JP2017197820A - Martensitic stainless cold rolled steel sheet for bicycle disc brake rotor excellent in hardenability and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and high-quality cold rolled martensitic stainless steel sheet for a bicycle rotor.SOLUTION: The cold rolled martensitic stainless steel sheet for a bicycle rotor is provided that contains, by mass%, C:0.020 to 0.060%, N:0.020 to 0.070%, Si:0.1 to 1.0%, Mn:1.0 to 1.5%, P:0.040% or less, S:0.015% or less, Ni:0.3% or less, Cr:10.5 to 13.5%, Cu:0.1% or less, V:0.3% or less, Al:0.001 to 0.010%, satisfying formula 1, γp in formula 2 being 90 to 120, and the balance Fe with inevitable impurities, a precipitate in the steel being 0.2 to 2% and sheet thickness being 0.5 to 2.5 mm. 0.03%≤C+0.5×N≤0.09%... formula 1, where N≥C, γp=420C+470 N+23 Ni+9Cu+7Mn-11.5Cr-11.5Si-52Al-12Mo-47Nb-7Sn-49Ti-48Zr-49V+189... formula 2, where element name in the formula 2 is content of the element (mass%).SELECTED DRAWING: None

Description

  The present invention mainly relates to a martensitic stainless cold-rolled steel sheet for a bicycle disc brake rotor, which is used as a bicycle disc brake rotor and has excellent hardenability, and a method for producing the same.

  Bicycle disc brakes are mainly used as braking devices for high-grade bicycles, and their rotors are required to have characteristics such as wear resistance, weather resistance, and lightness. Therefore, martensitic stainless steel and aluminum composite materials are used for the highest grade products, and martensitic stainless steel is used for the lower class. In martensitic stainless steel, SUS420J1 and SUS420J2 are generally used as steel types. Stainless steel for bicycle disc brake rotors is hot rolled, annealed and cold rolled to adjust the shape and hardness, then processed to the desired shape by press molding, adjusted to the desired hardness by quenching and tempering heat treatment After that, a disc brake rotor is obtained through a polishing and painting process.

  On the other hand, there is a disc brake rotor that is manufactured by adjusting the hardness only by quenching without performing tempering, and SUS410 martensitic stainless steel is used for this. As a result, the manufacturing cost was reduced and the range of use was expanded. Patent Document 1 discloses SUS410 martensitic stainless steel in which C + N is 0.04 to 0.10% and Mn is added to 1.0 to 2.5%. Patent Document 2 discloses SUS410 martensitic stainless steel to which Ni is added in an amount of 0.60% or less instead of Mn being 0.5 to less than 1%. However, these steels were developed mainly for motorcycles and were not necessarily optimal for bicycles.

  Recently, Patent Document 3 discloses a steel material that satisfies 38 to 44 HRC, which is harder than that for motorcycles, for bicycles.

  However, when a disc brake is used in a general-purpose bicycle for the purpose of further expansion of the range of use, the required braking force will be lower than before due to its actual use, so a martensitic stainless steel for disc brake rotors corresponding to that will be used. It became necessary.

JP-A-57-198249 JP 60-106951 A International Publication No. 2012/157680

In the martensitic stainless steel sheet described in the background art, the hardness after quenching is high, and many alloying elements are added to obtain the required hardness. It was.
An object of the present invention is a low-cost disc brake rotor material applicable to general-purpose bicycles, and is inexpensive, sufficiently excellent in quality, martensitic stainless cold-rolled steel plate for bicycle disc brake rotors with excellent hardenability, And providing a manufacturing method thereof.

  So far, the rotor material of a bicycle disc brake has been adjusted to 38 to 44 by HRC in view of braking force, wear resistance and the like. This is because a bicycle using a disc brake is a high-class bicycle such as a mountain bike, and excellent braking characteristics are required. Moreover, since the examination of the conditions of the manufacturing process after cold rolling is insufficient, there is a problem that the material being used varies greatly in hardness from lot to lot, and a material that is harder than necessary is used.

  On the other hand, when a disc brake is used for a general-purpose bicycle, such a braking force is not necessary, but rather it is important that it is inexpensive. Therefore, the required material properties must be changed.

  As a result of studies by the present inventors, it has been clarified that, for a general-purpose bicycle, a sufficient braking force can be maintained if the hardness is about 32 to 38 in HRC.

  If it is HRC32-38, the disc brake material for motorcycles can also be used, but the disc brake material for motorcycles usually uses a hot-rolled steel plate. The press workability could not be obtained. In addition, since the quenching conditions are greatly different, it is necessary to change the idea of the quenching hardness.

  Therefore, the present inventors have performed the optimum component design as a bicycle disc brake rotor material and also optimized the manufacturing process, and have completed the invention of a martensitic stainless steel plate as a disc brake rotor material for general-purpose bicycles.

The present inventors have studied in detail the necessary characteristics as a disc brake rotor material for general-purpose bicycles, and found that the following is obtained.
(A1) A cold-rolled steel sheet is desirable from the viewpoint of sheet thickness accuracy.
(A2) After cold rolling annealing, quenching by oil cooling results in a hardness of 32-38 HRC (A3) Quenching in a heat treatment furnace is desirable for low temperature and short time (excellent low temperature hardenability)
(A4) Even if the heat treatment conditions change, it is better that the hardness change is small (excellent quenching stability).

Furthermore, the present inventors worked on the development of a steel plate having these necessary characteristics, and obtained the following knowledge.
(B1) The cold-rolled annealed plate is different in hardenability from the hot-rolled annealed plate, and the cold-rolled annealed plate is more excellent in hardenability.
(B2) When N is larger than C, the low-temperature hardenability and quenching stability are excellent. (B3) The amount of precipitate centered on carbonitride is important, and the hardenability improves as the amount of precipitate decreases.

  The present invention has been made based on these findings, and means for solving the problems of the present invention, that is, the martensitic stainless steel sheet of the present invention is as follows.

(1) In mass%,
C: 0.020 to 0.060%,
N: 0.020 to 0.070%,
Si: 0.1 to 1.0%,
Mn: 1.0 to 1.5%
P: 0.040% or less,
S: 0.015% or less,
Ni: 0.3% or less Cr: 10.5 to 13.5%,
Cu: 0.1% or less,
V: 0.3% or less,
Al: 0.001 to 0.010%
Containing
And C and N satisfy Formula 1;
And γp which is a phase balance index at the time of hot rolling represented by Formula 2 is 90 to 120,
The balance consists of Fe and inevitable impurities,
The amount of precipitates in the steel is 0.2% or more and 2% or less,
A martensitic stainless cold-rolled steel sheet for bicycle disc brake rotors having a plate thickness of 0.5 mm or more and 2.5 mm or less and excellent in hardenability.
0.03% ≦ C + 0.5 × N ≦ 0.09% Formula 1
However, N ≧ C
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-52Al-12Mo-47Nb-7Sn-49Ti-48Zr-49V + 189 Equation 2
In addition, the element name in Formula 1 and Formula 2 means content (mass%) of each element. Zero if it contains only inevitable impurities.
(2) In mass%,
Mo: 0.01 to 0.5%,
Sn: 0.003-0.1%,
Nb: 0.001 to 0.3%,
Ti: 0.05% or less,
Zr: 0.05% or less,
B: 0.0002 to 0.0050%
The martensitic stainless steel cold-rolled steel sheet for a bicycle disc brake rotor having excellent hardenability as described in (1), wherein the balance is composed of Fe and one or more impurities, and the balance is Fe and inevitable impurities.
(3) The martensitic stainless steel cold-rolled steel sheet for bicycle disc brake rotors having excellent hardenability according to (1) or (2), wherein the steel sheet is a steel strip.
(4) The manufacturing process includes melting, casting, hot rolling, hot rolling sheet annealing, pickling, cold rolling, cold rolling sheet annealing, pickling, and the annealing temperature of the cold rolling sheet annealing is 700 to 800 ° C. The method for producing a martensitic stainless cold-rolled steel sheet for a bicycle disc brake rotor according to any one of (1) to (3).

The marsite stainless steel of the present invention makes it possible to manufacture a motorcycle disc brake rotor that is inexpensive and excellent in hardenability.
That is, according to the present invention, as an inexpensive disc brake rotor material applicable to a general-purpose bicycle, it is inexpensive, sufficiently superior in quality, and excellent in hardenability. A steel plate can be provided.

Embodiments of the present invention will be described below.

<Chemical component>
First, the reason which limited the steel composition of the stainless steel plate of this embodiment is demonstrated. In addition, the description of% about a composition means the mass% unless there is particular notice.

C: 0.020 to 0.060%
C increases the hardness during quenching, increases the austenite phase fraction during quenching heating, and increases the amount of martensite after quenching. In order to give the necessary hardness and braking force to the brake rotor of a general-purpose bicycle, 0.020% or more is necessary. On the other hand, if it exceeds 0.060%, the hardness becomes such that HRC exceeds 38, and problems such as squealing of the brake appear. Considering the balance between hardness and toughness, it is desirable to set it as 0.025 to 0.050%.

N: 0.0020 to 0.070%
N, like C, increases the hardness during quenching, increases the austenite phase fraction during quenching heating, and increases the amount of martensite after quenching. In order to give the necessary hardness and braking force to the brake rotor of a general-purpose bicycle, 0.020% or more is necessary. On the other hand, if it exceeds 0.070%, the hardness becomes such that HRC exceeds 38, and problems such as squealing of the brake appear. Considering the balance between hardness and toughness, it is desirable that the content be 0.030 to 0.050%.

0.03 ≦ C + 0.5 × N ≦ 0.09% Formula 1
Basically, the hardness of the steel sheet after quenching depends on the amount of C + 0.5 × N, although it is affected by other elements and the structure. In order to satisfy the hardness range of 32 to 38 HRC, the lower limit is 0.03% and the upper limit is 0.09%.

N ≧ C
In order to realize excellent hardenability, carbides and nitrides need to be dissolved quickly during quenching. In general, carbides tend to be coarser than nitrides, so that N ≧ C in the present invention. As a result, coarse carbides are less likely to be generated and can be sufficiently dissolved even by heating at a low temperature in a short time. As a result, the quenching hardness is improved. That is, excellent low-temperature hardenability can be obtained.

Si: 0.1 to 1.0%
Si is an element that improves high-temperature strength and oxidation resistance, and is also an element useful as a deoxidizer, and the effect is produced by addition of 0.1% or more. However, it is an element that reduces the martensite phase during quenching, lowers toughness, and increases hardness, so the upper limit was made 1.0%.
Preferably, it is 0.1 to 0.5%.

Mn: 1.0 to 1.5%
Mn is an element useful as a deoxidizer, and is an austenite forming element like Ni and Cu, and increases the amount of martensite during quenching. Further, as an effect unique to Mn, non-metallic inclusions (MnS) are formed, and the hot workability is improved. Furthermore, it has the effect of increasing the solubility of nitrogen in the molten steel, and when nitrogen is added in a large amount, it has the effect of suppressing the formation of bubble defects. In order to obtain these effects, the Mn content is at least 1.0%. However, if Mn is contained in a large amount, oxidation during quenching heating proceeds and it becomes difficult to remove the oxide film, and the surface quality of the material is lowered due to the coarsening of MnS. Furthermore, when Mn is contained in a large amount, it is difficult to reduce the squealing hardness during braking. Accordingly, the Mn content is 1.5% or less.

P: 0.040% or less P is an element having a large solid solution strengthening ability and a ferrite forming element. Since it is an element harmful to corrosion resistance, it is preferably as small as possible, and the upper limit is made 0.040%. When better corrosion resistance is required, 0.020% or less is preferable. However, excessive reduction increases the dephosphorization load and increases the manufacturing cost, so the lower limit is preferably made 0.005%.

S: 0.015% or less Since S forms sulfide inclusions and degrades general corrosion resistance (entire corrosion and pitting corrosion) of the steel sheet, the upper limit of the content is preferably small. %. 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 0.0001%. In addition, Preferably it is 0.0005 to 0.0050%.

Ni: 0.3% or less Ni is an austenite forming element like Mn and Cu, and increases the amount of martensite during quenching. However, since Ni is expensive, it is not actively added in the present invention, but is limited to the inevitable impurities mixed from scrap, and the allowable upper limit is set to 0.3%. However, it is an element effective for suppressing the progress of pitting corrosion, and the effect is stably exhibited by addition of 0.05% or more. In addition, it is effective for improving the toughness of the hot-rolled sheet. Therefore, the content is preferably 0.05% or more.

Cr: 10.5 to 13.5%
Cr is an essential element for ensuring corrosion resistance as a disc brake rotor. In order to form a passive film in the assumed environment, 10.5% or more is necessary, and this is the lower limit. On the other hand, since Cr is a ferrite-forming element, if the Cr content exceeds 13.5%, the austenite fraction during quenching heating decreases, the amount of martensite phase after quenching decreases, In this case, it is necessary to add an austenite-forming element (Ni, Cu, Mn) corresponding to the amount of Cr to ensure the austenite phase fraction during quenching heating. On the other hand, the securing of the phase fraction by the addition of the austenite-forming element is limited for various reasons and increases the cost, so the upper limit of the Cr content is 13.5%.

Cu: 0.1% or less Cu is an austenite forming element like Mn and Ni, and increases the amount of martensite during quenching. Moreover, it is an element which improves corrosion resistance. However, there is a problem that the oxide film formed by heat generation during sliding is changed to lower the disc brake squeal strength, so the content is made 0.1% or less.

V: 0.3% or less V is an element mixed as an inevitable impurity from the alloy raw material. Excessive content causes a reduction in martensite hardness due to the formation of carbonitrides, so the upper limit is 0.3%.

Al: 0.001 to 0.010%
Al is useful as a deoxidizing element, and the effect is manifested at 0.001% or more. However, excessive addition affects corrosion resistance and the like, so the upper limit is made 0.010%. When deoxidation is possible with other elements such as Si, 0.003% to 0.0008% is desirable in consideration of cost.

In addition to the limitation of these elements, the present invention is a martensitic stainless steel, and in order to generate a martensite phase (hereinafter referred to as M phase), it is necessary to generate an austenite phase (hereinafter referred to as γ phase) at a high temperature. In addition, since the amount is determined by the additive component, it is necessary to adjust each element to achieve a phase balance. The phase balance index is expressed by Equation 2, and this γp may be 90-120. If it is less than 90, the γ phase generated at a high temperature decreases, the M phase after quenching decreases, and the required hardness cannot be obtained. On the other hand, when γp exceeds 120, even if the γ phase is quenched, the M phase transformation does not occur, the stable γ phase increases, and this also decreases the M phase and the required hardness cannot be obtained. The most preferred γp is 90-110.

γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-52Al-12Mo-47Nb-7Sn-49Ti-48Zr-49V + 189 Equation 2

In addition, the element name in Formula 2 means content (mass%) of each element. Zero if it contains only inevitable impurities.
Formula 2 is also an index indicating the maximum value of the amount of austenite generated during heating at 1100 ° C., “Metal Treatment” 1964, p. This is an improvement of the Castro equation introduced in the literatures 230 to 245, and is a well-known equation as an empirical equation for estimating the maximum phase fraction of the γ phase.

  Furthermore, in order to improve corrosion resistance, you may contain 1 or more types of the following elements.

Mo: 0.01 to 0.5%
Mo may be added as necessary to improve the corrosion resistance. In order to exert these effects, the lower limit is preferably made 0.01%. On the other hand, excessive addition inhibits the formation of M phase, so the upper limit is made 0.5%.

Sn: 0.003-0.1%
Sn is an element effective for improving the corrosion resistance after quenching, and is preferably 0.003% or more, and is preferably added 0.02% or more as necessary. However, excessive addition promotes ear cracking during hot rolling, so the upper limit is 0.1%.

Nb: 0.001 to 0.3%
Nb is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. 0.001% or more is preferable. Furthermore, it is an element that greatly improves the heat resistance after quenching. Here, heat resistance means how hard it is to soften when subjected to heat after quenching, and is also called temper softening resistance.
However, when Nb is added excessively, formation of NbN in the disc brake rotor causes a decrease in toughness and squeal, which is not preferable, and the upper limit is 0.3%.

Ti: 0.05% or less Ti is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride, but the carbonitride tends to be coarse. Since it does not contribute to strengthening and is only for fixing C and N, 0.05% is made the upper limit.

Zr: 0.05% or less Zr is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride, but the carbonitride tends to be coarse. Since it does not contribute to strengthening and is only for fixing C and N, 0.05% is made the upper limit.

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 preferably 0.0010% or more. On the other hand, excessive addition impairs hardenability due to combined precipitation of boride and carbide, so the upper limit is made 0.0050%. In consideration of corrosion resistance, 0.0025% or less is desirable.

In addition to the elements described above, the elements of the present invention can be contained within a range not impairing the effects of the present invention. It is preferable to reduce as much as possible the aforementioned impurity elements P, S, Zn, Bi, Pb, Se, Sb, H, Ga, Ta, Ca, Mg, Zr, B and the like. On the other hand, the content ratio of these elements is controlled to the extent that the problems of the present invention are solved, and, if necessary, Zn ≦ 100 ppm, Bi ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm, Sb ≦ 500 ppm, H ≦ 100 ppm, Ga ≦ 500 ppm, Ta ≦ 500 ppm, Ca ≦ 120 ppm, Mg ≦ 120 ppm, Zr ≦ 120 ppm. “Ppm” is based on mass.
Further, the martensitic stainless cold-rolled steel sheet for bicycle disc brake rotor according to the present embodiment contains the above components, and the remainder is formed of Fe and inevitable impurities.

<Precipitate>
Moreover, the amount of precipitates in the steel of the cold-rolled steel sheet of the present invention is 0.2% or more and 2% or less. The amount of precipitate is evaluated by the extraction residue method, and is defined as the ratio of the residual residue amount to the dissolved amount of the base material in mass%. These precipitates are mainly carbonitrides, which act as pinning sites until they dissolve at the time of temperature rise during quenching, and prevent γ phase grain growth and prevent hardness reduction. If it is 0.2% or more, the effect is manifested. However, if it exceeds 2%, not only is the effect coarsened and the effect disappears, but the solid solution C and N are reduced, so the hardness of the M phase is insufficient, and the steel sheet as a whole is insufficient in hardness. Corrosion resistance also deteriorates. More preferably, it is 1 to 2%.

In the present application, the amount of precipitates can be controlled to 0.2% or more and 2% or less by controlling the C content, the N content, and the thermal history during production.
Among these, the C content and the N content can be controlled at the melting stage. If the amount is too small, the amount of precipitates is less than the lower limit, and if the amount is too large, the precipitates tend to exceed the lower limit. And it is sufficient.
However, the amount of the precipitate is not determined only by the C content and the N content, but can be adjusted by the heat history up to the final product. Specifically, it can be adjusted by the temperature of slab heating, the completion temperature of hot rolling, the cooling method, and the annealing method of hot rolled sheets. This is because the precipitates are repeatedly melted, precipitated or grown due to the thermal history.
On the other hand, the most important process for determining the amount of precipitates in the final product is final annealing (cold rolled sheet annealing). In particular, the amount of precipitates can be controlled by the difference in temperature. When the temperature is high, the amount of precipitates decreases, and when the temperature is low, the amounts increase. Therefore, what is necessary is just to set it as the suitable cold-rolled sheet annealing conditions of this invention so that it may mention later.
However, if the amount of precipitates cannot be controlled within a certain range before the final annealing, the final annealing alone cannot be controlled within the proper range.

  As the extraction residue method, here, a method is used in which a certain amount of steel is electrolyzed and dissolved in an electrolytic solution, which is filtered through a filter, and the residue remaining without filtration is evaluated as a precipitate. The amount of precipitates can be determined by comparing the mass of the electrolyzed steel and the residue. In the filter used for the extraction residue method, a precipitate having a size of 0.2 μm or less cannot usually be captured, and thus is not considered here.

<Steel plate thickness>
In addition, since the bicycle disc brake rotor uses a thin material as it is, a cold-rolled steel plate and a steel strip having a thickness of 0.5 to 2.5 mm are suitable as the material. If it is a hot-rolled steel sheet, the thickness accuracy is poor, and the brake performance may not be stable.

<Manufacturing method>
The martensitic stainless steel sheet of the present invention is a cold-rolled steel sheet, and its manufacturing process is a process including melting, casting, hot-rolling, hot-rolled sheet annealing, pickling, cold-rolling, cold-rolled sheet annealing, and pickling. is there. There are no particular restrictions on the production equipment, and known production equipment can be used. Cold-rolled steel sheets are usually manufactured in the form of a so-called steel strip that is very long in the rolling direction, and are wound and stored and moved in a coiled form.

  The conditions for hot rolling are not particularly specified, but the slab heating temperature is preferably 1100 ° C to 1250 ° C. The hot rolling finishing temperature is preferably 800 ° C. or higher. Furthermore, after hot rolling, it is cooled by air-water cooling or the like and wound up in a coil shape.

  An annealing method is not particularly defined, but a method called box annealing is preferable. The annealing temperature is preferably 800 to 900 ° C. If it is less than 800 ° C., it is not sufficiently softened and is difficult to cold-roll. If the temperature exceeds 900 ° C., the γ grains become coarse and the toughness decreases, which is not preferable. Moreover, although it is the cooling rate after annealing, the cooling rate from 800 ° C. to 450 ° C. is preferably 10 ° C./sec or less. When the cooling rate is faster than 10 ° C./sec, the M phase is likely to be produced and cold rolling is difficult, which is not preferable.

  There is no particular limitation for pickling, and the scale is removed with sulfuric acid or hydrofluoric acid. In order to remove the scale of the steel plate or introduce cracks, it may be subjected to shot blasting, coil bender or the like before pickling.

  In cold rolling, a hot-rolled steel sheet that has been annealed and pickled is cold-rolled to a thickness of 0.5 to 2.5 mm. The cold rolling method is not specified. If it is less than 0.5 mm, it is easy to deform, and if it exceeds 2.5 mm, it is too heavy and is not suitable as a disc brake rotor for bicycles.

Cold-rolled sheet annealing is an important point in the present invention.
The annealing temperature for cold-rolled sheet annealing is desirably 700 to 800 ° C. When the temperature is lower than 700 ° C., recrystallization is insufficient, which is not preferable. If the temperature exceeds 800 ° C., a γ phase is generated, and therefore, after cooling, it becomes an M phase and cracking may occur, which is not preferable. Moreover, in this temperature range, the amount of precipitates can be 0.2% to 2%. More preferably, it is 750-780 degreeC from coexistence of recrystallization and the amount of precipitates.

  The pickling after annealing can be pickled using a known method to obtain a cold-rolled steel sheet.

  Since the martensitic stainless cold-rolled steel sheet of the present invention has excellent hardenability, it can be suitably used after being quenched, particularly as a disc brake rotor material for bicycles.

  Hereinafter, the effects of the present invention will be described with reference to examples, but the present invention is not limited to the conditions used in the following examples.

<Example 1>
In this example, the slab obtained by melting and casting the steels of the components of Table 1-1 and Table 1-2 was heated to 1150 to 1250 ° C., and the finishing temperature was set within the range of 850 to 950 ° C. Hot rolled to a thickness of about 5 mm to obtain a hot rolled steel sheet. The hot-rolled steel sheet was cooled to 400 to 450 ° C. by air-water cooling. Then, it annealed at 1000-1100 degreeC, and cooled to normal temperature. At this time, the average cooling rate in the range of 800 to 450 ° C. was set to 10 ° C./s or more. Subsequently, the hot-rolled annealed plate was pickled and cold-rolled to obtain a cold-rolled plate having a thickness of 0.5 to 2.5 mm. Furthermore, after annealing at 700 to 800 ° C. for 1 minute, pickling was performed to obtain a cold-rolled steel sheet. Various tests were carried out using this as the test steel.
In addition, in Table 1-1 and Table 1-2, in addition to the components, the evaluation of N ≧ C (the example satisfying N ≧ C is ◯, the example not satisfying is ×), the results of Expressions 1 and 2, the plate thickness is also It is described. Moreover, in the following table | surfaces, what is underlined to each item shows that it is outside the proper range of this invention.

(Sediment investigation)
The amount of precipitates in the test steel was measured by the extraction residue method. That is, a certain amount of steel was electrolyzed and dissolved in an electrolytic solution, which was filtered with a filter having a maximum diameter of 0.2 μm, and the residue remaining without filtration was evaluated as a precipitate.

(Hardenability test)
Using an electric furnace, the rate of temperature rise was 10 ° C./s or less, held at 900 ° C., 1000 ° C., and 1050 ° C. for 10 minutes, oil cooled, and then the hardness (HRC) measurement was performed.
As the evaluation of the hardenability, first, any one of 900 ° C., 1000 ° C., and 1050 ° C. whose hardness deviated from 32-38 HRC was rejected.
Moreover, what showed 32-38 HRC at 900 degreeC was set as the low-temperature hardenability pass.
Next, among those that passed the hardness and the low-temperature hardenability, those having the same difference in hardness between 1000 ° C. and 1050 ° C. (within 2 HRC) were set as the quenching stability pass (◯), and further 900 ° C. A sample having a hardness difference of 1050 ° C. within 2 HRC was regarded as excellent quenching stability (（).

(Corrosion resistance test)
After holding at 1000 ° C. for 10 minutes, the oil-cooled material # 600 polished material was subjected to a salt water spray test (SST) in accordance with JIS Z, and the material that did not ignite in 4 h was accepted.
These results are shown in Table 2.

  As is apparent from Table 2, the inventive examples (A1 to A27) exhibited excellent low-temperature quenchability and quenching stability, and had no problem with corrosion resistance. Therefore, it turned out that it becomes an excellent bicycle disc brake rotor material.

  On the other hand, the comparative examples (B1 to B21) are steels that are not satisfactory as low-temperature hardenability, quenching stability, and corrosion resistance as shown below, and are not satisfactory as steel for brake disks. It was shown that the amount is out of the proper range and the steel is expensive.

Specifically, the C content of B1 is outside the upper limit of the appropriate range, N ≧ C and Formula 1 are not satisfied, the amount of precipitates exceeds the upper limit, and the quenching hardness is too high.
In B2, the C content was outside the lower limit of the appropriate range, and the quenching hardness was too low.
In B3, the Si content was the upper limit of the appropriate range, and Equation 2 was out of the lower limit, and the quenching hardness was too low.

In B4, the Si content was outside the lower limit of the appropriate range, and the corrosion resistance was rejected due to insufficient deoxidation.
In B5, the Mn content was outside the lower limit of the appropriate range, and the corrosion resistance was rejected.
In B6, the Mn content was outside the upper limit of the appropriate range, the quenching hardness was too low, and the corrosion resistance was also rejected.

In B7 and B8, the P and S contents were each outside the upper limit of the appropriate range, and the corrosion resistance was rejected.
In B9, the Cr content was outside the lower limit of the appropriate range, and the corrosion resistance was rejected.
In B10, the Cr content deviates from the upper limit of the appropriate range, and the lower limit of Formula 2 is also deviated, so that the quenching hardness is too low and the cost becomes high.

In B11, the Ni content deviated from the upper limit of the appropriate range, resulting in high cost.
In B12, the Cu content was outside the upper limit of the appropriate range, and squeal occurred.
In B13, the V content deviated from the upper limit of the appropriate range, the lower limit of Formula 2 was also deviated, and the low-temperature quenching hardness was unacceptable.
In B14, the N content was outside the lower limit of the appropriate range, N ≧ C was not satisfied, and the low-temperature quenching hardness and corrosion resistance were unacceptable.

In B15, the N content and the amount of precipitates were outside the upper limits of the appropriate ranges, and the quenching hardness was too high.
In B16, the Al content was outside the upper limit of the appropriate range, and the corrosion resistance was rejected.
For B17, Equation 2 was outside the upper limit of the appropriate range, and the quenching hardness was too low.
For B18, Formula 2 was outside the lower limit of the appropriate range, and the low-temperature hardenability was rejected.

B19 did not satisfy N ≧ C, and the low-temperature hardenability failed.
For B20, Equation 1 deviated from the upper limit of the appropriate range, and the quenching hardness was too low.
In B21, the C and N contents deviated from the lower limit of the appropriate range, and the lower limit of Formula 1 was also deviated. The quenching hardness was too low, and the corrosion resistance was also rejected.

<Example 2>
Of the cold-rolled steel sheets produced in <Example 1>, the same composition and plate thickness as A1 steel and A27 steel, whereas in <Example 1> the annealing temperature was set to 700 to 800 ° C., In <Example 2>, the annealing temperature was changed to 670-830 degreeC, and cold-rolled sheet annealing was performed, and other conditions obtained test steel on the same conditions as <Example 1>. Thereafter, the same evaluation as in <Example 1> was performed. The results are shown in Table 3.

  When the cold-rolled sheet annealing temperature is in the range of 700 to 800 ° C., the steel of the present invention showed excellent hardenability and had no problem with corrosion resistance (A1-2, A1-3, A1-4, A27-2, A27). -3, A27-4). However, when the annealing temperature of the cold-rolled sheet is lower than 700 ° C., recrystallization is insufficient, precipitates are not sufficiently dissolved, and corrosion resistance is not suitable (A1-1, A27-1). On the other hand, if the annealing temperature is higher than 800 ° C., the martensite (M) phase remains after the cold rolling annealing, and the precipitates are reduced and the hardness is lowered, which is not preferable (A1-5, A27-5). ).

  As is apparent from the above description, the martensitic stainless steel plate of the present invention has excellent hardenability and is therefore optimal for a bicycle disc brake rotor. By using this steel plate, an excellent bicycle disc brake is obtained. A rotor can be supplied and social contribution can be increased. In other words, the present invention has sufficient industrial applicability.

(1) In mass%,
C: 0.020 to 0.060%,
N: 0.020 to 0.070%,
Si: 0.1 to 1.0%,
Mn: 1.0 to 1.5%
P: 0.040% or less,
S: 0.015% or less,
Ni: 0.3% or less Cr: 10.5 to 13.5%,
Cu: 0.1% or less,
V: 0.08 % or less,
Al: 0.001 to 0.010%
Containing
And C and N satisfy Formula 1;
And γp which is a phase balance index at the time of hot rolling represented by Formula 2 is 90 to 120,
The balance consists of Fe and inevitable impurities,
The amount of precipitates in the steel is 0.2% or more and 2% or less,
A martensitic stainless cold-rolled steel sheet for bicycle disc brake rotors having a plate thickness of 0.5 mm or more and 2.5 mm or less and excellent in hardenability.
0.03% ≦ C + 0.5 × N ≦ 0.09% Formula 1
However, N ≧ C
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-52Al-12Mo-47Nb-7Sn-49Ti-48Zr-49V + 189 Equation 2
In addition, the element name in Formula 1 and Formula 2 means content (mass%) of each element .
(2) In mass%,
Mo: 0.01 to 0.5%,
Sn: 0.003-0.1%,
Nb: 0.001 to 0.3%,
Ti: 0.05% or less,
Zr: 0.05% or less,
B: 0.0002 to 0.0050%
The martensitic stainless steel cold-rolled steel sheet for a bicycle disc brake rotor having excellent hardenability as described in (1), wherein the balance is composed of Fe and one or more impurities, and the balance is Fe and inevitable impurities.
(3) The martensitic stainless steel cold-rolled steel sheet for bicycle disc brake rotors having excellent hardenability according to (1) or (2), wherein the steel sheet is a steel strip.
(4) The manufacturing process includes melting, casting, hot rolling, hot rolling sheet annealing, pickling, cold rolling, cold rolling sheet annealing, pickling, and the annealing temperature of the cold rolling sheet annealing is 700 to 800 ° C. The method for producing a martensitic stainless cold-rolled steel sheet for a bicycle disc brake rotor according to any one of (1) to (3).

In addition to the limitation of these elements, the present invention is a martensitic stainless steel, and in order to generate a martensite phase (hereinafter referred to as M phase), it is necessary to generate an austenite phase (hereinafter referred to as γ phase) at a high temperature. In addition, since the amount is determined by the additive component, it is necessary to adjust each element to achieve a phase balance. The phase balance index is expressed by Equation 2, and this γp may be 90-120. If it is less than 90, the γ phase generated at a high temperature decreases, the M phase after quenching decreases, and the required hardness cannot be obtained. On the other hand, when γp exceeds 120, even if the γ phase is quenched, the M phase transformation does not occur, the stable γ phase increases, and this also decreases the M phase and the required hardness cannot be obtained. The most preferred γp is 90-110.
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-52Al-12Mo-47Nb-7Sn-49Ti-48Zr-49V + 189 Equation 2
In addition, the element name in Formula 2 means content (mass%) of each element .
Formula 2 is also an index indicating the maximum value of the amount of austenite generated during heating at 1100 ° C., “Metal Treatment” 1964, p. This is an improvement of the Castro equation introduced in the literatures 230 to 245, and is a well-known equation as an empirical equation for estimating the maximum phase fraction of the γ phase.

Claims (4)

% By mass
C: 0.020 to 0.060%,
N: 0.020 to 0.070%,
Si: 0.1 to 1.0%,
Mn: 1.0 to 1.5%
P: 0.040% or less,
S: 0.015% or less,
Ni: 0.3% or less Cr: 10.5 to 13.5%,
Cu: 0.1% or less,
V: 0.3% or less,
Al: 0.001 to 0.010%
Containing
And C and N satisfy Formula 1;
And γp which is a phase balance index at the time of hot rolling represented by Formula 2 is 90 to 120,
The balance consists of Fe and inevitable impurities,
The amount of precipitates in the steel is 0.2% or more and 2% or less,
A martensitic stainless cold-rolled steel sheet for bicycle disc brake rotors having a plate thickness of 0.5 mm or more and 2.5 mm or less and excellent in hardenability.
0.03% ≦ C + 0.5 × N ≦ 0.09% Formula 1
However, N ≧ C
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-52Al-12Mo-47Nb-7Sn-49Ti-48Zr-49V + 189 Equation 2
In addition, the element name in Formula 1 and Formula 2 means content (mass%) of each element. Zero if it contains only inevitable impurities. % By mass
Mo: 0.01 to 0.5%,
Sn: 0.003-0.1%,
Nb: 0.001 to 0.3%,
Ti: 0.05% or less,
Zr: 0.05% or less,
B: 0.0002 to 0.0050%
The martensitic stainless steel cold-rolled steel sheet for a bicycle disc brake rotor having excellent hardenability according to claim 1, wherein the balance is made of Fe and inevitable impurities.   The martensitic stainless cold-rolled steel sheet for a bicycle disc brake rotor having excellent hardenability according to claim 1 or 2, wherein the steel sheet is a steel strip.   The manufacturing process includes melting, casting, hot rolling, hot rolling sheet annealing, pickling, cold rolling, cold rolling sheet annealing, pickling, and the annealing temperature of the cold rolling sheet annealing is 700 to 800 ° C The manufacturing method of the martensitic stainless cold-rolled steel plate for bicycle disc brake rotors which was excellent in the hardenability as described in any one of Claims 1-3.