Mixed-base solid solution strengthening vermicular graphite cast iron and preparation method thereof

Abstract

The invention provides mixed-base solid solution strengthening vermicular graphite cast iron and a preparation method thereof. The mixed-base solid solution strengthening vermicular graphite cast iron comprises the following components in percentage by mass: 2.80%-3.30% of C, 3.30%-3.80% of Si, 0.40%-0.80% of Mn, 0.010%-0.015% of S, 0-0.040% (not 0) of P, 0.30%-0.60% of Cu, 0.10%-0.30% of Mo, 0.15%-0.35% of Cr, 0.010%-0.025% of Mg, 0.010%-0.025% of rare earth elements and the balance of Fe and inevitable impurities. The mechanical property and the machining property of the mixed-base solid solution strengthening vermicular graphite cast iron are improved, the requirements for the mechanical property of the RuT450 grade are stably met, and good stability, consistency and traceability are kept.

Description

Technical Field

[0001] The invention relates to the technical field of cast iron processing, and in particular to mixed-base solid solution strengthened vermicular graphite cast iron and a preparation method thereof. Background Art

[0002] As a new type of cast iron material, vermicular graphite cast iron has high strength, high thermal conductivity, good density, wear resistance and casting performance. It is more and more widely used in the field of diesel engine materials. Most foundries use the punching method to produce vermicular graphite cast iron. The main disadvantages of this process are low magnesium absorption rate, strong magnesium smoke, unstable vermicular effect and poor working environment.

[0003] At present, the cylinder block and cylinder head of vermicular graphite cast iron engine are generally of RuT450 grade (technical requirements: vermicular rate ≥80%, tensile strength of casting body ≥400MPa, hardness 200HB~250HB, elongation ≥1%). In order to ensure higher mechanical properties, the traditional process adds more Cu, Sn, Mo, Ni alloy precious metals to the molten iron for high alloying process treatment to ensure that the pearlite content reaches more than 85%. The high alloying process not only greatly increases the production cost, but also with the increase of pearlite content, the complex structure of the cylinder block and cylinder head is cooled differently, resulting in aggravated hardness differences, causing serious tool wear and reducing machining performance. In addition, some companies use the punching method to produce solid solution strengthened ferrite vermicular graphite cast iron cylinder heads. The matrix structure is almost ferrite, and the hardness of the casting body is relatively low.

[0004] Therefore, the existing engine cylinder block and cylinder head made of high-grade RuT450 vermicular graphite cast iron and their production process still need to be improved. Summary of the invention

[0005] The main purpose of the present invention is to provide a mixed-base solid solution strengthened vermicular graphite cast iron and a preparation method thereof. The mechanical properties and machining properties of the mixed-base solid solution strengthened vermicular graphite cast iron of the present invention are improved, and the requirements of the mechanical properties of the RuT450 grade are stably met, and good stability, consistency and traceability are maintained.

[0006] In order to achieve the above objectives, the present invention provides the following technical solutions.

[0007] The first aspect of the present invention provides a mixed-base solid solution strengthened vermicular graphite cast iron, which includes the following components in mass percentage: C 2.80% to 3.30%, Si 3.30% to 3.80%, Mn 0.40% to 0.80%, S 0.010% to 0.015%, P0 to 0.040% and not 0, Cu 0.30% to 0.60%, Mo 0.10% to 0.30%, Cr 0.15% to 0.35%, Mg0.010% to 0.025%, rare earth elements 0.010% to 0.025%, and the balance is Fe and unavoidable impurities.

[0008] In some embodiments of the present invention, the microstructure of the vermicular graphite cast iron has the following characteristics: creep rate ≥ 80%, pearlite content ≥ 25%, tensile strength ≥ 400 MPa, hardness of 200 HB to 250 HB, and elongation of 4.5% to 5.5%.

[0009] The second aspect of the present invention provides a method for preparing the mixed-base solid solution strengthened vermicular graphite cast iron described in the first aspect, the preparation method comprising: adding alloy material into a ladle when the original molten iron is tapped; and sequentially performing vermicularization and inoculation wire feeding treatment, slag removal, temperature measurement, and pouring on the molten iron to obtain a mixed-base solid solution strengthened vermicular graphite cast iron casting.

[0010] In some embodiments of the present invention, scrap steel, recycled materials and pig iron raw materials are added to an induction furnace to melt and generate molten iron. The molten iron is tapped after its composition and thermal analysis liquidus temperature meet technical requirements. When the molten iron is tapped, alloy materials are added to the ladle.

[0011] In some embodiments of the present invention, the thermal analysis liquidus temperature of the molten iron is 1165°C to 1175°C.

[0012] In some embodiments of the present invention, the chemical composition of the molten iron includes, by mass percentage, C 2.80% to 3.30%, Si 3.10% to 3.60%, Mn 0.4% to 0.8%, P 0 to 0.04% and not 0, and S 0.010% to 0.015%.

[0013] In some embodiments of the present invention, the alloy material includes electrolytic copper, ferromolybdenum and ferrochromium.

[0014] In some embodiments of the present invention, the process of the creeping and inoculating wire feeding treatment includes: first feeding the creeping cored wire, and when the creeping cored wire is 4m to 8m left, the inoculated cored wire starts to be fed together with the creeping cored wire until the end.

[0015] In some embodiments of the present invention, the alloy powder of the vermicular cored wire includes the following components in mass percentage: Si 40% to 50%, Mg 7.0% to 7.4%, rare earth metals 6.0% to 8.0%, Ca 1.0% to 2.5%, Al 0 to 1.0% and not 0, and the balance is Fe.

[0016] In some embodiments of the present invention, the rare earth metal of the vermicular cored wire is selected from Ce and La, and the mass ratio of Ce to La is 3:2.

[0017] In some embodiments of the present invention, the alloy powder for inoculating the cored wire comprises the following components in mass percentage: Si 65% to 75%, Ca 1.0% to 2.5%, Al 0.8% to 1.8%, Ba 3% to 5%, and the balance is Fe.

[0018] In some embodiments of the present invention, the amount of the vermicular cored wire added per kilogram of molten iron depends on the sulfur content in the original molten iron.

[0019] In some embodiments of the present invention, the carbon and sulfur samples of the molten iron from the same furnace are taken twice and tested in front of the furnace respectively. The sulfur content of the molten iron is averaged by rounding off, and the amount of the creeping cored wire to be added is calculated based on the average.

[0020] In some embodiments of the present invention, when producing a vermicular iron cylinder head, when the S content in the original molten iron is 0.010%≤S<0.012%, the amount of vermicular cored wire added per kilogram of molten iron is 0.0085m / kg~0.010m / kg; when the S content in the original molten iron is 0.012%≤S≤0.015%, the amount of vermicular cored wire added per kilogram of molten iron is 0.0105m / kg~0.0120m / kg.

[0021] In some embodiments of the present invention, when producing a vermicular iron cylinder body, when the S content in the original molten iron is 0.010%≤S<0.012%, the amount of vermicular cored wire added per kilogram of molten iron is 0.0070m / kg~0.0085m / kg; when the S content in the original molten iron is 0.012%≤S≤0.015%, the amount of vermicular cored wire added per kilogram of molten iron is 0.0090m / kg~0.0105m / kg.

[0022] In some embodiments of the present invention, the feeding speed of the vermicular cored wire is 18 m / min to 25 m / min, and the feeding speed of the inoculated cored wire is 18 m / min to 25 m / min.

[0023] In some embodiments of the present invention, the temperature of the creeping and inoculating feeding wire treatment is 1430°C to 1470°C.

[0024] In some embodiments of the present invention, the liquidus temperature of the molten iron after the creeping and inoculating feeding line treatment is 1155°C to 1165°C in thermal analysis.

[0025] Compared with the prior art, the present invention achieves the following technical effects:

[0026] The mechanical properties and machining properties of the mixed-base solid solution strengthened vermicular graphite cast iron provided by the present invention are improved, and the requirements of the mechanical properties of the RuT450 grade are stably met, while maintaining good stability, consistency and traceability.

[0027] The present invention utilizes the wire feeding method to prepare mixed-base solid solution strengthened vermicular graphite cast iron, which has the advantages of high magnesium absorption rate and reduced environmental pollution, can accurately add vermicular cored wire and inoculated cored wire, stably control the creep rate, and maintain good stability, consistency and traceability.

[0028] The present invention utilizes the principle of low alloy solid solution strengthening. On the basis of silicon solid solution strengthening ferrite vermicular graphite cast iron, a small amount of ferrite is partially transformed into pearlite (pearlite content ≥25%) by adding a small amount of alloy, thereby improving the mechanical properties and machining properties of the vermicular graphite cast iron casting, and stably meeting the mechanical property requirements of RuT450 grade: creep rate ≥80%, tensile strength ≥400MPa, hardness of 200HB-250HB, and elongation ≥1%.

[0029] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only used for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. In the accompanying drawings:

[0031] Figure 1 The metallographic image of the mixed-base solid solution strengthened vermicular graphite cast iron cylinder head obtained in Example 1 of the present invention (worm-like graphite, x100 times);

[0032] Figure 2 This is the metallographic image (matrix structure, X100 times) of the mixed matrix solid solution strengthened vermicular graphite cast iron cylinder head obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which the present invention belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the specification and claims of the present invention and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0035] Some terms used in the present invention are explained below to facilitate understanding by those skilled in the art.

[0036] Vermicular graphite cast iron: A cast iron material in which carbon is mainly precipitated in the form of vermicular graphite in the metal matrix.

[0037] Silicon solid solution strengthening: Silicon element, as a solute atom, is dissolved in the ferrite matrix, causing a certain degree of lattice distortion and refining the grains of the casting matrix, thereby improving the strength and hardness of the casting.

[0038] Mixed matrix strengthening: The mixed structure of ferrite and pearlite in cast iron matrix is ​​called mixed matrix, or mixed matrix for short. Since the strength and hardness of pearlite structure are much greater than that of ferrite, the ferrite matrix strengthened by silicon solid solution is partially transformed into pearlite matrix through low alloying process, thus improving the strength and hardness of castings.

[0039] Pearlite: It is a mechanical mixture of ferrite and cementite. Its mechanical properties are between those of ferrite and cementite. It is the matrix structure that provides strength in the metallographic structure of the material.

[0040] Creep rate: Creep rate is a parameter that characterizes the proportion of vermicular graphite to the total graphite in the microstructure of vermicular graphite cast iron, that is, the percentage of the number (or area) of vermicular graphite to the total number of graphite (or total graphite area).

[0041] At present, most companies use the punching method to produce high-strength RuT450 grade vermicular graphite cast iron cylinder blocks and cylinder heads, which has the following disadvantages: 1. Low magnesium absorption rate, strong magnesium light smoke, and unstable vermicular effect; 2. Traditional processes use more Cu and Sn precious metals for alloying process treatment, and the production cost is high; 3. As the pearlite content increases, the complex structure of the cylinder block and cylinder head is cooled differently, causing the hardness difference to increase, resulting in serious tool wear, reduced machining performance, and increased processing costs.

[0042] The present invention is mainly aimed at engine cylinder blocks and cylinder heads made of high-grade RuT450 vermicular graphite cast iron, and at least solves the process deficiencies existing in the production of vermicular graphite cast iron by traditional processes and punching methods, as well as the problem of relatively low hardness of solid solution strengthened ferrite vermicular graphite cast iron.

[0043] The invention provides a mixed-base solid solution strengthened vermicular graphite cast iron. The mixed-base solid solution strengthened vermicular graphite cast iron comprises the following components in percentage by mass: 2.80% to 3.30% of C, 3.30% to 3.80% of Si, 0.40% to 0.80% of Mn, 0.010% to 0.015% of S, 0% to 0.040% of P and not 0, 0.30% to 0.60% of Cu, 0.10% to 0.30% of Mo, 0.15% to 0.35% of Cr, 0.010% to 0.025% of Mg, 0.010% to 0.025% of rare earth element (RE), and the balance being Fe and unavoidable impurities.

[0044] In an embodiment of the present invention, the rare earth elements include Ce and La, and the total mass percentage of Ce and La elements is 0.010% to 0.025%.

[0045] In the embodiment of the present invention, the microstructure of the mixed matrix solid solution strengthened vermicular graphite cast iron has the following characteristics: the creep rate ≥ 80%, the pearlite content ≥ 25%, the tensile strength ≥ 400 MPa, the hardness is 200 HB to 250 HB, and the elongation is 4.5% to 5.5%.

[0046] The present invention also provides a preparation method of the above-mentioned mixed-base solid solution strengthened vermicular graphite cast iron. The preparation method mainly utilizes the wire feeding method to directly insert the vermicular cored wire and the inoculated cored wire into the molten iron for vermicular treatment. On the basis of ensuring the creep rate ≥ 80%, the amount of alloy added is reduced. Through the principle of low-alloy mixed-base solid solution strengthening, the technical requirements of high-grade RuT450 (creep rate ≥ 80%, body tensile strength ≥ 400MPa, hardness of 200HB~250HB, elongation ≥ 1%) are achieved, and at the same time, the production and processing costs of high-grade vermicular graphite cast iron engine cylinder blocks and cylinder heads are reduced.

[0047] The preparation method of mixed-base solid solution strengthened vermicular graphite cast iron in the present invention is carried out according to the following steps.

[0048] (1) Smelting and iron tapping.

[0049] In the embodiment of the present invention, the raw molten iron is obtained by smelting scrap steel, high-purity pig iron, vermicular iron recycling material, ferrosilicon, carburizer and silicon carbide as raw materials.

[0050] In some embodiments of the present invention, the recarburizer may be, but is not limited to, graphitized petroleum coke.

[0051] In some embodiments of the present invention, the chemical composition of the raw iron water includes, by mass percentage: C 2.80% to 3.30%, Si 3.10% to 3.60%, Mn 0.4% to 0.8%, P 0 to 0.04% and not 0, S 0.010% to 0.015%.

[0052] In some embodiments of the present invention, various raw materials with good proportions are smelted in an induction furnace to obtain molten iron. For example, various raw materials are added into a medium frequency induction furnace to be smelted into molten iron.

[0053] In some embodiments of the present invention, during the smelting process, when the molten iron is heated to 1460°C to 1500°C, samples are taken for thermal analysis and furnace inspection, and the liquidus temperature and chemical composition of the original molten iron are adjusted accordingly. When the molten iron is heated to 1520°C to 1540°C, it is left to stand for 8min to 15min, and then the slag on the surface of the molten iron is cleaned.

[0054] In some embodiments of the present invention, the tapping method is ladle tapping, and alloy material is added to the ladle. The amount of alloy material added can be designed according to the composition of the target compacted graphite cast iron to meet the composition requirements.

[0055] In some embodiments of the present invention, the alloy material includes electrolytic copper, ferromolybdenum and ferrochromium.

[0056] In some embodiments of the present invention, the tapping weight is precisely controlled according to the requirements of each product, for example, the tapping weight is controlled within the range of ±2% kg of the target tapping amount.

[0057] (2) Creeping and inoculation feeding line treatment.

[0058] In an embodiment of the present invention, the process of creeping and inoculating wire feeding includes: firstly feeding the creeping cored wire, and when there are 4m to 8m of creeping cored wire left, the inoculated cored wire starts feeding along with the creeping cored wire until the end.

[0059] In some embodiments of the present invention, the alloy powder of the vermicular cored wire includes the following components in mass percentage: Si 40% to 50%, Mg 7.0% to 7.4%, rare earth metals 6.0% to 8.0%, Ca 1.0% to 2.5%, Al 0 to 1.0% and not 0, and the balance is Fe.

[0060] In some embodiments of the present invention, the rare earth metal of the vermicular cored wire is selected from Ce and La, wherein the mass ratio of Ce to La is 3:2.

[0061] In some embodiments of the present invention, the alloy powder for inoculating the cored wire includes the following components by mass percentage: Si 65% to 75%, Ca 1.0% to 2.5%, Al 0.8% to 1.8%, Ba 3% to 5%, and the balance is Fe.

[0062] In some embodiments of the present invention, a forklift is used to transfer molten iron to a vermicularizing station, the vermicularizing treatment temperature of the molten iron in the ladle is detected, and then, according to the preset lengths of the vermicularizing cored wire and the inoculated cored wire, a wire feeding machine is used to introduce the vermicularizing cored wire and the inoculated cored wire into the molten iron at a predetermined speed for vermicularizing and inoculating treatment.

[0063] In some embodiments of the present invention, the temperature of the creeping and inoculating feeding wire treatment is 1430°C to 1470°C.

[0064] In some embodiments of the present invention, the feeding speed of the vermicular cored wire and the inoculated cored wire is 18 m / min to 25 m / min.

[0065] In the embodiment of the present invention, in order to meet the creep rate of the vermicular iron cylinder body and cylinder head ≥ 80%, according to the actual production situation, the length of the creeping cored wire added to each kilogram of molten iron is calculated with reference to the data in Table 1, and the length of the inoculated cored wire added to each kilogram of molten iron is 2m to 3m.

[0066] Table 1 Reference table for calculation of added length of creeping cored wire

[0067]

[0068] It is worth mentioning that the sulfur (S) content of the original molten iron in Table 1 is obtained in the following way: the carbon and sulfur samples of the original molten iron from the same furnace are sampled twice, and the furnace tests are carried out respectively. The sulfur content (S) of the original molten iron is averaged by rounding off and recorded as the sulfur content shown in Table 1. The added length of the creeping cored wire is calculated based on the sulfur content.

[0069] The calculation methods for adding length of vermicular cored wire include:

[0070] According to the casting name (vermicular cast iron cylinder head or vermicular cast iron cylinder body) and the detected sulfur content of the original molten iron (S%), the corresponding length of the vermicular cored wire is found from Table 1 to ensure that the required vermicular elements can be evenly and fully introduced during the vermicular treatment process. It should be noted here that Table 1 is only a reference value. The amount of vermicular cored wire added should be selected and adjusted according to the actual casting product structure and weight to meet the technical requirement of creep rate ≥ 80%.

[0071] For example:

[0072] If mixed-base solid solution strengthened vermicular graphite cast iron cylinder head is produced, carbon and sulfur samples of the original molten iron from the same furnace are sampled twice and tested before the furnace respectively. The sulfur (S) content is 0.0113% and 0.0117% respectively. The sulfur content of the original molten iron is rounded off to an average of 0.0115%. The length of the vermicular cored wire can be calculated according to the following steps:

[0073] From Table 1, when the sulfur content of the original molten iron is 0.0115%, the corresponding length of the vermicular cored wire added per kilogram of molten iron is in the range of 0.0085m / kg to 0.010m / kg.

[0074] (3) Casting.

[0075] In the embodiment of the present invention, after step (2) is completed, the molten iron in the ladle is deslagging and the temperature is measured to ensure that the pouring is carried out within the pouring temperature, and a spectral sample of the casting is taken for composition inspection.

[0076] In an embodiment of the present invention, the pouring temperature may be 1390°C to 1420°C.

[0077] In an embodiment of the present invention, the spectral composition of the casting is: Si 3.30% to 3.80%, Mn 0.4% to 0.8%, P≤0.04%, Cr 0.15% to 0.35%, Mo 0.10% to 0.30%, Cu 0.30% to 0.60%, Mg 0.010% to 0.025%, and rare earth elements (RE) 0.010% to 0.025%.

[0078] In the embodiment of the present invention, when the cylinder block or cylinder head to be cast is cooled to below 400°C, it can be boxed and the molded casting can be taken out. The flash and burrs of the casting are removed, the surface of the casting is polished by a mechanical polisher, and the cut is ground, and then after inspection and powder spraying, a blank that can be put into material can be made.

[0079] The present invention also provides a use of the mixed-base solid solution strengthened vermicular graphite cast iron or the mixed-base solid solution strengthened vermicular graphite cast iron prepared by the above-mentioned preparation method in the preparation of an engine cylinder block and a cylinder head.

[0080] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the raw materials, instruments and equipment used in the following examples, etc., can all be purchased on the market or can be obtained by existing methods; the amounts of the experimental reagents, unless otherwise specified, are the amounts of reagents used in conventional experimental operations; the experimental methods, unless otherwise specified, are all conventional methods.

[0081] Example 1

[0082] A mixed-base solid solution strengthened vermicular graphite cast iron cylinder head, the preparation method of which includes: preparing raw materials according to the chemical composition ratio, wherein scrap steel accounts for 60%, high-purity pig iron accounts for 30%, and vermicular cast iron recycled materials account for 10%, and the addition amount of ferrosilicon, graphitized petroleum coke and silicon carbide is accurately calculated and added according to the requirements of the chemical composition. In the electric furnace smelting stage, the molten iron is heated to 1485°C, and the liquidus temperature and chemical composition of the molten iron are fine-tuned by sampling and analysis. The liquidus temperature of the original molten iron is 1172°C, and the chemical element composition of the original molten iron is: C 3.05%, Si 3.40%, Mn 0.45%, P 0.016%, S 0.0112%, 0.0118%.

[0083] The molten iron is heated to 1525℃, left to stand for 12 minutes, and the slag on the surface of the molten iron is cleaned. The tapping weight is 2000kg, and electrolytic copper, ferromolybdenum and ferrochrome are added to the ladle according to the preset proportion, and the tapping weight is controlled within the preset range of ±2%kg according to product requirements.

[0084] After the molten iron is transferred to the vermicularization station, the temperature of the molten iron is tested. The vermicularization treatment temperature is 1450℃, ensuring that it is within the appropriate temperature range for the vermicularization treatment. The length of the vermicularization cored wire added is 18.7m, and the length of the inoculated cored wire added is 5m. The vermicularization cored wire is evenly introduced into the molten iron at a speed of 21m / min using a wire feeder, and when there is 6m left, the inoculated wire is introduced at the same time at a speed of 20m / min to start feeding with the vermicular cored wire until the end.

[0085] The molten iron in the ladle was deslagging and the pouring temperature was detected to be 1415°C. After the composition was confirmed to be qualified by spectral inspection, the mixed matrix solid solution strengthened vermicular graphite cast iron cylinder head was produced.

[0086] After testing, the composition of the mixed matrix solid solution strengthened vermicular graphite cast iron cylinder head obtained in Example 1 is C 3.05%, Si 3.61%, Mn 0.45%, P 0.016%, S 0.0115%, Cu 0.35%, Cr 0.26%, Mo 0.18%, Mg 0.0162%, RE 0.0178%, and the balance is Fe and unavoidable impurities.

[0087] Example 2

[0088] A mixed-base solid solution strengthened vermicular graphite cast iron cylinder block, the preparation method of which includes: preparing raw materials according to the chemical composition ratio, wherein scrap steel accounts for 65%, high-purity pig iron accounts for 25%, and vermicular cast iron recycled materials account for 10%, and the addition amount of ferrosilicon, graphitized petroleum coke and silicon carbide is accurately calculated and added according to the requirements of the chemical composition. In the electric furnace smelting stage, the molten iron is heated to 1490°C, and the liquidus temperature and chemical composition of the molten iron are fine-tuned by sampling and analysis. The liquidus temperature of the original molten iron is 1170°C, and the chemical element composition of the original molten iron is: C 3.11%, Si 3.35%, Mn 0.52%, P 0.017%, S 0.0102%, 0.0110%.

[0089] The molten iron is heated to 1528℃, left to stand for 13 minutes, and the slag on the surface of the molten iron is cleaned. The tapping weight is 2000kg, and electrolytic copper, ferromolybdenum and ferrochrome are added to the ladle according to the preset proportion, and the tapping weight is controlled within the preset range of ±2%kg according to product requirements.

[0090] After the molten iron is transferred to the vermicularization station, the temperature of the molten iron is tested. The vermicularization treatment temperature is 1445℃, ensuring that it is within the appropriate temperature range for the vermicularization treatment. The length of the vermicularization cored wire added is 15.7m, and the length of the inoculated cored wire added is 4.5m. The vermicularization cored wire is evenly introduced into the molten iron at a speed of 22m / min using a wire feeder, and when there are 5m left, the inoculated wire is introduced at the same time at a speed of 20m / min to start feeding with the vermicular cored wire until the end.

[0091] The molten iron in the ladle was deslagging and the pouring temperature was detected to be 1425°C. After the composition was confirmed to be qualified by spectral inspection, the mixed matrix solid solution strengthened vermicular graphite cast iron cylinder block was produced.

[0092] After testing, the composition of the mixed matrix solid solution strengthened vermicular graphite cast iron cylinder head obtained in Example 2 is C 3.11%, Si 3.53%, Mn 0.52%, P 0.017%, S 0.0106%, Cu 0.48%, Cr 0.30%, Mo 0.25%, Mg 0.0128%, RE 0.0137%, and the balance is Fe and unavoidable impurities.

[0093] Performance Testing

[0094] The tensile strength, hardness, elongation, creep rate and pearlite content of the casting prepared in the embodiment were tested according to GB / T 26655-2022. The results are shown in Table 2.

[0095] Table 2 Summary of the physical and chemical properties of the castings prepared in the examples

[0096] Sample name Tensile strength / Mpa Hardness / HB Elongation / % Creep rate / % Pearlite / % Example 1 435 211 5.3 85 30 Example 2 474 220 4.9 85 40

[0097] In the preparation method of the present invention, a proper amount of creeping and inoculated cored wire is fed into molten iron at a certain wire feeding speed for creeping treatment; the principle of low alloy mixed matrix solid solution strengthening (matrix structure pearlite content ≥ 25%) is used to produce RuT450 grade vermicular graphite cast iron castings, and good stability, consistency and traceability are maintained. In this way, not only the production cost is low, the precise control of the creeping reaction time and speed advantage of the wire feeding process is maintained, but also the operation is simple, efficient and less polluting.

[0098] The present invention successfully prepares mixed-base solid solution strengthened vermicular graphite cast iron by precisely controlling key parameters such as raw material ratio, smelting temperature, vermicular treatment and casting pouring, providing a new preparation method and idea for the casting industry.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A mixed matrix solid solution strengthened vermicular graphite cast iron, characterized in that: It includes the following components in percentage by mass: C 2.80%~3.30%, Si 3.30%~3.80%, Mn 0.40%~0.80%, S 0.010%~0.015%, P0~0.040% and not 0, Cu 0.30%~0.60%, Mo 0.10%~0.30%, Cr 0.15%~0.35%, Mg0.010%~0.025%, rare earth elements 0.010%~0.025%, and the balance is Fe and unavoidable impurities.

2. The mixed matrix solid solution strengthened vermicular graphite cast iron according to claim 1, characterized in that: The microstructure of the vermicular graphite cast iron has the following characteristics: the creep rate is ≥80%, the pearlite content is ≥25%, the tensile strength is ≥400MPa, the hardness is 200HB-250HB, and the elongation is 4.5%-5.5%.

3. A method for preparing the mixed-base solid solution strengthened compacted graphite cast iron according to any one of claims 1 to 2, characterized in that: The preparation method comprises: adding alloy material into a ladle when raw molten iron is tapped; and sequentially performing vermicularization and inoculation wire feeding treatment, slag removal, temperature measurement and pouring on the molten iron to obtain a mixed-base solid solution strengthened vermicular graphite cast iron casting.

4. The preparation method according to claim 3, characterized in that: The composition and thermal analysis liquidus temperature of the molten iron meet the requirements before the iron is tapped, and the thermal analysis liquidus temperature of the molten iron is 1165° C. to 1175° C.; Preferably, the alloy material includes electrolytic copper, ferromolybdenum and ferrochromium.

5. The preparation method according to claim 3, characterized in that: The chemical composition of the raw iron water includes, by mass percentage, C 2.80% to 3.30%, Si 3.10% to 3.60%, Mn 0.4% to 0.8%, P 0 to 0.04% and not 0, and S 0.010% to 0.015%.

6. The preparation method according to claim 3, characterized in that: The process of the creeping and inoculating wire feeding treatment includes: firstly feeding the creeping cored wire, and when the creeping cored wire is 4m to 8m left, the inoculating cored wire starts to be fed together with the creeping cored wire until the end; Preferably, the feeding speed of the vermicular cored wire is 18 m / min to 25 m / min, and the feeding speed of the inoculated cored wire is 18 m / min to 25 m / min.

7. The preparation method according to claim 6, characterized in that: The alloy powder of the vermicular cored wire comprises the following components in percentage by mass: Si 40% to 50%, Mg 7.0% to 7.4%, rare earth metal 6.0% to 8.0%, Ca 1.0% to 2.5%, Al 0% to 1.0% and not 0, and the balance is Fe; Preferably, the rare earth metal of the vermicular cored wire is selected from Ce and La, and the mass ratio of Ce to La is 3:

2.

8. The preparation method according to claim 3, wherein the liquidus temperature of the molten iron after the creep and inoculation feeding wire treatment is 1155°C to 1165°C in thermal analysis; Preferably, the temperature of the creeping and inoculating feeding wire treatment is 1430°C to 1470°C.

9. The preparation method according to claim 6, characterized in that: The amount of the vermicular cored wire added per kilogram of molten iron is based on the sulfur content of the original molten iron; Preferably, the carbon and sulfur samples of the raw iron water from the same furnace are taken twice and tested in front of the furnace respectively, the sulfur content of the raw iron water is averaged by rounding off, and the addition amount of the creeping cored wire is calculated based on the average.

10. The preparation method according to claim 6 or 9, characterized in that: When producing vermicular cast iron cylinder heads, when the S content in the original molten iron is 0.010%≤S<0.012%, the amount of vermicular cast iron wire added per kilogram of molten iron is 0.0085m / kg~0.010m / kg; when the S content in the original molten iron is 0.012%≤S≤0.015%, the amount of vermicular cast iron wire added per kilogram of molten iron is 0.0105m / kg~0.0120m / kg; When producing vermicular iron cylinder blocks, when the S content in the original molten iron is 0.010%≤S<0.012%, the amount of vermicular cored wire added per kilogram of molten iron is 0.0070m / kg~0.0085m / kg; when the S content in the original molten iron is 0.012%≤S≤0.015%, the amount of vermicular cored wire added per kilogram of molten iron is 0.0090m / kg~0.0105m / kg.

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