A method for producing a thermal neutron shielding steel

Abstract

The application belongs to the technical field of metal materials and radiation protection, and particularly relates to a preparation method of a thermal neutron shielding steel. The method utilizes the gas-solid two-phase flow driving mechanism under a negative pressure environment to realize high-efficiency spray forming of B4C / 304 stainless steel composite material, B4C ceramic particles are uniformly dispersed and embedded in the 304 stainless steel matrix, and the B4C particles and the matrix form a firm interface bonding due to the strong driving force of the gas-solid two-phase flow. The process combines gas atomization and solid-phase medium particles to form a gas-solid two-phase mixed flow, greatly improves the atomization efficiency, refines the powder particle size, optimizes the distribution of the reinforcing phase, and opens up a new way for the preparation of high-performance thermal neutron shielding steel composite material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal materials and radiation protection, and particularly relates to a preparation method of a thermal neutron shielding steel. BACKGROUND

[0002] Nuclear energy, as an energy form with high efficiency and clean environmental protection characteristics, is widely used in military industry, energy, medical treatment and other fields, and becomes a key choice of countries in response to energy demand and environmental challenges. However, with the rapid development of China's nuclear industry, higher requirements are put forward for the comprehensive performance of the neutron shielding material required for high-performance spent fuel storage and transportation. The current thermal neutron shielding material is usually made by mixing polymers such as polyethylene and polyurethane with neutron shielding substances. The production process of such shielding material is complex and tedious, and the melting point is relatively low, about below 0℃, which becomes hard and brittle, lacking the ability to resist impact and vibration. In addition, B4C ceramic particles are introduced into the composite material by powder metallurgy and other methods to make it have a higher thermal neutron absorption cross section. However, this process has high production cost, and the shielding effect is not ideal. Moreover, the size and distribution state of B4C particles have certain influence on the mechanical properties and interface bonding of the composite material, which cannot meet the actual application requirements in the field of radiation protection technology. Therefore, it is necessary to develop a novel preparation method to meet the current market demand. SUMMARY

[0003] In view of the problems in the prior art, the application provides a preparation method of a thermal neutron shielding steel.

[0004] The technical scheme of the application is as follows:

[0005] A preparation method of a thermal neutron shielding steel, comprising the following steps:

[0006] Step (1) uses a double-vacuum cabin closed structure device to realize negative pressure environment injection: the double-vacuum cabin structure device is divided into a melting cabin, an intermediate package cabin and a spray deposition cabin, the intermediate package cabin is connected with the melting cabin and the spray deposition cabin, and is communicated and isolated through a pouring plug valve; the melting cabin is provided with a melting ladle, and a liftable intermediate package is preheated outside the cabin and then put into the intermediate package cabin; the melting cabin is communicated with a high vacuum pump set, and the vacuum degree of the melting cabin is ≤5×10 -2 Pa; the spray deposition cabin is separately provided with a high-speed vacuum pump set, and the environmental pressure under the input condition of the spray gas is maintained to be ≤5000 Pa;

[0007] Step (2) carries out vacuum medium-frequency induction melting of the 304 base alloy through the melting cabin, wherein the composition of the 304 base alloy is as follows: Cr 17.0-20%, Ni 10.0-16.0%, Mn 1.0-2.5%, B 0.1-0.5%, Ti 0.1-0.5%, C<0.04%, N≤10ppm, and the rest is Fe; the melting amount is 1-10 t;

[0008] Step (3) The 304 stainless steel alloy solution after smelting is controlled at a superheat degree of +40~80℃, the sealing door of the tundish is closed, the bottom argon blowing and degassing treatment is performed by the smelting ladle, the control valve a is opened, the pouring plug is closed, then the pouring plug valves of the smelting chamber and the spray deposition chamber are opened, the high-speed vacuum pump group is started, the tundish is lowered to a distance of 400~800mm from the deposition billet, the smelting ladle controls the flow rate through the bottom slide gate nozzle and pours the 304 stainless steel alloy solution into the tundish at a stable liquid level of 100~180mm, and the preheating temperature of the tundish is ≥1200℃;

[0009] Step (4) B4C particle surface modification: the B4C particles are ball-mixed with 304 stainless steel, Fe or Al powder in liquid argon, the mass fraction of B4C particles is more than 95%, and the grinding ball material is super S280 stainless steel; wherein the particle size of B4C is less than or equal to 2μm, the particle size of the metal powder is 20~30μm, the ball milling time is more than 24 hours, the ball milling speed is 280~320r / min, the metal powder is attached to the surface of the B4C particles to promote the wetting of the B4C particles and the 304 stainless steel alloy solution, and the proportion of the particles providing solidification heat transfer is more than 35%;

[0010] Step (5) After the B4C particles in step (4) are surface modified, the B4C particles are mixed with inert gas Ar in a gas-solid two-phase flow mixing and preheating device, preheated to form a gas-solid two-phase flow, and then enter the spray mechanism (11) through two-phase flow pipelines in two ways, the 304 stainless steel alloy solution is sprayed out through the spray mechanism, and the inert gas Ar blows the B4C particles into the alloy solution in the spray through the two-phase flow pipeline, and the two are gathered and deposited on the deposition billet

[0011] Step (6) The gas-solid two-phase flow disperses the 304 stainless steel alloy solution flowing out of the two sprue gates of the spray mechanism into uniform droplets in the spray deposition chamber, and completes the spray deposition of the deposition billet on the deposition disc;

[0012] Step (7) After the spray is completed, the temperature of the top of the billet is controlled to be ≤1350℃, the temperature of the bottom of the billet is controlled to be ≤1250℃, the billet is taken out and sent to a 1180℃ forging holding furnace for 2h, and then forged into a square billet for hot rolling, the final rolling thickness is 3.0~12mm, the billet plasticity is good, and no edge cracks occur during forging and hot rolling.

[0013] Further, the number of pores on the solidification end face in the spray deposition chamber is ≤5 / 10mm 2 , and the pore size is ≤1μm, and all the pores are compressed after forging in step (7).

[0014] Further, the preparation method of the thermal neutron shielding steel, the liquid phase is driven by gas-solid two-phase flow, and the solid phase exists as the coolant, neutron absorption functional phase and strengthening phase at the same time, after the hot rolling in step (7), the B4C mass fraction in the hot-rolled plate substrate is 3% or more, the B4C particle size is controlled to 800-1200 nm, is uniformly distributed on the substrate, and there is no grain boundary segregation phenomenon, the yield strength of the substrate is 350 MPa or more, the tensile strength is 700 MPa or more, and the room temperature elongation is 25% or more.

[0015] Further, the preparation method of the thermal neutron shielding steel, the preheating temperature of the B4C particles after surface modification in step (5) is ≥600 DEG C, and the powder feeding amount of the 500-1200 nm particle size B4C ceramic particles is 300-1250 g / min.

[0016] Further, in the preparation method of the thermal neutron shielding steel, in step (1), two water outlets are arranged horizontally at the lower end of the tundish, the water outlet diameter is φ4-10 mm, the single nozzle flow rate is 20-60 kg / min, the nozzle outlet flow rate is 1.0-1.8 m / min, the water outlet position is opposite to the 1 / 3 and 2 / 3 positions of the deposited blank radius, and the outer nozzle aperture area is 20% larger than the inner nozzle aperture.

[0017] Further, in the preparation method of the thermal neutron shielding steel, in step (5), the number of openings of the spraying mechanism is 12-20, the aperture is 4-8 mm, and the focal length is below the surface of 60-80 mm; the spraying deposition ring is made of heat-resistant stainless steel, the inner surface is plated with hard chromium, and the HRC is 52 or more; the spraying deposition ring has an inclination of -30 to +30 DEG, a scanning frequency of 0-2 Hz, a gas spraying pressure of 0.4-0.7 MPa, a single spraying deposition ring gas spraying amount of 15-45 m 3 / min, and a particle loading amount of 500-2500 g / min.

[0018] Further, in the preparation method of the thermal neutron shielding steel, in step (6), during the spraying deposition process, the distance between the deposition disc and the lower end of the spraying deposition ring is controlled to be 200-450 mm, the deposited blank diameter is 400-600 mm, the deposition disc rotation speed is 40-80 r / min, the descending speed is 50-120 mm / min, and the surface molten pool depth is controlled to be 1-2 mm.

[0019] The advantages and beneficial effects of the present application are as follows:

[0020] (1) The present application combines the principles of gas-solid two-phase flow and vacuum spray deposition technology to propose a method for preparing thermal neutron shielding steel materials. This method utilizes the driving mechanism of gas-solid two-phase flow in a negative pressure environment to achieve efficient spray forming of B4C / 304 stainless steel composite materials. In this process, B4C ceramic particles are uniformly dispersed and embedded in the 304 stainless steel matrix. Due to the strong driving force of gas-solid two-phase flow, a firm interface is formed between B4C particles and the matrix. This unique process not only promotes rapid solidification of the alloy, but also significantly improves the mechanical properties, corrosion resistance and high temperature resistance of the material, ensuring its excellent shielding performance and stability in the face of high radiation environments.

[0021] (2) The deposition process in a vacuum environment reduces material oxidation and contamination, reducing subsequent processing costs. This process combines gas atomization with solid-phase medium particles to form a gas-solid two-phase mixed flow, significantly improving atomization efficiency, refining powder particle size, and optimizing the distribution of reinforcing phases, opening up new ways for the preparation of high-performance thermal neutron shielding steel composites. This is of great significance for the demand for high-performance materials in the fields of nuclear industry, military industry, aerospace, etc.

[0022] (3) The present application uses a self-designed vacuum cavity structure to successfully perform spray deposition in a negative pressure environment of ≤5000 Pa (≤0.05 bar). By using B4C particles as a cooling medium, the heat absorption capacity of the mixed medium is improved, the gas flow input and flow rate are reduced, and the bubbles in the micro-pool are quickly discharged under negative pressure, eliminating most of the solidification shrinkage and porosity. The remaining part is also a negative pressure vacuum bubble, which is convenient for forging or extrusion compression.

[0023] (4) During the spray forming process of the present application, the droplets rapidly cool under high-speed gas flow, with a cooling speed of 102~103 K / s, which is a rapid solidification far higher than that of powder metallurgy and casting technologies. This rapid solidification characteristic, on the one hand, refines the grains and plays a role in fine-grain strengthening; on the other hand, it makes B4C uniformly distributed in the matrix as a second phase particle, hindering dislocation movement and thus improving the mechanical properties of the material.

[0024] (5) The formed billet in the present application has a relatively high temperature, and the ingot can be directly forged or perforated and rolled into a pipe after uniform sampling at high temperature, eliminating the slow cooling and heating steps and significantly reducing the heat emission of the forming. After the forging and hot rolling process, the B4C / 304 stainless steel composite material has a B4C mass fraction of more than 3% in the matrix, is uniformly distributed in the matrix, and has no grain boundary segregation phenomenon. The yield strength of the matrix is more than 350 MPa, the tensile strength is more than 700 MPa, and the room temperature elongation is more than 25% BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1Process flow chart for preparing the thermal neutron shielding steel of the present application;

[0026] In the figure: 1-high vacuum pump set; 2-control valve a; 3-melting cabin; 4-melting ladle; 5-tundish; 6-pouring plug valve; 7-tundish cabin sealing door; 8-tundish cabin; 9-gas-solid two-phase flow mixing and preheating device; 10-two-phase flow pipeline; 11-injection mechanism; 12-injection deposition cabin; 13-deposited billet; 14-deposition disc; 15-control valve b; 16-solid phase particle cyclone separator; 17-control valve c; 18-high speed vacuum pump set. DETAILED DESCRIPTION

[0027] The process flow chart for preparing the thermal neutron shielding steel of the present application is shown in Figure 1 The following detailed description of the specific embodiments of the present application is made in conjunction with the accompanying drawings and examples, which are used to illustrate the present application, but cannot be used to limit the scope of the present application.

[0028] In the following examples, the negative pressure environment injection is realized by using a double vacuum cabin closed structure device: the double vacuum cabin structure device is divided into a melting cabin 3, a tundish cabin 8 and a injection deposition cabin 12, the tundish cabin 8 is connected to the melting cabin 3 and the injection deposition cabin 12, and the communication and isolation are realized by a pouring plug valve 6; the melting cabin 3 is provided with a melting ladle 4, and a tundish 5 that can be lifted is placed into the tundish cabin 8 after being preheated outside the cabin; the melting cabin 3 is connected to a high vacuum pump set 1, and the injection deposition cabin 12 is separately provided with a high speed vacuum pump set 18. Example 1

[0029] In this embodiment, a preparation method of a thermal neutron shielding steel comprises the following steps:

[0030] Step (1) open control valve a 2, close pouring plug valve 6, adjust the vacuum degree of melting cabin 3 ≤ 5 × 10 -2 Pa, the environmental pressure under the input condition of the injection gas is ≤ 5000 Pa; two water outlets are horizontally arranged at the lower edge of the tundish 5, the water outlet diameter is φ4 mm, the single nozzle flow is 20 kg / min, the nozzle outlet flow speed is 1.0 m / min, the water outlet position is opposite to the 1 / 3 and 2 / 3 positions of the radius of the deposited billet, and the outer nozzle aperture area is 20% larger than the inner nozzle aperture;

[0031] Step (2) vacuum medium frequency induction melting 304 base alloy is carried out through the melting cabin 3, wherein the composition of the 304 base alloy is: Cr 17.0%, Ni 10%, Mn 1%, B 0.1%, Ti 0.1%, C 0.04%, N ≤ 10 ppm, and the rest is Fe; the melting amount is 1 t;

[0032] Step (3) The 304 stainless steel alloy solution after smelting is controlled at +40℃ overheat degree, and is subjected to argon bottom blowing deslagging and degassing treatment from the smelting ladle 4, the control valve a2 and the tundish cabin sealing door 7 are closed, then the control valve b15 and the control valve c17 are opened, then the smelting cabin 3 and the injection deposition cabin 12 pouring plug valve 6 are opened, the high-speed vacuum pump group 18 is started, the tundish 5 is lowered to 400mm away from the deposition blank, the smelting ladle 4 controls the flow through the bottom slide gate nozzle and pours the 304 stainless steel alloy solution into the tundish 100mm to stabilize the liquid level, the tundish 5 is preheated to 1200℃, and the tundish 5 is preheated to 1200℃.

[0033] Step (4) B4C particle surface modification: B4C particles are ball milled with 304 stainless steel, Fe or Al powder in liquid argon, the mass fraction of B4C particles is 95%, the grinding ball material is super S280 stainless steel; wherein the B4C particle size is 2μm, the metal powder particle size is 20μm, the ball milling time is 24 hours, the ball milling speed is 280r / min, the B4C particle surface is attached with metal powder, and the B4C particle and the 304 stainless steel alloy solution are fully wetted, wherein the particle provides a solidification heat transfer ratio of 35%;

[0034] Step (5) After the B4C particles in step (4) are surface modified, the B4C particles are mixed with inert gas Ar in the gas-solid two-phase flow mixing and preheating device 9, and are preheated to form a gas-solid two-phase flow, and are divided into two paths by the two-phase flow pipeline 10 to enter the injection mechanism 11, the 304 stainless steel alloy solution is sprayed out through the injection mechanism 11, the inert gas Ar blows the B4C particles into the alloy solution in the injection through the two-phase flow pipeline 10, and the two are gathered and deposited on the deposition blank 13; the preheating temperature of the surface modified B4C particles is 600℃, and the powder feeding amount of the 500nm particle size B4C ceramic particles is 300g / min; the injection mechanism 11 has 12 opening numbers of the injection deposition ring, the hole diameter is 4mm, and the focal length method surface below 60mm; the injection deposition ring is made of heat-resistant stainless steel, the inner surface is plated with hard chromium, and the HRC is above 52; the injection deposition ring inclination is-30°, the scanning frequency is 0Hz; the gas injection pressure is 0.4MPa, the single injection deposition ring gas injection amount is 15m 3 / min, and the particle loading amount is 500g / min;

[0035] Step (6) The gas-solid two-phase flow disperses the 304 stainless steel alloy solution flowing out of the two sprue gates of the injection mechanism 11 into uniform droplets in the injection deposition cabin 12, and completes the injection of the deposition blank 13 on the deposition disc 14; during the injection deposition process, the distance between the deposition disc 14 and the lower end of the injection deposition ring is controlled to be 200mm, the diameter of the deposition blank 13 is 400mm, the rotation speed of the deposition disc is 40r / min, the lowering speed is 50mm / min, and the surface molten pool depth is controlled to be 1mm;

[0036] After the spraying in step (7) is completed, the temperature of the top of the ingot blank is controlled at 1350℃, and the temperature of the bottom of the ingot blank is controlled at 1250℃. After the ingot blank is taken out, it is sent into a 1180℃ forging holding furnace for 2h, and then is forged into a square blank for hot rolling. The final rolling thickness is 3.0mm. The mass fraction of B4C in the hot-rolled plate substrate is 3%, the B4C particle size is controlled at 800nm, and the B4C particles are uniformly distributed on the substrate without grain boundary segregation. The yield strength of the substrate is 350MPa, the tensile strength is 700MPa, and the room temperature elongation is 25%.

[0037] The number of pores on the solidification end face in the spray deposition cabin is 5 / 10mm 2 , and the pore size is 1μm. After forging in step (7), all the pores are compressed. Embodiment 2

[0038] In this embodiment, a method for preparing a thermal neutron shielding steel includes the following steps:

[0039] Step (1): open the control valve a2, close the pouring plug valve 6, adjust the vacuum degree of the smelting cabin 3 to be less than or equal to 5×10 -2 Pa, and the environmental pressure under the input condition of the spray gas is less than or equal to 5000Pa. Two water outlets are horizontally arranged at the lower edge of the tundish 5, the water outlet diameter is φ6mm, the single nozzle flow rate is 40kg / min, the nozzle outlet flow rate is 1.4m / min, the water outlet position is opposite to the 1 / 3 and 2 / 3 positions of the deposition blank radius, and the outer nozzle aperture area is 20% larger than the inner nozzle aperture.

[0040] Step (2): vacuum medium-frequency induction smelting of the 304 base alloy is performed through the smelting cabin 3. The composition of the 304 base alloy is: Cr 15%, Ni 12%, Mn 2%, B 1%, Ti 0.3%, C 0.04%, N≤10ppm, and the rest is Fe. The smelting amount is 2t.

[0041] Step (3): the 304 stainless steel alloy solution after smelting in step (2) is controlled at a superheat degree of +60℃. The bottom argon blowing and degassing treatment is performed on the smelting ladle 4. The control valve a2 and the tundish cabin sealing door 7 are closed. Then, the control valve b15 and the control valve c17 are opened. Then, the pouring plug valve 6 of the smelting cabin 3 and the spray deposition cabin 12 is opened. The high-speed vacuum pump group 18 is started. The tundish 5 is lowered to a distance of 600mm from the deposition blank. The smelting ladle 4 controls the flow rate through the bottom slide gate and pours the 304 stainless steel alloy solution into the tundish 140mm to stabilize the liquid level. The preheating temperature of the tundish 5 is 1300℃.

[0042] Step (4) B4C particle surface modification: B4C particles are ball-milled with 304 stainless steel, Fe or Al powder in liquid argon, the mass fraction of B4C particles is 95%, the material of grinding ball is super S280 stainless steel; wherein, the particle size of B4C is 1.5 μm, the particle size of metal powder is 25 μm, the ball milling time is 30 hours, the ball milling speed is 300 r / min, the metal powder is attached to the surface of B4C particles to promote the wetting of B4C particles and 304 stainless steel alloy solution, and the proportion of solidification heat transfer provided by the particles is 35%;

[0043] Step (5) After the surface modification of B4C particles in step (4), the B4C particles are mixed with inert gas Ar in the gas-solid two-phase flow mixing and preheating device 9, and then preheated to form a gas-solid two-phase flow, and then the two-phase flow is divided into two paths by two-phase flow pipelines 10 and enters the injection mechanism 11, the 304 stainless steel alloy solution is sprayed out through the injection mechanism 11, the inert gas Ar blows the B4C particles into the alloy solution in the injection through the two-phase flow pipeline 10, and the two are gathered and deposited on the deposition blank 13; the preheating temperature of the surface modified B4C particles is 800℃, the feeding amount of 800 nm particle size B4C ceramic particles is 800 g / min; the number of opening holes of the injection deposition ring of the injection mechanism 11 is 14, the hole diameter is 6 mm, and the focal length is below the surface of 70 mm; the injection deposition ring is made of heat-resistant stainless steel, the inner surface is plated with hard chromium, and the HRC is above 52; the inclination angle of the injection deposition ring is 0°, and the scanning frequency is 1 Hz; the gas injection pressure is 0.5 MPa, the gas injection amount of a single injection deposition ring is 30 m 3 / min, and the particle loading amount is 1000 g / min;

[0044] Step (6) The gas-solid two-phase flow disperses the 304 stainless steel alloy solution flowing out of the two sprue gates of the injection mechanism 11 into uniform droplets in the injection deposition cabin 12, and completes the injection of the deposition blank 13 on the deposition disc 14; during the injection deposition process, the distance between the deposition disc 14 and the lower end of the injection deposition ring is controlled to be 350 mm, the diameter of the deposition blank 13 is 500 mm, the rotation speed of the deposition disc is 60 r / min, the descending speed is 80 mm / min, and the surface molten pool depth is controlled to be 1.5 mm;

[0045] Step (7) After the injection is completed, the temperature of the top of the ingot blank is controlled to be 1350℃, the temperature of the bottom of the ingot blank is controlled to be 1250℃, the ingot blank is taken out and then sent to a 1180℃ forging holding furnace for 2 hours, and then forged into a square billet for hot rolling, the final rolling thickness is 6.0 mm, the mass fraction of B4C in the hot rolled plate substrate is 3%, the size of B4C particles is controlled to be 1000 nm, the B4C particles are uniformly distributed on the substrate without grain boundary segregation, the yield strength of the substrate is 350 MPa, the tensile strength is 700 MPa, and the room temperature elongation is 30%;

[0046] The number of pores on the solidification end face in the injection deposition cabin is 8 per 10 mm 2, and the pore diameter is 1 μm, and all the pores are closed after forging in step (7). Example 3

[0047] In this embodiment, a method for preparing a thermal neutron shielding steel includes the following steps:

[0048] Step (1) open control valve a2, close pouring plug valve 6, adjust the vacuum degree of smelting cabin 3 to be less than or equal to 5*10 -2 Pa, the environmental pressure under the input condition of the jet gas is less than or equal to 5000 Pa; two water outlets are horizontally arranged at the lower edge of tundish 5, the diameter of the water outlet is φ10 mm, the single nozzle flow is 60 kg / min, the nozzle outlet flow rate is 1.8 m / min, the water outlet position is opposite to the 1 / 3 and 2 / 3 positions of the deposited billet radius, and the outer nozzle aperture area is 20% larger than the inner nozzle aperture area;

[0049] Step (2) vacuum medium-frequency induction smelting of 304 base alloy is carried out through smelting cabin 3, wherein the composition of the 304 base alloy is: Cr 20%, Ni 16.0%, Mn 2.5%, B 0.5%, Ti 0.5%, C 0.04%, N≤10 ppm, and the rest is Fe; the smelting amount is 10 t;

[0050] Step (3) the overheat degree of the 304 stainless steel alloy solution after smelting in step (2) is controlled to be +80℃, bottom argon blowing and degassing treatment are carried out on smelting ladle 4, control valve a2 and tundish cabin sealing door 7 are closed, then control valve b15 and control valve c17 are opened, then pouring plug valve 6 of smelting cabin 3 and jet deposition cabin 12 is opened, high-speed vacuum pump group 18 is started, tundish 5 is lowered to a distance of 800 mm from the deposited billet, smelting ladle 4 controls the flow through the bottom slide gate and injects the 304 stainless steel alloy solution into tundish 180 mm to stabilize the liquid level, and the preheating temperature of tundish 5 is 1400℃;

[0051] Step (4) surface modification of B4C particles: B4C particles are ball-milled with 304 stainless steel, Fe or Al powder in liquid argon, the mass fraction of B4C particles is 95%, and the grinding ball material is super S280 stainless steel; wherein the particle size of B4C is 2 μm, and the particle size of the metal powder is 30 μm, the ball-milling is carried out for 1 h, and then paused for 15 min; the ball-milling is carried out for 1 h, and then paused for 10 min; then the operation mode of ball-milling for 1 h and pausing for 5 min is repeated for 5 times, and the ball-milling speed is 320 r / min, which promotes the adhesion of metal powder on the surface of B4C particles and promotes the full wetting of B4C particles and the 304 stainless steel alloy solution, wherein the proportion of the particles providing solidification heat transfer is 35%;

[0052] Step (5) the B4C particles after surface modification in step (4) are mixed with inert gas Ar uniformly in the gas-solid two-phase flow mixing and preheating device 9 and preheated to form a gas-solid two-phase flow, and are divided into two paths by the two-phase flow pipeline 10 to enter the injection mechanism 11, and the 304 stainless alloy solution is sprayed out by the injection mechanism 11, the inert gas Ar blows the B4C particles into the alloy solution in the injection through the two-phase flow pipeline 10, and the two are converged and deposited on the deposition blank 13; the preheating temperature of the B4C particles after surface modification is 800℃, the powder feeding amount of the 1200nm particle size B4C ceramic particles is 1250g / min; the number of the spray deposition ring opening of the injection mechanism 11 is 16, the aperture is 8mm, and the focal length method surface below 80mm; the spray deposition ring is made of heat-resistant stainless steel, the inner surface is plated with hard chromium with HRC above 52; the spray deposition ring inclination is +30°, the scanning frequency is 2Hz; the gas injection pressure is 0.7MPa, the gas injection amount of a single spray deposition ring is 45m 3 / min, and the particle loading amount is 2500g / min;

[0053] Step (6) the gas-solid two-phase flow disperses the 304 stainless alloy solution flowing out of the two sprue gates of the injection mechanism 11 into uniform droplets in the spray deposition cabin 12, and completes the spray of the deposition blank 13 on the deposition disc 14; during the spray deposition process, the distance between the deposition disc 14 and the lower end of the spray deposition ring is controlled to be 450mm, the diameter of the deposition blank 13 is 600mm, the rotation speed of the deposition disc is 80r / min, the descending speed is 120mm / min, and the surface molten pool depth is controlled to be 2mm;

[0054] Step (7) after the spray is completed, the temperature of the top of the ingot blank is controlled to be 1350℃, the temperature of the bottom of the ingot blank is controlled to be 1250℃, the ingot blank is taken out and sent to the 1180℃ forging holding furnace for 2h, and then forged into a square billet for hot rolling, the final rolling thickness is 12.0mm, the mass fraction of B4C in the hot rolled plate substrate is 3%, the size of the B4C particles is controlled to be 1200nm, the B4C particles are uniformly distributed on the substrate without grain boundary segregation phenomenon, the yield strength of the substrate is 350MPa, the tensile strength is 700MPa, and the room temperature elongation is 25%;

[0055] The number of pores on the solidification end face in the spray deposition cabin is 6 / 10mm 2 , and the aperture is 1μm, and all the pores are pressed after forging in step (7).

Claims

1. A method for preparing thermal neutron shielding steel, characterized in that, Includes the following steps: Step (1) Use a double vacuum chamber closed structure device to achieve negative pressure environment spraying: The double vacuum chamber closed structure device is divided into a smelting chamber, an intermediate ladle chamber and a spray deposition chamber. The intermediate ladle chamber is connected to the smelting chamber and the spray deposition chamber. The connection and isolation are achieved through a pouring gate valve. The smelting chamber is equipped with a smelting ladle. The liftable intermediate ladle is preheated to the temperature outside the chamber and then placed into the intermediate ladle chamber. The melting chamber is connected to a high-vacuum pump unit, and the vacuum degree of the melting chamber is ≤5×10⁻⁶. -2 Pa; The jet deposition chamber is equipped with a separate high-speed vacuum pump group to maintain an ambient pressure ≤5000Pa under jet gas input conditions; Step (2) Vacuum medium-frequency induction melting of 304 matrix alloy is carried out in a melting chamber. The composition of 304 matrix alloy is: Cr 17.0~20%, Ni 10.0~16.0%, Mn 1.0~2.5%, B 0.1~0.5%, Ti 0.1~0.5%, C < 0.04%, N ≤ 10ppm, and the remainder is Fe; the melting amount is 1~10t. Step (3) Step (2) After smelting, the superheat of the 304 stainless steel alloy solution is controlled to be +40~80℃. The sealing door of the tundish is closed. The bottom blowing argon deslag removal and degassing treatment is carried out by the smelting ladle. The control valve a is opened, the casting gate valve is closed, and then the casting gate valves of the smelting chamber and the jet deposition chamber are opened. The high pumping speed vacuum pump group is started. The tundish is lowered to 400~800mm away from the deposition billet. The smelting ladle controls the flow rate through the bottom slide gate and injects the 304 stainless steel alloy solution into the tundish to stabilize the liquid level at 100~180mm. The tundish preheating temperature is ≥1200℃. Step (4) Surface modification of B4C particles: B4C particles are ball-milled with 304 stainless steel, Fe or Al powder in liquid argon. The mass fraction of B4C particles is above 95%, and the grinding ball material is super S280 stainless steel. The particle size of B4C is below 2μm, the particle size of metal powder is 20~30μm, the ball milling time is above 24 hours, and the ball milling speed is 280~320r / min. This promotes the adhesion of metal powder to the surface of B4C particles and promotes the full wetting of B4C particles and 304 stainless steel alloy solution. The particles provide more than 35% of the solidification heat transfer. Step (5) After the surface modification of B4C particles in step (4), they are mixed evenly with inert gas Ar in a gas-solid two-phase flow mixing and preheating device and then preheated to form a gas-solid two-phase flow. The flow is divided into two routes and enters the spraying mechanism through the two-phase flow pipe. The 304 stainless steel alloy solution is sprayed out through the spraying mechanism. The inert gas Ar blows the B4C particles into the alloy solution in the spray through the two-phase flow pipe. The two converge and are deposited on the deposited billet. Step (6) The gas-solid two-phase flow fully disperses the 304 stainless steel alloy solution flowing out of the two gates of the spraying mechanism into uniform droplets in the spraying deposition chamber, and completes the spraying of the deposited billet on the deposition plate. After the spraying in step (7), the temperature of the top of the billet is controlled at ≤1350℃ and the temperature of the bottom of the billet is controlled at ≤1250℃. After the billet is taken out, it is sent to a forging holding furnace at 1180℃ for 2 hours to be uniformly heated. Then it is forged into a square billet for hot rolling. The final rolling thickness is 3.0~12mm.

2. The method for preparing a thermal neutron shielding steel according to claim 1, characterized in that, The number of pores on the solidification end face inside the jet deposition chamber is ≤5 / 10mm 2 And the pore size is ≤1μm, and all the pores are pressed together after forging in step (7).

3. The method for preparing a thermal neutron shielding steel according to claim 1, characterized in that, After hot rolling in step (7), the mass fraction of B4C in the hot-rolled plate matrix is ​​more than 3%, the particle size of B4C is controlled at 800~1200nm, and it is uniformly distributed on the matrix without grain boundary segregation.

4. The method for preparing a thermal neutron shielding steel according to claim 1, characterized in that, In step (5), the preheating temperature of the surface-modified B4C particles is ≥600℃, and the powder feeding rate of B4C ceramic particles with a particle size of 500~1200nm is 300~1250g / min.

5. The method for preparing a thermal neutron shielding steel according to claim 1, characterized in that, In step (1), two nozzles are arranged horizontally along the lower edge of the tundish. The nozzle diameter is φ4~10mm, the single nozzle flow rate is 20~60kg / min, the nozzle outlet velocity is 1.0~1.8m / min, and the nozzle positions are directly opposite the 1 / 3 and 2 / 3 positions of the deposition billet radius. The outer nozzle orifice area is 20% larger than the inner orifice area.

6. The method for preparing a thermal neutron shielding steel according to claim 1, characterized in that, In step (5), the number of openings in the jet deposition ring of the jetting mechanism is 12-20, the diameter of the openings is 4-8mm, and the diameter of the openings is 60-80mm below the focal length normal. The jet deposition ring is made of heat-resistant stainless steel with hard chromium plating on the inner surface, and the diameter is HRC52 or higher. The tilt angle of the jet deposition ring is -30° to +30°, the scanning frequency is 0-2Hz, the gas jet pressure is 0.4-0.7MPa, and the gas jet volume of a single jet deposition ring is 15-45m³. 3 / min, particle loading rate 500~2500g / min.

7. The method for preparing a thermal neutron shielding steel according to claim 1, characterized in that, In step (6) during the spray deposition process, the distance between the deposition disk and the lower end of the spray deposition ring is controlled to be 200~450mm, the diameter of the deposition blank is 400~600mm, the rotation speed of the deposition disk is 40~80r / min, the descent speed is 50~120mm / min, and the depth of the surface molten pool is controlled to be 1~2mm.

Images