阅读说明：本技术 铸铁件、含有铸铁件的复合部件以及铸铁件的制造方法 (Iron casting, composite part comprising an iron casting, and method for producing an iron casting ) 是由 佐藤阳 畠山公一 大泉贵志 其他发明人请求不公开姓名 于 2019-03-29 设计创作，主要内容包括：本发明提供一种铸铁件,其目的在于改善对于EGR系统中发生的由硫酸等酸导致的腐蚀的耐腐蚀性。所述铸铁件含有2.9质量％～3.7质量％碳、1.8质量％～2.8质量％硅、0.5质量％～1.0质量％锰、0.05质量％～0.4质量％磷、0.12质量％以下硫、以及0.5质量％～3.0质量％铜,所述铸铁件含有A型石墨、且总石墨中A型石墨所占的比率在65％以下,从而利用该铸铁件能够实现上述目的。(The present invention provides an iron casting, which aims to improve corrosion resistance to corrosion caused by sulfuric acid and other acids occurring in an EGR system. The iron casting contains 2.9-3.7 mass% of carbon, 1.8-2.8 mass% of silicon, 0.5-1.0 mass% of manganese, 0.05-0.4 mass% of phosphorus, less than 0.12 mass% of sulfur and 0.5-3.0 mass% of copper, and contains A-type graphite, and the proportion of the A-type graphite in the total graphite is less than 65%, so that the purpose can be achieved by using the iron casting.)

1. An iron casting comprising 2.9 to 3.7 mass% of carbon, 1.8 to 2.8 mass% of silicon, 0.5 to 1.0 mass% of manganese, 0.05 to 0.4 mass% of phosphorus, 0.12 mass% or less of sulfur, and 0.5 to 3.0 mass% of copper,

the iron casting contains A-type graphite, and the proportion of the A-type graphite in the total graphite is less than 65%.

2. The iron casting of claim 1,

ferrite phases and cementite phases are alternately precipitated to constitute a pearlite phase, and the lamellar spacing of the pearlite phase is 0.5 to 2.5 [ mu ] m.

3. The iron casting according to claim 1 or 2,

the carbon equivalent C.E value of the iron casting is more than 2.6 and less than 3.8.

4. A composite part comprising the iron casting according to any one of claims 1 to 3 and a piston having a piston ring whose outer peripheral surface slides on the inner wall of the iron casting,

the outer peripheral surface of the piston ring is covered with a coating film selected from PVD and DLC.

5. A method for manufacturing iron castings comprises the following steps: an injection step of injecting a cast iron material into a mold, and a cooling step of cooling the cast iron material injected into the mold to obtain an iron casting,

the iron casting contains a type a graphite,

the temperature of the cast iron material injected in the injection step is adjusted, and the temperature of the mold and/or the cooling rate in the cooling step is/are adjusted so that the ratio of the a-type graphite in the total graphite becomes 65% or less.

Technical Field

The present invention relates to an iron casting having improved corrosion resistance suitable for a cylinder liner of an internal combustion engine and a method for manufacturing the same.

Background

In order to reduce the concentration of NOx in the exhaust gas from an internal combustion engine according to environmental requirements, an EGR system may be employed. Since the EGR gas of the EGR system contains sulfur components in the fuel, the condensed water of the EGR gas contains sulfuric acid, and corrosion of the inner wall of the cast iron cylinder liner may be caused.

A technique of reducing the distance between the ferrite phase and the cementite phase in the pearlite phase in order to cope with the corrosion caused by the EGR gas is disclosed (see patent documents 1 and 2).

On the other hand, since the cylinder liner slides at a high speed in the internal combustion engine, abrasion resistance is required not only to wear resistance but also to abrasion resistance that does not cause scratches due to sliding of the piston ring. Therefore, a cast iron containing a-type graphite is disclosed as a cast iron used for a cylinder liner having improved wear resistance and scuff resistance (see patent documents 3 and 4).

Disclosure of Invention

Problems to be solved by the invention

The present invention addresses the problem of providing an iron casting having improved corrosion resistance to corrosion caused by an acid such as sulfuric acid occurring in an EGR system.

Means for solving the problems

The present inventors have made extensive studies to solve the above problems and found that corrosion resistance can be improved by containing a fixed amount of copper in an iron casting and then reducing the ratio of a-type graphite, thereby completing the present invention.

The invention relates to an iron casting containing 2.9-3.7 mass% of carbon, 1.8-2.8 mass% of silicon, 0.5-1.0 mass% of manganese, 0.05-0.4 mass% of phosphorus, less than 0.12 mass% of sulfur, and 0.5-3.0 mass% of copper,

the iron casting comprises A-type graphite, and the proportion of the A-type graphite in the total graphite is less than 65%.

In the iron casting, the ferrite phase and the cementite are alternately precipitated to form a pearlite phase, and the lamella spacing (lamellar spacing) of the pearlite phase is preferably 0.5 μm or more and 2.5 μm or less, and the carbon equivalent C.E value is preferably 2.6 or more and 3.8 or less.

The present invention also relates, as another aspect, to a composite member including the above-described iron casting and a piston including a piston ring whose outer peripheral surface slides on an inner wall of the iron casting,

the outer peripheral surface of the piston ring is covered with a coating film selected from PVD and DLC.

The present invention also relates to a method for producing an iron casting, which includes a pouring step of pouring a cast iron material into a mold, and a cooling step of cooling the cast iron material poured into the mold to obtain an iron casting,

the iron casting contains a type a graphite,

the temperature of the cast iron material injected in the injection step is adjusted, and the temperature of the mold and/or the cooling rate in the cooling step is/are adjusted so that the ratio of the a-type graphite in the total graphite is 65% or less.

Effects of the invention

According to the present invention, there can be provided an iron casting which is less corroded by an acid and is excellent in corrosion resistance.

Drawings

FIG. 1 is a graph showing the results of the corrosion test in examples 1 to 4 and comparative example 1.

Detailed Description

One embodiment of the present invention is an iron casting containing 2.9 to 3.7 mass% of carbon, 1.8 to 2.8 mass% of silicon, 0.5 to 1.0 mass% of manganese, 0.05 to 0.4 mass% of phosphorus, 0.12 mass% or less of sulfur, and 0.5 to 3.0 mass% of copper. The iron casting contains A-type graphite, and the proportion of A-type graphite in the total graphite is 65% or less. The iron casting of the present embodiment may contain elements other than those described above, such as boron, chromium, nickel, molybdenum, and the like. When boron is contained, the content thereof may be 0.03 to 0.08% by mass, and the wear resistance can be improved by containing boron.

The iron casting in this embodiment contains a fixed amount of copper to improve corrosion resistance. Further, the iron casting contains copper and also contains a-type graphite, and the ratio of the a-type graphite in the total graphite is 65% or less, whereby the corrosion resistance to acid can be improved.

The iron casting of the present embodiment can improve the corrosion resistance to acid by containing a fixed amount of copper, and the content thereof is usually 0.5 mass% or more, may be 0.6 mass% or more, may be 0.8 mass% or more, and may be 1.0 mass% or more. In addition, the content is usually 3.0 mass% or less, may be 2.5 mass% or less, and may be 2.0 mass% or less.

In the case of an iron casting containing a type a graphite, the graphite in the iron casting is present in a non-directional, disorderly and uniformly distributed manner. In the present embodiment, the ratio of the a-type graphite in the total graphite is set to 65% or less, and corrosion resistance against corrosion by acid can be improved. The ratio of the a-type graphite in the total graphite may be 60% or less, 55% or less, 50% or less, 45% or less, or 40% or less. The lower limit is not limited, and may be more than 0%, 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, and 30% or more. In addition, when the ratio of a-type graphite is too high, ferrite precipitates, and thus corrosion resistance is lowered. Therefore, in the present embodiment, ferrite is preferably not precipitated.

In addition, when the proportion of the a-type graphite in the total graphite is too small, the wear resistance tends to be insufficient. Therefore, when the total graphite content of the iron casting is relatively low, it is preferable that the film covering the outer peripheral surface of the piston ring slidable on the inner wall of the iron casting be covered with a film having excellent wear resistance and low attack by other substances, such as PVD and DLC.

The iron casting may contain graphite other than A-type graphite, for example, B-type graphite, D-type graphite, and E-type graphite in fixed amounts, but generally the proportion of E-type graphite is large. The content of E-type graphite is usually 50% or less, but may be 40% or less, or may be 30% or less. The content of other graphite is usually not more than 30%, may not more than 20%, and may not more than 10%.

In the iron casting, the value of carbon equivalent C.E is usually not more than 3.8, but may be not more than 3.6, but may be not more than 3.5, and usually not less than 2.6, but may be not less than 3.2.

The carbon equivalent C.E is represented by (carbon amount + silicon amount/3.2), and the smaller the value, the more likely it is to be a hard and brittle iron casting.

The iron casting has pearlite as a lamellar structure of ferrite and cementite, and the lamellar spacing of the pearlite is usually 0.5 μm or more, but may be 0.7 μm or more, and is usually 2.5 μm or less, or may be 2.3 μm or less, or may be 2.0 μm or less, or may be 1.0 μm or less. By setting the above range, the corrosion resistance is improved.

The ratio of the a-type graphite in the total graphite can be determined by visual inspection. Specifically, the ratio (area ratio) of a-type graphite was measured based on astm a 247. The determination of the ratio of type a graphite is preferably carried out by a person skilled in the art and is preferably carried out at a plurality of places in the iron casting, for example at 2 or more, preferably at 4 or more, and the average value thereof is calculated.

Further, the lamellar spacing of pearlite was calculated by observing a plurality of places in the iron casting through a metal microscope and calculating the average lamellar spacing in the range of 20 μm. With regard to the lamella spacing, it is preferred that the measurement is carried out at a plurality of places in the iron casting, for example at 2 or more, preferably at 4 or more, and the average value thereof is calculated.

In the present embodiment, setting the ratio of the a-type graphite in the total graphite within the above range can be achieved by adjusting the temperature of the mold into which the cast iron material (melt) is injected; adjusting the temperature of the injected melt; adjusting a cooling rate of a cast iron material injected into a mold during a manufacturing process of the iron casting; adjusting the thickness of a mold agent layer coated on the mold; an element that inhibits graphitization and an element that promotes graphitization are introduced into a cast iron material.

Further, the lamellar spacing of pearlite can be achieved by adjusting the temperature of the mold into which the cast iron material is injected; accelerating the cooling rate of the cast iron material injected into the mold during the manufacturing process of the iron casting; the Cu content in the cast iron material is adjusted.

Hereinafter, a method for manufacturing a cast iron article according to the present embodiment will be described.

Another embodiment of the present invention is a method for manufacturing an iron casting, including an injection step of injecting a cast iron material into a mold, and a cooling step of cooling the cast iron material injected into the mold to obtain the iron casting,

in the method for manufacturing the iron casting, the iron casting contains A-type graphite, and the injection step and/or the cooling step are/is adjusted so that the proportion of the A-type graphite in the total graphite is 65% or less. The specific method for making the ratio of a-type graphite 65% or less in the injecting step and/or the cooling step is as described above.

The iron castings are generally manufactured by centrifugal casting, but may be manufactured by gravity casting.

In the injection step, a mold for forming an iron casting is prepared, and the molten cast iron material (melt) is injected into the mold. In this case, the temperature of the mold is usually 250 ℃ to 300 ℃ and preferably 260 ℃ to 290 ℃. The injected melt is a substance satisfying the composition of the cast iron material. The temperature of the melt injected into the mold is not particularly limited and may be appropriately set, but the cooling rate in the cooling step may be adjusted by the temperature of the melt.

The casting mold is internally coated with a casting coating containing a refractory, a binder, water, a surfactant, and the like. The thickness of the casting paint layer is not particularly limited and may be appropriately set, but the cooling rate in the cooling step may be adjusted by the thickness of the casting paint layer.

In the cooling process, the cast iron material injected into the mold is cooled, thereby obtaining an iron casting. In this case, the cooling temperature rate of the cast iron material is not particularly limited, and may be adjusted by an air cooling system or by adjusting an air conditioner. In addition, the cooling speed of the cast iron material can be adjusted by adjusting the type of the casting coating and the thickness of the casting coating layer.

The obtained iron casting is obtained by taking it out of the casting mould and removing the layer of cast coating on the surface from the iron casting by means of sand blasting.

In the iron casting of the present embodiment, the corrosion resistance against corrosion by acid is improved by setting the ratio of the a-type graphite to 65% or less of the total graphite, while the wear resistance may be insufficient by setting the ratio of the a-type graphite to a relatively low value. Therefore, when the cylinder liner is used in an engine together with a piston, it is preferable that a film covering the outer peripheral surface of a piston ring slidable on the inner wall of the iron casting is covered with a film having excellent wear resistance and low attack by other substances, such as PVD and DLC.

That is, another aspect of the present invention is a composite part including the above-described iron casting and a piston including a piston ring having an outer peripheral surface sliding on an inner wall of the iron casting, wherein the outer peripheral surface of the piston ring is covered with a film selected from PVD and DLC.

The coating film for covering the piston ring selected from PVD and DLC is more preferably DLC.