JPS6029420A - Manufacture of composite cylinder liner having high strength and toughness - Google Patents

Abstract

PURPOSE:To obtain a composite cylinder liner having high strength and toughness by welding and uniting an outside layer consisting of a specifically composed spheroidal graphite cast iron material and an inside layer consisting of a special cast iron material having excellent resistance to seizure and wear thereby constituting said cylinder liner. CONSTITUTION:An outside layer is composed, by weight %, of 2.8-4 C, 1.5- 3.5 Si, 0.2-1 Mn, <0.3 P, <0.04 S, <2.5 Ni, <0.8 Cr, <0.6 Mo, 0.03-1 Mg and the balance Fe and ordinary impurities. An inside layer is formed of a special cast iron material having excellent resistance to wear and seizure. The outside and inside layers are welded and joined to manufacture a composite cylinder liner. After the liner is held for 0.2-20hr at 800-860 deg.C, the liner is cooled at a cooling rate of 100-1,000 deg.C/hr. The outside layer is thus formed of the structure consisting essentially of the spheroidal graphite and the mixed two-phase base of ferrite and pearlite.

Description

[Detailed description of the invention] FIELD OF THE INVENTION The present invention relates to a method of manufacturing a tough cylinder liner.

Cylinder liners used in internal combustion engines must have wear resistance and seizure resistance because they must slide together with piston rings and maintain airtightness. For this purpose, conventional cylinder liner applications include type A graphite.
Special cast iron castings containing wear resistance enhancing elements such as M6 + Wb have been used exclusively.

However, with the recent increase in the size of internal combustion engines and the demand for lighter weight and lower fuel consumption, the above-mentioned conventional materials are insufficient in terms of strength, and there is a strong desire for improvements in strength.

For the purpose of improving strength, it is possible to choose a liner material with high strength, but abrasion resistance is an essential characteristic of cylinder liners.

There is a risk of impairing seizure resistance, and there is a practical limit.

It is also effective to increase the thickness of the liner, but this goes against the goal of reducing weight.

By the way, let's analyze the usage of cylinder liners and the causes of damage.

(1) The only part that requires wear resistance and seizure resistance is the part that contacts the piston ring, that is, the inner surface of the liner.

(It) Damage to the cylinder liner starts from its outer surface.

It is known that

The great invention focuses on this point and aims to improve the toughness of the outer layer material in particular by applying an unprecedented composite technology to the cylinder liner and subjecting it to a specific heat treatment that has never been seen before.

Regarding toughening by compounding, the invention was previously proposed in Japanese Patent Application No. 57-134050, and the great invention is characterized by the application of a new heat treatment technology. , What is the gist of the great invention?

C2, 8~4.0% N1 2.5% or less 81 1.5
~3.591 Or 0.8% or less Mn 0.2-1.
0% MoQ, 696 or less P 0.3% or less Mg 0
．． A composite cylinder liner is created by welding and joining an outer layer consisting of 03 to 0.1% by weight with the remainder νe and normal impurities, and an inner layer made of a special cast iron material with excellent wear resistance and seizure resistance. , and raise the temperature to 800-860°C by 0.2-2. OHr
After holding, the outer layer is cooled at a cooling rate of 100 to 1000°C 1/Hr, and then subjected to a series of heat treatments of holding at a temperature of 500 to 630°C for 2 to 3 QHr, thereby forming the outer layer into a two-phase mixture of spherical graphite and ferrite/pearlite. The structure is mainly composed of bases, and as a result, it does not impair the wear resistance and anti-seizure properties required as a whole.
We have succeeded in further improving the strength compared to 134050.

The present invention will be explained in detail below.

The composite cylinder liner obtained by the method of the present invention is
It has a structure as shown in FIG.

That is, the outer layer a is made of a spheroidal graphite cast iron material with excellent toughness, which will be detailed later, while the inner layer is made of a conventional special cast iron material with excellent seizure resistance and wear resistance.
The two are integrally welded together.

By welding and integrating the outer layer a and the inner layer.

A welded layer (intermediate layer) a+b having a composition intermediate between the outer layer a and the inner layer a+b is inevitably formed between the outer layer a and the inner layer. That is, by welding the inner layer to the outer layer, some degree of welding of the outer layer material into the inner layer cannot be avoided.

At this time, if the welding layer a causes problems depending on the purpose of use, prepare a separate intermediate layer material in advance as shown in Fig. This can also be achieved by interposing layer C. That is, if necessary, U/ + m ・M+J −a l
-11,M! M+y! d J-27L i -
'nkiru.

A composite cylinder liner having such a multilayer structure can be easily manufactured by centrifugal casting.

That is, after first casting the outer layer, the inner layer material is cast at an appropriate timing and the two are welded together.

For products with three or more layers, each layer may be similarly cast in order from the outer layer at appropriate timing.

Note that the centrifugal force casting method can be applied to any of the horizontal type, inclined type, and vertical type.

Next, the material of spheroidal graphite cast iron forming the outer layer of the composite cylinder liner of the invention will be explained.

The major invention is characterized by using a liner outer layer material with excellent toughness having the following component composition. That is, the outer layer has C2.8-4.0, 811.5-3.
5, Mn0.2-1.0, PC1.3 or less,
80.04 or less, lil 2.5 or less, Oro, 8
Below, Mo0.6 or less 1Mg0103~0.1 in weight%
The structure after the heat treatment of the great invention consists mainly of spherical graphite and a two-phase mixed base of ferrite and pearlite. The chemical components, microscopic structure after heat treatment, etc. are detailed below.

(1) Chemical composition C: 2.8-4.0% The outer layer's spheroidal graphite cast iron material consists of 1 spheroidal graphite and a matrix (
However, a small amount of cementite crystallization is not a problem), and toughness is particularly important. However, if the C2 content is less than 8%, the castability will deteriorate and the amount of cementite crystallized will increase, making the material brittle, while if it exceeds 4.0%, casting defects will occur and the product will become a prize.

Si: 1.5-3.5% 81 has the effect of promoting graphitization, and in the case of this material in which Mg is added as a graphite nodularizing agent, if it is less than 1.5%, the amount of cementite crystallization increases, This is because it becomes brittle. However, if it exceeds 3.5%, the base becomes ferrite and the yield strength deteriorates, and the sl dissolved into the ferrite makes the ferrite brittle.

Mn: 0.2 to 1.0% Mn usually combines with 1 to remove the adverse effects of 8, and also stabilizes the base pearlite and increases its strength.

If Mn is less than 0.2%, this effect cannot be expected;
．． If it exceeds 0%, it becomes brittle.

P: 0.3% or less P increases the fluidity of the molten metal, but it also generates phosphorus in the material, making the material brittle. This effect increases as the P content increases, but the upper limit is set at 0.3% as a range that does not cause any actual damage. Note that a lower P content is more advantageous in terms of toughness, but in practice it is difficult to reduce the P content to 0.1% or less due to cost considerations.

8: 0.04% or less S, like P, is generally understood as an impurity element and degrades mechanical properties. Also, since it has the effect of inhibiting the spheroidization of graphite, it should be kept at 0.04% or less.

Ni: 2.5% or lessN1 acts effectively on graphitization and strengthening the base, but 2.5% or less
If it exceeds %, it is not only disadvantageous in terms of economic efficiency, but also
This is because hardened structures (bainite, martensite) and untransformed structures are likely to occur, and the outer layer material no longer meets the purpose.

Cr: 0.8% or less Or has a strong effect of strengthening the base and stabilizing the cementite. That is, if Cr exceeds 0.8%.

This is because even if the outer layer material is adjusted to 0.0 or 81, the cementite crystallizes and becomes brittle, which does not meet the purpose of the outer layer material.

Mo: 0.6% or less MO is effective in strengthening the base, but increasing its content too much saturates the effect and is not economical.
Since it also has the effect of making it brittle, it should be kept at 0.6% or less.

Mg: 0.03 to 0.1% Mg is of course included to make graphite spheroidal, but if it is less than 0.03%, the effect is insufficient, while if it is less than 0.1%, the effect is insufficient.
This is because if it exceeds %, it is undesirable because the chilling effect of Mg and casting defects such as dross are likely to occur.

The spheroidal graphite cast iron material forming the outer layer of the cylinder liner contains one or more of each component, and basically consists of residual Fe and normal impurities.

Incidentally, in order to further improve the material properties of the spheroidal graphite cast iron material of the outer layer, a primary rare earth element -1an and Cu can be added, if necessary, instead of Fe.

Rare earth element: 0.05% or less If a rare earth element is added in combination with Mg, the spheroidization of graphite becomes better. At this time, the upper limit of the amount added is 0.05% by weight, at which the effect is saturated.

8n: 0.3% or less Depending on the casting conditions of the above outer layer material, excessive ferrite may be present in the matrix, resulting in a decrease in yield strength and fatigue strength. In that case, 8, which has a pearlite stabilizing effect,
It is effective to add n within a range of 0.3% by weight at which its effect is saturated.

Cu: 1.0% or less Same as 8n above, 9. It is also effective to add Cu in a range of 1.0% by weight or less.

(10 Inoculation of outer layer material Next, we will discuss the inoculation of the outer layer material. in general.

Inoculation is effective for refining the casting structure and assisting in graphitization. If the inoculation technique is applied to the outer layer material, a material in which graphite is more finely and uniformly distributed can be obtained. At this time, the inoculation amount is 0.05-1.81 minutes.
0% is appropriate. Namely.

If it is less than 0.05%, no vaccination effect can be expected;
This is because even if it exceeds %, a corresponding effect cannot be obtained.

%Cadi, FeB1 are suitable as inoculants. Note that the 81 content after inoculation is still the same as in 1. above.
It is adjusted to a range of 5 to 3.596.

Although the material of the outer layer has been described in detail above, the material of the inner layer of the liner, which requires wear resistance and seizure resistance, may be made of a special cast iron material as usual.

There are no special features.

Next, the heat treatment method carried out in the wood invention will be explained.

FIG. 1 shows a thermal curve of heat treatment according to the wood invention. In the same figure, the temperature is 800 to 860°C. In this temperature range, the outer layer material with a height of 81
Austenite coexists, and a ferrite-pearlite two-phase mixed structure is obtained by subsequent cooling. This ferrite-pearlite two-phase mixed structure has excellent toughness and is typical as shown in Examples below. In the invention, the temperature is limited to this range, but if the temperature is less than 800°C, the amount of ferrite is too large and the toughness is good, but the strength is lowered.

On the other hand, when the temperature exceeds 860°C, the ferrite-austenite coexistence region is exceeded and the steel becomes uniform austenite, resulting in a decrease in toughness. Note that (the holding time of jll depends on the temperature (in the case of low temperature, a long time is good)) 1. From the viewpoint of normal manufacturing work, continuous light is 0.2 to 2 Q Hr.

Next, as shown in the same figure, the cooling rate is important and changes the transformation status of the austenite part.If the cooling rate is slow at this time, the precipitated pearlite will become coarse.

Strength deteriorates. In addition, this results in a decrease in the hardness of the inner layer material, which requires wear resistance. On the other hand, the faster the cooling rate, the better;
There are limits to actual work. For the above reasons, 100~1O
OO'11;/I(r is appropriate. Note that (B) does not have a large effect on the toughness of the material.

(Q in the same figure will be explained next) (It only means to suppress recuperation before shifting to the effective temperature, and it is sufficient to be below the effective temperature. (D) in the same figure is for the purpose of stabilizing the structure and removing distortion. The appropriate temperature is 500 to 630°C, and the appropriate holding time is 2 to 3011 r.

Next, examples will be given and explained.

<Example> Composite cylinder liners A, B, and C in Table 1 below were manufactured under the following casting conditions.

Casting mold inner diameter near 20φ Outer layer casting thickness: 90m Inner layer casting thickness: 60 Cod heat treatment = 840°
/Hr (cooling) 500°C x 10Hr (distortion relief, heating holding: [Next page]! Figures 2 to 5 show the microscopic structure of the cylinder liner of A. That is, Figures 2 and 3 show the details of the outer layer material. These are micrographs (magnifications of 100 and 400).

Figures 4 and 5 are micrographs of the inner layer material (magnification: 10
0 and 400).

As observed in the photographs of FIGS. 2 and 3 above.

It can be seen that the base structure is a two-phase mixed structure of ferrite and pearlite. In addition, ferrite/bainite 2
Phase mixing, ferrite/martensite two-phase mixing is also possible, but it requires an increase in the content of one alloy.

This leads to an increase in the cooling rate, which is disadvantageous in terms of cost.

The mechanical properties of a composite cylinder liner subjected to the heat treatment of the present invention and one without heat treatment (same as the example of the present invention, same as that of Japanese Patent Application No. 57-1'34050) are shown below. show.

[Next page] *Comparative example 550°C x 15 hours: Strain relief heat treatment From Table 2 above, even if the chemical components of the outer layer were the same, the heat treatment of the present invention was performed.

It is clear that the mechanical strength was significantly improved compared to that without the heat treatment, and it was also found that the inner layer was similarly improved by applying the heat treatment of the present invention.

As mentioned above, the great invention uses a specific outer layer material.

For the inner layer, we created a composite cylinder liner using a conventional special cast iron material with excellent seizure resistance and wear resistance that matches the usage characteristics, and by applying a specific heat treatment to this material, we achieved the characteristics proposed earlier. Compared to the one made in Application No. 57-'134050, it has achieved even higher strength and toughness.

[Brief explanation of drawings]

Fig. 1 shows the thermal curve of heat treatment according to the present invention, Fig. 2 shows the outer layer material i of the liner of the present invention;
The figure shows the same (X 400') structure, Figure 4 shows the same structure (X 100'J) of the same inner layer material, and Figure 5 shows the same (X 400'J) structure.
) organization. 6 and 7 are structural cross-sectional views of the liner of the present invention. a: Outer layer, b: Inner layer Fig. 1 □ Dark area Hr Fig. 2 Fig. 3 η Ri Noka Fig. 4 Fig. 5 Fig. 6 Fig. 7

Claims (1)

[Claims] LC2.8-4.0% 81 1.5-3.596 Mn 0.2-1.0% P 0.3% or less 8 0.04% or less Ni 2.5% or less Cr 0. An outer layer containing up to 8% MoO, up to 6% MgO, and 03 to 0.1% by weight, with the balance consisting of FeJ and normal impurities, and an inner layer made of a special cast iron material with excellent wear resistance and seizure resistance. A composite cylinder liner is created by welding and joining, and this is heated to a temperature of 800 to 860°C for 0.2 to 20 hours.
After image retention, it is cooled at a cooling rate of 100 to 1000°C/Hr and then cooled at a temperature of 500 to 630°C for 2 to 30 Hr.
A method for manufacturing a composite cylinder liner with high toughness, characterized in that the outer layer has a structure mainly composed of spherical graphite and a two-phase mixed matrix of ferrite and pearlite by performing a series of image-retaining heat treatments.