Multi-component alloy special cast iron diesel engine body and casting method thereof
Through the multi-alloy special cast iron materials and optimized casting technology, the problems of insufficient tensile strength and poor wear resistance of gray cast iron diesel engines are solved, and casting performance is achieved with high-strength and good wear resistance, which is suitable for high-power railway locomotives and ship diesel engines.
Patent Information
- Application Number
- CN202510531439.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-25
- Publication Date
- 2025-07-29
AI Technical Summary
The existing gray cast iron diesel engine has insufficient tensile strength and poor wear resistance, and there are problems such as shrinkage, shrinkage, poor graphite morphology control and insufficient pearlite content in the matrix structure.
Multi-alloy special cast iron materials are used to control the graphite form to A through high carbon equivalent design, multi-alloyization and specific incubation treatment, to improve the pearlite content, avoid the use of pig iron, and combine with an optimized casting process to ensure the uniformity of the composition and promote the refinement of pearlite elements.
It significantly improves the tensile strength and wear resistance of the diesel engine body, reduces casting defects, and meets the performance requirements of high-power diesel engines.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of special cast iron materials and casting processes, and particularly relates to a multi-alloy special cast iron diesel engine body and a casting method thereof, which are particularly suitable for manufacturing the bodies of high-power railway locomotives and marine diesel engines. Background Art
[0002] Locomotives are the material basis of railway transportation, determining the weight and speed of trains. The level of their operating efficiency directly affects the utilization degree of railway transportation capacity and the resulting economic and social benefits. The operating efficiency of locomotives largely depends on the power and performance of diesel engines. Therefore, conducting research on high-power locomotive diesel engines has become a very important task. Diesel engines are mainly used as the main power of train internal combustion engines and are one of the important components of train internal combustion engines. Their performance directly affects the running of trains. As the main body part of the diesel engine, the performance of its body is the premise to ensure the normal operation of the diesel engine, and high requirements are imposed on the casting quality. On diesel engines, the body is one of the parts with the most demanding working conditions, with complex forces. It transmits the entire original power of the diesel engine during high-speed movement and bears extremely high loads. The body is one of the bottlenecks restricting the further strengthening of diesel engines. The design and quality of the body will directly affect the economy, reliability, and service life of the diesel engine.
[0003] For the body of a locomotive diesel engine, its working condition environment is harsh, and it bears alternating loads and thermal fatigue such as friction, high temperature, and high pressure for a long time. Good mechanical properties, metallographic structure, and density have a crucial impact on the body. If the chemical composition design is unreasonable, the cooling rate is too low or too high, etc., it will lead to shrinkage cavity and porosity defects, the casting stress becomes larger, resulting in problems such as tissue segregation, cracks, and poor wear resistance in the body.
[0004] The currently used gray cast iron diesel engine body has the advantages of high wear resistance, good shock absorption, and good comprehensive performance such as machinability. Gray iron material has become the preferred material for the body of locomotive diesel engines. However, its low tensile strength limits the application range. How to give full play to the advantages of gray cast iron, improve its disadvantage of low tensile strength, produce high-strength gray cast iron castings, and expand its application range has attracted more and more attention from the majority of scientific researchers and manufacturers. However, good casting performance depends on the performance of the matrix and the quantity, shape, size, and distribution of graphite. Among them, gray cast iron composed of a fine-grained pearlite matrix and fine flake A-type graphite has the best performance and the widest application range. A-type graphite is the normal and uniform distribution of hypoeutectic gray iron at a relatively high eutectic degree and with a small degree of undercooling, and it is also the most common graphite structure. It has a lower cutting effect on the metal. At the same time, the pearlite content of cast iron with this kind of graphite is high, so the strength and wear resistance are good. If B-type or D, E-type graphite appears, some ferrite will appear in the matrix, which not only softens the casting but also has low wear resistance.
[0005] Therefore, the traditional gray cast iron fuselage can no longer meet the fuselage performance requirements, and there are mainly the following problems:
[0006] 1. The low-carbon equivalent high-alloy solution is prone to casting defects such as shrinkage cavities and porosity;
[0007] 2. Poor control of graphite morphology, with too high a proportion of B-type or D-type graphite, reducing mechanical properties;
[0008] 3. Insufficient pearlite content in the matrix structure, affecting strength and wear resistance;
[0009] 4. Using pig iron as raw material in traditional processes results in thick graphite and limited tensile strength.
[0010] Therefore, for a diesel engine fuselage with complex structure, large size, thin and uneven wall thickness, increasing the pearlite content, obtaining a fine A-type graphite morphology, improving the strength and hardness of the fuselage, and enhancing the wear resistance of the fuselage are necessary improvements to improve the fuselage performance. Summary of the Invention
[0011] The technical problem solved by the present invention: Provide a multi-alloy special cast iron diesel engine fuselage and its casting method. The present invention aims to solve the technical problems such as insufficient tensile strength, poor wear resistance, and many casting defects existing in the existing diesel engine fuselage.
[0012] To achieve the above object, the technical solution adopted by the present invention:
[0013] A multi-alloy special cast iron diesel engine fuselage is melted from the following raw materials by weight: 75 - 80 parts of scrap steel, 16 - 20 parts of return material, 2.5 - 3 parts of carburizer, and 0.5 part of inoculant;
[0014] The chemical composition of the fuselage is by mass percentage: C: 3.0% - 3.1%, Si: 1.9% - 2.1%, Cu: 0.6% - 0.7%, Mo: 0.40% - 0.60%, Cr: 0.10% - 0.20%, Ni: 0.30% - 0.50%, and the balance is Fe and unavoidable impurities.
[0015] The carbon equivalent of the fuselage is 3.6% - 3.8%, and the Si / C ratio is 0.63 - 0.7.
[0016] The inoculant is a 75 ferrosilicon inoculant containing silicon, manganese, and zirconium elements.
[0017] The graphite morphology of the fuselage is A-type graphite, with a proportion of ≥90% and a graphite length of ≤16 mm.
[0018] The pearlite content in the matrix structure of the fuselage is > 95%, and the ferrite content is < 5%; the carburizer is a graphitizing carburizer with a fixed carbon content ≥ 95%.
[0019] A casting method for a diesel engine fuselage includes the following steps:
[0020] (1) Weigh each raw material according to the ratio;
[0021] (2) Add the carburizer and scrap steel to the melting furnace in batches and completely melt them at 1420°C - 1480°C;
[0022] (3) Then add the return material, melt and mix evenly;
[0023] (4) Pour the molten liquid into the pouring ladle at 1460°C - 1480°C, and at the same time add the inoculant, and then cast and form.
[0024] In step (2), the carburizer and scrap steel are added in 2 - 3 batches, with an interval of 60 - 90 minutes between each batch.
[0025] In step (3), the static time is 10 - 15 minutes at 1500°C - 1520°C.
[0026] In step (4), the inoculant needs to be added sequentially during the process of pouring the molten liquid into the pouring ladle.
[0027] Advantages of the present invention compared with the prior art:
[0028] 1. For the characteristics of the diesel engine fuselage with a complex structure, large size, thin and uneven wall thickness, this solution adopts a high carbon equivalent process. Starting from the perspective of multi - element low alloying while ensuring good casting performance, it promotes elements that refine pearlite, increases the pearlite content, and obtains a fine A - type graphite morphology, thereby improving the strength and hardness of the fuselage, enhancing the wear resistance of the fuselage, and making the performance, metallographic structure, surface quality and internal quality of the fuselage meet the technical requirements;
[0029] 2. Due to the complex structure of the diesel engine fuselage, high dimensional accuracy requirements, and the problems that high - alloy with low carbon equivalent is prone to shrinkage cavity and shrinkage porosity defects, and large casting stress, resulting in problems such as tissue segregation, cracks, and poor wear resistance in the fuselage. Through the design of high carbon equivalent (3.6% - 3.8%) and specific Si / C ratio (0.63 - 0.7), the number of graphite is small and fine, the graphite size is reduced, the tip of the graphite is relatively blunt, the effect of graphite cutting the matrix is weakened, and in addition, more Si in gray cast iron is dissolved in ferrite to strengthen it, thereby improving the tensile strength of the fuselage and obtaining fine A - type graphite; significantly improving the casting performance and reducing shrinkage cavity and shrinkage porosity defects;
[0030] 3. In this solution, by increasing the addition amount of scrap steel and return materials in the metallic charge and reducing or not using pig iron, and secondly, by carburizing with ordinary carburizer, a reasonable ratio of the five major elements of carbon, silicon, manganese, sulfur, and phosphorus is obtained, improving the metallurgical properties of the molten iron, enabling the inoculation treatment effect to be better exerted, and thus enhancing the strength of gray cast iron;
[0031] 4. Since the diesel engine body has relatively high requirements for tensile strength and also for the size of graphite. For gray cast iron, there are many thick graphite flakes distributed on the ferrite matrix, with poor strength and hardness; while on the pearlite matrix, there are uniform and fine graphite flakes distributed, with relatively higher strength and hardness. This solution selects the method of multi-element low alloying. By adding a small amount of various alloying elements such as copper, molybdenum, and chromium to the molten iron, the alloying elements have a synergistic effect, which can refine graphite and eutectic cells, increase the content of pearlite in the matrix, and refine the lamellar spacing of pearlite, etc., so as to achieve the purpose of improving the matrix structure of the casting, obtaining fine A-type graphite, increasing the tensile strength of the casting, and improving the performance of the casting;
[0032] 5. This solution completely uses scrap steel and return materials, avoiding the problem of graphite coarsening caused by pig iron, and optimizing the metallurgical properties in combination with carburizer; the unique melting process control ensures the composition uniformity, and the tensile strength can reach above 322 MPa; the proportion of A-type graphite is ≥90%, the graphite is fine and uniform, significantly reducing the splitting effect on the matrix. Description of the Drawings
[0033] Figure 1 It is the graphite morphology diagram of the body 1# in the embodiment of the present invention;
[0034] Figure 2 It is the microstructural morphology diagram of the body 1# in the embodiment of the present invention;
[0035] Figure 3 It is the graphite morphology diagram of the body 2# in the embodiment of the present invention;
[0036] Figure 4 It is the microstructural morphology diagram of the body 2# in the embodiment of the present invention;
[0037] Figure 5 It is the graphite morphology diagram of the body 3# in the embodiment of the present invention;
[0038] Figure 6 It is the microstructural morphology diagram of the body 3# in the embodiment of the present invention;
[0039] Figure 7 It is the graphite morphology diagram of the body 4# in the embodiment of the present invention;
[0040] Figure 8 It is the microstructural morphology diagram of the body 4# in the embodiment of the present invention. Detailed Embodiments
[0041] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.
[0042] Please refer to Figure 1-8 , and detail the embodiments of the present invention.
[0043] A special cast iron diesel engine body of a multi - element alloy is melted from the following raw materials in parts by weight: 75 - 80 parts of scrap steel, 16 - 20 parts of return material, 2.5 - 3 parts of carburizer, and 0.5 part of inoculant;
[0044] The chemical composition of the body is calculated by mass percentage as follows: C: 3.0% - 3.1%, Si: 1.9% - 2.1%, Cu: 0.6% - 0.7%, Mo: 0.40% - 0.60%, Cr: 0.10% - 0.20%, Ni: 0.30% - 0.50%, and the balance is Fe and unavoidable impurities;
[0045] The carbon equivalent of the body is 3.6% - 3.8%, and the Si / C ratio is 0.63 - 0.7.
[0046] The inoculant is a 75 ferrosilicon inoculant containing silicon, manganese, and zirconium elements.
[0047] The graphite morphology of the body is A - type graphite, with a proportion of ≥90%, and the graphite length ≤16 mm (magnified 100 times).
[0048] The pearlite content in the matrix structure of the body >95%, and the ferrite content <5%
[0049] The carburizer is a graphitizing carburizer with a fixed carbon content ≥95%.
[0050] Next, a detailed description will be given of the process for determining the component content of the multi - element alloy special cast iron diesel engine body material;
[0051] 1. Design of carbon equivalent CE and Si / C ratio
[0052] Under the condition of the same carbon equivalent, as the silicon-carbon ratio increases, the number of austenite dendrites in gray cast iron increases. High silicon causes austenite dendrites to form at a higher temperature and prolongs the growth time, increasing the amount of primary austenite and strengthening the austenite skeleton. At the same time, high silicon results in fewer and finer graphite during eutectic crystallization, with blunter graphite tips, reducing the effect of graphite cutting the matrix. In addition, more Si in gray cast iron can play a role in solid solution strengthening of ferrite in the matrix structure, correspondingly increasing the tensile strength. Therefore, according to the structural characteristics and technical requirements of the diesel engine body, combined with past production experience, the carbon equivalent is determined to be 3.6% - 3.8%, the C content is 3.0% - 3.1%, the Si content is 1.9% - 2.1%, and the Si / C ratio is 0.63 - 0.7.
[0053] 2. Design of the weight parts of scrap steel, return scrap and carburizer
[0054] Based on relevant data and the production practice of the engine body in recent years, pig iron, especially newly produced pig iron with a high carbon content, contains large graphite flakes. Although remelted, the melting point of graphite is above 2000°C, and graphite cannot be completely melted during the remelting process and becomes the core of graphite crystallization during crystallization, making the graphite coarser. Therefore, as the addition amount of cast iron increases, the tensile strength of gray cast iron decreases significantly. In the present invention, by increasing the addition amount of scrap steel and return scrap in the metal charge, without adding any pig iron, and at the same time selecting a common carburizer for carburization, the metallurgical properties of the molten iron are improved, the effect of inoculation treatment is enhanced, thereby refining the structure, obtaining fine A-type graphite, and improving the strength of the engine body. Finally, it is determined that the scrap steel is 75 - 80 parts, the return scrap is 16 - 20 parts, and the carburizer is 2.5 - 3 parts.
[0055] 3. Matching and design of multi-element low alloying elements
[0056] For the production of high-grade gray cast iron parts, the control of the matrix structure is particularly important. Usually, an appropriate carbon equivalent is selected and the matrix structure of cast iron is controlled by inoculation and modification means, but the required structure is often not obtained, and the strength and hardness do not meet the requirements of the parts. Especially when producing complex-shaped castings with a carbon equivalent greater than 3.6%, without adding appropriate and suitable alloying elements, it is difficult to obtain an ideal pearlite structure, and coarse graphite will also appear. At this time, even if corresponding inoculation measures are taken, it is difficult to ensure stable strength. The main mechanisms of adding alloying elements to gray cast iron to improve strength are as follows: (1) refining graphite and eutectic cells; (2) increasing the content of pearlite in the matrix and refining the interlamellar spacing of pearlite; (3) improving the thermal stability of cementite and preventing the decomposition of pearlite at high temperatures; (4) forming carbides or hardened phases containing alloying elements.
[0057] Since the diesel engine body material has relatively high requirements for tensile strength and also has high requirements for graphite size, a method of multi-element low alloying should be adopted. By adding a small amount of various alloying elements such as copper, molybdenum, chromium, and nickel to the molten iron, the purpose of improving the matrix structure and graphite morphology and increasing the tensile strength of the casting can be achieved.
[0058] Copper is an element that promotes graphitization. It can refine graphite and improve its distribution morphology, promote and refine pearlite, strengthen pearlite and ferrite, and reduce section sensitivity. Therefore, it can increase the strength and hardness of cast iron. For the diesel engine body of the present invention, the copper content is determined to be 0.6% - 0.7%.
[0059] Molybdenum is an element that forms medium-stable carbides and hinders graphitization. Molybdenum can refine and improve the graphite distribution, refine pearlite and increase its content. At the same time, molybdenum can also strengthen the ferrite in pearlite, thus effectively increasing the strength and hardness of cast iron. Therefore, it is often used to manufacture high-strength gray iron castings. For the diesel engine body of the present invention, the molybdenum content is determined to be 0.40% - 0.60%.
[0060] Chromium is an element that strongly stabilizes carbides and hinders graphitization. Adding about w(Cr) 0.5% to ordinary gray iron can refine graphite, increase the amount of pearlite, and improve the strength and hardness of cast iron. However, chromium also increases the risk of shrinkage cavity and porosity defects in the casting. For the diesel engine body of the present invention, the chromium content is determined to be 0.10% - 0.20%.
[0061] Nickel is an element that promotes graphitization, reduces the austenite transformation temperature, expands the austenite region, can refine and increase pearlite, and is beneficial to the improvement of tensile strength. For the diesel engine body of the present invention, the nickel content is determined to be 0.30% - 0.50%.
[0062] The materials such as carburizer, scrap steel, return scrap, and inoculant used in the present invention can all be purchased or made in the market.
[0063] A casting method for a diesel engine body material includes the following steps;
[0064] (1) Weigh each raw material according to the weight ratio of each component of the raw materials of the multi-element alloy special cast iron diesel engine body material;
[0065] (2) Add the carburizer and scrap steel to the melting furnace in batches and completely melt them at 1420°C - 1480°C;
[0066] (3) Then add the return scrap, melt and mix evenly;
[0067] (4) Pour the molten liquid into the pouring ladle at 1460°C - 1480°C, add the inoculant at the same time, and then pour and form to obtain the multi-element alloy special cast iron diesel engine body material.
[0068] In step (2), the recarburizer and scrap steel are added in 2 - 3 batches, with an interval of 60 - 90 minutes between each batch.
[0069] In step (3), the standing time is 10 - 15 minutes at 1500℃ - 1520℃.
[0070] In step (4), the inoculant needs to be added sequentially during the process of pouring the molten metal into the pouring ladle.
[0071] Taking a diesel engine body as a basis, an implementation verification is carried out to obtain fine A - type graphite and improve the tensile strength and wear resistance of gray cast iron. The mechanical properties and metallographic structure requirements of this body are shown in Table 1.
[0072] Table 1 Requirements for the mechanical properties and metallographic structure of the body
[0073]
[0074] Four bodies, namely body 1#, body 2#, body 3#, and body 4# are selected for testing. Among them,
[0075] The raw material ratio of body 1#: 77 parts of scrap steel, 20 parts of return scrap, and 3 parts of recarburizer; the composition of multi - element low - alloy elements in the formed melting liquid: the Cu content is 0.65%, the Mo content is 0.46%, the Cr content is 0.18%, and the Ni content is 0.34%; inoculation treatment: adding 0.5 parts of ferrosilicon - manganese - zirconium inoculant.
[0076] The raw material ratio of body 2#: 78 parts of scrap steel, 19 parts of return scrap, and 3 parts of recarburizer; the composition of multi - element low - alloy elements in the formed melting liquid: the Cu content is 0.60%, the Mo content is 0.40%, the Cr content is 0.20%, and the Ni content is 0.30%; inoculation treatment: adding 0.5 parts of ferrosilicon - manganese - zirconium inoculant.
[0077] The raw material ratios of body 3# and body 4# are the same, both are: 80 parts of scrap steel, 17 parts of return scrap, and 3 parts of recarburizer; the composition of multi - element low - alloy elements in the formed melting liquid: the Cu content is 0.70%, the Mo content is 0.50%, the Cr content is 0.20%, and the Ni content is 0.40%; inoculation treatment: adding 0.5 parts of ferrosilicon - manganese - zirconium inoculant.
[0078] The mechanical properties obtained from the above four bodies, namely body 1#, body 2#, body 3#, and body 4# are shown in Table 2, and the obtained metallographic structure is as Figure 1-8 shown.
[0079] Table 2 Test results of the mechanical properties of the body
[0080] Airframe number Tensile strength Hardness Graphite type Graphite length ≤ 16mm (proportion) Matrix Sampling location 1# 273MPa 228HB 100% A-type 90％ Bead 98 Attached-cast specimen 2# 271MPa 217HB 100% A-type 95％ Bead 98 Attached-cast specimen 3# 322MPa 232HB 100% A-type 97％ Bead 98 Attached-cast specimen 4# 314MPa 242HB 100% A-type 94％ Bead 98 Attached-cast specimen
[0081] The four fuselages have passed performance tests, metallographic structure tests, and dissection. The surface quality and internal quality of the fuselages both meet the technical requirements. The first fuselage is subjected to radiographic testing and penetrant testing, and the test results meet the technical requirements.
[0082] The present invention adopts a high carbon equivalent process. Starting from the perspective of multi-element low alloying while ensuring good casting performance, it enhances the elements that promote the refinement of pearlite, increases the pearlite content, and improves the graphite morphology, thereby improving the strength and hardness of the fuselage, enhancing the wear resistance of the fuselage, and avoiding problems such as shrinkage cavities, shrinkage porosity defects, increased casting stress, resulting in structure segregation, cracks, and poor wear resistance in the fuselage due to unreasonable chemical composition design, too low or too high cooling rate, etc.
[0083] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed within the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.
[0084] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A special cast iron diesel engine body made of multi-element alloy, characterized in that: Smelted from the following raw materials by weight: 75 - 80 parts of scrap steel, 16 - 20 parts of return material, 2.5 - 3 parts of carburizer, and 0.5 part of inoculant; The chemical composition of the fuselage is by mass percentage: C: 3.0% - 3.1%, Si: 1.9% - 2.1%, Cu: 0.6% - 0.7%, Mo: 0.40% - 0.60%, Cr: 0.10% - 0.20%, Ni: 0.30% - 0.50%, and the balance is Fe and unavoidable impurities.
2. The diesel engine body according to claim 1, characterized in that: The carbon equivalent of the fuselage is 3.6% - 3.8%, and the Si / C ratio is 0.63 - 0.
7.
3. A special cast iron diesel engine body made of multi-alloy, as described in claim 1, characterized in that: The inoculant is a 75 ferrosilicon inoculant containing silicon, manganese, and zirconium elements.
4. A special cast iron diesel engine body made of multi-alloy, as claimed in claim 1, characterized in that: The graphite morphology of the fuselage is type A graphite, with a proportion of ≥90%, and the graphite length ≤16 mm.
5. A special cast iron diesel engine body made of multi-element alloy according to claim 1, characterized in that: In the matrix structure of the fuselage, the pearlite content > 95%, and the ferrite content < 5%; the carburizer is a graphitizing carburizer with a fixed carbon content ≥95%.
6. A casting method for a diesel engine body as described in any one of claims 1-5, characterized in that: Including the following steps: (1) Weigh each raw material according to the ratio; (2) Add the carburizer and scrap steel to the melting furnace in batches and completely melt at 1420°C - 1480°C; (3) Then add the return material, melt and mix evenly; (4) Pour the molten liquid into the pouring ladle at 1460°C - 1480°C, add the inoculant at the same time, and then cast into shape.
7. The casting method according to claim 6, characterized in that: In step (2), the carburizer and scrap steel are added in 2 - 3 batches, with an interval of 60 - 90 minutes between each batch.
8. The casting method according to claim 6, characterized in that: In step (3), the static time is 10 - 15 minutes at 1500°C - 1520°C.
9. The casting method according to claim 6, characterized in that: In step (4), the inoculant needs to be added sequentially during the process of pouring the molten liquid into the pouring ladle.