JP2000337410A - Rotor for disc brake - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotor for a disc brake decreased in cost and having high friction resistance. SOLUTION: After gas soft nitrating treatment is applied on a material formed of JIS FC250 formed through sand mold casting finished in a rotor shape, the material is heated and held at temperature higher than an A1 transformation point and lower than an eutectic temperature and by causing isothermal transformation of a nitrogen diffusion layer formed through nitriding and a matrix through holding of it in a heat bath at a given temperature, a rigid nitrogen compound layer is formed on the surface of the rotor. Further, since the nitrogen diffusion layer at the lower layer of the nitrogen compound layer and the matrix are brought into a bainitic texture high in hardness, wear resistance of a rotor is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotor for a disc brake which is suitably used for applying a braking force to a vehicle or the like.

[0002]

2. Description of the Related Art Conventional automobile disk brakes are:
JIS (Japanese Industrial Standard) FC200 or FC25
It is the mainstream to use a normal cast iron rotor such as 0. Also,
As described in JP-A-51-27828, a method is known in which a rotor for a disc brake made of ordinary steel or nitrided steel is subjected to nitriding treatment to improve corrosion resistance and wear resistance.

[0003]

However, there has been a movement to use a sintered metal-based material as a friction material from the viewpoint of improving the performance and reducing the weight of a disc brake, but the sintered metal-based friction material is generally used in a resin. Since the friction material is harder and has a higher friction coefficient than the friction material of the system, the aggressiveness of the friction material to the rotor increases, and the conventional ordinary cast iron rotor cannot cope with the low wear resistance.

As disclosed in Japanese Patent Application Laid-Open No. 51-28828, a disk brake rotor made of ordinary steel or nitrided steel and subjected to nitriding treatment has a rotor like a motorcycle disk brake. Is effective because simple molding is possible when
In the case of a complicated shape such as having a cooling cavity and fins between a plurality of plates such as a rotor for a wheel brake for a wheel brake, etc., it is difficult to form ordinary steel or nitrided steel into a rotor shape itself. However, the processing cost increases.

The present invention has been made in view of the above problems, and has as its object to provide a disk brake rotor which can be easily formed into a rotor shape and has high wear resistance.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a molded article made of cast iron is subjected to nitriding treatment, and then heated and maintained at a temperature between the A1 transformation point and the eutectic temperature of the cast iron, and then quenched and held in a heat bath at a predetermined temperature. Then, the nitrogen diffusion layer and the base material generated by the nitriding are subjected to isothermal transformation.

In this manner, a nitriding treatment forms a nitrogen compound layer on the surface and a nitrogen diffusion layer therebelow, and then heats and maintains the cast iron at a temperature from the A1 transformation point to the eutectic temperature and then to a predetermined temperature. By quenching and holding in a heat bath at a temperature, the nitrogen diffusion layer and the base material are isothermally transformed to transform the matrix structure into a bainite structure.

Further, according to a second aspect of the present invention, after a molded body made of cast iron is subjected to nitriding treatment, it is heated and held at a temperature not lower than the A1 transformation point of the nitrogen diffusion layer and less than the A1 transformation point of the cast iron, and then heated in a heat bath at a predetermined temperature. And a nitrogen diffusion layer formed by nitriding is transformed by isothermal transformation.

[0009] With this configuration, a nitrogen compound layer is formed on the surface and a nitrogen diffusion layer is formed therebelow by the nitriding treatment. Thereafter, the nitrogen diffusion layer is heated and maintained at a temperature not lower than the A1 transformation point of the nitrogen diffusion layer and less than the A1 transformation point of the cast iron. Thus, only the nitrogen diffusion layer is transformed into an austenitic structure, and then quenched and held in a heat bath at a predetermined temperature, thereby isothermally transforming only the nitrogen diffusion layer to transform the base structure into a bainite structure.

[0010] Further, according to the invention of claim 3, after nitriding a molded body made of cast iron, it is heated and held at a temperature not lower than the A1 transformation point of the nitrogen diffusion layer and less than the A1 transformation point of the cast iron, and then at a temperature not lower than the martensitic transformation start point. It is characterized by quenching and holding in a heat bath at a temperature and then cooling to transform the nitrogen diffusion layer formed by nitriding into martensite.

[0011] With this configuration, a nitrogen compound layer is formed on the surface and a nitrogen diffusion layer is formed below the nitrogen compound layer by the nitriding treatment. Thereafter, the nitrogen diffusion layer is heated and maintained at a temperature not less than the A1 transformation point of the cast iron and less than the A1 transformation point of the cast iron. Thus, only the nitrogen diffusion layer is austenite-structured, then quenched and held in a heat bath at a temperature equal to or higher than the martensitic transformation start point, and air-cooled to form only the nitrogen diffusion layer with a martensite structure.

Further, according to the invention of claim 4, after the molded body made of cast iron is nitrided, the nitrogen diffusion layer is heated and maintained at a temperature from the A1 transformation point to a eutectic temperature, and then a temperature at a temperature not less than the martensitic transformation start point. After quenching in a heat bath and cooling,
The nitrogen diffusion layer generated by nitriding is transformed into martensite, and is oxidized and tempered by heating and maintaining it at a predetermined temperature.

According to this structure, a nitrogen compound layer is formed on the surface by the nitriding treatment, and a nitrogen diffusion layer is formed under the nitrogen compound layer. Thereafter, the nitrogen diffusion layer is heated and held at a temperature from the A1 transformation point to the eutectic temperature and below the eutectic temperature. From the quenching and holding in a heat bath at a predetermined temperature, only the nitrogen diffusion layer or the nitrogen diffusion layer and the base material are isothermally transformed to form an austenite structure of the base structure, and then in a heat bath at a temperature equal to or higher than the martensite transformation start point. By quenching and holding, and air cooling, only the nitrogen diffusion layer or the nitrogen diffusion layer and the base material are formed into a martensite structure. Further, the oxide (Fe3 O4) layer is formed on the surface of the nitrogen compound layer by oxidizing and tempering by heating and holding at a predetermined temperature, and only the nitrogen diffusion layer having a martensite structure or the nitrogen diffusion layer is formed. The layers and the base material are tempered.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1, 2, 3, and 4 of the present invention will be described below.

[0015]

Embodiment 1 In this embodiment, the present invention is applied to the manufacture of a rotor for a disc brake of a four-wheeled automobile (hereinafter referred to as a rotor).

First, JIS F prepared by sand casting is used.
The C250 material was processed to the required shape, dimensions and surface roughness by adding necessary processing. Subsequently, the rotor is cleaned with a vacuum cleaner using a hydrocarbon-based solvent to remove the grinding oil adhering to the rotor surface, and then the rotor is treated according to the heat treatment cycle shown in FIG.

(1) Gas soft nitriding treatment First, the rotor is inserted into a furnace for performing nitriding treatment, and the temperature is raised to the nitriding treatment temperature. At this time, the atmosphere in the furnace is set to nitrogen, which is an inert gas, so that the rotor is not oxidized by the influence of heat. Then, ammonia (N
H3): Nitrogen (N2): Carbon dioxide (CO2) = 60: 3
7: 3 atmosphere, processing temperature: T1 = 590 ° C.
Processing time: gas nitrocarburizing under the condition of t1 = 4.0 h. Thus, the rotor has a structure in which a nitrogen compound layer (mainly Fe3N) formed on the surface, a nitrogen diffusion layer formed below the nitrogen compound layer, and a base material below the nitrogen diffusion layer. At this time, the nitrogen content of the nitrogen compound layer is 8 to 10 w.
t%, and the nitrogen content in the nitrogen diffusion layer is 1 to 5 wt%.

(2) Austenite organization of the nitrogen diffusion layer and the base material The gas nitrocarburized rotor is treated at a processing temperature of T2 = 85.
When heated and maintained at 0 ° C. for a processing time of t2 = 20 min, as can be seen from the iron-nitrogen system phase diagram of FIG. 2, a nitrogen compound layer formed on the surface (nitrogen content: 8 to 10 wt%)
Although the Fe3N (ε) structure does not change even if the temperature changes to 850 ° C., the whole or a part of the base structure of the nitrogen diffusion layer becomes austenite.

Further, the base structure of the base metal under the nitrogen diffusion layer has a carbon content of about 3 to 4% by weight of ordinary cast iron. Therefore, as is clear from the iron-carbon phase diagram of FIG. (Γ) Transform into tissue.

Incidentally, cast iron is actually an alloy of iron and carbon,
Although it is a complex alloy containing silicon, manganese, phosphorus, sulfur, and other elements, it is considered that it basically constitutes an iron-carbon system containing carbon in excess of the maximum solid solubility carbon amount. Here, the description is given using the iron-carbon system phase diagram shown in FIG. 3 for convenience.

(3) Austempering Next, the rotor in which the nitrogen diffusion layer and the base material of the base material have been austenitized is subjected to NaNO 3 − bath temperature: T3 = 300 ° C.
When quenching in a bath of KNO3 molten salt under the condition of treatment time: t3 = 30 min, the nitrogen compound layer (nitrogen content: 8 to 10 wt%) formed on the surface becomes Fe3N.
(Ε) Without changing the structure, the austenite structure, which is the base structure of the nitrogen diffusion layer and the base material, transforms to bainite as shown in the isothermal transformation diagram of FIG. In the present embodiment, since the isothermal transformation is performed at 300 ° C., which is a relatively low temperature among the temperatures at which the bainite transformation occurs, a needle-like lower bainite is formed.

(4) Air Cooling and Grinding The rotor in which the base structure of the nitrogen diffusion layer and the base material is bainite-structured is air-cooled and then ground to finish to a predetermined surface roughness.

The rotor of Example 1 completed by the above steps (1) to (4) and the following Comparative Examples 1 and 2
Were subjected to (A) a microscopic observation test, (B) a cross-sectional hardness test, (C) a corrosion resistance test, and (D) a wear test.

Comparative Example 1 is a conventional disk brake rotor in which a material made of JIS FC250 is processed into a predetermined shape and dimensions, and then the surface is finished by grinding.

In Comparative Example 2, a material made of JIS FC250 was processed into a predetermined shape and dimensions, then subjected to the gas nitrocarburizing treatment of the example, and then cooled in oil, and then subjected to surface finishing by grinding. Rotor as described in
As shown in Japanese Patent No. 27828, the steel is simply subjected to a nitriding treatment generally performed to improve the surface hardness of the iron material.

(A) Microscope Observation Test After the mirror surface of the test specimen was mirror-finished, it was corroded with a corrosive liquid (5% nital liquid). As a result, Comparative Example 1 had a normal structure in which flake graphite was crystallized in the pearlite base material, but the outermost layers of Examples and Comparative Example 2 had a compound layer and a nitrogen diffusion layer having a thickness of about 15 μm. Was formed. Further, in the example, a bainite structure was formed in the nitrogen diffusion layer and the base material thereunder, and the structure was such that flaky graphite was distributed in the bainite structure.

(B) Cross-sectional hardness test The hardness distribution from the surface to the deep portion was determined using a Vickers hardness tester under a load of 100 gf, and the results are shown in FIG. In Comparative Example 1, the hardness is constant irrespective of the distance from the surface because the whole is made of JIS FC250 which is uniform.
Comparative Example 2 has a high hardness in the nitrogen compound layer and maintains a high level in the nitrogen diffusion layer even in a portion close to the nitrogen compound layer.
The hardness decreases to almost the same as that of Comparative Example 1 as approaching the base material. In Example 1, the hardness decreased as the distance from the surface of the nitrogen compound layer, the nitrogen diffusion layer, and the base material increased as in Comparative Example 2. It can be seen that the hardness of the material is high.

(C) Corrosion resistance test A corrosion resistance test was carried out based on JIS Z2371 salt spray test, and for each rotor as a test material, a rating number (JIS H850)
2) was determined, and the results are shown in Table 1. Compared with Comparative Example 1, the rotors of Comparative Example 2 and Example have excellent corrosion resistance, and
Since the example showed the same rating number as that of the comparative example 2, it can be seen that the corrosion resistance does not decrease even if (2) austenite organization and (3) austempering are performed.

[0029]

[Table 1]

(D) Dynamo test JASO (automobile standard) C406 Passenger car brake device The wear of the rotor is confirmed based on a dynamometer test method. This test was performed using a friction pad made of a copper-based sintered alloy friction material (sintered metallic friction material), and the results are shown in Table 2. It can be seen that the rotors of Comparative Example 2 and Example are superior to Comparative Example 1 in wear resistance. However, in this test, no difference was observed in the wear resistance between the rotors of Comparative Example 2 and the Example because the wear of the rotor was almost stopped at the nitrogen compound layer. Has a higher wear resistance than cast iron (material of the rotor of Comparative Example 1) because of the solid solution state of nitrogen, but is inferior in wear resistance to the nitrogen diffusion layer of the hard bainite-structured embodiment, Further, in the comparative example 2, the base material portion is the same cast iron as that of the comparative example 1 and thus has only the same wear resistance as the rotor of the comparative example 1. It has excellent wear resistance.

[0031]

[Table 2]

That is, in the comparative example 2, when the wear reaches the nitrogen diffusion layer and the base material portion, the wear resistance is rapidly reduced. On the other hand, in the example in which the nitrogen diffusion layer and the base material have a bainite structure, Even if the abrasion proceeds with the nitrogen diffusion layer and the base material, the abrasion resistance does not decrease rapidly.

As a result of the above tests (A) to (D), the rotor of the example is superior in corrosion resistance and wear resistance to the conventional rotor made of plain cast iron found in comparative example 1, and the comparative example It can be seen that the wear resistance is further improved without lowering the corrosion resistance even for the rotor obtained by subjecting ordinary cast iron to gas nitrocarburizing as shown in FIG.

In the above embodiment, the treatment temperature (T1) of the gas nitrocarburizing treatment is set at 590 ° C., but the treatment temperature is not limited to this. However, from the graph of the treatment temperature during the nitrocarburizing treatment and the rating number when corroding the nitrided cast iron shown in FIG.
It is apparent that when the temperature exceeds 90 ° C., the corrosion resistance decreases. In addition, when T1 becomes lower, the processing time becomes longer (for example, when T1 = 570 ° C., T1 = 59).
(It requires 1.5 to 2 times as much processing time as at 0 ° C.) Therefore, in order to improve the corrosion resistance and shorten the processing time,
(1) Gas nitrocarburizing treatment temperature: T1 is 580 to 59
About 0 ° C. is desirable.

In the above embodiment, the treatment temperature (T2) for austenite structuring is set to 850 ° C.
The temperature is not limited to this as long as the temperature at which both the nitrogen diffusion layer and the base material of the base material have an austenitic structure.
From the iron-nitrogen phase diagram of FIG. 2, T2 must be 590 ° C. or higher in order for the base structure of the nitrogen diffusion layer to transform into an austenitic structure. In addition, in order for the base material to transform into an austenitic structure, T2 must be in the region of austenite (γ) + graphite in the iron-carbon phase diagram of FIG. Here, there are various types of cast iron as a base material, but the carbon content is almost 2.0% or more in any cast iron. Therefore, in order for the cast iron (base material) to be transformed into an austenitic structure, T2 is required. It must be above the A1 transformation point and below the eutectic temperature. Therefore, (2) austenite structure processing temperature:
T2 must satisfy A1 transformation point ≦ T2 ≦ eutectic temperature.

In the above embodiment, (3) bath temperature during austempering: T3 at 300 ° C., and processing time: t3 at 30
Although it is set to min, it is not limited to these.
However, as shown in the isothermal transformation diagram of FIG.
Must be not less than the Ms point (martensite transformation start point) for transforming to bainite structure and not more than the nose temperature of the isothermal transformation line, and t3 is not less than the time from the start of transformation at T3 to the end of transformation. Must. At this time, if T3 is relatively high, feather-like upper bainite which is slightly inferior in hardness but excellent in toughness is formed, and if T3 is relatively low, lower bainite which is acicular and slightly inferior in toughness but excellent in hardness is formed. You.

Further, in the above embodiment, NaNO 3 was added to the heat bath.
Although -KNO3 is used, a molten salt having another structure may be used, and the hardness and toughness of the bainite structure can be changed by changing the bath temperature. Therefore, the hardness and toughness of the nitrogen diffusion layer and the base material can be changed by appropriately selecting the composition of the heat bath at the time of austempering, the bath temperature and the treatment time.

Further, in the above embodiment, it is possible to perform a simple and energy-efficient process for continuously controlling only the temperature and atmosphere in the furnace and the temperature of the heat bath.

In this embodiment, the rotor is described as a disk brake rotor for an automobile. However, it is used not only for a disk brake for an automobile which is desired to be low-cost because it is a mass-market product, but also for a high-speed railway. Even if it is used for a disc brake or the like, it is possible to provide a disc brake having high wear resistance at low cost.

[0040]

Embodiment 2 The rotor of Embodiment 2 is treated according to the heat treatment cycle shown in FIG. However, (1) the gas nitrocarburizing treatment is the same as that in the first embodiment, and the description is omitted.

(5) Austenite Organization of Nitrogen Diffusion Layer The rotor subjected to the gas nitrocarburizing treatment of (1) was heated in the same furnace while replacing the atmosphere with nitrogen.
When heating and holding at T4 = 650 ° C. and processing time t4 = 20 min, as can be seen from the iron-nitrogen system phase diagram of FIG. 2, the nitrogen compound layer (nitrogen content: 8 to 1) formed on the surface
0 wt%) is Fe ₃ N even if the temperature changes to 650 ° C.
(Ε) The structure does not change, but the whole or a part of the base structure of the nitrogen diffusion layer is austenitized.

Further, the matrix structure of the base material under the nitrogen diffusion layer is 65%, as is clear from the iron-carbon phase diagram of FIG.
At 0 ° C., no structural change occurs.

(6) Quenching Next, the rotor in which the base structure of the nitrogen diffusion layer was austenitized was treated in a NaNO ₃ -KNO ₃ molten salt bath at a bath temperature of T3 = 300 ° C. for a treatment time of t3 = 30 min. In a heat bath quenching, the nitrogen compound layer (nitrogen content: 8 to 10 wt%) formed on the surface does not change as Fe ₃ N (ε) structure, and the austenite structure which is the base structure of the nitrogen diffusion layer. Transforms into bainite as shown in the isothermal transformation diagram of FIG.

(7) Air Cooling and Grinding The rotor in which the base structure of the nitrogen diffusion layer is bainite-structured is air-cooled and then ground to finish to a predetermined surface roughness.

The rotor of Example 2 completed by the steps (1), (5) to (7) has only a bainite-free base material, and has a nitrogen compound layer and a nitrogen diffusion layer similar to those of Example 1. For the same reason, the wear resistance of the base material is inferior to that of the rotor of the first embodiment, but otherwise,
The same effect can be obtained with the rotor described above.

In the second embodiment, (5) the processing temperature for austenite organization: T5 is set at 650 ° C. However, the temperature is not limited to this as long as the base structure of the nitrogen diffusion layer becomes an austenite structure. Absent. In order for the matrix structure of the nitrogen diffusion layer to transform to the austenitic structure from the iron-nitrogen system diagram of FIG. 2, T4 must be 590 ° C. or higher (A1 transformation point of the nitrogen diffusion layer). Further, in order to prevent the base material from transforming into an austenitic structure, T4 must be lower than the A1 transformation point of the base material (cast iron). Therefore, (2) Austenite structure processing temperature: T4 is:
A1 transformation point of nitrogen diffusion layer ≦ T4 <A1 transformation point of base metal must be satisfied.

[0047]

Embodiment 3 The rotor of Embodiment 3 is treated according to the heat treatment cycle shown in FIG. However, (1) gas nitrocarburizing treatment is the same as in the first embodiment, and (5) austenite organization of the nitrogen diffusion layer is the same as in the second embodiment.

(8) Quenching treatment After the gas nitrocarburizing treatment of (1), the nitrogen diffusion layer is austenite-structured in (5), and the rotor in which the matrix structure of the nitrogen diffusion layer is austenitized is heated to a bath temperature: T5 = The temperature of the rotor is made uniform by quenching in a silicon oil bath at 180 ° C. for a processing time of t5 = 10 min. This is to make the temperature change from the martensitic transformation start point to the martensitic transformation end point gradual at the time of the subsequent air cooling, thereby preventing cracking or the like due to a rapid temperature change.

At this time, the bath temperature and the processing time T5
Must be within a time during which bainite transformation does not start at a temperature equal to or higher than the martensitic transformation point.

(9) Air Cooling and Grinding The rotor held in the heat bath until the temperature becomes uniform is pulled out of the heat bath and air-cooled, so that the rotor has a temperature below the martensitic transformation start point and has an austenitic structure. When the martensitic transformation of the nitrogen diffusion layer starts, and the temperature further decreases to the martensitic transformation end point, the nitrogen diffusion layer completely has a martensitic structure.

The rotor having a nitrogen diffusion layer having a matrix structure of martensite is ground to finish the surface to a predetermined surface roughness.

The rotor of the third embodiment completed by the steps (1), (5), (8) and (9) has a higher corrosion resistance and resistance to nitrogen compound layers than the conventional rotor made of ordinary cast iron. Abrasion can be improved.

The rotor of the third embodiment has a nitrogen diffusion layer even when compared to a conventional plain cast iron rotor in which only a nitriding treatment is performed to increase hardness and improve wear resistance. Is made to have a martensite structure to increase the hardness, so that when the wear progresses beyond the nitrogen compound layer on the surface, the wear resistance does not suddenly decrease. Further, in the rotor for Example 3, since only the nitrogen diffusion layer has a martensite structure without changing the matrix structure of the base material, the entire rotor becomes brittle by forming a martensite structure having poor toughness up to the base material. To prevent it from happening.

Also, since the rotor of the third embodiment uses cast iron, it can be easily formed into a complicated rotor shape by casting, and is formed of ordinary steel or nitrided steel.
The processing cost can be reduced as compared with the 27828 rotor.

Further, in the third embodiment, it is possible to perform a simple and energy-efficient process for continuously controlling only the temperature and atmosphere in the furnace and the temperature of the heat bath.

Although the third embodiment is described as a rotor for a disc brake of an automobile, it is used for a disc brake of an automobile which is desired to be inexpensive because it is a mass-produced product. Even if it is used for a disc brake or the like, it is possible to provide a disc brake having high wear resistance at low cost.

[0057]

Embodiment 4 The rotor of Embodiment 4 is treated according to the heat treatment cycle shown in FIG. However, (1) gas nitrocarburizing treatment and (2) austenite organization of the nitrogen diffusion layer and the base material are the same as those in Example 1, and (8) quenching treatment is the same as that in Example 3, so description thereof will be omitted. I do.

(10) Air cooling The rotor held in the heat bath until the temperature becomes uniform is pulled out of the heat bath and air-cooled, so that the rotor has a temperature below the martensitic transformation start point and has an austenitic structure. When the martensitic transformation of the nitrogen diffusion layer and the base material starts, and the temperature further decreases to the martensitic transformation end point, the nitrogen diffusion layer and the base material completely have a martensitic structure.

(11) Oxidation / Tempering Treatment The rotor in which the nitrogen diffusion layer and the base material have a martensite structure is subjected to vacuum cleaning to remove oil and dirt, and then treated in steam at a treatment temperature of T6 = 480 ° C. : T6 = 40m
Perform oxidation and tempering in. As a result, an oxide (Fe3 O4) layer having a thickness of 3 to 4 .mu.m is formed on the surface of the nitrogen compound layer, and the martensite-structured nitrogen diffusion layer and the base material are tempered to form a troostite structure. .

When the oxidation treatment is performed in steam, the oxidation reaction proceeds slowly at a treatment temperature of 450 ° C. or lower, and the oxidation reaction becomes rapid and the oxide layer becomes non-uniform at 550 ° C. Layer unevenness or peeling occurs, or Fe2 O3 called red rust occurs, resulting in non-uniform organization. Therefore, the processing temperature is desirably 450 to 500C.

Further, when the treatment temperature is 400 to 500 ° C., it becomes troostite, and when it is 500 to 600 ° C., it becomes sorbite. However, although the hardness is slightly lower than that of martensite, it is excellent in toughness, and any structure may be used. . However, here, the tempering and the oxidation treatment are set to be performed at the same time.
It has a troostite structure.

(12) Air Cooling and Grinding The oxidized and tempered rotor is air cooled and then ground to finish to a predetermined surface roughness.

The above (1), (2), (10) to (12)
The rotor of Example 4 completed by the above process and Comparative Examples 1 and 2 were subjected to the corrosion resistance test (C) described above.
(D) It was subjected to a wear test.

(C) Corrosion resistance test A corrosion resistance test was performed based on JIS Z2371 salt spray test, and for each rotor as a test material, the rating number (JIS H850)
2) was determined, and the results are shown in Table 3. It can be seen that the rotors of the examples have better corrosion resistance than the comparative examples 1 and 2.

[0065]

[Table 3]

The above (1), (2), (10) to (12)
The rotor of Example 4 completed by the above process has improved corrosion resistance and abrasion resistance due to the oxide layer, compared to a conventional rotor made of ordinary cast iron material or a rotor that has just been subjected to nitriding treatment.

Further, in the rotor of Example 4, the hardness is increased by forming the nitrogen diffusion layer and the base material into a troostite structure, so that when the wear proceeds more than the oxide layer and the nitrogen compound layer on the surface. The abrasion resistance does not suddenly decrease and the corrosion resistance is also excellent.

Further, the rotor for the fourth embodiment is similar to that of the third embodiment.
Unlike the rotor described above, the martensite structure having poor toughness is tempered to form a troostite structure having excellent toughness, so that the entire rotor does not become brittle.

Further, since the rotor of Example 4 is made of cast iron, it can be easily formed into a complicated rotor shape by casting, and is formed of ordinary steel or nitrided steel.
The processing cost can be reduced as compared with the 27828 rotor.

Further, in the fourth embodiment, a simple and energy-efficient treatment for continuously controlling only the temperature and atmosphere in the furnace and the temperature of the heat bath can be performed. And can be performed simultaneously.

In Example 4, the austenite structure was formed at a processing temperature of T2 = 850 ° C. (between the A1 transformation point of the cast iron and the eutectic temperature), so that the nitrogen diffusion layer and the base metal were austenitized and finally formed. Although the treatment temperature is higher than the A1 transformation point of the nitrogen diffusion layer and less than the A1 transformation point of the cast iron, only the nitrogen diffusion layer is austenitized and finally tempered to a troostite structure or sorbite structure. Is also good. In this case, the hardness of the base material does not improve, but the hardness and toughness of the nitrogen diffusion layer improve.

In the fourth embodiment, since the oxidation / tempering treatment is performed in steam, a uniform oxide layer can be formed. However, the oxide layer can be formed in air or carbon dioxide.

In the fourth embodiment, the rotor is used as a disc brake rotor for an automobile. However, the rotor is used for a disc brake of an automobile which is desired to be inexpensive because it is a mass-market product. It is possible to provide a low-cost, highly wear-resistant disk brake even when used for such a disk brake.

[0074]

The rotor for a disc brake of the present invention has the following features.
After nitriding the molded body made of cast iron, the cast iron is heated and maintained at a temperature from the A1 transformation point to the eutectic temperature and then quenched and held in a heat bath at a predetermined temperature to form a nitrogen compound layer on the surface. Since the base structure below the compound layer is composed of a nitrogen diffusion layer having a bainite structure and a base material, corrosion resistance and wear resistance can be improved as compared with a conventional rotor made of ordinary cast iron material.

The rotor of the present invention also has a nitrogen diffusion layer and a nitrogen diffusion layer in comparison with a conventional plain cast iron rotor in which only a nitriding treatment is performed to increase hardness and improve wear resistance. Since the hardness is increased by forming the base material portion into a bainite structure, abrasion resistance does not suddenly decrease when abrasion progresses beyond the nitrogen compound layer on the surface.

Further, since the rotor for a disc brake of the present invention uses cast iron, it can be easily formed into a complicated rotor shape by casting, and is disclosed in JP-A-51-27828 in which ordinary steel or nitrided steel is formed. The processing cost can be reduced as compared with the case of the rotor described above.

Further, in the rotor for a disc brake according to the second aspect of the present invention, after the molded body made of cast iron is nitrided, the rotor is heated and maintained at a temperature not lower than the A1 transformation point of the nitrogen diffusion layer and less than the A1 transformation point of the cast iron. Quenching and holding in a temperature bath,
The nitrogen diffusion layer formed by nitriding is composed of a nitrogen compound layer on the surface by isothermal transformation, a nitrogen diffusion layer having a bainite-structured base structure under the nitrogen compound layer, and a base material of cast iron material. In addition, compared with a conventional rotor made of ordinary cast iron material, the corrosion resistance and wear resistance of the nitrogen compound layer can be improved.

The rotor of the present invention has a nitrogen diffusion layer even when compared to a conventional plain cast iron rotor in which only a nitriding treatment is performed to increase hardness and improve wear resistance. Since the hardness is increased by forming a bainite structure, abrasion resistance does not suddenly decrease when abrasion progresses beyond the nitrogen compound layer on the surface.

Further, since the rotor for a disc brake of the present invention uses cast iron, it can be easily formed into a complicated rotor shape by casting, and is disclosed in JP-A-51-27828 in which ordinary steel or nitrided steel is formed. The processing cost can be reduced as compared with the case of the rotor described above.

In the rotor for a disc brake according to the third aspect of the present invention, after the molded body made of cast iron is nitrided, the rotor is heated and held at a temperature not lower than the A1 transformation point of the nitrogen diffusion layer and less than the A1 transformation point of the cast iron. After quenching and holding in a heat bath at a temperature equal to or higher than the transformation start point, cooling is performed, and the nitrogen diffusion layer formed by nitriding is transformed into martensite to form a nitrogen compound layer on the surface and a base structure below the nitrogen compound layer becomes martensite. Since it is composed of a nitrogen diffusion layer with a site organization and a base material of cast iron material, it is possible to improve the corrosion resistance and wear resistance by the nitrogen compound layer as compared with a conventional rotor made of ordinary cast iron material. .

The rotor of the present invention has a nitrogen diffusion layer even when compared to a conventional plain cast iron rotor in which only a nitriding treatment is performed to increase hardness and improve wear resistance. Since the hardness is increased by forming a martensite structure, abrasion resistance does not suddenly decrease when abrasion progresses beyond the nitrogen compound layer on the surface.

Since the martensite structure is more excellent in wear resistance than the bainite structure, the wear resistance in the nitrogen diffusion layer is better than the disk brake rotor according to the first and second aspects of the present invention.

Further, in the disk brake rotor of the present invention, since only the nitrogen diffusion layer is formed into a martensite structure without changing the base structure of the base material, the rotor is formed by forming a martensite structure having poor toughness down to the base material. This prevents the whole from becoming brittle. In addition, the rotor for a disc brake of the present invention can be easily formed into a complicated rotor shape by casting because cast iron is used, and the rotor of Japanese Patent Application Laid-Open No. 51-28828 for forming ordinary steel or nitrided steel can be used. Compared with this, the processing cost can be reduced.

Further, in the rotor for a disc brake according to the invention of claim 4, after the molded body made of cast iron is nitrided, the nitrogen diffusion layer is heated and held at a temperature not lower than the eutectic temperature or higher than the A1 transformation point,
After that, it is quenched and held in a heat bath at a temperature equal to or higher than the martensitic transformation start point and then cooled, and only the nitrogen diffusion layer formed by nitriding or the nitrogen diffusion layer and the base material are martensite transformed and heated and maintained at a predetermined temperature. Oxide layer, a nitrogen compound layer below the oxide layer, a nitrogen diffusion layer in which the base structure under the nitrogen compound layer has tempered martensite,
Because it is composed of a base material of cast iron material or a base material tempered martensite, compared to a conventional rotor made of ordinary cast iron material or a rotor that has just been nitrided,
The oxide layer improves corrosion resistance and abrasion resistance.

The rotor of the present invention has a nitrogen diffusion layer even when compared to a conventional plain cast iron rotor in which only a nitriding treatment is performed to increase hardness and improve wear resistance. Since the hardness is increased by tempering martensite, the abrasion resistance does not suddenly decrease when abrasion progresses beyond the nitrogen compound layer on the surface, and the corrosion resistance is also excellent.

In addition, the structure obtained by tempering martensite is superior in toughness to the structure of martensite.
The disadvantages of the invention, such as the brittleness of the disk brake rotor, can be overcome. Therefore, it became possible to increase the hardness by forming a martensite structure in the base material portion and performing tempering.

Further, since the rotor for a disc brake of the present invention uses cast iron, it can be easily formed into a complicated rotor shape by casting, and is disclosed in JP-A-51-27828 in which ordinary steel or nitrided steel is formed. The processing cost can be reduced as compared with the case of the rotor described above.

Further, the disk brake rotor according to the present invention can perform a simple and energy-efficient treatment for continuously controlling only the temperature in the furnace and the atmosphere and the temperature of the heat bath, The treatment and the tempering treatment can be performed simultaneously.

[Brief description of the drawings]

FIG. 1 is a graph showing a change over time of a processing temperature of a rotor according to Examples 1 and 2 of the present invention.

FIG. 2 is an iron-nitrogen system phase diagram.

FIG. 3 is an iron-carbon system phase diagram.

FIG. 4 is an isothermal transformation diagram of carbon steel.

FIG. 5 is a graph showing a change over time of a processing temperature of a rotor according to a third embodiment of the present invention.

FIG. 6 is a graph showing the results of a cross-sectional hardness test of the rotor of Example 1 and the rotors of Comparative Examples 1 and 2.

FIG. 7 is a graph showing a change in corrosion resistance when a gas nitrocarburizing treatment temperature is changed.

FIG. 8 is a graph showing a change over time of a processing temperature of a rotor according to a fourth embodiment of the present invention.

Claims (4)

[Claims] Claims 1. After nitriding a molded product made of cast iron, the cast iron is heated and held at a temperature from the A1 transformation point to a eutectic temperature,
A rotor for a disc brake, wherein the rotor is quenched and held in a heat bath at a predetermined temperature to transform a nitrogen diffusion layer and a base material generated by nitriding at an isothermal temperature. 2. After nitriding a molded body made of cast iron, the body is heated and maintained at a temperature not lower than the A1 transformation point of the nitrogen diffusion layer and less than the A1 transformation point of the cast iron, and then quenched and held in a heat bath at a predetermined temperature. A rotor for a disc brake, characterized by isothermally transforming a nitrogen diffusion layer generated by the above. 3. A molded body made of cast iron is subjected to a nitriding treatment, and then heated and held at a temperature not lower than the A1 transformation point of the nitrogen diffusion layer and less than the A1 transformation point of the cast iron, and then quenched in a heat bath at a temperature not lower than the martensitic transformation start point. A rotor for a disc brake, wherein the rotor is cooled after holding, and a nitrogen diffusion layer generated by nitriding is transformed into martensite. 4. A molded body made of cast iron is nitrided, heated and maintained at a temperature from the A1 transformation point of the nitrogen diffusion layer to a eutectic temperature, and then quenched and held in a heat bath at a temperature at or above the martensitic transformation start point. After cooling, the nitrogen diffusion layer generated by nitriding is transformed into martensite and heated to a predetermined temperature.
A disc brake rotor characterized by being oxidized and tempered by holding.