JPH044374B2 - - Google Patents

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 heat resistance because they must slide together with piston rings and maintain airtightness. For this purpose, conventional cylinder liners use A-type graphite.
Special iron castings containing wear-resistance-enhancing elements such as Cr, B, P, V, Mo, and Nb have been exclusively used. 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. In order to improve the strength, it is possible to select a liner material with high strength, but there is a risk that the abrasion resistance and seizure resistance, which are originally necessary characteristics of cylinder liners, may be impaired, so there is a practical limit. There is. It is also effective to increase the thickness of the liner, but this goes against the goal of reducing weight. By the way, when we analyze the usage conditions and causes of damage to cylinder liners, we find that () parts that require wear resistance and seizure resistance are:
Only the contact portion with the piston ring, that is, the inner surface of the liner. () Damage to the cylinder liner starts from its outer surface. It is known that Focusing on this point, the present invention aims to particularly improve the toughness of the outer layer material by applying an unprecedented composite technology to the cylinder liner and subjecting it to a specific heat treatment that has never been seen before. be. Here, regarding toughening by compounding, this application has previously proposed in Japanese Patent Application No. 134050/1982, and the present invention is characterized by applying a new heat treatment technology to that invention. , the gist of the present invention is as follows: C 2.8-4.0%, Ni 2.5% or less, Si 1.5-3.5%, Cr 0.8% or less Mn 0.2-1.0%, Mo 0.6% or less, P 0.3% or less, Mg 0.03-0.1%. A composite cylinder liner is created by welding and bonding the outer layer, which contains each weight percent with the balance Fe and normal impurities, to the inner layer, which is made of a special cast iron material that has excellent wear resistance and seizure resistance. 0.2 to 800 to 860℃ temperature
After holding for 20 hours, the outer layer is cooled at a cooling rate of 100 to 1000°C/hour, and then held at a temperature of 500 to 630°C for 2 to 30 hours to form a two-phase mixture of spherical graphite and ferrite/pearlite. The structure is based on bases, and as a result, the overall strength is further improved compared to the patent application No. 134050 of 1983 without compromising the wear resistance and anti-seizure properties necessary for use. It was extremely successful. The present invention will be explained in detail below. The composite cylinder liner obtained by the method of the present invention 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 b is made of a conventional special cast iron material with excellent seizure resistance and wear resistance, and both are welded together. It is structured as follows. Furthermore, by welding and integrating the outer layer a and the inner layer b,
A welded layer (intermediate layer) a+b having a composition intermediate between the outer layer a and the inner layer b is inevitably formed. That is, by welding the inner layer b to the outer layer a, it is inevitable that the material of the outer layer will melt into the inner layer b to some extent. At this time, if the molten layer a+b causes a problem 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 an intermediate layer c between the inner layer b and the inner layer b. That is, if necessary, the liner structure can be formed into three or more layers. A composite cylinder liner having such a multilayer structure can be easily manufactured by centrifugal casting.
That is, first, after the outer layer is cast, the inner layer material is cast at an appropriate timing, and the two are welded and integrated.
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 spheroidal graphite cast iron material forming the outer layer of the composite cylinder liner of the present invention will be explained. The present invention is characterized by using a material having the following component composition as a liner outer layer material having excellent toughness. That is, the outer layer is C2.8~4.0, Si1.5
~3.5, Mn0.2~1.0, P0.3 or less, S0.04 or less,
Ni2.5 or less, Cr0.8 or less, Mo0.6 or less, Mg0.03~
The structure after the heat treatment of the present invention becomes a spheroidal graphite casting heat mainly composed of spheroidal graphite and a ferrite-pearlite two-phase mixed base. Therefore, the chemical composition of the above-mentioned specific material, the microscopic structure after heat treatment, etc. will be explained in detail below. () Chemical composition C: 2.8 to 4.0% The spheroidal graphite cast iron material of the outer layer consists of spheroidal graphite and a matrix (however, a small amount of cementite crystallization is not a problem), and toughness is particularly important. However, if C is less than 2.8%, castability deteriorates and the amount of cementite crystallized increases, making the material brittle. On the other hand, if C exceeds 4.0%, casting defects are likely to occur. Si: 1.5-3.5% Si has the effect of promoting graphitization, and in the case of this material in which Mg is added as a graphite nodularizing agent,
This is because if it is less than 1.5%, the amount of cementite crystallized increases and becomes brittle. However, if it exceeds 3.5%, the base becomes ferrite and the proof strength deteriorates, and the Si dissolved in the ferrite makes the ferrite brittle. Mn: 0.2 to 1.0% Mn usually combines with S to eliminate the adverse effects of S, and also stabilizes the base pearlite and increases its strength. If Mn is less than 0.2%, this effect cannot be expected, while if it exceeds 1.0%, it will become brittle. P: 0.3% or less P increases the fluidity of the molten metal, but it also creates phosphorus eutectic in the material, making it brittle. This effect increases as the P content increases, but the upper limit is set at 0.3% without causing any actual damage. Note that a lower P content is advantageous in terms of toughness, but in practice it is difficult to reduce the P content to 0.01% or less due to cost considerations. S: 0.04 or less Like P, S is generally understood as an impurity element, and deteriorates the mechanical properties of the material.
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 less Ni has an effective effect on graphitization and strengthening of the matrix, but if it exceeds 2.5%, it is not only disadvantageous in terms of economy, but also damages the quenched structure (bainite, martensite) and untransformed structure. This is because it becomes more likely to occur and does not meet the purpose of the outer layer material. Cr: 0.8% or less Crb not only strengthens the base but also has a large stabilizing effect on cementite. i.e. Cr0.8%
This is because if it exceeds this, cementite will crystallize and become brittle even if C and Si are adjusted, and the purpose of the outer layer material will not be met. Mo: 0.6% or less Mo is effective in strengthening the base, but if the content is increased too much, the effect will become saturated and it is not economical, and it will also have the effect of making the material hard and brittle, so it should be kept at 0.6% or less. Mg: 0.03-0.1% Mg is of course included to make graphite spheroidized, but if it is less than 0.03%, its effect is insufficient, while if it exceeds 0.1%, it may cause the chilling effect of Mg and the casting of dross etc. This is because it is undesirable because defects are likely to occur. The spheroidal graphite cast iron material forming the outer layer of the cylinder niner contains each of the above components, with the balance basically consisting of Fe and normal impurities. Note that the following rare earth elements, Sn and Cu can be added to the spheroidal graphite cast iron material of the outer layer, if necessary, in place of Fe in order to further improve the material properties. Rare earth elements: 0.05% or less If rare earth elements are added in combination with Mg, the sphericity of graphite becomes better. At this point, the added amount saturates its action and effect.
The upper limit is 0.05% by weight. Sn: 0.3% or less Depending on the casting conditions, the above outer layer material may contain too much ferrite in the base, leading to a decrease in yield strength and fatigue strength. In that case, it is effective to add Sn, which has a pearlite stabilizing effect, within a range of 0.3% by weight at which its effect is saturated. Cu: 1.0% or less From the same standpoint as Sn above, it is also effective to add Cu in a range of 1.0% by weight or less. () Inoculation of exterior material Next, we will discuss inoculation of the outer layer material. In general, inoculation is effective for refining the casting structure and promoting 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 appropriate amount of inoculation is 0.05 to 1.0% as Si content. That is, if it is less than 0.05%, no inoculation effect can be expected, and on the other hand, if it exceeds 1.0%, a corresponding effect cannot be obtained. As an inoculant, CaSi,
FeSi is preferred. In addition, Si after inoculation
The content is also adjusted to the above range of 1.5 to 3.5%. 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 before, and there is no special feature. Next, the heat treatment method carried out in the present invention will be explained. FIG. 1 shows a thermal curve of heat treatment according to the present invention. In the figure, A is a temperature of 800 to 860°C. In this temperature range, ferrite and austenite coexist in the high-Si outer layer material, and a ferrite-pearlite two-phase mixed structure is obtained by subsequent cooling. This ferrite-pearlite two-phase mixed structure has excellent toughness, as shown in the examples below. In the present invention, the temperature is limited to this because if it is less than 800°C, the amount of ferrite becomes too large and the toughness is good, but the strength is reduced.
On the other hand, when the temperature exceeds 860°C, the ferrite-austenite coexistence region is exceeded and the material becomes uniform austenite, resulting in a decrease in toughness. Note that the holding time of A depends on the temperature (longer times are better at lower temperatures), but from the standpoint of normal manufacturing operations, 0.2 to 20 hours is appropriate. Next, the cooling rate shown in Figure B is important and changes the transformation state of the austenite portion. If the cooling rate is slow at this time, the precipitated pearlite will become rough and the strength will deteriorate. In addition, this results in a decrease in the hardness of the inner layer material, which requires wear resistance. On the other hand, although a faster cooling rate is better, there is a limit in practical work. For the above reasons, 100 to 1000°C/Hr is appropriate. Note that B does not have a large effect on the toughness of the material. C in the figure only serves to suppress recuperation before moving to temperature D, which will be described next, and the temperature may be lower than temperature D. This is for the purpose of stabilizing the structure and eliminating strain in D in the same figure, and the appropriate temperature is 500 to 630°C, and the appropriate holding time is 2 to 30 hours. Next, examples will be explained. <Example> A, B, and C in Table 1 below were cast under the following casting conditions.
A composite cylinder liner was manufactured. Casting mold inner diameter: 720φ Outer layer casting thickness: 90mm Inner layer casting thickness: 60mm Heat treatment: 840゜×4Hr (temperature raising and holding) 400℃/Hr (cooling) 500℃×10Hr (strain relief, heating and holding) [Next page] ]

[Table] The microscopic structure of No. A cylinder liner is shown in the second table.
- Shown in Figure 5. That is, Figures 2 and 3 are micrographs (magnifications of 100 and 400) of the outer layer material,
Figures 4 and 5 are micrographs (magnified) of the inner layer material.
100 and 400). As observed in the photographs of FIGS. 2 and 3, it can be seen that the matrix structure is a two-phase mixed structure of ferrite and pearlite. Note that a two-phase mixture of ferrite and bainite and a two-phase mixture of ferrite and martensite are also possible, but this leads to an increase in the alloy content and 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 are compared with those not subjected to heat treatment (same as the example of the present invention, same as that of Japanese Patent Application No. 57-134050). show. [Next leaf]

[Table] From Table 2 above, it is clear that even if the chemical components of the outer layer are the same, those that were subjected to the heat treatment of the present invention had significantly improved mechanical strength compared to those that were not subjected to the heat treatment. Moreover, it can be seen that the inner layer is similarly improved by applying the heat treatment of the present invention. As described above, the present 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. Gansho 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 microscopic structure of No. A of the outer layer material of the liner of the present invention (X100), Fig. 3 shows the microscopic structure of the same (X400), and Fig. 4 shows the same structure of the inner layer material of the same. Organization (X100), Figure 5 is the same (X400)
FIGS. 6 and 7 are structural sectional views of the liner of the present invention. a: outer layer, b: inner layer.

Claims (1)

[Claims] 1 C 2.8-4.0% Si 1.5-3.5% Mn 0.2-1.0% P 0.3% or less S 0.04% or less Ni 2.5% or less Cr 0.8% or less Mo 0.6% or less Mg 0.03-0.1% Each weight A composite cylinder liner is created by welding and bonding an outer layer consisting of Fe and normal impurities with the balance being Fe and an inner layer made of a special cast iron material with excellent wear resistance and seizure resistance. 0.2 to 860℃ temperature
After holding for ~20Hr, cool at a cooling rate of 100~1000℃/Hr, then at a temperature of 500~630℃ for 2~30Hr.
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 ferrite/pearlite two-phase mixed base by performing a series of heat treatments to maintain the structure.