting mold slag, adversely affecting the continuous casting operation and ingot quality. Furthermore, the hard and brittle boride (Fe, Cr)B crystallizes in the as-cast structure of boron-added stainless steel, resulting in poor hot workability. Furthermore, the amount of this boride increases with increasing boron addition, further deteriorating the hot workability of the boron-added stainless steel. Summary of the Invention

[0004] In order to solve some or all of the technical problems existing in the above-mentioned prior art, the present invention provides a method for preparing a neutron absorber material blank for spent fuel storage. The blank produced by this method has a high boron content and the boron element is evenly distributed in the blank, which improves the material's hot forming ability and lays a foundation for product preparation.

[0005] The technical solutions of the present invention are as follows:

[0006] In a first aspect, the present invention provides a method for preparing a neutron absorbing material blank for spent fuel storage, characterized in that the blank contains the following chemical elements in the following percentages:

[0007] C: 0.03% to 0.06%, Si: 0.20% to 0.50%, Mn: 0.20% to 0.50%, P: ≤0.010%, S: ≤0.003%, Cr: 13.0% to 16.0%, Ni: 0.10% to 0.50%, Ti: 3.2% to 4.0%, B: 1.6% to 1.8%, Mo: 0.01% to 0.06%, N: ≤0.05%, the rest are Fe and unavoidable impurities;

[0008] The preparation method comprises the following steps:

[0009] Ingot preparation: The raw materials are smelted by vacuum induction smelting to make the percentage of chemical elements in the molten steel reach: C: 0.03% to 0.06%, Si: 0.20% to 0.50%, Mn: 0.20% to 0.50%, P: ≤0.010%, S: ≤0.003%, Cr: 13.0% to 16.0%, Ni: 0.10% to 0.50%, Ti: 3.2% to 4.0%, B: 1.6% to 1.8%, Mo: 0.01% to 0.06%, N: ≤0.05%, and the remainder is Fe and unavoidable impurities, and then the steel ingot is cast;

[0010] Ingot annealing: When the ingot is heated to 700℃, keep it at this temperature for 4-6 hours and then cool it down. When the temperature drops below 400℃, take it out of the furnace.

[0011] Electroslag remelting: Bake the annealed steel ingot for 15-25 minutes; the baking melting rate is between 450kg / h and 550kg / h, the slag baking temperature is ≥600℃, and the baking holding time is ≥4h.

[0012] Furthermore, when vacuum induction smelting is used, the vacuum degree is ≤2.6×10 -2 mba, the melting power is between 500KW and 1000KW.

[0013] Furthermore, when vacuum induction smelting is adopted, after the molten steel is melted, the molten steel is electromagnetically stirred for 4 to 6 minutes. When the temperature of the molten steel reaches 1610°C to 1620°C and the power is reduced to 300KW to 400KW, the smelting is carried out for 60 to 90 minutes. Subsequently, the chemical elements used to prepare the steel ingot are added and the electromagnetic stirring is continued for 4 to 6 minutes to complete the preparation of the billet. The finished billet is sampled and tested, and the steel is tapped with electricity after the composition is qualified.

[0014] Furthermore, when performing electroslag remelting, the annealed steel ingot needs to be pretreated.

[0015] Furthermore, the pretreatment method is: sawing off the head and tail of the annealed steel ingot to make the outer diameter of the steel ingot uniform and the end surface flat, and polishing the surface of the steel ingot to make it smooth.

[0016] Furthermore, during the electroslag remelting time, the annealed steel ingot is a round ingot between 5t and 8t, using the same steel grade ingot starter plate and arc starting chips, the slag system is: 55F / 20 / 3 / 22+3% TiO2+Al particles, and the slag amount is: 160kg~170kg.

[0017] Furthermore, during electroslag remelting, the ambient humidity before power supply is less than 40%, and the oxygen content in the crystallizer is less than 8%.

[0018] Further, during electroslag remelting, protective gas is introduced, and the protective gas is temporarily stopped during the slag adding process of electroslag remelting.

[0019] Further, the protective gas is argon or nitrogen.

[0020] In a second aspect, the present application provides a blank of neutron absorption material for spent fuel storage and transportation, which is prepared by the method for preparing the blank of neutron absorption material for spent fuel storage and transportation.

[0021] The main advantages of the technical solution of the present application are as follows:

[0022] The method for preparing the blank of neutron absorption material for spent fuel storage and transportation of the present application is aimed at the problem that the formation of large-size borides of boron elements in the material leads to uneven distribution of boron elements, and further leads to poor hot forming ability of the material. The method of vacuum induction furnace smelting, induction ingot annealing and electroslag remelting is used to produce high-quality blank with high boron element content and uniform distribution, thereby improving the hot forming ability of the material and laying a foundation for the preparation of subsequent products. BRIEF DESCRIPTION OF DRAWINGS

[0023] The drawings described herein are used to provide further understanding of the embodiments of the present application, and form a part of the present application. The schematic embodiments of the present application and the descriptions thereof are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0024] Figure 1 It is a flowchart of the method for preparing the blank of neutron absorption material for spent fuel storage and transportation of the present application;

[0025] Figure 2 It is a process flowchart of the blank prepared by the method for preparing the blank of neutron absorption material for spent fuel storage and transportation of the present application;

[0026] Figure 3 It is a process coordinate graph of the steel ingot annealing in the method for preparing the blank of neutron absorption material for spent fuel storage and transportation of the present application.

[0027] Figure 4 It is a process coordinate graph of the electroslag remelting in the method for preparing the blank of neutron absorption material for spent fuel storage and transportation of the present application. DETAILED DESCRIPTION

[0028] To make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be described clearly and completely in combination with specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] The technical solutions provided by the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0030] The present invention provides a method for preparing a neutron-absorbing material blank for spent fuel storage, which is suitable for special-purpose stainless steel with a high boron content, such as materials used in nuclear reactors or thermonuclear materials. It can solve the adverse effects of adding a large amount of boron on the product manufacturing process, enable the boron element to play its positive role in absorbing neutrons, and obtain high-performance stainless steel, making certain reference and contributions to the development of the nuclear power industry.

[0031] Example 1

[0032] As attached Figures 1 to 3 As shown, an embodiment of the present invention provides a method for preparing a neutron absorbing material blank for spent fuel storage, the method comprising:

[0033] The neutron absorbing material blank for spent fuel storage prepared by this method contains the following chemical elements in the following percentages:

[0034] C: 0.03% to 0.06%, Si: 0.20% to 0.50%, Mn: 0.20% to 0.50%, P: ≤0.010%, S: ≤0.003%, Cr: 13.0% to 16.0%, Ni: 0.10% to 0.50%, Ti: 3.2% to 4.0%, B: 1.6% to 1.8%, Mo: 0.01% to 0.06%, N: ≤0.05%, the rest are Fe and unavoidable impurities;

[0035] The preparation method comprises the following steps:

[0036] Ingot preparation: The raw materials are smelted by vacuum induction smelting to make the percentage of chemical elements in the molten steel reach: C: 0.03% to 0.06%, Si: 0.20% to 0.50%, Mn: 0.20% to 0.50%, P: ≤0.010%, S: ≤0.003%, Cr: 13.0% to 16.0%, Ni: 0.10% to 0.50%, Ti: 3.2% to 4.0%, B: 1.6% to 1.8%, Mo: 0.01% to 0.06%, N: ≤0.05%, and the remainder is Fe and unavoidable impurities, and then the steel ingot is cast;

[0037] Ingot annealing: When the ingot is heated to 700℃, keep it at this temperature for 4-6 hours and then cool it down. When the temperature drops below 400℃, take it out of the furnace.

[0038] Electroslag remelting: the annealed steel ingot is baked, the baking time is between 15min-25min; the baking melting rate is between 450kg / h~550kg / h, the baking temperature of the slag is ≥600℃, and the baking holding time is ≥4h.

[0039] Specifically, during vacuum induction smelting: the vacuum degree is ≤2.6×10 -2 MBA, refining power 500KW~1000KW, electromagnetic stirring for 4min~6min after refining, temperature 1610℃~1620℃, power is reduced to 300KW~400KW after 60min~90min smelting, alloy package for preparing the chemical elements of the steel ingot is added, and electromagnetic stirring is performed again for 4min~6min, then the finished product is sampled, and the composition is detected to be qualified before electrically tapping.

[0040] Specifically, as shown in Figure 2 and Figure 3 When the steel ingot is annealed, since the vacuum induction smelting method is used for smelting, the steel ingot manufactured will generate electromagnetic induction after being electrified, so the steel ingot is an induction steel ingot. When the electromagnetic induction steel ingot is annealed: the furnace is heated to 700℃±10℃, and after holding for 4h~6h, the temperature is lowered, and the furnace can be discharged for cooling or the next process when the temperature is lower than 400℃. Specifically, when electroslag remelting is performed, the annealed steel ingot needs to be pretreated. Similarly, the vacuum induction smelting method is used for smelting, so the steel ingot manufactured will generate electromagnetic induction after being electrified, so the steel ingot is an induction steel ingot. The method for pretreating the annealed steel ingot (induction steel ingot) is: the head and tail of the annealed steel ingot (induction steel ingot) are sawed off and polished to serve as an electrode blank.

[0041] It should be noted that when the annealed steel ingot is pretreated, the surface of the steel ingot needs to be polished, and the roughness of the surface of the steel ingot is not less than Ra3.2.

[0042] Specifically, when electroslag remelting is performed: a 5t-8t round ingot is used, the same steel grade is used for the ingot plate and the arc scrap; the slag system is 55F / 20 / 3 / 22+3%TiO2+Al particles, the slag amount is 160kg~170kg, which can be adjusted according to the actual situation; before power transmission, the environmental humidity is required to be <40%, and the oxygen content in the crystallizer is <8%; the electrode blank is baked, the baking time is between 15min-25min; the melting rate is 450kg / h~550kg / h; the baking temperature of the slag is ≥600℃, and the baking holding time is ≥4h; the protective gas is argon or nitrogen, and nitrogen is not allowed to be used during the slag adding process.

[0043] Therefore, the application solves the problem of the segregation of boron elements in the smelting and solidification process affecting the hot working performance of the material.

[0044] Therefore, the above method solves the problem that the boron element forms large-sized borides, resulting in uneven distribution of the boron element and thus poor hot forming ability of the material.

[0045] It should be noted that when the boron content is greater than 0.5%, hot ductility at 1200°C is zero, and area reduction at high temperatures decreases with increasing boron content. When the boron content is ≥1.0%, cracks may appear on the edges during rolling below 1000°C. Boron easily forms borides that accumulate within the material, affecting its properties. Therefore, a vacuum melting and electroslag remelting process is used to smelt high-boron materials, ensuring that the borides are evenly dispersed throughout the material, enhancing its properties.

[0046] Specifically, the functions of the main elements in the present invention are:

[0047] Mn: In the neutron absorber material of the present invention, the primary function of Mn is to act as a strong austenite-forming element, increasing the hardenability of the steel and lowering its transition temperature and critical cooling rate. The Mn content in the present invention is preferably 0.2%-0.5%. This is because excessive Mn content in steel tends to coarsen grains, increase the steel's susceptibility to temper brittleness, and easily lead to segregation and cracking in the ingot, thus degrading the performance of the steel plate. Therefore, a Mn content of 0.2%-0.5% in the present invention satisfies the hardenability requirements while preventing segregation and cracking, ensuring the superior mechanical properties of the mold steel.

[0048] In some optional implementations of this embodiment, in order to obtain better implementation effects and a wider range of applications, the content of the Mn element may be adjusted to between 0.1% and 0.6% or between 0.05% and 0.8%, and preferably between 0.2% and 0.5%.

[0049] Cr: In the neutron absorber material of the present invention, the primary function of Cr is to significantly improve the steel's oxidation resistance, increase its corrosion resistance, reduce its critical cooling rate, and enhance its hardenability. Cr also prevents or slows the precipitation and aggregation of carbides during tempering, improving the steel's tempering stability. Therefore, in the present invention, the Cr content is set at 13.0% to 16.0%, allowing it to form various carbides in the steel, thereby enhancing the steel's strength and hardness.

[0050] In some optional implementations of this embodiment, in order to obtain better implementation effects and a wider range of applications, the content of the Cr element may be adjusted to between 11.5% and 18.5%.

[0051] Ni: In the neutron absorbing material blank of the present application, the main role of the Ni element is to expand the austenite zone, effectively reduce the critical cooling rate, and improve the hardenability of the steel. Therefore, in the present application, the content of the Ni element is set to 0.10% to 0.50%, avoiding the formation of δ ferrite, and at the same time, since the Ni element can be mutually soluble with Fe in any proportion, the low temperature toughness of the steel is improved by refining the ferrite grain, and the cold brittle transformation temperature is significantly reduced. However, when the content of the Ni element in the steel is too high, it is easy to cause the oxide skin on the surface of the steel plate to be difficult to fall off, and significantly increase the production cost, because the content of the Ni element in the present application is set to 0.10% to 0.50%.

[0052] In some optional implementations of the present embodiment, in order to obtain better implementation effects and a wider range of use, the content of the Ni element can be adjusted to between 0.05% and 0.60%.

[0053] Mo: In the neutron absorbing material blank of the present application, the main role of the Mo element is to effectively refine the grains, improve the strength, toughness and corrosion resistance of the steel. Therefore, in the present application, the content of the Mo element is set to 0.01% to 0.06%, by setting the content of the Mo element to 0.01% to 0.06%, and the Mo element exists in the solid solution phase and the carbide phase in the steel, at the same time, the Mo element reduces the brittleness of tempering and improves the tempering stability, so that the molybdenum-containing steel has the effects of solid solution strengthening and carbide dispersion strengthening.

[0054] In some optional implementations of the present embodiment, in order to obtain better implementation effects and a wider range of use, the content of the Mo element can be adjusted to between 0.05% and 1%.

[0055] N: In the neutron absorbing material blank of the present application, N partially replaces Ni to avoid the formation of δ ferrite; at the same time, it partially replaces C to improve the strength, hardness and corrosion resistance of the steel. In the present application, the content of the N element is set to less than 0.05%, and can be optionally between 0.08% and 0.15%.

[0056] Specifically, as shown in Figures 1 to 4 the preparation method of the neutron absorbing material blank for spent fuel storage and transportation of the present application includes:

[0057] (1) Vacuum induction furnace smelting

[0058] Vacuum degree actual control: 2.3 x 10 -2mba; melting power: 680kW; electromagnetic stirring for 5 minutes after melting; smelting temperature: 1610°C, smelting time: 80 minutes after power reduction to 350kW, adding an alloying ladle of chemical elements used to prepare the ingot, electromagnetic stirring for 5 minutes, sampling and casting to obtain qualified components into a vacuum induction ingot weighing 6 tons. The specific composition is as follows: C: 0.04%, Si: 0.35%, Mn: 0.28%, P: 0.008%, S: 0.001%, Cr: 14.5%, Ni: 0.35%, Ti: 3.8%, B: 1.7%, Mo: 0.04%, N: 0.03%, and the remainder is iron and unavoidable impurities.

[0059] (2) Induction ingot annealing

[0060] The induction ingot is heated to 700℃ along with the furnace, kept warm for 5 hours and then cooled down. It is taken out of the furnace when the temperature drops to 380℃.

[0061] (3) Electroslag remelting

[0062] First, the head and tail of the induction ingot are sawed off and the surface is polished to make it into an electrode blank. The ingot body should be free of oil, water stains, etc.

[0063] The steel grades of the ingot starter plate and arc starting chips are made of the same high-boron stainless steel; the 55F / 20 / 3 / 22+3% TiO2+Al granular slag system is used, the slag amount is 160kg, the ambient humidity is 35%, and the oxygen content in the crystallizer is 6%; the electrode blank baking time is 20min; the melting rate is 500kg / h; the slag baking temperature is 750℃, and the baking holding time is 4h; and argon protection is used.

[0064] The seamless round tube with an outer diameter of 294 mm, a wall thickness of 6 mm, and a length of 4700 mm made from the high-boron stainless steel billet obtained through the above process steps has good mechanical properties and is free of defects. The performance results of three groups of samples tested are shown in Table 1.

[0065] Table 1:

[0066] Performance indicators Rp0.2,Mpa Rm, Mpa A，％ KV2, J Sample 1 367 562 19 3.9 / 4.2 Sample 2 350 560 17.5 3.8 / 4.1 Sample 3 358 551 20 4.2 / 4.7

[0067] Therefore, the embodiment of the present invention provides a special-purpose stainless steel material billet suitable for high boron content prepared by a method for preparing a neutron absorbing material billet for spent fuel storage, which solves the adverse effect of hard and brittle boride (Fe, Cr) B crystallized in the cast structure of boron-added stainless steel on the hot workability of the cast billet, enables the boron element to play its positive role in absorbing neutrons, and the performance of the high-performance stainless steel seamless steel pipe made from the billet obtained by the present invention fully meets more construction requirements.

[0068] Example 2

[0069] The present invention provides a neutron absorber material blank for spent fuel storage, which is prepared using the method for preparing a neutron absorber material blank for spent fuel storage described in Example 1. The high-boron stainless steel blank produced using this method has a high and uniformly distributed boron content and excellent hot forming capability. This blank can be used to produce seamless steel pipes and other materials through a hot extrusion process.

[0070] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In addition, "front", "back", "left", "right", "upper" and "lower" in this document are all referenced to the placement states shown in the accompanying drawings.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing neutron absorbing material blanks for spent fuel storage, characterized in that: The billet is used as a material for a nuclear reactor or a thermonuclear material, and contains the following chemical elements in the following percentages: C: 0.03%~0.06%, Si: 0.20%~0.50%, Mn: 0.20%~0.50%, P: ≤0.010%, S: ≤0.003%, Cr: 13.0%~16.0%, Ni: 0.10%~0.50%, Ti: 3.2%~4.0%, B: 1.6%~1.8%, Mo: 0.01%~0.06%, N: ≤0.05%, the rest are Fe and unavoidable impurities; The preparation method comprises the following steps: Ingot preparation: The raw materials are smelted by vacuum induction smelting to make the percentage of chemical elements in the molten steel reach: C: 0.03%~0.06%, Si: 0.20%~0.50%, Mn: 0.20%~0.50%, P: ≤0.010%, S: ≤0.003%, Cr: 13.0%~16.0%, Ni: 0.10%~0.50%, Ti: 3.2%~4.0%, B: 1.6%~1.8%, Mo: 0.01%~0.06%, N: ≤0.05%, and the rest is Fe and unavoidable impurities, and then the steel ingot is cast; Ingot annealing: When the ingot is heated to 700℃, keep it at this temperature for 4-6 hours and then cool it down. When the temperature drops below 400℃, take it out of the furnace. Electroslag remelting: The annealed steel ingot is baked for 15-25 minutes at a melting rate of 450-550 kg / h, the slag baking temperature is ≥ 600°C, and the baking holding time is ≥ 4 hours. When vacuum induction smelting is used, the vacuum degree is ≤2.6×10 -2 mba, melting power is between 500KW~1000KW; When vacuum induction smelting is used, after the molten steel is melted, it is electromagnetically stirred for 4 to 6 minutes. When the temperature of the molten steel reaches 1610 to 1620 degrees Celsius and the power is reduced to 300 kW to 400 kW, it is smelted for 60 to 90 minutes. Then, the chemical elements used to prepare the steel ingot are added and electromagnetic stirring is continued for 4 to 6 minutes to complete the preparation of the billet. The finished billet is sampled and tested. After the composition is qualified, the steel is tapped with electricity. When performing electroslag remelting, the annealed steel ingot needs to be pretreated; The pretreatment method comprises: sawing off the head and tail of the annealed steel ingot to make the outer diameter of the steel ingot uniform and the end surface flat, and polishing the surface of the steel ingot to make it smooth, and the surface roughness of the steel ingot is not less than Ra3.2; During the electroslag remelting time, the annealed steel ingot is a round ingot between 5t and 8t, using the same steel grade ingot starter plate and arc starter chips, and the slag amount is: 160kg~170kg; During electroslag remelting, the ambient humidity before power supply is less than 40%, and the oxygen content in the crystallizer is less than 8%; During electroslag remelting, a protective gas is introduced, and the introduction of the protective gas is suspended during the slag adding process of the electroslag remelting.

2. The method for preparing a neutron absorbing material blank for spent fuel storage according to claim 1, characterized in that: The protective gas is argon or nitrogen.

3. A neutron absorbing material blank for spent fuel storage, characterized in that: The blank is prepared by the method for preparing a neutron absorbing material blank for spent fuel storage according to any one of claims 1 to 2.

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