Cast iron sliding member and method for producing same

Abstract

The invention belongs to the technical field of sliding component casting, and particularly relates to a cast iron sliding component and a preparation method thereof.The cast iron sliding component is made of silicon solid solution ferrite nodular cast iron, the structure of the material is uniform and single ferrite, and the cast iron sliding component comprises, by mass, 2.90%-3.20% of C, 3.9%-4.35% of Si, smaller than or equal to 0.4% and not larger than 0 of Mn, smaller than or equal to 0.04% and not larger than 0 of P, smaller than or equal to 0.02% and not larger than 0 of S and the balance Fe and inevitable impurities. The alloy comprises the following components in percentage by weight: less than or equal to 0.020% of S but not 0, 0.040-0.060% of Mg, 0.005-0.009% of Sb and the balance of iron and inevitable trace elements. The sliding component has a full-ferrite matrix structure and is good in structure uniformity, machining residual stress is reduced, meanwhile, the thermal expansion coefficient is reduced, nitriding deformation is avoided, annealing heat treatment is not needed after casting knockout and before honing, secondary honing after nitriding is omitted, and the non-uniformity of the final nitriding structure is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of sliding component casting, and in particular to a cast iron sliding component and a preparation method thereof. Background Art

[0002] The cylinder of the hydraulic plunger pump is generally made of ordinary ductile iron, and the plunger hole is nitrided to meet the surface hardness requirements. However, due to the uneven distribution of the cast iron material structure, including ferrite and pearlite, the processing stress is large, and the dimensional deformation is large after nitriding heat treatment, further processing is required. In addition, the white bright layer on the surface after processing is uneven, and the surface hardness of the material is uneven, which leads to the problem of plunger sticking during use.

[0003] Therefore, the existing plunger pump still needs to be improved, and the present invention is specially proposed. Summary of the invention

[0004] The main purpose of the present invention is to propose a cast iron sliding component and a preparation method thereof. The present invention adopts solid solution ferrite ductile iron instead of conventional alloy ductile iron as a sliding component to obtain a full ferrite matrix structure with good structural uniformity, reduce processing residual stress, and reduce the thermal expansion coefficient, avoid nitriding deformation, and do not require annealing heat treatment after boxing and before honing of the casting. At the same time, the secondary honing after nitriding is cancelled, thereby reducing the unevenness of the final nitrided structure.

[0005] The first aspect of the present invention provides a cast iron sliding component, the material of the cast iron sliding component is silicon solid ferrite ductile iron, and the material structure is a uniform single ferrite, including the following components in mass percentage: C2.90%~3.20%, Si 3.9%~4.35%, Mn≤0.4% and not 0, P≤0.04% and not 0, S≤0.020% and not 0, Mg 0.040%~0.060%, Sb 0.005%~0.009%, and the balance is iron and inevitable trace elements.

[0006] In some embodiments of the present invention, the tensile strength of the cast iron sliding component is ≥600 MPa, the elongation is ≥10%, the hardness is 200 HBW-220 HBW, and the hardness difference at different positions of the same casting is <10 HB.

[0007] The second aspect of the present invention provides a method for preparing the cast iron sliding component described in the first aspect, the preparation method comprising: obtaining a casting by a smelting and pouring process, the boxing temperature after pouring is below 200°C, and the casting does not need to be subjected to stress relief annealing treatment; and sequentially performing rough machining, fine machining, honing, nitriding treatment and polishing treatment on the casting to obtain the cast iron sliding component; wherein the nitriding treatment adopts two-stage gas soft nitriding, and the nitriding temperature is <560°C.

[0008] In some embodiments of the present invention, the two-stage gas soft nitriding process includes: the first stage nitriding temperature is 510°C to 530°C, the holding time is 4.5h to 5.5h, and the strong nitriding potential is 3.0 to 5.0; the second stage nitriding temperature is 540°C to 560°C, the nitriding time is 22h to 24h, the diffusion nitrogen potential is 1.0 to 2.0, and the nitrogen is cooled to 200°C and air-cooled out of the furnace.

[0009] In some embodiments of the present invention, after the nitriding treatment, the surface nitriding hardness of the casting is ≥600HV1, the depth of the nitriding layer is ≥0.12mm, the thickness of the white bright layer is 0.003mm-0.008mm, and the cylindricity is 0.006-0.008.

[0010] In some embodiments of the present invention, the smelting and pouring process includes smelting raw iron water, wire feeding spheroidization and inoculation treatment, secondary inverted ladle inoculation treatment and pouring flow inoculation treatment.

[0011] In some embodiments of the present invention, in the smelting and pouring process, the composition of the original molten iron is calculated and adjusted according to the chemical composition of the casting, the eutectic carbon equivalent is 4.4-4.6 and the inoculated silicon is 0.4%-0.6%, the S content is ≥0.010%, and the iron output control deviation is within ±30kg.

[0012] In some embodiments of the present invention, in the wire feeding spheroidization and inoculation treatment, the wire feeding temperature is 1450°C to 1490°C, the spheroidized cored wire is selected from rare earth-free Mg-Sb cored wire, wherein the mass ratio of Mg to Sb is 10:1; and the inoculated cored wire core powder is selected from silicon-barium inoculant.

[0013] In some embodiments of the present invention, the secondary inoculation treatment uses a silicon-barium inoculant, and the mass percentage of the inoculant added per kilogram of raw iron water is 0.5% to 0.8%.

[0014] In some embodiments of the present invention, the pouring inoculation treatment uses a silicon-barium or silicon-zirconium inoculant, and the mass percentage of the inoculant added per kilogram of raw iron water is 0.010% to 0.15%.

[0015] Compared with the prior art, the present invention achieves the following technical effects:

[0016] 1) Using solid solution ferrite ductile iron instead of conventional alloy ductile iron as sliding components to obtain a full ferrite matrix structure with good uniformity, reduce processing residual stress, reduce thermal expansion coefficient, avoid nitriding deformation, and eliminate annealing heat treatment after boxing and before honing. At the same time, the secondary honing after nitriding is cancelled to reduce the unevenness of the final nitrided structure.

[0017] 2) Reduce costs. Through silicon solid solution strengthening, the material's tensile strength and elastic modulus can reach the same level as alloy ductile iron. At the same time, the addition of alloys such as copper and tin can be reduced, thereby reducing the cost of casting alloys.

[0018] 3) Reduce the number of processes, do not anneal the castings, control the casting boxing temperature, and avoid secondary stress distribution during annealing and cooling.

[0019] 4) By precisely controlling the smelting process parameters + multiple inoculations + rare earth-free Mg-Sb spheroidizing line, round graphite and single solid solution ferrite are obtained for the casting, achieving uniformity of structure and hardness, reducing residual stress during processing, and eliminating the need for post-finishing annealing to ensure the cylindricity requirements of the sliding hole.

[0020] 5) After the solid solution ferrite matrix is ​​treated with silicon solution, the crystal structure becomes more stable, and the silicon content increases, which reduces the thermal expansion coefficient. The material has better dimensional stability when the temperature changes. Combined with uniform graphite, the increase in cylindricality after nitriding is reduced, which further reduces the difficulty of honing before nitriding. At the same time, the secondary honing after nitriding is cancelled, ensuring the uniformity of the white bright layer.

[0021] 6) Reduce peeling and jamming. The material elongation can generally reach more than 10%, which is more than 3 times the elongation of alloy ductile iron with the same strength. The impact toughness is improved. At the same time, the nitriding performance can reach the level of alloy cast iron, but the thickness of the white bright layer is low and the brittleness is reduced, avoiding falling off during operation and causing jamming.

[0022] 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

[0023] 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:

[0024] Figure 1 It is the metallographic matrix organization diagram of ductile iron before nitriding; Figure 1 (a) is the metallographic matrix structure (without pearlite) of silicon-solid-solution ferrite ductile iron before nitriding in Example 1 of the present invention, Figure 1 (b) is the metallographic matrix structure (pearlite 75%) of alloy ductile iron before nitriding in the prior art;

[0025] Figure 2 The metallographic structure diagram of silicon-solution ferrite ductile iron after nitriding in Example 1 of the present invention;

[0026] Figure 3 The distribution of nitrogen elements in the EDS scan in Example 1 of the present invention;

[0027] Figure 4 This is the dimensional deformation of the cylinder body after nitriding in Example 1 of the present invention, with a cylindricity of 0.0069 / 0.0068. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, 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 known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0029] 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.

[0030] In the description of the embodiments of the present invention, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0031] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] In the description of the embodiments of the present invention, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0033] In the description of the embodiments of the present invention, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0034] In the description of the embodiments of the present invention, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

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

[0036] Solid solution strengthened ferritic cast iron: Ductile iron mainly strengthened by silicon solid solution and with ferrite matrix as the main component.

[0037] Nitrocarburizing: A gas thermal diffusion process that simultaneously infiltrates nitrogen and carbon into the workpiece surface.

[0038] The existing "Design and Research on High-Pressure and Large-Flow Straight-Shaft Plunger Pump Cylinder" mentions two solutions. One is to use 38CrMoAlA and other quenched and tempered nitrided cylinders inlaid with a 1mm brass sleeve as a friction pair. The other is to use alloy ductile iron (QT500-7, QT600-3) directly as a friction pair after gas soft nitriding.

[0039] However, the processing technology of inserting a copper sleeve in the cylinder bore of the cylinder block is complex and costly, while the strength and elastic modulus of the alloy ductile iron after nitriding meet the requirements of the friction pair, but there are shortcomings such as uneven structure, large residual stress during processing, unstable dimensions after heat treatment, and excessive precision such as cylindricity. Further honing processing is required, which leads to the problem of uneven wear-resistant layer on the material surface.

[0040] In order to solve the problems of large processing stress caused by uneven structure of cast iron materials, large dimensional deformation after nitriding heat treatment, and uneven white bright layer after processing, the present invention provides a cast iron sliding component with small processing deformation and excellent impact resistance and wear resistance and a manufacturing method thereof.

[0041] The invention provides a cast iron sliding component. The material of the cast iron sliding component is silicon solid-solution ferrite ductile iron, and the material structure is uniform and single ferrite. The cast iron sliding component comprises the following components in mass percentage: C 2.90% to 3.20%, Si 3.9% to 4.35%, Mn≤0.4% and not 0, P≤0.04% and not 0, S≤0.020% and not 0, Mg 0.040% to 0.060%, Sb 0.005% to 0.009%, and the balance is iron and inevitable trace elements.

[0042] In an embodiment of the present invention, solid solution ferrite ductile iron is used instead of conventional alloy ductile iron as a sliding component to obtain a full ferrite matrix structure with good structural uniformity, reduce processing residual stress, and at the same time reduce the thermal expansion coefficient to avoid nitriding deformation. The casting does not require annealing heat treatment after boxing and before honing, and the secondary honing after nitriding is eliminated, thereby reducing the unevenness of the final nitrided structure.

[0043] In an embodiment of the present invention, the mass percentage of carbon (C) in the cast iron sliding component provided by the present invention can be one of 2.90%, 3.0%, 3.10%, 3.20% or any value satisfying the above range value. The mass percentage of silicon (Si) can be one of 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.35% or any value satisfying the above range value. The mass percentage of manganese (Mn) can be one of 0.1%, 0.2%, 0.3%, 0.4% or any value satisfying the above range value. The mass percentage of phosphorus (P) can be one of 0.01%, 0.02%, 0.03%, 0.04% or any value satisfying the above range value. The mass percentage of sulfur (S) can be one of 0.010%, 0.020% or any value satisfying the above range value. The mass percentage of magnesium (Mg) can be one of 0.040%, 0.050%, 0.060% or any value within the above range. The mass percentage of antimony (Sb) can be one of 0.005%, 0.006%, 0.007%, 0.008%, 0.009% or any value within the above range.

[0044] In an embodiment of the present invention, silicon-solution ferrite ductile iron is used instead of conventional alloy ductile iron as a sliding member to ensure strength while improving toughness and reducing impact deformation. The tensile strength of the cast iron sliding member is ≥600MPa, the elongation is ≥10%, the hardness is 200HBW~220HBW, and the hardness difference at different positions of the same casting is <10HB. Exemplarily, the tensile strength of the cast iron sliding member can reach 619MPa, the elongation is 17%, the hardness is 208HBW, and the hardness difference at different positions is <10HB. Of course, the hardness of the cast iron sliding member provided by the present invention can be one of 200HBW, 202HBW, 204HBW, 205HBW, 208HBW, 210HBW, 212HBW, 214HBW, 215HBW, 218HBW, 220HBW or any value that meets the above range value.

[0045] In the embodiment of the present invention, the cast iron sliding component may be, but is not limited to, a plunger pump cylinder.

[0046] The present invention also provides a method for preparing the above-mentioned cast iron sliding component, the key of which is to adopt a melting and pouring process to obtain a casting, the boxing temperature after pouring is below 200°C, and the casting does not need to be subjected to stress relief annealing treatment; and the casting is subjected to rough machining, fine machining, honing, nitriding treatment and polishing treatment in sequence to obtain a cast iron sliding component; wherein the nitriding treatment adopts a two-stage gas soft nitriding, and the nitriding temperature is <560°C.

[0047] The preparation method of the cast iron sliding component in the present invention mainly comprises: smelting-pouring-boxing-cleaning-rough machining-fine machining-honing-nitriding-polishing, which is specifically carried out according to the following steps.

[0048] Melting and pouring

[0049] In an embodiment of the present invention, the smelting and pouring steps include batching, melting molten iron in an electric furnace, wire feeding spheroidizing and inoculation treatment, secondary inverted package inoculation and pouring flow inoculation. According to the above steps, the material of the casting is silicon solid solution ferrite ductile iron, and the material structure is a uniform single ferrite. The chemical composition of the casting includes the following components in mass percentage: C 2.90%~3.20%, Si 3.9%~4.35%, Mn≤0.4% and not 0, P≤0.04% and not 0, S≤0.020% and not 0, Mg 0.040%~0.060%, Sb 0.005%~0.009%.

[0050] In the embodiment of the present invention, the ingredients include the following components in mass percentage: 10% to 30% of high-purity pig iron, 30% to 70% of scrap steel, 0% to 40% of recycled materials, and recarburizer, silicon carbide and ferrosilicon, etc. The amount of recarburizer, silicon carbide and ferrosilicon is accurately calculated and added according to the requirements of chemical composition. After the original molten iron is melted and left to stand at high temperature, the iron is tapped.

[0051] In an embodiment of the present invention, the composition of the original molten iron is calculated and adjusted according to the chemical composition of the casting, the eutectic carbon equivalent is 4.4-4.6 and the inoculated silicon is 0.4%-0.6%, the S content is ≥0.010%, and the iron output control deviation is within ±30kg. Exemplarily, the original molten iron includes the following components in mass percentage: C3.0%-3.20%, Si 3.5%-3.75%, Mn≤0.4% and not 0, P≤0.04% and not 0, S≤0.020% and not 0.

[0052] In an embodiment of the present invention, during the wire feeding spheroidization and inoculation treatment, the wire feeding temperature is 1450°C to 1490°C. According to the casting temperature, the temperature drop during the wire feeding and pouring process is calculated, and the wire feeding temperature is adjusted. The actual temperature is controlled within the upper and lower limits of 20°C. Exemplarily, the wire feeding temperature can be one of 1450°C, 1460°C, 1470°C, 1480°C, 1490°C, or any value that satisfies the above range.

[0053] In an embodiment of the present invention, during the wire feeding process, the spheroidized cored wire is selected from a rare earth-free Mg-Sb cored wire, wherein the mass ratio of Mg to Sb is 10:1.

[0054] In the embodiment of the present invention, the core powder for inoculating the cored wire and the inoculant for inverting the cored wire are each independently selected from silicon-barium inoculants.

[0055] In an embodiment of the present invention, in the secondary inoculation treatment, the mass percentage of the inoculant added per kilogram of the original iron water is 0.5% to 0.8%. For example, the mass percentage of the inoculant added can be one of 0.5%, 0.6%, 0.7%, 0.8% or any value that meets the above range.

[0056] In an embodiment of the present invention, the pouring inoculation treatment adopts a silicon-barium or silicon-zirconium inoculant, and the mass percentage of the inoculant added per kilogram of raw iron water is 0.010% to 0.15%. For example, the mass percentage of the inoculant added can be 0.010%, 0.020%, 0.030%, 0.040%, 0.050%, 0.060%, 0.070%, 0.080%, 0.090%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15% or any value that meets the above range.

[0057] In an embodiment of the present invention, the pouring temperature may be 1350° C. to 1380° C., for example, it may be one of 1350° C., 1360° C., 1370° C., 1380° C. or any value satisfying the above range.

[0058] Packing and cleaning

[0059] In the embodiment of the present invention, after pouring is completed, the boxing temperature of the casting must reach below 200° C., and the casting does not need to be subjected to stress relief annealing heat treatment.

[0060] In the embodiment of the present invention, the cleaning adopts the shot blasting cleaning in the prior art.

[0061] In the embodiment of the present invention, after cleaning, a silicon-solid ferrite ductile iron casting is obtained, the tensile strength of the casting is ≥600MPa, the elongation is ≥10%, the hardness is 200HBW-220HBW, and the hardness difference at different positions of the same casting is <10HB. The matrix structure in the metallographic structure is all ferrite, and this part is mainly controlled to obtain silicon-solid ferrite cast iron. Different casting structures and components may have deviations, but they are all within the protection scope of the present invention.

[0062] In an embodiment of the present invention, by precisely controlling the smelting process parameters + multiple inoculations + rare earth-free Mg-Sb spheroidizing line, rounded graphite and a single solid solution ferrite of the casting are obtained, and the uniformity of the structure and hardness is achieved. At the same time, the process steps are reduced, and the residual stress is reduced by extending the boxing time and controlling the boxing temperature, thereby avoiding secondary stress distribution caused by too many steps.

[0063] Roughing, finishing and honing

[0064] In an embodiment of the present invention, the casting obtained through the above steps is a blank. After rough machining and fine machining of the blank, stress relief annealing in a nitrogen atmosphere is not required, and the sliding hole can be directly honed. The upper limit of the cylindricity in the hole after honing is calculated and controlled according to the cylindricity after nitriding - (0.0015~0.002).

[0065] Nitriding and polishing

[0066] In the embodiment of the present invention, the casting obtained after the above steps is subjected to two-stage gas soft nitriding, and the specific process includes: the first stage nitriding temperature is 510℃~530℃, the holding time is 4.5h~5.5h, and the strong nitriding potential is 3.0~5.0; the second stage nitriding temperature is 540℃~560℃, the nitriding time is 22h~24h, the diffusion nitrogen potential is 1.0~2.0, and the nitrogen is cooled to 200℃ and air-cooled out of the furnace. Finally, after polishing, it is directly assembled.

[0067] In an embodiment of the present invention, the first stage nitriding temperature may be one of 510°C, 520°C, 530°C or any value satisfying the above range. The holding time may be one of 4.5h, 4.6h, 4.7h, 4.8h, 4.9h, 5.0h, 5.1h, 5.2h, 5.3h, 5.4h, 5.5h or any value satisfying the above range. The strong nitriding potential may be one of 3.0, 4.0, 5.0 or any value satisfying the above range.

[0068] In an embodiment of the present invention, the second stage nitriding temperature may be one of 540°C, 550°C, 560°C or any value within the above range. The nitriding time may be one of 22h, 23h, 24h or any value within the above range. The diffusion nitrogen potential may be one of 1.0, 2.0 or any value within the above range.

[0069] In an embodiment of the present invention, by designing the nitriding process parameters, the nitriding temperature is lower than 560°C, and air cooling is carried out when the nitriding is cooled to 200°C, thereby further reducing the deformation of the material. At the same time, the nitriding performance of silicon-solution ferrite ductile iron reaches the nitriding performance level of alloy ductile iron, the thickness of the white bright layer is uniform and moderate, and the brittle tendency is reduced.

[0070] In an embodiment of the present invention, after nitriding treatment, the surface nitriding hardness of the casting is ≥600HV1, the depth of the nitriding layer is ≥0.12mm, the thickness of the white bright layer is 0.003mm-0.008mm, and the cylindricity is 0.006-0.008. For example, the surface hardness of the casting reaches 661HV1, the depth of the nitriding layer is 0.15mm, the thickness of the white bright layer is 3.07μm, and the cylindricity is 0.00558.

[0071] 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.

[0072] Example 1

[0073] A plunger pump cylinder is prepared by sand casting technology, and the casting process includes: batching - melting of raw molten iron - wire feeding treatment - secondary inoculation - flow inoculation - pouring - boxing - cleaning - rough machining - fine machining - nitriding - polishing.

[0074] 1) The ingredients are 20% pig iron, 60% scrap steel, 20% recycled materials, as well as carburizer, silicon carbide and ferrosilicon, etc. The chemical composition of the original molten iron is: C 3.09%, Si 3.68%, Mn 0.32%, P 0.021%, S 0.014%, Ti0.011%, and the balance is iron and inevitable trace elements.

[0075] 2) Select spheroidized cored wire with 20% Mg-2% Sb and silicon-barium inoculated wire without rare earth for wire feeding treatment. The wire feeding treatment temperature is 1470°C. When pouring, silicon-barium inoculant is added at 0.5% per kilogram of iron output, silicon-zirconium is inoculated at 0.15%, and the pouring temperature is 1362°C.

[0076] 3) The casting is cooled to 180℃ in the sand box and then boxed. After boxing, it is shot blasted. The chemical composition of the casting includes: C 3.04%, Si 4.31%, Mn 0.032%, S 0.009%, P 0.021%, Mg 0.048%, Sb 0.0077%, and the balance is iron and inevitable trace elements. According to GB / T1348 ductile iron casting performance test, the casting material has a tensile strength of 619MPa, an elongation of 17%, and a hardness of 208HBW. Compared with the metallographic structure of the existing alloy ductile iron (see Figure 1 (b)) It can be seen that the metallographic structure of the casting in Example 1 does not contain pearlite (see Figure 1 (as shown in (a)).

[0077] 4) Cylinder body is processed by rough machining, fine machining and honing of plunger hole. The honing cylindricality is controlled to be less than 0.0060 and actually reaches 0.00558.

[0078] 5) The cylinder body is subjected to nitriding heat treatment. The first stage nitriding temperature is 520°C, the temperature is kept for 4.8 hours, the strong nitriding potential is 4.0, the second stage nitriding temperature is 550°C, the nitriding time is 22 hours, the diffusion nitrogen potential is 1.5, the nitriding is cooled to 200°C and air-cooled, and finally assembled directly after polishing.

[0079] The present invention performs metallographic image analysis on the silicon-solid-solution ferrite ductile iron obtained in Example 1 after nitriding treatment. Figure 2 As shown, the surface hardness is 661HV1, the depth of the nitrided layer is 0.15mm, and the thickness of the white bright layer is 3.07μm. The nitrogen element distribution is scanned by EDS, and the results are shown in Figure 3 As shown, the nitriding condition can be observed, the nitriding performance meets the requirements, and the accuracy after nitriding meets the requirements (see Figure 4 As shown), no further processing is required to ensure the uniformity of the white bright layer.

[0080] The present invention obtains silicon solid solution ferrite cast iron with uniform structure by adjusting the components, and achieves the required nitriding performance by optimizing the nitriding parameters.

[0081] 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 cast iron sliding component, characterized in that: The material of the cast iron sliding component is silicon solid-solution ferrite ductile iron, and the material structure is uniform and single ferrite, including the following components in mass percentage: C 2.90% to 3.20%, Si 3.9% to 4.35%, Mn≤0.4% and not 0, P≤0.04% and not 0, S≤0.020% and not 0, Mg 0.040% to 0.060%, Sb 0.005% to 0.009%, and the remainder is iron and inevitable trace elements.

2. The cast iron sliding member according to claim 1, characterized in that The cast iron sliding component has a tensile strength of ≥600MPa, an elongation of ≥10%, a hardness of 200HBW-220HBW, and a hardness difference of <10HB at different positions of the same casting.

3. A method for preparing a cast iron sliding component according to claim 1 or 2, characterized in that: The preparation method comprises: The casting is obtained by a melting and pouring process, the boxing temperature after pouring is below 200°C, and the casting does not need to be subjected to stress relief annealing treatment; and The casting is subjected to rough machining, fine machining, honing, nitriding and polishing in sequence to obtain the cast iron sliding component; wherein the nitriding treatment adopts two-stage gas soft nitriding, and the nitriding temperature is less than 560°C.

4. The preparation method according to claim 3, characterized in that: The two-stage gas soft nitriding process includes: the first stage nitriding temperature is 510°C to 530°C, the holding time is 4.5h to 5.5h, and the strong nitriding potential is 3.0 to 5.0; the second stage nitriding temperature is 540°C to 560°C, the nitriding time is 22h to 24h, the diffusion nitrogen potential is 1.0 to 2.0, and the nitrogen is cooled to 200°C and then air-cooled out of the furnace.

5. The preparation method according to claim 3 or 4, characterized in that: After the nitriding treatment, the surface nitriding hardness of the casting is ≥600HV1, the depth of the nitriding layer is ≥0.12mm, the thickness of the white bright layer is 0.003mm-0.008mm, and the cylindricity is 0.006-0.

008.

6. The preparation method according to claim 3, characterized in that: The smelting and pouring process includes smelting raw iron water, wire feeding spheroidization and inoculation treatment, secondary inverted ladle inoculation treatment and pouring flow inoculation treatment.

7. The preparation method according to claim 3 or 6, characterized in that: In the smelting and pouring process, the original molten iron composition is calculated and adjusted according to the chemical composition of the casting, the eutectic carbon equivalent is 4.4-4.6 and the inoculated silicon is 0.4%-0.6%, the S content is ≥0.010%, and the iron output is controlled within ±30kg.

8. The preparation method according to claim 6, characterized in that: In the wire feeding spheroidization and inoculation treatment, the wire feeding temperature is 1450° C. to 1490° C., the spheroidized cored wire is selected from rare earth-free Mg-Sb cored wire, wherein the mass ratio of Mg to Sb is 10:1; and the core powder of the inoculated cored wire is selected from silicon-barium inoculants.

9. The preparation method according to claim 3, characterized in that: The secondary inoculation treatment uses silicon-barium inoculant, and the mass percentage of the inoculant added per kilogram of raw iron water is 0.5% to 0.8%.

10. The preparation method according to claim 3, characterized in that: The pouring inoculation treatment adopts silicon-barium or silicon-zirconium inoculants, and the mass percentage of the inoculants added per kilogram of raw iron water is 0.010% to 0.15%.

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