Ductile steel cylinder liner and preparation method thereof

Abstract

The present invention provides a ductile steel cylinder liner comprising 1.4-1.6 wt% C, 1.5-1.8 wt% Si, 0.6-0.8 wt% Mn, 2.0-3.0 wt% Mo, 3.0-4.0 wt% Ni, 0.04-0.06 wt% Nb, and the balance Fe. The present application also provides a method for preparing a ductile steel cylinder liner. The ductile steel cylinder liner provided in the present application facilitates the formation of bainite by introducing Mo, Ni, and Nb; at the same time, the combination of a water-cooled metal mold centrifugal casting process, austempering, and tempering facilitates improving the tensile strength and hardness of the ductile steel cylinder liner. Experimental results show that the tensile strength of the ductile steel cylinder liner provided in the present application reaches above 1200 MPa, and the hardness is greater than 38 HRC.

Description

Technical Field

[0001] The present invention relates to the technical field of cylinder liners, and in particular to a ductile steel cylinder liner and a preparation method thereof. Background Art

[0002] The cylinder liner is a cylindrical component placed in the cylinder bore of the engine body and held in place by the cylinder head. The piston reciprocates within the bore, cooled by cooling water. Together with the cylinder head and piston, the cylinder liner forms the working space of the cylinder.

[0003] The implementation of the National VI emission standards for internal combustion engines has placed higher demands on internal combustion engines and their components. Cylinder liners, as one of the key components and the heart of internal combustion engines, are now required to meet the engine's power, reliability, economy, emissions, noise, and other technical requirements. High-performance new internal combustion engines are placing increased demands on cylinder liners for tensile strength and wear resistance. Therefore, new materials with high strength and wear resistance exceeding 1200MPa are urgently needed. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a ductile steel cylinder liner and a preparation method thereof. The ductile steel cylinder liner provided in the present application has excellent tensile strength and wear resistance.

[0005] In view of this, the present application provides a ductile steel cylinder liner, which comprises, by mass percentage:

[0006]

[0007] The balance is Fe.

[0008] Preferably, the content of Mo is 2.2-2.7 wt%.

[0009] Preferably, the Ni content is 3.2-3.8 wt%.

[0010] Preferably, the Nb content is 0.042-0.055 wt%.

[0011] Preferably, the C content is 1.45-1.55 wt%.

[0012] Preferably, the Si content is 1.55-1.78 wt%.

[0013] Preferably, the content of Mn is 0.65-0.78 wt%.

[0014] The present application also provides a method for preparing the ductile steel cylinder liner, comprising the following steps:

[0015] A) Q235 steel scrap and carburizer are mixed according to the composition ratio, the obtained mixture is melted, placed at high temperature, furnace composition tested and refined, the refined molten steel is spheroidized and inoculated, and then slag is skimmed;

[0016] B) preparing a ductile steel cylinder liner blank by casting using a water-cooled metal mold centrifugal casting process, and processing the blank;

[0017] C) austempering the semi-finished cylinder liner obtained in step B), and then tempering the semi-finished cylinder liner to obtain a ductile steel cylinder liner.

[0018] Preferably, the casting temperature of the water-cooled metal mold centrifugal casting process is 1500-1600°C, the pouring machine speed is 1300-1500r / min, the mold preheating temperature is 250-350°C, the coating is wet coating with a thickness of 0.5-1mm, and the casting demolding temperature is 800-850°C.

[0019] Preferably, the temperature of the austempering is 850-950°C, the cooling medium of the austempering is nitrate with a temperature of 250-350°C, the cooling time is 2-3h, and the temperature of the tempering is 200-250°C.

[0020] The present application provides a ductile steel cylinder liner, which includes 1.4-1.6wt% C, 1.5-1.8wt% Si, 0.6-0.8wt% Mn, 2.0-3.0wt% Mo, 3.0-4.0wt% Ni, 0.04-0.06wt% Nb and the balance Fe. The present application introduces Mo, Ni and Nb into the ductile steel cylinder liner and adjusts the contents of the three to facilitate the formation of bainite during austempering of the ductile steel cylinder liner, thereby facilitating the improvement of tensile strength and wear resistance.

[0021] Furthermore, the present application also provides a method for preparing a ductile steel cylinder liner, which obtains a cast metallographic structure of spherical graphite and pearlite through centrifugal casting. After rough processing, it is subjected to austempering and tempering to obtain a cylinder liner with a metallographic structure of spherical graphite and bainite matrix, which is beneficial to improving the tensile strength and hardness of the cylinder liner. Experimental results show that the tensile strength of the cylinder liner prepared in the present application reaches more than 1200MPa and the hardness is greater than 38HRC. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a metallographic photograph of a ductile steel cylinder liner prepared in Example 2 of the present invention, magnified 100 times;

[0023] Figure 2 This is a metallographic photograph of the substrate of the ductile steel after austempering prepared in Example 2 of the present invention, magnified 500 times;

[0024] Figure 3 This is a metallographic photograph of the casting blank prepared in Comparative Example 1 of the present invention;

[0025] Figure 4 This is a metallographic photograph of the matrix structure of the ductile steel cylinder liner prepared in Comparative Example 2 of the present invention, magnified 100 times;

[0026] Figure 5 This is a metallographic photograph of the matrix structure of the ductile steel cylinder liner prepared in Comparative Example 2 of the present invention, magnified at 500×;

[0027] Figure 6 This is a metallographic photograph of the matrix structure of the ductile steel cylinder liner prepared in Comparative Example 3 of the present invention, magnified 100 times;

[0028] Figure 7 This is a metallographic photograph of the matrix structure of the ductile steel cylinder liner prepared in Comparative Example 3 of the present invention, magnified at 500 degrees. DETAILED DESCRIPTION

[0029] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0030] In view of the requirements of the prior art for the tensile strength and wear resistance of cylinder liners, the present application provides a ductile steel cylinder liner and a preparation method thereof. For the ductile steel cylinder liner, the present application regulates the alloy composition and content thereof, thereby facilitating the formation of bainite in the metallographic structure of the cylinder liner. For the preparation method of the ductile steel cylinder liner, centrifugal casting is combined with austempering and tempering, so that the metallographic structure of the cylinder liner is spherical graphite and bainite matrix, thereby improving the tensile strength and wear resistance of the ductile steel cylinder liner. Specifically, an embodiment of the present invention discloses a ductile steel cylinder liner, which, in terms of mass percentage, comprises:

[0031]

[0032]

[0033] The balance is Fe.

[0034] In the ductile steel cylinder liner provided in the present application, the C content indicates that the cylinder liner of the present application belongs to steel, and its content is 1.4-1.6wt%. Specifically, the C content is 1.40wt%, 1.41wt%, 1.42wt%, 1.43wt%, 1.44wt%, 1.45wt%, 1.46wt%, 1.47wt%, 1.48wt%, 1.49wt%, 1.50wt%, 1.51wt%, 1.52wt%, 1.53wt%, 1.54wt%, 1.55wt%, 1.56wt%, 1.57wt%, 1.58wt%, 1.59wt% or 1.60wt%.

[0035] The content of Si is 1.5-1.8wt%. Specifically, the content of Si is 1.50wt%, 1.51wt%, 1.52wt%, 1.53wt%, 1.54wt%, 1.55wt%, 1.56wt%, 1.57wt%, 1.58wt%, 1.59wt%, 1.60wt%, 1.61wt%, 1.62wt%, 1.63wt%, 1.64wt%, 1.65wt%, 1.66wt%, 1.67wt%, 1.68wt%, 1.69wt%, 1.70wt%, 1.71wt%, 1.72wt%, 1.73wt%, 1.74wt%, 1.75wt%, 1.76wt%, 1.77wt%, 1.78wt%, 1.79wt% or 1.80wt%.

[0036] The Mn content is 0.6-0.8wt%. Specifically, the Mn content is 0.60wt%, 0.61wt%, 0.62wt%, 0.63wt%, 0.64wt%, 0.65wt%, 0.66wt%, 0.67wt%, 0.68wt%, 0.69wt%, 0.70wt%, 0.71wt%, 0.72wt%, 0.73wt%, 0.74wt%, 0.75wt%, 0.76wt%, 0.77wt%, 0.78wt%, 0.79wt% or 0.80wt%.

[0037] The content of Mo is 2.0-3.0 wt %, specifically, the content of Mo is 2.2-2.7 wt %. The introduction of high Mo reduces the Ms temperature, promotes bainite transformation, and expands the bainite transformation zone.

[0038] The Ni content is 3.0-4.0 wt %, specifically 3.2-3.8 wt %. The introduction of Ni facilitates solid solution of austenite, expands the austenite region, shifts the upper C curve to the right, and improves hardenability. The total Mo and Ni content of the present application reaches the 5% range for medium alloy steel, causing the upper C curve to shift to the right while the lower C curve shifts to the right slowly, which is beneficial for bainite transformation.

[0039] The Nb content is 0.04-0.06wt%, specifically, the Nb content is 0.041wt%, 0.042wt%, 0.043wt%, 0.044wt%, 0.045wt%, 0.046wt%, 0.047wt%, 0.048wt%, 0.049wt%, 0.050wt%, 0.051wt%, 0.052wt%, 0.053wt%, 0.054wt%, 0.055wt%, 0.056wt%, 0.057wt%, 0.058wt%, 0.059wt% or 0.060wt%. The introduction of Nb can inhibit carbon diffusion, and the combined addition of Nb and Mo promotes bainite transformation.

[0040] Furthermore, the present application also provides a method for preparing a ductile steel cylinder liner, comprising the following steps:

[0041] A) Q235 steel scrap and carburizer are mixed according to the composition ratio, the obtained mixture is sequentially smelted, placed at high temperature, subjected to furnace composition inspection and refining, the refined molten steel is spheroidized and inoculated, and slag is skimmed;

[0042] B) preparing a ductile steel cylinder liner blank by casting using a water-cooled metal mold centrifugal casting process, and processing the blank;

[0043] C) austempering the semi-finished cylinder liner obtained in step B), and then tempering the semi-finished cylinder liner to obtain a ductile steel cylinder liner.

[0044] In the preparation process of ductile iron cylinder liners, this application first mixes Q235 scrap steel and a recarburizer according to a composition ratio, then sequentially smelts the resulting mixture, places it at high temperature, inspects its composition before use, and refines it. The refined molten steel is then spheroidized and inoculated, followed by slag removal. The smelting, high temperature standing, inspection of its composition before use, refining, spheroidization and inoculation, and slag removal are all well-known techniques to those skilled in the art and are not specifically limited in this application. For example, the refining can be performed in an LF furnace, and the spheroidization and inoculation are performed using wire-feed spheroidization.

[0045] The present application then casts the melt obtained above, specifically adopting a water-cooled metal mold centrifugal casting process to prepare a ductile steel cylinder liner blank; the casting temperature is 1500~1600℃, the casting machine speed is 1300~1500r / min, the mold preheating temperature is 250℃~350℃, the coating is wet coating, the thickness is 0.5~1mm, and the casting demolding temperature is 800℃~850℃. More specifically, the casting temperature is 1500~1560℃, the casting machine speed is 1320~1450r / min, the mold preheating temperature is 280℃~320℃, the thickness is 0.5~0.8mm, and the casting demolding temperature is 810℃~840℃.

[0046] After casting, the obtained blank is processed, specifically machining, to form a semi-formed cylinder liner. The machining is a processing method well known to those skilled in the art, and this application does not impose any special restrictions on this.

[0047] Finally, the semi-finished cylinder liner is austempered and then tempered to obtain a ductile steel cylinder liner. The austempering temperature is 850-950°C, the cooling medium is nitrate at a temperature of 250-350°C, the cooling time is 2-3 hours, and the tempering temperature is 200-250°C. Specifically, the austempering temperature is 890-910°C to austenitize the semi-finished cylinder liner. The liner is then quenched in a nitrate bath at 290-310°C and held for 2-3 hours. The tempering temperature is 220-240°C.

[0048] In the preparation process of ductile steel cylinder liners, steel refining and ductile iron wire feeding methods are combined before casting, and centrifugal casting is used to produce ductile steel. The matrix is ​​strengthened by austempering, and a ductile steel cylinder liner with a metallographic structure of spheroidal graphite and a bainite matrix is ​​obtained. The tensile strength reaches more than 1200 MPa and the hardness is greater than 38 HRC. That is, the ductile steel cylinder liner provided in this application has excellent tensile strength and wear resistance.

[0049] In order to further understand the present invention, the ductile steel cylinder liner and the preparation method thereof provided by the present invention are described in detail below in conjunction with the embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0050] Example 1

[0051] A ductile steel cylinder liner produced by centrifugal casting, the chemical composition of which is shown in Table 1 in terms of weight percentage;

[0052] Table 1 Composition data of ductile steel cylinder liner

[0053]

[0054] The production method of the ductile steel cylinder liner produced by centrifugal casting comprises the following steps:

[0055] 1) Batching and smelting: Q235 scrap steel + carburizer are batched, and then smelted in a medium frequency induction furnace, placed at high temperature, and the composition of the furnace is tested. The qualified high-temperature molten iron enters the LF furnace for refining. The refined molten steel undergoes wire feeding, spheroidization, and inoculation treatment. The molten steel is then skimmed.

[0056] 2) Casting: The cylinder liner blank is produced using a water-cooled metal mold centrifugal casting process, with a casting temperature of 1520°C, a pouring machine speed of 1350 r / min, a mold preheating temperature of 290°C, a coating of ordinary wet coating with a thickness of 0.8mm, a blank weight of 15 kg, a maximum wall thickness of 16 mm, and a controlled ejection temperature of the casting of 820°C;

[0057] 3) After demoulding, the casting is cooled to room temperature in air, and the casting blank is directly processed into a semi-finished cylinder liner;

[0058] 4) The cylinder liner is austenitized at 900℃, 3 minutes per millimeter, quenched to 310℃ nitrate bath and kept isothermal for 2 hours, and then tempered at 220℃ after being taken out of the furnace. After tempering, it is processed into finished product.

[0059] The metallographic structure of the wear surface of the finished cylinder liner is spherical graphite + bainite, with a hardness of 39.5HRC, a tensile strength of 1280MPa, and an elastic modulus of 172GPa.

[0060] Example 2

[0061] A ductile steel cylinder liner produced by centrifugal casting, the chemical composition of which is shown in Table 2 in terms of weight percentage;

[0062] Table 2 Composition data of ductile steel cylinder liner

[0063]

[0064] The production method of the ductile steel cylinder liner produced by centrifugal casting comprises the following steps:

[0065] 1) Batching and smelting: Q235 scrap steel + carburizer are batched, and then smelted in a medium frequency induction furnace, placed at high temperature, and the composition of the furnace is tested. The qualified high-temperature molten iron enters the LF furnace for refining. The refined molten steel undergoes wire feeding, spheroidization, and inoculation treatment. The molten steel is then skimmed.

[0066] 2) Casting: The cylinder liner blank is produced by water-cooled metal mold centrifugal casting process, with a casting temperature of 1540℃, a pouring machine speed of 1400r / min, a mold preheating temperature of 300℃, a coating of ordinary wet coating with a thickness of 0.1mm, a blank weight of 14.92Kg, a maximum wall thickness of 16mm, and a controlled casting ejection temperature of 850℃;

[0067] 3) After demoulding, the casting is cooled to room temperature in air, and the casting blank is directly processed into a semi-finished cylinder liner;

[0068] 4) The cylinder liner is austenitized at 910℃, 3 minutes per mm, quenched to 290℃ in a nitrate bath and kept isothermal for 2 hours, and then tempered at 220℃ after being taken out of the furnace. After tempering, it is processed into a finished product.

[0069] The metallographic structure of the wear surface of the finished cylinder liner is spherical graphite + bainite, with a hardness of 41HRC, a tensile strength of 1300MPa, and an elastic modulus of 174GPa.

[0070] Figure 1 This is a metallographic photograph of the ductile steel cylinder liner prepared in this embodiment, magnified 100 times. Figure 2 This is a metallographic photograph of the matrix structure of the ductile steel after austempering prepared in this embodiment, magnified 500 times; Figure 1 and Figure 2 It can be seen that the metallographic structure of the ductile steel cylinder liner prepared in this embodiment is spherical graphite and bainite.

[0071] Comparative Example 1

[0072] The preparation method is the same as that of Example 1, except that step 4) is omitted. The metallographic photograph of the blank is as follows: Figure 3 shown by Figure 3 It can be seen that a large amount of spherical graphite is used in the cast blank.

[0073] Comparative Example 2

[0074] The preparation method is the same as that of Example 1, except that: Step 4) is specifically: annealing the cylinder liner at 860° C. for 4 h, furnace cooling to 200° C., and air cooling.

[0075] The finished cylinder liner has a hardness of 170 HBW, a tensile strength of 536 MPa, and an elastic modulus of 184 GPa. Figure 4 and Figure 5 The metallographic photographs of the matrix structure of the ductile steel cylinder liner prepared in this comparative example are magnified 100 times and 500 times, respectively. It can be seen from the figures that the matrix metallographic structure of the ductile steel cylinder liner is ferrite.

[0076] Comparative Example 3

[0077] The preparation method is the same as that of Example 1, except that: Step 4) is specifically: the cylinder liner is kept at 880° C. for 2 hours and air-cooled.

[0078] The finished cylinder liner has a hardness of 280 HBW, a tensile strength of 967 MPa, and an elastic modulus of 192 GPa. Figure 6 and Figure 7The metallographic photographs of the matrix structure of the ductile steel cylinder liner prepared in this comparative example are magnified 100 times and 500 times respectively. It can be seen from the figures that the matrix metallographic structure of the ductile steel cylinder liner is pearlite + ferrite.

[0079] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0080] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A ductile steel cylinder liner, comprising, by mass percentage: The metallographic structure of the ductile steel cylinder liner is spherical graphite and bainite matrix; The semi-finished ductile steel cylinder liner is austempered and then tempered to obtain a ductile steel cylinder liner; the austempering temperature is 850-950°C, the cooling medium for the austempering is nitrate with a temperature of 250-350°C, the cooling time is 2-3h, and the tempering temperature is 200-250°C.

2. The ductile steel cylinder liner according to claim 1, characterized in that: The content of Mo is 2.2-2.7 wt%.

3. The ductile steel cylinder liner according to claim 1, characterized in that: The Ni content is 3.2-3.8 wt%.

4. The ductile steel cylinder liner according to claim 1, characterized in that: The content of Nb is 0.042-0.055 wt%.

5. The ductile steel cylinder liner according to claim 1, characterized in that: The C content is 1.45-1.55 wt%.

6. The ductile steel cylinder liner according to claim 1, characterized in that: The Si content is 1.55-1.78 wt%.

7. The ductile steel cylinder liner according to claim 1, characterized in that: The content of Mn is 0.65-0.78 wt%.

8. The method for preparing the ductile steel cylinder liner according to claim 1, comprising the following steps: A) Q235 steel scrap and carburizer are mixed according to the composition ratio, the obtained mixture is melted, placed at high temperature, furnace composition tested and refined, the refined molten steel is spheroidized and inoculated, and then slag is skimmed; B) preparing a ductile steel cylinder liner blank by casting using a water-cooled metal mold centrifugal casting process, and processing the blank; C) austempering the semi-finished cylinder liner obtained in step B), and then tempering the semi-finished cylinder liner to obtain a ductile steel cylinder liner; The temperature of the austempering is 850-950°C, the cooling medium of the austempering is nitrate with a temperature of 250-350°C, the cooling time is 2-3h, and the temperature of the tempering is 200-250°C.

9. The preparation method according to claim 8, characterized in that The casting temperature of the water-cooled metal mold centrifugal casting process is 1500-1600°C, the pouring machine speed is 1300-1500r / min, the mold preheating temperature is 250-350°C, the coating is wet coating with a thickness of 0.5-1mm, and the casting demolding temperature is 800-850°C.

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