A method for smelting boron-containing steel for neutron shielding materials

Abstract

This invention discloses a method for smelting boron-containing steel for neutron shielding materials, comprising vacuum smelting and electroslag remelting processes; the vacuum smelting process includes: refining time ≥ min; after refining, argon gas at 10000-30000 Pa is introduced into the furnace, and alloying is performed after the gas introduction, with an alloying time ≥ min; M is the mass of molten steel smelted in the vacuum furnace, in kg; the electroslag remelting process uses a slag system of pre-melted slag and Al powder, the pre-melted slag containing B2O3; the B2O3 content in the pre-melted slag [B2O3]% is determined according to the B content in the vacuum ingot, [B2O3]% = [(2.4×+3.3)]%, where a is the percentage content of B in the vacuum ingot; the Al powder addition amount is 0.2%-0.4% of the mass of the pre-melted slag. This method effectively controls the ingot quality from the start of vacuum smelting, ensuring the uniformity of the solidification structure and composition of the electroslag product, improving the cold and hot working properties of the material, and simplifying the smelting process. It is of great significance for the stable industrial production of this type of product.

Description

Technical Field

[0001] This invention relates to the field of special materials technology, and in particular to a method for smelting boron-containing steel for neutron shielding materials. Background Technology

[0002] Boron-containing steel, a special type of boron steel, is widely used as a shielding material for control rods, thermal neutron shielding in nuclear reactors, and nuclear waste storage racks. It is based on stainless steel, using iron, which has good shielding properties against gamma radiation, as the matrix. Combined with boron's superior shielding properties for thermal neutrons and its ability to suppress and trap gamma rays, boron steel possesses comprehensive shielding performance for both neutrons and gamma rays. Currently, boron-containing stainless steel has become an indispensable protective material in radiation protection design devices.

[0003] Generally, boron-containing steel for neutron shielding materials can be prepared using two methods: smelting and hot isostatic pressing (HIP). HIP uses natural ferroborone powder and 304 stainless steel powder as raw materials, obtaining a near-dense bulk material through hot isostatic pressing, followed by forging and hot rolling. This process is complex and costly. Smelting methods include electric furnaces, non-vacuum induction furnaces, and vacuum induction furnaces. However, precise control of boron content and uniform microstructure are limiting factors in boron-containing steel smelting. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for smelting boron-containing steel for neutron shielding materials with precise composition and uniform structure.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: it includes vacuum smelting and electroslag remelting processes;

[0006] The vacuum smelting process: The vacuum smelting process: After refining, argon gas at 10000–30000 Pa is introduced into the furnace. After the gas introduction is completed, alloying is carried out, with an alloying time ≥0.5 × 10⁻⁶ Pa. M represents the mass of molten steel smelted in a vacuum furnace, in kg.

[0007] The electroslag remelting process uses a slag system consisting of pre-melted slag and Al powder. The pre-melted slag contains B2O3. The B2O3 content [B2O3]% in the pre-melted slag is determined based on the B content in the vacuum ingot. Wherein, a is the percentage content of B in the vacuum ingot; the amount of Al powder added is 0.2% to 0.4% of the mass of the pre-melted slag.

[0008] Furthermore, in the electroslag remelting process, the pre-melted slag composition is: CaF2 40%–47%, CaO 20%–25%, MgO 3%–5%, Al2O3 20%–25%, SiO2 4%–7%, and B2O3.

[0009] Furthermore, in the vacuum smelting process, the molten steel tapping temperature is 40–60°C above the liquidus line.

[0010] Furthermore, in the electroslag remelting process, the melting rate v = (0.013~0.015) × D is controlled during the constant melting rate smelting process. 结 Where v is the melting rate (kg / min) and D is the diameter of the electroslag furnace crystallizer (mm).

[0011] The beneficial effects of adopting the above technical solution are as follows: This invention innovatively employs a dual smelting process of vacuum induction and electroslag remelting. In the vacuum smelting process, by designing a reasonable refining time and fully utilizing the vacuum carbon deoxidation capacity, the content of O, N, and H gases and harmful elements in the molten steel is minimized, creating favorable conditions for the subsequent alloying process. Furthermore, in the alloying process, the B content is precisely controlled by adjusting the furnace pressure and alloying time. In the electroslag remelting process, a six-element slag system is designed. By adding a certain proportion of B2O3, SiO2, and Al powder to the fixed slag system, the oxidation and burning loss of B and Si elements during the electroslag process is effectively suppressed, and the content of each element is precisely controlled. Furthermore, the electroslag process, through low melting rate control, fully ensures the uniformity of the electroslag solidification structure and composition, guaranteeing the cold and hot working performance of the material in subsequent hot working processes.

[0012] This invention effectively controls the quality of ingots from the vacuum smelting stage, ensuring the uniformity of solidification structure and composition of electroslag products, improving the cold and hot working properties of materials, and simplifying the smelting process. It is of great significance for the stable industrial production of such products. Detailed Implementation

[0013] The present invention will now be described in further detail with reference to specific embodiments.

[0014] This neutron shielding material uses a boron-containing steel smelting method. The boron-containing steel has the following chemical composition by mass percentage: Si 0.2%–2%, Mn 0.5%–3%, Ni 11%–15%, Cr 5%–20%, B 0.5%–3%, P ≤ 0.02%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurity elements. This smelting method employs vacuum smelting and electroslag remelting processes, and the process steps are as follows:

[0015] (1) Vacuum smelting process: including batching, charging, melting, refining, alloying and casting of steel;

[0016] (1.1) Batching: The vacuum smelting materials are calculated according to the composition requirements of boron-containing steel. Industrial pure materials are used as the main raw materials, and industrial pure iron, electrolytic nickel plate, metallic chromium, carbon powder, industrial silicon, electrolytic manganese and ferroboron are selected. All elements in the metal materials are considered and the batching is calculated accurately.

[0017] (1.2) Loading the furnace: Place the nickel plate and metallic chromium at the bottom of the crucible of the vacuum furnace, and place pure iron in the middle; load the secondary hopper with carbon powder, industrial silicon, electrolytic manganese and ferroboron; dry the chute and ingot mold and place them in the corresponding positions.

[0018] (1.3) Melting: Evacuate the chamber to a vacuum level of ≤5Pa, then heat it with electricity until the steel material in the crucible is completely melted.

[0019] (1.4) Refining process: After all the metal in the crucible has melted completely, refining begins by adding carbon powder and industrial silicon to the molten steel; the refining time shall not be less than M represents the mass of molten steel smelted in a vacuum furnace, expressed in kg.

[0020] (1.5) Alloying and refining process: After refining, argon gas at 10000-30000 Pa is introduced into the furnace. After the gas is introduced, electrolytic manganese and ferroboron are added for alloying. The alloying time is not less than M represents the mass of molten steel smelted in a vacuum furnace, expressed in kg.

[0021] (1.6) Casting process: After the composition test is qualified, the temperature of the molten steel is adjusted to 40-60°C above the liquidus line, and the steel is cast under electric current. After the ingot is completely solidified, it can be demolded.

[0022] (2) Electroslag remelting process: adopts the pre-smelting preparation, arc ignition and slag removal and constant melting rate smelting process, with argon protection throughout the process;

[0023] (2.1) Preparation before smelting: Cut off the cap part of the vacuum smelting ingot to ensure that there is no shrinkage cavity at the end and ensure that there is no oxide layer on the surface of the ingot. If surface grinding is required, weld it to the auxiliary electrode after pretreatment.

[0024] The slag system is prepared by using pre-melted slag and additionally added Al powder. The pre-melted slag components have the following mass percentages: CaF2 40%–47%, CaO 20%–25%, MgO 3%–5%, Al2O3 20%–25%, SiO2 4%–7%, and B2O3. The B2O3 content is determined based on the B content in the vacuum-cast ingot. Wherein, 'a' represents the mass percentage of B in the vacuum ingot, and '[B2O3]%' represents the mass percentage of B2O3 in the pre-melted slag. The amount of Al powder added is 0.2% to 0.4% of the mass of the pre-melted slag. After the pre-melted slag is stirred and mixed evenly, it is placed in a heating furnace for baking and prepared for use. Al powder is added again before use.

[0025] (2.2) Arc ignition and slag formation process: Place an ingot plate of the same material on the bottom water tank of the electroslag, place arc ignition chips of the same material in the center of the ingot plate, install the crystallizer, protective fume hood and consumable electrode, ignite the arc, and slowly add the slag material of the above slag system after the arc light stabilizes.

[0026] (2.3) Constant melting rate smelting process: After slag formation, control the melting rate v = (0.013~0.015)×D 结 Where v is the melting rate, in kg / min; D 结 The diameter of the electroslag furnace crystallizer is in mm. Feeding is performed when a certain weight of consumable electrode remains during melting. After feeding, the melting power is turned off. Once the electroslag ingot has completely solidified, it can be demolded to obtain a boron-containing steel electroslag ingot. Argon gas is continuously introduced as a protective gas throughout the melting process, with the atmosphere pressure maintained at 500 Pa or higher above atmospheric pressure, ensuring that the oxygen content in the atmosphere is ≤10 ppm throughout the entire melting process.

[0027] Example 1:

[0028] (1) Three furnaces were smelted using a 500Kg vacuum induction furnace and a 1t protective atmosphere electroslag furnace, namely No.1, No.2 and No.3. The target values ​​of the smelting composition are shown in Table 1-1.

[0029] Table 1-1: Target Chemical Composition of Example 1 (wt%)

[0030]

[0031]

[0032] In Table 1, the balance is Fe and unavoidable impurity elements.

[0033] (2) The vacuum smelting process: The ingot mold used for casting is a Φ220×1700mm ingot shape. The mass of molten steel smelted in the vacuum furnace is 500kg; the refining time is not less than... Alloying time not less than

[0034]

[0035] The electroslag remelting process uses a Φ300×1500mm crystallizer. The total mass of the pre-melted slag is 25kg, and the B2O3 content in the pre-melted slag is... The additional Al powder added is 25 × (0.2~0.4)% = 0.05kg~0.1kg. The melting rate is controlled at (0.013~0.015) × D. 结 =(0.013~0.015)×300=3.9kg / min~4.5kg / min.

[0036] The smelting process parameters for furnaces 1 to 3 in this embodiment are shown in Table 1-2, and the slag composition for furnaces 1 to 3 is shown in Table 1-3.

[0037] Table 1-2: Smelting process parameters of Example 1

[0038]

[0039] In Table 2, TL represents the liquidus temperature.

[0040] Table 1-3: Slag Components of Example 1

[0041]

[0042] (3) After demolding, slice the ingot 200 mm from the bottom of the electroslag ingot. Take two samples at each of the three locations: the center of the cross section, the R / 2 position, and the edge, and perform chemical composition analysis. The results of the chemical composition analysis are shown in Table 1-4.

[0043] Table 1-4: Chemical composition (wt%) of electroslag ingots #1 to #3 in Example 1

[0044]

[0045]

[0046] Through tissue observation and chemical composition testing, the electroslag ingots obtained from furnaces #1 to #3 were found to have qualified composition, with uniform solidification structure and composition.

[0047] Example 2:

[0048] (1) Three furnaces were smelted using a 1.5t vacuum induction furnace and a 1.5t protective atmosphere electroslag furnace, namely No. 1, No. 2 and No. 3. The target values ​​of the smelting composition are shown in Table 2-1.

[0049] Table 2-1: Target Chemical Composition (wt%) of Example 2

[0050] To Mn P S Cr In B 2 0.5 ≤0.02 ≤0.02 5 15 3

[0051] In Table 1, the balance is Fe and unavoidable impurity elements.

[0052] (2) The vacuum smelting process: The ingot mold used for casting is a Φ380×1800mm ingot shape. The mass of the molten steel smelted in the vacuum furnace is 1500kg; the refining time is not less than... Alloying time not less than

[0053] The electroslag remelting process uses a Φ500×1000mm crystallizer. The total mass of the pre-melted slag is 85kg, and the B2O3 content in the pre-melted slag is... The additional Al powder added is 85 × (0.2~0.4)% = 0.17kg~0.34kg. The melting rate is controlled at (0.013~0.015) × D. 结 =(0.013~0.015)×500=6.5kg / min~7.5kg / min.

[0054] The smelting process parameters for furnaces 1 to 3 in this embodiment are shown in Table 2-2, and the slag composition for furnaces 1 to 3 is shown in Table 2-3.

[0055] Table 2-2: Smelting process parameters of Example 2

[0056]

[0057]

[0058] In Table 2, TL represents the liquidus temperature.

[0059] Table 2-3: Slag Components of Example 2

[0060]

[0061] (3) After demolding, slice the electroslag ingot 200 mm from the bottom. Take two samples at each of the three locations: the center of the cross section, the R / 2 position, and the edge, and perform chemical composition analysis. The results of the chemical composition analysis are shown in Table 2-4.

[0062] Table 2-4: Chemical composition (wt%) of electroslag ingots #1 to #3 in Example 2

[0063]

[0064] Through tissue observation and chemical composition testing, the electroslag ingots obtained from furnaces #1 to #3 were found to have qualified composition, with uniform solidification structure and composition.

[0065] Example 3:

[0066] (1) Three furnaces were smelted using a 3t vacuum induction furnace and a 3t protective atmosphere electroslag furnace, namely No. 1, No. 2 and No. 3. The target values ​​of the smelting composition are shown in Table 3-1.

[0067] Table 3-1: Target Chemical Composition (wt%) of Example 3

[0068]

[0069] In Table 1, the balance is Fe and unavoidable impurity elements.

[0070] (2) The vacuum smelting process: The ingot mold used for casting is a Φ420×2900mm ingot shape. The mass of molten steel smelted in the vacuum furnace is 3000kg; the refining time is not less than... Alloying time not less than

[0071] The electroslag remelting process uses a Φ530×2000mm crystallizer. The total mass of the pre-melted slag is 100kg, and the B2O3 content in the pre-melted slag is... The additional Al powder added is 100 × (0.2~0.4)% = 0.2kg~0.4kg. The melting rate is controlled at (0.013~0.015) × D. 结 =(0.013~0.015)×530=6.89kg / min~7.95kg / min.

[0072] The smelting process parameters for furnaces 1 to 3 in this embodiment are shown in Table 3-2, and the slag composition for furnaces 1 to 3 is shown in Table 3-3.

[0073] Table 3-2: Smelting process parameters of Example 3

[0074]

[0075] In Table 2, TL represents the liquidus temperature.

[0076] Table 3-3: Slag Components of Example 3

[0077]

[0078] (3) After demolding, slice the electroslag ingot 200 mm from the bottom. Take two samples at the center, R / 2 and edge of the cross section and perform chemical composition analysis. The results of the chemical composition analysis are shown in Table 3-4.

[0079] Table 3-4: Chemical composition (wt%) of electroslag ingots #1 to #3 in Example 3

[0080]

[0081]

[0082] Through tissue observation and chemical composition testing, the electroslag ingots obtained from furnaces #1 to #3 were found to have qualified composition, with uniform solidification structure and composition.

Claims

1. A method for smelting boron-containing steel for neutron shielding materials, characterized in that: It includes vacuum smelting and electroslag remelting processes; The vacuum smelting process: refining time ≥ √M min; after refining, argon gas of 10000~30000Pa is introduced into the furnace, and alloying is carried out after the gas is introduced, with an alloying time ≥ 0.5×√M min; where M is the mass of molten steel smelted in the vacuum furnace, in kg; The electroslag remelting process uses a slag system consisting of pre-melted slag and Al powder. The pre-melted slag contains B2O3. The B2O3 content in the pre-melted slag, [B2O3]%, is determined based on the B content in the vacuum ingot, where [B2O3]% = [(2.4 × √a + 3.3)]%, and a is the percentage of B in the vacuum ingot. The Al powder is added at a rate of 0.2% to 0.4% of the mass of the pre-melted slag.

2. The smelting method of boron-containing steel for neutron shielding materials according to claim 1, characterized in that: The electroslag remelting process has the following pre-melted slag composition: CaF2 40%–47%, CaO 20%–25%, MgO 3%–5%, Al2O3 20%–25%, SiO2 4%–7%, and B2O3.

3. The smelting method of boron-containing steel for neutron shielding materials according to claim 1, characterized in that: In the vacuum smelting process, the molten steel tapping temperature is 40–60°C above the liquidus line.

4. A method for smelting boron-containing steel for neutron shielding materials according to claim 1, 2, or 3, characterized in that: In the electroslag remelting process, the melting rate is controlled as v = (0.013~0.015)×D during the constant melting rate smelting process. 结 Where v is the melting rate (kg / min) and D is the diameter of the electroslag furnace crystallizer (mm).

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