Alloy cast iron, alloy cast iron cylinder liner and preparation method

Abstract

The present invention belongs to the technical field of alloy cast iron materials, and specifically relates to an alloy cast iron, a cylinder liner blank, an alloy cast iron cylinder liner, and a preparation method. By limiting the content of various elements in the alloy cast iron, particularly precisely controlling the content of elements such as Nb, Sn, V, Ti, and B, the present invention improves the material's processing performance, makes it easy to manufacture, is low-cost, and offers improved performance. Using this material as a cylinder liner blank, particularly in clean fuel engine cylinder liners, overcomes the problems of prior art, such as poor processing performance of corrosion-resistant cylinder liners, high tool change frequency during machining, and inability to achieve automated production.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy cast iron materials, and in particular relates to alloy cast iron, an alloy cast iron cylinder liner and a preparation method thereof. Background Art

[0002] As one of the core components of an internal combustion engine, the cylinder liner, along with the cylinder head, piston, and piston rings, forms the combustion chamber and is the engine's power source. As truck and large bus engines increasingly strive for higher power, lower fuel consumption, and lower pollution, the requirements for cylinder liners are becoming increasingly stringent.

[0003] Traditional cylinder liners generally use cast iron cylinder liners, which have the advantages of good toughness, high strength, and good wear resistance. However, during the test installation process, it was found that traditional cylinder liners that only meet mechanical performance requirements can no longer meet the operating needs of the engine. The reason is that with increasingly stringent environmental protection requirements, there are more and more lightweight and compact aluminum cylinder clean fuel engines. Since these fuels are mostly natural gas, methanol, ammonia, etc., during use, clean fuels and their combustion products will mix with the lubricating oil and cause severe corrosion and wear on the engine cylinder liners. For example, when using methanol as fuel, the inner wall of the cylinder liner will contact with the corrosive products (such as formic acid) generated by the combustion of methanol, causing acid corrosion on the cylinder liner, which in turn causes corrosion failure of the cylinder liner, resulting in engine inoperability.

[0004] To solve the above problems, the prior art discloses some alloy materials and cylinder liners with good corrosion resistance, wear resistance and mechanical properties. However, the machining performance cannot meet the machining performance requirements of cast-in cylinder liners for lightweight aluminum cylinder blocks. The cutting performance is poor, the frequency of machining tool changes is high, and they are not suitable for large-scale machining production. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the cast iron alloy materials with good corrosion resistance, wear resistance and mechanical properties in the prior art, such as poor machining performance, high frequency of machining tool changes, and unsuitability for large-scale machining production, thereby providing an alloy cast iron, an alloy cast iron cylinder liner and a preparation method.

[0006] To this end, the present invention provides the following technical solutions:

[0007] The present invention provides an alloy cast iron, comprising the following components in percentage by mass: 2.0-3.0% of C; 0.02-0.08% of S; 2.8-3.5% of Si; less than 0.08% of P; 0.3-0.8% of Mn; 0.2-0.6% of Cr; 0.1-0.8% of Cu; less than 0.1% of Nb; 0.05-0.3% of Sn; less than 0.1% of V+Ti; less than 0.01% of B; and the balance being Fe.

[0008] Optionally, the steel comprises the following components in percentage by mass: 2.5-2.7% C; 0.03-0.05% S; 2.8-3.1% Si; ≤0.05% P; 0.4-0.5% Mn; 0.35-0.55% Cr; 0.15-0.25% Cu; <0.05% Nb; 0.10-0.20% Sn; <0.03% V; <0.035% Ti; <0.008% B; and the balance is Fe.

[0009] The reasons for the numerical limitation of the alloy composition in the alloy cast iron of the present invention are described in detail below:

[0010] Carbon: Carbon exists as a graphitization-promoting element. Properly increasing the carbon content is beneficial for improving the casting properties of cast iron, resulting in Type A graphite. The carbon content is generally controlled between 3.0-3.3%. However, since this material is used for corrosion-resistant cylinder liners, a high carbon content results in a higher graphite phase. Graphite has the highest potential in cast iron, so a lower carbon content helps reduce the number of micro-galvanic cells and electrochemical corrosion. Therefore, from the perspective of reducing corrosion, the lower the better. The present invention minimizes the carbon content while ensuring a good metallographic structure of the graphite, limiting it to 2-3%, preferably 2.5-2.7%.

[0011] Sulfur: A sulfur content within the range of 0.03-0.12% is beneficial for cast iron to obtain type A graphite. Sulfur also reacts with manganese to form manganese sulfide, which lubricates tools during machining and improves cutting performance. However, excessive sulfur content will reduce the corrosion resistance of cast iron. Based on comprehensive considerations, the present invention controls the sulfur content within the range of 0.03-0.05%.

[0012] Silicon: It has a strong graphitization-promoting effect and promotes the formation of gray cast iron. In the present invention, it is beneficial to increase the carbon equivalent and obtain a better graphite structure without increasing the amount of graphite. In addition, a higher silicon element is solid-dissolved in ferrite, which not only helps to increase the hardness of ferrite, but also forms a thin silicon dioxide protective film after oxidation, which plays a role in slowing down the corrosion of the substrate in an electrolyte environment. However, too high a silicon element content will increase the brittleness of the cast iron and form a larger amount of free ferrite.

[0013] Manganese: Manganese is a carbide-forming element. An appropriate amount of manganese content is beneficial for the casting to obtain pearlite structure and improve the strength of the casting. Manganese can also react with sulfur to form manganese sulfide, which is beneficial for lubricating the tool during machining and improving cutting performance. However, if the manganese content is too high, it will segregate between grains and form intergranular carbides. The intergranular carbides have high hardness and are easy to make the tool passivated, which is not conducive to improving the cutting performance of cast iron. The preferred manganese content of the present invention is 0.3-0.8%, preferably 0.35-0.5%.

[0014] Phosphorus: Phosphorus is a harmful element in the alloy cast iron material of the present invention. It will form a phosphorus eutectic hard phase in the cast iron. The phosphorus eutectic has a high microhardness, which is not conducive to tool cutting. Therefore, the lower the better. However, since the furnace charge (mainly pig iron) used to produce castings has a certain phosphorus content, it must be limited. Generally, the phosphorus content is below 0.1%. The effect of the formed phosphorus eutectic on the machining tool cutting of cast iron is not obvious. Therefore, in the present invention, the phosphorus content is controlled below 0.08%, preferably ≤0.05%.

[0015] Chromium: As a strong carbide-promoting element, its primary function is to stabilize carbides and pearlite. Furthermore, its solid solution in the matrix helps increase the matrix's potential, reduce the potential difference between graphite and the matrix, and slow corrosion. However, high levels of chromium can lead to the formation of primary carbides, reducing the overall performance and machinability of the cast iron. The most suitable control range for this invention is 0.35-0.55%.

[0016] Copper: The main function of copper in the present invention is to increase the potential of the substrate and slow down the corrosion of cast iron in organic acids. Through experiments, the copper content is between 0.15-0.8%. The change of copper content has little effect on improving the corrosion resistance of cast iron. In order to reduce production costs, the copper element is controlled between 0.15-0.25%.

[0017] Tin: Tin is an element that strongly promotes pearlite. It not only promotes the formation of pearlite, but also can be dissolved into the matrix. It has a strong anti-corrosion effect, but its content is too high will lead to reduced strength of cast iron and increase the brittleness of cast iron.

[0018] Niobium: Niobium reacts with N / C in molten iron to form Nb(CN) phase. Nb(CN) solid solution in the matrix is ​​extremely beneficial to improving the strength of cast iron. However, since the microhardness of Nb(CN) can reach 2000-2500 HV, it can easily make machining tools blunt, seriously affecting tool life. Therefore, the lower the content in the material of the present invention, the better. Considering the production raw material problem, its content is limited to no more than 0.05%.

[0019] Vanadium and titanium: Vanadium and titanium react easily with carbon in molten iron to form a vanadium-titanium hard phase in cast iron. The vanadium-titanium hard phase in cast iron has an extremely high hardness, which can reach over 2000 HV. Therefore, in order to control the amount of vanadium-titanium phase in the cast iron matrix, the vanadium-titanium content must be controlled. According to our research and test data, V+Ti≤0.07% has little effect on the machining performance of cast iron. Therefore, in the present invention, V+Ti is limited to 0.1%, and preferably V<0.03% and Ti<0.035%.

[0020] Boron: Boron is a strong carbide-forming element. Even at very low boron content, it easily reacts with carbon and iron in molten iron to form a large number of boron-carbon composite compounds. These compounds have extremely high hardness, which is not conducive to improving cutting performance. However, when the boron content is lower than 0.01%, the amount of boron-carbon compounds formed is extremely small. Therefore, the boron content is limited to no more than 0.01%, preferably ≤0.008%.

[0021] The present invention provides a cylinder liner blank, the composition of which is the same as that of the alloy cast iron.

[0022] The present invention also provides an alloy cast iron cylinder liner, comprising the above-mentioned cylinder liner blank.

[0023] Optionally, an aluminum silicon alloy coating is also included.

[0024] Optionally, the thickness of the aluminum-silicon alloy coating is 0.07-0.35 mm.

[0025] Optionally, the aluminum-silicon alloy coating comprises: ZAlSi12 alloy and oxidation products of ZAlSi12 alloy.

[0026] The present invention also provides a method for preparing the alloy cast iron cylinder liner, comprising the following steps:

[0027] S1, smelting and inoculation of raw materials to obtain molten iron;

[0028] S2, centrifugally pouring the obtained molten iron to obtain a blank;

[0029] S3, rough machining the obtained blank to obtain a semi-finished cylinder liner, and spraying an aluminum-silicon alloy coating on the outer diameter of the cylinder liner;

[0030] S4, die casting and fine machining to obtain the alloy cast iron cylinder liner.

[0031] Among them, rough machining is a routine operation in the field, for example, generally including rough cutting - rough reaming of inner hole - rough turning of outer circle - fine reaming of inner hole - fine turning of outer circle and other processes.

[0032] Optionally, in step S1, the smelting temperature is 1520-1550°C.

[0033] Optionally, in step S2, the centrifugal pouring temperature is 1400-1430°C, the ejection temperature is 750-850°C, and the centrifugal speed is 1400-1460 r / min.

[0034] Optionally, in step S3, an aluminum-silicon alloy coating is sprayed on the outer wall of the blank by thermal spraying.

[0035] Optionally, in step S1, a silicon strontium inoculant is added during the inoculation process.

[0036] Optionally, the number of eutectic cells in the blank metallographic structure is 1000-4000 per centimeter. 2 .

[0037] Typically, but not limiting, the outer wall of the blank is a burr-shaped cylinder liner, and only the inner hole of the cylinder liner is processed; the blank can also be processed into a cylinder liner with a threaded outer wall or a press-in cylinder liner with both the inner and outer walls processed.

[0038] In the actual production process, the semi-finished cylinder liner obtained in step S3 is generally transported to the cylinder block factory for subsequent processing. The cylinder block factory puts the cylinder liner into the cylinder block mold and casts the cylinder liner into the cylinder block through die casting. Then, the cylinder liner and cylinder block are processed simultaneously on the machining center to process the cylinder liner inner hole to the cylinder liner inner hole size required by the engine. Therefore, the better the cylinder liner processing performance, the longer the tool life and the lower the tool change frequency, which is conducive to mass production.

[0039] The technical solution of the present invention has the following advantages:

[0040] The alloy cast iron provided by the present invention comprises the following components by weight: 2.0-3.0% C; 0.02-0.08% S; 2.8-3.5% Si; <0.08% P; 0.3-0.8% Mn; 0.2-0.6% Cr; 0.1-0.8% Cu; <0.1% Nb; 0.05-0.3% Sn; <0.1% V+Ti; <0.01% B; the balance being Fe. By limiting the content of each element in the alloy cast iron, particularly precisely controlling the content of elements such as Nb, Sn, V, Ti, and B, the present invention improves the material's processing properties, making it easy to manufacture, low-cost, and offering better performance. Using it as a cylinder liner blank, particularly in clean fuel engine cylinder liners, overcomes the problems of poor processing performance of corrosion-resistant cylinder liners in the prior art, high tool change frequency during machining, and inability to achieve automated production. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 is a process flow chart for preparing the alloy cast iron cylinder liner in Example 1 of the present invention;

[0043] Figure 2 This is a diagram of the matrix structure of the blank obtained in Example 1 of the present invention under a 100x optical microscope;

[0044] Figure 3 This is a diagram of the matrix structure of the blank obtained in Example 1 of the present invention under a 500x optical microscope;

[0045] Figure 4 This is a morphology picture of the eutectic cell obtained in Example 1 of the present invention under a 50x optical microscope. DETAILED DESCRIPTION

[0046] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0047] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0048] Example 1 (Production of L83 Product)

[0049] This embodiment provides an alloy cast iron cylinder liner, and its preparation process is as follows: Figure 1 As shown, the specific preparation method includes the following steps:

[0050] Raw materials were inspected, and the alloying elements were smelted and then inoculated to obtain molten iron. The smelting temperature was controlled at 1520°C. The inoculant used during inoculation was a silicon strontium inoculant from Ningxia Zhufeng. The spectral detection components are shown in Table 1.

[0051] The obtained molten iron is centrifugally poured into a blank, the pouring temperature is controlled at 1410°C, the centrifugal speed during the pouring process is 1460r / min, and the blank is taken out of the mold at 800°C. Figure 2 This is the matrix organization diagram of the blank obtained under a 100x optical microscope. From the figure, it can be seen that the matrix organization is pearlite and a small amount of evenly distributed carbides, and the organization is particularly uniform. Figure 3 This is the matrix organization diagram of the blank obtained under a 500x optical microscope. Figure 3 It can be seen that the morphology of carbides is blocky, which is beneficial to improving the wear resistance of the material, but has little effect on the mechanical properties and cutting performance of the matrix. Figure 4 This is the morphology of the eutectic group of the blank under a 50x optical microscope. It can be seen from the figure that the grain boundaries of the eutectic group are not obvious, but the grain boundaries have obvious characteristics of the segregation phase of tin-containing compounds.

[0052] The blank is rough-machined (rough cutting - rough reaming inner hole - rough turning outer circle - fine reaming inner hole - fine turning outer circle), and the outer wall of the cylinder liner is sprayed with an aluminum-silicon alloy coating (the specific composition of the aluminum-silicon alloy is: ZAlSi12 alloy and the oxidation product of ZAlSi12 alloy) by thermal spraying, with a coating thickness of 0.09-0.2mm.

[0053] The cylinder liners are transported to the die casting factory for die casting and finishing.

[0054] Example 2 (Production of L83 Product)

[0055] This embodiment provides an alloy cast iron cylinder liner, the specific preparation method of which includes the following steps:

[0056] The alloy elements were smelted and then inoculated to obtain molten iron. The smelting temperature was controlled at 1550° C. The inoculant used during inoculation was a silicon strontium inoculant from Ningxia Zhufeng. The spectral detection components are shown in Table 1.

[0057] The obtained molten iron is centrifugally poured into a blank, the pouring temperature is controlled at 1430°C, the centrifugal speed is 1400r / min during the pouring process, and the blank is taken out of the mold at 800°C.

[0058] The blank is rough-machined (rough cutting - rough reaming inner hole - rough turning outer circle - fine reaming inner hole - fine turning outer circle), and the outer wall of the cylinder liner is sprayed with an aluminum-silicon alloy coating (the specific composition of the aluminum-silicon alloy is: ZAlSi12 alloy and the oxidation product of ZAlSi12 alloy) by thermal spraying, with a coating thickness of 0.15-0.25mm.

[0059] The cylinder liners are transported to the die casting factory for die casting and finishing.

[0060] Example 3 (Production of L83 Product)

[0061] This embodiment provides an alloy cast iron cylinder liner, the specific preparation method of which includes the following steps:

[0062] The alloy elements were smelted and then inoculated to obtain molten iron. The smelting temperature was controlled at 1550° C. The inoculant used during inoculation was a silicon strontium inoculant from Ningxia Zhufeng. The spectral detection components are shown in Table 1.

[0063] The obtained molten iron is centrifugally poured into a blank, the pouring temperature is controlled at 1430°C, the centrifugal speed is 1400r / min during the pouring process, and the blank is taken out of the mold at 800°C.

[0064] The blank is rough-machined (rough cutting - rough reaming inner hole - rough turning outer circle - fine reaming inner hole - fine turning outer circle), and the outer wall of the cylinder liner is sprayed with an aluminum-silicon alloy coating (the specific composition of the aluminum-silicon alloy is: ZAlSi12 alloy and the oxidation product of ZAlSi12 alloy) by thermal spraying, with a coating thickness of 0.2-0.35mm.

[0065] The cylinder liners are transported to the die casting factory for die casting and finishing.

[0066] The cylinder liner composition was tested using a photoelectric direct reading spectrometer according to GB / T24234-2009 "Determination of multiple elements in cast iron - Spark discharge atomic emission spectrometry". The test results showed that the cylinder liner composition was:

[0067] Table 1 Composition of cylinder liner blank in the embodiment (wt%)

[0068]

[0069]

[0070] Comparative Examples 1-6 (L83 products produced using traditional classic cast-in cylinder liner compositions)

[0071] Comparative Examples 1-6 provide an alloy cast iron cylinder liner, the specific preparation method of which includes the following steps:

[0072] The alloy elements were smelted and then inoculated to obtain molten iron. The smelting temperature was controlled at 1520° C. The inoculant used during inoculation was a silicon strontium inoculant from Ningxia Zhufeng. The spectral detection components are shown in Table 2.

[0073] Centrifugal casting, rough machining, die casting and fine machining were carried out according to the method of Example 1 to obtain an alloy cast iron cylinder liner.

[0074] Table 2 Composition of cylinder liner blank in comparative example (wt%)

[0075] Example C S Si P Mn Cr Cu Nb Sn B V Ti Comparative Example 1 3.15 0.06 2.35 0.11 0.85 0.25 0.31 0.0016 0.03 0.004 0.021 0.032 Comparative Example 2 2.61 0.046 2.81 0.07 0.45 0.55 0.22 0.351 0.145 0.041 0.027 0.034 Comparative Example 3 3.02 0.045 2.26 0.28 1.12 0.33 0.84 0.184 0.167 0.005 0.031 0.042 Comparative Example 4 2.71 0.055 2.83 0.07 0.77 0.26 0.47 0.002 0.137 0.005 0.028 0.057 Comparative Example 5 3.07 0.057 2.13 0.05 0.89 0.30 0.41 0.003 0.018 0.007 0.071 0.031 Comparative Example 6 3.01 0.066 2.09 0.11 0.77 0.31 0.32 0.031 0.007 0.045 0.018 0.061

[0076] Test Case

[0077] Samples were taken from the blanks obtained in each embodiment and comparative example, and the blanks were processed into test specimens for testing. The testing method was as follows:

[0078] A. Test the hardness according to GB / T 231.1-2018 "Metallic Materials Brinell Hardness Test Part 1: Test Method";

[0079] B.Using universal material testing machine WDW-300, according to GB / T228.1-2010 "Metallic materials tensile test part 1: room temperature test method" standard test, the test results are tensile strength;

[0080] C. According to GB / T 22315-2008 "Test method for elastic modulus and Poisson's ratio of metallic materials", the test results are: Young's elastic modulus;

[0081] D. Test the corrosion resistance of the material according to the JB / T 7901 metal material laboratory uniform corrosion full immersion test method (corrosive solution: pour 100mL formic acid into 500mL water, add 2.5g sodium chloride to dissolve, dilute to 1000mL, and maintain constant temperature at 80℃).

[0082] E. Valin CBN superhard cutting tools were used to conduct cutting tests on the inner bores of semi-finished cylinder liners made of different materials. The equipment was a Yamazaki Mazak CNC machine tool QUICK TURN 250L. The fine boring cutting process was as follows: cutting depth 0.12mm, feed rate 0.107mm / r, cutting speed 870m / min, cutting length 53982m. Tool tip wear was measured to compare the cutting performance of cylinder liner materials.

[0083] Table 3

[0084]

[0085] From the data in the above table, it can be seen that although the cutting performance of the present invention is not as good as that of the ordinary cast-in material cylinder liner in Comparative Example 1, it has corrosion resistance that ordinary cast-in cylinder liners do not have. Comparative Example 1 can no longer meet the requirements of clean fuel engines for cylinder liner materials; the mechanical properties and corrosion resistance of the embodiment are basically equivalent to those of Comparative Example 3, but the machining and cutting performance are better; although the mechanical properties of the embodiment are not as good as those of Comparative Examples 2 and 4, it has good cutting performance; the corrosion resistance and cutting performance of the embodiment are better than those of Comparative Examples 5 and 6, indicating that the provided material is suitable for mechanized mass production and can meet the requirements of use. In summary, the alloy cast iron cylinder liner provided by the present invention not only has excellent manufacturing performance (cutting performance), but also has excellent use performance (mechanical properties and corrosion resistance).

[0086] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. An alloy cast iron, characterized in that: The composition includes the following mass percentages: 2.0~3.0% C; 0.02~0.08% S; 2.85~3.5% Si; <0.08% P; 0.3-0.8% Mn; 0.2-0.6% Cr; 0.1-0.8% Cu; <0.1% Nb; 0.05~0.3% Sn; <0.03% V; <0.035% Ti; <0.01% B; the balance is Fe.

2. The alloy cast iron according to claim 1, characterized in that The composition includes the following mass percentages: 2.5~2.7% C; 0.03~0.05% S; 2.85~3.1% Si; ≤0.05% P; 0.4-0.5% Mn; 0.35-0.55% Cr; 0.15-0.25% Cu; <0.05% Nb; 0.10~0.20% Sn; <0.03% V; <0.035% Ti; <0.008% B; balance Fe.

3. A cylinder liner blank, characterized in that: The composition of the cylinder liner blank is the same as the alloy cast iron according to claim 1 or 2.

4. An alloy cast iron cylinder liner, characterized in that: Including the cylinder liner blank as described in claim 3.

5. The alloy cast iron cylinder liner according to claim 4, characterized in that: Also includes aluminum silicon alloy coating, The thickness of the aluminum-silicon alloy coating is 0.07-0.35 mm; The aluminum-silicon alloy coating comprises: ZAlSi12 alloy and oxidation products of ZAlSi12 alloy.

6. A method for preparing the alloy cast iron cylinder liner according to claim 5, characterized in that: The steps include: S1, smelting and inoculation of raw materials to obtain molten iron; S2, centrifugally pouring the obtained molten iron to obtain a blank; S3, performing rough machining on the obtained blank to obtain a cylinder liner blank, and spraying an aluminum-silicon alloy coating; S4, die casting and fine machining to obtain the alloy cast iron cylinder liner.

7. The method for preparing the alloy cast iron cylinder liner according to claim 6, characterized in that: In step S1, the smelting temperature is 1520-1550°C.

8. The method for preparing the alloy cast iron cylinder liner according to claim 6, characterized in that: In step S2, the temperature of the centrifugal pouring is 1400-1430°C, the mold temperature is 750-850°C, and the centrifugal speed is 1400-1460r / min.

9. The method for preparing the alloy cast iron cylinder liner according to claim 6, characterized in that: In step S3, an aluminum-silicon alloy coating is sprayed on the outer wall of the blank by thermal spraying.

10. The method for preparing an alloy cast iron cylinder liner according to any one of claims 6 to 9, characterized in that: In step S1, a silicon strontium inoculant is added during the inoculation process.

Images