Carburizing type plastic die steel electroslag material and preparation method thereof

Abstract

The invention belongs to the technical field of electroslag remelting metallurgy, and particularly relates to carburizing type plastic die steel electroslag charge and a preparation method thereof. The carburizing type plastic die steel electroslag material comprises the following components in percentage by mass: 50%-60% of CaF2, 15%-20% of Al2O3, 5%-8% of BaO, 3%-5% of NaCl, 5%-10% of CaO, 10%-15% of MgO and the balance of inevitable impurities. The invention solves the problems of high melting point, high viscosity, insufficient inclusion removal capability, unstable later viscosity and the like of the existing slag charge during electroslag remelting.

Description

Technical Field

[0001] This invention belongs to the field of electroslag remelting metallurgical technology, and in particular relates to an electroslag material for carburizing plastic mold steel and its preparation method. Background Technology

[0002] Carburizing plastic mold steel is an ideal material for manufacturing plastic molds requiring high wear resistance, corrosion resistance, toughness, and polishing performance. It is widely used in the production of high-precision, complex-structured plastic parts molds, such as gears, cams, and micro-motor parts, where the requirements for inclusion content are extremely strict. In the preparation of carburizing plastic mold steel, the electroslag remelting process plays a crucial role. During the melting process, the electroslag remelting slag comes into deep contact with the molten metal droplets and undergoes a chemical reaction. This process directly affects the purity, microstructure, and performance of the steel, determining the final product quality of the carburizing plastic mold steel. Currently, there are two main conventional slag systems used in the electroslag remelting process for carburizing plastic mold steel. One is a binary slag system with a CaF2 to Al2O3 mass ratio of 7:3 ("3:7"). This slag system has a relatively high melting point of 1350–1400℃, and a high Al2O3 content, resulting in a relatively weak ability to remove oxide inclusions, making it difficult to fully purify the molten steel and affecting the quality of the steel. Another type is the ternary slag system with a mass ratio of CaF2, Al2O3, and MgO of 13:6:1. Compared to the binary slag system, its melting point is 1300–1345℃, which is lower. It also prevents hydrogen absorption during the process and has an improved ability to remove inclusions. However, it still has certain shortcomings in terms of high polishability and corrosion resistance due to inclusions in the steel, especially chromium trioxide inclusions. With the increasing demands for surface quality in plastic molds, existing slag systems are no longer sufficient to meet production needs. Developing new electroslag remelting slag systems to improve the overall performance of carburizing plastic mold steel has become an urgent problem to be solved.

[0003] Patent application number 202211674173.2 discloses an electroslag remelting slag system for mirror die steel electroslag remelting process, containing eight components: CaF2, BaF2, MgF2, CaO, MgO, Al2O3, SiO2, and Li2O. While the addition of multiple components that lower the melting point of the slag system reduces its melting point, the viscosity at 1500℃ is not effectively reduced, remaining at 0.15–0.35 Pa·s, compared to 0.148 Pa·s for conventional slag at the same temperature. The viscosity of the slag system actually increases after the addition of these components, primarily because the addition of Li2O raises the crystallization temperature of the slag phase. Furthermore, the added SiO2, being a network of tetrahedral oxides at high temperatures, has a relatively high viscosity, further increasing the viscosity and hindering the capture of inclusions in the molten metal droplets. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a carburizing plastic mold steel electroslag material and its preparation method, which solves the problems of high melting point, high viscosity, insufficient removal of inclusions and unstable viscosity in the later stage when existing slag materials are electroslag remelted.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A carburizing type plastic mold steel electroslag material, the composition by mass percentage is: CaF2: 50%~60%, Al2O3: 15%~20%, BaO: 5%~8%, NaCl: 3%~5%, CaO: 5%~10%, MgO: 10%~15%, the remainder being unavoidable impurities.

[0007] The function of each component:

[0008] As a key component, CaF2 effectively lowers the melting point of slag, improves its fluidity, and promotes full contact and reaction between slag and steel during electroslag remelting. Its content of 50%–60% ensures effective control over melting point and fluidity without adversely affecting other properties due to excessive content.

[0009] Al2O3 helps adjust the viscosity and conductivity of slag, while also adsorbing and removing inclusions in molten steel. A content range of 15% to 20% allows for a good balance between viscosity, conductivity, and inclusion removal capacity in the slag.

[0010] The addition of BaO is one of the key innovations of this invention. In slag, BaO can synergistically work with other components to effectively inhibit the precipitation of magnesium chromium spinel. Its content of 5% to 8% ensures the inhibitory effect without introducing too many other negative impacts.

[0011] NaCl is also an important component in the slag composition design of this invention. It can further lower the melting point of the slag system, improve the wettability of the liquid slag to inclusions, thereby enhancing the removal capacity of Cr2O3 inclusions and the like. A content of 3% to 5% can optimize the slag performance while ensuring its stability.

[0012] CaO participates in metallurgical reactions, effectively desulfurizing and dephosphorizing, and improving the purity of molten steel. A content of 5% to 10% can fully exert its desulfurization and dephosphorization effects, while also working in conjunction with other components to maintain the stability of the overall performance of the slag.

[0013] Although MgO can form magnesium chromium spinel with Cr2O3 when used alone, in the composite slag system of this invention, by properly proportioning it with other components within a content range of 10% to 15%, its positive effects of reducing melting point and viscosity can be fully realized, while its negative effects can be effectively suppressed.

[0014] A method for preparing electroslag slag for carburizing plastic mold steel includes the following steps:

[0015] 1) Raw material pretreatment: Calcine CaF2 powder at 800-1000℃ for 2-3 hours to remove moisture and volatile impurities. Ball mill Al2O3 powder for 4-6 hours to refine the powder particle size to 5-10 μm.

[0016] 2) Ingredient mixing: According to the formula, put the dry CaO, BaO, NaCl, MgO powder and the pretreated CaF2 and Al2O3 powder into the mixer and mix at a speed of 300-500 r / min for 30-60 min. During the mixing process, nitrogen gas is introduced as a protective gas.

[0017] 3) Smelting and slag formation: The uniformly mixed raw materials are placed in an electric resistance furnace for smelting. The heating rate is controlled at 10-15℃ / min. The temperature is raised to 1500-1600℃ and held at this temperature for 2-3 hours to form a uniform slag.

[0018] 4) Casting: The molten slag is poured into the mold. During the casting process, the casting temperature is controlled at 1400-1500℃ and the casting speed is 3-5 kg / min. After cooling to room temperature, the dense slag block is removed from the mold.

[0019] 5) Crushing and grinding: The slag casting blocks are crushed into blocks with a particle size of less than 5mm using a crusher. Then, the crushed slag is put into a ball mill for grinding. The grinding time is 8 to 12 hours, so that the particle size of the slag reaches 0.1 to 0.5mm.

[0020] 6) Sealed packaging.

[0021] In step 3), during the smelting process, the slag is stirred by a stirring device at a speed of 50-80 r / min.

[0022] In step 4), a water-cooled copper mold is used.

[0023] In step 5), the crusher is a jaw crusher.

[0024] Compared with existing technologies, the beneficial effects of this invention are:

[0025] 1. By adding BaO and NaCl, the melting point of the slag was effectively lowered to 1200–1300℃. Simultaneously, at 1500℃, the viscosity was controlled at 0.2–0.4 Pa·s, significantly improving the slag's fluidity. This not only reduced energy consumption during the electroslag remelting process—actual tests showed a reduction of approximately 15%–20%—but also improved the formation rate and stability of the slag pool, increasing production efficiency by approximately 20%–30%.

[0026] 2. The synergistic effect of Al2O3, BaO, and NaCl: BaO reduces the viscosity of the slag, making it easier to flow; Al2O3 regulates the chemical activity of the slag, enhancing its reactivity with inclusions; and NaCl further optimizes the slag structure and reduces interfacial tension. The combined effect of these three components overcomes the shortcomings of individual components in terms of viscosity, activity, or interfacial tension, thereby significantly improving wettability and greatly enhancing the wettability of the slag to inclusions. Experimental results show that after electroslag remelting using the slag material of this invention, the inclusion content in the molten steel is significantly reduced, especially the removal effect on Cr2O3 inclusions. Compared with the use of "Sanqi" slag, the Cr2O3 inclusion content in the molten steel is reduced by approximately 50%–60%, effectively improving the purity of the molten steel and providing a guarantee for the production of high-quality carburizing plastic mold steel.

[0027] 3. BaO plays a crucial role in the slag. BaO preferentially reacts with Cr2O3 to form BaCrO4, thus consuming Cr2O3 and reducing the likelihood of it reacting with MgO to form MgCr spinel. This effectively inhibits the formation of high-melting-point, high-hardness MgCr spinel between MgO and Cr2O3. Throughout the electroslag remelting process, the viscosity of the slag remains stable, avoiding the problem of a sharp increase in viscosity later due to MgCr spinel precipitation. This allows the mass and heat transfer processes between slag and steel to proceed continuously and stably, ensuring the stability and consistency of ingot quality, reducing the generation of internal defects in the ingot, and improving the product qualification rate. Detailed Implementation

[0028] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. The reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0029] A carburizing type plastic mold steel electroslag material, the composition by mass percentage is: CaF2: 50%~60%, Al2O3: 15%~20%, BaO: 5%~8%, NaCl: 3%~5%, CaO: 5%~10%, MgO: 10%~15%, the remainder being unavoidable impurities.

[0030] A method for preparing electroslag slag for carburizing plastic mold steel includes the following steps:

[0031] 1) Raw material pretreatment: Using CaF2, Al2O3, BaO, NaCl, CaO, and MgO powders with a purity ≥98% as raw materials, calcine the CaF2 powder at 800–1000℃ for 2–3 hours to remove moisture and volatile impurities, improving its purity and stability, and enhancing its reactivity in subsequent smelting processes. Ball mill the Al2O3 powder for 4–6 hours to refine the particle size to 5–10 μm, increasing its specific surface area and improving its dispersibility in the slag and its reaction efficiency with other components. Store the CaO powder in a dry environment to prevent it from absorbing moisture and carbon dioxide from the air and deteriorating, ensuring its effective component content and chemical activity in the slag. Maintain a dry and clean environment for the BaO, NaCl, and MgO powders during storage and handling to avoid contamination by impurities.

[0032] 2) Ingredient Mixing: Weigh the raw materials according to the proportions and put them into a high-speed mixer. Mix at a speed of 300-500 r / min for 30-60 min. During the mixing process, nitrogen gas is introduced as a protective gas to prevent the raw materials from oxidizing or becoming damp, ensuring that all components are mixed evenly and laying the foundation for the full chemical reaction in the subsequent smelting process.

[0033] 3) Smelting and Slag Formation: The uniformly mixed raw materials are placed in an electric resistance furnace for smelting. The heating rate is controlled at 10–15℃ / min, raising the temperature to 1500–1600℃ and holding it at this temperature for 2–3 hours to allow the raw materials to fully melt and react, forming a uniform slag. During the smelting process, the slag is moderately stirred using a stirring device at a stirring speed of 50–80 r / min to further homogenize the components in the slag, making the composition and properties of the slag more stable and uniform.

[0034] 4) Casting: After smelting, the molten slag is poured into the mold through the pouring gate. The mold is a water-cooled copper mold, utilizing its excellent thermal conductivity to accelerate the cooling rate of the molten slag, allowing it to solidify rapidly and obtain a dense slag ingot. During casting, the casting temperature is controlled at 1400–1500℃, and the casting speed is 3–5 kg / min to ensure the stability and continuity of the casting process and avoid casting defects.

[0035] 5) Crushing and Grinding: The cooled slag ingots are removed from the mold and crushed into blocks with a particle size of less than 5 mm using a jaw crusher. Then, the crushed slag is put into a ball mill for grinding for 8 to 12 hours, so that the particle size of the slag reaches 0.1 to 0.5 mm, which meets the particle size requirements of the electroslag remelting process for carburizing plastic mold steel, and ensures the reactivity and uniformity of the slag in the electroslag remelting process.

[0036] 6) Quality Inspection: A comprehensive quality inspection is conducted on the prepared slag material. X-ray fluorescence spectrometry is used to analyze the chemical composition of the slag material to ensure that the content of each component meets the design requirements.

[0037] A laser particle size analyzer was used to determine the particle size distribution of the slag material to ensure its uniformity and that the particle size distribution range met the set standards.

[0038] The melting point and viscosity of the slag were tested using a thermogravimetric analyzer and a rotational viscometer, respectively. The melting point was between 1200 and 1300°C, meeting the requirements for reduced energy consumption and rapid slag pool formation. The viscosity at 1500°C was 0.2–0.4 Pa·s, ensuring good mass and heat transfer between slag and steel. The qualified slag was sealed and stored to prevent moisture, oxidation, or contamination with impurities, for subsequent electroslag remelting.

[0039] To make the objectives, technical solutions, and technical effects of this invention clearer, the technical solutions in the embodiments of this invention are now described clearly and completely. However, the embodiments described below are only some embodiments of this invention, not all embodiments. All other embodiments obtained by those skilled in the art in conjunction with the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] Example 1

[0041] A method for preparing electroslag slag for carburizing plastic mold steel includes the following steps:

[0042] 1) Raw material pretreatment: Weigh 120 kg of CaF2 powder with a purity of 98% and calcine it at 800℃ for 3 h; weigh 36 kg of Al2O3 powder with a purity of 99% and ball mill it for 6 h to obtain Al2O3 powder with a particle size of 5-10 μm; weigh 18 kg of CaO powder with a purity of 98% and store it in a dry environment for later use; weigh 12 kg of BaO powder with a purity of 99%; weigh 6 kg of NaCl powder with a purity of 98%; weigh 30 kg of MgO powder with a purity of 99% for later use.

[0043] 2) Ingredient mixing: Place CaF2, Al2O3, CaO, BaO, NaCl and MgO powders into a high-speed mixer and mix at 300 r / min for 60 min, while purging with nitrogen for protection.

[0044] 3) Smelting and slag formation: The uniformly mixed raw materials are placed in an electric resistance furnace and heated to 1500℃ at a heating rate of 10℃ / min, and held at that temperature for 3 hours. During the smelting process, the mixture is stirred at a speed of 50r / min using a stirring device.

[0045] 4) Casting: The molten slag is cast into a water-cooled copper mold at a casting temperature of 1400℃ and a casting speed of 3kg / min. After cooling, the slag ingot is obtained.

[0046] 5) Crushing and grinding: The cooled slag casting blocks are crushed into blocks with a particle size of less than 5 mm using a jaw crusher, and then ground in a ball mill for 12 hours to obtain slag products with a particle size of 0.1 to 0.5 mm.

[0047] 6) Quality Inspection: The chemical composition of the slag was analyzed using X-ray fluorescence spectrometry, with the following mass percentages: CaF2: 60%, Al2O3: 18%, CaO: 9%, BaO: 6%, NaCl: 3%, MgO: 14%. The particle size distribution was determined to be uniform using a laser particle size analyzer. Tests using a thermogravimetric analyzer and rotational viscometer showed that the slag had a melting point of 1220℃ and a viscosity of 0.25 Pa·s at 1500℃, meeting the performance requirements.

[0048] Example 2

[0049] A method for preparing electroslag slag for carburizing plastic mold steel includes the following steps:

[0050] 1) Raw material pretreatment: Weigh 100 kg of CaF2 powder with a purity of 99% and calcine it at 900℃ for 2.5 h; weigh 30 kg of Al2O3 powder with a purity of 99.5% and ball mill it for 5 h to obtain Al2O3 powder; weigh 10 kg of CaO powder with a purity of 99%; weigh 10 kg of BaO powder with a purity of 99%; weigh 4 kg of NaCl powder with a purity of 98%; weigh 22 kg of MgO powder with a purity of 99% for later use.

[0051] 2) Ingredient mixing: Put all raw materials into a high-speed mixer and mix at a speed of 400 r / min for 45 min, and then purge with nitrogen for protection.

[0052] 3) Smelting and slag formation: The mixed raw materials are placed in an electric resistance furnace and heated to 1550℃ at a heating rate of 12℃ / min. The temperature is held for 2.5 hours. The stirring speed during the smelting process is 60r / min.

[0053] 4) Casting: At a casting temperature of 1450℃, molten slag is cast into a water-cooled copper mold at a casting speed of 4 kg / min. After cooling, slag ingots are obtained.

[0054] 5) Crushing and grinding: After crushing the slag casting, ball milling for 10 hours to obtain qualified slag products.

[0055] 6) Quality inspection: The chemical composition of the slag was tested and found to be as follows (by mass percentage): CaF2: 50%, Al2O3: 15%, CaO: 5%, BaO: 5%, NaCl: 2%, MgO: 13%.

[0056] The slag has uniform particle size, a melting point of 1280℃, and a viscosity of 0.35 Pa·s at 1500℃.

[0057] Application Example 1

[0058] The slag material prepared in Example 1 was used in the electroslag remelting production of 3Cr2MnNiMo carburizing plastic mold steel. The electrode was a 3Cr2MnNiMo steel billet, the current was 3000A, and the voltage was 40V.

[0059] Application Example 2

[0060] The slag material prepared in Example 2 was used to produce 20CrMnTi carburizing plastic mold steel by electroslag remelting. The electrode was a 20CrMnTi steel billet, the current was 4000A, and the voltage was 45V.

[0061] Comparative Example 1

[0062] The traditional "three-seven" slag (CaF2-Al2O3 binary slag system, mass ratio CaF2:Al2O3=70:30) was used to remelt 3Cr2MnNiMo carburizing plastic mold steel using the same electroslag remelting process as in Application Example 1.

[0063] Comparative Example 2

[0064] Using slag material with only MgO (15% by mass) added to the "Sanqi" slag of Comparative Example 1, 20CrMnTi carburizing plastic mold steel was electroslag remelted according to the same electroslag remelting process as in Application Example 2.

[0065] After remelting, the steel ingots were tested, and the results are shown in the table below;

[0066]

[0067] By comparing the examples and comparative examples, it can be clearly seen that the slag material and formulation method for electroslag remelting of carburizing plastic mold steel prepared by the present invention have significant advantages in reducing melting point and viscosity, enhancing the ability to remove inclusions, and inhibiting the precipitation of magnesium chromium spinel, which can effectively improve the quality and production of carburizing plastic mold steel.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A carburizing plastic mold steel electroslag ramming material, characterized by, The ingredients are as follows in percentage by mass: CaF2: 50-60%, Al2O3: 15-20%, BaO: 5-8%, NaCl: 3-5%, CaO: 5-10%, MgO: 10-15%, and the rest are inevitable impurities.

2. A method of producing a carburizing plastic mold steel electroslag material according to claim 1, characterized in that, The method comprises the following steps: 1) raw material pretreatment: CaF2 powder is calcined at 800-1000°C for 2-3h to remove water and volatile impurities, and Al2O3 powder is ball milled for 4-6h to refine the particle size to 5-10μm; 2) batching and mixing: dry CaO, BaO, NaCl, MgO powders and pretreated CaF2, Al2O3 powders are put into a mixer according to the ratio, mixed at a speed of 300-500r / min for 30-60min, and nitrogen is introduced as a protective gas during the mixing process; 3) smelting and slagging: the mixed raw materials are put into an electric resistance furnace for smelting, the heating rate is controlled at 10-15°C / min, the temperature is raised to 1500-1600°C, and the temperature is kept at this temperature for 2-3h to form a uniform molten slag; 4) casting and forming: the molten slag is cast into a mold, the casting temperature is controlled at 1400-1500°C during the casting process, the casting speed is 3-5kg / min, and the dense slag block is taken out from the mold after cooling to room temperature; 5) crushing and grinding: the slag block is crushed into a blocky material with a particle size of less than 5mm by a crusher, and then the crushed slag is put into a ball mill for grinding, the grinding time is 8-12h, and the particle size of the slag is 0.1-0.5mm.

3. A method of producing a carburizing plastic mold steel electroslag material according to claim 2, characterized in that, In step 3), the molten slag is stirred by a stirring device during smelting, and the stirring speed is 50-80r / min.

4. The method of claim 2, wherein the carburized plastic mold steel electroslag material is prepared by the steps of: preparing a powder mixture of the carburized plastic mold steel; and sintering the powder mixture at a temperature of 1,300°C to 1,500°C for 1 to 5 hours in a vacuum or an inert gas atmosphere. In step 4), the mold is a water-cooled copper mold.

5. The method of claim 2, wherein the carburized plastic mold steel ESR feedstock is prepared by the steps of: providing a steel ingot; heating the steel ingot to a temperature of about 1,500°C to about 1,600°C; and pouring the steel ingot into a mold to form a billet. In step 5), the crusher is a jaw crusher.

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