Austempering plastic die steel and its preparation method

Abstract

This invention discloses an age-curing plastic mold steel and its preparation method, belonging to the field of metal materials technology. The chemical composition of the age-curing plastic mold steel of this invention is: C: 0.25-0.35%, Si: 0.6-1.0%, Mn: 14-16%, P≤0.015%, S≤0.010%, Cr: 3.8-4.2%, Mo: 0.5-0.7%, V: 0.8-1.2%, Ni: 1-1.5%, Al: 0.3-0.4%, Ni / Al: 3-5%, with the balance being Fe and unavoidable impurities. The preparation process includes vacuum induction melting, electroslag remelting, forging, and heat treatment. This invention yields a high-manganese, low-nickel age-curing plastic mold steel with a hardness ≥43.6 HRC after aging and a hardness deviation ≤1.7 HRC, making it a preferred material for mold steel used in thermoplastic molding.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, and specifically relates to an age-curing plastic mold steel and its preparation method. Background Technology

[0002] In recent years, with the rapid development of my country's mold industry, the consumption of plastic mold steel has also increased significantly. In 2010, my country's demand for plastic mold steel was 200,000 tons; by 2020, it had reached 500,000 tons, 2.5 times that of 2010. It is projected that by 2030, my country's demand for plastic mold steel will reach 1 million tons. Currently, the qualified output of mold steel in China is around 400,000 tons, and the demand for high-end products such as age-hardening and high-corrosion-resistant mold steels is entirely dependent on imports. Compared with some industrialized countries, the service life of domestic plastic mold steel is generally shorter, only about 1 / 5 to 1 / 3 of that of imported steel. The reasons for this, besides machining precision, include a significant gap in metallurgical quality, particularly in inclusion content, microstructure uniformity, and surface hardness, compared to imported mold steel.

[0003] To improve product performance, age-hardening mold steels are generally smelted, forged, and subjected to high-temperature quenching (solution treatment). Then, while the steel is in a softened state and its microstructure is a single supersaturated solid solution, it undergoes aging treatment (heated to a relatively low temperature and held for a period of time). Fine, dispersed intermetallic compounds precipitate from the matrix, thereby strengthening and hardening the steel. This type of steel is divided into high-nickel martensitic aging steel and low-nickel aging steel. Representative grades of high-nickel aging steel include the 18Ni (250), (300), and (350) series. A typical representative of low-nickel aging steel is the American P21 steel. Similar products in various countries are developed based on P21, such as Daido Steel's NAK55 and NAK80, Hitachi Metals' HPM7, and domestic products such as 10Ni3MnCuA1 (code PMS), 25CrNi3MoAl, and Y20CrNi3AMnMo (code SM2).

[0004] Nickel is added to all age-hardening mold steels, primarily to improve the microstructure stability of the steel matrix. However, even in low-nickel grades of age-hardening mold steel, the nickel content is around 3%, which not only increases alloy costs but also represents an excessive consumption of strategic national resources such as nickel. Therefore, it is urgent to research new steel grades with even lower nickel content and product performance that fully meets the requirements for the use of age-hardening mold steels.

[0005] Publication number CN110295314A discloses a 10Ni3MnCuAl-ESR age-hardening plastic mold steel with the following chemical composition: C 0.10–0.20%, Si 0.23–0.38%, Ni 2.5–3.5%, Mn 0.08–1.70%, Mo 0.16–0.34%, Cu 0.5–1.8%, Al 0.08–1.2%, P 0.01–0.02%, S≤0.005%, with the balance being Fe. This invention is based on the 10Ni3MnCuAl composition system, which generally reduces the alloy content, but the nickel content remains high at 2.5–3.5%, resulting in a relatively high cost. Apart from this, no other age-hardening plastic mold steel with a new composition system has been published.

[0006] Publication number CN108441613A discloses a method for controlling white spots in age-hardening plastic mold steel. The purpose of this invention is to prevent white spots in 10Ni3MnCuAl mold steel after forging. The focus is on improving the comprehensive mechanical properties of the material, but it does not fundamentally solve the development problem of age-hardening plastic mold steel. Summary of the Invention

[0007] The purpose of this invention is to provide a low-cost age-hardening plastic mold steel with high Mn and low Ni by substituting manganese for nickel through reasonable composition design, and to ensure that the material meets the performance requirements of age-hardening mold steel products through reasonable process design.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an age-hardening plastic mold steel, wherein the chemical composition and mass percentage of the plastic mold steel are: C: 0.25-0.35%, Si: 0.6-1.0%, Mn: 14-16%, P≤0.015%, S≤0.010%, Cr: 3.8-4.2%, Mo: 0.5-0.7%, V: 0.8-1.2%, Ni: 1-1.5%, Al: 0.3-0.4%, Ni / Al: 3-5, and the balance is Fe and unavoidable impurities.

[0009] The plastic mold steel of the present invention has a hardness ≥43.6HRC after aging, and a hardness deviation ≤1.7HRC.

[0010] The metallographic structure of the plastic mold steel of the present invention is austenite as the matrix, with fine and dispersed carbides and Ni3Al intermetallic compounds distributed on it.

[0011] Another object of the present invention is to provide a method for preparing the above-mentioned age-curing plastic mold steel, the method comprising the following steps:

[0012] (1) Vacuum induction melting: The materials are distributed according to the design, and the materials are smelted in a vacuum induction furnace and cast into consumable electrodes for electroslag remelting.

[0013] (2) Electroslag remelting: Electroslag remelting under argon protection conditions;

[0014] (3) Forging: After heating and holding the electroslag ingot, forging is carried out at 950-1150℃ with a forging ratio ≥7. After forging, the ingot is air-cooled to room temperature.

[0015] (4) Heat treatment: After water quenching at 1130-1150℃ and aging at 460-500℃, the forging is air-cooled to room temperature.

[0016] In step (2) of the present invention, the slag composition is CaF2: 58-62%, CaO: 20-22%, Al2O3: 13-15%, SiO2: 3-7%.

[0017] In the forging process of step (3) of the present invention, the electroslag ingot is heated with the furnace at an initial rate of ≤60℃ / h. When it reaches 700~750℃, it is held for 2~3h, and then rapidly heated to 1180~1200℃ and held for 6~8h.

[0018] In the heat treatment process of step (4) of the present invention, during water quenching, the initial heating rate of the forging is ≤60℃ / h, and after reaching 700~750℃, it is held for 1~2h, and then rapidly heated to 1130~1150℃, with a holding time of 2~3min × billet thickness; during aging, it is held at 460~500℃ for 1~2min × billet thickness; the billet thickness is in mm.

[0019] In step (1) of the present invention, the alloying process is as follows: stop the vacuum, fill with 10000-20000Pa argon gas, adjust the temperature to 1550-1580℃, and add single crystal silicon, carbon powder, ferrovanadium, electrolytic manganese and aluminum granules in sequence; tapping: adjust the temperature to 1510-1530℃ and cast with electricity.

[0020] In step (2) of the present invention, the process of electroslag remelting is as follows: arc initiation and slag formation: energize to initiate an arc, add slag material, adjust the voltage to 25-45V and the current to 2500-5500A to form slag, and the slag formation period is 25-50min; remelting: adjust the voltage to 45-51V, the current to 4500-7500A, and the melting rate to 3.5-5.5kg / min, and replenish the remaining electrode when the remaining electrode is 30-50kg.

[0021] In step (2) of the electroslag remelting process described in this invention, the feeding period is 30-40 minutes. During this feeding period, the voltage and current gradually decrease from 45-48V and 4500-5500A to 25-35V and 2500-3000A. The melting process ends after the feeding period.

[0022] The beneficial effects of adopting the above technical solution are as follows:

[0023] 1. The beneficial effects of adopting the above technical solution are as follows: the composition design has been comprehensively optimized, manganese has been used to replace nickel, reducing the content of the precious metal Ni, and 14-16% Mn has been added to expand the austenite region. Through water toughening treatment, a single-phase austenite structure is obtained, ensuring the uniformity of material properties. The high Mn content design also increases the hardness of the matrix. Appropriate amounts of carbide-forming elements such as Mo and V, as well as Al, are added to form Ni3Al intermetallic compounds, which serve as precipitation strengthening phases and improve the strength of the matrix. The addition of 0.6-1.0% Si is designed to play a solid solution strengthening role.

[0024] 2. Without affecting the austenitic structure, adding 3.8–4.2% Cr not only provides solid solution strengthening but also forms Cr... 23 C6 dispersed phase strengthens the matrix and can also form a Cr2O3+α-Al2O3 anti-oxidation film with Al, compensating for the loss of matrix anti-oxidation capacity due to reduced Al content.

[0025] 3. The process designed in this invention is vacuum induction melting, electroslag remelting, forging, and heat treatment. The entire process is relatively simple and can effectively control harmful components such as P, S, and inclusions. The hit rate of elements such as C, Si, Mn, Cr, Mo, and V is also high. In particular, after electroslag remelting, the uniformity of Mn element composition is guaranteed. Moreover, each process has a clear purpose, good reproducibility, strong operability, and is easy to promote. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments.

[0027] The preparation process of the age-curing plastic mold steel of this invention includes: vacuum induction melting, electroslag remelting, forging, and heat treatment, as detailed below:

[0028] (1) Vacuum induction melting:

[0029] Furnace loading: According to the design, some pure iron is placed at the bottom of the crucible, metallic chromium, electrolytic nickel, and ferromolybdenum are placed in the middle, and the remaining pure iron is loaded in the top. The secondary hopper is loaded with carbon powder, monocrystalline silicon, electrolytic manganese, ferrovanadium, and aluminum granules.

[0030] Melting and refining: Vacuum to ≤5Pa, power on to melt, after all melted, heat to 1600~1640℃, adjust vacuum to ≤0.1Pa, until the molten steel is sampled and tested for [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0031] Alloying: Stop the vacuum, fill with 10000~20000Pa argon gas, adjust the temperature to 1550~1580℃, and add single crystal silicon, carbon powder, ferrovanadium, electrolytic manganese and aluminum granules in sequence. After melting and cleaning, test the composition and fine-tune it to meet the requirements.

[0032] Steel tapping: Adjust the temperature to 1510-1530℃ and cast it into an electroslag consumable electrode while energized.

[0033] (2) Electroslag remelting

[0034] Preparation: Baking of a slag system containing 58-62% CaF2, 20-22% CaO, 13-15% Al2O3, and 3-7% SiO2; stress-relief annealing, grinding, and welding of the vacuum ingot; sequentially laying the ingot plate and arc-starting agent in the bottom water tank, and installing the crystallizer and electrodes;

[0035] Arc initiation and slag formation: Lower the electrode, apply current to initiate the arc, add slag material, adjust the voltage to 25-45V and the current to 2500-5500A to perform slag formation, and the slag formation period is 25-50 minutes.

[0036] Remelting: After entering the remelting period, adjust the voltage to 45-51V, the current to 4500-7500A, and the melting rate to 3.5-5.5kg / min, and replenish the electrode when the remaining electrode weight is 30-50kg.

[0037] Compensation period: During the compensation period of 30 to 40 minutes, the voltage and current gradually decrease from 45 to 48V and 4500 to 5500A to 25 to 35V and 2500 to 3000A. The melting process ends after the compensation period.

[0038] (3) Forging

[0039] Heating: The electroslag ingot is heated with the furnace at an initial rate of ≤60℃ / h. When it reaches 700~750℃, it is held for 2~3h, and then rapidly heated to 1180~1200℃ and held for 6~8h.

[0040] Forging: The initial forging temperature is 1150℃, and the final forging temperature is 950℃. The forging is repeatedly upsetting and drawing three times within this temperature range, and then forged into the finished product shape. The forging pressure ratio is ≥7. The forging is air-cooled to room temperature.

[0041] (4) Heat treatment

[0042] Water toughening: When loading the forging into the furnace, the initial heating rate is ≤60℃ / h. When the temperature reaches 700~750℃, hold for 1~2h, then rapidly heat to 1130~1150℃ and hold for (2~3)min × billet thickness (mm). After that, take it out and place it in water at ≤30℃. Take it out at room temperature.

[0043] Aging: Load the forging into the furnace, slowly heat it to 460-500℃, hold it for (1-2) min × billet thickness (mm), and then remove it for air cooling. Example 1

[0044] Based on the design composition of the age-curing plastic mold steel provided in Table 1, the materials were prepared in batches of 500 kg each to prepare the age-curing plastic mold steel of this invention. The process steps are as follows:

[0045] 1) Vacuum induction furnace smelting

[0046] Furnace loading: Place 190kg of pure iron at the bottom of the crucible, 19.8kg of metallic chromium, 7kg of electrolytic nickel, and 5.1kg of ferromolybdenum (60% molybdenum content) in the middle, and then load another 186kg of pure iron on top. The secondary hopper is filled with 1.5kg of carbon powder, 4.2kg of monocrystalline silicon, 75kg of electrolytic manganese, 8.8kg of ferrovanadium (50% vanadium content), and 2kg of aluminum granules.

[0047] Melting and refining: Vacuum to 5Pa, power on to melt, after all the furnace charge in the crucible has melted, heat to 1600℃, adjust vacuum to 0.1Pa, and refine until the molten steel [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0048] Alloying: Stop the vacuum, fill with 10000Pa argon gas, adjust the temperature to 1550℃, and add single crystal silicon, carbon powder, ferrovanadium, electrolytic manganese, and aluminum granules in sequence. After melting and cleaning, test the composition and fine-tune it to meet the requirements.

[0049] Steel tapping: Adjust the temperature to 1510℃ and cast it into an electrode with a diameter of Φ200*1800mm while energized.

[0050] 2) Electroslag remelting

[0051] Preparation: Bake 25kg of slag system containing 58%CaF2, 22%CaO, 13%Al2O3, and 7%SiO2; Stress-relief annealing, grinding, and welding of vacuum ingots; Lay Φ250*30mm ingot plates and 300g of iron filings of the same material in the bottom water tank in sequence, and install Φ300*1300mm crystallizer and electrodes;

[0052] Arc initiation and slag formation: Lower the electrode, apply current to initiate the arc, add slag material, adjust the voltage to 25-35V and the current to 2500-4500A to form slag, and the slag formation period is 25 minutes;

[0053] Remelting: After entering the remelting period, adjust the voltage to 45-48V, the current to 4500-5500A, and the melting rate to 3.5kg / min, and replenish the remaining electrode when 30kg remains.

[0054] Compensation period: During the compensation period of 30 minutes, the voltage and current gradually decrease from 45V and 4500A to 25V and 2500A. The melting process ends after the compensation period.

[0055] 3) Forging

[0056] Heating: After the electroslag ingot is loaded into the furnace, the temperature is raised along with the furnace. The initial rate is 55℃ / h. When it reaches 725℃, it is held for 2-3 hours. Then, the temperature is rapidly raised to 1180℃ and held for 6 hours.

[0057] Forging: After the electroslag ingot is taken out of the furnace, it is forged in multiple directions at a temperature of 950-980℃ with multiple heats, upsetting and drawing, and a forging ratio of 7. After forging, it is air-cooled to room temperature.

[0058] The first upsetting and drawing process involves upsetting a Φ300mm electroslag ingot to Φ500mm, then drawing it to a length of 400mm×400mm square billet. The second upsetting and drawing process involves upsetting the 400mm×400mm square billet to 550mm×550mm square billet, then drawing it to a length of 460mm×460mm square billet. The third upsetting and drawing process involves upsetting the 460mm×460mm square billet to 600mm×600mm square billet, then drawing it to a length of 500mm×500mm square billet. Finally, the billet is forged into a finished steel block forging of 200mm×430mm×706mm.

[0059] 4) Heat treatment

[0060] Water quenching: Forgings are loaded into the furnace, and the initial heating rate of the forgings is 58℃ / h. After reaching 700℃, they are held for 2 hours, and then rapidly heated to 1130℃ and held for 400 minutes (for billet thickness of 200mm). The forgings are then removed and placed in water, and removed at room temperature.

[0061] Aging: Load the forgings into the furnace again, heat to 460℃, hold for 200 minutes, and air cool to room temperature.

[0062] The hardness of the forgings after aging treatment was tested at the center of the two end faces, 1 / 4 of the diagonal, and 1 / 2 of each side, and was found to be 45.0 to 46.2 HRC. Example 2

[0063] Based on the design composition of the age-curing plastic mold steel provided in Table 1, the materials were prepared in batches of 500 kg each to prepare the age-curing plastic mold steel of the present invention.

[0064] The process for each step is as follows:

[0065] 1) Vacuum induction furnace smelting

[0066] Furnace loading: Place 200kg of pure iron at the bottom of the crucible, 19kg of metallic chromium, 5kg of electrolytic nickel, and 4.6kg of ferromolybdenum (60% molybdenum content) in the middle, and then load another 180kg of pure iron on top. The secondary hopper is filled with 1.7kg of carbon powder, 3.1kg of monocrystalline silicon, 72kg of electrolytic manganese, 9.4kg of ferrovanadium (50% vanadium content), and 1.8kg of aluminum granules.

[0067] Melting and refining: Vacuum to 3Pa, power on to melt, after all the furnace charge in the crucible has melted, heat to 1620℃, adjust vacuum to 0.1Pa, and refine until the molten steel [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0068] Alloying: Stop the vacuum, fill with 15000Pa argon gas, adjust the temperature to 1580℃, and add single crystal silicon, carbon powder, ferrovanadium, electrolytic manganese, and aluminum granules in sequence. After melting and cleaning, test the composition and fine-tune it to meet the requirements.

[0069] Steel tapping: Adjust the temperature to 1520℃ and cast it into an electrode with a diameter of Φ200*1800mm while energized.

[0070] 2) Electroslag remelting

[0071] Preparation: Bake 25kg of slag system containing 62%CaF2, 20%CaO, 15%Al2O3, and 3%SiO2; Stress-relief annealing, grinding, and welding of vacuum ingots; Lay Φ250*30mm ingot plates and 300g of iron filings of the same material in the bottom water tank in sequence, and install Φ300*1300mm crystallizer and electrodes;

[0072] Arc initiation and slag formation: Lower the electrode, apply current to initiate the arc, add slag material, adjust the voltage to 25-35V and the current to 2500-3300A to form slag, and the slag formation period is 25 minutes;

[0073] Remelting: After entering the remelting period, adjust the voltage to 45-48V, the current to 5000-6000A, and the melting rate to 3.7kg / min, and replenish the material when the remaining electrode is 40kg.

[0074] Compensation period: During the compensation period of 35 minutes, the voltage and current gradually decrease from 45V and 5000A to 30V and 3000A. The melting process ends after the compensation period.

[0075] 3) Forging

[0076] Heating: After the electroslag ingot is loaded into the furnace, the temperature is raised along with the furnace. The initial rate is 60℃ / h. When it reaches 710℃, it is held for 3 hours. Then, the temperature is rapidly raised to 1190℃ and held for 6 hours.

[0077] Forging: After the electroslag ingot is taken out of the furnace, it is forged in multiple directions, including upsetting and drawing, at a temperature of 965-990℃, with a forging ratio of 9. After forging, it is air-cooled to room temperature.

[0078] The first upsetting and drawing process involves upsetting a Φ300mm electroslag ingot to Φ500mm, then drawing it to a length of 450mm×450mm square billet. The second upsetting and drawing process involves upsetting the 450mm×450mm square billet to 550mm×550mm square billet, then drawing it to a length of 460mm×460mm square billet. The third upsetting and drawing process involves upsetting the 460mm×460mm square billet to 600mm×600mm square billet, then drawing it to a length of 450mm×450mm square billet. Finally, the billet is forged into a finished steel block forging of 180mm×564mm×564mm.

[0079] 4) Heat treatment

[0080] Water quenching: Forgings are loaded into the furnace, and the initial heating rate of the forgings is 53℃ / h. After reaching 735℃, they are held for 1 hour, and then rapidly heated to 1135℃ and held for 360 minutes (for billet thickness 180mm). The forgings are then removed and placed in water, and removed at room temperature.

[0081] Aging: Then load the forgings into the furnace, heat to 465℃, hold for 180 minutes, and air cool to room temperature.

[0082] The hardness of the forgings after aging treatment was tested at the center of the two end faces, 1 / 4 of the diagonal, and 1 / 2 of each side, and the results were 45.3 to 45.8 HRC. Example 3

[0083] Based on the design composition of the age-curing plastic mold steel provided in Table 1, the materials were prepared in a quantity of 1000 kg to prepare the age-curing plastic mold steel of the present invention.

[0084] The process for each step is as follows:

[0085] 1) Vacuum induction furnace smelting

[0086] Furnace loading: Place 360kg of pure iron at the bottom of the crucible, 40kg of metallic chromium, 12kg of electrolytic nickel, and 8.3kg of ferromolybdenum (60% molybdenum content) in the middle, and then load another 356kg of pure iron on top. The secondary hopper is filled with 32kg of carbon powder, 10.4kg of monocrystalline silicon, 161kg of electrolytic manganese, 16kg of ferrovanadium (50% vanadium content), and 4.3kg of aluminum granules.

[0087] Melting and refining: Vacuum to 4Pa, power on to melt, after all the furnace charge in the crucible has melted, heat to 1640℃, adjust vacuum to 0.05Pa, and refine until the molten steel [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0088] Alloying: Stop the vacuum, fill with 20000Pa argon gas, adjust the temperature to 1580℃, and add single crystal silicon, carbon powder, ferrovanadium, electrolytic manganese, and aluminum granules in sequence. After melting and cleaning, test the composition and fine-tune it to meet the requirements.

[0089] Steel tapping: Adjust the temperature to 1530℃ and cast it into an electrode with a diameter of Φ290*2000mm while energized.

[0090] 2) Electroslag remelting

[0091] Preparation: Bake 50kg of slag system containing 60% CaF2, 20% CaO, 13% Al2O3, and 7% SiO2; Stress-relief annealing, grinding, and welding of vacuum ingots; Lay Φ350*40mm ingot plates and 600g of iron filings of the same material in the bottom water tank in sequence, and install Φ400*1300mm crystallizer and electrodes;

[0092] Arc initiation and slag formation: Lower the electrode, apply current to initiate the arc, add slag material, adjust the voltage to 35-45V and the current to 2800-5500A to carry out slag formation, and the slag formation period is 45 minutes.

[0093] Remelting: After entering the remelting period, adjust the voltage to 47-51V, the current to 5500-7500A, and the melting rate to 5.5kg / min, and replenish the remaining electrode when it reaches 50kg.

[0094] Compensation period: During the compensation period of 40 minutes, the voltage and current gradually decrease from 47V and 5500A to 35V and 3000A. The melting process ends after the compensation period.

[0095] 3) Forging

[0096] Heating: After the electroslag ingot is loaded into the furnace, the temperature is raised along with the furnace. The initial rate is 58℃ / h. When it reaches 750℃, it is held for 2.8h. Then, the temperature is rapidly raised to 1200℃ and held for 8h.

[0097] Forging: After the electroslag ingot is taken out of the furnace, it is forged in multiple directions, including upsetting and drawing, at a temperature of 955-975℃, with a forging ratio of 13. After forging, it is air-cooled to room temperature.

[0098] The first upsetting and drawing process involves upsetting a Φ400mm electroslag ingot to Φ600mm, then drawing it to a length of 520mm×520mm square billet. The second upsetting and drawing process involves upsetting the 520mm×520mm square billet to 650mm×650mm square billet, then drawing it to a length of 490mm×490mm square billet. The third upsetting and drawing process involves upsetting the 490mm×490mm square billet to 630mm×630mm square billet, then drawing it to a length of 550mm×550mm square billet. Finally, the billet is forged into a finished steel block forging of 240mm×664mm×780mm.

[0099] 4) Heat treatment

[0100] Water quenching: Forgings are loaded into the furnace, and the initial heating rate of the forgings is 48℃ / h. After reaching 720℃, they are held for 2 hours, and then rapidly heated to 1150℃ and held for 720 minutes (for billet thickness 240mm). The forgings are then removed and placed in water, and removed at room temperature.

[0101] Aging: Then load the forgings into the furnace, heat to 500℃, hold for 480 minutes, and air cool to room temperature.

[0102] Hardness tests were performed on the center of the two end faces, the 1 / 4 of the diagonal, and the 1 / 2 of each side of the forging after aging treatment, and the results were 43.6 to 45.2 HRC. Example 4

[0103] Based on the design composition of the age-curing plastic mold steel provided in Table 1, the materials were prepared in a quantity of 1000 kg to prepare the age-curing plastic mold steel of the present invention.

[0104] The process for each step is as follows:

[0105] 1) Vacuum induction furnace smelting

[0106] Furnace loading: Place 360kg of pure iron at the bottom of the crucible, 41kg of metallic chromium, 13kg of electrolytic nickel, and 11.3kg of ferromolybdenum (60% molybdenum content) in the middle, and then load another 362kg of pure iron on top. The secondary hopper is filled with 26kg of carbon powder, 9.2kg of monocrystalline silicon, 150kg of electrolytic manganese, 22.4kg of ferrovanadium (50% vanadium content), and 3.7kg of aluminum granules.

[0107] Melting and refining: Vacuum to 1 Pa, power on to melt, after all the furnace charge in the crucible has melted, heat to 1640℃, adjust vacuum to 0.1 Pa, and refine until the molten steel [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0108] Alloying: Stop the vacuum, fill with 15000Pa argon gas, adjust the temperature to 1580℃, and add single crystal silicon, carbon powder, ferrovanadium, electrolytic manganese, and aluminum granules in sequence. After melting and cleaning, test the composition and fine-tune it to meet the requirements.

[0109] Steel tapping: Adjust the temperature to 1530℃ and cast it into an electrode with a diameter of Φ290*2000mm while energized.

[0110] 2) Electroslag remelting

[0111] Preparation: Bake 50kg of slag system containing 59%CaF2, 21%CaO, 13%Al2O3, and 7%SiO2; Stress-relief annealing, grinding, and welding of vacuum ingots; Lay Φ350*40mm ingot plates and 600g of iron filings of the same material in the bottom water tank in sequence, and install Φ400*1300mm crystallizer and electrodes;

[0112] Arc initiation and slag formation: Lower the electrode, apply current to initiate the arc, add slag material, adjust the voltage to 35-45V and the current to 2800-5300A to carry out slag formation, and the slag formation period is 50 minutes.

[0113] Remelting: After entering the remelting period, adjust the voltage to 45-50V, the current to 5300-7000A, and the melting rate to 5kg / min, and then feed the remaining electrode when it reaches 50kg.

[0114] Compensation period: During the compensation period of 50 minutes, the voltage and current gradually decrease from 45V and 5300A to 33V and 2800A. The melting process ends after the compensation period.

[0115] 3) Forging

[0116] Heating: After the electroslag ingot is loaded into the furnace, the temperature is raised along with the furnace. The initial rate is 45℃ / h. When it reaches 730℃, it is held for 2.5h. Then, the temperature is rapidly raised to 1185℃ and held for 8h.

[0117] Forging: After the electroslag ingot is taken out of the furnace, it is forged in multiple directions, including forging, drawing and forging at a temperature of 980-1020℃, with a forging ratio of 16. After forging, it is air-cooled to room temperature.

[0118] The first upsetting and drawing process involves upsetting a Φ400mm electroslag ingot to Φ600mm, then drawing it to a length of 520mm×520mm square billet. The second upsetting and drawing process involves upsetting the 520mm×520mm square billet to 650mm×650mm square billet, then drawing it to a length of 490mm×490mm square billet. The third upsetting and drawing process involves upsetting the 490mm×490mm square billet to 630mm×630mm square billet, then drawing it to a length of 550mm×550mm square billet. Finally, the billet is forged into a finished steel block forging of 200mm×730mm×770mm.

[0119] 4) Heat treatment

[0120] Water quenching: Forgings are loaded into the furnace, and the initial heating rate of the forgings is 50℃ / h. After reaching 740℃, the temperature is held for 1.5h, and then the temperature is rapidly increased to 1140℃ and held for 500min (for billet thickness of 200mm). The forgings are then removed and placed in water, and removed at room temperature.

[0121] Aging: Then load the forgings into the furnace, heat to 480℃, hold for 300 minutes, and air cool to room temperature.

[0122] Hardness tests were performed on the center of the two end faces, the 1 / 4 of the diagonal, and the 1 / 2 of each side of the forging after aging treatment, and the results were 44.3 to 46.0 HRC. Example 5

[0123] Based on the design composition of the age-curing plastic mold steel provided in Table 1, the materials were prepared in a quantity of 1000 kg to prepare the age-curing plastic mold steel of the present invention.

[0124] The process for each step is as follows:

[0125] 1) Vacuum induction furnace smelting

[0126] Furnace loading: Place 355kg of pure iron at the bottom of the crucible, 42kg of metallic chromium, 11kg of electrolytic nickel, and 11.7kg of ferromolybdenum (60% molybdenum content) in the middle, and then load another 360kg of pure iron on top. The secondary hopper is filled with 37kg of carbon powder, 7.8kg of monocrystalline silicon, 163kg of electrolytic manganese, 21.4kg of ferrovanadium (50% vanadium content), and 3.8kg of aluminum granules.

[0127] Melting and refining: Vacuum to 1 Pa, power on to melt, after all the furnace charge in the crucible has melted, heat to 1640℃, adjust vacuum to 0.05 Pa, and refine until the molten steel [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0128] Alloying: Stop the vacuum, fill with 20000Pa argon gas, adjust the temperature to 1580℃, and add single crystal silicon, carbon powder, ferrovanadium, electrolytic manganese, and aluminum granules in sequence. After melting and cleaning, test the composition and fine-tune it to meet the requirements.

[0129] Steel tapping: Adjust the temperature to 1530℃ and cast the electrode into a Φ250*2600mm electrode while it is energized.

[0130] 2) Electroslag remelting

[0131] Preparation: Bake 40kg of slag system containing 60% CaF2, 22% CaO, 14% Al2O3, and 4% SiO2; Stress-relief annealing, grinding, and welding of vacuum ingots; Lay Φ320*40mm ingot plates and 600g of iron filings of the same material in the bottom water tank in sequence, and install Φ350*1600mm crystallizer and electrodes;

[0132] Arc initiation and slag formation: Lower the electrode, apply current to initiate the arc, add slag material, adjust the voltage to 30-45V and the current to 2800-5000A to form slag, and the slag formation period is 40 minutes.

[0133] Remelting: After entering the remelting period, adjust the voltage to 45-48V, the current to 5000-6500A, and the melting rate to 4.5kg / min, and replenish the material when the remaining electrode is 40kg.

[0134] Compensation period: During the compensation period of 35 minutes, the voltage and current gradually decrease from 45V and 5000A to 30V and 2500A. The melting process ends after the compensation period.

[0135] 3) Forging

[0136] Heating: After the electroslag ingot is loaded into the furnace, the temperature is raised along with the furnace. The initial rate is 47℃ / h. When it reaches 720℃, it is held for 2 hours. Then, the temperature is rapidly raised to 1195℃ and held for 6.5 hours.

[0137] Forging: After the electroslag ingot is taken out of the furnace, it is forged in multiple directions, including upsetting and drawing, at a temperature of 985-1040℃, with a forging ratio of 8. After forging, it is air-cooled to room temperature.

[0138] The first upsetting and drawing process involves upsetting a Φ350mm electroslag ingot to Φ500mm, then drawing it to a length of 430mm×430mm square billet. The second upsetting and drawing process involves upsetting the 430mm×430mm square billet to 550mm×550mm square billet, then drawing it to a length of 410mm×410mm square billet. The third upsetting and drawing process involves upsetting the 410mm×410mm square billet to 600mm×600mm square billet, then drawing it to a length of 500mm×500mm square billet. Finally, it is forged into a finished steel block forging of 310mm×600mm×625mm.

[0139] 4) Heat treatment

[0140] Water quenching: Forgings are loaded into the furnace, and the initial heating rate of the forgings is 55℃ / h. After reaching 745℃, they are held for 1-2 hours, and then rapidly heated to 1145℃ and held for 920 minutes (for billet thickness 310mm). The forgings are then removed and placed in water, and removed at room temperature.

[0141] Aging: Load the forgings into the furnace again, heat to 495℃, hold for 560 minutes, and air cool to room temperature.

[0142] Hardness tests were performed on the center of the two end faces, the 1 / 4 of the diagonal, and the 1 / 2 of each side of the forging after aging treatment, and the results were 43.8 to 44.7 HRC. Example 6

[0143] Based on the design composition of the age-curing plastic mold steel provided in Table 1, the materials were prepared in a quantity of 1000 kg to prepare the age-curing plastic mold steel of the present invention.

[0144] The process for each step is as follows:

[0145] 1) Vacuum induction furnace smelting

[0146] Furnace loading: Place 350kg of pure iron at the bottom of the crucible, 42kg of metallic chromium, 15kg of electrolytic nickel, and 10.7kg of ferromolybdenum (60% molybdenum content) in the middle, and then load 366kg of pure iron on top. The secondary hopper is filled with 35kg of carbon powder, 8.6kg of monocrystalline silicon, 155kg of electrolytic manganese, 24kg of ferrovanadium (50% vanadium content), and 3.3kg of aluminum granules.

[0147] Melting and refining: Vacuum to 1 Pa, power on to melt, after all the furnace charge in the crucible has melted, heat to 1640℃, adjust vacuum to 0.05 Pa, and refine until the molten steel [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0148] Alloying: Stop the vacuum, fill with 20000Pa argon gas, adjust the temperature to 1580℃, and add single crystal silicon, carbon powder, ferrovanadium, electrolytic manganese, and aluminum granules in sequence. After melting and cleaning, test the composition and fine-tune it to meet the requirements.

[0149] Steel tapping: Adjust the temperature to 1530℃ and cast it into an electrode with a diameter of Φ290*2000mm while energized.

[0150] 2) Electroslag remelting

[0151] Preparation: Bake 40kg of slag system containing 61%CaF2, 20%CaO, 15%Al2O3, and 4%SiO2; Stress-relief annealing, grinding, and welding of vacuum ingots; Lay Φ320*40mm ingot plates and 600g of iron filings of the same material in the bottom water tank in sequence, and install Φ350*1600mm crystallizer and electrodes;

[0152] Arc initiation and slag formation: Lower the electrode, apply current to initiate the arc, add slag material, adjust the voltage to 30-43V and the current to 2800-5000A to perform slag formation, and the slag formation period is 43 minutes.

[0153] Remelting: After entering the remelting period, adjust the voltage to 43-45V, the current to 5000-6000A, and the melting rate to 4kg / min, and replenish the material when the remaining electrode is 40kg.

[0154] Compensation period: During the compensation period of 45 minutes, the voltage and current gradually decrease from 43V and 5000A to 30V and 2500A. The melting process ends after the compensation period.

[0155] 3) Forging

[0156] Heating: After the electroslag ingot is loaded into the furnace, the temperature is raised along with the furnace. The initial rate is 40℃ / h. When it reaches 700℃, it is held for 3 hours. Then, the temperature is rapidly raised to 1180℃ and held for 7 hours.

[0157] Forging: After the electroslag ingot is taken out of the furnace, it is forged in multiple directions, including upsetting and drawing, at a temperature of 990-1050℃, with a forging ratio of 15. After forging, it is air-cooled to room temperature.

[0158] The first upsetting and drawing process involves upsetting a Φ350mm electroslag ingot to Φ600mm, then drawing it to a length of 420mm×420mm square billet. The second upsetting and drawing process involves upsetting the 420mm×420mm square billet to 600mm×600mm square billet, then drawing it to a length of 450mm×450mm square billet. The third upsetting and drawing process involves upsetting the 450mm×450mm square billet to 580mm×580mm square billet, then drawing it to a length of 500mm×500mm square billet. Finally, it is forged into a finished steel block forging of 120mm×830mm×1140mm.

[0159] 4) Heat treatment

[0160] Water quenching: Forgings are loaded into the furnace, and the initial heating rate of the forgings is 60℃ / h. After reaching 750℃, they are held for 1 hour, and then rapidly heated to 1140℃ and held for 240 minutes (for billet thickness 120mm). The forgings are then removed and placed in water, and removed at room temperature.

[0161] Aging: Load the forgings into the furnace again, heat to 470℃, hold for 160 minutes, and air cool to room temperature.

[0162] Hardness tests were performed on the center of the two end faces, the 1 / 4 of the diagonal, and the 1 / 2 of each side of the forging after aging treatment, and the results were 45.1 to 46.8 HRC.

[0163] Table 1 shows the chemical composition (wt%) of the plastic mold steel in each embodiment.

[0164]

[0165] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are all within the scope of the present invention.

Claims

1. An age-curing plastic mold steel, characterized in that: The chemical composition and mass percentage of the plastic mold steel are as follows: C: 0.25-0.35%, Si: 0.6-1.0%, Mn: 14-16%, P≤0.015%, S≤0.010%, Cr: 3.8-4.2%, Mo: 0.5-0.7%, V: 0.8-1.2%, Ni: 1-1.5%, Al: 0.3-0.4%, Ni / Al: 3-5, with the balance being Fe and unavoidable impurities.

2. The age-curing plastic mold steel according to claim 1, characterized in that: The hardness of the plastic mold steel after aging is ≥43.6HRC, and the hardness deviation is ≤1.7HRC.

3. The age-curing plastic mold steel according to claim 1, characterized in that: The metallographic structure of the plastic mold steel is austenite matrix with finely dispersed carbides and Ni3Al intermetallic compounds distributed on it.

4. A method for preparing an age-curing plastic mold steel according to any one of claims 1-3, characterized in that: The preparation method includes the following steps: (1) Vacuum induction melting: The materials are distributed according to the design, and the materials are smelted in a vacuum induction furnace and cast into consumable electrodes for electroslag remelting. (2) Electroslag remelting: Electroslag remelting under argon protection conditions; (3) Forging: After heating and holding the electroslag ingot, forging is carried out at 950-1150℃ with a forging ratio ≥7. After forging, the ingot is air-cooled to room temperature. (4) Heat treatment: After water quenching at 1130-1150℃ and aging at 460-500℃, the forging is air-cooled to room temperature.

5. The method for preparing an age-curing plastic mold steel according to claim 4, characterized in that: In step (2) of the electroslag remelting process, the slag composition is CaF2: 58-62%, CaO: 20-22%, Al2O3: 13-15%, SiO2: 3-7%.

6. The method for preparing an age-curing plastic mold steel according to claim 4, characterized in that: In the forging process of step (3), the electroslag ingot is heated with the furnace. The initial heating rate is ≤60℃ / h. When it reaches 700~750℃, it is held for 2~3h. Then it is rapidly heated to 1180~1200℃ and held for 6~8h.

7. A method for preparing an age-curing plastic mold steel according to any one of claims 4-6, characterized in that: In the heat treatment process of step (4), during water quenching, the initial heating rate of the forging is ≤60℃ / h, and after reaching 700~750℃, it is held for 1~2h, and then rapidly heated to 1130~1150℃, with a holding time of 2~3min × billet thickness; during aging, it is held at 460~500℃ for 1~2min × billet thickness; the billet thickness is in mm.

8. A method for preparing an age-curing plastic mold steel according to any one of claims 4-6, characterized in that: In step (1) of the vacuum induction melting process, alloying: stop the vacuum, fill with 10000-20000Pa argon gas, adjust the temperature to 1550-1580℃, and add single crystal silicon, carbon powder, ferrovanadium, electrolytic manganese and aluminum granules in sequence; tapping: adjust the temperature to 1510-1530℃ and cast with electricity.

9. A method for preparing an age-curing plastic mold steel according to any one of claims 4-6, characterized in that: In step (2) of the electroslag remelting process, the process is as follows: arc initiation and slag formation: energize to initiate an arc, add slag material, adjust the voltage to 25-45V and the current to 2500-5500A to form slag, and the slag formation period is 25-50min; remelting: adjust the voltage to 45-51V, the current to 4500-7500A, and the melting rate to 3.5-5.5kg / min, and replenish the remaining electrode when the remaining electrode is 30-50kg.

10. A method for preparing an age-curing plastic mold steel according to any one of claims 4-6, characterized in that: In step (2) of the electroslag remelting process, the feeding period is 30 to 40 minutes. During this feeding period, the voltage and current gradually decrease from 45 to 48V and 4500 to 5500A to 25 to 35V and 2500 to 3000A. The melting process ends after the feeding period.

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