JP6615255B2 - Disc brake rotor for automobile - Google Patents

Description

  The present invention relates to a disc brake rotor, and more particularly to a martensitic stainless steel automobile disc brake rotor having excellent workability and corrosion resistance.

  Conventionally, cast iron has been used for an automotive disc brake rotor. The reason is that when the disc brake rotor generates heat due to contact and friction with the pad, it is necessary to maintain sufficient strength against the generated heat. However, the cast iron disc brake rotor has a problem that it is spoiled during use due to its low corrosion resistance, and the disc brake rotor is located in the wheel of the tire, so this problem has been difficult to recognize.

  On the other hand, since the brake disc rotor for motorcycles is easy to touch the eyes, the design of the appearance is given priority. Therefore, the rotor is made of martensitic stainless steel having excellent weather resistance and high strength. Has been used.

  In recent years, with the increasing number of electric vehicles and hybrid vehicles, the use of regenerative brakes in vehicles has been promoted. For this reason, the load regarding braking performance is reduced with respect to the disc brakes of automobiles, and an environment in which martensitic stainless steel, which has been considered to be unusable, has been used.

  In addition, with the change in the design of automobiles, the number of vehicle types in which the disc brake rotor can easily be seen has increased, and the occurrence of the disc rotor is becoming visible. For this reason, martensitic stainless steel with low rustability has attracted attention as a material for the rotor.

  However, since the disc brake rotor for automobiles is located in the wheel of the tire as described above, the hat shape shown in FIG. 1 is often required. In such a case, extremely excellent workability is required for the material. However, since martensitic stainless steel has high strength, there is a problem that the workability is poor.

  One method for processing high-strength materials is a technique called hot stamping. This technique is a technique in which a material having a desired shape is obtained by performing press working in a state where the material is heated to a high temperature and then rapidly cooling in a mold. According to this method, not only the dimensional accuracy can be increased, but also martensite can be generated during the rapid cooling in the mold, so that the strength of the member having a desired shape can be increased. That is, hot stamping is a technique suitable for processing martensitic stainless steel.

  There are also many disc brake rotors that are not integrated and have a hat part and a collar part. In the rotor of such a form, the request | requirement with respect to the workability of the collar part which is a sliding part is reduced. It is also possible to use martensitic stainless steel only for this part.

  However, when martensitic stainless steel is applied to an automobile disc brake rotor, the plate thickness is somewhat large, so that the toughness after quenching is low. For this reason, there is a possibility that damage due to an impact at the time of component manufacture and use or cracking of the processed surface during processing after quenching may occur.

  Patent Literature 1 discloses a disc brake rotor for automobiles that uses martensitic Cr-containing steel and is manufactured by employing a hot stamp.

JP, 2006-117925, A JP-A-2006-65301

3rd Edition Steel Handbook IV Steel Materials, Testing / Analysis, p. 327

  However, the technology disclosed in Patent Document 1 has a wide range of steel components and does not sufficiently refer to the characteristics (for example, toughness, strength, and corrosion resistance) required for the disk brake rotor for automobiles. Patent Document 1 does not disclose toughness after quenching.

  As described above, there is no literature that clearly shows the relationship between a material having a predetermined component or structure and the characteristics required for an automobile disc brake rotor. In other words, it has excellent toughness, strength, and corrosion resistance. It can be said that there was no material suitable for the disc brake rotor.

  This invention is made | formed in view of the said situation, The objective is to provide the disk brake rotor which can express a required characteristic (toughness, intensity | strength, and corrosion resistance).

  The present inventors have examined the application of martensitic stainless steel to a disc brake rotor for automobiles. Among them, the present inventors have noticed that breakage due to impact during parts manufacture and use, or cracks in the machined surface during machining after quenching can occur. This is due to the low toughness after quenching, and when the structure of the rotor is only martensite or martensite and ferrite, the structure is coarse and poor toughness. This is because it is easy to break.

  As a result of investigating improving the above-described damage and cracks, the present inventors have found that the coarsening of the structure can be suppressed by leaving a part of the carbonitride in a high temperature state during quenching. Specifically, the inventors left the carbonitride left in this high temperature state after hot stamping, in other words, the structure of the rotor material, a structure containing martensite and carbonitride, Or the knowledge that it was important to set it as the structure | tissue containing a martensite, a ferrite, and a carbonitride was acquired.

  In addition to the above knowledge, the present inventors have determined a component range having sufficient strength and corrosion resistance, and have completed the present invention. That is, the present invention has been made based on the above findings, and the gist thereof is as follows.

  [1] A disc brake rotor characterized by having a structure containing martensite and carbonitride and optionally containing ferrite.

  [2] The disc brake rotor according to [1], wherein the carbonitride is 0.02% to 2% by mass.

[3] By mass%,
C: 0.02-0.10%,
N: 0.01-0.10%
Si: 0.05 to 1.0%,
Mn: 0.5 to 1.5%
P: 0.040% or less,
S: 0.015% or less,
Ni: 0.01 to 2.0%
Cr: 10.5 to 16.0%,
Cu: 0.01 to 1.0%
V: 0.01% to 0.50%, and Al: 0.001 to 0.010%
And the balance is Fe and inevitable impurities,
The disc brake rotor according to the above [1] or [2], wherein the hot phase balance index γp represented by the following formula (1) is 70 to 120.
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-52Al-12Mo-47Nb-7Sn-49Ti-48Zr-49V + 189 (1)

[4] Furthermore, in mass%,
Mo: 0.01 to 1.0%,
Sn: 0.003-0.10%,
Nb: 0.001 to 0.30%,
Ti: 0.05% or less,
B: 0.0002 to 0.0050%
The disc brake rotor according to [3] above, which contains at least one of the following.

  [5] The disc brake rotor according to any one of [1] to [4], wherein the plate thickness is 4 to 10 mm.

  [6] The disc brake rotor according to any one of [1] to [5], which is used as a disc brake rotor of an automobile.

  [7] The disc brake rotor according to any one of [1] to [6], which is made of martensitic stainless steel.

  The disc brake rotor according to the present invention has a predetermined structure. For this reason, the disk brake rotor according to the present invention exhibits necessary characteristics (toughness, strength, and corrosion resistance).

FIG. 1 is a diagram showing a hat-shaped automotive disc brake rotor.

  Hereinafter, embodiments of the disc brake rotor according to the present invention will be described in detail.

<Disc brake rotor>
The disc brake rotor of the present embodiment has at least a structure optimized in order to obtain excellent characteristics (toughness, strength, corrosion resistance, etc.) suitable for a disc brake rotor for automobiles.

[Chemical composition]
First, the reason for limiting the composition for obtaining a structure suitable as a disc brake rotor will be described. In addition, the description of% about a composition means the mass% unless there is particular notice.

C: 0.02-0.10%
C is an essential element for obtaining a predetermined hardness after quenching, and is added in combination with N so as to obtain a predetermined hardness level. If it is less than 0.02%, a sufficient martensite phase is not generated, and the strength is insufficient, which is not preferable. If it exceeds 0.10%, the strength becomes too high and brake noise tends to occur, which is not preferable. A preferable range of C is 0.03 to 0.08%. The brake squeal is a phenomenon in which vibration occurs due to a frictional force generated between a pad and a rotor included in the brake system.

N: 0.01-0.10%
N is an essential element for obtaining a predetermined hardness after quenching in the same manner as C, and is added in combination with C so as to obtain a predetermined hardness level. It is also effective in improving corrosion resistance. If it is less than 0.01%, a sufficient martensite phase is not generated, and the strength is insufficient, which is not preferable. If it exceeds 0.10%, the strength becomes too high and brake noise tends to occur, which is not preferable. A preferable range of N is 0.03 to 0.07%.

Si: 0.05% to 1.0%
In addition to being necessary for deoxidation during melting and refining, Si is also useful for suppressing the formation of oxide scale during quenching heat treatment, and the effect is manifested at 0.05% or more. However, since Si is mixed from raw materials such as hot metal, excessive reduction leads to an increase in cost. For this reason, it is preferable to make it 0.20% or more. Further, excessive addition of Si narrows the austenite single-phase temperature range and impairs quenching stability, so the content is made 1.0% or less. In addition, in order to reduce the addition amount of an austenite stabilization element and to reduce cost, it is preferable to make it 0.6% or less.

Mn: 0.5% to 1.5%
Mn is an element added as a deoxidizer, and contributes to improving the hardenability by expanding the austenite single phase region. The effect appears clearly at 0.5% or more. However, in order to ensure hardenability stably, it is preferable to make it 1.1% or more. In addition, excessive addition of Mn promotes the generation of oxide scale during quenching heating and increases the subsequent polishing load. In consideration of a decrease in corrosion resistance due to granulated materials such as MnS, the content is preferably 1.3% or less.

P: 0.040% or less P is an element contained as an impurity in main raw materials such as hot metal and ferrochrome. Since P is an element harmful to the toughness of the hot-rolled annealed sheet, it is set to 0.040% or less. More preferably, it is 0.030% or less. Since excessive reduction leads to an increase in cost, such as making it necessary to use a high-purity raw material, the lower limit of P is preferably 0.010%.

S: 0.015% or less S forms sulfide inclusions and degrades the general corrosion resistance (entire corrosion and pitting corrosion) of steel materials. Moreover, S reduces hot workability, specifically, makes it easy to generate an ear crack in a hot-rolled steel sheet. For this reason, the upper limit of the content is preferably as low as 0.015%. Further, the smaller the S content, the better the corrosion resistance. However, since the desulfurization load increases and the production cost increases for lowering the S content, the lower limit is preferably made 0.001%. Note that a more preferable range of S is 0.002 to 0.008%. Note that the edge cracking is a phenomenon that occurs at the edge of the rolled plate, and the material flows in the width direction of the rolled plate, so that stretching is insufficient, and tension in the rolling direction is generated to break the edge.

Ni: 0.01% to 2.0%
Ni is an element effective for suppressing the progress of pitting corrosion, and its effect is stably exhibited by addition of 0.01% or more, so the lower limit is made 0.01%. On the other hand, addition of a large amount may cause a decrease in press formability due to solid solution strengthening in the hot-rolled annealed steel sheet and is an expensive element, so the upper limit is made 2.0%. A preferable range of Ni is 0.01 to 1.0%.

Cr: 10.5% to 16.0%
In the present embodiment, Cr is an essential element for securing oxidation resistance and corrosion resistance. Specifically, the Cr carbonitride generated at the grain boundary in the hot-rolled steel sheet also has an effect of suppressing the coarsening of crystal grains when kept at a high temperature during quenching. If it is less than 10.5%, sufficient weather resistance and the like cannot be obtained. On the other hand, if it exceeds 16.0%, the formation of martensite becomes poor and sufficient strength cannot be obtained. A more preferable range of Cr is 11.0 to 15.5%.

Cu: 0.01% to 1.0%
Cu is effective in improving the corrosion resistance of the martensite structure containing δ ferrite, and the effect is manifested at 0.01% or more. Further, Cu may be positively added as an austenite stabilizing element to improve hardenability. On the other hand, excessive addition leads to a decrease in hot workability and an increase in raw material cost. In consideration of the occurrence of acid rain and the like, the lower limit is preferably 0.02% or more. A more preferable value of the upper limit value of Cu is 0.50%.

V: 0.01% to 0.50%
V is generally contained in the range of 0.01 to 0.10% because it is mixed as an impurity in the ferritic stainless steel alloy raw material and is difficult to remove in the refining process. If it is less than 0.01%, an increase in steelmaking cost is caused. V is an element that forms fine carbonitrides and improves the wear resistance of brake discs, and also has an effect of improving corrosion resistance. is there. Since the effect is stably manifested by addition of 0.02% or more, the lower limit is preferably 0.02%. On the other hand, if excessively added, there is a risk of causing coarsening of precipitates. Also, if the Cr nitride at the grain boundary is excessively reduced, the grain boundary is likely to become coarser, both of which reduce the toughness after quenching. Therefore, the upper limit is made 0.50%. As a result, the toughness after quenching decreases, so the upper limit is made 0.50%. In view of manufacturing cost and manufacturability, 0.03% to 0.2% is preferable.

Al: 0.001% to 0.010%
In addition to being added as a deoxidizing element, Al is an element that improves oxidation resistance. The effect is obtained at 0.001% or more. On the other hand, excessive addition facilitates the formation of large oxide inclusions. In this embodiment, since the weather resistance of the parent phase is reduced to the limit for cost reduction, the presence of inclusions greatly affects the weather resistance. This is because inclusions tend to be starting points. Under such circumstances, the upper limit of Al is made 0.010% in order to make inclusions small and small. The Al content is preferably as low as possible, and is preferably 0.003% or less from the viewpoint of deoxidation and cost. Of course, Al may not be contained. In addition, the content of Al here is T.I. Means Al.

  In the present embodiment, in addition to each element described above, at least one of the following elements can be contained in order to improve weather resistance, heat resistance, hot workability, and the like.

Mo: 0.01% to 1.0%
Mo is effective in improving the corrosion resistance of the martensite structure containing δ ferrite, and the effect is manifested at 0.01% or more. Since Mo is effective for improving hardenability and improving heat resistance after quenching, it is more preferably 0.02% or more. When the steel is quenched and then tempered, the hardness decreases. Here, the corrosion resistance after quenching means the degree of a small reduction margin and is also called “temper softening resistance”. Brake discs are hardened and used, but the disc material is heated by resistance heat generated by braking during use. Therefore, temper softening resistance is important. Mo is a stabilizing element of the ferrite phase, and excessive addition impairs the quenching characteristics by narrowing the austenite single phase temperature range, so the upper limit is preferably made 1.0%. A more preferable upper limit of Mo is 0.8%.

Sn: 0.003% to 0.10%
Sn is an element effective for improving the corrosion resistance after quenching, and is preferably 0.003% or more, and more preferably 0.02% or more if necessary. However, excessive addition promotes ear cracking during hot rolling, so it is preferably made 0.10% or less, more preferably 0.05% or less.

Nb: 0.001% to 0.30%
Nb is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride, and is preferably 0.001% or more. Furthermore, considering that Nb is an element that greatly improves the heat resistance after quenching, 0.05% or more is more preferable. Here, the heat resistance means difficulty in softening when subjected to heat after quenching, and is also referred to as “temper softening resistance”. However, when Nb is added excessively, formation of NbN in the brake disk causes a reduction in toughness and brake squeal, which is not preferable. The upper limit is 20%.

Ti: 0.05% or less Ti forms a large TiN in the brake disk, which causes a decrease in toughness and brake squeal. Therefore, the upper limit is preferably 0.05% or less. Further, considering the toughness in winter, it is more preferable to make it 0.01% or less. However, since it is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride, it is more preferably 0.001% or more, 0.005 % Or more is more preferable.

B: 0.0002% to 0.0050%
B is an element effective for improving hot workability, and the effect is manifested at 0.0002% or more, so 0.0002% or more may be added. In order to improve the hot workability in a wider temperature range, the content is more preferably 0.0010% or more. On the other hand, excessive addition impairs the hardenability due to the combined precipitation of boride and carbide, so 0.0050% is preferable as the upper limit. Considering corrosion resistance, it is more preferable to set it to 0.0025% or less.

  In addition to the elements described above, the disc brake rotor of this embodiment includes Fe and inevitable impurities as the balance. Here, the inevitable impurities refer to impurities mixed from ores, scraps, or production environments as raw materials when the disc brake rotor is industrially manufactured. Inevitable impurities include Zn, Pb, Se, Sb, Ga, Ta, Ca, Mg, Zr, etc., in addition to the aforementioned P, S, and V, which are general impurity elements. These elements are preferably reduced as much as possible.

  On the other hand, the content ratio of these elements is controlled within the limits to solve the problems of the present invention, and if necessary, Zn ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm, Sb ≦ 500 ppm, Ga ≦ 500 ppm, Ta ≦ 500 ppm, Ca ≦ 120 ppm, Mg ≦ 120 ppm, Zr ≦ 120 ppm may be contained.

[Organization]
γp: 70 to 120
The disc brake rotor of this embodiment is made of martensitic stainless steel. In order to obtain martensite (hereinafter referred to as M), it is necessary to generate austenite (hereinafter referred to as γ) at a high temperature. In addition, since the amount of martensite is determined by the additive component, it is necessary to balance each element by adjusting each other.

An index indicating the phase balance is γp represented by the following formula (2).
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-52Al-12Mo-47Nb-7Sn-49Ti-48Zr-49V + 189 (2)

  In the present embodiment, γp needs to be 70 to 120. If it is less than 70, γ generated at high temperature decreases, M after quenching decreases, and the required hardness cannot be obtained. On the other hand, when γp exceeds 120, martensite transformation does not occur even when γ is quenched, the stable γ is excessively increased, the martensite is excessively decreased, and the required hardness cannot be obtained. γp is more preferably 90 to 120.

Specific metal structure: martensite and carbonitride (optionally ferrite)
The metal structure of the disc brake rotor of the present embodiment is a structure containing martensite and carbonitride and optionally containing ferrite. In addition, it is permissible that austenite is present in less than 1% by volume.

  Each metal structure can be distinguished by etching with aqua regia chemicals and then observing with an optical microscope. When it is necessary to observe in more detail, it is also possible to observe using a microstructure observation method after etching using Murakami reagent or an EBSD (Electron Backscatering Diffraction) method as shown in Patent Document 2. .

  By containing martensite and carbonitride and austenite being less than 1%, the structure can be made finer, and as a result, toughness can be increased.

  Regarding the structure of the disc brake rotor of the present embodiment, the merit including carbon nitride in particular is as follows. That is, when carbonitride is present in a high temperature state at the time of quenching, the coarsening of crystal grains can be suppressed, and the structure after transformation can be refined by the carbonitride left in the high temperature state, A rotor having excellent toughness can be obtained. In particular, in the hot stamping method, when the time of exposure to high temperature is long, it is more effective if carbonitride is present.

  Carbonitride is preferably 0.02% to 2% by mass. If the carbonitride is less than 0.02%, the effect of suppressing grain coarsening is not exhibited, and if it exceeds 2%, not only the toughness is lowered but also solid solution C and N are reduced. It is not preferable because the hardness of the site is lowered and the strength is slightly lowered.

  The amount of carbonitride can be determined by a general extraction residue method. In the present embodiment, in accordance with the technique described in Non-Patent Document 1, a solution in which a certain amount of steel sheet is dissolved by electrolysis is filtered through a filter, the remaining residue is quantified, and the residual rate is calculated from the ratio with the dissolved amount. The desired method can be adopted. In this embodiment, the residue is considered to be almost carbonitride, and the amount of residue is defined as the amount of carbonitride.

[Rotor thickness]
In the disc brake rotor of the present embodiment, the plate thickness is preferably 4 to 10 mm. If the rotor plate thickness is 4 mm or less, it is too thin as an automobile disk rotor, and if it exceeds 10 mm, it is too thick and the entire brake system becomes too large. A more preferable plate thickness of the disc brake rotor is 4 to 8 mm.

  The disc brake rotor of the present embodiment described above has at least a predetermined structure. For this reason, according to the disc brake rotor which concerns on this embodiment, required characteristics (toughness, intensity | strength, and corrosion resistance) can be expressed.

<Method of manufacturing disc brake rotor>
Next, the manufacturing method of the disc brake rotor of this embodiment will be described in detail.

[Preparation process of martensitic stainless steel sheet]
First, a martensitic stainless steel sheet having the above composition is prepared. Specifically, a steel sheet can be produced through processes usually used, that is, melting / casting, hot rolling, and hot-rolled sheet annealing. Here, the hot-rolled sheet annealing may be omitted. Moreover, removal of the scale by shot blasting or pickling can be employed as the final step.

  The plate thickness of the steel plate used for the rotor is preferably 4 to 9 mm. If it is less than 4 mm, it is difficult to produce a hot-rolled steel sheet. On the other hand, if it exceeds 9 mm, the entire brake system becomes too large.

[Process of exposing steel sheet to high temperature]
Next, the predetermined martensitic stainless steel sheet is exposed to a high temperature of 950 ° C. or higher and 1150 ° C. or lower for a time of 1 second or longer and 30 minutes or shorter. In this step, the structure of the steel sheet is changed from ferrite phase + carbonitride to austenite phase + carbonitride. In addition to the austenite phase + carbonitride, a part of the ferrite phase may remain.

  When the temperature at which the steel plate is exposed is less than 950 ° C., the austenite phase is small and the hardness after quenching is low. On the other hand, when it exceeds 1150 ° C., the crystal grains of the austenite phase during heating become too large and the toughness after quenching decreases. In addition, since a stable austenite phase that does not cause martensitic transformation is also generated, the hardness after quenching decreases. Similarly, if the exposure time of the steel sheet is less than 1 sec, the austenite phase is small and the hardness after quenching is low, whereas if it exceeds 30 min, the austenite phase crystal grains during heating become too large, Not only the toughness and the like are lowered, but also a stable austenite phase that does not cause martensitic transformation is generated, so that the hardness after quenching is also lowered. More preferably, the predetermined martensitic stainless steel sheet is exposed to a high temperature of 1000 ° C. or higher and 1110 ° C. or lower for a time of 1 minute or longer and 20 minutes or shorter.

  As for the combination of temperature and time at which the steel plate is exposed to a high temperature, the temperature and time may be within the above ranges, but if a relatively low temperature is selected, select a relatively long time, and set a relatively high temperature. When selecting, it is preferable to select a relatively short time in order to obtain a good balance between hardness and toughness after quenching.

[Process to process into a predetermined shape by pressing]
Thereafter, the steel plate is processed into a predetermined shape by pressing. In the press working, it is preferable that the temperature at the start is 800 ° C. or higher from the viewpoint of sufficiently causing martensitic transformation. In addition, it does not specifically limit about other various conditions regarding press work. In this way, an intermediate body having a predetermined shape is obtained.

[Step of cooling the intermediate processed into a predetermined shape by pressing]
Furthermore, by using the die used in the press working as it is, the intermediate body obtained by the press working is cooled as it is in the die to obtain a disc brake rotor. In this process, austenite is transformed into martensite and the strength is improved. Even after this martensitic transformation, some residual austenite may exist in the rotor, but the microstructure at the time of becoming the rotor is basically martensite + carbonitride, or martensite. Any of + carbonitride + ferrite may be used. However, it is permissible for the residual austenite to be present in an extremely small amount (5% or less in terms of area ratio when measured from the rotor surface at a depth half the plate thickness). Further, if carbonitride is eliminated, the grain boundary pinning effect is lost, and the austenite grain growth at high temperatures becomes remarkable and coarse, which is not preferable.

  The cooling rate is preferably 10 ° C./min to 100 ° C./s. Regarding the quenching condition, the correlation with the amount of carbonitride is important, and the quenching condition is such that the amount of carbonitride after quenching is measured by the extraction residue method and is 0.02% to 2% in mass%. Is preferable in that a rotor having excellent toughness can be obtained. In addition, about hardening, the hot stamping method which combined hot press and hardening other than the form in this embodiment is also employable.

  In the manufacturing method of the disc brake rotor of this embodiment, it cools to at least 200 degreeC after press work. Thereby, martensitic transformation occurs, and the rotor can obtain the required hardness. In order to further enhance this effect, it is preferable to cool to room temperature.

  Examples of the present application will be shown below to demonstrate the effects of the present invention.

<Example 1>
[Production of rotor]
Steel A1 to A24 of each component shown in Table 1 and steels a1 to a18 were melted in a 50 kg ingot and hot-rolled to obtain a hot-rolled sheet having a thickness of 4 to 9 mm. Then, box annealing of 850 degreeC and 10 hours was performed, and it washed with sulfuric acid, and obtained hot-rolled steel plates B1-B24 and hot-rolled steel plates b1-b18. In Table 1, equation (2) γp is the value of γp in equation (2) described above.

  Thereafter, for each of the hot-rolled steel plates B1 to B24 and the hot-rolled steel plates b1 to b18, a ring-shaped member having an outer diameter of 100 mm and an inner diameter of 50 mm used for a disk rotor divided into a hat portion and a flange portion. Samples C1 to C24 and samples c1 to c18 were punched out.

  Finally, among these samples, mold quenching was performed on sample C1 (using A1 steel) and sample C2 (using A2 steel) by changing the quenching conditions as shown in Table 2. And the surface and end surface were ground with respect to the sample after hardening, and the rotors D1-D8 and the rotors d1-d8 shown in FIG. 2 were produced.

[Evaluation of rotor structure, carbonitride content (extraction residue), and mechanical properties]
Next, for each of the rotors D1 to D8 and the rotors d1 to d8, the structure is observed, the amount of carbonitride (related to the extraction residue) is measured, and further, mechanical properties (toughness, hardness, and corrosion resistance) are measured. Was evaluated, and comprehensive evaluation was performed based on these results.

(Organization)
About the structure | tissue, after etching with aqua regia, it observed with the optical microscope, and confirmed presence or absence of a ferrite, a martensite, a carbonitride, and austenite. And the case where it is a structure | tissue containing a martensite and a carbonitride, or the case where it is a structure | tissue containing a martensite, a carbonitride, and a ferrite was made into this invention, and the other case was made outside this invention. The results are shown in Table 3.

(Carbonitride content)
The extraction residue was collected by electrolysis from the sample for extraction residue, and the amount of carbonitride was evaluated. The case where the amount of carbonitride was 0.02% to 2% was included in the present invention, and the other cases were excluded from the present invention. The results are also shown in Table 3.

(Toughness)
About toughness, the Charpy impact test based on JISZ2242 was done. As the sample, a sub-size test piece in which a V notch having a depth of 2 mm was cut into the plate thickness was used. The case where the energy required for breaking the test piece was 10 J / cm ² or more was good, and the case where it was 5 J / cm ² or more and less than 10 J / cm ² was good, while the case where it was less than 5 J / cm ^{2 was} judged as bad. The results are also shown in Table 3. In the present specification, “excellent” and “good” are acceptable and “impossible” is unacceptable.

(Hardness)
As an index of strength, hardness was measured by a Rockwell C scale (HRC) test in accordance with JIS Z 2245, and the case of 30 to 40 was excellent, and the case of 25 to 30 was good. On the other hand, if it is less than 25, it is not preferable because the deformation at the time of use becomes too large, and if it exceeds 40, it is not preferable because the noise of the brake at the time of use becomes large. The results are also shown in Table 3.

(Corrosion resistance)
As for corrosion resistance, a salt spray test (SST) based on JIS Z 2371 was carried out for 24 hours, and no rusting was observed and 5 or less flow rusts were evaluated as good, while more than 5 flow rusts were not permitted. The results are also shown in Table 3.

  And comprehensive evaluation was performed about each of rotor D1-D8 and rotor d1-d8 in consideration of the above evaluation results (toughness, hardness, and corrosion resistance) comprehensively. The results are also shown in Table 3.

  As is apparent from Tables 1 to 3, it can be seen that the necessary characteristics (toughness, strength, and corrosion resistance) are expressed in the rotors D1 to D8 having a predetermined structure. On the other hand, it can be seen that at least one of the necessary characteristics (toughness, strength, and corrosion resistance) is not expressed in the rotors d1 to d8 that do not have the predetermined structure.

<Example 2>
About each of samples C1-C24 and samples c1-c1 obtained in Example 1, after holding at 1000 to 1050 ° C. for 5 to 30 seconds, mold quenching was performed, and then the surface and end face were ground in the same manner as in Example 1. Thus, rotors E1 to E24 and rotors e1 to e18 were produced. And the evaluation test similar to Example 1 was done with respect to these rotors E1-E24 and rotors e1-e18. The results are shown in Table 4. In the remarks column of Table 4, e4 was deficient due to insufficient Si, and e11 and e12 had a large amount of γ because Ni and Cu were added excessively.

  As is apparent from Tables 1 and 4, the rotors E1 to E24 having a predetermined structure, and e1, e3 to e10, e13, and e15 to e18 have necessary characteristics (toughness, strength, and corrosion resistance). ) Is expressed. On the other hand, for the rotors e2, e11, e12, and e14 that do not have a predetermined structure, it can be seen that at least one of the necessary characteristics (toughness, strength, and corrosion resistance) is not expressed.

Claims (4)

% By mass
C: 0.02-0.10%,
N: 0.01-0.10%
Si: 0.05 to 1.0%,
Mn: 0.5 to 1.5%
P: 0.040% or less,
S: 0.015% or less,
Ni: 0.01 to 0.20 %
Cr: 10.5 to 16.0%,
Cu: 0.01 to 0.50 %
V: 0.01% to 0.50%, and Al: 0.001 to 0.010%
And the balance is Fe and inevitable impurities,
Phase balance index γp is 70-120 der during hot represented by the following formula (1) is,
A structure containing martensite and carbonitrides and optionally containing ferrite;
The carbonitride is 0.02 to 2% by mass,
A disc brake rotor for automobiles having a plate thickness of 4 to 10 mm .
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-52Al-12Mo-47Nb-7Sn-49 Ti- 49V + 189 (1)
Here, the content of the element is substituted for each element symbol in the formula (1). Furthermore, in mass%,
Mo: 0.05 to 1.0%,
Sn: 0.003-0.10%,
Nb: 0.01 to 0.10 %,
Ti: 0.005 to 0.05 %,
B: 0.0002 to 0.0050%
The automobile disc brake rotor according to claim 1, comprising at least one of the following. The disk brake rotor for automobiles according to claim 1 or 2 , which is used as a disk brake rotor for automobiles . The disc brake rotor for automobiles according to any one of claims 1 to 3 , wherein the disc brake rotor is made of martensitic stainless steel.

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