JP5757755B2 - Cast iron and cylinder liner manufactured by the cast iron - Google Patents

Description

  The present invention relates to cast iron suitable for use as a cylinder liner of an internal combustion engine, and a cylinder liner manufactured using the cast iron.

  Cylinder liners of internal combustion engines need to be slidably inserted and held while maintaining airtightness of pistons and piston rings that reciprocate at high speed. It is desirable to be able to slide well without causing any wear, and to prevent the piston and the piston ring from being worn or the like without violently attacking the piston and the piston ring over a long period of time.

For this reason, various improvements have been made in the past, and various types of alloy cast iron having a structure in which graphite and carbide are dispersed in a predetermined manner have been proposed, but are excellent in scuff resistance and wear resistance. As cast iron, for example, flake graphite cast iron (grey cast iron) as shown in FIG. 7 is often employed.
In addition, Patent Document 1, Patent Document 2, and Patent Document 3 describe examples of improving the cylinder liner material.

Japanese Patent Laid-Open No. 05-214482 JP 2006-206986 A JP 2008-106357 A

  Here, it is an important subject to purify the exhaust from the internal combustion engine to suppress the expansion of air pollution. As one of the systems (apparatus) for this purpose, a part of the exhaust from the internal combustion engine is removed from the combustion chamber A so-called EGR (Exhaust Gas Recirculation) system for reducing the concentration of nitrogen oxides (hereinafter referred to as NOx) (exhaust amount) in the exhaust gas by lowering the combustion temperature by recirculation and re-combustion. It has been adopted.

  In such an EGR system, since EGR gas is recirculated to the combustion chamber, the EGR gas may be expanded and cooled in the combustion chamber during an intake stroke or the like, and condensed water may be generated from the EGR gas.

  In recent years, in order to reduce the NOx emission amount even more effectively, the EGR gas amount is increased by cooling the EGR gas to be recirculated into the combustion chamber by using an EGR cooler or the like. Condensed water is more likely to be generated from EGR gas, and there is a high possibility that EGR gas condensed water will adhere to the combustion chamber wall (particularly, the inner wall of the cylinder liner having a low temperature).

  Here, since the EGR gas contains sulfur in the fuel, the condensed water contains sulfuric acid. Therefore, if the condensed water containing sulfuric acid adheres to or stays on the inner wall of the combustion chamber of the internal combustion engine, etc. There is a risk of causing corrosion or damage to the cylinder liner made of cast iron or the like.

  In such a use environment, the cylinder liner is required to have corrosion resistance, but the flake graphite cast iron (gray cast iron), which is a cylinder liner material with excellent lubricating properties and excellent wear resistance, has been improved. As a cast iron material aimed at improving corrosion resistance, there is a cast iron material as described in Patent Document 2.

  The cast iron material described in Patent Document 2 is a cast iron material having a structure in which a steadite phase of a hard phase and a flake graphite phase are dispersed in a matrix structure called a pearlite phase. .

  However, the cast iron material described in Patent Document 2 may have good wear resistance and corrosion resistance when used for a cylinder liner material of an internal combustion engine that does not perform EGR, but has an EGR system. When used as a cylinder liner material for an internal combustion engine, the corrosion resistance is not sufficient, and there is a high possibility that corrosion wear occurs on the inner peripheral surface of the cylinder liner and the durability is lowered.

  In addition, as a method for improving such corrosion wear, for example, surface treatment such as nitriding treatment is performed on the inner peripheral surface of the cylinder liner, but in the case of such surface treatment, However, there is a situation that only the corrosion resistance is improved in the nitride layer on the surface, and it is not an effective countermeasure against corrosion and wear after the nitride layer is worn.

  The present invention has been made in view of such a situation, and has a simple and low-cost configuration, and has excellent scuff resistance and wear resistance, and is suitable for a cylinder liner material excellent in corrosion resistance, and the cast iron. An object of the present invention is to provide a cylinder liner made of cast iron.

Therefore, the cast iron according to the present invention is
% By mass
C: 3.1-3.6%
Si: 1.8 to 2.3%
Mn: 0.5 to 0.9%
P: 0.2 to 0.4%
S: 0.15% or less
Cu: 1.0 to 3.0%
And having the remainder as Fe and inevitable impurities, and adding Sn to the chemical composition,
The pearlite is a base phase consisting path Raito, a hard phase containing steadite, which has a flake graphite phases, were dispersed to a predetermined tissue,
In the pearlite phase, the precipitation interval between the ferrite phase and the cementite phase is 0.5 μm or less on average .

  In the present invention, the precipitation ratio of the cementite phase of the ferrite phase and the cementite phase precipitated in a layered manner in the pearlite phase may be 70% or more.

  A cylinder liner for an internal combustion engine according to the present invention is manufactured by the cast iron according to the present invention.

  According to the present invention, it is possible to provide a cast iron suitable for a cylinder liner material that is excellent in wear resistance and excellent in corrosion resistance while having a simple and low-cost configuration, and a cylinder liner manufactured using the cast iron. .

FIG. 2 is a structure diagram of a pearlite phase in flake graphite cast iron according to an embodiment of the present invention, the right side is a structure part (conventional structure) deposited with sparse lamella spacing, and the left side is deposited with lamella spacing dense It is the made tissue part (tissue which concerns on this invention). It is the perspective view (photograph after the corrosion by an acid) which looked at the structure | tissue chart which image | photographed the pearlite phase of FIG. FIG. 3 is a cross-sectional view taken along a direction (a straight line portion in FIG. 2) in which the ferrite phase and the cementite phase in the pearlite phase according to the present embodiment are substantially orthogonal to each other, and is a view for explaining a lamellar interval L; . It is a figure which shows the corrosion wear test result which shows the relationship between the precipitation space | interval (lamellar space | interval) L of the ferrite phase and cementite phase in the pearlite phase which concerns on this Embodiment, and the corrosion wear amount (wear depth) by an acid. It is sectional drawing which took the cross section along the direction (straight part of FIG. 2) of the ferrite phase and cementite phase in the pearlite phase which concerns on this Embodiment, Comprising: About the increase in the lamellar space | interval and the precipitation rate of a cementite phase It is a figure for demonstrating. The ratio of precipitation of cementite phase (cementite phase width / lamellar spacing) of ferrite phase and cementite phase precipitated in layers in the pearlite phase according to the present embodiment, and the amount of corrosion wear due to acid (wear depth) It is a figure which shows the corrosion wear experiment result which shows a relationship. It is an organization chart showing an example of conventional flake graphite cast iron (gray cast iron).

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. The present invention is not limited to the embodiments described below.

  As a result of various examinations and experiments based on flake graphite cast iron (gray cast iron), which is a cylinder liner material with excellent lubrication characteristics and excellent wear resistance, the present inventors have achieved wear resistance. We have found a cast iron material that is excellent in corrosion resistance as well as excellent.

  That is, in the prior art so far, as described in Patent Document 1 to Patent Document 3 and the like, dispersion of a steadite phase or flake graphite (for example, A-type flake graphite) phase with respect to the base structure of the pearlite phase. Alternatively, attention has been paid to the method of precipitation (see FIG. 7 and the like), and the properties of cast iron materials have been improved or improved by the dispersion or the method of precipitation. Assuming that there is a limit to the compatibility between wear resistance and corrosion resistance, and as a result of various experimental studies, both the wear resistance and corrosion resistance must be achieved at a high level by the following methods. I came to find a cast iron that can be used.

  The present inventor is based on flake graphite cast iron (gray cast iron), which is a cylinder liner material with excellent lubrication characteristics and excellent wear resistance as cast iron material, while focusing on the pearlite phase that is the base structure An attempt was made to change the precipitation of the ferrite phase and cementite phase constituting the pearlite phase.

  As a result, it was confirmed that the corrosion resistance can be greatly improved by narrowing (reducing) the precipitation interval (lamellar spacing) of the ferrite phase and the cementite phase constituting the pearlite phase. .

  FIG. 1 shows a structure diagram of the pearlite phase according to the present embodiment. In FIG. 1, the right side is a tissue portion (conventional tissue) deposited with sparse lamella spacing, and the left side in FIG. 1 is a tissue portion (tissue according to the present invention) deposited with lamella spacing dense.

  Further, FIG. 2 is a perspective view (photo after corrosion by acid) of the structure chart obtained by photographing the pearlite phase of FIG.

  As shown in FIGS. 1 and 2, reducing the precipitation interval (lamellar interval) between the ferrite phase 20 </ b> A and the cementite phase 20 </ b> B constituting the pearlite phase 20 means that the pearlite phase 20 is fine. By including elements such as Cu (copper) and Sn (tin), which are chemical elements, during casting, it can be achieved relatively easily by controlling the solidification rate and the like.

Specifically, in mass%,
C: 3.1-3.6%
Si: 1.8 to 2.3%
Mn: 0.5 to 0.9%
P: 0.2 to 0.4%
S: 0.15% or less Cu: 1.0-3.0%
And having a chemical composition in which the balance is Fe and inevitable impurities,
While having a structure in which a hard phase containing steadite and a flake graphite phase are dispersed in a predetermined manner in a pearlite phase that is a base phase mainly composed of pearlite,
In the pearlite phase, the precipitation interval (lamellar interval) between the ferrite phase and the cementite phase is narrowed to a predetermined value.
Note that Sn (tin), which is a pearlite phase refinement element, can be included in the chemical composition.

  FIG. 3 shows a cross section of the ferrite phase 20A and the cementite phase 20B constituting the pearlite phase 20 according to the present embodiment taken in a direction substantially orthogonal (see the straight line portion in FIG. 2). As shown in FIG. 4, it was confirmed by a corrosion test that the corrosion level becomes slight by setting the interval (lamellar interval) L to about 0.5 μm or less.

  Ferrite 20A is a solid solution of up to 0.02% carbon (C) in α-iron of body-centered cubic lattice. It is the softest and most ductile in the steel structure. There is a characteristic that it is easily corroded.

  Cementite 20B is a structure of iron carbide (Fe3C iron carbide), and has a characteristic that it is a very hard and brittle structure but hardly corrodes.

  In the cast iron material according to the present embodiment, the precipitation interval (lamellar interval) between the ferrite phase 20A constituting the pearlite phase 20 and the cementite phase 20B (lamellar interval) is narrowed, thereby attacking by condensed water (sulfuric acid) derived from EGR gas. Thus, even if the ferrite phase 20A corrodes to some extent and the surface portion recedes, the adjacent cementite phase 20B does not wear, so oil (lubricating oil) can be held between the cementite phases 20B.

  Therefore, even after the ferrite phase 20A is corroded to some extent by attack with condensed water (sulfuric acid) or the like derived from EGR gas, the oil retaining ability between the cementite phases 20B does not advance the corrosion wear of the ferrite phase 20A beyond a certain level. Corrosivity can be improved.

  Further, in the cast iron material according to the present embodiment, since the corrosion wear of the ferrite phase 20A does not proceed, the cementite phase 20B is firmly supported by the ferrite phase 20A, and thus the cementite phase 20B is prevented from falling off. Therefore, it is possible to realize good lubrication characteristics that hardly cause scuffing and the like, and thus good wear characteristics.

  In addition, the oil (lubricating oil) retaining function between the cementite phases 20B maintains the lubrication characteristics well over a long period of time, which also realizes good lubrication characteristics that are unlikely to cause scuffing and the like, and thus good wear characteristics. be able to.

  Further, the cast iron material according to the present embodiment is based on flake graphite cast iron (grey cast iron), and a steadite phase with respect to the base structure of the pearlite phase 20 (not shown in FIG. 7 because it is finely and widely dispersed) and flakes. The method of dispersing (precipitating) the graphite phase can be equivalent to the conventional method shown in FIG. 7, so that the good lubricating and wear properties of flake graphite cast iron (grey cast iron) are maintained as they are, and the reliability is improved. A high level of sex can also be achieved.

  By the way, as described in the present embodiment, the amount of corrosion wear can be reduced by narrowing the precipitation interval (lamellar interval) L between the ferrite phase 20A and the cementite phase 20B constituting the pearlite phase 20. Furthermore, in the cross section shown in FIG. 5, the amount of corrosion wear can be reduced by increasing the precipitation ratio of the cementite phase 20B among the ferrite phase 20A and the cementite phase 20B constituting the pearlite phase 20. Has been confirmed.

  Specifically, as shown in FIG. 6, by increasing the precipitation ratio of the cementite phase 20B, for example, the cementite phase occupies about 70% or more of the lamellar spacing, so that the corrosion level is slight. It was confirmed by the corrosion test.

  That is, for example, the precipitation interval (lamellar interval) L between the ferrite phase 20A and the cementite phase 20B constituting the pearlite phase 20 is about 0.5 μm or less, and about 70% or more of the lamellar interval L is about 70% of the cementite phase. By making it occupy, the corrosion level can be further reduced.

  By the way, among the ferrite phase 20A and the cementite phase 20B that constitute the pearlite phase 20 and are deposited in a layered manner, increasing the precipitation ratio of the cementite phase is the fact that Cu (copper), Sn (tin), which is the refining element of the pearlite phase 20. ) And the like can be relatively easily achieved by the inclusion of an element such as) during the casting, and management of the solidification rate and the like.

  In this way, the pearlite phase 20 is also formed by increasing the precipitation ratio of the cementite phase, which is the hard phase, of the ferrite phase 20A and the cementite phase 20B that constitute the pearlite phase 20 and precipitate in a layered manner. In the same manner as when the precipitation interval (lamellar interval) L between the ferrite phase 20A and the cementite phase 20B is narrowed, the ferrite phase 20A corrodes to some extent due to attack by condensed water (sulfuric acid) derived from EGR gas, and the surface portion recedes. Even so, since the adjacent cementite phase 20B does not wear, oil (lubricating oil) can be held between the cementite phases 20B.

  Therefore, even after the ferrite phase 20A corrodes to some extent due to attack by condensed water (sulfuric acid) or the like derived from EGR gas, the corrosion wear of the ferrite phase 20A does not progress beyond a certain level due to the oil retaining ability between the cementite phases 20B. Further, the corrosion resistance can be improved.

  In addition, by increasing the precipitation ratio of the cementite phase, which is a hard phase, the cementite phase 20B can be more self-supported by itself, and the corrosion wear of the ferrite phase 20A can be prevented from further progressing. Therefore, the cementite phase 20B is more firmly supported by the ferrite phase 20A, and the fall off of the cementite phase 20B is further suppressed, so that scuffing is less likely to occur. As a result, good wear characteristics can be realized.

  Furthermore, by increasing the precipitation ratio of the cementite phase, which is a hard phase, the oil (lubricating oil) retaining function between the cementite phases 20B maintains the lubrication characteristics better over a long period of time. Therefore, it is possible to realize good lubrication characteristics and good wear characteristics.

  By the way, the cast iron material according to the present embodiment is suitable as a cylinder liner material of an internal combustion engine, but is not limited to this, and is not limited to other uses, and has various purposes and requirements. It can be used for various purposes depending on the situation.

  In addition, the internal combustion engine in which the cylinder liner made of cast iron according to the present embodiment is used is not limited to a diesel combustion engine, and can be an internal combustion engine that uses gasoline or other fuels. Regardless, it can be any mobile / stationary internal combustion engine.

  Furthermore, the cast iron material according to the present embodiment can be used as a cylinder liner material for an external combustion engine.

Further, the cast iron material according to the present embodiment is used as a cylinder material for an air compressor that does not accompany combustion, a reciprocating actuator, a valve device that slidably accommodates a piston-like valve body, and reciprocates in a cylinder. You can also
In this case, when the working fluid is highly corrosive, it is beneficial to use the cast iron material according to the present invention as a cylinder material.

  Moreover, it is not limited to a cylinder shape, The cast iron material which concerns on this Embodiment can be utilized as a member applied to all sliding parts.

  The embodiment according to the present invention described above is merely an example for explaining the present invention, and various modifications can be made without departing from the gist of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can provide a cast iron suitable for a cylinder liner material that is excellent in wear resistance and excellent in corrosion resistance while having a simple and low-cost configuration, and a cylinder liner manufactured using the cast iron. There is industrial applicability.

1 Cast iron 10 Graphite phase 20 Pearlite phase 20A Ferrite phase 20B Cementite phase

Claims (3)

% By mass
C: 3.1-3.6%
Si: 1.8 to 2.3%
Mn: 0.5 to 0.9%
P: 0.2 to 0.4%
S: 0.15% or less
Cu: 1.0 to 3.0%
And having the remainder as Fe and inevitable impurities, and adding Sn to the chemical composition,
The pearlite is a base phase consisting path Raito, a hard phase containing steadite, which has a flake graphite phases, were dispersed to a predetermined tissue,
Cast iron characterized in that, in the pearlite phase, the precipitation interval between the ferrite phase and the cementite phase is 0.5 μm or less on average . 2. The cast iron according to claim 1, wherein a precipitation ratio of the cementite phase of the ferrite phase and the cementite phase precipitated in layers in the pearlite phase is 70% or more. A cylinder liner for an internal combustion engine manufactured by the cast iron according to claim 1 or 2 .