JPS616250A - Corrosion resistant cast iron - Google Patents

Abstract

PURPOSE:To obtain corrosion resistant cast iron giving a cast layer with improved resistance to lamellar exfoliation by adding prescribed amounts of Cu, Cr and Ni to cast iron manufactured by melting in a copola at a relatively low cost. CONSTITUTION:Cast iron having 3.8-4.5wt% C equiv. and consisting of, by weight, 2.8-4% C, 1.5-3% Si, 0.3-1.2% Mn, <0.2% P, 0.06-0.25% S and the balance Fe with impurities is manufactured by melting in a cupola, and 0.15- 3.5% Cu, 0.05-0.5% Cr and 0.05-0.5% Ni are added to the cast iorn. The resulting cast iron is effectively used as a material for automobile parts under going wear by sliding such as a brake disk, a brake drun, clutch parts and engine parts.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a corrosion-resistant cast iron, and particularly to a corrosion-resistant cast iron with improved delamination resistance of a rust layer, which is most suitable as a constituent material of automobile parts that undergo sliding wear.

For example, salt (
In areas where Na (Idl, etc.) is sprayed, cast iron brake discs are in a corrosive environment due to the salt and moisture, and frictional heat is generated by sliding with the friction pad, so corrosion of the brake disc increases significantly. , a rust layer is formed on the surface. When this rust layer grows to a certain thickness,
Partial or total peeling causes steps on the sliding surface of the brake disc. The flatness of the brake disc sliding surface is normally required to be 10 pm or less, but if the rust layer grows to about 200 to 1500 μm, delamination phenomenon of the rust layer will occur, so the sliding surface should be stepped. This causes a problem in that the vibration increases and the feeling during braking is impaired.

In order to deal with this problem, a cast iron is required in which the growth of the rust layer is slow and the delamination of the rust layer can be suppressed, but such a cast iron has not been developed to date.

Therefore, in order to absorb the heat generated by the brake disc and prevent the corrosion reaction from progressing, attempts have been made to increase the weight of the brake disc in order to increase the heat capacity of the brake disc more than necessary. This is not a good idea as it runs counter to current demands for reducing vehicle weight and reducing fuel consumption.

The problems associated with the delamination phenomenon of the rust layer are not only caused by brake discs that are in a corrosive environment due to salt, etc., but also to other parts such as pressure discs that are in a corrosive environment due to moisture, clutch parts such as flywheels, and gasoline. and an engine block in a corrosive environment due to salts containing S in oil, salts containing Cjl in oil, and moisture;
The same problem occurs with engine parts such as engine sleeves.

In view of the above-mentioned conventional problems, the present invention has been developed by adding a predetermined amount of C13% Cr to relatively low-cost cast iron obtained by cupola melting etc.
To provide a corrosion-resistant cast iron that significantly retards the growth of a rust layer in various corrosive environments by adding Ni and Ni, suppresses the oxidation increase in the rust layer, and improves the delamination resistance of the rust layer. purpose.

That is, in a carbon equivalent range of 3.8 to 4.5% by weight, C2,
Contains 8-4.0 wt% and Si L5-3.0 wt%, and further contains 0.3-1.2 wt% Mn, PO920
Weight% or less, 50.06 to 0.25% by weight, Cu 0
．． 15 to 3.5% by weight, Cr 0.05 to 0.5% by weight, Ni 0.05 to 0.5% by weight, and the balance Fe
It is characterized by containing impurities.

The reason for limiting the content of each of the above constituent elements is as follows.

(About alc, Si) C and Si are the basic elements constituting cast iron, and the graphite form and structure of the quantified area change depending on their quantitative combination.

Generally, the carbon equivalent (0% by weight + 1/33i weight%) is 4
．． When it exceeds 5% by weight, crystallization of primary graphite and generation of free ferrite increase, resulting in a decrease in tensile strength and hardness of cast iron. On the other hand, if the carbon equivalent is less than 3.8% by weight, the cast iron becomes white and the hardness of the cast iron becomes excessively high, impairing machinability. Therefore, the carbon equivalent is limited to 3.8 to 4.5% by weight, the C2 is limited to 8 to 4.0% by weight, and the Si is limited to 1.5 to 3.0% by weight.

Mn) About Mn Mn combines with S in cast iron to produce fine particles of MnS,
For automobile parts that are subject to sliding wear, the lubricating properties of the parts are improved, and there is an effect of suppressing wear on mating materials as well. However, if the Mn content is less than 0.3% by weight, the amount of MnS produced is small, although it depends on the amount of S, and the above effects cannot be obtained. On the other hand, if the Mn content exceeds 1.2%, the tendency to white iron increases, and the hardness of cast iron increases, impairing machinability. Therefore, the Mn content is 0.3 to 1.
Limited to 2% by weight.

(For QI P, if the P content exceeds 0.20% by weight, it has the effect of improving the fluidity of the molten metal, but on the other hand, it generates phosphorus in the quantified soil, making the cast iron brittle. Limited to content.

Regarding fdl S, S is necessary to produce MnS as described in the above section, but if the S content is less than 0.06% by weight, Mn
The production of S is small, while when it exceeds 0.25% by weight, Mn
The amount of S generated increases, resulting in an increase in the amount of Mn added, which increases the tendency to white iron and impairs the machinability of cast iron. Therefore, the content of S is limited to 0.06 to 0.25 times.

(e) About Cu Cu is completely dissolved in the quantified soil to densify the pearlite structure and suppress the elution of Fe ions.
a It has the effect of greatly retarding the growth of the rust layer of cast iron in an environment containing C1 and Ox, and suppressing the delamination phenomenon of the rust layer to improve corrosion resistance. Further, Cu has the effect of suppressing the generation of free ferrite and promoting graphitization. If the CU content is less than 0.15% by weight, the above-mentioned effects cannot be obtained, while if it exceeds 3.5% by weight, the hardness of the iron fabric and the rust layer increases excessively, deteriorating the sliding properties. Therefore, a phenomenon in which the rust layer partially peels off occurs. Therefore C
The content of u is limited to 0.15 to 3.5% by weight.

(f) About Cr and Ni When Cr and Ni are added independently, it is effective in suppressing the corrosion increase in cast iron, especially the oxidation increase, but it is effective in suppressing the delamination phenomenon of the rust layer. It has no effect at all. However, when Cr and Ni are added together with Cu, in addition to the above-mentioned effect of suppressing oxidation weight gain, there is an effect of suppressing the phenomenon of partial delamination of the rust layer. However, the Cr and Ni contents are 0.
．． If the amount is less than 0.05% by weight, there is no effect of suppressing the above-mentioned partial delamination phenomenon. Moreover, when the Cr content exceeds 0.5% by weight,
The occurrence of chromium carbides increases, making the material brittle, and the hardness also increases, impairing machinability, while the Ni content is 0.
．． When it exceeds 5% by weight, machinability is impaired as in the case of Cr. Therefore, the Cr and Ni contents are each 0
．． It is limited to 0.05 to 0.5% by weight.

Figure 1 shows that various samples with different Cu contents were cast, with 0.06% Cr and 0.07% Ni by weight.
This figure shows the probability of initial delamination of the rust layer relative to the CI3 content when a rust layer generation test was conducted on them.

For the rust layer generation test, the sample is heated at 250±50℃ for 60 minutes in an oxidation furnace, and then the sample is heated in a bath temperature of 20 to 90℃.
for 5 minutes in a supersaturated NaCl bath, after which the samples were exposed indoors for 1 to 10 hours.

As is clear from Figure 1, the Cu content is 0.15% by weight.
At above 0.15, the delamination phenomenon of the rust layer does not occur.
When the amount is less than % by weight, the delamination phenomenon of the rust layer increases rapidly.

Figure 2 shows the probability of peeling of the rust layer with respect to the thickness of the rust layer when the above rust layer generation test was performed on cast iron containing Cr and Ni with a Cu content of less than 0.15% by weight. When it grows to a thickness of 0.3 to Q, 4 + n,
The layered ff, lI separation phenomenon occurs, and the thickness of the rust layer is 1.
It can be seen that when the rust layer grows for 2 ms, 100% of the rust layer is peeled off.

In the present invention, by setting the Cu content to 0.15% by weight or more, the pearlite structure is strengthened, so F
The elution of s ions is suppressed, and the growth of the rust layer is significantly delayed and does not grow to a thickness that would cause peeling. As a result of the test, Cu0
．． In cast iron containing 67% by weight, 0.06% by weight of Cr, and 0.07% by weight of Ni, the average thickness of the rust layer was 0.15n or less.

In addition, in cast iron that contains Cr and Ni and has a Cu content of 0.15% by weight or more, a rust layer is formed densely, so the progress of corrosion is delayed. In cast iron with a Cu content of 0.15% by weight or less, the delamination phenomenon of the rust layer occurs 3 to 6 times, but in cast iron with the Cu content of 0.15% by weight or more, the delamination phenomenon of the rust layer does not occur at all. There wasn't.

FIG. 3 shows the relationship between the corrosion increase and loss with respect to the Cu content when each sample was subjected to 94 cycles (135 days elapsed) of the above-mentioned test.

(A) is Cu0.67% by weight and Cr0.06% by weight.

The case of the same sample as the present invention containing 0.07% by weight of Ni is shown, and in (A), the delamination phenomenon of the rust layer does not occur, so the rust layer is in the process of increasing in weight by oxidation, but the increase in weight is small. be.

(B) is a sample with a Cu content of 1.11% by weight, (C
) shows the case of a sample with a Cu content of 1.24% by weight. In both samples, the Cu content is within the range of the present invention, but since they do not contain Cr and Ni, the oxidation weight increase is (
More than A).

(D) - (I+) do not contain Cr and Ni, and C
The u content is 0.15% by weight or less, that is, (D)...0.
10% by weight, ([ri...0.14% by weight, (F)...
・0.03% by weight, (G)...0.02% by weight, (H
) 0.01% by weight is shown. In these cases, the delamination phenomenon of the rust layer occurs 3 to 6 times, so it can be seen that the corrosion weight loss is significant. Also (D) ~ (H
), the first delamination phenomenon occurs in 16 cycles, so even in a simple comparison, (^) is (D) to (11)
It can be said that it is more than 5 times better than that.

As described above, according to the present invention, a predetermined amount of Cu, Cr, and N is added to relatively low-cost cast iron obtained by cupola melting or the like.
By adding i, the growth of the rust layer in various corrosive environments is significantly delayed, and the oxidation increase in the rust layer is suppressed.
Furthermore, we can provide corrosion-resistant cast iron with improved delamination resistance of the rust layer, and can be used for automotive parts that undergo sliding wear, such as brake discs, brake drums, clutch parts (pressure discs, flywheels), and engine parts (engine blocks). , engine sleeves), etc.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the probability of initial delamination of the rust layer and the Cu content, Figure 2 is a graph showing the relationship between the probability of peeling and the thickness of the rust layer, and Figure 3 is the increase and decrease in corrosion as a function of the Cu content. It is a graph showing the relationship between quantities. □Funeral circle 1m! ”!5aii'il!ItlJy-;

Claims (1)

[Claims] In the range of carbon equivalent 3.8-4.5% by weight, C2.8-4
．． 0% by weight and 1.5-3.0% by weight of Si,
Further, Mn0.3-1.2% by weight, P0.20% by weight or less, S0.06-0.25% by weight, Cu0.15-3.
5% by weight, Cr0.05-0.5% by weight, Ni0.05
Corrosion-resistant cast iron with improved delamination resistance of a rust layer, characterized by containing ~0.5% by weight and the balance Fe and impurities.