KR100940819B1 - Brake disk - Google Patents

Abstract

PURPOSE: A brake disk is provided to have the heat resistance against high temperature, abrasion resistance, and shock resistance by adding cobalt and by applying graphite having coefficient of form of 0.20~0.525. CONSTITUTION: A brake disk is made of carbon(C) of 3.6 ~ 4.2 weight%, silicon(Si) of 2.0 ~ 3.0 weight%, manganese(Mn) of 1.0 weight% or less, phosphorus(P) of 0.05 weight% or less, sulfur(S) of 0.03 weight% or less, nickel(Ni) of 1.0 ~ 2.0 weight%, chrome(Cr) of 0.2 ~ 0.5 weight%, iron(Fe) including the impurities, and cobalt(Co) of 0.5 ~ 3.0 weight%. The coefficient of form of graphite is 0.20~0.525.

Description

Brake Discs {BRAKE DISK}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brake disc, and more particularly, to a brake disc capable of maintaining excellent braking characteristics even in a severe braking environment due to its excellent wear resistance, thermal cracking resistance, mechanical strength and thermal conductivity.

The brake disc is installed on the axle of the vehicle and is configured to be braked by frictional contact with the brake pads. Since such brake discs are in frictional contact with the brake pads at high pressures, they must have good wear resistance, heat resistance and impact resistance.

In general, the brake disc is configured by adding an alloying element to flake graphite cast iron, and distributes the hard pearlite on the matrix structure to improve the wear resistance.

By the way, the flake graphite cast iron brake disk is excellent in wear resistance, but has a disadvantage in that the mechanical strength is insufficient, there is a problem in that it is vulnerable to thermal stress, mechanical stress, thermal shock and the like. In particular, since it is vulnerable to thermal stress, mechanical stress, thermal shock, etc., it is pointed out that a defect that is easily thermally deformed and broken or damaged prematurely during frictional contact with the brake pad.

In view of this, there is a method of constructing the material of the brake disc with spherical graphite iron having high mechanical strength.

However, spherical graphite cast iron brake discs have high mechanical strength, but casting defects such as shrinkage holes and bubbles are more likely to occur inside the casting during casting. There is a disadvantage that can not be.

And it is pointed out that the heat cracking phenomenon occurs in the disk when continuously exposed to high temperature frictional heat because of these disadvantages.

On the other hand, in view of this, many brake discs which have improved castability, thermal conductivity and mechanical strength have been proposed.

As an example, there is a "CV graphite cast iron brake disc and its manufacturing method" of Korean Patent Publication No. 1996-0006452.

This technique improves the constituents and the ratio of components of the brake disc, and makes the shape of graphite into silkworm form, and has the intermediate properties of nodular cast iron and flake graphite cast iron. Therefore, it has both high mechanical strength, which is characteristic of spheroidal graphite cast iron, and excellent thermal conductivity, which is characteristic of flake graphite cast iron. As a result, a brake disc with improved mechanical strength and thermal conductivity can be obtained.

However, such brake discs have the disadvantage that, although mechanical strength and thermal conductivity are improved, they still lack mechanical strength and thermal conductivity.

In particular, in recent years, as various vehicles become larger and higher in speed, more and more cases are exposed to extreme braking environments. In this case, a conventional brake disc that lacks mechanical strength and thermal conductivity has an extreme braking environment, that is, extremely high temperature. The problem of being unable to cope with frictional heat, extreme frictional force and impact force has been pointed out.

As a result, it is pointed out that the conventional brake disc is unsuitable for use in a large-sized and high-speed vehicle, for example, a high-speed railway vehicle, a large truck, a highway bus, and the like.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and an object thereof is to provide a brake disc capable of maintaining excellent braking characteristics even in an extreme braking environment by configuring to have excellent mechanical strength and thermal conductivity.

Another object of the present invention is to provide a brake disc that can be applied to a large-sized and high-speed vehicle that requires extremely high heat resistance, extreme wear resistance and impact resistance by being configured to maintain excellent braking characteristics even in an extreme braking environment. .

In order to achieve the above object, in the brake disc according to the present invention, in the brake disc, carbon (C) is 3.6% by weight to 4.2% by weight based on the total weight ratio of the disk, and silicon (Si) is the total weight ratio of the disk. 2.0% to 3.0% by weight, manganese (Mn) is 1.0% by weight or less based on the total weight of the disk, phosphorus (P) 0.05% by weight or less, based on the total weight of the disk, sulfur (S) is 0.03% or less based on the total weight ratio of the disc, nickel (Ni) 1.0% to 2.0% by weight based on the total weight ratio of the disk, and chromium (Cr) 0.2% to 0.5 based on the total weight ratio of the disk By weight, molybdenum (Mo) is composed of 0.3% by weight to 1.2% by weight based on the total weight ratio of the disk, the remainder is characterized by consisting of iron (Fe) containing impurities.

Preferably, the cobalt (Co) is further included, characterized in that the cobalt is contained in 0.5% by weight to 3.0% by weight based on the total weight ratio of the disk. And the shape coefficient of graphite is 0.20 to 0.525.

The brake disc according to the present invention has an effect of having a CV graphite structure excellent in abrasion resistance, thermal crack resistance, mechanical strength and thermal conductivity because the components and the component ratio are greatly improved.

In addition, because of excellent wear resistance, thermal cracking resistance, mechanical strength and thermal conductivity, it is possible to maintain excellent braking characteristics even in extreme braking environment. In particular, even when exposed to extremely high frictional heat and extreme impact force has an effect that can maintain excellent braking characteristics continuously.

In addition, since it is possible to maintain excellent braking characteristics even in an extreme braking environment, there is an effect that can be applied to a large-sized, high-speed vehicle that requires extreme heat resistance, wear resistance and impact resistance.

Hereinafter, a preferred embodiment of the brake disc according to the present invention will be described in detail.

First, the brake disc of the present invention is manufactured by casting a molten raw material, and is composed of Fe-c cast iron, and includes iron (Fe) and carbon (C).

Carbon includes both carbon crystallized in graphite (Gr) and carbon dissolved in iron (Fe). Such carbon is preferably formed in the range of 3.6% by weight to 4.2% by weight based on the total weight ratio of the brake disc.

The reason for this is that in order to increase the castability and crack resistance of the brake disc, the carbon content should be increased to lower the solid solution carbon and increase the amount of CV graphite. By the way, when carbon content exceeds 4.2 weight% in order to increase carbon content, the coarsening phenomenon of CV graphite structure will arise at the time of manufacture, and it will lower the mechanical performance of a product.

Therefore, the optimum carbon content for increasing the castability and crack resistance of the brake disc preferably does not exceed 4.2% by weight. Most preferably, it is in the range of 3.8 weight%-4.0 weight% based on the total weight ratio of a disk.

The brake disc of the present invention includes silicon (Si), manganese (Mn), phosphorus (P), and sulfur (S).

Silicon plays a role of promoting the crystallization of CV graphite while being dissolved in iron and is preferably formed in the range of 2.0% by weight to 3.0% by weight based on the total weight ratio of the brake disc.

This is because crystallization of CV graphite decreases when the content of silicon is less than 2.0% by weight, and degradation reaction occurs in the crystallized CV graphite structure when the content of silicon exceeds 3.0% by weight, thereby lowering the mechanical strength of the entire disc.

Therefore, it is preferable that the optimal silicon content which promotes crystallization of graphite is in the range of 2.0 weight%-3.0 weight% based on the total weight ratio of a disk.

Manganese has strong affinity with sulfur, and reacts with sulfur to form a manganese sulfide (MnS) compound. The manganese formed with this MnS compound neutralizes the harmful action of sulfur, which inhibits the crystallization of CV graphite.

Such manganese is preferably composed of 1.0% by weight or less based on the total weight ratio of the disk.

Phosphorus improves abrasion resistance and weather resistance of the disk, and is preferably made up to 0.05% by weight or less based on the total weight ratio of the disk. This is because if the content of phosphorus exceeds 0.05% by weight, a ternary process compound called Steadite may be formed in the cast iron structure, thereby embrittling the material of the disk and degrading workability.

Sulfur plays a role of improving the machinability, corrosion resistance, heat resistance, and the like of the disk, and is preferably composed of 0.03% by weight or less based on the total weight ratio of the disk.

This is because when the content of sulfur exceeds 0.03% by weight, it is harmful to obtain CV graphite structure by preventing CV formation of graphite.

And the brake disc of this invention contains nickel (Ni), chromium (Cr), and molybdenum (Mo).

Nickel is an effective element for strengthening the matrix structure to improve strength and hardness. In particular, it serves to reduce the tendency of chilling of the matrix by the addition of chromium, molybdenum and the like.

Such nickel is preferably contained in the range of 1.0% by weight to 3.0% by weight based on the total weight ratio of the disk.

This is because if the content of nickel is less than 1.0% by weight, the pearlite phase of the matrix structure may grow coarse. If the content of nickel exceeds 3.0% by weight, the matrix structure tends to martensite in the kitchen state. Most preferably, the nickel content is contained in the range of 1.0% by weight to 2.0% by weight based on the total weight ratio of the disk.

Chromium is a pearlite-promoting element that refines the pearlite structure. Therefore, it serves to greatly improve the high temperature strength and wear resistance of the brake disc.

Such chromium is preferably contained in the range of 0.2% by weight to 0.5% by weight based on the total weight ratio of the disk. In particular, it is preferable that the content of chromium does not exceed 0.5% by weight.

This is because if the content of chromium exceeds 0.5% by weight, carbides may be formed to inhibit CV graphite.

In addition, since chromium may form a composite phosphorus-chromium carbide when phosphorus (P) is contained in the molten metal at the time of casting at 0.1% by weight or more, much caution is required during casting.

Molybdenum plays a role of increasing strength at high temperatures and improving thermal fatigue resistance, and the molybdenum is preferably contained in a range of 0.3% by weight to 1.2% by weight based on the total weight ratio of the disk. In particular, it is preferable that the content of molybdenum does not exceed 1.2% by weight.

This means that when the content of molybdenum exceeds 1.2% by weight, M ₂₃ C ₆ or M ₂₃ C ₆ carbides are locally generated at the grain boundary and segregated in the thick portion having a slow cooling rate, thereby achieving the present invention. It is because there exists a possibility that the heat-resistant cracking characteristic at high temperature may fall.

The brake disc of the present invention further includes cobalt (Co).

Cobalt is a useful element for improving high temperature strength and thermal crack resistance. In particular, it serves to reduce the tendency of chilling of the matrix by the addition of chromium, molybdenum and the like.

Such cobalt is preferably contained in the range of 0.5% by weight to 3.0% by weight based on the total weight ratio of the disk.

This is because if the content of cobalt is less than 0.5% by weight, the thermal cracking performance is drastically reduced, and even if the content of cobalt is more than 3.0% by weight, the thermal cracking performance is poor. On the other hand, such cobalt may not be included in some cases.

The brake disc, which is composed of the above components and composition ratio, has a CV graphite structure having excellent abrasion resistance, thermal crack resistance, mechanical strength and thermal conductivity.

Therefore, excellent braking characteristics can be maintained even in an extreme braking environment. In particular, excellent braking characteristics can be maintained even when exposed to extremely high frictional heat and extreme impact forces. As a result, the present invention can be applied to large-sized and high-speed vehicles that require extreme heat resistance, wear resistance, and impact resistance.

Next, the present inventors manufactured brake discs with different constituents and component ratios as shown in Table 1 and Table 2, and compared and tested the mechanical properties of the manufactured brake discs.

Table 1 shows examples of brake discs manufactured by different components and component ratios, and Table 2 shows the results of comparative tests of the embodiments of Table 1 with several items.

In this case, Examples 1-4 are examples in which the components and the component ratios are differently formed within the above-mentioned ranges, and Comparative Examples are examples in which the components and the component ratios are out of the above-described ranges. It is the case that I made. As test conditions, a 1-inch-Y specimen was used as a test piece for measuring mechanical properties, and the CV graphing rate and shape coefficient were measured using an image analyzer.

TABLE 1

Ingredient (% by weight) Carbon (C) Silicon (Si) Manganese (Mn) Phosphorus (P) Sulfur (S) Nickel (Ni) Chromium (Cr) Molybdenum (Mo) Copper (Cu) Cobalt (Co) Remarks Example 1 3.65 2.56 0.23 0.04 0.018 1.15 0.45 1.15 - - Example 2 3.76 2.45 0.25 0.03 0.020 1.54 0.32 1.02 - 0.7 Example 3 3.89 2.17 0.24 0.04 0.012 1.85 0.25 0.52 - 2.4 Example 4 4.12 1.53 0.27 0.04 0.013 1.98 0.21 0.59 - 2.4 Comparative example 3.20 2.3 0.25 0.06 0.015 1.20 0.34 0.30 0.80 -

TABLE 2

division Tensile Strength (MPa) Hardness (HB) Graphite  Remarks CV graphite rate Shape factor of graphite Example 1 446 215 89% 0.20 Example 2 442 224 94% 0.52 Example 3 467 245 84% 0.42 Example 4 462 248 82% 0.52 Comparative example 430 235 80% 0.40 to 0.50

As a result of the test, the brake discs of Examples 1-4 in which the constituents and the component ratios were formed within the above-mentioned ranges showed that the CV graphitization rate and the shape coefficient of graphite (0.20 to 0.525) were relatively higher than those of the comparative example. In addition, the tensile strength and hardness also appeared to be superior to the comparative example.

As a result, the brake disc produced by the present invention was superior in both tensile strength and hardness than the conventional brake disc, thereby showing a very good wear resistance and thermal crack resistance and mechanical strength and thermal conductivity.

Although the preferred embodiments of the present invention have been described above by way of example, the scope of the present invention is not limited to these specific embodiments, and may be appropriately changed within the scope of the claims.

Claims (3)

Carbon (C) is 3.6% to 4.2% by weight based on the total weight ratio of the disk, silicon (Si) is 2.0% to 3.0% by weight based on the total weight ratio of the disk, and manganese (Mn) is the total weight ratio of the disk. 1.0% by weight or less, phosphorus (P) is 0.05% by weight or less based on the total weight of the disk, sulfur (S) is 0.03% or less by weight based on the total weight of the disk, nickel (Ni) is the total weight by weight of the disk 1.0% to 2.0% by weight, chromium (Cr) is 0.2% to 0.5% by weight based on the total weight of the disk, molybdenum (Mo) 0.3% to 1.2% by weight based on the total weight of the disk In the brake disk is composed of iron, and the rest is composed of iron (Fe) containing impurities, Cobalt (Co) is further contained in 0.5% to 3.0% by weight based on the total weight ratio of the disk, the brake disk characterized in that the shape coefficient of graphite is 0.20 to 0.525. delete delete