Bainite ductile cast iron, method for producing the same, and bainite ductile cast iron cylinder liner

Abstract

The application provides a bainite ductile cast iron, which comprises the following components: C 3.4-4.0 wt%, Si 2.5-3.0 wt%, Ni 0.9-1.5 wt%, Mo 0.6-1.1 wt%, V 0.1-0.2 wt%, B 0.01-0.03 wt%, Sn 0.04-0.08 wt%, Mg 0.03-0.05 wt%, RE 0.02-0.05 wt%, and Fe as the balance. The application also provides a preparation method of the bainite ductile cast iron. The matrix structure of the bainite ductile cast iron provided by the application is a bainite matrix, which is beneficial to improving the strength of the cast iron, making the cylinder sleeve have higher anti-explosion performance, and further adding vanadium and boron, thereby further increasing the wear resistance and hardness.

Description

Technical Field

[0001] This invention relates to the field of cast iron technology, and in particular to a bainitic ductile iron, its preparation method, and a bainitic ductile iron cylinder liner. Background Technology

[0002] The known as-cast bainitic gray cast iron (patent CN1493781A) has a relatively low strength of approximately 400-480 MPa, making it unsuitable for use in existing high-strength, high-explosion-pressure engines. Controlled-cooling bainitic ductile iron cylinder liners (Chinese patent CN108559903A provides a controlled-cooling bainitic ductile iron cylinder liner; although this type of cylinder liner can achieve a strength of 850 MPa, the poor wear and corrosion resistance of bainite often leads to early wear and corrosion. Chinese patent CN1361301A provides isothermal-quenched bainitic ductile iron, but its strength is less than 400 MPa. Chinese patent CN103225036A provides boron carbide-reinforced wear-resistant bainitic ductile iron grinding balls and their manufacturing method; the strength of the prepared bainitic ductile iron grinding balls is less than 800 MPa.

[0003] As explained above, bainitic cast iron generally has a strength of 400–480 MPa and moderate resistance to cavitation corrosion. Pearlitic ductile cast iron also has relatively low strength, typically around 850 MPa. Even after isothermal quenching to bainite, the lack of wear-resistant hard phases outside the matrix limits its wear resistance. While some wear-resistant hard phases may be present, the strength, corrosion resistance, and pressure resistance do not meet requirements. Therefore, finding a material that achieves high strength, high pressure resistance, wear resistance, and corrosion resistance is a key research direction for engine engineers. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a bainitic ductile iron that simultaneously possesses the characteristics of high strength, resistance to high burst pressure, wear resistance, and corrosion resistance.

[0005] In view of this, this application provides a bainitic ductile iron, comprising: C 3.4–4.0 wt%, Si 2.5–3.0 wt%, Ni 0.9–1.5 wt%, Mo 0.6–1.1 wt%, V 0.1–0.2 wt%, B 0.01–0.03 wt%, Sn 0.04–0.08 wt%, Mg 0.03–0.05 wt%, RE 0.02–0.05 wt%, and Fe balance.

[0006] Preferably, S 0–0.02 wt%, P 0–0.05 wt%, and Mn 0–0.35 wt%.

[0007] Preferably, the content of V is 0.11 to 0.16 wt%, and the content of B is 0.015 to 0.027 wt%.

[0008] This application also provides a method for preparing the aforementioned bainitic ductile iron, comprising the following steps:

[0009] A) Prepare the raw materials according to the composition ratio of bainitic ductile iron, mix them, and then smelt them to obtain molten iron;

[0010] B) The molten iron is transferred to a holding furnace, then to a spheroidizing ladle, and after spheroidizing, it is transferred to a casting ladle for casting to obtain a casting. The primary inoculation and spheroidizing treatment of the molten iron transferred to the spheroidizing ladle are added by wire feeding. The casting ladle is pre-lined with a secondary inoculant, and the casting is carried out simultaneously with co-current inoculation.

[0011] C) The casting is placed on a conveyor belt for air cooling, and then placed in a tunnel furnace for heat preservation to obtain a blank;

[0012] D) After rough machining, the blank is tempered to obtain bainitic ductile iron.

[0013] Preferably, in step A), the ingredient preparation process specifically includes:

[0014] Pig iron, scrap steel, and recycled materials are mixed in a mass ratio of 4:6:1 and smelted. After melting, silicon-manganese alloy, ferrochrome alloy, ferrovanadium alloy, ferroboron alloy, ferromolybdenum alloy, electrolytic nickel, and electrolytic tin are added.

[0015] Preferably, the smelting temperature is 1500–1600℃, and the holding time is 10–20 min; the composition of the molten iron includes: C 4.05–4.25 wt%, Si 1.1–1.3 wt%, Ni 0.9–1.5 wt%, Mo 0.6–1.1 wt%, V 0.1–0.2 wt%, B 0.01–0.03 wt%, Sn 0.04–0.08 wt%, S 0–0.02 wt%, P 0–0.05 wt%, Mn 0–0.35 wt%, and Fe balance.

[0016] Preferably, in step B), the temperature of the molten iron in the holding furnace is 1500–1540°C; the inoculant used in the primary inoculation is a barium silicon inoculant, and its addition amount is 0.2–0.4 wt% of the molten iron mass; the spheroidizing agent used in the spheroidizing treatment is a rare earth magnesium spheroidizing agent, and its addition amount is based on the residual magnesium and rare earth in the molten iron reaching 0.03–0.05 wt% Mg and 0.02–0.05 wt% Ce.

[0017] Preferably, in step B), the inoculant for the secondary inoculation is a silicon-strontium inoculant, and its addition amount is 0.2 to 0.3 wt% of the molten iron mass; the inoculant for the co-current inoculation is a silicon-strontium inoculant, and its addition amount is 0.1 to 0.2 wt% of the molten iron mass; and the pouring temperature is 600 to 850°C.

[0018] Preferably, the air cooling temperature is 400-500℃, the tunnel furnace temperature is 350-400℃, the tunnel furnace length is L (m), the moving speed is V (m / min), and L / V ≥ 120; the tempering temperature is 500-600℃, and the time is 2-3 hours.

[0019] This application also provides a bainitic ductile iron cylinder liner, which is prepared by the chemical composition of the bainitic ductile iron or by the preparation method described above.

[0020] This application provides a bainitic ductile iron comprising: C 3.4–4.0 wt%, Si 2.5–3.0 wt%, Ni 0.9–1.5 wt%, Mo 0.6–1.1 wt%, V 0.1–0.2 wt%, B 0.01–0.03 wt%, Sn 0.04–0.08 wt%, Mg 0.03–0.05 wt%, RE 0.02-0.05 wt%, Fe balance; The bainitic ductile iron provided in this application incorporates vanadium and boron. Vanadium can form vanadium nitrides, carbides, and carbonitrides with carbon and nitrogen, while boron can form boron carbide compounds with carbon. The hardness of vanadium nitride can reach 3000 HV, and the hardness of boron carbide can reach 1300 HV. The vanadium compounds are distributed in a diffuse dot-like pattern, while the boron carbide compounds are distributed in a diffuse blocky or discontinuous network pattern, thereby increasing the wear resistance of the matrix. Moreover, the high microhardness of the vanadium compounds is firmly embedded in the metal matrix, which reduces wear and separates the two friction surfaces, thus reducing the coefficient of friction. At the same time, the presence of the alloying element nickel and the boron carbide at the grain boundaries gives the matrix good corrosion resistance and cavitation resistance.

[0021] This application also provides a method for preparing bainitic ductile iron, which includes the following sequential processes: batching, melting, transfer, holding furnace, casting ladle, spheroidizing and inoculation, casting (secondary inoculation, in-flow inoculation), demolding, air blowing, bainitic heat preservation, rough machining, and tempering. In the above process, ductile iron is produced by wire feeding spheroidizing and inoculation in the casting ladle. At the same time, air cooling and heat preservation utilize the residual heat of the casting to directly generate as-cast bainite, which is beneficial to improving the strength and hardness of as-cast bainitic ductile iron. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the bainitic ductile iron preparation process of the present invention;

[0023] Figure 2 The microstructure of the bainitic ductile iron prepared in Example 1 of this invention is 100 times larger than that after polishing.

[0024] Figure 3 The microstructure of the bainitic ductile iron prepared in Example 1 of this invention is shown at 100 times magnification of the matrix after polishing and acid etching.

[0025] Figure 4 The microstructure of the bainitic ductile iron matrix prepared in Example 1 of this invention is shown as 500 times the size of the matrix. Detailed Implementation

[0026] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0027] In view of the existing requirements for cylinder liners to have high strength, high corrosion resistance and high wear resistance, this application provides a bainitic ductile iron, which has high strength, corrosion resistance and wear resistance, and in particular, increased resistance to formic acid corrosion. Cylinder liners made from it have excellent performance and can meet the requirements of modern engines for high strength, high explosion pressure, corrosion resistance and cavitation resistance of cylinder liners. Specifically, this application first adjusts the composition of bainitic ductile iron by adding boron and vanadium and adjusting their content. The bainitic ductile iron comprises: C 3.4-4.0 wt%, Si 2.5-3.0 wt%, Ni 0.9-1.5 wt%, Mo 0.6-1.1 wt%, V 0.1-0.2 wt%, B 0.01-0.03 wt%, Sn 0.04-0.08 wt%, Mg 0.03-0.05 wt%, RE 0.02-0.05 wt%, and Fe balance.

[0028] In this application, vanadium can form vanadium nitrides, carbides, and carbonitrides with carbon and nitrogen, and boron can also form boron carbides with carbon. The hardness of vanadium nitride can reach 3000 HV, and the hardness of boron carbides can reach 1300 HV. The vanadium compounds are distributed in a diffuse dot-like pattern, while the boron carbides are distributed in a diffuse blocky or discontinuous network pattern, thereby increasing the wear resistance of the matrix. Moreover, because the high microhardness vanadium compounds are firmly embedded in the metal matrix, both the amount of wear is reduced, and the friction coefficient is reduced by separating the two friction surfaces. Specifically, the V content is 0.11–0.16 wt%, and the B content is 0.015–0.027 wt%.

[0029] Furthermore, the presence of the alloying element nickel and boron carbides at the grain boundaries gives the matrix good corrosion resistance and cavitation resistance. Specifically, the Ni content is 0.95–1.40 wt%.

[0030] More specifically, the C content is 3.50–3.95 wt%, the Si content is 2.65–2.85 wt%, the Mo content is 0.75–1.05 wt%, the V content is 0.11–0.18 wt%, the Sn content is 0.045–0.070 wt%, the Mg content is 0.035–0.045 wt%, and RE can be selected from Ce, with a content of 0.026–0.045 wt%.

[0031] Meanwhile, this application specifies the contents of S, P and Mn. Specifically, the content of S is 0 to 0.02 wt%, the content of P is 0 to 0.05 wt%, and the content of Mn is 0 to 0.35 wt%; more specifically, the content of S is 0.005 to 0.015 wt%, the content of P is 0.01 to 0.04 wt%, and the content of Mn is 0.10 to 0.32 wt%.

[0032] This application also provides a method for preparing bainitic ductile iron, the specific process of which is as follows: Figure 1 As shown, it includes the following steps:

[0033] A) Prepare the raw materials according to the composition ratio of as-cast bainitic ductile iron, mix them, and then smelt them to obtain molten iron;

[0034] B) The molten iron is transferred to a holding furnace, then from the holding furnace to a spheroidizing ladle, and then from the spheroidizing ladle to a casting ladle for pouring to obtain a casting; the primary inoculation and spheroidizing treatment of the molten iron transferred to the spheroidizing ladle are added by wire feeding method, the casting ladle is pre-lined with a secondary inoculant, and the pouring is carried out simultaneously with co-current inoculation;

[0035] C) The casting is placed on a conveyor belt for air cooling, and then placed in a tunnel furnace for heat preservation to obtain a blank;

[0036] D) After rough machining, the blank is tempered to obtain as-cast bainitic ductile iron.

[0037] In the preparation process of bainitic ductile iron, this application first prepares the raw materials according to the composition ratio of as-cast bainitic ductile iron, mixes them, and then melts them to obtain molten iron. In this application, pig iron, scrap steel, and recycled materials are added in a mass ratio of 4:6:1 according to the composition of as-cast bainitic ductile iron. The mixture is initially melted in an electric furnace. After complete dissolution, ferroalloys such as silicon-manganese alloy, ferrochrome, ferrovanadium, ferroboron, and ferromolybdenum, as well as electrolytic nickel and electrolytic tin, are added. The temperature is raised to 1500–1600℃ and held at that temperature for 10–20 minutes to obtain molten iron. The specific composition of the molten iron is controlled within the following range: C 4.05–4.25 wt%, Si 1.1–1.3 wt%, Ni 0.9–1.5 wt%, Mo 0.6–1.1 wt%, V 0.1–0.2 wt%, B 0.01–0.03 wt%, Sn 0.04–0.08 wt%, S 0–0.02 wt%, P 0–0.05 wt%, Mn 0–0.35 wt%, Fe balance. The above temperature rise is more specifically 1550–1600 °C.

[0038] The application then removes slag from the molten iron to ensure that there are no impurities such as iron slag in the molten iron, and then uses a transfer ladle to transfer the molten iron into a holding furnace. The temperature of the molten iron when entering the holding furnace is 1520-1560℃, and the temperature inside the holding furnace is controlled at 150-1540℃.

[0039] According to the present invention, casting is then performed, and the specific process is as follows:

[0040] Molten iron is transferred from the holding furnace to the spheroidizing ladle, and then from the spheroidizing ladle to the casting ladle. The amount of molten iron in the casting ladle should be enough to be poured within 15 minutes. The primary inoculation and spheroidizing treatment of the molten iron transferred to the spheroidizing ladle are both carried out using the wire feeding method. The spheroidizing agent used in the spheroidizing treatment is a rare earth magnesium spheroidizing agent, and the amount added is based on the residual magnesium and rare earth in the molten iron reaching 0.03% to 0.05% for magnesium and 0.020% to 0.05% for cerium. The inoculant used in the primary inoculation is a silicon barium inoculant, and the amount added is converted to 0.2% to 0.4% of the weight of the molten iron. After spheroidizing and inoculation are completed, slag removal should be carried out to purify the molten iron, and the ladle should be covered to prevent rapid temperature loss.

[0041] The casting ladle is pre-filled with a secondary inoculant, which is a silicon-strontium inoculant, added at a rate of 0.2wt% to 0.3wt% of the molten iron. The casting temperature is controlled at 1450 to 1500℃. During casting, a second co-current inoculation is performed, using a silicon-strontium inoculant added at a rate of 0.1% to 0.2% of the molten iron. The inoculants are all automatically fed using an automatic feeding system.

[0042] The casting process described in this application is carried out using a fully automatic multi-station casting machine. The casting machine employs a conventional centrifugal casting process using a metal mold wet coating to produce cylinder liner castings. The multi-station casting machine includes steps such as automatic spraying, upper baffle plate installation, pouring, water jetting, cooling, and automatic cylinder unloading; the cylinder unloading temperature is 600–850℃. In this application, the composition of the cast parts is specifically the same as that of the final-state bainitic ductile iron.

[0043] This application then places the casting on a conveyor belt and cools it to 400-500°C using air cooling. After air cooling, the casting is moved along the conveyor belt into a tunnel furnace for heat preservation, with the temperature controlled at 350-400°C. During this process, the bainitic transformation is completed, resulting in a blank. The length of the tunnel furnace is L (m), and the moving speed is V (m / min), where L / V ≥ 120.

[0044] According to the present invention, the blank obtained above is cleaned and roughly processed into a semi-finished product, and then tempered. The tempering temperature is 500-600°C and the time is 2-3 hours; more specifically, the tempering temperature is 520-550°C and the time is 2 hours.

[0045] This application also provides a bainitic ductile iron cylinder liner, which includes the above-mentioned chemical composition or is prepared according to the above-mentioned preparation method.

[0046] To further understand the present invention, the preparation method of bainitic ductile iron cylinder liner provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0047] Example 1

[0048] A manufacturing process for a high-strength and high-wear-resistant bainitic ductile iron cylinder liner includes the following steps:

[0049] 1. Cylinder liner blank production

[0050] ① Iron smelting: Pig iron, scrap steel and recycled materials are used. The mass ratio of pig iron, scrap steel and recycled materials is controlled at 4:6:1. Smelting is carried out in an electric furnace. After all the materials are melted, alloys (ferroalloys such as silicon-manganese alloy, ferrochrome, ferrovanadium, ferroboron, ferromolybdenum, etc., as well as electrolytic nickel, electrolytic tin, etc.) are added. The temperature is further raised to 1580℃. The furnace lid is covered and the material is kept at the temperature for 15 minutes. The material is then finely adjusted so that its composition is controlled as shown in Table 1.

[0051] Table 1. Iron Composition Data for Example 1

[0052] Item C S Si P Mn Ni Mo V B Sn Require 3.82 0.012 1.15 0.04 0.31 0.98 1.05 0.15 0.027 0.055

[0053] ② Transfer of molten iron to holding furnace: Remove slag from the molten iron to ensure that there are no impurities such as iron slag in the molten iron. Transfer the molten iron to the holding furnace using a transfer ladle. The temperature of the molten iron entering the holding furnace is controlled at 1550℃, and the temperature of the holding furnace is controlled within the range of 1525℃.

[0054] ③ Casting:

[0055] Hot metal transfer, spheroidizing, and inoculation: Hot metal is automatically poured from the holding furnace into the transfer ladle. The amount of hot metal in the transfer ladle should be completed within 15 minutes. Both the primary inoculation and spheroidizing treatments use the wire feeding method. The spheroidizing agent is a rare earth magnesium spheroidizing agent, and the amount added is based on the residual magnesium and rare earth in the hot metal: magnesium: 0.035%, Ce: 0.036%. The primary inoculating agent is a silicon barium inoculating agent, and the amount added is converted to 0.37% of the weight of the hot metal. After spheroidizing and inoculation are completed, slag removal should be performed to purify the hot metal, and the ladle should be covered to prevent rapid temperature loss.

[0056] The ladle is pre-filled with a secondary inoculant, which is a silicon-strontium inoculant, and the amount added is 0.24% of the weight of the molten iron. The tapping temperature is 1470℃. During the pouring process, a second co-current inoculation is carried out, with the amount added being 0.13% of the molten iron. All inoculants are added automatically using an automatic feeding system.

[0057] The production is carried out using a fully automatic multi-station casting machine. The casting machine adopts the conventional process of centrifugal casting with wet coating in metal mold to produce cylinder liner castings. The multi-station casting machine includes steps such as automatic spraying, upper baffle, pouring, water jetting, cooling and automatic cylinder discharge. The cylinder discharge temperature is controlled at 730℃. The final composition of the cylinder liner is shown in Table 2.

[0058] Table 2 Composition data of cylinder liner castings

[0059] Item C S Si P Mn Ni Mo V B Sn Mg Ce Require 3.82 0.012 2.80 0.04 0.31 0.98 1.05 0.15 0.027 0.055 0.035 0.036

[0060] ④ Air cooling: The cylinder liners coming out of the automatic casting machine are automatically placed on the conveyor belt and cooled by blowing air with a fan. The temperature of the cylinder liners entering the tunnel furnace is 440℃.

[0061] ⑤ Bainitic thermal transformation: After being cooled by air, the cylinder liner is pushed into the tunnel furnace for thermal insulation by the conveyor belt. The temperature of the tunnel furnace is controlled at 380℃. The length of the tunnel furnace is 20 (m) and the moving speed is 0.15 (m / min).

[0062] ⑥ Coating cleaning: The cylinder liner coming out of the tunnel furnace is cleaned by an automatic coating cleaning device;

[0063] ⑦ Framing: The cleaned cylinder liners are automatically framed by robots;

[0064] 2. Rough machining: The cast blank is rough machined into a semi-finished product;

[0065] 3. Tempering: Temper the semi-finished product at 520℃ for 2 hours;

[0066] 4. Finishing: The tempered cylinder liner is then machined into a finished product according to the drawings;

[0067] 5. The sample cylinder liner was tested for hardness, tensile strength, elastic modulus, standard acid corrosion resistance, standard formic acid corrosion resistance, cavitation corrosion resistance and wear resistance. The test results are shown in Table 3.

[0068] Figures 2-4 These are metallographic images of the bainitic ductile iron cylinder liner at different magnifications, prepared in this embodiment. Figure 2 It can be seen that the graphite in the matrix is ​​uniformly distributed in a spherical shape; Figure 3 In the middle, the matrix structure consists of bainite, boron-containing carbides and spheroidal graphite; Figure 4 In the middle, the matrix structure is mainly bainite, containing boron-containing carbides, and a small amount of spheroidal graphite is distributed.

[0069] Example 2

[0070] A manufacturing process for a high-strength and high-wear-resistant bainitic ductile iron cylinder liner includes the following steps:

[0071] 1. Cylinder liner blank production

[0072] ① Iron smelting: Pig iron, scrap steel and recycled materials are used. The mass ratio of pig iron, scrap steel and recycled materials is controlled at 4:6:1. Smelting is carried out in an electric furnace. After all the materials are melted, alloys (ferroalloys such as silicon-manganese alloy, ferrochrome, ferrovanadium, ferroboron, ferromolybdenum, etc., as well as electrolytic nickel, electrolytic tin, etc.) are added. The temperature is further raised to 1565℃. The furnace lid is covered and the material is kept at the temperature for 15 minutes. The material is then finely adjusted so that its composition is controlled as shown in Table 3.

[0073] Table 3. Iron Composition Data from Example 2

[0074] Item C S Si P Mn Ni Mo V B Sn Require 3.92 0.08 1.28 0.025 0.20 1.35 0.78 0.11 0.019 0.065

[0075] ② Transfer of molten iron to holding furnace: Remove slag from the molten iron to ensure that there are no impurities such as iron slag in the molten iron. Transfer the molten iron to the holding furnace using a transfer ladle. The temperature of the molten iron entering the holding furnace is controlled at 1535℃, and the temperature of the holding furnace is controlled within the range of 1518℃.

[0076] ③ Casting:

[0077] Hot metal transfer spheroidizing and inoculation: Hot metal is automatically poured from the holding furnace into the transfer ladle. The amount of hot metal in the transfer ladle should be completed within 15 minutes. Both the primary inoculation and spheroidizing treatments use the wire feeding method. The spheroidizing agent for the primary inoculation is a rare earth magnesium spheroidizing agent, and the amount added is based on the residual magnesium and rare earth in the hot metal: magnesium: 0.041%, Ce: 0.043%. The inoculant for the primary inoculation is a silicon barium inoculant, and the amount added is converted to 0.26% of the weight of the hot metal. After spheroidizing and inoculation are completed, slag removal should be performed to purify the hot metal, and the ladle should be covered to prevent rapid temperature loss.

[0078] The ladle is pre-filled with a secondary inoculant, which is a silicon-strontium inoculant, added at 0.26% of the weight of the molten iron. The tapping temperature is 1460℃. During pouring, a second co-current inoculation is carried out, added at 0.16% of the weight of the molten iron. The inoculant is added automatically using an automatic feeding system.

[0079] The cylinder liner castings are produced using a fully automatic multi-station casting machine. The casting machine adopts the conventional process of centrifugal casting with wet coating in metal mold to produce cylinder liner castings. The multi-station casting machine includes steps such as automatic spraying, upper baffle, pouring, water jetting, cooling and automatic cylinder discharge. The cylinder discharge temperature is controlled at 720℃. The final composition of the cylinder liner is shown in Table 4.

[0080] Table 4. Composition data of cylinder liner castings

[0081] Item C S Si P Mn Ni Mo V B Sn Mg Ce Require 3.92 0.08 2.76 0.025 0.20 1.35 0.78 0.11 0.019 0.065 0.041 0.043

[0082] ④ Air cooling: The cylinder liners coming out of the automatic casting machine are automatically placed on the conveyor belt and cooled by blowing air with a fan. The temperature of the cylinder liners entering the tunnel furnace is 455℃.

[0083] ⑤ Bainitic thermal transformation: After being cooled by air, the cylinder liner is pushed into the tunnel furnace for thermal insulation by the conveyor belt. The temperature of the tunnel furnace is controlled at 370℃. The length of the tunnel furnace is 20 (m) and the moving speed is 0.14 (m / min).

[0084] ⑥ Coating cleaning: The cylinder liner coming out of the tunnel furnace is cleaned by an automatic coating cleaning device;

[0085] ⑦ Framing: The cleaned cylinder liners are automatically framed by robots;

[0086] 2. Rough machining: The cast blank is rough machined into a semi-finished product;

[0087] 3. Tempering: Temper the semi-finished product at 520℃ for 2 hours;

[0088] 4. Finishing: The tempered cylinder liner is then machined into a finished product according to the drawings;

[0089] 5. The sample cylinder liner was tested for hardness, tensile strength, elastic modulus, standard acid corrosion resistance, standard formic acid corrosion resistance, cavitation corrosion resistance and wear resistance. The test results are shown in Table 5.

[0090] Table 5. Performance test results of the cylinder liners prepared in the examples.

[0091]

[0092] Comparative Example 1

[0093] Except for the following, everything else is the same as in Example 1:

[0094] Eliminate the two steps of ④ air cooling and ⑤ bainitic thermal transformation, and directly cool in the air before cleaning and framing.

[0095] The test results for each performance aspect are shown in Table 9.

[0096] Comparative Example 2 (without boron and vanadium)

[0097] Except for the following contents, everything else is the same as in Example 1;

[0098] Table 6. Composition data of gas-jacketed steel castings in Comparative Example 2.

[0099] Item C S Si P Mn Ni Mo Sn Mg Ce Require 3.82 0.012 2.80 0.04 0.31 0.98 1.05 0.055 0.035 0.036

[0100] The test results for each performance aspect are shown in Table 9.

[0101] Comparative Example 3 (without boron)

[0102] Except for the following contents, everything else is the same as in Example 1;

[0103] Table 7. Composition data of gas-jacketed steel castings for Comparative Example 3.

[0104]

[0105] The test results for each performance aspect are shown in Table 9.

[0106] Comparative Example 4 (without vanadium)

[0107] Except for the following contents, everything else is the same as in Example 1;

[0108] Table 8. Composition data of gas-jacketed steel castings (Comparative Example 4)

[0109]

[0110] The test results for each performance aspect are shown in Table 9.

[0111] Table 9. Performance test results of the gas-jacketed cylinder castings prepared in the comparative examples and embodiments.

[0112]

[0113]

[0114] As can be seen from Table 9, in Comparative Example 1, since the matrix is ​​pearlitic rather than bainitic, its strength and hardness are relatively low; in Comparative Example 2, since it does not contain boron and vanadium, its gas corrosion resistance, wear resistance, and pitting corrosion resistance are all poor; in Comparative Example 3, since it does not contain boron, and in Comparative Example 4, since it does not contain vanadium, all its properties deviate from those of Example 1. It can be seen that adding boron or vanadium alone can slightly improve the various properties (compared to those without boron and vanadium), but the improvement is limited and there is still a certain gap compared with those containing both boron and vanadium. Therefore, in this application, the effects of boron and vanadium are synergistic and work together, and adding either element alone (boron or vanadium) cannot achieve this effect.

[0115] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0116] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing bainitic ductile iron, wherein the bainitic ductile iron comprises: C 3.82~4.0wt%, Si 2.5~3.0wt%, Ni 0.9~1.5wt%, Mo 0.6~1.1wt%, V 0.1~0.2wt%, B 0.01~0.03wt%, Sn 0.04~0.08wt%, Mg 0.03~0.05wt%, RE 0.02~0.05wt%, Fe balance; Includes the following steps: A) Prepare the raw materials according to the composition ratio of bainitic ductile iron, mix them, and then smelt them to obtain molten iron; B) The molten iron is transferred to a holding furnace, then to a spheroidizing ladle, and after spheroidizing, it is transferred to a casting ladle for casting to obtain a casting. The primary inoculation and spheroidizing treatment of the molten iron transferred to the spheroidizing ladle are added by wire feeding. The casting ladle is pre-lined with a secondary inoculant, and the casting is carried out simultaneously with co-current inoculation. C) The casting is placed on a conveyor belt for air cooling, and then placed in a tunnel furnace for heat preservation to obtain a blank; the air cooling temperature is reduced to 400~500℃, the temperature of the tunnel furnace is 350~400℃, the length of the tunnel furnace is L (m), the moving speed is V (m / min), and L / V≥120. D) After rough machining, the blank is tempered to obtain bainitic ductile iron; the tempering temperature is 500~600℃ and the time is 2~3h.

2. The method for preparing bainitic ductile iron according to claim 1, characterized in that, S 0~0.02wt%, P 0~0.05wt%, Mn 0~0.35wt%.

3. The method for preparing bainitic ductile iron according to claim 1, characterized in that, The content of V is 0.11~0.16wt%, and the content of B is 0.015~0.027wt%.

4. The method for preparing bainitic ductile iron according to claim 1, characterized in that, In step A), the ingredient preparation process specifically includes: Pig iron, scrap steel, and recycled materials are mixed in a mass ratio of 4:6:1 and smelted. After melting, silicon-manganese alloy, ferrochrome alloy, ferrovanadium alloy, ferroboron alloy, ferromolybdenum alloy, electrolytic nickel, and electrolytic tin are added.

5. The method for preparing bainitic ductile iron according to claim 1, characterized in that, In step B), the temperature of the molten iron in the holding furnace is 1500~1540℃; the inoculant for the primary inoculation is a barium silicon inoculant, and its addition amount is 0.2~0.4wt% of the mass of the molten iron; the spheroidizing agent for the spheroidizing treatment is a rare earth magnesium spheroidizing agent, and its addition amount is based on the residual magnesium and rare earth in the molten iron reaching 0.03~0.05wt% Mg and 0.02~0.05wt% Ce.

6. The method for preparing bainitic ductile iron according to claim 5, characterized in that, In step B), the inoculant for the secondary inoculation is a silicon-strontium inoculant, and its addition amount is 0.2~0.3wt% of the mass of molten iron; the inoculant for the co-current inoculation is a silicon-strontium inoculant, and its addition amount is 0.1~0.2wt% of the mass of molten iron; the pouring temperature is 600~850℃.

7. Bainitic ductile iron prepared by the method for preparing bainitic ductile iron according to any one of claims 1 to 6.

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