JP3297150B2 - Cast iron having excellent corrosion resistance and wear resistance, and a cylinder liner formed from the cast iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast iron having excellent corrosion resistance and wear resistance, and more particularly to a cast iron suitable for a cylinder liner of an internal combustion engine such as a diesel engine equipped with an EGR device, and a cast iron formed from the cast iron. Related to cylinder liners.

[0002]

2. Description of the Related Art Generally, a cylinder liner of an internal combustion engine includes:
A cast iron having good wear resistance, for example, a cast iron having a matrix mainly composed of pearlite and having a structure in which a hard phase composed of a stadite and a boron compound and flaky graphite are dispersed in the matrix is used. This cast iron is usually C. : 2.9 to 3.5%, Si: 1.8
To 2.6%, Mn: 0.5 to 1.0%, P: 0.1 to
0.4%, S: 0.12% or less, Cr: 0.1 to 0.4
%, B: 0.03-0.12%, with the balance being Fe.

[0003] Although this material has good wear resistance, it does not have sufficient corrosion wear resistance. Therefore, when this material is used for a cylinder liner for a diesel engine to which an EGR device is added,
Significant corrosive wear occurs on the inner peripheral surface of the cylinder liner, resulting in insufficient durability. As an attempt to increase the corrosion and wear resistance of a cylinder liner, nitriding is generally performed on the inner peripheral surface of the cylinder liner. In this case, only the corrosion wear resistance of the nitrided layer on the surface is improved, so that corrosion wear after the nitrided layer is worn cannot be prevented.

[0004] Further, improvement of the corrosion resistance of the cast iron material itself (for example, see Japanese Patent Publication No. 4-68373) has been studied. According to this publication, Cu and Ni are added to austenite the cast iron structure to improve sulfuric acid corrosion. However, this cast iron has a disadvantage that its wear resistance is inferior to that of the conventional pearlite structure cast iron.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cast iron having excellent wear resistance and corrosion wear resistance that can be suitably used even in a cylinder liner of a diesel engine to which an EGR device is added.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a cast iron having the following constitution. That is, the present invention is a mass%, C: 2.5 to 3.
6%, Si: 1.4 to 2.6%, Mn: 0.5 to 1.0
%, P: 0.1 to 0.4%, S: 0.12% or less, C
r: 0.1 to 0.4%, B: 0.03 to 0.12%, C
u: 0.2 to 2.0%, Co: 1.0 to 10%,
Having a chemical composition consisting of the balance Fe and unavoidable impurities,
Further, it is characterized by a cast iron having a structure in which a hard phase composed of a steroidite and a boron compound and flaky graphite are dispersed in a matrix composed of pearlite .

Another object of the present invention is to provide a cylinder liner cast using such cast iron as a raw material. Further, the surface of the cylinder liner is subjected to a nitriding treatment to further improve the corrosion and wear resistance. Is provided. The present invention is to manufacture and provide a cylinder liner for a diesel engine to which an EGR device is added or for a diesel engine with a higher load.

[0008]

The function of each component of the cast iron of the present invention and the reasons for limiting the composition will be described below. The present invention is based on the above-described chemical components of cast iron used for cylinder liners of internal combustion engines as basic components, and Cu and Co are added to these components. Cu has a function of dissolving in the matrix to improve its corrosion resistance. In order to produce this effect, it is necessary to add Cu at least 0.2% or more. On the other hand, if Cu exceeds 2%, an ε phase in which Fe forms a solid solution in Cu precipitates and causes a decrease in strength. Further, since the effect of improving corrosion resistance is saturated, the upper limit of the amount of Cu added is set to 2%.

Co, like Cu, forms a solid solution in the matrix,
Although the corrosion resistance is improved, the corrosion wear resistance is further improved by the complex addition with Cu. In order to exhibit this effect, Co needs to be 1% or more. However, Co is 1
If it exceeds 0%, the effect of improving the corrosion resistance decreases and the effect becomes ineffective for the cost, so the upper limit is made 10%. When Mo: 0.2 to 0.5% is added to the present chemical component, scuffing resistance, abrasion resistance and strength are improved.

[0010] The melt of cast iron consisting of the components was poured into a mold, the desired shape, for example, casting the cylinder liner of an internal combustion engine, the matrix pearlite structure the cooling rate at this time is cooled by the cooling medium speed to, and allowed to disperse and <br/> hard substance phase and graphite flake consisting steadite boronic compound to the matrix. The amount of the hard substance phase in the range 3 to 14% and the amount of graphite flakes is in the range 8 to 18%.

The cylinder liner cast in this way has excellent wear resistance and good corrosion resistance. If it is necessary to further improve the wear resistance, the sliding surface of the cylinder liner is subjected to nitriding.

[0012]

EXAMPLES Cast iron, steel scrap, Cu and Co were blended, and cast irons having the compositions shown in Table 1 were melted in a high frequency induction furnace. This molten metal was inoculated with ferrosilicon, and a round bar having a diameter of 30 mm was produced by sand casting. The mechanical properties of the cast irons of the examples were in the following ranges.

Tensile strength: 28-32 kg / mm ² The metal structure of the cast iron in the examples is generally 1% or less of free ferrite, and the pearlite matrix contains 6 hard phases mainly composed of steadite and boron compounds. %, Size 4
This was a structure in which A-type graphite of -6 was dispersed by 90%. Next, reciprocating wear test specimens were produced from cast iron round bars having the various compositions described above. Two types of reciprocating abrasion test specimens were prepared, one which was further subjected to nitriding treatment and the other which was not treated. The conditions of the nitriding treatment are as follows: nitriding method, gas nitriding treatment, temperature: 590 ° C., and time: 30 minutes. By the above nitriding treatment, a nitride layer of a compound layer (thickness 7 μm) and a nitrogen diffusion layer (thickness 100 μm) having a hardness of HV870 was formed on the sliding surface.

As a sliding partner of these reciprocating wear test specimens, a hard Cr-plated steel was used.

[0015]

[Table 1]

A reciprocating abrasion test was performed with the above-described sliding pair under a corrosive environment shown in Table 2 to evaluate the corrosive wear characteristics of the cast iron material. FIG. 1 schematically shows the arrangement and structure of a test piece and a mating material of a reciprocating wear tester. In the drawing, reference numeral 1 denotes a wear test piece (cast iron) which reciprocates in the direction of the arrow. Reference numeral 2 denotes a mating material, the contact end of which was formed into a spherical shape of R18, and was subjected to Cr plating 3. 4
Is a pipe for supplying lubricating oil, and 5 is a pipe for supplying dilute sulfuric acid.

The wear of the Cr plating was measured by using a shape measuring instrument. The amount of abrasion of the abrasion test piece was similarly measured by the abrasion level difference using a shape measuring instrument.

[0018]

[Table 2]

Table 1 shows the results of the reciprocating wear test in a corrosive environment. According to this, the wear amount of the cast iron material of the example was extremely small as compared with the wear amount of the comparative example, and at the same time, the wear of the mating material was also small. Furthermore, it is shown that the cast iron material of the example subjected to nitriding treatment has a smaller wear amount and less wear of the mating material. The corrosion-resistant wear-resistant cast iron of the present invention can be manufactured by any casting method such as sand casting and centrifugal casting.

[0020]

The cast iron material of the present invention has excellent corrosion and abrasion resistance, so that it can be suitably used as a cylinder liner for a diesel engine to which an EGR device is added.

[Brief description of the drawings]

FIG. 1 is a schematic view of a corrosion and wear test apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wear test piece 2 ... Counterpart material 3 ... Cr plating layer 4 ... Lubricating oil supply pipe 5 ... Dilute sulfuric acid supply pipe

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F16J 10/04 F16J 10/04 (56) References JP-A-60-121254 (JP, A) JP-A-5-86966 (JP, A) JP-A-61-147844 (JP, A) JP-A-2-8344 (JP, A) JP-A-61-281849 (JP, A) JP-A-5-31566 (JP, A) JP-A-61-96058 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 37/00 C22C 37/04 C22C 37/10 C23C 8/26 F16J 10/04

Claims (3)

(57) [Claims] (1) In terms of mass% , C: 2.5 to 3.6%, S
i: 1.4 to 2.6%, Mn: 0.5 to 1.0%, P:
0.1-0.4%, S: 0.12% or less, Cr: 0.1
-0.4%, B: 0.03-0.12%, Cu: 0.2
To 2.0% Co: it includes 1.0 to 10%, has the chemical composition and the balance Fe and unavoidable impurities, and Pala
A cast iron having excellent corrosion resistance and abrasion resistance, characterized in that it has a structure in which a hard phase composed of steroidite and a boron compound and flaky graphite are dispersed in a matrix composed of graphite. 2. A cylinder liner having excellent corrosion resistance and wear resistance, wherein the cylinder liner is formed of the cast iron according to claim 1. 3. The cylinder liner according to claim 2, having a nitrided layer on the surface.