JPS6117900B2 - - Google Patents

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, in areas where salt (NaCl, etc.) is sprayed on roads as a snow melting agent or antifreeze agent during the severe winter,
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 pads, so corrosion of the brake disc increases significantly and a rust layer is formed on the surface. When this rust layer grows to a certain thickness, it peels off partially or completely, causing steps on the sliding surface of the brake disc. The flatness of the brake disc sliding surface is normally required to be 10 μm or less, but if the rust layer grows to about 200 to 1500 μm, delamination of the rust layer will occur, so the sliding surface must 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 problem associated with the delamination phenomenon of the rust layer is not only the brake disc which is in a corrosive environment due to salt etc., but also other parts such as clutch parts such as pressure discs and flywheels which are in a corrosive environment due to moisture. The same problem occurs in engine parts such as engine blocks and engine sleeves that are in a corrosive environment due to salts containing S in gasoline and oil, salts containing Cl in oil, and moisture.

In view of the above-mentioned conventional drawbacks, the present invention has been developed to produce a predetermined amount of relatively low-cost cast iron obtained by cupora melting etc.
By adding Cu, Cr, and Ni, we provide corrosion-resistant cast iron that significantly retards the growth of the rust layer in various corrosive environments, suppresses the oxidation increase in the rust layer, and further improves the delamination resistance of the rust layer. The purpose is to

That is, in the range of carbon equivalent 3.8 to 4.5% by weight, C2.8
Contains ~4.0 wt% and Si1.5~3.0 wt%, plus Mn0.3~1.2 wt%, P0.20 wt% or less, S0.06
~0.25wt%, Cu0.15~3.5wt%, Cr0.05~0.5
wt%, Ni0.05-0.5wt% and balance Fe
It is characterized by containing impurities.

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

(a) About C and Si C and Si are the basic elements that make up cast iron.
The graphite morphology and the structure of the iron fabric change depending on their quantitative combination. In general, carbon equivalent (C weight %
+1/3Si weight%) exceeds 4.5% 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 iron, and the hardness of the cast iron becomes excessively high, impairing machinability. Therefore, the carbon equivalent is limited to 2.8 to 4.0 weight % and Si 1.5 to 3.0 weight % within the range of 3.8 to 4.5 weight %.

(b) About Mn Mn combines with S in cast iron to produce fine particles of MnS, which is useful for automobile parts that wear due to sliding.
Its lubrication properties are improved, and it has the effect of suppressing wear, including on the mating material. However, the Mn content
If it is less than 0.3% by weight, MnS
is produced in small quantities, and the above effects cannot be obtained. On the other hand, if the Mn content exceeds 1.2% by weight, the tendency to white iron increases, and the hardness of cast iron increases, impairing machinability. Therefore, the Mn content is limited to 0.3 to 1.2% by weight.

(c) Regarding P When the content of P exceeds 0.20% by weight, it has the effect of improving the fluidity of the molten metal, but on the other hand, it generates phosphoric acid in the iron fabric and makes the cast iron brittle, so the above content is limited in quantity.

(d) About S S is necessary to generate MnS as described in the above (b), but when the S content is less than 0.06% by weight, the production of MnS is small;
If it exceeds , the amount of MnS produced increases, and as a result
This results 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 S content is limited to 0.06 to 0.25% by weight.

(e) About Cu Cu is completely dissolved in the iron material to densify the pearlite structure, suppress the elution of Fe ions, and significantly inhibit the growth of the rust layer on cast iron, especially in environments containing NaCl and O ₂ . This has the effect of delaying corrosion and suppressing the delamination phenomenon of the rust layer, thereby improving corrosion resistance. Cu also 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 effects cannot be obtained, while if it exceeds 3.5% by weight, the hardness of the iron fabric and the rust layer will increase excessively, deteriorating the sliding properties, and the rust layer will A partial peeling phenomenon occurs. Therefore, the Cu content is
Limited to 0.15-3.5% by weight.

(f) About Cr and Ni When Cr and Ni are added alone, they are effective in suppressing the increase in corrosion of cast iron, especially the increase in oxidation, but they are not effective at all in suppressing the delamination phenomenon of the rust layer. has no effect. but
Adding Cr and Ni together with Cu has the effect of suppressing the phenomenon of partial delamination of the rust layer in addition to the above-mentioned effect of suppressing weight gain due to oxidation. However, if the Cr and Ni contents are less than 0.05% by weight, there is no effect of suppressing the above-mentioned partial delamination phenomenon. Also, the Cr content is 0.5% by weight.
If the Ni content exceeds 0.5% by weight, the occurrence of chromium carbides will increase, making the material brittle, and the hardness will also increase, impairing the machinability.On the other hand, if the Ni content exceeds 0.5% by weight, the machinability will decrease as in the case of Cr. spoil. Therefore, the Cr and Ni contents are each 0.05~
Limited to 0.5% by weight.

Figure 1 shows Cr0.06% by weight and Ni0.07% by weight.
Cu when various samples with different Cu contents were cast and a rust layer formation test was performed on them.
This shows the probability of initial delamination of the rust layer relative to the content.

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 to a bath temperature of 20~50℃.
After immersion in a supersaturated NaCl bath at 90° C. for 2 minutes, the samples were exposed indoors for 1 to 10 hours.

As is clear from FIG. 1, when the Cu content is 0.15% by weight or more, the delamination phenomenon of the rust layer does not occur, but when it is less than 0.15% by weight, the delamination phenomenon of the rust layer increases rapidly.

Figure 2 shows the peeling probability with respect to the thickness of the rust layer when the rust layer formation test is performed on cast iron that does not contain Cr or Ni and has a Cu content of less than 0.15% by weight. It can be seen that when the rust layer grows to 0.3 to 0.4 mm, the delamination phenomenon occurs, and when the rust layer grows to a thickness of 1.2 mm, 100% of the rust layer peels off.

In the present invention, by setting the Cu content to 0.15% by weight or more, the pearlite structure is strengthened, so elution of Fe ions is suppressed, and the growth of the rust layer is significantly delayed and does not grow to a thickness that leads to peeling. As a result of the test, the average thickness of the rust layer was 0.15 mm or less in cast iron containing 0.67% by weight of Cu, 0.06% by weight of Cr, and 0.07% by weight of Ni.

In addition, in cast iron containing Cr and Ni with a Cu content of 0.15% by weight or more, a dense rust layer is formed, slowing down the progress of corrosion, and when the above test is repeated.
In cast iron that does not contain Cr or Ni and has 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 a Cu content of 0.15% by weight or more, the delamination of the rust layer does not occur. No phenomena occurred at all.

Figure 3 shows 94 cycles (135 days elapsed) for each sample, with the above test as one cycle.
This figure shows the relationship between the increase and decrease in corrosion with respect to the Cu content.

A shows the same sample as the present invention containing 0.67% by weight of Cu, 0.06% by weight of Cr, and 0.07% by weight of Ni. In A, the rust layer is oxidized because the delamination phenomenon of the rust layer does not occur. It is in the process of increasing its volume, but the increase is small.

B is a sample with a Cu content of 1.11% by weight, C is a sample with a Cu content of 1.11% by weight.
The case of a sample with a Cu content of 1.24% by weight is shown. In both samples, the Cu content is within the range of the present invention, but since they do not contain Cr and Ni, the weight gain due to oxidation is greater than that in A.

D to H do not contain Cr and Ni, and the Cu content is 0.15% by weight or less, that is, D...0.1% by weight, E...
...0.14% by weight, F...0.03% by weight, G...0.02% by weight, and H...0.01% by weight. For these, the delamination phenomenon of the rust layer occurred 3 to 6 times. It can be seen that the corrosion loss is significantly reduced. In addition, for D to H, the initial delamination phenomenon was 16
Since it occurs in cycles, even a simple comparison shows that A
It can be said that it is 5 times or more superior to D to H.

As described above, according to the present invention, a predetermined amount of cast iron, which is relatively low cost and can be obtained by cupora melting, etc.
By adding Cu, Cr and Ni, we have created corrosion-resistant cast iron that significantly retards the growth of the rust layer in various corrosive environments, suppresses the oxidation increase in the rust layer, and further improves the delamination resistance of the rust layer. It is effective as a constituent material for automobile parts that undergo sliding wear, such as brake discs, brake drums, clutch parts (pressure discs, flywheels), and engine parts (engine blocks, engine sleeves).

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the probability of initial delamination of a 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 a graph showing the relationship between the probability of peeling and the thickness of the rust layer.
The figure is a graph showing the relationship between corrosion increase and loss with respect to Cu content.

Claims (1)

[Claims] 1 Carbon equivalent range of 3.8 to 4.5% by weight, C2.8 to 4.0
wt% and Si1.5-3.0 wt%, and further
Mn0.3~1.2wt%, P0.20wt% or less, S0.06~
The delamination resistance of the rust layer is characterized by containing 0.25% by weight of Cu, 0.15-3.5% by weight of Cu, 0.05-0.5% by weight of Cr, 0.05-0.5% by weight of Ni, and the balance containing Fe and impurities. Cast iron with improved corrosion resistance.