JPH08170144A - Combined cylinder liner - Google Patents

Abstract

PURPOSE: To produce a combined cylinder liner excellent in seizure resistance and wear resistance by integrally constituting a cylinder liner, for use in internal combustion engine, by welding an inner layer made of graphite-crystallized-type high chromium cast iron to an outer layer made of iron and steel excellent in toughness. CONSTITUTION: The cylinder liner, used for internal combustion engine, is constituted by casting, by a centrifugal casting method, an iron and steel material, such as graphite steel and spheroidal graphite cast iron, excellent in toughness as an outer layer 1 and further casting, after the solidification of the outer layer, a cast iron containing, by weight, 2.4-3.4% C, 2.0-3.4% Si, 0.5-1.5% Mn, <0.15% P, <0.08% S, 4.5-10% Ni, 5-10% Cr, and 0.2-1.5% Mo as an inner layer 2. By this procedure, a two layer structure, having a structure in which a part of C is precipitated, by the presence of Si and Ni, in the form of graphite excellent in thermal conductivity and acting as a lubricant and the balance is finely precipitated in the form of chromium carbide increased in strength and hardness and excellent in wear resistance, is formed. Then, stress relief annealing is performed. By this method, the combined cylinder liner excellent in seizure resistance and wear resistance can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tough cylinder liner used in an internal combustion engine.

[0002]

2. Description of the Related Art A cylinder liner used in an internal combustion engine basically requires wear resistance and seizure resistance because a piston ring slides at a high speed. For this reason, as a material for conventional cylinder liners, special cylinder liner materials that have A-type graphite to secure seizure resistance and contain wear resistance improving elements such as Cr, B, P, V, Mo, and Nb are included. Cast iron material is used.

However, with the recent demands for larger size, lighter weight, and lower fuel consumption of internal combustion engines, the conventional materials described above are lacking in strength, and improvement in strength is required. Therefore, a composite cylinder liner has been proposed in which the inner layer made of the wear-resistant cast iron material is formed on the inner surface of the outer layer made of a steel material having toughness, and the strength is improved. As a compound cylinder liner, Japanese Patent Publication No. 3-31545
As disclosed in Japanese Patent Laid-Open Publication No. 2000-242242, there is one in which a special cast iron material is cast on the inner surface of the outer layer made of graphite steel to form the inner layer.
Japanese Patent Publication No. 3-31545 proposes a composite cylinder liner in which the outer layer is made of spheroidal graphite cast iron and the inner layer is made of special cast iron material for cylinder liner having A-type graphite.

[0004]

Since the inner layer of the composite cylinder liner is the portion that slides on the piston ring,
Abrasion resistance and seizure resistance are required, and as described above, a cast iron material for an abrasion resistant liner having A-type graphite is used. This cast iron material is improved in wear resistance by containing a small amount of P, B and the like, but it cannot be said to be sufficient.

The present invention has been made in view of the above problems, and an object thereof is to provide a cylinder liner having seizure resistance and excellent wear resistance.

[0006]

The composite cylinder liner according to the present invention has a chemical composition of% by weight and C: 2.4 to 3.4.
%, Si: 2.0 to 3.4%, Mn: 0.5 to 1.5%,
P: 0.15% or less, S: 0.08% or less, Ni: 4.5 to
10.0%, Cr: 5.0 to 10.0%, Mo: 0.2 to 1.5%,
Remainder: An inner layer made of graphite crystallized high chromium cast iron material having graphite in the structure and composed of Fe and unavoidable impurities, and an outer layer formed of a steel material having toughness are welded and joined. .

[0007]

In the present invention, since the inner layer of the composite cylinder liner is formed of the graphite crystallization type high chromium cast iron material, fine crystallized graphite and chromium carbide coexist in the matrix structure.
Since graphite existing in the inner layer structure plays a role of a lubricant, seizure hardly occurs. Furthermore, since graphite has an oil retaining function, oil spilling is prevented and seizure resistance is improved. Further, since graphite has good thermal conductivity, it helps dissipate frictional heat. Further, since the chromium carbide in the matrix has high hardness, wear resistance is improved. Therefore, the composite cylinder liner of the present invention has excellent wear resistance and seizure resistance due to the combined action of the crystallized graphite and the crystallized chromium carbide.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The composite cylinder liner of the present invention has a structure as shown in FIG. That is, the outer layer 1
Is made of a steel material having toughness, while the inner layer 2 is made of a graphite crystallized high chromium cast iron material having graphite in the structure, and both are bonded and integrated by a casting method.

As the outer layer material, a steel material having excellent toughness is used as in the conventional case. For example, graphite steel, spheroidal graphite cast iron, pseudo spheroidal graphite cast iron, caterpillar graphite cast iron, etc. can be used. In particular, in the present invention, since high chromium cast iron having graphite is used as the inner layer material, if graphite steel is used as the outer layer material, it is difficult to form a layer containing a large amount of carbide at the boundary between the outer layer and the inner layer, and the high chromium content is high. Since the Young's modulus is similar to the high Young's modulus of cast iron materials, stress concentration does not occur during use.

On the other hand, the inner layer material is characterized by having the following chemical composition. That is, the inner layer is% by weight, C: 2.4 to 3.4%, Si: 2.0 to 3.4
%, Mn: 0.5 to 1.5%, P: 0.15% or less, S:
0.08% or less, Ni: 4.5-10.0%, Cr: 5.0-1
It is a graphite crystallization type high chromium cast iron material having 0.0%, Mo: 0.2 to 1.5%, the balance: Fe and unavoidable impurities, and having graphite in the structure.

The reasons for limiting the above chemical composition will be described below. C: 2.4 to 3.4% C combines with Cr to form a chromium carbide, and is crystallized into fine graphite by the graphite-forming elements of Si and Ni described later. However, if it is less than 2.4%, the crystallization of graphite will almost disappear when the chromium carbide decreases, and the desired high chromium cast iron will not be obtained. on the other hand,
When it exceeds 3.4%, in the case of the present invention, Cr: 10% or less is suppressed, so that supersaturated carbon has a high concentration of Si and Ni.
Therefore, a large amount of graphite is formed, and the amount of crystallized graphite becomes excessive, resulting in deterioration in wear resistance. Si: 2.0 to 3.4% Si is necessary for crystallizing graphite in a high chromium material,
If it is less than 2.0%, this effect does not exist, and if it exceeds 3.4%, graphite crystallization becomes excessive and wear resistance deteriorates. Incidentally, Si
For the addition of, it is effective to crystallize graphite that the content of Si before casting is kept lower than the above range of ingredients, inoculation is performed during casting, and the content of the final product is adjusted within the above range. Is. Mn: 0.5 to 1.5% Mn is positively added together with Si for deoxidation of the molten metal. This is because if it is less than 0.5%, this effect is insufficient, and if it exceeds 1.5%, deterioration is remarkable in mechanical properties, particularly in terms of toughness. Ni: 4.5-10.0% Ni is positively contained for the purpose of improving the matrix structure and crystallization of graphite. However, if it is less than 4.5%, no crystallization of graphite is observed, and if it exceeds 10.0%, the amount of crystallized graphite becomes excessive as in the case of Si. Is stable and becomes a problem in terms of resistance to rough skin during use. Cr: 5.0-10.0% Cr combines with C to form chromium carbide, but 5.0
If it is less than%, the amount of carbide is small and the wear resistance is inferior.
This is because if it exceeds 0.0%, it becomes difficult to crystallize graphite in the above Ni and Si component ranges. Mo: 0.2-3.0% Mo increases the quenching and tempering resistance and enters the carbide,
It is effective to increase the hardness of carbides and at the same time improve the resistance to temper softening, but if its content is less than 0.2%, this effect is small, while if it exceeds 3.0%, the tendency to white pig iron becomes strong. This is because crystallization of graphite cannot be obtained.

In the cast iron material of the present invention, in addition to the above alloy components, the balance is substantially formed of Fe. Impurity S
Is inevitably mixed from the raw material, but it is desirable that the content is small because it makes the material brittle, and it is preferable to keep it at 0.08% or less. On the other hand, since P generally makes the material brittle, the smaller the better, the better. However, as a sliding wear resistant material, a P eutectic structure is formed to improve seizure resistance and wear resistance.
It is desirable that the content be 8% or less.

The amount of graphite (flake graphite) crystallized in the inner layer structure is preferably 5 to 20% in area%. 5
If it is less than%, the effect due to crystallization of graphite is reduced and the seizure resistance is deteriorated. If it exceeds 20%, the strength and Young's modulus are lowered, and the rigidity is also lowered. The composite cylinder liner having the multilayer structure of the present invention can be easily manufactured by centrifugal casting. That is, first, the outer layer is cast, then the inner layer material is cast at an appropriate timing, and both are integrated by welding. The centrifugal casting method can be applied to any of horizontal type, inclined type, and vertical type, and is not limited to the centrifugal casting method.
Cylinder liners can also be cast by the ordinary casting method. At that time, it is preferable to inoculate with an inoculum such as Fe-Si to promote graphitization.

The composite cylinder liner of the present invention is
As in the past, usually, a temperature below the austenite range (usually about 400 to 600 ° C) for removing residual stress after casting
Strain relief annealing is performed. When the heat treatment is performed at the austenite temperature or higher (800 to 1000 ° C.), the wear resistance and the toughness can be further improved. Next, specific examples of the composite cylinder liner according to the present invention will be described. (1) First, a composite cylinder liner according to Examples 1 and 2 (outer diameter 600 mmφ, outer layer casting thickness 8) was formed by centrifugal casting.
0 mm, inner layer casting thickness 50 mm) was manufactured. Its chemical composition is as shown in Table 1 below. Further, as the composite cylinder liner according to the conventional example (outer diameter 720 mmφ, outer layer cast thickness 90 mm, inner layer cast thickness 50 mm), the inner layer made of cast iron material for cylinder liner having A-type graphite is used, and its chemical composition Is also shown in Table 1.

[0015]

[Table 1]

(2) Subsequently, for the example and the conventional example,
After maintaining at 900 ° C for 2 hours and air cooling, at 600 ° C for 5 hours
Strain relief annealing was carried out to hold. (3) Plate-shaped test pieces were taken from the inner layers of the example and the conventional example after the heat treatment, and the rotating ring was pressed against the fixed test pieces to measure the specific wear amount. The measurement results are shown in Table 2 below.

Test conditions Rotor ring material: SUJ2 carburizing and quenching (HRC: 60-6)
2) Initial load: 18.0 kgf Sliding speed: 3.4 m / sec Sliding distance: 200 m

[0018]

[Table 2]

(4) From Table 2, the inner layer made of the graphite crystallized high chromium cast iron material of the present invention has a lower specific wear amount on the material surface than the inner layer made of the conventional cast iron material for cylinder liners. It was confirmed that the wear resistance was excellent. Further, in both the example and the conventional example, no seizure was observed during the test.

[0020]

As described above, in the composite cylinder liner of the present invention, since the inner layer is formed of the graphite crystallization type high chromium cast iron material having the specific chemical composition having graphite in the structure, good seizure resistance is obtained. The wear resistance can be improved while having the above. Moreover, since the outer layer is formed of a steel material having toughness, the necessary and sufficient strength can be secured without impairing the wear resistance and seizure resistance that are the original properties of the inner layer.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structural example of a composite cylinder liner according to the present invention.

[Explanation of symbols]

 1 outer layer 2 inner layer

Claims (1)

[Claims] 1. The chemical composition is% by weight, C: 2.4 to 3.4%, Si: 2.0 to 3.4%, Mn: 0.5 to 1.5%, P: 0.15% or less, S: 0.08% or less, Ni: 4.5 to 10.0. %, Cr: 5.0 to 10.0%, Mo: 0.2 to 1.5%, balance: Fe and unavoidable impurities, inner layer formed of graphite crystallized high chromium cast iron material with graphite in the structure, and toughness A composite cylinder liner characterized by being welded and joined to an outer layer formed of a steel material having.