A high shielding performance boron-containing stainless steel and a method for manufacturing the same

Abstract

The application discloses a boron-containing stainless steel with high shielding performance and a preparation method thereof, relates to the field of fusion reactor irradiation shielding materials, and can also be applied to other fields requiring shielding of neutrons and gamma rays, such as fission reactors, nuclear power devices, nuclear waste storage racks and the like. The boron steel contains the following components in percentage by weight: Cr 7.5-25%, Ni 8.5-18.5%, Mn 0.5-4.3%, B 1.8-4.5%, C 0.02%-0.06%, and the balance is Fe and inevitable impurities. The components of the alloy are proportioned according to the application, atomized, mixed, sintered and machined, and finally, a block boron steel with high boron content, high density, uniform boride distribution and good shielding performance is obtained. The high-performance boron steel shielding material improves the shielding efficiency of thermal neutrons, and provides support for the development of DEMO reactors, compact fusion reactors and other shielding fields.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nuclear radiation shielding materials, in particular to a high shielding performance boron-containing stainless steel and a preparation method thereof. BACKGROUND

[0002] With the development of supporting technologies such as superconducting technology in recent years, the development of controlled nuclear fusion has entered a fast track. However, high-performance shielding materials are needed to shield the neutrons and gamma rays generated by deuterium-tritium fusion reactions to prevent energy deposition into superconducting magnets, which can cause damage to the superconducting magnets and quench. High boron steel is the preferred material for nuclear fusion shielding materials due to its good thermal neutron moderation and absorption capacity, as well as its high gamma ray shielding capacity.

[0003] In high boron steel 10 B and thermal neutrons have a large reaction cross section for the (n, α) reaction, which is the main element for thermal neutron shielding and absorption. Therefore, composite materials containing B4C or high boron steel are commonly used for neutron shielding. The heavy metal iron in high boron steel has excellent shielding performance for gamma rays, so high boron steel has superior shielding performance for both neutrons and gamma rays, making it the preferred shielding material for reactors. However, the solubility of boron in α-iron and γ-iron at various temperatures is very low, and it easily reacts with iron to form brittle iron borides. Therefore, appropriate preparation methods are needed to increase the content of boron.

[0004] Currently, the highest boron content in high boron steel used in large-scale applications is the shielding material 304B7 used by the international ITER, which contains 1.75-2.25wt% boron. With the development of DEMO reactor and subsequent miniaturization of fusion devices, the shielding performance of shielding materials is becoming increasingly demanding, so appropriate preparation methods are needed to increase the content of boron in high boron steel to improve the shielding performance.

[0005] This material can also be used in other fields that require shielding of neutrons and gamma rays, such as fission reactors, nuclear power plants, and nuclear waste storage racks. SUMMARY

[0006] To meet the shielding requirements of reactor nuclear radiation, the present application provides a high-performance boron steel shielding material with high boron content. By increasing the content of boron, the overall shielding performance of the material is enhanced.

[0007] The technical solution adopted by the present application is as follows:

[0008] A high shielding performance boron-containing stainless steel, the weight percentage of the components of the boron-containing stainless steel based on the total weight of the boron-containing stainless steel is: Cr 7.5-25%, Ni 8.5-18.5%, Mn 0.5-4.3%, B 1.8-4.5%, C 0.02%-0.06%, and the balance is Fe.

[0009] Specifically, a high shielding performance boron-containing stainless steel, the component weight percentage of the boron-containing stainless steel is: Cr 7.5-25%, Ni 8.5-18.5%, Mn 0.5-4.3%, B 1.8-4.5%, C 0.02%-0.06%, the balance is Fe and inevitable impurities, based on the total weight of the boron-containing stainless steel.

[0010] The high boron content can be used to shield the absorbed thermal neutrons, and the iron base has good shielding performance for gamma rays, which can realize effective shielding of neutrons and gamma rays

[0011] Preferably, the component weight percentage is: Cr 17.4-22.4%, Ni 11.6-15.6%, Mn 0.5-3.5%, B 2.0-4.0%, C 0.03%-0.05%, the balance is Fe and inevitable impurities, based on the total weight of the boron-containing stainless steel.

[0012] Further, the weight percentage of Cr is 7.5-25%, for example, the weight percentage of Cr is 7.5%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, based on the total weight of the boron-containing stainless steel.

[0013] Further, the weight percentage of Ni is 8.5-18.5%, for example, the weight percentage of Ni is 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or 18.5%, based on the total weight of the boron-containing stainless steel.

[0014] Further, the weight percentage of Mn is 0.5-4.3%, for example, the weight percentage of Mn is 0.5%, 0.6%, 1%, 1.3%, 1.6%, 1.9%, 2.2%, 2.5%, 2.8%, 3.1%, 3.4%, 3.6%, 3.8% or 4.3%, based on the total weight of the boron-containing stainless steel.

[0015] Further, the weight percentage of B is 1.8-4.5%, for example, the weight percentage of B is 1.8%, 1.9%, 2.2%, 2.5%, 2.8%, 3.1%, 3.4%, 3.6%, 3.8%, 4.3% or 4.5%, based on the total weight of the boron-containing stainless steel.

[0016] Further, the weight percentage of C is 0.02%-0.06%, based on the total weight of the boron-containing stainless steel.

[0017] The application discloses a preparation method of high-performance high-boron-content boron steel shielding material.

[0018] Preferably, the step specifically comprises the following steps:

[0019] a. Powdering: uniformly alloyed powder is obtained by powdering chromium iron, nickel and pure iron according to a required ratio and sieving.

[0020] b. Mixing powder: boron iron powder is added into the alloyed powder according to a required ratio, and the powder is mixed in a three-dimensional mixer to obtain uniform powder.

[0021] c. Sintering: the mixed powder is sintered by hot pressing or hot isostatic pressing to obtain high-boron steel.

[0022] Preferably, the sieve mesh number in the step a is 60-300 meshes; and the heating temperature in the step c is 1150-1350 DEG C, and the holding time is 2-4 hours.

[0023] The application has the following beneficial effects:

[0024] The application adopts the hot pressing or hot isostatic pressing process to improve the uniformity of element distribution, the density and the mechanical properties of the material, and can realize effective shielding of neutrons and gamma rays. The material is not only a preferred shielding material for fusion reactor nuclear radiation, but also can be used in other fields requiring shielding of neutrons and gamma rays, such as fission reactor, nuclear power device and nuclear waste storage rack. The sufficient mixing during powdering improves the sintering activity of B element material and the uniformity of B element distribution in the material. Compared with the iron matrix of the material, the boron-containing phase has little deformation capacity, and as the B content increases, the volume fraction of the boron-containing phase in the material will also increase. Therefore, when the boron content increases to form a network structure of the boron-containing phase, the breaking strength of the material will be greatly reduced. When the large high-boron steel is prepared by the melting method, the boron-containing phase is more likely to segregate at the interface of the iron matrix to form a network structure, which is not conducive to the mechanical properties of the material. The high-boron steel prepared by the hot isostatic pressing method has more dispersed boron-containing phase and is not easy to form a network structure, so that the high-boron steel has a higher upper limit of boron content under the premise of maintaining certain mechanical properties. Meanwhile, the hot isostatic pressing has the possibility of large-scale production of large high-boron steel. Considering the shielding performance and the mechanical properties, the boron content in the application is limited to 4.5wt.%. The high-boron steel prepared by the application has a density greater than 99%, the tensile strength of the material is greater than 750 MPa, and the boron density in the material is 0.15-0.3 g / cm 3 . BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1is the microstructure diagram of the high boron steel obtained by embodiment one of the present application.

[0026] Figure 2 is a tensile property diagram of the shielding material prepared in embodiment 1. DETAILED DESCRIPTION

[0027] The embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0028] REFERENCE Figure 1 A high shielding performance boron-containing stainless steel with high boron content, the component weight percentage is: Cr 7.5-25%, Ni 8.5-18.5%, Mn 0.5-4.3%, B 1.8-4.5%, C 0.02%-0.06%, the rest is Fe and inevitable impurities.

[0029] The high boron steel provided by the present application contains 7.5-25% of Cr, preferably 17.4-22.4%, in terms of weight percentage. The present application controls Cr in the above range to eliminate the magnetism of the alloy and improve the corrosion resistance of the alloy.

[0030] The high boron steel provided by the present application contains 8.5-18.5% of Ni, preferably 11.6-15.6%, in terms of weight percentage. The present application controls Ni in the above range to form austenite at room temperature and improve the mechanical properties of the alloy.

[0031] The high boron steel provided by the present application contains 0.5-4.3% of Mn, preferably 0.5-3.5%, in terms of weight percentage. The present application controls Mn in the above range to improve the mechanical properties of the alloy.

[0032] The high boron steel provided by the present application contains 1.8-4.5% of B, preferably 2.0-4.0%, in terms of weight percentage. The present application controls B in the above range to shield slow thermal neutrons.

[0033] The preparation process of the high-performance high-boron steel shielding material with high boron content of the present application includes: powder making, powder mixing, sintering, machining and other processes, so that the bulk shielding material can be obtained. The above steps include:

[0034] a. Powder making: uniformly alloyed powder is obtained by powdering chromium iron, nickel and pure iron according to the required ratio and sieving.

[0035] b. Powder mixing: boron iron powder is added to the alloy powder according to the required proportion, and the powder is mixed in a three-dimensional mixer to obtain uniform powder.

[0036] c. Sintering: the mixed powder is sintered by hot pressing or hot isostatic pressing process to obtain high boron steel.

[0037] Preferably, the sieve mesh number in step a is 60-300 mesh; the heating temperature in step c is greater than 1150-1350℃, and the holding time is greater than 3 hours.

[0038] Case 1

[0039] The shielding material composition provided by the embodiment is B: 3.6wt.%, Ni: 14.3wt.%, Cr: 18.9wt.%, Mn: 1.3wt.%, C: 0.043wt.%, and the balance is Fe.

[0040] As shown in the SEM of the embodiment Figure 1 The preparation of the high-boron steel alloy in the embodiment includes the following steps in sequence:

[0041] (1) Powdering: 30 parts by weight of chromium-iron alloy (Cr: 63wt.%, C<0.03wt.%, Si<1wt.%, P<0.03wt.%, and the balance is iron, based on the total mass of the chromium-iron alloy), 14.3 parts by weight of electrolytic nickel, and 34.3 parts by weight of pure iron are mixed according to the required ratio, and then sieved to obtain uniform alloy powder with a mesh size of 60-300;

[0042] (2) Powder mixing: 20 parts by weight of boron-iron alloy powder with a particle size of 60-80 mesh (B is 18wt.%, Si<2wt.%, Al<0.05wt.%, S<0.01wt.%, P<0.1wt.%, Mn<0.5wt.%, and the balance is iron, based on the total mass of the boron-iron alloy powder), and 1.4 parts by weight of manganese-iron alloy powder (Mn is about 85wt.%, C<0.2wt.%, Si<1.0wt.%, P<0.1wt.%, S<0.02wt.%, and the balance is Fe, based on the total mass of the MnFe alloy) are added to the alloy powder, and the powder is mixed in a three-dimensional mixer for 8 hours to obtain a uniform powder;

[0043] (3) Vacuum degassing: the powder obtained after mixing is placed in a pre-prepared stainless steel jacket, the jacket is vacuumed at a temperature of 300℃, and when the vacuum degree in the jacket reaches less than 10 -2 Pa, the opening is sealed;

[0044] (4) Hot isostatic pressing sintering: hot isostatic pressing sintering is performed at a sintering temperature of 1200℃, a holding time of 3h, and a pressure of 135Mpa, and then the furnace is cooled, the jacket skin is removed by machining, and the shielding material is obtained.

[0045] By Figure 1As can be seen, the dark part in the SEM image is the brittle boron-containing phase which is basically unable to deform, and the light part is the ductile gamma iron phase, and the regular black dots are pores in the material, and the fuzzy black area is impurities on the surface of the material. The tensile strength of the material during the fracture process depends on the continuity of the iron phase. During the preparation of the material, the boron-containing phase is preferentially formed. When the temperature reaches below 1206℃, the boron-containing phase and the gamma iron phase are precipitated at the same time. The preferential nucleation site of the boron-containing phase is on the previously formed boron-containing phase. Therefore, with the increase of the boron content, the dark boron-containing area will increase and be connected, and once the boron phase forms a continuous network structure, the iron phase will no longer be connected, and the tensile strength of the material will rapidly decrease. Therefore, by changing the process and controlling the boron doping amount, the boron-containing phase is ensured to be not connected into a network.

[0046] Figure 2 The tensile curve of the shielding material prepared in Example 1 is shown, and the cross-sectional area of the tensile sample is 1.5*5mm 2 , and the tensile strength of the sample is greater than 850MPa, and the national standard of the tensile strength of 304 steel is 515MPa. Figure 1 The regular black area accounts for a percentage of the total area, and the black area pixel is less than 1%, which proves from the micro level that the area shot by the SEM is densified to more than 99%. The density of the material obtained in Example 1 is 7.44g / cm 3 , the molar density of the elemental substance of the material composition elements is calculated, the weighted average density of the material is obtained from the atomic percentage, the actual measured density is compared, and the material density is greater than 99%. Therefore, from the overall level of the material, the densification is greater than 99%. Finally, the boron-containing density of the material obtained in Example 1 is 0.24g / cm 3 , which is higher than that of 304B7.

[0047] The part of the application not described in detail belongs to the known technology of those skilled in the art. The above-described examples only describe the preferred embodiments of the application, and the preferred examples do not describe all the details and limit the application to the specific embodiments described. Without departing from the design spirit of the application, various modifications and improvements of the technical solutions of the application made by those skilled in the art shall fall within the protection scope of the claims of the application.

Claims

1. A method for preparing boron-containing stainless steel with high shielding performance, characterized in that: Based on the total weight of the boron-containing stainless steel, the weight percentage of the components of the boron-containing stainless steel is as follows: Cr 18-25%, Ni 8.5-18%, Mn 0.5-3.5%, B 3.6-4.5%, C 0.02%-0.06%, with the balance being Fe; The method specifically includes the following steps: a. Powdering: Mix ferrochrome, nickel and pure iron, grind them into powder, and sieve to obtain uniform alloy powder; b. Powder mixing: Add ferroboron powder to the alloy powder and mix them in a three-dimensional mixer to obtain uniform powder; c. Sintering: The mixed powder is sintered by hot pressing or hot isostatic pressing to obtain the boron-containing stainless steel; The sieve mesh size in step a is 60-300 mesh; The heating temperature in step c is 1150-1350℃, and the holding time is 2-4 hours; The obtained material has a density greater than 99%.

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