JPH0358826B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to a method for casting a brake disc material for a vehicle with improved fatigue strength and thermal cracking resistance. (Prior art) In order to effectively brake trains, materials for vehicle brake discs have traditionally been selected based on friction properties such as stability of friction coefficient and wear resistance. Flake graphite cast iron has been widely used as a material. However, as train speeds have increased in recent years, the negative energy rate of brakes has increased significantly, and as a result, conventional materials do not have sufficient properties in terms of strength or thermal cracking, and the sliding surface In many cases, components must be replaced before they are used to their maximum capacity. On the other hand, ferritic graphite cast iron with improved heat cracking resistance is also known, but this material has a large amount of ferrite and has not necessarily achieved satisfactory properties in terms of fatigue strength. Furthermore, Japanese Patent Application Laid-Open No. 134537/1983 describes a technique for improving wear resistance by changing the base structure to pearlite in vermicular graphite cast iron in which the spheroidization rate of graphite is reduced to 50% or less. ing. Namely, these are a method of adding pearlite stabilizing elements, a method of heat treating the entire cast article, and a method of subjecting only the surface of the cast article to heat treatment by high frequency. Furthermore, Mn and Cu are known as pearlite stabilizing elements in spheroidal graphite cast iron. In this case, the Mn content is usually about 0.2 to 0.4% by weight, but for pearlite stabilization it is 0.6 to 0.8%.
It is said to be about % by weight. On the other hand, the content of Cu is about 0.2 to 0.5% by weight when added alone (New Edition Steel Technology Course Volume 5 "Steel Castings/Cast Iron Castings")
270 pages Edited by Japan Iron and Steel Institute, May 30, 1978 Co., Ltd.
Published by Jijin Shokan). (Problem to be solved by the invention) However, as stated in the above publication,
In the method of adding a pearlite stabilizing element, it is necessary to add a large amount of an expensive element to form pearlite, and there is a problem that castability and machinability are reduced. Furthermore, in the case of pearlitizing the entire cast article by heat treatment, a large amount of thermal energy is required, resulting in an increase in cost. In addition, in the case of heat treatment of the surface of the cast article,
Only the surface portion can be hardened (the hardening depth is relatively shallow), and the rest becomes a ferrite-based structure. Therefore, even if this method is applied to brake discs for high-speed vehicles, which have a large energy negative rate, it is difficult to secure the necessary strength as a disc structure, and furthermore, the presence of graphite causes burnout. There are also problems with cracking and deformation during heat treatment. Furthermore, it is possible to inoculate the base to make pearlite, but Cu-Sn is used as an inoculant.
Even if a type of material is used, the Mn content is 0.2 to 0.4.
If it is about 0.5% by weight, the amount of inoculum is 0.5% by weight.
degree is required. In other words, the object of the present invention is to improve the graphite shape and appropriately control the base structure without causing the above-mentioned problems, and to improve the fatigue strength while ensuring excellent braking performance. Another object of the present invention is to provide a method for casting a brake disc material for a vehicle, which can significantly slow down the growth of thermal cracks. (Means for Solving the Problems) The present invention solves these problems by providing a solution to the molten metal.
While the spheroidization rate of graphite is controlled through CV treatment by adding a CV agent, the base structure is made into pearlite by controlling the mold release conditions after inoculation and pouring. By using a molten metal containing a pearlite stabilizing element, it is possible to achieve pearlite formation with a small amount of pearlite stabilizing inoculant, and by using a graphitization promoting element in this inoculant, chilling is prevented. The aim is to make it possible to produce pearlite at the same time. That is, the specific means for this purpose is a method for casting vehicle brake disc materials made of cast iron containing a mixture of spheroidal graphite and CV graphite, in which a molten metal containing 0.6 to 0.99% by weight of Mn as a pearlite stabilizing element is used. , a CV treatment in which a CV agent was added to increase the spheroidization rate of graphite to 30 to 60% as determined by the NIK method, and an inoculation treatment in which a Cu-Sn-Si-Fe-based inoculant was added. By controlling the demolding time after hot water, a pearlite structure base with a ferrite ratio of 50% or less is created, which improves fatigue strength and heat cracking resistance. In the above casting method, the spheroidization rate of graphite is reduced by CV treatment by adding a CV agent to the molten metal.
Spheroidal graphite and 30-60% determined by NIK method
The reason why a CV graphite mixed structure is obtained is as follows. That is, the purpose is to ensure excellent braking performance (frictional properties) in the vehicle brake disc material while improving its fatigue strength and heat cracking resistance. In this case, the CV graphite ensures stability of the friction coefficient and wear resistance, and the spheroidization of the graphite improves fatigue resistance. It has the effect of relaxing, suppressing the occurrence of thermal cracks, and further slowing down the growth of thermal cracks. The reason for the limitation on the spheroidization rate of graphite is that the spheroidization rate is
If it is less than 30%, the fatigue strength is not much different from that of conventional flake graphite cast iron, and a sufficient improvement in fatigue strength due to graphite spheroidization cannot be expected, and the spheroidization rate is 60%.
%, although the above-mentioned fatigue strength can be improved, the friction coefficient decreases and good braking performance cannot be ensured. Furthermore, the reason why the ferrite ratio in the matrix structure is set to 50% or less is to suppress the ferrite ratio so that a large amount of pearlite structure appears, thereby preventing a decrease in friction wear resistance and fatigue strength. In other words, the reason for limiting the ferrite ratio is that if it exceeds 50%, the thermal conductivity improves and it is advantageous in terms of preventing thermal cracking, but the friction wear resistance and fatigue strength decrease, making it difficult to achieve the intended purpose. It lies in not being able to achieve enough. Therefore, in this case, the ferrite ratio may be controlled in relation to the pad material applied to the brake disc material. (Function) <Function of each element> - Adjustment of molten metal - In the present invention, the amount of Mn in molten metal ○ is increased. In other words, the amount of Mn is usually set to a level that eliminates the harmful effects of S (graphitization inhibiting element), for example, 0.3% by weight.
It would be good if it were strong, but in the present invention, the amount is increased to 0.6 to 0.99% by weight, so that the pearlite of the matrix structure can be stabilized. In this case, if the amount of Mn is less than 0.6% by weight, the pearlite stabilizing effect described above cannot be obtained sufficiently, and if the amount of Mn exceeds 0.99% by weight, the adverse effects of chilling will increase and the cost will increase. It will also be disadvantageous. - Inoculant - Cu and Sn in the inoculant are pearlite stabilizing elements and contribute to pearlite formation of the matrix structure. In addition, Cu and Si in the inoculant are elements that promote graphitization and contribute to controlling the graphite structure.
Suppresses base tissue chilling. Fe in the inoculant is alloyed with the above-mentioned Si and is useful for controlling the graphitization reaction. - Control of demolding time - The amount of pearlite in the matrix structure can be adjusted by controlling the standing time from pouring to demolding, that is, the demolding time. That is, by shortening the demolding time, the amount of pearlite can be increased. <Actions due to the binding of each element> - Reduction in the amount of inoculant - In the present invention, by adjusting the molten metal, selecting the inoculant, and controlling the mold release conditions, the amount of ferrite in the base structure is suppressed and the pearlite structure is increased. I try to appear. In this case, when converting the base structure into pearlite, instead of simply inoculating the base structure, a molten metal containing a large amount of Mn as a pearlite stabilizing element is used, and the mold breaking conditions after pouring are controlled. Since it is also used in combination, the amount of inoculant added can be reduced. That is, as mentioned above, Mn contributes to stabilizing pearlite, and pearlite formation can be achieved by controlling the mold release time after pouring, so the amount of inoculum can be reduced to, for example, 0.04% by weight. Can be lowered. Therefore, when compared with the conventional inoculant amount of 0.5% by weight for molten metal with a small amount of Mn, when the present invention is used, the inoculant amount can be reduced to about 1/10 of the conventional method. This makes it possible to prevent casting defects caused by too much inoculant and improve castability. - Prevention of Chilling of Base Structure - The reason for using Cu as the inoculant for stabilizing pearlite is that it also has the function of promoting graphitization. That is, as mentioned above, Mn contributes to stabilizing pearlite, but if its amount is too large, it tends to cause chilling. On the other hand, since Cu is a pearlite stabilizing element and a graphitization promoting element,
Together with Si, which is another graphitization promoting element, it prevents the base structure from being chilled. -Improved machinability- And in this way, the components contained in the molten metal
Mn and the inoculants Cu and Sn can transform the base structure into pearlite, while the inoculants Cu and Si can prevent chilling, resulting in improved machinability. Regarding the machinability, the graphite has a mixed structure of spheroidal graphite and CV graphite, and the spheroidization rate of graphite is 30 to 60%, so it does not have a negative effect on machinability. Since ferrite is mixed in the base, this is also advantageous in terms of machinability. (Effects of the Invention) Therefore, according to the present invention, the spheroidization rate is controlled to 30 to 60% as determined by the NIK method by CV treatment of the molten metal, and a mixed structure of spheroidal graphite and CV graphite is obtained. Using a molten metal containing Mn as a pearlite stabilizing element, by inoculating with a Cu-Sn-Si-Fe-based inoculant and controlling the mold release conditions, we can suppress chilling and achieve pearlite with a small amount of inoculant. , it is possible to obtain a pearlite structure base with a ferrite rate of 50% or less. Therefore, excellent effects can be obtained in that fatigue strength, thermal crack propagation resistance, and friction wear resistance can be improved while ensuring excellent braking performance without impairing castability and machinability. (Example) Hereinafter, an example of the present invention will be described based on the drawings. Example 1 The brake disc material of this example was obtained by processing molten metal having the chemical composition shown in Table 1. In the same table, the proportions are shown in % by weight.

[Table] In other words, in this example, the Mn amount is 0.99
% of molten metal, 15Ca-
CV treatment with 3Mg-based CV agent and 25Cu−18Sn
- Inoculation treatment with an inoculant of Si--Fe was carried out, and after pouring, the mold was removed for about 1 hour. In this case, the amount of the CV agent added to the molten metal is 0.6% by weight, and the amount of inoculant is 0.04% by weight. The metal structure of the brake disc material obtained by this casting is shown in FIG. 1 as a micrograph (100x magnification). The graphite spheroidization rate of this brake disc material was determined by the NIK method to be 50%, and the ferrite rate was less than 5%, and the photograph shows that it has a mixed structure of CV graphite and spheroidal graphite. Here, the NIK method is an evaluation table that ranks the degree of spheroidization based on the shape of graphite that appears in a micrograph (rank ranges from 0 to 1, with flaky graphite being 0 and approximately circular graphite being 1). ), calculate the number of graphite in each rank within a predetermined range of the micrograph, and calculate the sum of the graphite numbers multiplied by the degree of spheroidization (coefficient) of each rank. This is a method of determining the rate. This determination method is stipulated by the Japan Foundry Association. On the other hand, the ferrite ratio can be determined by etching the cross section of the metal and observing it under a microscope.
Judgment was made by calculating the area ratio. In the case of this example, the amount of CV agent added was 0.6% by weight.
By doing this, the spheroidization rate of graphite was made to be 50%, but this spheroidization rate depends on the amount of CV agent added,
It can be controlled to a desired value by adjusting the type, etc., and further by adjusting the amount of inoculant containing Cu and Si as graphite promoting elements. Further, S in the above molten metal is 0.014% by weight,
Generally, the amount of Mn required to eliminate the influence of graphitization inhibition (harmful chilling) caused by S is 1.7×S%+0.3%, but in this example, this is increased to 0.99%. Therefore, this excess Mn generates carbides to form double carbides with cementite, and has the effect of stabilizing pearlite. Cu and Sn in the inoculant are pearlite stabilizing elements, but as mentioned above, Mn contributes to stabilizing pearlite, so the amount of inoculant containing Cu and Sn can be reduced. It is something. Furthermore, since the ferrite rate, and therefore the amount of pearlite, is controlled by the demolding conditions (the demolding time), the amount of the inoculant added can be reduced. Incidentally, as the demolding time increases, the amount of ferrite increases. Since Cu is a pearlite-stabilizing element and also a graphitization-promoting element, Si, which is another graphitization-promoting element in the inoculant,
Together with this, it is possible to more effectively prevent the base tissue from being chilled. Next, the brake disc material of this example (FCV
50) and the conventional brake disc material made of flake graphite cast iron (FC28) shown in Fig. 2.
Brake performance and fatigue strength are compared based on tests. Brake performance test is based on initial speed (speed just before braking)
The test results are shown in Figure 3, which examines the relationship between the average coefficient of friction and the initial speed and the braking distance. From the characteristic diagram in the figure, it can be seen that there is almost no difference in brake performance between the material of this example (FCV50) and the conventional material (FC28). On the other hand, in the fatigue strength test, the specimen temperature was 300℃.
At 500°C, a load is applied to the test piece to achieve a predetermined strain rate by tensile compression at a rate of 1 cycle per 2 minutes, and then the load is removed to determine the number of cycles until the test piece breaks. The test results are shown in Figure 4. From the characteristic diagram in the same figure, the material of this example (FCV50) is better than the conventional material (FCV50) at both 300℃ and 500℃.
It can be clearly seen that the fatigue strength is superior to that of 28). Therefore, from FIGS. 3 and 4 above, it can be seen that in this example, the brake performance can be made comparable to that of the conventional material, while the fatigue strength can be greatly improved. Furthermore, when a separate durability test was conducted to generate thermal cracks, it was confirmed that the material of this example had improved durability and a lifespan of about 20% longer than conventional materials. Example 2 The brake disc material of this example was obtained by treating molten metal having the chemical composition shown in Table 2 in the same manner as in Example 1. The percentages in the table are expressed in % by weight.

[Table] The spheroidization rate of graphite was the same as that in Example 1.
By changing the mold release conditions, ferrite percentages of 10%, 30%, and 50% were obtained. In this case, the demolding time for each of the above ferrite ratios is as follows. Ferrite rate Demolding time 10% 1 to 2 hours 30% 12 hours 50% 24 hours Three types of brake disc materials (FCV materials) with different ferrite rates in this example and conventional material (FC28)
When friction performance tests were conducted using different lining materials, the results shown in Table 3 were obtained. The test speed is 15.5m/sec. In the table,
Synthetic type RD-18 consists of metal powder, graphite, rubber, and phenol resin (base material), and sintered type AI-1632 consists of SiO ₂ Al ₂ O ₃ , Bi, graphite, and bronze (base material). . Moreover, the wear amount of the lining material is the average of two pieces.

[Table] In Table 3, the disk material of this example (FCV material) has less wear than the conventional material (FC28) at a ferrite ratio of 10 to 50%.
In addition, the wear amount of the lining material, which is the mating material, is less in this example, and there is almost no difference in the average friction coefficient between this example and the conventional example, and the ferrite ratio is in the range of 10 to 50%. It can be seen that sufficiently good braking performance can be obtained.

[Brief explanation of drawings]

Fig. 1 is a micrograph showing the metallographic structure of the disc brake material according to the present invention, Fig. 2 is a photomicrograph showing the metallographic structure of the conventional disc brake material, and Fig. 3 shows the braking performance of the present invention and the conventional example. Fig. 4 is a graph showing a comparison of the fatigue strength of the present invention and a conventional example.

Claims (1)

[Claims] 1. A method for casting a vehicle brake disc material made of cast iron containing a mixture of spheroidal graphite and CV graphite, in which Mn is a pearlite stabilizing element of 0.6 to 0.99.
CV treatment in which a CV agent is added to the molten metal containing % by weight to make the graphite spheroidization rate 30 to 60% as determined by the NIK method, and inoculation in which a Cu-Sn-Si-Fe based inoculant is added. A brake for a vehicle characterized by increasing fatigue strength and heat cracking resistance by forming a base of a pearlite structure with a ferrite ratio of 50% or less by performing a treatment and controlling the demolding time after pouring. Casting method for disc material.