JP6147584B2 - Cylinder liner - Google Patents

Description

  The present invention relates to a cast iron cylinder liner suitable for a cylinder liner of an internal combustion engine, preferably a diesel engine for a marine engine, and more particularly to an increase in strength of the cylinder liner.

A cylinder liner used for an inner peripheral surface of a cylinder of an internal combustion engine plays a role of sliding with a piston ring to maintain airtightness in the cylinder. Therefore, the liner material is required to have excellent sliding characteristics at high temperatures, that is, wear resistance and seizure resistance.
Conventionally, flake graphite cast iron having excellent sliding characteristics has been used for a cylinder liner of a marine engine diesel engine. This flake graphite cast iron is said to be a cast iron that has a hard phase composed of B carbide and steadite dispersed uniformly and is excellent in sliding properties. However, recently, regulations on exhaust gas to internal combustion engines have been strengthened, and in order to achieve complete combustion of fuel, fuel is injected at a high pressure to form a spray so that mixing of fuel and air is promoted. However, the internal pressure of the cylinder tends to increase, and in particular, improvement in seizure resistance is required.

  In response to such a request, for example, Patent Document 1 and Patent Document 2 describe cast iron for cylinder liners having excellent high-temperature wear resistance and seizure resistance. The technology described in Patent Document 1 is, by weight, C: 3.1 to 3.8%, Si: 2.8 to 3.5%, Mn: 1.0 to 1.8%, P: 0.1 to 0.4%, Cr: 0.15 to 0.5%, Cu : 0.5 to 1.5%, Ni: 0.2 to 0.5%, B: 0.02 to 0.06%, and the balance is a technique related to cast iron substantially consisting of Fe. Moreover, the technique described in patent document 2 is weight%, C: 3.1-3.8%, Si: 2.8-3.5%, Mn: 1.0-1.8%, P: 0.1-0.4%, Cr: 0.15-0.5% B: 0.02 to 0.06%, and the balance is a technique related to cast iron substantially consisting of Fe. According to the techniques described in Patent Documents 1 and 2, since the specific components are adjusted, the high-temperature wear resistance and seizure resistance can be improved as compared with the conventional technology.

JP 07-145446 A JP 07-145445 A

Along with the recent demand for higher output of diesel engines, the cylinder liner of marine engine diesel engines, in particular, has excellent sliding characteristics, and is preferably 30 mm or more so that it can withstand high loads. There is a demand for maintaining a high strength with a tensile strength of 250 MPa or more, which is thick and higher than before.
However, in the techniques described in Patent Documents 1 and 2, the Si content may be high, ferrite is likely to precipitate, the resulting strength is low, and there is a problem in application to thick and high strength products. It was. In addition, Patent Documents 1 and 2 do not refer to thick cast iron having high strength, and only show examples of thin cast iron.

  The present invention advantageously solves the problems of the prior art, and is suitable for a large-sized marine engine diesel engine, and preferably has a thickness of 30 mm or more and a high tensile strength: 250 MPa or more, and is inexpensive. An object of the present invention is to provide a marine liner for marine engines made of flake graphite cast iron.

In order to achieve the above-described object, the present inventors first conducted intensive research on various factors that affect the strength improvement of a thick-walled cylinder liner suitable for a large-sized marine engine diesel engine.
As a result, in order to stably produce a cylinder liner having a thickness of 30 mm or more and a high tensile strength: 250 MPa or more, the present inventors need to refine graphite and strengthen the pearlite base. I thought of that.

  Conventionally, a large amount of Mo, Ni, V or the like has been contained in order to finely distribute graphite. This is because Mo refines graphite and strengthens the base by dissolving it in the base. Ni also promotes graphitization and solidifies in ferrite to strengthen the matrix. Furthermore, V combines with carbon to form a carbide, and further finely and uniformly distributes graphite. For these reasons, a large amount of Mo, Ni, and V has been conventionally contained.

  However, these elements are all expensive, and a large amount of these elements is problematic in terms of providing an inexpensive product. Therefore, the present inventors pay attention to Mn, which is relatively inexpensive, strengthens the base by solid solution in the base, and refines the graphite, and aims to contain a large amount of Mn. In order to increase the strength by dispersing an appropriate amount of carbides, the inventors have come to the idea of reducing the Si content that causes the strength reduction as much as possible.

And by further examination by the present inventors, the Si content is less than 2.8% by mass compared to the prior art, and Mn is contained in a large amount of 1.1 to 3.0% by mass, and further, B is contained in an appropriate amount. It has been found that, without containing Mo, Ni, and V, it can be realized at a low price and with a tensile strength of 250 MPa or more even in a thick product of 30 mm or more.
The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.

(1) A cylinder liner made of flake graphite cast iron, wherein the cylinder liner has a thickness of 30 to 350 mm, and the flake graphite cast iron is, by mass%, C: 2.4 to 3.6%, Si: 0.8% More than 2.8%, including Mn: 1.1 to 3.0%, further containing P: 0.01 to 0.6%, B: 0.001 to 0.2%, and further selected from Sn: 0.3% or less, Sb: 0.3% or less Cast iron having a composition comprising one or two of these, the balance consisting of Fe and inevitable impurities, and a structure in which carbide containing steadite is dispersed in an area ratio of 8% or less, and has a tensile strength of 250 MPa or more A cylinder liner for a marine engine characterized by that.

(2) A cylinder liner for a marine engine according to (1), further comprising, in addition to the above composition, S: more than 0.01% and not more than 0.15% by mass.
(3) In (1) or (2), in addition to the above composition, 0.1% to 6.0% in total of one or more selected from Cu, Cr, Mo, and Ni are contained in mass%. A cylinder liner for a marine engine.

(4) In any one of (1) to (3), in addition to the above composition, in addition to the above composition, one or two or more selected from W, V, and Nb are added in 0.01% to 5.0% in total. A cylinder liner for a marine engine characterized by containing .

  According to the present invention, a cylinder liner for a marine engine having a large thickness of 30 to 350 mm and a high tensile strength: 250 MPa or more and suitable for a large marine engine diesel engine can be manufactured at low cost. Has an exceptional effect.

FIG. 3 is an explanatory diagram schematically showing an external shape of a cylinder liner 1. It is a top view which shows the shape of the tension test piece used by the tension test of the Example.

  The cylinder liner for marine engine of the present invention is made of flake graphite cast iron having a cylindrical shape and a thickness of 30 to 350 mm, schematically shown in FIG. The flake graphite cast iron contains, in mass%, C: 2.4 to 3.6%, Si: 0.8% to less than 2.8%, Mn: 1.1 to 3.0%, P: 0.01 to 0.6%, B: 0.001 to 0.2% Or one or more selected from Cu, Cr, Mo and Ni in a total of 0.1 to 6.0% and / or one selected from W, V and Nb Or 2 or more types in total 0.01 to 5.0%, and / or Sn: 0.3% or less, Sb: 0.3% or less, and / or S: more than 0.01% 0.15% The following are selected and contained, and have a composition composed of the balance Fe and inevitable impurities.

  The cylinder liner for a marine engine of the present invention is a cylinder liner having a wall thickness of 30 to 350 mm. When the wall thickness exceeds 350 mm, the above composition decreases the strength, and it becomes impossible to ensure a high strength of a desired tensile strength of 250 MPa or more. On the other hand, if the wall thickness is less than 30 mm, with the above composition, the amount of carbide increases, and the graphite shape becomes uneven, the strength decreases, and the desired high strength cannot be ensured. For these reasons, the cylinder liner for marine engines of the present invention has a wall thickness limited to a range of 30 to 350 mm.

First, the reasons for limiting the composition of flake graphite cast iron will be described. Hereinafter, unless otherwise specified, mass% is simply expressed as%.
C: 2.4-3.6%
C is an element having an important function of improving the self-lubricity by crystallization of graphite while increasing the strength of the base (cast iron) using pearlite as the base structure. In order to acquire such an effect, it is necessary to contain 2.4% or more. On the other hand, an excessive content exceeding 3.6% significantly increases the crystallization of graphite and causes a significant decrease in strength, making it impossible to secure a desired high strength. For this reason, C was limited to the range of 2.4 to 3.6%. In addition, Preferably it is 2.6 to 3.4%.

Si: 0.8% or more and less than 2.8%
Si is one of the basic elements of cast iron and is an essential element for crystallization of graphite and needs to be contained at 0.8% or more. On the other hand, when it contains excessively as 2.8% or more, intensity | strength will fall and it will become impossible to ensure desired high intensity | strength. For this reason, Si was limited to the range of 0.8% or more and less than 2.8%. From the viewpoint of preventing ferritization, the content is preferably in the range of 0.8 to 2.4%.

Mn: 1.1-3.0%
Mn is an element that has the effect of refining graphite and strengthening pearlite, which is a base structure. Further, Mn combines with S to form MnS, improving workability, particularly machinability. In order to ensure such an effect, a content of 1.1% or more is required. On the other hand, if the content exceeds 3.0%, graphite crystallization is hindered and the self-lubricating property is lowered. For this reason, Mn was limited to the range of 1.1 to 3.0%.

P: 0.01-0.6%
P crystallizes steadite, increases the hardness of cast iron, and improves wear resistance. In order to acquire such an effect, it is desirable to contain 0.01% or more. On the other hand, if the content exceeds 0.6%, a large amount of steadite is formed, and the partner aggression is increased, and the toughness and workability are reduced. For this reason, P was limited to the range of 0.01 to 0.6%. In addition, from the viewpoint of workability, it is preferably 0.01 to 0.4%.

B: 0.001-0.2%
B forms carbides, increases the hardness of cast iron, and improves wear resistance. In order to acquire such an effect, it is desirable to contain 0.001% or more. On the other hand, if the content exceeds 0.2%, the amount of carbide increases, the toughness decreases and the opponent aggression increases. For this reason, when it contained, B was limited to 0.001 to 0.2% of range. In addition, Preferably it is 0.001 to 0.06%.

  In the present invention, in addition to this basic composition, S: more than 0.01% and 0.15% or less and / or 1 selected from Cu, Cr, Mo, Ni A total of 0.1 to 6.0% of species or two or more species, and / or a total of 0.01 to 5.0% and / or Sn: 0.3% of one or more species selected from W, V, and Nb Hereinafter, one or two selected from Sb: 0.3% or less can be selected and contained.

S: more than 0.01% and not more than 0.15% S is an element that combines with Mn to form MnS and contributes to improved machinability, and is preferably contained as necessary. In order to acquire such an effect, it is desirable to contain more than 0.01%. On the other hand, if the content exceeds 0.15%, the yield of Mn decreases, and the desired strength cannot be ensured. For this reason, when it contains as a selection element, it is preferable to limit to the range of more than 0.01% and 0.15% or less. Even when not added, S is contained in the cast iron as an inevitable impurity in an amount of 0.001 to 0.01%.

One or more selected from Cu, Cr, Mo, Ni: 0.1-6.0% in total
Cu, Cr, Mo, and Ni are all elements that increase the hardness of cast iron. If necessary, one or more elements can be selected and contained in a total amount of 0.1 to 6.0%. If one or more selected from Cu, Cr, Mo, and Ni is less than 0.1% in total, the above-described effects cannot be expected. On the other hand, if it is contained in a large amount exceeding 6.0%, it is an expensive element and causes a rise in material cost. For this reason, when contained, it is preferable to limit one or more selected from Cu, Cr, Mo, and Ni to a total range of 0.1 to 6.0%.

  Cu dissolves in the base and strengthens the base, increasing the hardness of the cast iron and improving the corrosion resistance. In order to ensure such an effect, it is desirable to contain 0.1% or more. On the other hand, if the content exceeds 2.0%, the material cost will rise, which is economically disadvantageous. For this reason, when it contains, it is preferable to limit Cu to 2.0% or less within the range of the total amount mentioned above. In addition, 0.1 to 1.5% is more preferable.

Cr strengthens the base by densifying the base and increases the hardness of the cast iron. In order to ensure such an effect, it is desirable to contain 0.1% or more. On the other hand, if the content exceeds 1.5%, the amount of carbide increases and the strength increases, but the workability and toughness are reduced. For this reason, when contained, Cr is preferably limited to 1.5% or less within the range of the total amount described above.
Mo dissolves in the base to strengthen the base and increase the hardness of the cast iron. In order to ensure such an effect, it is desirable to contain 0.1% or more. On the other hand, if the content exceeds 1.5%, whitening occurs and toughness decreases. For this reason, when it contains, it is preferable to limit Mo to 1.5% or less within the range of the total amount described above. In addition, More preferably, it is 1.0% or less.

  Ni strengthens the base by strengthening the base, promotes graphitization, and improves heat resistance. In order to ensure such an effect, it is desirable to contain 0.1% or more. On the other hand, if the content exceeds 1.5%, the effect is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, when Ni is contained, Ni is preferably limited to 1.5% or less within the above-mentioned total amount range.

One or more selected from W, V and Nb: 0.01 to 5.0% in total
W, V, and Nb are all elements that form carbides and improve wear resistance. If necessary, one or more elements can be selected and contained in a total range of 0.01 to 5.0%. . If the total of one or more selected from W, V, and Nb is less than 0.01%, the above-described effects cannot be expected. On the other hand, if the content is more than 5.0%, a large amount of carbide is formed, the workability is lowered, and the opponent aggression is increased. For this reason, when it is contained, it is preferable to limit one or more selected from W, V, and Nb to a range of 0.01 to 5.0% in total.

W forms carbides and improves wear resistance. In order to acquire such an effect, it is desirable to contain 0.1% or more. On the other hand, if it contains more than 1.0%, the processability decreases and the opponent aggression increases. For this reason, when it contains, it is preferable to make W into 0.1 to 1.0% within the range of the total amount mentioned above.
V forms carbides and improves wear resistance. In order to acquire such an effect, it is desirable to contain 0.1% or more. On the other hand, if it contains more than 3.0%, the processability decreases and the opponent aggression increases. For this reason, when it contains, it is preferable to set V as 0.1 to 3.0% within the range of the total amount mentioned above.

  Nb forms carbides and improves wear resistance. In order to acquire such an effect, it is desirable to contain 0.1% or more. On the other hand, if it contains more than 1.0%, the processability decreases and the opponent aggression increases. For this reason, when it contains, it is preferable to make Nb into 0.1 to 1.0% within the range of the total amount mentioned above.

One or two selected from Sn: 0.3% or less, Sb: 0.3% or less
Both Sn and Sb are elements that promote the formation of pearlite at the base, and can contain one or two as necessary.
Sn is an element that prevents precipitation of ferrite and promotes the formation of pearlite at the base. In order to acquire such an effect, it is desirable to contain 0.01% or more. On the other hand, even if it is contained in a large amount exceeding 0.3%, the effect is saturated and an effect corresponding to the content cannot be expected, which is economically disadvantageous. For this reason, when it contains, it is preferable to limit Sn to 0.3% or less. In addition, More preferably, it is 0.01 to 0.1%.

Sb is an element that prevents precipitation of ferrite and promotes the formation of pearlite at the base. In order to acquire such an effect, it is desirable to contain 0.01% or more. On the other hand, when it contains more than 0.3%, a carbide | carbonized_material will be formed and it will cause toughness fall. For this reason, when it contains, it is preferable to limit Sb to 0.3% or less. In addition, More preferably, it is 0.01 to 0.1%.
The balance other than the components described above consists of Fe and inevitable impurities.

The cylinder liner for a marine engine of the present invention is made of flake graphite cast iron having the above-described composition, and has a structure in which flake graphite is dispersed in the base and the carbide dispersion is limited to 8% or less in terms of area ratio.
Next, the reason for organization limitation will be described.
The base will be perlite. If the base is other than pearlite, the desired high strength cannot be secured.

  In the present invention, B, W, Nb, and V are contained, and an appropriate amount of carbide is dispersed in the matrix to further increase the strength. If the carbide is dispersed in an area ratio exceeding 8%, the strength is remarkably lowered, and a desired high strength cannot be secured, and the machinability is lowered. For this reason, carbides are limited to 8% or less in terms of area ratio. It is preferably 6% or less from the viewpoint of workability.

The manufacturing method of the cylinder liner having the above composition and structure is not particularly limited, and a molten metal having the above composition is melted by a conventional melting method such as an electric furnace and a cupola, and a sand mold, a self-curing mold, etc. Is cast into a conventional mold to form a casting having a desired shape, and a cylinder liner having a desired size and shape as shown in FIG. 1 is obtained by processing such as cutting.
Hereinafter, based on an Example, this invention is demonstrated further.

Molten metal having the composition shown in Table 1 is melted in an electric furnace, poured into a sand mold having a predetermined liner shape, and a cylindrical shape (outer diameter: 1200 mmφ) schematically shown in FIG. 1 is 30 mm to 350 mm thick. A cylinder liner was used.
From the obtained cylinder liner, a specimen for tissue observation was collected, the cross section in the thickness direction was polished, corroded with a corrosive solution: 3% nital, observed with an optical microscope (magnification: 50 times), imaged 33 mm ^The carbide area ratio (%) was measured by image analysis for a photograph of size ² . In addition, polished and corroded specimens for structure observation were observed with an optical microscope (magnification: 200 times), and those that could be confirmed to be 10% or more in area ratio were identified as base structures.

In addition, a tensile test piece (parallel part size: 5.0 mmφ x 7.0 mm distance between gauge points) with the dimensions shown in FIG. Tensile speed (1 mm / min) was carried out to determine tensile properties (tensile strength TS).
The obtained results are shown in Table 2.

Each of the examples of the present invention is a cylinder liner having a high strength of tensile strength: 250 MPa or more even when the thickness is 30 mm or more. On the other hand, the comparative example which is outside the scope of the present invention does not ensure the desired high strength.
Since the comparative examples (cylinder liners No. 33 and No. 34) in which the C content deviates from the range of the present invention are thin, the structure (graphite distribution) is uneven, and the tensile strength is reduced. Further, in the comparative example (cylinder liner No. 29) in which the C content deviates from the scope of the present invention, the crystallization of graphite increases and the tensile strength decreases. Further, in the comparative example (cylinder liner No. 28) in which the Mn content falls outside the scope of the present invention, the base structure is not sufficiently strengthened, and the tensile strength is lowered. Further, in the comparative examples (cylinder liners No. 31 and No. 32), since the liner became thick, the amount of reinforcing element was insufficient and the tensile strength was reduced. In addition, in the comparative examples (cylinder liner No. 35, No. 36) in which the Mn content is outside the range of the present invention, since the liner was thin, the carbide content exceeded 8% and the graphite distribution (structure) was uneven. Thus, the tensile strength is reduced. In addition, in the comparative example (cylinder liner No. 30) in which the C and Mn contents deviate from the scope of the present invention, the tensile strength is lowered because the graphite is often crystallized and the base structure is not sufficiently strengthened. ing. Further, in the comparative example (cylinder liner No. 37), since the liner became thin, the amount of carbide increased by more than 8%, and the tensile strength decreased. Further, in the comparative example (liner No. 38) in which Si is outside the range of the present invention, the graphite distribution is uneven and the tensile strength is lowered. In the comparative example (liner No. 39) in which Si is out of the range of the present invention, the precipitation of ferrite is excessive and the tensile strength is reduced. Further, in the comparative example (liner No. 40) in which P and B are outside the scope of the present invention, the amount of carbide increases, the structure (graphite distribution) becomes nonuniform, and the tensile strength decreases.

1 Cylinder liner

Claims (4)

A cylinder liner made of flake graphite cast iron, and the thickness of the cylinder liner is 30 to 350 mm,
The flake graphite cast iron contains, in mass%, C: 2.4 to 3.6%, Si: 0.8% to less than 2.8%, Mn: 1.1 to 3.0%, P: 0.01 to 0.6%, B: 0.001 to 0.2 In addition, Sn: 0.3% or less, Sb: containing one or two selected from 0.3% or less, the composition comprising the balance Fe and unavoidable impurities, and carbide containing steadite is the area Cylinder liner for marine engines, characterized in that it is cast iron having a structure in which the ratio is 8% or less and has a tensile strength of 250 MPa or more.   The cylinder liner for marine engines according to claim 1, further comprising S: more than 0.01% and not more than 0.15% by mass% in addition to the composition.   In addition to the said composition, 0.1 to 6.0% in total of 1 type, or 2 or more types chosen from Cu, Cr, Mo, and Ni was further contained by the mass%. The cylinder liner for marine engines as described. 4. In addition to the composition, the composition further comprises 0.01 to 5.0% in total of one or more selected from W, V and Nb by mass%. A cylinder liner for marine engines as described in 1 .

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