High-performance nodular cast iron and method for producing same

Abstract

The application discloses high-performance nodular cast iron and a preparation method thereof, and relates to the technical field of metal material casting. The preparation method of the high-performance nodular cast iron comprises the steps of preparing a composite spheroidizing cored wire, preparing a nano-enhanced inoculant, pre-inoculating molten iron, and obtaining nodular cast iron. The preparation of the composite spheroidizing cored wire adopts raw materials including pure iron, pure silicon, pure nickel, pure yttrium, pure magnesium, silicon-calcium alloy powder, silicon-barium alloy powder, nano zirconium oxide and low-carbon steel strips. The preparation of the nano-enhanced inoculant adopts raw materials including titanium-iron, boron-iron, high-purity graphite powder, 75 silicon-iron and low-carbon steel strips. The high-performance nodular cast iron prepared by the method has good mechanical properties, excellent graphite spheroidization quality and excellent wear resistance.

Description

Technical Field

[0001] This invention relates to the field of metal casting technology, specifically to a high-performance ductile iron and its preparation method. Background Technology

[0002] Due to its high strength, high toughness, and good casting and machinability, ductile iron has become the preferred material for key components of high-end equipment such as automobile engine crankshafts, hydraulic components of construction machinery, and braking components of rail transit. As the global equipment manufacturing industry rapidly develops towards lightweight, high reliability, and long service life, more stringent requirements are being placed on the spheroidization quality, strength-toughness matching, and wear resistance of ductile iron.

[0003] Traditional ductile iron is generally prepared using a single rare-earth magnesium-silicon ferrospheroidizing agent combined with a common ferrosilicon inoculant. This method suffers from inherent defects such as violent splashing during the spheroidization reaction, high magnesium loss rate, and rapid spheroidization decay. It is difficult to obtain a graphite spheroid structure with high roundness and uniform distribution, and the matrix grains are coarse, making it difficult to balance strength and toughness, thus failing to meet the service requirements of high-end components. Existing technologies modify the material by adding large amounts of alloying elements or external nanoparticles, but these methods generally suffer from problems such as easy agglomeration of nanoparticles, weak interfacial bonding, and easy introduction of impurities. Furthermore, existing spheroidizing agents have poor resistance to interference from anti-spheroidizing elements such as Sb and Pb, and are prone to poor spheroidization when recycling remelted materials. These factors severely restrict the stable industrial production and widespread application of high-performance ductile iron. The prior art disclosed in CN118773506A is a smelting method for preparing high-performance ductile iron by adding silicon carbide. This prior art uses a pretreatment agent composed of a mixed powder of silicon carbide, molybdenum disilicide, nickel silicide, and calcium boride to achieve simultaneous carbon and silicon increase by utilizing the slow dissolution characteristics of silicon carbide. At the same time, carbon atom clusters are formed as the basis for graphite nucleation, effectively reducing the tendency of white iron and improving the microstructure of cast iron. Nanoscale molybdenum carbide, hafnium silicide, and other heterogeneous nucleation particles are introduced into the inoculant and the in-flow inoculant to significantly increase the number and roundness of graphite spheres. However, this prior art still uses traditional high-magnesium-content rare earth magnesium-silicon iron spheroidizing agent, which has a high magnesium element burn-off rate, violent spheroidization reaction and easy slag inclusion, and limited resistance to spheroidization decay. The nano carbide particles in the inoculant are all simple physical additions, which have problems such as easy agglomeration of nanoparticles and weak bonding force with the matrix interface, making it difficult to achieve uniform distribution and limiting the improvement of toughening effect.

[0004] In summary, although the existing technical solutions have improved some properties of ductile iron to a certain extent, the following technical problems still exist: insufficient mechanical properties, poor graphite spheroidization quality, and poor wear resistance. Summary of the Invention

[0005] In order to solve the above-mentioned problems in the prior art, the present invention provides a high-performance ductile iron and its preparation method, and achieves the following objectives: to prepare a high-performance ductile iron with good mechanical properties, excellent graphite spheroidization quality and wear resistance.

[0006] To achieve the above objectives, the following technical solution is adopted: A method for preparing high-performance ductile iron includes the steps of preparing composite spheroidized cored wire, preparing nano-reinforcing inoculant, pre-inoculating with molten iron, and obtaining ductile iron. The preparation of composite spheroidized cored wire involves mixing pure iron, pure silicon, pure nickel, and pure yttrium, heating to 1550-1560℃, melting completely, cooling to 1020-1030℃, adding pure magnesium, immediately sealing, purging with argon gas, starting electromagnetic stirring at 10-15% power, and holding at this temperature for 10-15 minutes. The mixture is then poured into a cast iron mold, cooled to room temperature, and crushed and air-jet ground to obtain a pre-alloyed powder with a particle size of 200-300 mesh. The pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia are mixed evenly, ball-milled, and vacuum-dried to obtain core powder for the cored wire. A low-carbon steel strip is used as the outer sheath, and the core powder is rolled and coated using a cored wire forming machine to produce a spheroidized cored wire with an outer diameter of 13mm. The core powder filling amount is controlled at 250-280g / m, and the joints are compacted and sealed to obtain the composite spheroidized cored wire.

[0007] Furthermore, the mass ratio of pure iron, pure silicon, pure nickel, pure magnesium, and pure yttrium is (45-47):(40-43):(2-2.5):(6-7):(1.5-2). The mass ratio of the pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia is (94.8-95.2):(3.1-3.3):(1.3-1.4):(0.22-0.28). The ball milling is performed using a planetary ball mill, with anhydrous ethanol as the grinding aid, argon gas protection, a ball-to-material ratio of 5:1, a rotation speed of 200-300 rpm, and a milling time of 30-40 minutes. The vacuum drying is performed at a temperature of 80-85℃, a vacuum degree of -0.09MPa to -0.095MPa, and a drying time of 2-2.5 hours. The thickness of the low-carbon steel strip is 0.4 mm.

[0008] The preparation of the nano-reinforced inoculant involves mixing ferrotitanium, ferroboron, and high-purity graphite powder, ball milling the mixture, adding 75% ferrosilicon, mixing thoroughly, crushing, and sieving to obtain nano-reinforced inoculant particles with a particle size of 1-3 mm.

[0009] Furthermore, the mass ratio of the ferrotitanium, ferroboron, high-purity graphite powder, and 75% ferrosilicon is (6-8):(2-2.5):(0.2-0.3):(15-18). The ball milling process employs a planetary ball mill, using anhydrous ethanol as a grinding aid, argon gas protection, a ball-to-material ratio of 10:1, a rotation speed of 400-500 rpm, and milling for 3-5 hours.

[0010] Using low-carbon steel strip as the outer sheath, nano-reinforcing inoculant particles are rolled and coated onto the cored wire using a cored wire forming unit to produce an inoculated cored wire with an outer diameter of 9mm. The core powder filling amount is controlled at 180-200g / m, resulting in a nano-reinforced inoculated cored wire. The thickness of the low-carbon steel strip is 0.3mm.

[0011] The pre-inoculation of molten iron involves adding primary iron, scrap steel, and recycled materials to a medium-frequency induction furnace, heating to 1450-1460℃, and removing the slag from the surface of the molten iron after complete melting. Pure aluminum wire is then added and mixed thoroughly. Nano-reinforcing inoculant particles are added to the bottom of the spheroidized ladle, and then molten iron is poured in, reacting for 5-8 minutes. After the reaction is complete, pre-inoculated molten iron is obtained.

[0012] Furthermore, the amount of pure aluminum wire used is 0.04-0.06% of the mass of the molten iron. The amount of nano-reinforcing inoculant particles used is 0.12-0.15% of the mass of the molten iron.

[0013] The process for producing ductile iron involves: removing surface slag from pre-inoculated molten iron and feeding it into a wire feeding and spheroidizing station. The molten iron temperature is controlled at 1440-1460℃, and a double-wire feeding method is used, simultaneously feeding composite spheroidized cored wire and nano-reinforced inoculated cored wire. The feeding speed is 10-12 m / min, and the feeding depth is 2 / 3-3 / 4 below the molten iron surface. Then, the molten iron temperature is controlled at 1380-1400℃ and poured into a casting ladle. During the ladle guiding process, a flowing inoculant is added using a funnel. After casting, the ladle is held at the temperature for 2-3 hours and then cooled to room temperature. Finally, the ladle is subjected to sand removal and shot blasting treatments to obtain ductile iron.

[0014] Furthermore, the composition of the ductile iron is as follows: C 3.55-3.65wt%, Si 2.30-2.45wt%, Mn 0.25-0.35wt%, Ti 0.02-0.04wt%, B 0.003-0.006wt%, Mg 0.035-0.055wt%, P≤0.05wt%, S≤0.018wt%, and the remaining portion less than 100wt% is Fe and other trace elements.

[0015] The amount of the composite spheroidized cored wire added is 0.7-0.9% of the mass of the pre-inoculated molten iron.

[0016] The amount of nano-reinforced inoculated cored wire added is 0.06-0.08% of the mass of the pre-inoculated molten iron.

[0017] The amount of the inoculant added is 0.1-0.2% of the mass of the molten iron.

[0018] The in-flow inoculant is a silicon-strontium inoculant with a particle size of 0.2-0.7 mm; the composition of the silicon-strontium inoculant is: Si 70-75 wt%, Sr 0.6-1.2 wt%, Ca≤0.1 wt%, Al≤0.5 wt%.

[0019] The casting process employs a wet sand vertical molding technique and a casting system that relies on the weight of the molten iron to fill the mold, including bottom and middle pouring.

[0020] The beneficial effects of this invention are as follows: (1) This invention reduces the burn-off rate of magnesium in high-temperature molten iron through a low-temperature sealed magnesium addition process, making the spheroidization reaction stable and mild. Magnesium, as a rapid spheroidizing element, can reduce the interfacial energy of graphite in a short time, promoting the transformation of graphite from flakes to spheres; Yttrium can effectively neutralize anti-spheroidizing elements such as Sb, Pb, and Bi, prolonging the spheroidization decay time, refining graphite spheres, and improving the roundness of graphite spheres. Nickel atoms are dissolved in the ferrite matrix, producing a solid solution strengthening effect, further improving the strength and toughness of the matrix.

[0021] This invention prepares an inoculant by mixing ferrotitanium, ferroboron, and high-purity graphite powder, and generates TiC and TiB2 nanoparticles in situ in molten iron at high temperature. TiB2, as an efficient heterogeneous nucleation core for graphite, can improve the nucleation rate of graphite spheres and refine the graphite spheres. TiC and TiB2 simultaneously provide austenite nucleation sites, refine the matrix grains, and improve the yield strength, toughness, and plasticity of the matrix.

[0022] (2) The high-performance ductile iron of the present invention has excellent mechanical properties. The tensile strength of the prepared ductile iron is 562-577MPa, the yield strength is 379-386MPa, the elongation is 11.2-12.5%, and the Brinell hardness is 234-246HBW.

[0023] (3) The high-performance ductile iron of the present invention has high graphite spheroidization quality. The graphite spheroidization level of the prepared ductile iron is all grade 1, the graphite spheroid size level is all grade 7, and the spheroidization rate is 98.2-98.7%.

[0024] (4) The high-performance ductile iron of the present invention has excellent wear resistance. The mass loss rate of the prepared ductile iron is 0.11-0.14% in the wear test. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0026] Example 1: A high-performance ductile iron and its preparation method A method for preparing high-performance ductile iron, comprising the following steps: Step 1: Preparation of composite spheroidized cored wire Pure iron, pure silicon, pure nickel, and pure yttrium are mixed and heated to 1550℃ until completely melted. The mixture is then cooled to 1020℃, pure magnesium is added, and the mixture is immediately sealed. Argon gas is introduced for protection, and electromagnetic stirring is started at 10% power for 15 minutes. The mixture is then poured into a cast iron mold, cooled to room temperature, and crushed and milled using an air jet mill to obtain a pre-alloyed powder with a particle size of 200 mesh. The pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia are mixed evenly, ball-milled, and vacuum-dried to obtain core powder for cored wire. Low-carbon steel strip is used as the outer sheath, and the core powder is rolled and coated onto the core powder using a cored wire forming machine to produce a spheroidized cored wire with an outer diameter of 13mm. The core powder filling amount is controlled at 250g / m, and the joints are compacted and sealed to obtain a composite spheroidized cored wire.

[0027] The mass ratio of pure iron, pure silicon, pure nickel, pure magnesium, and pure yttrium is 45:40:2:6:1.5.

[0028] The mass ratio of the pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia is 94.8:3.1:1.3:0.22.

[0029] The ball milling process involved a planetary ball mill, anhydrous ethanol as a grinding aid, argon gas protection, a ball-to-material ratio of 5:1, a rotation speed of 200 rpm, and a milling time of 40 minutes.

[0030] The vacuum drying process involves a temperature of 80℃, a vacuum degree of -0.09MPa, and a drying time of 2.5 hours.

[0031] The thickness of the low-carbon steel strip is 0.4 mm.

[0032] Step 2: Preparation of nano-enhanced inoculants Titanium iron, boron iron, and high-purity graphite powder were mixed and ball-milled. Then, 75% silicon iron was added, mixed evenly, crushed, and sieved to obtain nano-reinforced inoculant particles with a particle size of 1 mm.

[0033] The mass ratio of the ferrotitanium, ferroboron, high-purity graphite powder, and 75% ferrosilicon is 6:3.5:0.2:15.

[0034] The ball milling process involved a planetary ball mill, using anhydrous ethanol as a grinding aid, argon gas protection, a ball-to-material ratio of 10:1, a rotation speed of 400 rpm, and a milling time of 5 hours.

[0035] Using low-carbon steel strip as the outer sheath, nano-reinforcing inoculant particles are rolled and coated by a cored wire forming unit to produce an inoculated cored wire with an outer diameter of 9mm. The core powder filling amount is controlled at 180g / m to obtain a nano-reinforced inoculated cored wire.

[0036] The thickness of the low-carbon steel strip is 0.3 mm.

[0037] Step 3: Pre-inoculation of molten iron Raw iron, scrap steel, and recycled materials are added to a medium-frequency induction furnace and heated to 1450℃. After complete melting, the slag on the surface of the molten iron is removed, and pure aluminum wire is added and mixed evenly. Nano-reinforcing inoculant particles are added to the bottom of the spheroidizing ladle, and then molten iron is poured in and reacted for 5 minutes. After the reaction is complete, pre-inoculated molten iron is obtained.

[0038] The amount of pure aluminum wire used is 0.04% of the mass of the molten iron.

[0039] The amount of the nano-reinforced inoculant particles used is 0.12% of the mass of the molten iron.

[0040] Step 4: Obtaining ductile iron After removing surface slag from the pre-inoculated molten iron, it is fed into the wire feeding and spheroidizing station. The temperature of the molten iron is controlled at 1440℃, and double-wire feeding is used, simultaneously feeding composite spheroidized cored wire and nano-reinforced inoculated cored wire. The wire feeding speed is 10m / min, and the wire feeding depth is 2 / 3 below the molten iron surface. Then, the temperature of the molten iron is controlled at 1380℃ and poured into the casting ladle of the casting machine. During the ladle guiding process, the inoculant is added with a funnel. After casting, it is kept at the temperature for 3 hours and then naturally cooled to room temperature. Sand removal and shot blasting are then performed to obtain ductile iron.

[0041] The composition of the ductile iron is as follows: C 3.55wt%, Si 2.45wt%, Mn 0.25wt%, Ti 0.04wt%, B 0.003wt%, Mg 0.035wt%, P 0.05wt%, S 0.018wt%, with the remainder of less than 100wt% being Fe and other trace elements.

[0042] The amount of the composite spheroidized cored wire added is 0.7% of the mass of the pre-inoculated molten iron.

[0043] The amount of nano-reinforced inoculated cored wire added is 0.08% of the mass of the pre-inoculated molten iron.

[0044] The amount of the inoculant added is 0.2% of the mass of the molten iron.

[0045] The casting process employs a wet sand vertical molding technique and a bottom-pouring casting system.

[0046] Example 2: A high-performance ductile iron and its preparation method A method for preparing high-performance ductile iron, comprising the following steps: Step 1: Preparation of composite spheroidized cored wire Pure iron, pure silicon, pure nickel, and pure yttrium were mixed and heated to 1560℃ until completely melted. The mixture was then cooled to 1020℃, and pure magnesium was added. The mixture was immediately sealed, protected with argon gas, and electromagnetic stirring was started at 15% power for 15 minutes. The mixture was then poured into a cast iron mold, cooled to room temperature, and crushed and milled using an air jet mill to obtain a pre-alloyed powder with a particle size of 300 mesh. The pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia were mixed evenly, ball-milled, and vacuum-dried to obtain core powder for cored wire. Low-carbon steel strip was used as the outer sheath, and the core powder was rolled and coated onto the core powder using a cored wire forming machine to produce a spheroidized cored wire with an outer diameter of 13mm. The core powder filling amount was controlled at 270g / m, and the joints were compacted and sealed to obtain a composite spheroidized cored wire.

[0047] The mass ratio of pure iron, pure silicon, pure nickel, pure magnesium, and pure yttrium is 46:42:2.5:7:2.

[0048] The mass ratio of the pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia is 95:3.2:1.4:0.25.

[0049] The ball milling process involved a planetary ball mill, anhydrous ethanol as a grinding aid, argon gas protection, a ball-to-material ratio of 5:1, a rotation speed of 300 rpm, and a milling time of 35 minutes.

[0050] The vacuum drying process involves a temperature of 85°C, a vacuum degree of -0.095 MPa, and a drying time of 2.5 hours.

[0051] The thickness of the low-carbon steel strip is 0.4 mm.

[0052] Step 2: Preparation of nano-enhanced inoculants After uniformly mixing ferrotitanium, ferroboron, and high-purity graphite powder, the mixture is crushed and sieved to obtain nano-reinforced inoculant particles with a particle size of 2 mm.

[0053] The mass ratio of the ferrotitanium, ferroboron, high-purity graphite powder, and 75% ferrosilicon is 6.5:4:0.3:16.

[0054] The ball milling process involved using anhydrous ethanol as a grinding aid, argon gas protection, a ball-to-material ratio of 10:1, a rotation speed of 500 rpm, and milling for 4 hours.

[0055] Using low-carbon steel strip as the outer sheath, nano-reinforcing inoculant particles are rolled and coated by a cored wire forming unit to produce an inoculated cored wire with an outer diameter of 9mm. The core powder filling amount is controlled at 190g / m to obtain a nano-reinforced inoculated cored wire.

[0056] The thickness of the low-carbon steel strip is 0.3 mm.

[0057] Step 3: Pre-inoculation of molten iron Raw iron, scrap steel, and recycled materials are added to a medium-frequency induction furnace and heated to 1460℃. After complete melting, the slag on the surface of the molten iron is removed, and pure aluminum wire is added and mixed evenly. Nano-reinforcing inoculant particles are added to the bottom of the spheroidizing ladle, and then molten iron is poured in and reacted for 7 minutes. After the reaction is complete, pre-inoculated molten iron is obtained.

[0058] The amount of pure aluminum wire used is 0.05% of the mass of the molten iron.

[0059] The amount of the nano-reinforced inoculant particles used is 0.14% of the mass of the molten iron.

[0060] Step 4: Obtaining ductile iron After removing surface slag from the pre-inoculated molten iron, it is fed into the wire feeding and spheroidizing station. The molten iron temperature is controlled at 1450℃, and double-wire feeding is used, simultaneously feeding composite spheroidized cored wire and nano-reinforced inoculated cored wire. The wire feeding speed is 12m / min, and the wire feeding depth is 3 / 4 below the molten iron surface. Then, the molten iron temperature is controlled at 1390℃ and poured into the casting ladle of the casting machine. During the ladle guiding process, the inoculant is added using a funnel. After casting, it is kept at the temperature for 3 hours and then naturally cooled to room temperature. Sand removal and shot blasting are then performed to obtain ductile iron.

[0061] The composition of the ductile iron is as follows: C 3.6wt%, Si 2.4wt%, Mn 0.3wt%, Ti 0.03wt%, B 0.005wt%, Mg 0.045wt%, P 0.05wt%, S 0.017wt%, with the remaining less than 100wt% being Fe and other trace elements.

[0062] The amount of the composite spheroidized cored wire added is 0.8% of the mass of the pre-inoculated molten iron.

[0063] The amount of nano-reinforced inoculated cored wire added is 0.07% of the mass of the pre-inoculated molten iron.

[0064] The amount of the inoculant added is 0.2% of the mass of the molten iron.

[0065] The casting process employs a wet sand vertical molding technique and a bottom-pouring casting system.

[0066] Example 3: A high-performance ductile iron and its preparation method A method for preparing high-performance ductile iron, comprising the following steps: Step 1: Preparation of composite spheroidized cored wire Pure iron, pure silicon, pure nickel, and pure yttrium were mixed and heated to 1560℃ until completely melted. The mixture was then cooled to 1030℃, and pure magnesium was added. The mixture was immediately sealed, protected with argon gas, and electromagnetic stirring was started at 15% power for 10 minutes. The mixture was then poured into a cast iron mold, cooled to room temperature, and crushed and milled using an air jet mill to obtain a pre-alloyed powder with a particle size of 300 mesh. The pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia were mixed evenly, ball-milled, and vacuum-dried to obtain core powder for cored wire. Low-carbon steel strip was used as the outer sheath, and the core powder was rolled and coated onto the core powder using a cored wire forming machine to produce a spheroidized cored wire with an outer diameter of 13mm. The core powder filling amount was controlled at 280g / m, and the joints were compacted and sealed to obtain a composite spheroidized cored wire.

[0067] The mass ratio of pure iron, pure silicon, pure nickel, pure magnesium, and pure yttrium is 47:43:2.5:7:2.

[0068] The mass ratio of the pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia is 95.2:3.3:1.4:0.28.

[0069] The ball milling process involved a planetary ball mill, using anhydrous ethanol as a grinding aid, argon gas protection, a ball-to-material ratio of 5:1, a rotation speed of 300 rpm, and a milling time of 30 minutes.

[0070] The vacuum drying process involves drying at 85°C for 2 hours under a vacuum of -0.095 MPa.

[0071] The thickness of the low-carbon steel strip is 0.4 mm.

[0072] Step 2: Preparation of nano-enhanced inoculants After uniformly mixing ferrotitanium, ferroboron, and high-purity graphite powder, the mixture is crushed and sieved to obtain nano-reinforced inoculant particles with a particle size of 3 mm.

[0073] The mass ratio of the ferrotitanium, ferroboron, high-purity graphite powder, and 75% ferrosilicon is 7:4:0.3:18.

[0074] The ball milling process involved using anhydrous ethanol as a grinding aid, argon gas protection, a ball-to-material ratio of 10:1, a rotation speed of 500 rpm, and milling for 3 hours.

[0075] Using low-carbon steel strip as the outer sheath, nano-reinforcing inoculant particles are rolled and coated by a cored wire forming unit to produce an inoculated cored wire with an outer diameter of 9mm. The core powder filling amount is controlled at 200g / m to obtain a nano-reinforced inoculated cored wire.

[0076] The thickness of the low-carbon steel strip is 0.3 mm.

[0077] Step 3: Pre-inoculation of molten iron Raw iron, scrap steel, and recycled materials are added to a medium-frequency induction furnace and heated to 1460℃. After complete melting, the slag on the surface of the molten iron is removed, and pure aluminum wire is added and mixed evenly. Nano-reinforcing inoculant particles are added to the bottom of the spheroidizing ladle, and then molten iron is poured in and reacted for 8 minutes. After the reaction is complete, pre-inoculated molten iron is obtained.

[0078] The amount of pure aluminum wire used is 0.06% of the mass of the molten iron.

[0079] The amount of the nano-reinforced inoculant particles used is 0.15% of the mass of the molten iron.

[0080] Step 4: Obtaining ductile iron After removing surface slag from the pre-inoculated molten iron, it is fed into the wire feeding and spheroidizing station. The molten iron temperature is controlled at 1460℃, and double-wire feeding is used, simultaneously feeding composite spheroidized cored wire and nano-reinforced inoculated cored wire. The wire feeding speed is 12m / min, and the wire feeding depth is 3 / 4 below the molten iron surface. Then, the molten iron temperature is controlled at 1400℃ and poured into the casting ladle. During the ladle guiding process, inoculant is added using a funnel. After casting, it is held at the temperature for 2 hours and then naturally cooled to room temperature. Sand removal and shot blasting are then performed. The furnace is cooled to below 300℃, and then air-cooled to room temperature to obtain ductile iron.

[0081] The composition of the ductile iron is as follows: C 3.65wt%, Si 2.30wt%, Mn 0.35wt%, Ti 0.02wt%, B 0.006wt%, Mg 0.055wt%, P 0.04wt%, S 0.018wt%, with the remainder of less than 100wt% being Fe and other trace elements.

[0082] The amount of composite spheroidized cored wire added is 0.9% of the mass of the pre-inoculated molten iron.

[0083] The amount of nano-reinforced inoculated cored wire added is 0.06% of the mass of the pre-inoculated molten iron.

[0084] The amount of the inoculant added is 0.1% of the mass of the molten iron.

[0085] The casting process employs a wet sand vertical molding technique and a center-pour casting system.

[0086] Comparative Example 1 A method for preparing high-performance ductile iron, comprising the following steps: Step 1: Preparation of nano-enhanced inoculants This step is the same as the "Preparation of Nano-Enhanced Inoculant" step in Example 2.

[0087] Step 2: Pre-inoculation of molten iron This step is the same as the "pre-inoculation of molten iron" step in Example 2.

[0088] Step 3: Obtaining ductile iron In this step, the composite spheroidized cored wire is replaced with a spheroidized cored wire made of rare earth magnesium silicon iron spheroidizing agent, and the other operations are the same as the "preparation of ductile iron" step in Example 2.

[0089] The rare earth magnesium spheroidizing agent has the following composition: Si 35wt%, Mg 25wt%, RE 2wt%, Ba 1wt%, Ca 0.5wt%, Bi 0.3wt%, with the remainder less than 100wt% being Fe; the spheroidizing agent has a particle size of 1mm.

[0090] Comparative Example 2 A method for preparing high-performance ductile iron, comprising the following steps: Step 1: Preparation of composite spheroidized cored wire This step is the same as the "Preparation of Composite Spheroidized Cored Wire" step in Example 2.

[0091] Step 2: Pre-inoculation of molten iron In this step, the nano-reinforced inoculated cored wire is replaced with an inoculated cored wire made of ferrosilicon inoculant, and the other operations are the same as the "molten iron pre-inoculation" step in Example 2.

[0092] The silicon-iron inoculant has the following composition: Si 74-78%, Ca 0.5-1.0%, Al 0.8-1.5%; and a particle size of 2 mm.

[0093] Step 3: Obtaining ductile iron In this step, the nano-reinforced inoculated cored wire is replaced with an inoculated cored wire made of ferrosilicon inoculant, and the nano-reinforced inoculant particles are replaced with ferrosilicon inoculant. The other steps of "obtaining ductile iron" in Example 2 are the same.

[0094] The silicon-iron inoculant has the following composition: Si 74-78%, Ca 0.5-1.0%, Al 0.8-1.5%; and a particle size of 2 mm.

[0095] Example 4 Performance Testing (a) Basic mechanical properties of the ductile iron prepared in Examples 1-3 and Comparative Examples 1-2 were tested according to the test methods specified in GB / T 1348-2009, including tensile strength, yield strength, elongation, and Brinell hardness. The specific test results are shown in Table 1.

[0096] Table 1 As shown in Table 1, the ductile iron prepared in Examples 1-3 has a tensile strength of 562-577 MPa, a yield strength of 379-386 MPa, an elongation of 11.2-12.5%, and a Brinell hardness of 234-246 HBW. This demonstrates that the ductile iron prepared in this invention possesses excellent mechanical properties.

[0097] (II) The spheroidization properties of the ductile iron prepared in Examples 1-3 and Comparative Examples 1-2 were tested. The graphite spheroidization level, graphite spheroid size level, and spheroidization rate were tested according to the test methods specified in GB / T9441-2009. Specific test results are shown in Table 2.

[0098] Table 2 As shown in Table 2, the graphite spheroidization level of the ductile iron prepared in Examples 1-3 was all grade 1, the graphite spheroid size grade was all grade 7, and the spheroidization rate was 98.2-98.7%. This proves that the composite spheroidized cored wire prepared by the present invention can significantly improve the spheroidization quality and improve the graphite morphology and distribution.

[0099] (III) Wear resistance tests were conducted on the ductile iron prepared in Examples 1-3 and Comparative Examples 1-2. Mass wear tests were performed according to the test methods specified in GB / T12444-2006. The wear piece was a GCr15 steel ring with a hardness of HRC60-62, a load of 200 N, a sliding speed of 0.5 m / s, and a wear time of 30 min. The mass loss rate was calculated. Specific test results are shown in Table 3.

[0100] Table 3 As shown in Table 3, the ductile iron prepared in Examples 1-3 exhibited a mass loss rate of 0.11-0.14% in the wear test. This demonstrates the excellent wear resistance of the ductile iron prepared by this invention.

[0101] The specific parameters of the raw materials used in this invention are as follows: The silicon-calcium alloy powder has a particle size of 200 mesh.

[0102] The particle size of the silicon-barium alloy powder is 200 mesh.

[0103] The titanium content of the ferrotitanium is 28-32%, and the particle size is 1-3 mm.

[0104] The ferroboron has a boron content of 19-21% and a particle size of 1-3 mm.

[0105] The high-purity graphite powder has a purity of ≥99.9% and a particle size D50 of 5-10μm.

[0106] The particle size of the 75% ferrosilicon is 1-3 mm.

[0107] The composition requirements for the primary iron are: C 4.3-4.4wt%, Si 1.3-2wt%, Mn≤0.2wt%, Ti≤0.03wt%, S≤0.02wt%, P≤0.04wt%, Sb≤0.005wt%, Al≤0.004wt%, and the remaining portion less than 100wt% is Fe.

[0108] The composition requirements for the scrap steel are as follows: C≤0.2wt%, Si≤0.3wt%, Mn≤0.3wt%, S≤0.03wt%, P≤0.03wt%, Cr≤0.05wt%, Mo≤0.05wt%, Cu≤0.05wt%, V≤0.01wt%, and the remaining portion less than 100wt% is Fe.

[0109] The composition requirements for the recycled material are: C 3.7-4wt%, Si 2.15-2.93wt%, Mn 0.46-0.66wt%, Mg 0.027-0.050wt%, P≤0.027wt%, S≤0.016wt%, and the remaining portion less than 100wt% is Fe and other trace elements.

[0110] The in-flow inoculant is a silicon-strontium inoculant with a particle size of 0.2-0.7 mm; the composition of the silicon-strontium inoculant is: Si 70-75 wt%, Sr 0.6-1.2 wt%, Ca≤0.1 wt%, Al≤0.5 wt%.

[0111] Obviously, there are many other possible implementation methods under the concept of this invention. It should be stated here that any changes made under the inventive concept of this invention will fall within the protection scope of this invention.

Claims

1. A method for preparing high-performance ductile iron, characterized in that: The process includes steps such as preparing composite spheroidized cored wire, preparing nano-reinforcing inoculant, pre-inoculation with molten iron, and obtaining ductile iron. The preparation of the composite spheroidized cored wire involves: mixing pure iron, pure silicon, pure nickel, and pure yttrium, heating to melt, cooling, adding pure magnesium, sealing, purging with argon gas, turning on electromagnetic stirring, and maintaining the temperature; then pouring into a cast iron mold, cooling, crushing, and air-jet milling to obtain pre-alloyed powder; mixing the pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia evenly, ball milling, and vacuum drying to obtain core powder for the cored wire; using low-carbon steel strip as the outer sheath, rolling and coating the core powder to obtain the composite spheroidized cored wire; The preparation of the nano-reinforced inoculant involves: mixing ferrotitanium, ferroboron, and high-purity graphite powder, ball milling, then adding 75% ferrosilicon, mixing evenly, crushing and sieving to obtain nano-reinforced inoculant particles; using a low-carbon steel strip as the outer sheath, rolling and coating the nano-reinforced inoculant particles to obtain nano-reinforced inoculant cored wire; The pre-inoculation of molten iron involves adding primary iron, scrap steel, and recycled materials to a medium-frequency induction furnace, heating and melting them, removing the slag from the surface of the molten iron, adding pure aluminum wire, and mixing them evenly; adding nano-reinforcing inoculant particles to the bottom of the spheroidized ladle, pouring in the molten iron, reacting, and obtaining pre-inoculated molten iron. The process for producing ductile iron involves: removing surface slag from pre-inoculated molten iron and feeding it into a wire feeding and spheroidizing station. The molten iron temperature is controlled at 1440-1460℃, and a double-wire feeding method is used, simultaneously feeding composite spheroidized cored wire and nano-reinforced inoculated cored wire. The wire feeding speed is 10-12 m / min, and the wire feeding depth is 2 / 3-3 / 4 below the molten iron surface. Then, the molten iron is poured into a casting ladle, and a flow-inoculating agent is added during the ladle guiding process. After heat preservation and cooling, the molten iron undergoes sand removal and shot blasting treatments to obtain ductile iron.

2. The method for preparing high-performance ductile iron according to claim 1, characterized in that: The composition of the ductile iron is as follows: C 3.55-3.65wt%, Si 2.30-2.45wt%, Mn 0.25-0.35wt%, Ti 0.02-0.04wt%, B 0.003-0.006wt%, Mg 0.035-0.055wt%, P≤0.05wt%, S≤0.018wt%, and the remaining less than 100wt% is Fe and other trace elements.

3. The method for preparing high-performance ductile iron according to claim 1, characterized in that: In the step of preparing the composite spheroidized cored wire, the mass ratio of pure iron, pure silicon, pure nickel, pure magnesium, and pure yttrium is (45-47):(40-43):(2-2.5):(6-7):(1.5-2).

4. The method for preparing high-performance ductile iron according to claim 1, characterized in that: In the step of preparing the composite spheroidized cored wire, the mass ratio of pre-alloyed powder, silicon-calcium alloy powder, silicon-barium alloy powder, and nano-zirconia is (94.8-95.2):(3.1-3.3):(1.3-1.4):(0.22-0.28).

5. The method for preparing high-performance ductile iron according to claim 1, characterized in that: In the step of preparing the nano-enhanced inoculant, the mass ratio of ferrotitanium, ferroboron, high-purity graphite powder, and ferrosilicon is (6-8):(2-2.5):(0.2-0.3):(15-18).

6. The method for preparing high-performance ductile iron according to claim 1, characterized in that: The outer diameter of the composite spheroidized cored wire is 13mm, and the core powder filling amount is controlled at 250-280g / m; the outer diameter of the nano-reinforced inoculated cored wire is 9mm, and the core powder filling amount is controlled at 180-200g / m.

7. The method for preparing high-performance ductile iron according to claim 1, characterized in that: In the molten iron pre-inoculation step, the amount of pure aluminum wire used is 0.04-0.06% of the mass of molten iron; the amount of nano-reinforcing inoculant particles used is 0.12-0.15% of the mass of molten iron.

8. The method for preparing high-performance ductile iron according to claim 1, characterized in that: In the process of preparing ductile iron, the amount of composite spheroidized cored wire added is 0.7-0.9% of the mass of the pre-inoculated molten iron.

9. The method for preparing high-performance ductile iron according to claim 1, characterized in that: In the process of preparing ductile iron, the amount of nano-reinforced cored wire added is 0.06-0.08% of the mass of the pre-inoculated molten iron; the amount of in-flow inoculant added is 0.1-0.2% of the mass of the molten iron, and the in-flow inoculant is selected as silicon-strontium inoculant.

10. A high-performance ductile iron, characterized in that: It is prepared by the preparation method of any one of claims 1-9.

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