JPS59584B2 - Rocker arm material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high chromium cast iron rocker arm material.

High chromium cast iron materials exhibit excellent wear resistance, particularly against abrasion, and are known as wear-resistant materials in high-temperature or corrosive environments.

However, high chromium cast iron has a carbide and matrix structure that changes greatly depending on the content of Cr and C, and its properties also change accordingly, so it is a material that requires consideration of its optimal composition depending on the purpose of use. As a result of various studies, the present inventors have determined that the amount and ratio of Cr and C contained, as well as the amount of other metal components, etc. in high chromium cast iron, whose structure and properties vary greatly depending on its composition. Casting that satisfies various properties such as wear resistance, pitting resistance, and scuffing resistance at the same time by keeping it within a specific range, and also has sufficient wear resistance even when using precision casting methods that involve heating the mold. I found out that you can get the goods.

That is, the material for a valve rocker arm of the present invention is a 30% high chromium cast iron, and is characterized by having a composition of Cr/C-9 to 13 and Cr/C/5i=15 or more. be.

The high chromium cast iron used in the present invention may contain Cr in an amount of around 30%, but the C content is 214%.
~3.2%, and the Cr content is 25~35%, especially 2
It is preferably 7 to 32%.

If the C content is less than 244%, the wear resistance and scuffing resistance will not be sufficiently high. Also 382%
If the amount is higher than this, wear resistance and pitting resistance will deteriorate. Cr
If it is less than 27%, good results will not be obtained in any of the wear resistance, pitting resistance, and scuffing resistance, and if it exceeds 32%, the wear resistance will begin to deteriorate. Further, it is preferable that the Mn content is less than 1.0%, and the Si content is Cr/C-9 to C-13 and C/
From the requirement of C/5i≧15, it is less than 0.87%.
The high chromium cast iron obtained by the present invention has excellent wear resistance, scuffing resistance, and pitting resistance.
It is particularly suitable as a material for valve rocker arms used to open and close intake valves or exhaust valves in internal combustion engines of automobiles. It is desirable for a valve rocker arm to have the above-mentioned characteristics for its purpose of use, and therefore, a valve rocker arm made of the cast iron material of the present invention has less wear and can withstand long-term use. The various characteristics of the material for rocker arm of the 30-coupled high chromium cast iron of the present invention will be explained in more detail with reference to Test Example 1 below.

Test Example 1 A valve rocker arm test piece was cast from high chromium cast iron having the composition shown in Table 1.

Both rocker arms use shell molds,
Casting was carried out at a casting temperature of 1450 to 1500°C. Among the test pieces shown in Table 1, for /161 to 6 and 47 to 12, the former had the chromium (Cr) content in the alloy constant at approximately 30% and the carbon (C) content varied; For the latter, on the contrary, the amount of carbon (0) was kept constant at about 3.0 and the amount of Cr was varied.At this time, consideration was given to keep the alloy composition in the eutectic or slightly hypereutectic region. Test piece A5,
6,ll,l2 intentionally increases the amount of Si, Cr/C/Si
lowered the ratio. Further, the Mn content of /161 to 12 was kept to below 0.8 coefficient, and the Mn content of /16.13 and 14 was set to 1.0 coefficient or more. AMI. 3 and 14 are test pieces prepared to examine the influence of Mn. The various test specimens obtained above were machined, taking into account that the surface roughness of the pad surface was the same, and then they were assembled into an engine and subjected to a continuous durability test for 200 hours. Abrasion resistance, pitting resistance, and scuffing resistance were investigated using the following test methods.

Measurement of Wear Amount As shown in FIG. 1, the surface of the rocker arm pad 1 after the durability test is scanned with a surface roughness meter in the direction indicated by the arrow x in the figure to measure the amount of pad wear.

The pad surface is preferably scanned at the most worn area (distance indicated by a in the figure, for example, 2 to 3 mm). The pitching 2 that appeared on the surface of the rocker arm pad 1 after the pitting resistance durability test was visually inspected, and as shown in Fig. 2a ''=
Evaluation is performed as follows using e as a standard.

Figure 2 a...Rating 10 (no pitching) Figure 2 b...
... 〃 8 Fig. 2 C... 〃 6 Fig. 2 d... 〃 4 Fig. 2 e... 〃 2 Scruffing resistance As shown in Fig. 3 A and b, the locker after the durability test The total area S and depth d of the damaged portion 3 of the arm pad 1 are measured and evaluated according to the table below.

The results are shown in Table 3.

In Table 3, the amount of wear, pitching score, and scuffing score are all evaluated on the surface of the rocker arm pad after the test, and the pitching score and scuffing score are evaluated on a scale of 10 to 10.

In practice, it has been confirmed that there is no problem if both ratings are 8 points or higher, but preferably both ratings are 10 points or higher. Three test pieces each were subjected to the test,
The evaluation is the average value of those three. As is clear from the table above, when Cr/C is less than 9 (test piece/16
4, 7), when the wear amount, pitting score, and scuffing score deteriorate, and even if Cr/C is 9 or more, Cr/C/Si is 15 or less (test piece/16
5, 6, 11, and 12), all test evaluations also tend to deteriorate.

On the other hand, test piece A. The amount of C is low as seen in Cr/
When C exceeds 13, the evaluation becomes poor across all test items, as in the case where Cr/C is 9 or less. Cr/C
, Cr/C/Si are all within the range of the present invention, but the test piece/I6.9. The reason why the rating of IO is slightly lower is because the amount of Cr is high. Therefore, the amount of Cr is approximately 30%,
It is especially desirable to be in the 27th to 32nd ranks. Furthermore, from the test results of test piece 413.14, Cr/C, Cr/C/S
Even if i satisfies 9 to 13.15 or more and the C content and Cr content are within the ranges of 2.4 to 3.2% and 27 to 32%, respectively, when the Mn content is high, the amount of wear increases. However, since the characteristics of the material of the present invention cannot be fully exhibited, it is understood that the Mn content is desirably 1.0 or less. Furthermore, the 30% high chromium cast iron rocker arm material of the present invention exhibits excellent wear resistance even when cast using a high-temperature mold.

In general, wear resistance is greatly influenced by the morphology of the carbides and matrix structure in high chromium cast iron, and in particular, the formation of relatively large alignment of primary carbides and finely dispersed crystallization of the eutectic matrix structure improves wear resistance. It is said to be effective in ensuring wear resistance. Therefore, for high-chromium cast iron materials with conventional compositions, it is preferable to apply a precision casting method such as the lost wax method, which involves heating the mold, because the cooling rate after pouring is significantly lower than that of a normal mold. It was difficult to secure an organization. However, high chromium cast iron materials with a limited composition range as in the present invention, even when cast using high-temperature cast iron,
The abrasion resistance of the resulting cast product does not deteriorate compared to when a mold at normal temperature is used, and it can sufficiently withstand long-term use. A more detailed explanation will be given below using Test Example 2.

Test, Test Example 2 A valve rocker arm, which is one of the engine parts, was selected as a part to investigate the wear resistance, which is one of the features of high chromium cast iron, and a valve rocker arm with the composition shown in Table 4 was selected. Various test beads (TP) were manufactured.

A shell mold and a ceramic shell mold were used as molds for both rocker arms, and especially for the latter, the mold was preheated to 1000° C. during casting. Casting temperature is 1450-150
Casting was carried out at 0°C. After completing the machining process, taking care to maintain the same conditions such as surface roughness of the pad surface, the pads were assembled into an engine, and a durability test was conducted for 200 hours continuously to investigate the amount of wear. The following considerations were taken into consideration when selecting the test pieces shown in Table 4. T
PA-1 to 6, B-1 to 6 are those in which the amount of chromium in the alloy is kept almost constant and the amount of carbon is varied, TPA-7 to 12,
B-7 to B-12, on the other hand, have a constant carbon content and a varying chromium content.

At this time, care was taken to ensure that the alloy composition was in the eutectic or slightly hypereutectic region. Among these, TPA-5, 6, 11.1
2 and B-5.6, 11, and 12, the amount of silicon was intentionally increased and the Cr/C/Si ratio was lowered. Also TPA-1
-12 and B-1 to B-12, the manganese content was all kept below 0.8. TPA-13.14, B-13, and 14 were prepared to examine the influence of manganese. Note that A is TP manufactured using a shell mold, and B is TP manufactured using a high temperature (1000
This indicates that the TP was manufactured using a ceramic shell mold that was heated to 10°C.

After operating the engine under the conditions shown below using the test bead described above, the amount of wear on the pad surface was examined.

The results are shown in Table 5. Three pieces of each TP were tested.
The evaluation shows the average value of those three. Engine operating conditions Rotation speed IOOOrpm time 200hr Oil
From Table 5, the following ~ can be found.

i) Cr/C ratio is 9 from TPA-4.7, B-4.7
As the diameter becomes smaller, the wear resistance decreases.

Items manufactured using high-temperature molds tend to be particularly bad. TPA-5, 6, 7, 11, 12, B-5, 6, 7
, 11, 12, even if the value of Cr/C is larger than Cr/C/
Similarly to when the Si value is 15 or less, the wear resistance is reduced.

Similarly, products manufactured using high-temperature molds tend to be particularly bad. Also, the value of Cr/C, Cr/C/
Even if there are 9 or more Si boxes each, TPA-1, B-1
As can be seen, when the carbon content is low and the Cr/C ratio exceeds 13, the wear resistance deteriorates as when the CrlC ratio is 9 or less.

Furthermore, as seen in TPA-10, B-9, and 10, it can be seen that too high a chromium content is also undesirable. TPA-1
3,14,B-13,14, the value of Cr/C, Cr
/C/Si values each satisfy the claimed range, and
Even if the amount of carbon and chromium meet the required ranges, if the amount of manganese is high, the wear resistance will decrease, so the amount of manganese is preferably 1.0 coefficient or less.

As is clear from the above, when using high chromium cast iron within the composition range of the present invention, even if the product is manufactured using a high-temperature mold such as the lost wax method, a product that is sufficiently satisfactory from the viewpoint of wear resistance can be obtained. be able to.

This makes it possible to reduce the machining costs for high-chromium cast iron products, which are difficult to machine due to their high hardness, or to dramatically expand the possibility of manufacturing products with good texture. As is clear from the above description, the high chromium cast iron rocker arm material 30 of the present invention can satisfy wear resistance, pitting resistance, scuffing resistance, etc. at the same time, and in particular,
It is suitable as a material for valve rocker arms of automobile internal combustion engines.

Further, the high chromium cast iron material of the present invention does not deteriorate its wear resistance even when cast using a high temperature mold, so it becomes possible to carry out precision casting such as the lost wax method.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the direction in which the wear amount of the rocker arm pad is measured. Figure 2 a"e is a schematic diagram showing the degree of pitching that occurs in the rocker arm pad after the test. Figure 3 a. is a schematic diagram showing the degree of scuffing that occurs in the rocker arm pad after the test, and b is a cross-sectional view thereof. In the figure, 1... rocker arm pad, 2...
. . . pitching portion, 3 . . . representing scuffing portion.

Claims (1)

[Claims] 1 27-32% chromium, 2.4-3.2% carbon, 100% or less manganese, less than 0.87% silicon, and the remainder is iron and normal impurities, with a Cr/C composition ratio of 9
13 and a composition ratio of Cr/C/Si of 15 or more. 30% high chromium cast iron rocker arm material.