KR20100076709A

KR20100076709A - Cast iron with high thermal resistancce for railway vehicle brake discs

Info

Publication number: KR20100076709A
Application number: KR1020080134839A
Authority: KR
Inventors: 구병춘; 임충환
Original assignee: 한국철도기술연구원
Priority date: 2008-12-26
Filing date: 2008-12-26
Publication date: 2010-07-06

Abstract

The present invention relates to a cast iron for a high heat resistant railway vehicle brake disc, and more particularly, to improve the heat resistance and abrasion resistance of a brake disc which is installed on the side or axle of a wheel and generates a braking force while friction with the brake pad. The present invention relates to a cast iron for a brake disc of a heat resistant railway vehicle.

The present invention is a cast iron used to manufacture a brake disc for rolling stock, the cast iron in weight percent of carbon (C) 3.0 to 3.8, silicon (Si) 2.0 to 2.6, manganese (Mn) 0.3 to 1.0, phosphorus (P) 0.01 to 0.04, sulfur (S) 0.01 to 0.12, copper (Cu) 0.1 to 0.6 and iron (Fe) is characterized in that it comprises a 92.0 to 94.0.

Description

Cast iron with high thermal resistancce for railway vehicle brake discs}

In general, the brake disk of the railway vehicle is installed on the side of the wheel or the axle to play a role of generating a braking force while friction with the brake pad.

In recent years, in the current railway vehicles, which are on the verge of increasing speed, there is an urgent need for a brake disc having excellent friction braking force and having abrasion resistance and heat resistance, which are requirements to be provided as a brake disc.

Cast iron is usually used as a material for manufacturing a brake disc for a railway vehicle. An example of cast iron used in a conventional brake disc is made of a composition as shown in FIG.

In the brake disc for railroad cars, high heat of 600 ° C. or more is generated by friction with the brake pads, and heat repeatedly acting causes thermal cracks in the brake disc. However, as shown in FIG. 1, carbon (C) 3.00 to 3.40, silicon (Si) 1.70 to 2.20, manganese (Mn) 0.60 to 0.90, phosphorus (P) 0.07 or less, and sulfur (S) 0.12 or less, as shown in FIG. The brake disc for railroad cars made of cast iron made of iron (Fe) and unavoidable impurities, which have poor heat resistance, easily undergoes thermal cracking, and as a result, the wear of the brake disc progresses rapidly, thereby shortening the lifespan. there was.

The present invention has been made to solve the above problems, an object of the present invention is to develop a material for manufacturing a brake disk for a railway vehicle having a high resistance to thermal load to improve the heat resistance and wear resistance of the brake disk and heat crack It is to provide a cast iron for a high temperature resistant rail vehicle brake disk that can prevent the occurrence of the prolonged life of the brake disk.

The present invention for achieving the above objects,

In cast iron used to manufacture brake discs for rolling stock, the cast iron is expressed in weight percent of carbon (C) 3.0 to 3.8, silicon (Si) 2.0 to 2.6, manganese (Mn) 0.3 to 1.0, phosphorus (P) 0.01 to 0.08 , Sulfur (S) 0.01 ~ 0.12, copper (Cu) 0.1 ~ 0.7 and iron (Fe) 92.0 ~ 93.0 is characterized in that it is configured to include.

At this time, the cast iron is characterized in that it further comprises chromium (Cr) 0.1 ~ 0.3 by weight percent.

In addition, the cast iron may further include chromium (Cr) 0.3 to 0.6, molybdenum (Mo) 0.1 to 0.6, and nickel (Ni) 0.8 to 1.5 in weight percent, and iron (Fe) containing 89.5 to 93.0 wt%. It features.

In addition, the cast iron is characterized in that it further comprises 0.01 to 0.03% by weight of magnesium (Mg).

In addition, the cast iron is characterized in that it further comprises 0.3 to 1.3 weight percent of cobalt (Co).

At this time, the cast iron is characterized in that the carbide is 0.01 ~ 5.00%.

In addition, the cast iron is characterized in that the ferrite and the carbide is 0.01 ~ 5.00%, respectively.

According to the cast iron for a high heat-resistant railroad vehicle brake disc according to the present invention configured as described above, copper (Cu), chromium (Cr), and the like, carbon (C), silicon (Si), manganese (Mn), etc. , Molybdenum (Mo), Nickel (Ni), Magnesium (Mg), Cobalt (Co) is added to improve the heat resistance and wear resistance of cast iron to improve the heat resistance and wear resistance of the brake disc and to prevent the occurrence of thermal cracks It has an excellent effect to prolong its life.

Hereinafter, with reference to the accompanying drawings will be described in detail preferred embodiments of the cast iron for a high heat-resistant railway vehicle brake disk according to the present invention.

2 is a table showing the weight ratio of the chemical composition of the cast iron (I ~ V) for high-temperature railroad brake disk according to the present invention, Figure 3 is a view of the cast iron (I ~ V) having the chemical composition shown in FIG. The characteristics are shown in a table comparing with the conventional cast iron, Figure 4 (a), (b) is a conventional cast iron the length of the thermal crack according to the thermal fatigue test of the cast iron (I ~ V) having the chemical composition shown in Figure 2 5 (a), (b) is a friction coefficient and abrasion amount according to the friction characteristics test of cast iron (I ~ V) having the chemical composition shown in Figure 2 compared with the conventional cast iron It is a graph shown.

The present invention relates to a cast iron for a high heat resistant railway vehicle brake disc for improving the heat resistance and abrasion resistance of the brake disc which is installed on the side of the wheel or the axle to generate a braking force while friction with the brake pad. Cast iron for brake discs of heat-resistant rail vehicles includes carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S) and copper (Cu), and the rest is iron (Fe) and It is composed of impurities that are inevitably included in the manufacturing process.

In more detail, the cast iron is 3.0 to 3.8 wt% of carbon, 2.0 to 2.6 wt% of silicon, 0.3 to 1.0 wt% of manganese, 0.01 to 0.08 wt% of phosphorus, 0.01 to 0.12 wt% of sulfur, 0.1 to 0.7 wt% of copper, and 92.0 to 93.0% by weight of iron is configured to be included, which has the effect of significantly improved heat resistance by adding copper to the conventional cast iron composition shown in FIG.

That is, carbon (C) is an element that has a great influence on the corrosion resistance, abrasion resistance, and castability of cast iron, but when the content is less than 3% by weight, carbides cannot be sufficiently precipitated, so the carbon content cannot be more than a certain hardness. If it exceeds 4% by weight, the corrosion resistance and abrasion resistance is lowered, so the content is preferably 3.0 to 3.8% by weight. Silicon (Si) has the effect of promoting carbide-free structure and improving castability, but the content is 2 If it is less than the weight%, it is difficult to expect such an action, and if the content exceeds 3% by weight, the deterioration of the mechanical properties, that is, the brittleness and the thermal conductivity may be lowered, so that the content is preferably 2.0 to 2.6% by weight.

Further, the purpose of limiting the content of manganese (Mn) is to obtain a structure free of carbides, but when the content is less than 0.25% by weight, it is difficult to improve the mechanical properties, and when the content exceeds 1.0% by weight, the mechanical properties are greatly improved. When there is no action and the content is 0.3 to 0.5% by weight, the tendency to absorb hydrogen can be reduced to minimize the risk of pin holes, so the content is preferably 0.3 to 1.0% by weight.

On the other hand, since phosphorus (P) reduces ductility, toughness, weldability, and is also harmful to the integrity of the casting, the maximum content should be limited to 0.08% by weight or less, and sulfur (S) does not affect the matrix structure, but ferrite ( Ferrite) depends on the ratio of manganese and sulfur (Mn / S Ratio), it is preferable to limit the maximum content to 0.12% by weight or less.

In addition, since copper (Cu) is a reddish metal and has excellent electrical and thermal conductivity, copper (Cu) effectively conducts frictional heat generated during braking of railroad cars, thereby preventing cracks in the brake disc. In addition, copper serves to increase strength by increasing the amount of pearlite in the tissue. The content of copper contained in the cast iron was adjusted to 0.1 to 0.7% by weight in consideration of the ratio with other components.

Next, it is preferable to further include chromium (Cr) in the cast iron having the composition as described above, because the chromium improves the strength of the cast iron and protects the surface of the cast iron by forming a thin oxide film easily in contact with oxygen. Because it plays a role. The content of chromium was adjusted to 0.1 to 0.3% by weight or 0.3 to 0.6% by weight in consideration of the ratio with other components.

In addition, the cast iron may further include molybdenum (Mo) and nickel (Ni). First, molybdenum serves to improve mechanical properties at high temperatures as an element capable of producing pearlite. At this time, the content of the molybdenum is preferably to be 0.1 to 0.6% by weight, the reason is that when the content of molybdenum is 0.1 to 0.6% by weight creep excellent in strength increase at high temperature and prevent the occurrence of cracks (Creep) This is because it has an effect of greatly increasing the resistance.

In addition, the nickel serves to improve corrosion resistance, abrasion resistance and crack resistance and at the same time increase the yield strength. Herein, the nickel content was adjusted to 0.8 to 1.2% by weight in consideration of the ratio with other components.

On the other hand, the cast iron may further include magnesium (Mg), the magnesium has the effect of improving the structure and strength of the cast iron is added to the flow of the molten iron during manufacture. In addition, due to the addition of magnesium, the graphite has a serpentine (Vermicular) structure to improve the friction, wear characteristics of the tissue. At this time, the magnesium content was adjusted to 0.01 to 0.03% by weight in consideration of the ratio with other components.

In addition, the cast iron may further include cobalt (Co), which promotes graphitization and increases resistance to thermal shock even if a small amount is added, thereby prolonging the life of the brake disc by slowing the occurrence of thermal cracking and its development. It can play a role. At this time, the cobalt content is preferably 0.3 to 3.0% by weight in consideration of the ratio with other components.

And, except for the content of the above-mentioned components, the remaining content is occupied by iron (Fe), the content of the iron (Fe) in consideration of the content of the above-described components to 92.0 to 93.0% by weight or 89.5 to 93.0% by weight Adjusted. That is, when the cast iron component contains carbon, silicon, manganese, phosphorus, sulfur, copper, and chromium, the iron content is 92.0 to 93.0 wt%, and molybdenum, nickel, magnesium, and cobalt are selectively added to the component. If included, the iron content was adjusted to 89.5 ~ 93.0% by weight.

On the other hand, the cast iron for the high heat-resistant railroad car brake disc according to the present invention having the composition as described above is preferably to be less than 5.00% ferrite and carbide, respectively, because the content of ferrite and carbide is 5.00% If it exceeds, the strength and wear resistance of the cast iron is weakened and the effect of suppressing the occurrence and progress of heat cracking is inferior. In this case, when magnesium (Mg) is included among the components of the cast iron, since the tissue of graphite has a serpentine-like structure (Vermicular) instead of flake graphite, ferrite is hardly generated, so only the content of carbide is 5.00% or less. It is preferable to

Based on the above, the chemical composition of the five embodiments (material I to material V) of the cast iron for the high heat-resistant railway vehicle brake disk according to the present invention is shown in FIG. At this time, since the portions except the contents of the components shown in FIG. 2 are all iron contents, the iron content will not be described separately.

Preparation of the cast iron is based on the composition and content (% by weight) shown in Figure 2 by mixing the above-mentioned components in a melting furnace of 1500 ~ 1550 ℃, and then in a sand mold with a Furan resin (Current resin) as a binder Injected and solidified, cooled to 350 ° C. in the mold, and then the foundry sand was broken and naturally cooled. FeSi system was used as the inoculum, and material V was maintained at 830 ° C. for one hour to reduce hardness, and then the same procedures as those of the other materials (materials I to IV) were followed. The structure of graphite in the matrix is a serpentine structure (Vermicular) for material IV, and flake graphite is obtained for the remaining cast irons.

The results of testing the properties of the tensile strength and hardness of the cast irons prepared as described above are shown in FIG. Here, a comparative material means the conventional cast iron shown in FIG.

As shown in FIG. 3, it can be seen that the cast iron made of the materials I to V is significantly improved compared to the conventional cast iron, and the strength is improved by increasing the number of process cells per unit area.

In addition, thermal fatigue tests were performed using cylindrical specimens of diameter 20mm and length 80mm to evaluate the heat resistance of each cast iron (material I to material V) for each composition.The heating was used as an induction heater and the cooling was used as tap water. . In addition, the thermal fatigue test temperature range was set to the heating temperature 600 ℃, the cooling temperature 40 ℃ based on the specimen surface temperature, respectively, and the temperature was controlled using a thermocouple.

At this time, the non-contact heating by the induction current is mainly concentrated on the metal surface part, so the induction heater output value is adjusted to increase the total heating time, so that the thermocouple temperature sensor can follow the actual temperature change well, thereby achieving more accurate heating-cooling control. To lose. In addition, in the thermal fatigue test, the time required for the specimen to be heated to 600 ° C by the induction coil was about 84 seconds, and the time to cool to 40 ° C by the coolant was about 18 seconds, and the temperature of the coolant was 25 The temperature was controlled by a cooling water circulation system so that there was no temperature change of ± 2 ° C or more.

The thermal fatigue test was performed for all specimens for a total of 400 cycles. During the thermal fatigue test, at the beginning of the experiment up to the first 50 cycles, the specimen surface was observed with an optical microscope every 5 cycles, resulting in relatively small thermal fatigue. The specimen surface was observed to be cracked at the beginning of its life, and the progress and state changes of cracks were observed by setting the observation cycle to 10 cycles from 50 to 250 cycles, and the observation cycle was set to 30 cycles from 250 cycles to 400 cycles. The progress and state of cracks were observed.

In addition, since the occurrence of heat cracks depends on the observation position of the specimen, a total of five locations were observed. FIG. 4 (a) is a graph showing the total length of the heat cracks observed in the second observation region, and FIG. b) shows the sum of the lengths of the heat cracks observed in the fifth observation area. At this time, in Fig. 4 (a), (b) is indicated by Conv is a test result taken from the cast iron used in the conventional brake disc manufacturing shown in Fig. 1, I to V is shown in the present invention shown in Fig. According to the test results obtained in five examples (material I to material V) of cast iron for a high temperature resistant railway vehicle brake disc according to the present invention.

As shown in (a) and (b) of FIG. 4, the total crack length of the thermal crack at 400 cycles for the cast iron made of the materials I to V is only about 50 to 60% of the conventional cast iron, thereby improving thermal cracking. It can be seen that it has sex.

In addition, to evaluate the friction characteristics of cast iron (material I to material V) for each composition, a friction test was performed using a small dynamometer. The test conditions are as follows.

First, braking tests at the initial braking speeds of 1,000 rpm (37 km), 2,000 rpm (73 km), and 2,500 rpm (91 km) were applied to the brake pads while applying pressure of 4.5 bar, 5.5 bar and 6.5 bar, respectively. At this time, the flywheel inertia mass used in the test was set to 0.125kgf.ms ² . After 50 braking tests according to each pressure buoyancy and initial speed, the average coefficient of friction was obtained, and the amount of wear of the brake pads was measured. The average friction coefficient of material V) is compared with the conventional cast iron shown in FIG. 1, and FIG. 5B shows the cast irons (material I to material V) for each composition when applying a pressure of 5.5 bar. It is a graph which shows the wear amount of the brake pad compared with the conventional cast iron shown in FIG.

As shown in (a) and (b) of FIG. 5, it can be confirmed that the average friction coefficient of most cast irons except material III and the wear amount of the brake pads are improved compared to the conventional cast irons.

On the other hand, Figures 6 to 11 are 100 times before etching (a), 100 times after etching (b), after etching, respectively, in order to observe the structure of the cast iron and the cast iron made of the material I to material V according to the present invention in comparison with the conventional As shown in the photograph taken at 400 magnification (c), as can be seen in Figures 7 to 11, it can be seen that the size of the graphite is appropriate in all materials compared to Figure 6 and evenly distributed throughout the base. . In addition, when looking at the etching portion, Figure 6 is a high specific gravity distribution of the ferrite, while not evenly distributed, while Figures 7 to 11 shows the precipitation of some ferrite in the base pearlite, but the ferrite and carbide is less than 5% It can be confirmed.

Therefore, according to the cast iron for brake disc of the high heat resistance railway vehicle according to the present invention can improve the heat resistance and wear resistance of the cast iron to improve the heat resistance and abrasion resistance of the brake disc and to prevent the occurrence of thermal cracks can extend the life of the brake disc, etc. There are a variety of advantages.

Although the above embodiments have been described with respect to the most preferred examples of the present invention, it is not limited to the above embodiments, and it will be apparent to those skilled in the art that various modifications are possible without departing from the technical spirit of the present invention.

1 is a table showing the weight ratio of cast iron used in the manufacture of a conventional brake disc.

2 is a table showing the weight ratio of the chemical composition of the cast iron (I ~ V) for a high heat-resistant railway vehicle brake disk according to the present invention.

Figure 3 is a table showing the characteristics of the cast iron (I ~ V) having the chemical composition shown in Figure 2 compared with the conventional cast iron.

Figure 4 (a), (b) is a graph showing the length of the heat crack according to the thermal fatigue test of the cast irons (I ~ V) having the chemical composition shown in Figure 2 compared with the conventional cast iron.

Figure 5 (a), (b) is a graph showing the coefficient of friction and the amount of wear according to the friction characteristics test of cast irons (I ~ V) having the chemical composition shown in Figure 2 compared with the conventional cast iron.

6 (a) to 6 (c) are views showing photographs in which the structure of cast iron used in conventional brake disc manufacturing is divided into 100 times or 400 times before and after etching.

7 to 11 (a) to (c) is a view showing a photograph enlarged by 100 or 400 times divided by the structure of the cast iron (I ~ V) having the chemical composition shown in Figure 2 before and after etching.

Claims

In cast iron used to manufacture brake discs for rolling stock,

The cast iron has a weight percentage of carbon (C) 3.0 to 3.8, silicon (Si) 2.0 to 2.6, manganese (Mn) 0.3 to 1.0, phosphorus (P) 0.01 to 0.08, sulfur (S) 0.01 to 0.12, copper (Cu) Cast iron for brake discs of high heat resistance railway vehicle, characterized in that it comprises 0.1 ~ 0.7 and iron (Fe) 92.0 ~ 93.0.

The method of claim 1,

The cast iron is cast iron for a high heat-resistant railroad car brake disc, characterized in that it further comprises chromium (Cr) 0.1 to 0.3 by weight.

The method of claim 1,

The cast iron further comprises a chromium (Cr) 0.3 ~ 0.6, molybdenum (Mo) 0.1 ~ 0.6, nickel (Ni) 0.8 ~ 1.5 in weight percent, iron (Fe) is characterized in that 89.5 ~ 93.0% by weight Cast iron for brake discs of highly heat-resistant railway vehicles.

The method of claim 3, wherein

The cast iron is cast iron for a high heat-resistant railroad car brake disc, characterized in that it further comprises 0.3 to 3.0 weight percent cobalt (Co).

The method of claim 3, wherein

The cast iron is magnesium (Mg) cast iron for a high heat-resistant railroad car brake disc, characterized in that it further comprises 0.01 to 0.03 weight percent.

The method of claim 5,

The cast iron is a cast iron for a high-temperature railroad car brake disc, characterized in that the carbide is 0.01 ~ 5.00%.

The method according to any one of claims 1 to 4,

The cast iron is a cast iron for a high-temperature railroad car brake disc, characterized in that the ferrite and the carbide is 0.01 ~ 5.00%, respectively.