Nodular cast iron cam shaft and preparation method thereof

Abstract

The invention discloses a nodular cast iron camshaft and a preparation method thereof, and belongs to the technical field of cast iron alloy camshafts. The nodular cast iron camshaft comprises, by mass, 3.6%-3.8% of C, 2.4%-2.6% of Si, 0.5%-0.7% of Mn, 0.5%-1.0% of Cu, smaller than or equal to 0.07% of P, smaller than or equal to 0.02% of S and the balance Fe. The nodular cast iron camshaft is subjected to heat treatment in medium-frequency quenching equipment with the power of 130 kW-150 kW and the frequency of 5.5 kHz-6. 5kHz, the heating time is 5s-6s, the cooling time is 5s-6s, normal-temperature water is adopted for cooling, the graphite grade of the prepared nodular cast iron camshaft is 2-3, the pearlite content is 85% or above, the hardness of a peach tip of the cam is 57 HRC or above, the hardness of a base circle of the cam is 58 HRC or above, and the service life of the nodular cast iron camshaft is prolonged. The depth of a cam hardening layer is 3.5 mm or above, and the cam has good hardness and toughness. By the adoption of the nodular cast iron camshaft and the preparation method thereof, the problems that an existing nodular cast iron camshaft is low in pearlite content and low in hardness can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of cast iron alloy camshafts, and particularly to a ductile iron camshaft and a preparation method thereof. Background Art

[0002] The camshaft is a part of the engine valve train, specifically responsible for driving the valves to open and close on time. Its function is to ensure that the engine inhales fresh combustible mixture into the cylinder regularly during operation and discharges the exhausted gas after combustion from the cylinder in time. The main body of the camshaft is a cylindrical rod approximately the same length as the cylinder block, with several cams sleeved on it for driving the valves.

[0003] Ductile iron has the characteristics of high strength and stiffness, can withstand high pressure and resist external loads, and has excellent corrosion resistance, being not prone to rust and corrosion. Therefore, camshafts are often made of ductile iron.

[0004] The existing patent CN 102230122 B discloses a production method of a QT600-10 ductile iron camshaft, which contains less than 0.35% of Cu element and less than 0.01% of Mo element by mass percentage, resulting in lower hardness and toughness of the prepared ductile iron camshaft.

[0005] The existing patent CN 108588545 B discloses a GGG70L ductile iron and a preparation method thereof, including the following chemical components by weight percentage: C: 3.4-3.8%, Si: 2.0-2.4%, Mn: 0.5-0.6%, P≤0.06%, S≤0.01%, Mo: 0.45-0.55%, Cu: 0.9-1.0%, Ni: 0.9-1.0%, Mg: 0.04-0.06%, Sn: 0.015-0.025%, Cr: 0.1-0.15%, and the balance Fe. The pearlite content in the core of the GGG70L ductile iron is above 85%-87%, and the hardness of the casting after quenching is 55HRC-57HRC. The hardness of the ductile iron prepared in the above patent is still relatively low, and the pearlite content is relatively small, affecting the toughness of the ductile iron. Summary of the Invention

[0006] The purpose of the present invention is to provide a ductile iron camshaft and a preparation method thereof, so as to solve the problems of relatively low pearlite content and low hardness of the existing ductile iron camshafts.

[0007] To achieve the above purpose, the present invention provides a ductile iron camshaft, including the following components by mass percentage: C: 3.6%-3.8%, Si: 2.4%-2.6%, Mn: 0.5%-0.7%, Cu: 0.5%-1.0%, P≤0.07%, S≤0.02%, and the balance Fe.

[0008] The preparation method of the above ductile iron camshaft includes the following steps:

[0009] S1. Molding, producing a coated sand mold on a sand mold molding device;

[0010] S2. Batching, weighing pig iron, scrap steel, return material, copper, ferrosilicon and ferromanganese according to the component ratio of the ductile iron camshaft;

[0011] S3. Melting, sequentially adding the weighed pig iron, scrap steel and return material into a melting device. After the pig iron, scrap steel and return material are completely melted, add copper, ferrosilicon and ferromanganese to the solution; detect the components of the melted solution and adjust the components of the solution;

[0012] S4. After the solution is discharged from the furnace, wire feeding and spheroidizing are carried out to spheroidize the solution, and an inoculant is added for inoculation treatment;

[0013] S5. Pouring, skimming the solution after spheroidization and inoculation treatment, pouring the solution into the coated sand mold, cooling to room temperature, and removing the mold to obtain a camshaft casting;

[0014] S6. Heat treatment, roughly grinding the obtained camshaft casting to remove the oxide layer and impurities on the surface of the casting, and putting the casting into an intermediate frequency quenching device for heat treatment.

[0015] Preferably, in the S1, the curing time of the coated sand mold is 80 s to 100 s, the curing temperature is 190 °C to 230 °C, and the mold pressing time is 0.5 min - 3 min.

[0016] Preferably, in the S2, the mass percentage of pig iron in the raw materials is 10% - 20%, the mass percentage of scrap steel in the raw materials is 50% - 70%, and the mass percentage of return material in the raw materials is 10% - 30%.

[0017] Preferably, in the S2, the purity of copper is not less than 99.9%.

[0018] Preferably, in the S3, the melting device is a steel shell intermediate frequency induction furnace, and the melting temperature is 1580 °C - 1650 °C.

[0019] Preferably, in S4, the tapping temperature is 1550°C - 1580°C, the spheroidizing agent for wire feeding spheroidization is a heavy rare earth spheroidizing wire, the dosage of the spheroidizing agent is 15 m / T - 19 m / T, and the composition of the spheroidizing agent is 40% - 60% Si, 4.0% - 6.5% RE, 20% - 35% Mg; the inoculant includes an inoculating wire and in-stream inoculant. The composition of the inoculating wire is 60% - 75% Si, 1% - 3% Ba, 1% - 5% Ca, and the balance is iron. The diameter of the inoculating wire is 13 mm, and the dosage is 15 m / T - 19 m / T; the composition of the in-stream inoculant is 65% - 75% Si, 1% - 4% Ba, 1% - 3% Ca, and the balance is iron. The dosage of the in-stream inoculant is 0.3% - 0.5% of the total melt.

[0020] Preferably, in S5, the pouring temperature is 1340°C - 1420°C, the time from inoculation to the completion of pouring ≤ 12 min; the cooling time after pouring ≥ 30 min.

[0021] Preferably, in S5, the power of the intermediate frequency quenching equipment is 130 kW - 150 kW, the frequency is 5.5 kHz - 6.5 kHz, the heating time is 5 s - 6 s, the cooling time is 5 s - 6 s, and the cooling is water cooling with normal temperature water.

[0022] Preferably, the sand mold molding device includes a workbench. Above the workbench is provided a molding box, which is connected to the workbench through guide columns. The top of the molding box is provided with an opening. Above the molding box is provided a sand hopper for adding coated sand into the interior of the molding box. The top of the molding box is provided with a cover plate for closing the top opening of the molding box. The cover plate is slidably connected to the molding box. Inside the molding box is provided an axle mold. Between the molding box and the workbench is provided a guide plate. On the workbench is provided a cylinder for driving the guide plate to move up and down. The guide plate is provided with through holes for the guide columns to pass through. On the upper surface of the guide plate are evenly provided a number of ejector pins for ejecting the axle mold out of the molding box. On the bottom plate of the molding box are provided through holes corresponding to the ejector pins one by one for the ejector pins to pass through. On the cover plate is provided a first heating element for heating the coated sand, and on the molding box is provided a second heating element for heating the coated sand. The first heating element, the second heating element, and the cylinder are all connected to the controller.

[0023] The advantages and positive effects of the ductile iron camshaft and its preparation method of the present invention are as follows:

[0024] 1. In the present invention, by increasing the content of copper element, the copper element increases and refines the pearlite in the matrix structure, improving the strength and plastic toughness of the ductile iron camshaft. Copper precipitates during the aging process, forming dispersed hard particles in the structure, causing resistance to dislocations and increasing the hardness of the ductile iron camshaft.

[0025] 2. By increasing the content of manganese element, the present invention increases the pearlite area in the structure, effectively avoids the influence of coarse cementite on toughness, and improves the toughness of the ductile iron camshaft.

[0026] 3. The ductile iron camshaft is heat-treated by an intermediate frequency induction device. The heat treatment has high efficiency and forms a martensite structure with very high hardness on the surface of the ductile iron camshaft, effectively improving the surface hardness of the camshaft.

[0027] 4. The sand mold of the coated sand is molded by a sand mold molding device. The structure is simple and very convenient to use, effectively reducing the cost of the coated sand molding.

[0028] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of an embodiment of the production flow chart of the present invention;

[0030] Figure 2 It is a schematic structural diagram of an embodiment of the sand mold molding device of the present invention.

[0031] Figure 3 It is the microscopic structure diagram of Embodiment 2 of the present invention.

[0032] Reference Signs

[0033] 1. Workbench; 2. Molding box; 3. Shaft mold; 4. Cover plate; 5. Sand hopper; 6. Guide rail; 7. First heating element; 8. Second heating element; 9. Guide plate; 10. Cylinder; 11. Guide post; 12. Thimble; 13. Controller. Detailed Embodiments

[0034] The technical solution of the present invention will be further described below through the drawings and embodiments.

[0035] Carbon. Carbon is an element that promotes graphitization. As the carbon content increases, the spherical graphite in ductile iron increases. However, when the carbon content is too high, the hardness of the casting is too high and the brittleness is large, affecting the performance of the casting. When the carbon content is too low, it will affect the fluidity of the solution, resulting in the formation of defects such as shrinkage porosity and shrinkage cavities in the casting, affecting the performance of the casting. Therefore, the present invention controls the carbon element content within 3.6% - 3.8%.

[0036] Manganese. Manganese is a carbide-forming element with an anti-spheroidizing effect, which affects the spheroidizing effect of cast iron. Generally, the content of Mn element in ductile iron is strictly controlled to be below 0.2%. When the content of manganese element is too low, the pearlite area in ductile iron is small, which affects the toughness of the ductile iron camshaft. However, when the manganese element is too high, the manganese element segregates severely in the ductile iron structure, which will promote the formation of coarse cementite and also affect the toughness of the ductile iron camshaft. Therefore, the content of Mn element is controlled at 0.5%-0.7%.

[0037] Silicon. Silicon can reduce the solubility of carbon in the iron solution, thus promoting graphitization. However, silicon can dissolve in α-ferrite, and through solid solution strengthening, it promotes the formation of ferrite. Considering graphitization and the content of ferrite comprehensively, the content of Si element is limited to 2.4%-2.6%.

[0038] Copper. Copper is an element that promotes graphitization and can reduce or eliminate the formation of free cementite. Copper has the effect of stabilizing austenite, can increase and refine the pearlite in the matrix structure, and reduce or completely inhibit the formation of ferrite. During the aging process, copper can precipitate from the solid solution to form age hardening, improving the hardness of the ductile iron camshaft. Copper can also improve hardenability and improve the uniformity of the cross-sectional structure and properties of the casting. However, when the copper content is too high, massive graphite and yellow copper-rich phases will appear in the structure, affecting the toughness of the ductile iron camshaft. Therefore, the content of Cu element is limited to 0.5%-1.0%.

[0039] A ductile iron camshaft comprises the following components by mass percentage: C: 3.6%-3.8%, Si: 2.4%-2.6%, Mn: 0.5%-0.7%, Cu: 0.5%-1.0%, P≤0.07%, S≤0.02%, and the balance is Fe.

[0040] As Figure 1 shown. The preparation method of the above ductile iron camshaft comprises the following steps:

[0041] S1. Molding, producing a coated sand mold on a sand mold molding device.

[0042] The curing time of the coated sand mold is 80s - 100s, the curing temperature is 190°C - 230°C, and the mold pressing time is 0.5min - 3min.

[0043] S2. Batching, weighing pig iron, scrap steel, return material, copper, ferrosilicon and ferromanganese according to the component ratio of the ductile iron camshaft.

[0044] The mass percentage of pig iron in the raw materials is 10%-20%, the mass percentage of scrap steel in the raw materials is 50%-70%, and the mass percentage of return material in the raw materials is 10%-30%. The purity of copper is not less than 99.9%.

[0045] S3. Melting: The weighed pig iron, scrap steel, and return scrap are successively added to the melting equipment. After the pig iron, scrap steel, and return scrap are completely melted, copper, ferrosilicon, and ferromanganese are added to the solution. The composition of the melted solution is detected and adjusted.

[0046] The melting equipment is a steel shell intermediate frequency induction furnace, and the melting temperature is 1580°C - 1650°C.

[0047] S4. After the solution is discharged from the furnace, wire feeding is carried out to spheroidize the solution for spheroidizing treatment, and an inoculant is added for inoculation treatment.

[0048] The tapping temperature is 1550°C - 1580°C. The spheroidizing agent for wire feeding spheroidization is a heavy rare earth spheroidizing wire, and the dosage of the spheroidizing agent is 15m / T - 19m / T. The composition of the spheroidizing agent is 40% - 60% Si, 4.0% - 6.5% RE, and 20% - 35% Mg; the inoculant includes an inoculation wire and a stream inoculant. The composition of the inoculation wire is 60% - 75% Si, 1% - 3% Ba, 1% - 5% Ca, and the balance is iron. The diameter of the inoculation wire is 13mm, and the dosage is 15m / T - 19m / T; the composition of the stream inoculant is 65% - 75% Si, 1% - 4% Ba, 1% - 3% Ca, and the balance is iron. The dosage of the stream inoculant is 0.3% - 0.5% of the total melt. S5. Pouring: The solution after spheroidizing and inoculation treatment is skimmed, and the solution is poured into a coated sand mold, cooled to room temperature, and the mold is removed to obtain a camshaft casting.

[0049] The pouring temperature is 1340°C - 1420°C, and the time from inoculation to the completion of pouring ≤ 12min; the cooling time after pouring ≥ 30min.

[0050] S6. Heat treatment: The obtained camshaft casting is rough ground to remove the oxide layer and impurities on the surface of the casting, and the casting is put into an intermediate frequency quenching equipment for heat treatment.

[0051] The power of the intermediate frequency quenching equipment is 130kW - 150kW, the frequency is 5.5kHz - 6.5kHz, the heating time is 5s - 6s, and the cooling time is 5s - 6s. Cooling is carried out by water cooling with normal temperature water.

[0052] Such as Figure 2As shown in the figure. The sand mold molding device includes a workbench 1, and the workbench 1 is fixed on the ground. Above the workbench 1, there is a molding box 2, and the workbench 1 and the molding box 2 are fixedly connected through guide columns 11. The guide columns 11 are located at the four corners of the workbench 1 and the molding box 2, improving the connection stability between the workbench 1 and the molding box 2. The top of the molding box 2 is provided with an opening, which facilitates the injection of coated sand into the interior of the molding box 2 through the opening at its top. Above the molding box 2, there is a sand hopper 5, and the sand hopper 5 contains coated sand. The bottom of the sand hopper 5 is of a funnel-shaped structure and is used to inject the coated sand in the sand hopper 5 into the interior of the molding box 2. At the bottom discharge port of the sand hopper 5, there is a valve for controlling the opening or closing of the opening at the bottom of the sand hopper 5, and the discharge port is located in the middle of the molding box 2, which is beneficial to improving the uniformity of the distribution of the coated sand in the molding box 2.

[0053] The top of the molding box 2 is provided with a cover plate 4, and the cover plate 4 is used to close the top opening of the molding box 2 and compact the coated sand in the molding box 2. On both sides of the molding box 2, there are guide rails 6, and on both sides of the cover plate 4, there are guide grooves adapted to the guide rails 6. The guide rails 6 are located in the guide grooves and are slidably connected to the guide grooves. The guide rails 6 and the guide grooves play a guiding role in the sliding of the cover plate 4. A sliding cylinder for driving the cover plate 4 to slide on the molding box 2 can be provided on the molding box 2.

[0054] An axle mold 3 is arranged inside the molding box 2, and the axle mold 3 is placed inside the molding box 2. An annular support platform for supporting the axle mold 3 can be arranged inside the molding box 2, and a gasket is arranged at the edge between the support platform and the axle mold 3 to prevent the coated sand from falling from the edge of the axle mold 3. In order to improve the placement stability of the axle mold 3 inside the molding box 2, positioning blocks or positioning columns can be arranged at the bottom of the molding box 2 to position the axle mold 3. The cover plate 4 is provided with a first heating element 7 for heating the coated sand, and the molding box 2 is provided with a second heating element 8 for heating the coated sand. The first heating element 7 and the second heating element 8 can be selected from heating tubes, heating rods or heating wires according to needs.

[0055] A guide plate 9 is arranged between the molding box 2 and the workbench 1, and a cylinder 10 for driving the guide plate 9 to move up and down is arranged on the workbench 1. The cylinder 10 is fixed on the workbench 1, and the workbench 1 is provided with a through hole through which the piston rod of the cylinder 10 passes, and the piston rod is slidably connected to the through hole. The piston rod of the cylinder 10 is fixedly connected to the guide plate 9. Two cylinders 10 are respectively located on both sides of the guide plate 9, improving the support stability of the guide plate 9. The guide plate 9 is provided with a through hole through which the guide column 11 passes, and the guide column 11 is slidably connected to the guide plate 9. A number of ejector pins 12 are evenly and fixedly arranged on the upper surface of the guide plate 9. The ejector pins 12 are located directly below the axle mold 3 and are used to lift the axle mold 3. Through holes corresponding to the ejector pins 12 one by one and through which the ejector pins 12 pass are arranged on the bottom plate of the molding box 2, and the ejector pins 12 are slidably connected to the through holes.

[0056] The first heating element 7, the second heating element 8, and the cylinder 10 are all connected to the controller 13 using existing technologies as needed.

[0057] During use, first place the shaft mold 3 in the molding box 2, then add coated sand into the interior of the molding box 2 through the sand hopper 5, and spread the coated sand in the molding box 2 evenly. Slide the cover plate 4, and the cover plate 4 covers the top of the molding box 2. Start the first heating element 7 and the second heating element 8 to heat the coated sand; start the cylinder 10, and the cylinder 10 drives the ejector pin 12 to move upward through the guide plate 9, and the ejector pin 12 drives the shaft mold 3 to move upward to press the coated sand. After the molding is completed, slide the cover plate 4, and the cylinder 10 continues to rise, and the shaft mold 3 is jacked out of the molding box 2 through the ejector pin 12 to complete the molding of the coated sand mold.

[0058] Example 1

[0059] A ductile iron camshaft includes the following components by mass percentage: C: 3.6%, Si: 2.6%, Mn: 0.5%, Cu: 0.7%, P ≤ 0.07%, S ≤ 0.02%, and the balance is Fe.

[0060] The preparation method of the above ductile iron camshaft includes the following steps:

[0061] S1. Molding, producing a coated sand mold on a sand mold molding device.

[0062] The curing time of the coated sand mold is 80 s, the curing temperature is 200 °C, and the molding time is 2 min.

[0063] S2. Batching, weighing pig iron, scrap steel, return material, copper, ferrosilicon, and ferromanganese according to the component ratio of the ductile iron camshaft.

[0064] The mass percentage of pig iron in the raw materials is 20%, the mass percentage of scrap steel in the raw materials is 52%, and the mass percentage of return material in the raw materials is 25%. The purity of copper is not less than 99.9%.

[0065] S3. Melting, adding the weighed pig iron, scrap steel, and return material into the melting equipment in sequence. After the pig iron, scrap steel, and return material are completely melted, add copper, ferrosilicon, and ferromanganese into the solution; perform component detection on the melted solution and adjust the components of the solution.

[0066] The melting equipment is a steel shell intermediate frequency induction furnace, and the melting temperature is 1600 °C.

[0067] S4. After the solution is poured out of the furnace, wire feeding and spheroidizing are carried out to perform spheroidizing treatment on the solution, and an inoculant is added for inoculation treatment

[0068] The tapping temperature is 1550°C. The spheroidizing agent for wire feeding spheroidization is a heavy rare earth spheroidizing wire, with a dosage of 15 m / T. The composition of the spheroidizing agent is 40% - 60% Si, 4.0% - 6.5% RE, and 20% - 35% Mg. The inoculant includes an inoculating wire and in-mold inoculant. The composition of the inoculating wire is 60% - 75% Si, 1% - 3% Ba, 1% - 5% Ca, and the balance is iron. The diameter of the inoculating wire is 13 mm, and the dosage is 16 m / T. The composition of the in-mold inoculant is 65% - 75% Si, 1% - 4% Ba, 1% - 3% Ca, and the balance is iron. The dosage of the in-mold inoculant is 0.3% of the total melt.

[0069] S5. Pouring: Skim the slag from the solution that has been spheroidized and inoculated, then pour the solution into the coated sand mold, cool it to room temperature, and remove the mold to obtain the camshaft casting.

[0070] The pouring temperature is 1350°C, and the time from inoculation to the completion of pouring is ≤ 12 min; the cooling time after pouring is 30 min.

[0071] S6. Heat treatment: Rough grind the obtained camshaft casting to remove the oxide layer and impurities on the casting surface, and then put the casting into an intermediate frequency quenching device for heat treatment.

[0072] The power of the intermediate frequency quenching device is 130 kW, the frequency is 6 kHz, the heating time is 5 s, and the cooling time is 5 s. Cooling is carried out by water cooling with normal temperature water.

[0073] Example 2

[0074] A ductile iron camshaft includes the following components by mass percentage: C: 3.8%, Si: 2.5%, Mn: 0.7%, Cu: 0.9%, P ≤ 0.07%, S ≤ 0.02%, and the balance is Fe.

[0075] The preparation method of the above ductile iron camshaft includes the following steps:

[0076] S1. Molding: Produce a coated sand mold on a sand mold molding device.

[0077] The curing time of the coated sand mold is 100 s, the curing temperature is 230°C, and the mold pressing time is 1 min.

[0078] S2. Batching: Weigh pig iron, scrap steel, return scrap, copper, ferrosilicon, and ferromanganese according to the composition ratio of the ductile iron camshaft.

[0079] The mass percentage of pig iron in the raw materials is 12%, the mass percentage of scrap steel in the raw materials is 60%, and the mass percentage of return scrap in the raw materials is 24%. The purity of copper is not less than 99.9%.

[0080] S3. Melting: The weighed pig iron, scrap steel, and return materials are successively added to the melting equipment. After the pig iron, scrap steel, and return materials are completely melted, copper, ferrosilicon, and ferromanganese are added to the solution. The composition of the melted solution is detected and adjusted.

[0081] The melting equipment is a steel shell medium frequency induction furnace, and the melting temperature is 1620 °C.

[0082] S4. After the solution is discharged from the furnace, wire feeding and spheroidizing are carried out to spheroidize the solution, and an inoculant is added for inoculation treatment.

[0083] The tapping temperature is 1570 °C. The spheroidizing agent for wire feeding and spheroidizing is a heavy rare earth spheroidizing wire, and the dosage of the spheroidizing agent is 19 m / T. The composition of the spheroidizing agent is Si 40 - 60%, RE 4.0 - 6.5%, Mg 20 - 35%. The inoculant includes an inoculation wire and a stream inoculant. The composition of the inoculation wire is 60% - 75% Si, 1% - 3% Ba, 1% - 5% Ca, and the balance is iron. The diameter of the inoculation wire is 13 mm, and the dosage of the inoculation wire is 19 m / T. The composition of the stream inoculant is 65% - 75% Si, 1% - 4% Ba, 1% - 3% Ca, and the balance is iron. The dosage of the stream inoculant is 0.4% of the total melt.

[0084] S5. Pouring: The solution after spheroidizing and inoculation treatment is skimmed, and then the solution is poured into a furan resin sand mold, cooled to room temperature, and the mold is removed to obtain a camshaft casting.

[0085] The pouring temperature is 1400 °C, and the time from inoculation to the completion of pouring ≤ 12 min; the cooling time after pouring is 60 min.

[0086] S6. Heat treatment: The obtained camshaft casting is roughly ground to remove the oxide layer and impurities on the surface of the casting, and then the casting is put into a medium frequency quenching equipment for heat treatment.

[0087] The power of the medium frequency quenching equipment is 150 kW, the frequency is 6 kHz, the heating time is 5 s, and the cooling time is 6 s. The cooling is carried out by water cooling with normal temperature water.

[0088] Example 3

[0089] A ductile iron camshaft includes the following components by mass percentage: C: 3.7%, Si: 2.4%, Mn: 0.5%, Cu: 0.6%, P ≤ 0.07%, S ≤ 0.02%, and the balance is Fe.

[0090] The preparation method of the above ductile iron camshaft includes the following steps:

[0091] S1. Molding: Produce a furan resin sand mold on a sand mold molding device.

[0092] The curing time of the coated sand mold is 100 s, the curing temperature is 200 °C, and the mold pressing time is 3 min.

[0093] S2. Batching: Weigh pig iron, scrap steel, return scrap, copper, ferrosilicon, and ferromanganese according to the component ratio of the ductile iron camshaft.

[0094] The mass percentage of pig iron in the raw materials is 16%, the mass percentage of scrap steel in the raw materials is 69%, and the mass percentage of return scrap in the raw materials is 12%. The purity of copper is not less than 99.9%.

[0095] S3. Melting: Add the weighed pig iron, scrap steel, and return scrap to the melting equipment in sequence. After the pig iron, scrap steel, and return scrap are completely melted, add copper, ferrosilicon, and ferromanganese to the solution; conduct component detection on the melted solution and adjust the components of the solution.

[0096] The melting equipment is a steel shell medium frequency induction furnace, and the melting temperature is 1640 °C.

[0097] S4. After the solution is tapped, wire feeding and nodulizing are carried out for nodulizing treatment, and an inoculant is added for inoculation treatment.

[0098] The tapping temperature is 1580 °C. The nodulizer for wire feeding and nodulizing is a heavy rare earth nodulizing wire, and the dosage of the nodulizer is 17 m / T. The components of the nodulizer are Si 40 - 60%, RE 4.0 - 6.5%, Mg 20 - 35%. The inoculant includes an inoculation wire and a stream inoculant. The components of the inoculation wire are 60% - 75% Si, 1% - 3% Ba, 1% - 5% Ca, and the balance is iron. The diameter of the inoculation wire is 13 mm, and the dosage of the inoculation wire is 18 m / T. The components of the stream inoculant are 65% - 75% Si, 1% - 4% Ba, 1% - 3% Ca, and the balance is iron. The dosage of the stream inoculant is 0.5% of the total melt.

[0099] S5. Pouring: Conduct slag skimming on the solution after nodulizing and inoculation treatment, pour the solution into the coated sand mold, cool it to room temperature, and remove the mold to obtain the camshaft casting.

[0100] The pouring temperature is 1380 °C, and the time from inoculation to the completion of pouring ≤ 12 min; the cooling time after pouring is 120 min.

[0101] S6. Heat treatment: Rough grind the obtained camshaft casting to remove the oxide layer and impurities on the casting surface, and put the casting into the medium frequency quenching equipment for heat treatment.

[0102] The power of the medium frequency quenching equipment is 130 kW, the frequency is 6 kHz, the heating time is 6 s, and the cooling time is 6 s. The cooling is water cooling with normal temperature water.

[0103] The microstructure of the ductile iron camshaft prepared in Example 2 was observed, and the results are as Figure 3 shown. The spheroidization grade of the graphite in the prepared ductile iron camshaft is grade 2, the size of the graphite spheroidization is grade 5, the pearlite content is 95%, and the free carbide is ≤1%. The spheroidization grade of the graphite in the ductile iron camshaft prepared in Example 1 is grade 2, the size of the graphite spheroidization is grade 6, the pearlite content is 87%, and the free carbide is ≤1%. The spheroidization grade of the graphite in the ductile iron camshaft prepared in Example 3 is grade 3, the size of the graphite spheroidization is grade 6, the pearlite content is 90%, and the free carbide is ≤1%.

[0104] The mechanical properties of the ductile iron camshafts prepared in Examples 1-3 were tested. The matrix hardness of the ductile iron camshaft prepared in Example 1 is 268 HBW, the hardness of the cam nose is 57 HRC, the hardness of the cam base circle is 57 HRC, the hardened layer depth of the cam nose is 3.7 mm, the hardened layer depth of the cam base circle is 3.5 mm, and the martensite grade is grade 5. The matrix hardness of the ductile iron camshaft prepared in Example 2 is 273 HBW, the hardness of the cam nose is 57 HRC, the hardness of the cam base circle is 58 HRC, the hardened layer depth of the cam nose is 3.9 mm, the hardened layer depth of the cam base circle is 3.7 mm, and the martensite grade is grade 4. The matrix hardness of the ductile iron camshaft prepared in Example 3 is 270 HBW, the hardness of the cam nose is 57 HRC, the hardness of the cam base circle is 58 HRC, the hardened layer depth of the cam nose is 3.9 mm, the hardened layer depth of the cam base circle is 3.7 mm, and the martensite grade is grade 4.

[0105] The tensile strength and elongation of the ductile iron camshafts prepared in Examples 1-3 were tested. The tensile strength R m of the ductile iron camshaft prepared in Example 1 is 789 MPa, and the elongation is 6.5%; the tensile strength R m of the ductile iron camshaft prepared in Example 2 is 813 MPa, and the elongation is 5.9%; the tensile strength R m of the ductile iron camshaft prepared in Example 3 is 766 MPa, and the elongation is 7.3%.

[0106] Therefore, by adopting the above ductile iron camshaft and its preparation method, the present invention can solve the problems of relatively low pearlite content and low hardness of the existing ductile iron camshafts.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A ductile iron camshaft, characterized in that, Comprising components with the following mass percentages: C: 3.6% - 3.8%, Si: 2.4% - 2.6%, Mn: 0.5% - 0.7%, Cu: 0.5% - 1.0%, P ≤ 0.07%, S ≤ 0.02%, and the balance being Fe.

2. A method for preparing a ductile iron camshaft according to claim 1, characterized in that, Including the following steps: S1. Molding, producing a coated sand mold on a sand mold molding device; S2. Batching, weighing pig iron, scrap steel, return material, copper, ferrosilicon, and ferromanganese according to the composition ratio of the ductile iron camshaft; S3. Melting, successively adding the weighed pig iron, scrap steel, and return material into a melting device. After the pig iron, scrap steel, and return material are completely melted, add copper, ferrosilicon, and ferromanganese to the solution; conduct component detection on the melted solution and adjust the composition of the solution; S4. After the solution is out of the furnace, wire feeding and spheroidizing are carried out for spheroidizing treatment, and an inoculant is added for inoculation treatment; S5. Pouring, carrying out slag skimming on the solution that has undergone spheroidizing and inoculation treatment, pouring the solution into the coated sand mold, cooling to room temperature, and unpacking to obtain the camshaft casting; S6. Heat treatment, rough grinding the obtained camshaft casting to remove the oxide layer and impurities on the surface of the casting, and putting the casting into an intermediate frequency quenching device for heat treatment.

3. The preparation method of a ductile iron camshaft according to claim 2, characterized in that: In S1, the curing time of the coated sand mold is 80s - 100s, the curing temperature is 190°C - 230°C, and the mold pressing time is 0.5min - 3min.

4. The preparation method of a ductile iron camshaft according to claim 2, characterized in that: In S2, the mass percentage of pig iron in the raw materials is 10% - 20%, the mass percentage of scrap steel in the raw materials is 50% - 70%, and the mass percentage of return material in the raw materials is 10% - 30%.

5. The preparation method of a ductile iron camshaft according to claim 2, characterized in that: In S2, the purity of copper is not less than 99.9%.

6. The preparation method of a ductile iron camshaft according to claim 2, characterized in that: In S3, the melting device is a steel shell intermediate frequency induction furnace, and the melting temperature is 1580°C - 1650°C.

7. The preparation method of a ductile iron camshaft according to claim 2, characterized in that: In S4, the tapping temperature is 1550°C - 1580°C, the spheroidizing agent for wire feeding and spheroidizing is a heavy rare earth spheroidizing wire, the dosage of the spheroidizing agent is 15m / T - 19m / T, and the composition of the spheroidizing agent is 40% - 60% Si, 4.0% - 6.5% RE, 20% - 35% Mg; the inoculant includes an inoculation wire and a stream inoculant. The composition of the inoculation wire is 60% - 75% Si, 1% - 3% Ba, 1% - 5% Ca, and the balance being iron. The diameter of the inoculation wire is 13mm, and the dosage is 15m / T - 19m / T; The composition of the stream inoculant is 65% - 75% Si, 1% - 4% Ba, 1% - 3% Ca, and the balance being iron. The dosage of the stream inoculant is 0.3% - 0.5% of the total melt.

8. The preparation method of a ductile iron camshaft according to claim 2, characterized in that: In S5, the pouring temperature is 1340°C - 1420°C, the time from inoculation to the completion of pouring ≤ 12min; the cooling time after pouring ≥ 30min.

9. The preparation method of a ductile iron camshaft according to claim 2, characterized in that: In S5, the power of the intermediate frequency quenching device is 130kW - 150kW, the frequency is 5.5kHz - 6.5kHz, the heating time is 5s - 6s, the cooling time is 5s - 6s, and the cooling is water cooling with normal temperature water.

10. The preparation method of a ductile iron camshaft according to claim 2, characterized in that: The sand mold molding device includes a workbench, above which a molding box is arranged. The workbench and the molding box are connected by guide columns. An opening is provided at the top of the molding box. Above the molding box, a sand hopper for adding coated sand into the interior of the molding box is arranged. A cover plate for closing the top opening of the molding box is arranged at the top of the molding box. The cover plate is slidably connected to the molding box. An axial mold is arranged inside the molding box. A guide plate is arranged between the molding box and the workbench. A cylinder for driving the guide plate to move up and down is arranged on the workbench. The guide plate is provided with through holes through which the guide columns pass. A plurality of ejector pins for ejecting the axial mold out of the molding box are evenly arranged on the upper surface of the guide plate. Through holes corresponding to the ejector pins one by one and allowing the ejector pins to pass through are arranged on the bottom plate of the molding box. A first heating element for heating the coated sand is arranged on the cover plate. A second heating element for heating the coated sand is arranged on the molding box. The first heating element, the second heating element, and the cylinder are all connected to a controller.

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