JPS5839907B2 - Surface damage resistant alloy cast iron - Google Patents

Description

[Detailed description of the invention] The present invention relates to surface damage resistant alloyed cast iron.

Mechanical or engine parts that slide under high stress are highly susceptible to surface damage such as wear, scuffing, and pitting.

For this reason, various methods have been used to increase the hardness of the sliding parts and improve the surface damage resistance.

For example, if we take the camshaft of an automobile engine as an example,
Carburized steel, hardened steel, and hardened cast iron are used, but these materials have various drawbacks as follows.

In other words, since steel is a forged product, its manufacturing cost is higher than that of cast iron, and in terms of performance, it is more prone to scuffing and wear. Hardened cast iron has poor machinability and is not only expensive to manufacture, but also suffers from scuffing. Since it is easy to cause wear and tear, it can hardly be used especially in engines with high contact stress.

Although cast iron is considerably improved in terms of cost and surface damage resistance compared to the above three, the hardness of the chilled portion is low and pitting occurs, so it cannot be said to be perfect.

However, chilled cast iron is Cr. There are some products in which alloys such as Mo and Ni are added to increase the pitching, but the hardness of the cut part increases, resulting in poor machinability, and the manufacturing cost is unavoidably high.

The present invention aims to solve the above-mentioned drawbacks by using alloyed chilled cast iron with increased m1 surface damage resistance without impairing machinability. Based on this knowledge, chilled cast iron with a CE value of 4.1 or higher, which was not conventionally used due to pitting in cams, etc., is added with chilling promoting elements and chilling suppressing elements to prevent deterioration of workability etc. It is intended to be used as cast iron.

As a result of conducting various studies on cast iron alloys, the present inventors found that the hardness of the cam nose part of an automobile camshaft must be Hv 500 or more, as shown in Figure 1, which shows the relationship between the hardness of the cam nose part and the pitching area ratio. Yes, C%+1/3
It has been found that there is a relationship as shown in FIG. 2 between the CE value (carbon equivalent) expressed in Si% and the hardness of the chilled portion.

The pitching area ratio is determined by placing a square like a net on the pitching area and counting the number of square days, and calculating the pitching area.
Further, it was calculated using the following formula.

In addition, if we take into account the variations in Figure 2, the chill hardness Hv 5
In order to make it 00 or more, the CE value needs to be 4.1 or more.

It is known that the chill depth generally decreases as the CE value increases, but in chilled cast iron, when the CE value increases, the chill depth tends to become extremely shallow, and the cam action surface becomes a soft non-chill part. , resulting in a significant deterioration of surface damage resistance.

The present inventors have determined that in order to reconcile the above two contradictory phenomena, silicon (Si) and carbon (C) should be adjusted to 20φ<Si≦3.0 width and 3.1 coefficient≦C in the cast iron used. An effective means is to contain it in a range of ≦4.0%, increase the CE value, increase the chill hardness, and compensate for the decrease in chill depth with chilling promoting elements such as Mn, Cr, W, V, etc. The present invention was completed based on this knowledge.

However, if too much of the chilling-promoting element is added, chill will also enter the processed area, so it is necessary to suppress the addition of the chilling-promoting element or to avoid reducing the chill depth of the area to which the cold metal is applied. Elements that suppress chilling of the cut portion, such as P, Cu, Ni, etc., are added at the same time.

However, if the CE value is 5.0 or more, it is necessary to add a large amount of chilling promoting elements, which increases the cost, so the CE value is set at 4.
．． It was limited to 1 to 5.0.

The reason why the amount of Si is limited to the above range in the present invention is that Si is an element that helps graphitization, and when it is less than 2.0 yen, the tendency to chill increases, and chill enters areas where chill should not normally enter. This is because the rigidity is impaired, and when the CE value exceeds 3.0φ, it becomes difficult to generate chill even if a chilling promoting element is used in the range of the above CE value.

Regarding the amount of C, if it is less than 3.1%, the required hardness cannot be obtained, and if it is more than 4.0%, the above CE value cannot be obtained, so the pitching area ratio is low and the chill depth is extremely shallow. Therefore, it is limited as above.

If the amount of the chilling promoting element added is 2% or more, the castability will deteriorate and cavities will easily form. 0
．． The range was 1 to 2.0 yen.

The amount of the chilling suppressing element added may not be necessary depending on the chilling promoting element, but if it exceeds 0.5%, it will reduce the chill hardness and worsen the wear resistance.
．． The range was set at 5% or less.

Next, the alloy cast iron of the present invention will be specifically explained using examples.

Example 1 Returning material equivalent to FC25 was melted in a high-frequency furnace, a recarburizing agent and 75% Fe-8i and Fe-Mn were added to adjust the composition, and the melt was kept at 1500°C for 10 minutes before being tapped. The pouring was carried out at 1370°C.

The chemical composition of this molten metal is C3.51 and Si2.16.

Mn 0.96%, others 80.054%, Po, 037%
The balance was Fe.

In addition, examples in which the Mn content of the chilling promoting element in Example 1 was changed (Examples 2 to 3), and those in which the Mn content in the chilling promoting element in Example 1 was changed to W, Cr, and V (Examples 4-12),
In addition to the chill-promoting elements, chill-inhibiting elements (P, Cu, N
Cast iron alloys of the present invention were manufactured, including those to which i) was added (Examples 13 to 21) and two or more chill promoting elements (Examples 22 to 24).

The alloy compositions of Examples 1 to 24 are shown in Table 1.

An automobile camshaft shown in FIGS. 3 and 4 was manufactured using the cast iron alloy of the present invention obtained in the above example.

FIG. 3 is a sectional view of an automobile camshaft, and FIG. 4 is a sectional view taken along the line A-A in FIG. 3. A camshaft having a chilled cam part 2 and a cutting part 1 as shown in FIG. The investigation was conducted using the following measurement method.

OCE value: A portion of the obtained product was cut out and chemically analyzed to determine the content of C and Si, and the CE value was calculated using the following formula.

CE-C%+1/3Si 0 Chill depth...The clear chill depth from the top of the cam part toward the center was determined as the chill depth.

○Chill hardness: Cut the cam part 2 in a direction perpendicular to the axis, and measure the average of the values measured at three arbitrary points two degrees from the surface near the top of the cam using a Vickers hardness tester with a load of 20 kg. I asked for it.

0 Cutting part hardness...Cutting part 1 is cut in a direction perpendicular to the axis, and a load of 20 kg is applied to any 5 points at two positions from the surface.
It was determined by averaging the values measured with a Vickers hardness tester.

The results are shown in Table 1.

In addition, in order to compare with the alloy cast iron of the present invention, a conventionally used alloy cast iron was manufactured as follows.

Conventional method I Melt the returning material equivalent to FC25 in a high frequency furnace, add recarburizer and 75φFe-8i to adjust the composition,
After holding at 500'C for 10 minutes, take out the hot water and heat it to 1370'
Pouring was carried out at C.

The chemical composition of this molten metal is C3, 21%, Si 1.
98% and also Mn0.64 t, 80.052, Po,
037, and the remainder was Fe.

Conventional method 2 A return material equivalent to FC25 is melted in a high frequency furnace, and a recarburized material and 75% Fe-8i, Fe-Mo, F
e -Cr was added to adjust the composition and 1 at 1500°C.
After holding for 0 minutes, the hot water was tapped and poured at 1370'C.

The chemical composition of this molten metal is C3, 22%. Si 2.46
%, Mo 0.30%, CrO, 51%, and Mn 0.61%, 80.049%, Po, 038%
The balance was iron.

The alloy cast irons of Conventional Methods 1 and 2 were subjected to CE in the same manner as in the Examples.
The alloying elements, chill depth (Hv), and chill hardness (Hv) were measured.

The results are shown in Table 3.

The cast iron alloy of the present invention shown in Table 1 is prepared by increasing C or C and Si to increase the CE value and adding one or two chilling promoting elements, or by adding a chilling promoting element and a chilling inhibiting element. The chill effect was adjusted by adding It was also found that there was a significant increase.

As described above, the cast iron alloy of the present invention achieves both the hardness of the chilled part and the depth of the chill, which cannot be obtained with conventional products, which are convenient for camshafts, and at the same time, it is possible to manufacture camshafts without impairing machinability. This makes it possible to apply this method not only to the manufacture of camshafts, but also to sliding parts under high stress.

[Brief explanation of drawings]

FIG. 1 shows a graph showing the relationship between cam nose hardness and pitching area ratio. FIG. 2 shows a graph showing the relationship between the CE value and the chill portion. Figure 3 shows a cross-sectional view of an automobile camshaft. FIG. 4 is a sectional view taken along the line A--A in FIG. 3. In the figure, 1 is the cutting part, 2 is the cam part that generates the chill, and 3 is the chiller.

Claims (1)

[Claims] 1 Silicon (Si) and carbon (C) in a weight ratio of 2.0
In alloyed cast iron with a CE value (carbon equivalent) of 4.1 to 5.0, which is contained in the range of %<Si≦3.0 and 3.1φ≦C≦4.0%, chilling promoting elements o, 1 % to 2.0%, surface damage resistant alloy cast iron that is chilled only in necessary parts. 2 Silicon (Si) and carbon (C) at a weight ratio of 2.0
%<Si≦3.0% and 3.1 coefficient≦C≦4.0% in alloyed cast iron having a CE value (carbon equivalent) of 4.1 to 5.0, containing 0.0% of the chilling promoting element. 1 to 2.0% and 0.5% or less of a chilling-inhibiting element, and is chilled only in necessary areas.