JPS63239342A - Cylinder head for cast iron internal combustion engine and manufacture thereof - Google Patents

Abstract

PURPOSE:To aim at improvements is abrasion resistance and high temperature corrosion resistance, etc., by forming a cylinder head body from cast iron, and forming a specific alloyed cast iron layer in a valve seat part with specified depth, while specifying the structure and hardness of the alloyed cast iron layer. CONSTITUTION:A cylinder head rough section 1 is formed of case iron. And a valve seat part 2 is made up of an alloyed cast iron layer 3 in which one kind or more than two kinds of a metal element higher in a carbide forming trend than Fe are contained at 0.1-10wt% in total, and one side or both of A10.1-3wt% or Si0.1-15wt% are contained at 15wt% in total, over a depth of more than 0.2mm. And, the alloyed cast iron layer 3 is formed with ferrite and/or pearlite of the ground, while residual cementite of 2-15% exists in it, and it is set to a layer of hardness Hv250-400 consisting of such a structure that massive graphite is crystallized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a cast iron cylinder head used in an internal combustion engine such as an automobile diesel engine and a method for manufacturing the same, and in particular a cylinder head with an improved valve seat portion and a method for manufacturing the same. It is related to.

As is well known in the art, the valve seat portion of the cylinder head of an internal combustion engine is required to have excellent wear resistance and heat resistance. Therefore, in cast iron cylinder heads as well, a sintered alloy such as Cr--MO based alloy having excellent wear resistance has been inserted into the valve seat portion. However, when inserted, the contact surface between the insert member and the cylinder head base material becomes a thermal barrier, resulting in poor heat conduction, which causes problems with heat dissipation and cooling from the valve seat surface, especially when the heat load is high. . Further, in such a method using an insert, the insert member must be manufactured and processed separately in advance, which causes a problem that the process becomes complicated.

Therefore, a method has already been proposed in "Industrial Materials" No. 32 to alloy the valve seat part of a cast iron cylinder head with Cr using a high-density energy source such as a laser to improve the high-temperature wear resistance of the valve seat part without using an insert. Volume No. 3 P3
Articles 1 to 39 “Surface treatment by laser” (especially P3
5-36).

Problems to be Solved by the Invention The Qr alloyed layer formed by the laser on the valve seat portion in the previous report was extremely hard, with a hardness of lv 700 to 800, and lv 10 It can be inferred from the description that the structure is composed mainly of Cr carbide by alloying Cr with a high concentration of more than 1.5%.

This type of valve seat is extremely difficult to process because of its high hardness, and even if the valve seat itself has good wear resistance, there is a problem that the valve face of the mating valve will be severely worn out. Therefore, it was not practical as a valve seat for a cylinder head.

Therefore, the present inventors attempted to improve the wear resistance of the valve seat portion of a cast iron cylinder head by alloying using high-density energy such as a laser as shown in the above report, and A cast iron cylinder head that has excellent wear resistance at the same time as well as prevents wear on the mating valve face surface, has excellent heat resistance, excellent workability, and prevents chipping of the valve seat, and its manufacture. A method has been proposed in Japanese Patent Application No. 17183/1983.

The cast iron cylinder head proposed above has a main body made of cast iron, and the surface of the portion corresponding to the valve seat portion is made of Fe.
Metal elements with a higher tendency to form carbides than Cr, M
A total of 0.1 to 10% by weight of one or more of O, etc.
The contained alloyed cast iron layer is formed over a depth of 0.2M or more, and the alloyed cast iron layer has pearlite or pearlite as the base and 2 to
It is characterized by a layer having a hardness Hv of 250 to 400 and consisting of a structure in which 15% of residual cementite exists and massive graphite is crystallized.

In addition, in the method for manufacturing a cast iron cylinder head proposed above, after a cylinder head body is cast using cast iron as a raw material, a metal element having a higher tendency to form carbides than Fe is added to the surface of a portion of the cylinder head body corresponding to the valve seat portion. For example, one or more of CrJ4o, an alloy thereof, or an alloy of one or more of these and iron is placed, and high-density energy such as a laser or TIG arc is irradiated from above to rapidly By melting and rapidly resolidifying, the total concentration of one or more of the metal elements is reduced to 0.
．． The metal element is alloyed with cast iron to form a chilled alloy layer so as to have a concentration of 1 to 10% by weight, and then the chilled alloy layer is placed in a humidity range above the A1 transformation point and below the solidus temperature. Heat treatment is performed by heating and then cooling, and the base is made of pearlite as well.
An alloyed cast iron layer with a hardness lv 250-400 consisting of a structure in which residual cementite exists and massive graphite crystallizes. It is characterized by being formed over a depth greater than or equal to the depth.

In the cast iron cylinder head proposed above, by making the valve seat part an alloyed cast iron layer with the structure described above, it has excellent wear resistance and at the same time is less aggressive against the valve face surface as a mating material. It can be made smaller, has better workability, and is also advantageous in terms of toughness. In other words, the pearlite base structure itself is more advantageous in terms of wear resistance than the ferrite base structure, and the presence of residual cementite in the base structure significantly improves the wear resistance. . Furthermore, the alloyed cast iron layer of the valve seat part contains metal elements such as Cr and Mo that have a high tendency to form carbides, thereby strengthening and stabilizing the cementite 1~ that constitutes the residual cementite and pearlite in the structure. The wear resistance and heat resistance are significantly improved compared to the case without these additives.

However, after repeated experiments and studies by the present inventors, it was found that although the cast iron cylinder head proposed above has the above-mentioned excellent characteristics, it has new problems. In other words, in the cylinder head proposed above, since the carbide-forming elements are alloyed, the valve seat part is significantly chilled during the alloying process, and as a result, bead cracking is likely to occur due to solidification shrinkage, resulting in a high rejection rate. There is a problem of lower yield.

In addition, since the amount of cementite in the alloy layer after alloying treatment is large and the cementite is strengthened, it is necessary to decompose the cementite during heat treatment after alloying treatment to obtain the required amount of residual cementite. It takes a considerable amount of time, and therefore, there is a problem that the heat treatment time becomes long and the productivity decreases.

Generally speaking, the cast iron cylinder head proposed above is still insufficient in terms of high temperature oxidation resistance and high temperature corrosion resistance of the valve seat portion, and further improvement is desired.

The present invention was made against the background of the above-mentioned circumstances, and is a further improvement of the above-mentioned proposal to achieve performance equivalent to or close to that of the cast iron cylinder block proposed above in terms of wear resistance of the valve seat portion and attack resistance. To provide a cast iron cylinder head and a method for manufacturing the same which prevent cracking of the alloyed cast iron layer of the valve seat part, shorten heat treatment time, and significantly improve high temperature oxidation resistance and high temperature corrosion resistance. It is the purpose.

Means for Solving the Problems In the cast iron cylinder head of the first invention, the main body is made of cast iron, and the surface of the portion corresponding to the valve seat portion is coated with Fe.
A total of 0.1 to 10% by weight of one or more metal elements having a higher tendency to form carbides than Afl
An alloyed cast iron layer containing a total of 15 wt % or less of either 0.1 to 3 wt % or Si 0.1 to 15 wt % is formed over a depth of 0.2 mm or more, and The alloyed cast iron layer has a hardness of 250 to 400 Hv and consists of a base of ferrite and/or pearlite, 2 to 15% residual cementite, and a structure in which massive graphite is crystallized. It must be characterized by

Further, in the method for manufacturing a cast iron cylinder head of the second invention, after casting a cylinder head body using cast iron as a raw material, a metal having a higher tendency to form carbides than Fe is coated on the surface of a portion of the cylinder head body corresponding to a valve seat portion. One or more elements and A1. By arranging one or both of s+ or an alloy thereof and irradiating high-density energy from above to rapidly melt and rapidly resolidify Fe, Fe
One or two of the above metal elements having a higher tendency to form carbides
Contains 0.1 to 10% by weight of seeds or more in total and AJ20
．． An alloy layer is formed that is alloyed and chilled to contain a total of 15% by weight or less of one or both of 1% to 3% by weight and 0.1% to 15% by weight of Si, and then the deltened alloy layer is formed. A heat treatment was performed to heat the product to a temperature range above the A1 transformation point and below the solidus temperature, and then cool it, so that the base was made of ferrite and/or pearlite, and 2 to 15% of residual cementite was present, and massive graphite was crystallized. A 0.2 m layer of alloyed cast iron with a hardness of Hv 250 to 400 is
It is characterized by being formed over a depth of m or more.

The cast iron that forms the main body of the cylinder head has castability, t
From the viewpoint of JuT property and cost, JIS FC20°F
Ordinary cast iron such as C25 is preferable, and its composition is not particularly limited, but usually the main component C is 2.0 to 2.0.
The content of Si is about 4.0% by weight, and the content of Si is about 3.0% by weight or less. Furthermore, cast iron to which trace amounts of Ce, Mg, etc. are added for deoxidation can also be used.

In this invention, in the above-mentioned cast iron cylinder head made of ordinary cast iron, etc., parts that require particularly wear resistance, that is, parts corresponding to valve seats for intake valves and exhaust valves, are provided with the following. An alloyed cast iron layer is formed to a depth of 0.2 mm or more.

In addition to the cast iron component of the main body, this alloyed cast iron layer contains metal elements that have a higher tendency to form carbides than Fe, such as Or, Mo, W, Ta, Nb, Ti, Zr, or Mn. Total of 0 or more metal elements
．． Ail'0.
It contains 1 to 3% by weight or/and 3ro, t to 15% by weight within a total range of 15% by weight or less.

In addition, the structure of the alloyed cast iron layer is said to consist of ferrite 1 and/or pearlite as a base, 2 to 15% of residual cementite, and massive crystallized graphite.
Its hardness is said to be within the range of Hv 250 to 400.

As mentioned above, by containing metal elements such as CrJ4o that have a high tendency to form carbides, the alloyed cast iron layer of the valve seat part is strengthened by the residual cementite in its structure and the cementite constituting the pearlite. stabilized, and the wear resistance and heat resistance are significantly improved compared to the case without these additions. That is, the valve seat part is 150 to 250' in the part facing the intake valve.
C, 250 to 400 in the part for the exhaust valve
'C, but the structure and hardness do not change significantly even at such temperatures, and the wear resistance of the valve seat does not deteriorate. Here, Cr, Mo in the alloyed cast iron layer
If the content of carbide-forming elements, such as Since it is difficult to adjust the hardness and structure to such a degree, the content of the carbide-forming element was set within the range of 0.1 to 10% by weight.

Note that within this range, a range of 0.5 to 3.0% by weight is particularly preferable.

Roughly, the alloyed cast iron layer in the valve seat area, together with carbide forming elements such as Or and MO, contains 8! Or/and Si are alloyed, and by including Al or/and Si in this way, excessive chilling during the alloying process is prevented, so that the alloy layer during the alloying process is prevented from becoming excessively chilled. This effectively prevents cracks (bead cracks) from occurring in the alloy layer due to the smaller solidification shrinkage. In addition, by alloying Al and/or Si together with carbide-forming elements, it is possible to prevent the cementite in the alloy layer before heat treatment from being excessively strengthened, and also to prevent cementite in the alloy layer in the state before heat treatment. The amount of cementite is also smaller than when only carbide-forming elements are alloyed, so in the final heat treatment to decompose excess cementite and adjust the amount of residual cementite to 2 to 15%,
This means that the heat treatment time can be shortened. Zaranihachi! , Si
Both are effective elements for improving high-temperature oxidation resistance and high-temperature corrosion resistance. Therefore, by alloying AI and/or Si, the valve seat portion made of the alloyed cast iron layer improves high-temperature oxidation resistance and high-temperature corrosion resistance. .

Note that the higher the concentration of Al and Si in the alloyed cast iron layer, the better the high-temperature oxidation resistance and high-temperature corrosion resistance, but if Al exceeds 3% or the S1 amount exceeds 15% by weight. In this case, the residual cementite 1 becomes difficult to remain and the wear resistance is sharply reduced. In addition, the above-mentioned effect can be increased by 1 whether Al or Si is added alone or in combination with both, but the total difference in the case of combined addition is 15%. If it exceeds this amount, sufficient wear resistance cannot be obtained for the same reason as mentioned above, so the total amount of composite additions must also be 15% by weight or less. On the other hand, Aj2.
If sr is less than 0.1% by weight, the above-mentioned effects cannot be sufficiently obtained. Therefore, in this invention, Afo, 1~
The total amount of either or both of 0.1 to 15% Si by weight was defined as 15% by weight or less. Naohachi! ,
Most preferably, the total amount of one or both of the Sis is in the range of 1 to 12% by weight.

Regarding the metallographic structure of the roughly alloyed cast iron layer, in addition to alloying the carbide-forming elements, by creating the structure as described above, it has excellent wear resistance and at the same time is less aggressive against the valve face surface as a mating material. (Abrasion resistance to mating material) can be reduced, and workability is also improved, and it is also advantageous in terms of toughness, making it difficult for chipping to occur.

In other words, as already mentioned, the wear resistance is improved by the presence of residual cementite in the base structure consisting of ferrite or pearlite, but if the residual cementite is less than 2%, the wear resistance is insufficient. gender cannot be guaranteed.

On the other hand, if the amount of residual cementite increases, it is advantageous only from the standpoint of wear resistance, but the wear on the mating valve face increases and the workability also decreases.

According to experiments conducted by the inventors, in order to ensure the wear resistance of the valve seat surface, reduce the wear of the mating valve face surface, and obtain good workability, the amount of residual cementite must be 1.
It has been found that it is necessary to keep it below 5%.
Therefore, the residual cementite value was set within the range of 2 to 15%. On the other hand, since the graphite crystallized in the structure has a lumpy shape, it has an advantage in terms of toughness compared to flaky graphite such as ordinary cast iron, and can prevent chipping of the valve seat surface. The base structure of the alloyed cast iron layer may be composed of only ferrite or pearlite, but it is usually a mixed phase structure of ferrite and pearlite.

Regarding the hardness of the alloyed cast iron layer, if the hardness is less than Hv 250, the wear resistance of the valve face cannot be ensured, whereas if it exceeds Hv 400, the wear of the mating valve seat will be excessive and the workability will also be reduced. , Hv250~40
It must be within the range of 0.

If the depth of the alloyed cast iron layer having the above-mentioned composition, structure, and hardness is 0.2 m, sufficient wear resistance and heat resistance cannot be ensured, so the depth should be set to 0.2 m or more. is necessary.

As described above, a predetermined structure in which a predetermined amount of carbide-forming elements such as Cr and Mo is alloyed with Al or/and Si;
By forming an alloyed cast iron layer with a predetermined hardness and a predetermined depth on the valve seat surface, we can ensure the wear resistance of the valve seat surface itself, prevent wear of the mating valve face surface, and ensure workability. Not only can it prevent chipping and ensure heat resistance, but it can also
By also containing i, it is possible to prevent cracking of the alloy layer during alloying treatment and shorten the heat treatment time.
In general, we were able to improve the high-temperature oxidation resistance and high-temperature corrosion resistance of the valve seat.

Next, a method for manufacturing a cylinder head having an alloyed cast iron layer on the valve seat surface as described above, that is, the second invention will be described.

First, the cylinder head body may be manufactured by using a cast iron material such as the above-mentioned ordinary cast iron as a raw material and casting it by a normal casting method such as sand mold casting, metal mold casting, or various pressure casting methods.

The obtained cylinder head body was first treated with Cr, M0. W, Ta, Nb, V,
An alloying process is performed between A1 and/or Si and a carbide-forming element such as Ti, Zr, or Mn. In other words, the above-mentioned Cr, MO, etc. are applied to the surface of the valve face, which requires particularly wear resistance and heat resistance, in the cylinder head body.
One or more carbide-forming elements such as Al and/or S11 or their alloys (hereinafter collectively referred to as alloying materials) are arranged, and then laser, electron beam, plasma arc, TIG arc By irradiating high-density energy such as ! Or/and Si are alloyed, and then the molten alloy layer is instantaneously and rapidly solidified by moving the energy irradiation position or stopping the irradiation. Here, the mass of the part melted by high-density energy irradiation is much smaller than the mass of the entire cylinder head, so by moving the high-density energy irradiation position or stopping irradiation, the melting occurs due to heat transfer to the cylinder head base material side. The alloy layer instantly solidifies and becomes a chilled alloy layer. However, the degree of chilling is less than that in the case where Al and Si are not alloyed, so solidification shrinkage is also reduced and bead cracking is prevented.

Specific methods for placing the alloying material on the valve face surface of the cylinder head body include, for example, placing or thermal spraying powder, green compacts, thin plates, etc. of the alloyed material, or applying it as a slurry. All you have to do is make a groove in the required area and fill it.

Furthermore, the blending form of the alloying material is Cr, Mo.
An elemental metal of one of the carbide-forming elements, two or more of these elements, an alloy of two or more of them, or one or more of these elements and iron. Al or Si, or an alloy of these and iron, may be used in a mixed state such as a mixed powder or in a layered state, or one or more carbide-forming elements and Al or /1J may be used. -3 and Si
or even one or more carbide-forming elements! or/and S
A powder made of an alloy of i and iron may be used.

In the alloying process using high-density heating energy as described above, a so-called chill cast iron structure is formed in the alloy layer, which has a hardness of Hv 550 or more and a cementite +
It exhibits a troustite-martensitic structure. This type of chilled cast iron structure is too hard and causes significant wear on the mating valve face surface, and is brittle and easily chipped.Furthermore, machining itself is difficult, so it cannot be used as is on the valve seat surface of the cylinder head. There is a problem in using it. Therefore, after the alloying treatment, heat treatment is performed to adjust the alloy layer of the chilled cast iron structure to the above-mentioned hardness and structure.

In this heat treatment, by heating and holding in a temperature range above the A1 transformation point and below the solidus temperature, austenitization of the matrix structure (troostite, martensite), partial decomposition and agglomeration of cementite, and graphitization progress. The amount of residual cementite is adjusted to 2 to 15%, and massive graphite is crystallized. In the cooling process after heating and holding, transformation into ferrite and/or pearlite progresses, and the above-mentioned structure is finally obtained.

The heating holding time in this heat treatment is not particularly limited, but
As already mentioned in the case of this invention! or/and S
: Alloying prevents excessive strengthening of cementite due to alloying treatment, and when the amount of cementite immediately after alloying treatment does not alloy Al or/and Si (in the case of alloying only carbide-forming elements). Since the amount is relatively small, it is possible to partially decompose the cementite in a relatively short time and adjust the amount of residual cementite to 2 to 15%, and therefore, the heating and holding time is sufficient to be about 30 seconds to 10 minutes. Of course, the specific optimum heat treatment temperature and time will vary depending on the amount of alloyed Ati, sr, type and amount of carbide-forming elements, etc. However, if there are many alloying elements added, or if the added alloying element has a particularly strong tendency to form carbides (for example, Ti, Zr, Nb, etc.), it is desirable to heat at a relatively high temperature for a long time. However, as mentioned above, compared to the case where Al and/or Si are not alloyed, it goes without saying that a short heating time is sufficient. Cooling conditions also vary depending on the amount of alloyed Al and/or Si and the type and type of carbide-forming elements, but air cooling is usually sufficient.

In the above heat treatment, it is desirable to use local heating that heats only the delta alloy layer, such as high-frequency induction heating or flame heating (burner heating), from the viewpoint of thermal efficiency, but in some cases, the cylinder head Furnace heating may be used to heat the whole.

As described above, by forming a chilled alloy layer of cast iron with carbide-forming elements such as Cr and Mo, Al or Si, and cast iron on the surface layer by alloying treatment using high-density energy, and then performing heat treatment. , an alloyed cast iron layer having the structure and hardness described above can be formed on the valve seat surface.

After the heat treatment described above, mechanical processing such as grinding or polishing may be performed as appropriate to finally produce a cylinder head product.

Example [Example 1] Cr-A1 with two types of compounding ratios shown in A and B in Table 1 was applied as an alloying material to the surface of a cast iron base material made of JIS Fe12.
The mixed powder (150 to 350 meshes) was thermally sprayed to the thickness shown in Table 1, and then alloyed and chilled using a TIG arc.

The processing conditions are: average current 100A, feed rate 3/It
FII/SeC was used, and argon gas at a flow rate of 121'/min was used as a shielding gas. Through this alloying/chilling treatment, an alloyed chilled layer having a cps degree and an Al concentration as shown in Table 1 was formed. Next, each sample was heated in a furnace at 1000'CX for 3 minutes, and then air-cooled.

A human wear test was conducted on each of the alloyed cast iron layers formed by the treatments shown in Table 1 and above using valve material S-3 as a mating material. The test conditions were a sliding distance of 100 m, a sliding speed of 0.31 m/Sec, and a final load of 6.3 meters. The wear test results are shown in FIG. 1 together with the test results for comparative materials. As a comparative material, JIS Fe
A cast iron base material made of No. 12 alloyed with only Cr was used. The alloying/chill treatment conditions and heat treatment conditions using TIG arc for this comparative material are the same as those described above, and the Qr concentration in the alloyed cast iron layer in that case is 1.5% by weight.

Further, the same test pieces as those used in the above wear test were subjected to an oxidation test at 500° C. for 100 hours in the atmosphere, and the weight gain by oxidation before and after the test was investigated. The results are shown in FIG.

As shown in Figs. 1 and 2, when 0r-Ai' is alloyed (invention materials A and B), the amount of wear increases compared to the comparative material in which only Cr is alloyed. It was possible to reduce oxidation weight gain without causing any problems.

In other words, to! Through alloying, we were able to improve high-temperature oxidation resistance.

[Example 2] Cr- alloyed with three types of compounding ratios shown as C, D, and E in Table 2 was applied to the surface of a cast iron base material made of JIS Fe12 as an alloying material.
Si mixed powder (150 to 300 mesh) was added to the second
The material was thermally sprayed to the thickness shown in the table, and then alloyed and chilled using a TIG arc. The processing conditions were the same as in Example 1. Through such alloying/chilling treatment, an alloyed chilled layer having an Or concentration and an S1 concentration as shown in Table 2 was formed. Next, heat treatment was performed by heating in a furnace at 1000''CX for 3 minutes and cooling in air.

For each alloyed cast iron layer formed by the treatments shown in Table 2 and above, a wear test was conducted under the same conditions as in Example 1. The results of the oxidation test are shown in Figure 3. The results obtained under these conditions are shown in FIG. In FIGS. 3 and 4, the comparative material is one in which only Cr is alloyed at a concentration of 1.5% by weight, similar to the case shown in Example 1.

As shown in Figs. 3 and 4, in the alloyed cast iron layer alloyed with Qr-Si (invention materials C, D, and E), the wear amount is c
Although there is almost no difference from the case where only r is alloyed (comparative material), it can be seen that as Sim increases, the oxidation weight gain decreases significantly, that is, the high temperature oxidation resistance improves.

[Example 3] In manufacturing a 4-cylinder cylinder head for a 2400 cc diesel engine, a cylinder head rough profile was first cast using JISFC25 cast iron using a conventional method.

Next, as shown in FIG. 5, the intake and exhaust valve seat parts 2 of the cylinder head rough profile 1 are prefabricated, and Cr-4 of 150 to 350 mesh is applied to these parts.
A mixture of 0% Ala powder was kneaded with polyvinyl alcohol as a binder and applied to a thickness of 0.5M.
After drying, alloying and chilling were performed using TIG arc. The conditions for this process are: average current 75A, feed rate 3#
M1/SeC was used, and argon gas at a flow rate of 121/min was used as a shielding gas. With this process,
Depth 2.6s in valve seat part, Or concentration 3.9% by weight
, an alloyed/chilled layer with a He2 concentration of 2.2% was formed. Next, each valve seat portion was subjected to a heat treatment of heating at 1000'CX for 1 minute using a high frequency induction heating device and then cooling in air.

Through the above treatment, a Cr-A1 alloy containing 3.9% by weight of Cr and 12.2% by weight of A, whose metal structure consists of a residual cementitious ferrite base of massive graphite + 14%, and a hardness of 310 Hv is formed in the valve seat part. A cast iron layer was formed. An outline of the state is shown in FIG. In FIG. 6, 3 indicates the alloyed cast iron layer.

Note that finishing processing was performed after the above-mentioned heat treatment.

Figure 7 shows an overview of the valve seat area and its vicinity after finishing. The depth of the alloyed cast iron layer 3 after finishing is i
, is.

[Comparative example] Instead of the Cr-60% Ni mixed powder in Example 3,
Alloying was applied to the valve seat of a cast iron cylinder head using the same method and conditions as in Example 3, except that pure Cr powder (150 to 350 mesh) was used and the heat treatment conditions were 1000°QX for 3 minutes. Chill treatment and heat treatment were performed.

As a result, the valve seat part contained 1.5% by weight of Cr and had a metal structure of massive graphite + 8% residual cementite.
A Cr-alloyed cast iron layer having a hardness of Hv360 was formed, consisting of a pearlite base. The depth of the Cr alloyed cast iron layer after finishing processing is 0.8. It is.

The results of an investigation regarding the defective product rate in the cylinder heads according to the third embodiment and the comparative example described above will be described.

When creating the cylinder head of the comparative example, bead cracking occasionally occurred in the alloy layer due to solidification shrinkage due to chill formation immediately after solidification during alloying treatment using TIG arc, and the probability of this occurring was 2%. . When creating a cylinder head with 4 cylinders and 2 valves per cylinder, it is necessary to treat 8 places per car, but if a bead crack occurs in even one of the 8 places per car, that head will be defective. The total defect rate is approximately 16%.

On the other hand, when producing the cylinder head according to Example 3 of the present invention, almost no bead cracking occurred in the alloy layer during the alloying treatment by TIG arc, and the defective rate due to bead cracking was almost 0%. This is because chilling is reduced by alloying Al at the same time, and therefore solidification shrinkage during alloying treatment is reduced.

[Example 4] Cr-40% in Example 3! Instead of powder, (
: r-70% Si mixed powder (150-350 mesh)
The valve seat portion of the cast iron cylinder head was alloyed and chilled using the same method and conditions as in Example 3. Through this treatment, the valve seat part is made into an Or-Si alloy containing 8% by weight of Orl, 5.3% by weight of Si, whose metal structure is composed of residual cementite and ferrite base of massive graphite + 9%, and has a hardness of 290 Hv. The cast iron layer is 2 deep
．． It was formed over 4M. Even when producing the cylinder head according to Example 4, it was confirmed that almost no bead cracking occurred due to the alloying treatment. The reason is the same as that already described for the third embodiment.

Effects of the Invention The valve seat surface of the cast iron cylinder head for an internal combustion engine of the present invention has a predetermined alloyed cast iron layer, so it not only has excellent wear resistance but also has less aggressiveness against the mating valve face surface. It has a variety of excellent performances, including a low incidence of defective products due to bead cracking, and excellent high-temperature oxidation resistance and high-temperature corrosion resistance. Further, in the cylinder head of the present invention, cast iron having excellent castability and workability, such as ordinary cast iron, can be used for the main body portion, so that castability and workability are not impaired and there is no particular disadvantage in terms of cost. Roughly speaking, the cylinder head of this invention is
Unlike conventional sintered alloy insert materials used on the valve seat surface, the alloyed cast iron layer on the valve seat surface is continuous with the main body, so there is no thermal barrier between them. Cooling performance near the valve seat is improved, making it possible to increase the output of the internal combustion engine than before, and simplifying the manufacturing process compared to the case where insert materials are used, resulting in cost reduction.

Furthermore, according to the cylinder head manufacturing method of the present invention, a cast iron cylinder head having excellent valve seat performance as described above can be manufactured at substantially low cost, and in particular, the heat treatment time after alloying treatment can be reduced. Since the time can be shortened, productivity can be increased.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the wear test results in Example 1,
FIG. 2 is a graph showing the oxidation test results in Example 1,
FIG. 3 is a graph showing the wear test results in Example 2,
FIG. 4 is a graph showing the oxidation test results in Example 2,
FIG. 5 is a schematic vertical cross-sectional view showing the vicinity of the valve seat portion of the cylinder head rough profile in Example 3, and FIG.
Figure 7 is a schematic vertical cross-sectional view showing the state in which an alloyed cast iron layer is formed on the valve seat portion of the cylinder head rough section. FIG. 1... Cylinder head rough shape material, 2... Valve seat portion, 3... Alloyed cast iron layer.

Claims (2)

[Claims] (1) The main body is made of cast iron, and the surface of the portion corresponding to the valve seat contains a total of 0.1 to 10% by weight of one or more metal elements that have a higher tendency to form carbides than Fe. and 0.1 to 3% by weight of Al or 0.1 to 3% by weight of Si.
An alloyed cast iron layer containing a total of 15% by weight or less of one or both of 1 to 15% by weight is formed over a depth of 0.2 mm or more, and the alloyed cast iron layer has a base of ferrite and/or Alternatively, a cylinder head made of cast iron for an internal combustion engine, characterized in that it is made of pearlite and has a layer having a hardness of 250 to 400 Hv and is composed of a structure in which 2 to 15% of residual cementite exists and crystallized massive graphite. (2) After casting a cylinder head body using cast iron as a raw material, the surface of the part of the cylinder head body corresponding to the valve seat is coated with one or more metal elements that have a higher tendency to form carbides than Fe and Al. , Si, or an alloy thereof, and irradiates high-density energy from above to cause rapid melting and rapid resolidification of one or two of the metal elements that have a higher tendency to form carbides than Fe. Alloyed and chilled to contain 0.1 to 10% by weight of the above in total, and 15% by weight or less of one or both of 0.1 to 3% by weight of Al and 0.1 to 15% by weight of Si. The chilled alloy layer is then heated to a temperature range above A_1 transformation point and below the solidus temperature, and then cooled to form a base of ferrite and/or pearlite. 15%
An alloyed cast iron layer with a hardness of 250 to 400 Hv, consisting of a structure in which residual cementite exists and massive graphite crystallizes, is
．． A method for manufacturing a cast iron cylinder head for an internal combustion engine, characterized in that the cylinder head is formed over a depth of 2 mm or more.