JPWO2012157680A1 - Martensitic stainless steel sheet for bicycle disc brake rotor and method for manufacturing the same - Google Patents

Abstract

The present invention provides a martensitic stainless steel plate for a disc brake rotor of a bicycle that is excellent in braking characteristics and anti-squealing performance as a bicycle disc brake rotor and is used while being quenched. The gist of the martensitic stainless steel sheet according to the present invention is C: 0.070 to 0.120%, N: 0.015 to 0.060%, and satisfies C + N: 0.09 to 0.15%. Low carbon / low nitrogen stainless steel, Cu: 0.1% or less and Mn: 1.0-1.4%, and γp, which is an index representing the phase balance during hot rolling, is 80 -120 is satisfied, the balance is Fe and inevitable impurities, and the hardness after quenching is 38-44 in HRC.

Description

  The present invention relates to a martensitic stainless steel plate and a method for producing the same as a disc brake rotor of a bicycle, which are excellent in braking characteristics of a brake and excellent in press formability when processed into a rotor shape.

  Bicycle disc brake rotors are required to have characteristics such as wear resistance, weather resistance, and light weight. Therefore, martensitic stainless steel or a composite material of martensitic stainless steel and aluminum is used. For martensitic stainless steel, SUS420J1 and SUS420J2 are generally used. The disc brake rotor is hot-rolled stainless steel, cold-rolled after annealing, adjusted in shape and hardness, then processed into a predetermined shape by press molding, and hardened and tempered by heat treatment. Then, the disc brake rotor is manufactured through processes such as polishing and painting.

  Similar martensitic stainless steel is used for motorcycle disc brakes. Compared to a bicycle, it is a high-speed and heavy vehicle body, and therefore requires a high braking force. Therefore, it is manufactured by annealing a hot-rolled steel sheet of martensitic stainless steel and quenching it after press forming. The wear resistance generally increases as the hardness of the steel increases, but if the hardness is too high, a so-called brake “brake noise” occurs between the brake rotor and the pad. For this reason, the hardness of the disc brake rotor of a motorcycle cannot be made very high, and 34 ± 3 HRC (Rockwell hardness C scale) is required.

  In the manufacture of motorcycle disc brake rotors, low carbon (C) and low nitrogen (N) stainless steel is being applied to eliminate the tempering step after quenching. A low carbon martensitic stainless steel with a weight ratio of C + N: 0.04 to 0.10% and Mn added to 1.0 to 2.5% is disclosed as a material for motorcycle disc brakes.

Moreover, in patent document 2, in order to improve the descaling property of a hot-rolled sheet, Mn is set to 1.0% or less, and the calculated value H shown by the following formula | equation is the range of 32-40. Materials for use are disclosed.
H = 223C-2.6Si + 2.8Mn + 9.2Ni-4.6Cr + 3.6Cu + 188N + 74.0 (Each element symbol indicates a numerical value by weight of the element.)
This calculated value H is said to correspond well with the actual measured value of the maximum quenching hardness.

  However, while the steels described in these publications have characteristics suitable for motorcycle disc brake applications, they are unsuitable as materials for bicycle disc brake rotors, and their application has not progressed. This is due to the following problems.

  When martensitic stainless steel developed for motorcycle disc brakes is used for a bicycle disc brake rotor, the wear is large, and surface damage due to wear affects the running performance. That is, when the quenching hardness is in the range of 32 to 40, the hardness is low, and a sufficient braking force cannot be obtained as a disc brake rotor of a bicycle such as a mountain bike.

  In order to increase the braking force, it is effective to increase the quenching hardness by increasing the C amount as in SUS420J1 and SUS420J2. However, in low-carbon martensitic stainless steel developed for motorcycle disc brakes, increasing the carbon (C) amount and increasing the hardness improves the braking force, but generates squeal during braking. There was a problem of damaging brake performance.

JP-A-57-198249 JP 60-106951 A

Conventionally, SUS420J1 and SUS420J2 that are generally used for bicycle disc brake rotors have a hardness of 50 HRC or more when quenched, and therefore need to be tempered. Therefore, a process is long and the improvement of the productivity is a subject.
On the other hand, martensitic stainless steel for motorcycles has insufficient quenching hardness as described above, and cannot be used for a disc brake rotor for bicycles. Further, there is a problem that squealing is likely to occur when carbon (C) is increased in order to increase the quenching hardness.
Therefore, there is a problem of obtaining martensitic stainless steel having a hardness suitable for a bicycle disc brake rotor without being tempered, that is, as it is quenched.
The present invention advantageously solves the above-mentioned problems of the prior art, suppresses the occurrence of squeal during braking, has excellent brake braking characteristics, and is used while being quenched, martensitic stainless steel for a disc brake rotor of a bicycle It aims at providing a steel plate and its manufacturing method.

  The present inventors have intensively studied to solve the above problems, and have obtained the following knowledge to complete the present invention.

Martensitic stainless steel for bicycle brake disc rotors needs to have a hardness of 38 HRC or higher in order to obtain the necessary braking force. This hardness is characterized by being higher than the hardness of 32 HRC or more required for a motorcycle disc brake rotor.
On the other hand, when the quenching hardness is increased to increase the braking force, an abnormal noise accompanied by vibration called “Brake noise” becomes a problem in a disc brake rotor of a bicycle. Squeaking can be suppressed by quenching and tempering stainless steel such as SUS420J1 and SUS420J2 to a hardness of 43 HRC or less. However, for the technology that omits tempering, if stainless steel is used for motorcycle disc brake rotors, squealing occurs even at 38 HRC, so it is possible to find a hardness range that achieves both braking force and squeal prevention. There wasn't.

This is similar to the problem of sliding noise (abnormal noise), called squeal, which is a problem with motorcycle disc brake rotors. In order to prevent squealing in motorcycle disc brake rotors, the hardness is generally set to 38 HRC or less, and the hardness is controlled to 32 HRC or more necessary for obtaining braking force, and the hardness is controlled to 38 HRC or less which starts to squeal. Yes.
In a bicycle, in order to obtain a required braking force, the hardness of the disc brake rotor of 38 HRC or more is required. Considering the variation in hardness after quenching, the hardness range of 38 to 43 HRC is considered necessary.
As a result of examining methods for suppressing squealing in this hardness range, the influence of the base material component through the slight oxide film formed on the disc brake rotor surface during sliding, squealing is suppressed. In addition, the present inventors have found that it is necessary to limit the Cu content of the base material to 0.1% or less and to make the Mn content in the range of 1.0 to 1.4%. Furthermore, in order to improve the corrosion resistance of the disc brake rotor, it is desirable that the structure after quenching is a structure in which carbides are slightly dispersed in the martensite matrix, and the precipitation amount is 0.04% in terms of the weight percentage of Fe. It is necessary to:

  The gist of the present invention completed based on the above knowledge resides in the following martensitic stainless steel plate for a disc brake rotor of a bicycle and a manufacturing method thereof.

(1) In mass%,
C: 0.070 to 0.120%,
N: 0.015-0.060%,
Si: 0.10 to 0.50%,
Mn: 1.0 to 1.4%
P: 0.035% or less,
S: 0.015% or less Ni: 0.3% or less,
Cr: 11.5 to 13.5%,
Cu: 0.1% or less V: 0.3% or less Al: 0.001% to 0.010%
And C + N: 0.09 to 0.15% is satisfied, and γp, which is an index representing the phase balance during hot rolling represented by the following formula (1), satisfies 80 to 120, and the balance is A martensitic stainless steel plate for a disc brake rotor of a bicycle comprising Fe and inevitable impurities and having a hardness after quenching of 38 to 44 in HRC.
γp = 420 [% C] +470 [% N] +23 [% Ni] +9 [% Cu] +7 [% Mn] −11.5 [% Cr] −11.5 [% Si] −52 [% Al] − 12 [% Mo] -47 [% Nb] -7 [% Sn] -49 [% Ti] -48 [% Zr] -49 [% V] +189 (1)
[% C] indicates the content (% by mass) of carbon (C).
Similarly, [% N] [% Ni] [% Cu] [% Mn] [% Cr] [% Si] [% Al] [% Mo] [% Nb] [% Sn] [% Ti] [% Zr] [% V] is N, Cu, Mn, Cr, Si, Al, Mo, Nb, Sn, Ti, Zr, V, respectively.
Content (mass%).
0 when no element is contained.

(2) Furthermore, in mass%,
Mo: 0.05-0.5%
Sn: 0.003-0.5%,
Nb: 0.03-0.15%,
Ti: 0.05% or less,
Zr: 0.05% or less,
B: 0.0005 to 0.0030%,
The martensitic stainless steel plate for disc brake rotors of bicycles according to (1), characterized in that it contains one or more of the following.

  (3) When a martensitic stainless steel plate having the steel composition described in (1) or (2) above is quenched to form a disc brake rotor for a bicycle, the amount of undissolved carbide precipitated is the amount of Fe. A martensitic stainless steel plate for a disc brake rotor of a bicycle, characterized by being 0.04% or less.

  (4) After annealing the stainless steel hot-rolled sheet of the component described in (1) or (2) above, cold rolling with a total rolling reduction of 20 to 70% is performed once, or intermediate annealing is performed 2 While performing cold rolling, the cold rolling rate of finish cold rolling should be 20% or more, and the hardness of the cold rolled product or the product after annealing after cold rolling and pickling should be 220HV to 260HV. A method for producing a martensitic stainless steel sheet for a disc brake rotor of a bicycle.

  As described above, according to the present invention, a martensitic stainless steel plate for a disc brake rotor for a bicycle that is excellent in braking characteristics as a disc disc rotor for a bicycle, for example, excellent in braking force and squealing performance, and used for quenching. However, the industrial effect is very large.

It is a figure which shows the influence of the component C + N which acts on the brake braking performance and steel plate hardness of the bicycle disc brake rotor manufactured by quenching the martensitic stainless cold rolled product in this embodiment. FIG. 1A is a diagram showing the relationship between C + N and Rockwell hardness, and FIG. 1B is a diagram showing the relationship between C + N and bicycle braking performance and squeal. It is a graph which shows the influence of the reduction rate (rolling rate) of finish cold rolling which affects the Vickers hardness of the martensitic stainless steel cold-rolled product in this embodiment, and the droop at the time of press molding. FIG. 2 (a) is a diagram showing the relationship between the reduction ratio of finish cold rolling and the steel sheet hardness (Vickers hardness), and FIG. 2 (b) is the reduction ratio of finish cold rolling and the amount of punched holes. It is a figure which shows the relationship. The relationship between the precipitation amount of undissolved carbide (precipitation Fe amount) and the rate of rusting in a salt spray test in a bicycle disc brake rotor manufactured from a martensitic stainless steel cold-rolled product in this embodiment is shown. FIG.

  Hereinafter, the present invention will be described in detail.

  First, the reason for limiting the steel composition of the martensitic stainless steel plate for the disc brake rotor of the bicycle of the present invention will be described. In addition, the description of% about a composition means the mass% unless there is particular notice.

(C: 0.070 to 0.120%)
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 bicycle disc brake rotor, 0.070% or more is required. However, since the squealing is liable to occur due to an increase in the quenching hardness with too much C content, the content is set to 0.120% or less. In order to stably secure the target hardness, 0.070 to 0.100%, preferably 0.080% to 0.100%, more preferably 0.080 to 0.090% Is preferred.

(N: 0.015-0.060%)
N, like C, is a component that increases the hardness of martensite during quenching and gives a sufficient amount of martensite as a strong austenite former. Therefore, 0.015% or more is necessary. However, if the N content is too large, the amount of nitride increases and the solution is coarsened, so that the solution temperature rises and the solution time becomes longer, so that the quenching stability is impaired. Further, the upper limit of the N content is set to 0.060% or less in order to form bubble defects during casting and impair the corrosion resistance. In order to stably obtain the target hardness, it is desirable that the lower limit is 0.018% and the upper limit is 0.045%. More desirably, the lower limit is 0.019% and the upper limit is 0.040%.

(Si: 0.10 to 0.50%)
Si is an element that reduces the amount of martensite during quenching and lowers the toughness, so the upper limit was made 0.50%. However, it is an element preferable for deoxygenation during steelmaking and improvement of hot water flow during casting, and improves operability and surface quality. Therefore, the lower limit was made 0.10%. However, considering the reduction of raw material costs and the improvement of productivity by shortening the refining time, it is desirable that the lower limit is 0.20% and the upper limit is 0.40%. More desirably, the lower limit is 0.25% and the upper limit is 0.035%.

(Mn: 1.0-1.4%)
Mn, like Ni and Cu, is an austenite former 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 exhibits the effect of suppressing the formation of bubble defects. In addition, similarly to Si, it has an effect as a deoxidizing element during steelmaking. In order to obtain such effects, the Mn content is at least 1.0%. However, if Mn is contained in a large amount, oxidation during quenching heats up 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 becomes a problem to reduce the squealing hardness during braking (the minimum hardness at which squeal occurs). For these reasons, the Mn content is set to 1.4% or less. Considering reduction of raw material costs and high temperature ductility during hot rolling depending on austenite balance, it is desirable that the lower limit is 1.1% and the upper limit is 1.3%. More desirably, the lower limit is 1.15% and the upper limit is 1.25%.

(P: 0.035% or less)
P is an element having a large solid solution strengthening ability and a ferrite former. Moreover, since it is an element harmful to corrosion resistance and toughness, it is preferable that it be as small as possible.

  P is contained as an impurity in ferrochrome, which is a raw material of stainless steel. However, it is very difficult to remove P from molten stainless steel, so 0.010% or more is preferable. The P content is almost determined by the purity and amount of the ferrochrome raw material to be used. Since P is a harmful element, the purity of P of the ferrochrome raw material is preferably low. However, since low P ferrochrome is expensive, it is limited to 0.035% or less, which is a range in which the material and corrosion resistance are not greatly deteriorated. . Note that the content is preferably limited to 0.030% or less.

(S: 0.015% or less)
Since S forms a granulated inclusion and deteriorates the general corrosion resistance (pitting corrosion) of the steel material, the upper limit of the content is preferably small, and is limited to 0.015% or less. Further, the smaller the S content, the better the corrosion resistance. However, reducing the sulfur content increases the desulfurization load, increases the production cost, and CaS formed in the slag with strengthening of the desulfurization mixes in the steel and impairs the corrosion resistance. % Is preferable. The upper limit is preferably 0.010%. More preferably, the upper limit is 0.008%.

(Ni: 0.3% or less)
Ni is an austenite former like Mn and Cu and increases the amount of martensite during quenching. However, since Ni is expensive, in the present invention, it is limited to the extent that it is 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 excessive reduction requires the use of a high-purity raw material, leading to an increase in raw material cost, so the lower limit is preferably made 0.01% or more. In consideration of improvement in toughness after quenching, 0.05 to 0.15% is desirable.

(Cr: 11.5 to 13.5%)
In order to ensure the corrosion resistance required for the brake disc, Cr needs to be 11.5% or more. However, since it is a ferrite former, it is necessary to add an austenite former (Ni, Cu, Mn) according to the Cr amount to ensure the austenite phase fraction during quenching heating. However, there is a limit to the adjustment of the phase balance by the austenite former for various reasons as described above or below. Therefore, the upper limit of the Cr content is set to 13.5%. In consideration of manufacturability and high temperature ductility, it is desirable that the lower limit is 11.8% and the upper limit is 13.2%. More preferably, the lower limit is 12.0% and the upper limit is 13.0%.

(Cu: 0.1% or less)
Cu, like Mn and Ni, is an austenite former that increases the amount of martensite during quenching and increases hardness. However, since it becomes a problem to reduce the squealing hardness of the disc brake rotor by changing the oxide film formed by heat generation during sliding, its content is limited to 0.1% or less. However, since Cu is mixed into other alloy raw materials as impurities, extreme reduction is not preferable because it requires the use of high-purity raw materials, so the lower limit is preferably made 0.01% or more. Taking into account the efficiency of component management during production, it is preferably 0.02 to 0.05%.

(V: 0.3 or less)
V is an element mixed as an inevitable impurity from the alloy raw material. Excessive reduction requires the use of high-purity raw materials and increases raw material costs, so the lower limit is desirably 0.01%. On the other hand, the excessive content lowers the hardness of martensite due to the formation of carbonitrides, so the upper limit is 0.3%. In order to suppress the squealing of the brake disc rotor that accompanies the formation of a large carbonitride, it is more desirable to make it 0.1% or less.

(Al: 0.001 to 0.010%)
Al is a strong deoxidizing element and adjusts the slag basicity during refining to increase the desulfurization ability of slag. Since the effect is stably obtained from 0.001%, the lower limit is made 0.001%. On the other hand, excessive addition increases the basicity of the slag and causes the water-soluble inclusion CaS to crystallize, thereby greatly impairing the corrosion resistance. Therefore, the upper limit is made 0.010% or less. In order to stably obtain the deoxygenation ability at the time of refining, it is more desirable to make it 0.003% to 0.008%.

(C + N: 0.09 to 0.15%)
C and N are elements that govern the hardness of martensite, and in order to obtain HRC 38 to 44, which is an indispensable hardness for obtaining a braking force required for the disc brake rotor of the bicycle, C + N is set to 0. 09% or more and 0.15% or less are necessary. Preferably, the lower limit of C + N is 0.095%, the upper limit is 0.13%, and more preferably the lower limit is 0.10% to 0.12%. In addition, when considering the decrease in solid solution C and N due to carbonitride forming elements that are inevitably mixed as inevitable impurities, and the increase in martensite strength due to solid solution and precipitation strengthening elements, 0.11 to 0.14%, Preferably it is 0.11 to 0.13%.

(Γp = 80 to 120 which is an index representing the phase balance during hot rolling heating)
The following formula (1) of γp is an index representing the quenching heating temperature and the phase balance during hot rolling heating for producing the material. As γp decreases, the ferrite fraction increases, the amount of martensite during quenching decreases, the quenching hardness decreases, the wear rate of the disc brake rotor increases, and the brake braking performance decreases. Furthermore, the ferrite fraction during hot rolling increases, and cracks occur at the interface between δ ferrite and austenite due to differences in strength and deformability between δ ferrite and austenite, which causes ear cracks. Therefore, in order to improve quenching hardness and improve hot workability, γp is set to 80 or more, preferably 85 or more. More preferably 90 or more.

On the other hand, if γp is too high, S is segregated at the austenite grain boundaries during the hot rolling, and ear cracks are likely to occur due to the grain boundary embrittlement. Therefore, a minimum amount of δ ferrite is required to dissolve S and make it harmless. Therefore, the upper limit of γp is 120 or less, preferably 110 or less. More preferably, it is good to be 105 or less.
γp = 420 [% C] +470 [% N] +23 [% Ni] +9 [% Cu] +7 [% Mn]
-11.5 [% Cr] -11.5 [% Si] -52 [% Al] -12 [% Mo] -47 [% Nb] -7 [% Sn] -49 [% Ti] -48 [% Zr] -49 [% V] +189 (1)
Here, the component described in the above formula means mass% of the component contained in the steel.
Note that γp equation (1) is 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.

  In the present invention, in addition to the above elements, Mo: 0.05 to 0.5%, Sn: 0.003 to 0.5%, Nb: 0.03 to 0.15%, Ti: 0.05 % Or less, Zr: 0.05% or less, and B: 0.0005 to 0.0030%, or the upper limit is preferably controlled using a high-purity raw material.

(Mo: 0.05-0.5%)
Mo may be added as necessary to enhance corrosion resistance, and the lower limit is preferably made 0.05% in order to exert its effect. On the other hand, Mo is a ferrite former like Cr, and excessive addition reduces the austenite fraction at the time of quenching heating and lowers the quenching hardness, so is 0.5% or less. However, it is an expensive element, and 0.1% to 0.3% is desirable in order to exhibit an effect of improving corrosion resistance commensurate with the addition and to suppress an increase in raw material cost.

(Sn: 0.003-0.5%)
Sn may be added as necessary to enhance the corrosion resistance, and in order to exert its effect, the lower limit is made 0.003%, preferably 0.03%. On the other hand, Sn is a ferrite former like Cr and Mo, and excessive addition reduces the austenite fraction during quenching heating and lowers the quenching hardness, so is 0.5% or less. However, it is an expensive element, and 0.01% to 0.3% is desirable in order to exhibit an effect of improving corrosion resistance commensurate with the addition and to suppress an increase in raw material cost.

(Nb: 0.03-0.15%)
Nb may be added as necessary to increase the temper softening resistance, and in order to exert its effect, the lower limit is preferably 0.03%. On the other hand, excessive addition requires a longer time for hot-rolled sheet annealing and greatly impedes productivity, so the upper limit is made 0.15%. In consideration of a decrease in martensite hardness and a decrease in the amount of solute Nb due to the formation of carbonitride, 0.05 to 0.10% is more preferable.

(Ti: 0.05% or less)
In order to promote the squeal of the brake disc rotor by precipitating Ti as hard coarse nitride TiN, it is preferable to perform upper limit regulation as necessary. In order to suppress coarse TiN precipitation, the upper limit is preferably 0.05% or less. However, since it is contained as an impurity in other alloy raw materials, it is preferable to use a high-purity raw material to reduce it extremely, leading to an increase in raw material cost, so the lower limit is preferably made 0.0005%.

(Zr: 0.05% or less)
Zr is preferably precipitated as hard coarse nitride ZrN so as to promote the squealing of the brake disc rotor, and the upper limit is preferably set as necessary. In order to suppress coarse ZrN precipitation, the upper limit is preferably 0.05% or less. However, since it is contained as an impurity in other alloy raw materials, extreme reduction makes it necessary to use high-purity raw materials and leads to an increase in raw material costs. Therefore, the lower limit is preferably made 0.0005%.

(B: 0.0005% to 0.0030%)
B may be added as necessary in order to improve the hot ductility during hot rolling and to reduce the yield reduction due to the ear cracks of the hot-rolled sheet, and in order to exert its effect, the lower limit is 0. .0005% or more is desirable. However, excessive addition impairs toughness and corrosion resistance due to precipitation of Cr2B and (Cr, Fe) 23 (C, B) 6, so the upper limit is made 0.0030%. In view of workability and manufacturing cost, 0.0008 to 0.0015% is more preferable.

(The amount of precipitation of undissolved carbide is 0.04% or less as the amount of Fe)
In the present invention, in addition to the above elements, the amount of undissolved carbide in the martensite phase after quenching is preferably controlled to 0.04% or less as the amount of Fe precipitated as carbide. Thereby, the corrosion resistance of the disc brake rotor can be increased and the braking performance can be improved.

That is, the amount of solid solution C increases as the amount of undissolved carbide [(FeCr) ₂₃ C ₆ ] after quenching increases and the hardness of martensite increases. Further, it is preferable because it is possible to suppress a decrease in corrosion resistance due to sensitization accompanying carbide precipitation (sensitivity of stainless steel to intergranular corrosion due to precipitation of carbide at the grain boundary). In order to acquire the effect, 0.04% or less is desirable as the precipitation amount of Fe as a carbide. In order to measure the amount of Fe precipitated as carbide, a constant potential electrolytic etching method (SPEED method) using a non-aqueous solvent electrolyte was used. If the corrosion resistance is not taken into consideration, there is no problem even if it exceeds 0.04%, but the hardness becomes low and is close to the lower limit value of the target hardness, so 0.04% or less is preferable. In order for the precipitation amount of insoluble carbide [(FeCr) ₂₃ C ₆ ] to be 0.04% or less as the amount of Fe, the temperature range of 800 to 600 ° C. is preferably 0.3 ° C./s or more, preferably May be cooled at a cooling rate of 3 ° C./s or more, more preferably 10 ° C./s or more.

  Next, the manufacturing method of the martensitic stainless steel plate in this embodiment is demonstrated.

  The manufacturing method of the martensitic stainless steel sheet according to the present embodiment is the method of manufacturing the martensitic stainless steel having the above steel composition, and after hot rolling the cast steel piece (slab) after steelmaking. Then, hot-rolled sheet annealing is performed, and after pickling, cold rolling is performed. In the cold rolling step, intermediate annealing-pickling and finish annealing-pickling are performed as necessary.

In steelmaking in this embodiment, a smelting method is preferred in which the steel containing the essential components and components added as necessary is refined in a converter and subsequently subjected to secondary refining.
Next, the molten steel is made into a slab according to a known casting method (continuous casting). Then, this slab is heated to a predetermined temperature and hot-rolled to a predetermined plate thickness to obtain a hot-rolled steel sheet (hot-rolled sheet). In addition, the finish rolling finish temperature of hot rolling shall be the range of 800-950 degreeC.
Next, after finish rolling, the hot rolled steel sheet is wound into a coil. Cooling up to the winding is preferably performed by air cooling so that the winding temperature is in the range of 700 to 900 ° C. in order to shorten the hot-rolled sheet annealing time. Since a hot-rolled steel sheet is hard as it is hot-rolled and is difficult to cold-roll, it is annealed in, for example, a batch-type annealing furnace. The annealing temperature is set to 800 to 900 ° C., and after the coldest point exceeds 800 ° C., it is annealed for 1 to 10 hours, cooled in the annealing furnace for a certain time, and then transferred to the outside of the furnace. Cool to room temperature. The coldest point means a part where the temperature is most unlikely to rise in an object to be heated in a batch-type annealing furnace. In a hot-rolled coil, the part that is in contact with the furnace bottom at the central part in the longitudinal direction of the coil is shown. After that, the surface oxide scale is removed by mechanical descaling such as shot blasting and chemical descaling with acid, and then cold rolling is performed to obtain a cold rolled product. The cold-rolled product adjusts the cold-rolling rate so that the hardness is 220 to 260 HV, but it is also possible to perform final annealing on the cold-rolled plate and adjust the hardness according to the annealing temperature. The annealing temperature at this time is preferably in the range of 650 to 750 ° C. Depending on the thickness of the hot-rolled sheet, intermediate annealing and pickling are performed during cold rolling, but even in this case, the hardness can be adjusted by controlling the cold rolling rate of finish cold rolling. is there. Intermediate annealing is performed in consideration of the capability of the cold rolling mill, because the hardness increases due to work hardening when the total cold rolling reduction ratio increases, but depending on the capability of the cold rolling mill, intermediate annealing may be omitted. It is also possible to manufacture by one cold rolling. Intermediate annealing also has the effect of increasing the thickness accuracy. There is an appropriate hardness measurement method depending on the hardness level. In the present invention, Vickers hardness (HV) and Rockwell hardness (HRC) are properly used.

  Below, the reason for limitation of the cold rolling rate in this embodiment is demonstrated.

  In the present embodiment, the total cold rolling rate of cold rolling performed once or twice is set to 20 to 70%, and the cold rolling rate of finish cold rolling is 20% or more. And the hardness of the cold-rolled product or cold-rolled-annealed-pickled product is set to 220 HV to 260 HV. The cold rolling is performed once or twice by appropriately selecting the thickness of the hot rolled sheet and the thickness of the product. Moreover, in order to improve plate | board thickness precision, cold rolling may be performed twice. Furthermore, the cold rolling of 1 time or 2 times can be selected suitably according to the installation and production amount to be used.

  Further, the cold-rolled product means a product that is shipped as cold-rolled, and is generally called a hard material. The pickled product means a product finished by performing annealing and pickling after cold rolling (finish is 2D or 2B finish, see JIS G4305). The hardness of the product can be controlled either by controlling the hardness by work hardening during cold rolling or by controlling the hardness at the annealing temperature.

  By performing cold rolling, the plate thickness accuracy of the product is improved, and it is possible to increase the plate thickness dimensional accuracy when press-molding into the shape of the disc brake rotor. In order to increase the thickness accuracy of martensitic stainless steel to 50 μm or less, it is desirable to set the total cold rolling rate to 20% or more. The improvement of the plate thickness accuracy can increase the working efficiency in the polishing process after quenching. Excessively increasing the cold rolling rate decreases productivity, so the total cold rolling rate is set to 70% or less.

  Moreover, in order to improve the dimensional accuracy at the time of press molding, it is desirable to set the hardness of a cold-rolled sheet, or cold rolling, annealing, and pickling sheet to 220 to 260 HV. The dimensional accuracy at the time of press forming is evaluated by the amount of sheared surface at the time of press forming (punching). By setting the hardness to 220 HV or higher as compared with the amount of dripping when an annealed pickling material having a hardness of 130 to 200 HV is press-molded, it becomes possible to reduce the amount of the sacrificial amount to ½ or less. As a method for setting the hardness to 220 HV or higher, it is possible to set the cold rolling rate of finish cold rolling to 20% or higher, or by combining cold rolling and annealing at a cold rolling rate of 20% or higher. However, if the hardness is excessively high, the wear of the mold is accelerated, so 260 HV or less. Further, the finish cold rolling reduction ratio is preferably 60% or less. The annealing for controlling the hardness is preferably performed, for example, in the range of 650 to 780 ° C. and in the range of 10 to 120 seconds.

  Hereinafter, the investigation results for explaining the reasons for limiting the component (C + N) range, the cold rolling rate range, the product hardness range, and the amount of undissolved carbide after quenching will be shown.

  In FIG. 1, after changing the C + N amount of the martensitic stainless steel according to the present embodiment and casting into a plurality of steel ingots, the hot rolling temperature was set to 850 ° C. and hot rolling was performed to a plate thickness of 4 mm. . Then, after winding up at 780 degreeC, hot-rolled sheet annealing was performed at 850 degreeC for 4 hours, and it cooled slowly to normal temperature in the furnace. The hot-rolled steel sheet was shot blasted, washed with sulfuric acid, descaled, and then cold-rolled to obtain a cold-rolled product having a thickness of 1.8 mm. The product was press-molded into a disc brake rotor shape for bicycles, then subjected to quenching treatment and surface polishing to obtain a disc brake rotor. The hardness after quenching was measured with a Rockwell hardness meter. In addition, the braking performance of the disc brake was evaluated in an actual vehicle running test, and the braking performance and squeal characteristics were rated in three stages. Here, the evaluation of braking performance is based on the braking performance test specified in JIS D9301, where the braking distance at 25 km / h is the braking distance L0 when the rotor is new, the brake hydraulic pressure is 1.0 MPa, and the wheel rotational speed is 2 rps. A comparison was made by the braking distance LB after a load test equivalent to 5 km. Ratio of L0 and LB, L0 / LB is less than 0.7 x (failed), 0.7 or more and less than 0.9 ○ (failed), 0.9 or more ◎ (pass level is excellent Was). The evaluation of squeal is x (failure) when you can hear a squeal in a 45 dB environment at a brake hydraulic pressure of 1.0 MPa and a wheel speed of 2 rps. (Between and excellent ones), the interval between them was marked as ◯ (failed).

  As can be seen from FIG. 1, by setting C + N to 0.09% or more, the hardness after quenching is 38 HRC or more, and the braking force is increased. It can also be seen that when C + N exceeds 0.015%, the hardness becomes 44 HRC or more and squeal occurs. In the present invention, the hardness after quenching is aimed at 38 to 44 HRC.

  The steel composition of the martensitic stainless steel used to investigate the relationship shown in FIG. 1 is 12.3% Cr, 0.3% Si, 1.1% Mn, 0.04% to 0.14%. C, 0.02% N, 0.027% P, 0.008% S, 0.2% Ni, 0.02% Cu, 0.04% V, 0.008% Al.

  In FIG. 2, after martensitic stainless steel according to the present embodiment was cast into a steel ingot, the hot rolling temperature was set to 850 ° C. and hot rolled to a plate thickness of 5 mm. Then, after winding up at 780 degreeC, hot-rolled sheet annealing was performed at 850 degreeC for 4 hours, and it cooled slowly to normal temperature in the furnace. The hot rolled steel sheet was shot blasted, washed with sulfuric acid and descaled, and then the surface was ground to 1.8 to 5.0 mm. Subsequently, a cold rolled product having a thickness of 1.8 mm was obtained by cold rolling. The surface hardness of the product was measured with a Rockwell hardness meter. The product was pressed into a disc brake rotor shape for bicycles, and the amount of dripping in the press holes was measured. For the evaluation of the amount of drool, after performing a press test with a punch outer diameter of 18 mm, a die inner diameter of 19 mm, a clearance of 0.5 mm and a punching speed of 700 mm / min, the height of the person is measured over the circumference and the average is obtained. It was. An average height of 100 μm or more was evaluated as x (failed), 50 μm or more and less than 100 μm was evaluated as ◯ (failed), and less than 50 μm was evaluated as ◎ (acceptable level and excellent).

  As is apparent from FIG. 2, it can be seen that by setting the cold rolling to 20% or more, the hardness of the product becomes 220 HV or more, and the amount of anyone decreases. Hardness increases with an increase in the cold rolling rate, and becomes 270 HV at a cold rolling rate of 70%, which is undesirable because the load on the mold during press molding increases.

  The steel composition of the martensitic stainless steel used to investigate the relationship shown in FIG. 2 is 12.3% Cr, 0.3% Si, 1.1% Mn, 0.08% C, 0.02. % N, 0.026% P, 0.008% S, 0.2% Ni, 0.02% Cu, 0.04% V, 0.003% Al.

  In FIG. 3, after martensitic stainless steel according to the present embodiment was cast into a steel ingot, the hot rolling temperature was set to 850 ° C. and hot rolled to a plate thickness of 4 mm. Then, after winding up at 780 degreeC, hot-rolled sheet annealing was performed at 850 degreeC for 4 hours, and it cooled slowly to normal temperature in the furnace. The hot-rolled steel sheet was shot blasted, pickled with sulfuric acid, descaled, and then cold-rolled to obtain a cold-rolled product having a thickness of 1.8 mm. The product was press-molded into a disc brake rotor shape for bicycles, then subjected to quenching treatment at various heating temperatures, times and cooling rates, and surface polishing was performed to obtain a disc brake rotor. A 20 × 30 mm plate was cut out from the disc brake rotor, and the entire surface was polished with sandpaper No. 600, and then the precipitate was extracted by the SPEED method, and the extracted precipitate was chemically analyzed to obtain Fe in the precipitation. The amount of Cr was measured. The corrosion resistance of the disc brake was rated by the rust area ratio after a 24-hour salt spray test. The salt spray test was performed according to JIS Z2371. The area ratio of the rust was less than 10% (excellent at an acceptable level), 10% or more and less than 30% was evaluated as ◯ (failed), and 30% or more was evaluated as x (failed).

  As is clear from FIG. 3, when the amount of Fe precipitates is increased, the rusting rate in the salt spray test is increased and the corrosion resistance rank is decreased.

  The steel composition of the martensitic stainless steel used for investigating the relationship shown in FIG. 3 is 13.1% Cr, 0.3% Si, 1.4% Mn, 0.2Ni, 0.085% C. 0.015% N, 0.017% P, 0.003% S, 0.1% Ni, 0.2% Cu, 0.01% V, 0.01% Al.

  As described above, according to the martensitic stainless steel according to the present invention, since C + N is 0.09% to 0.15%, the quenching hardness can be 38 HRC to 44 HRC. As a result, it is possible to achieve the braking performance and noise reduction necessary for a disc brake rotor of a bicycle.

According to the method for producing martensitic stainless steel according to the present invention, by optimizing the cold rolling rate and controlling the hardness before press forming, it becomes possible to reduce dripping during press forming and quenching. The amount of subsequent polishing can be reduced. Further, productivity can be improved, for example, the polishing load can be leveled.
In the quenching treatment, the heating temperature range is 800 ° C. or higher, preferably 950 ° C. or higher, more preferably 1000 ° C. or higher and 1100 ° C. or lower, the holding time is 1 second to 20 minutes, and the cooling rate is 0.1 to 1000 ° C./s. This should be done under the following conditions. For example, in the case of a vacuum furnace, the cooling rate can be 0.1 to 10 ° C./s at 800 to 1100 ° C. (heating temperature) × 1 second to 20 minutes (holding time). In a continuous annealing furnace, the cooling rate can be 0.5 to 70 ° C./s at 800 to 1100 ° C. (heating temperature) × 1 to 600 seconds (holding time), or oil cooling, water cooling, or die quenching.

The martensitic stainless steel disc brake rotor according to the present invention can increase the corrosion resistance by controlling the amount of undissolved carbide [(FeCr) ₂₃ C ₆ ], and can add value other than brake performance. Can be increased.

  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.

  In the present invention, first, steel having the composition shown in Tables 1 and 2 (the balance is Fe and inevitable impurities) was melted and cast into a slab. In Tables 1 and 2, examples satisfying the present invention regarding the components are examples of the present invention. In addition, steel material No. 28, 37 to 41, 28-2, 37-2, 39-2, the content of the selective element (Mo, Sn, Nb, B, Ti) exceeds the inevitable impurity level, and the content of the selective element The upper limit of the amount is also exceeded. After heating this slab to 1230 degreeC, finishing temperature was made into the range of 800-950 degreeC, it hot-rolled to plate thickness 2.5-5.0 mm, and it wound up at 780 degreeC, and was set as the hot-rolled steel strip.

  Subsequently, the hot-rolled steel sheet was annealed at 850 ° C. for 4 hours, and then slowly cooled in a furnace. The hot-rolled annealed plate was shot blasted and washed with sulfuric acid to remove scale. Cold rolling was performed to obtain a 1.8 mm cold rolled product. In cold rolling, some materials were subjected to intermediate annealing at 750 ° C. and pickling. In addition, some materials were subjected to finish annealing at 700 ° C. after cold rolling and pickling. These manufacturing conditions are shown in Table 2. The surface hardness of the cold-rolled product and the cold-rolled annealed pickled product thus manufactured was measured with a Rockwell hardness meter. The Rockwell hardness test was performed according to JIS Z2245.

  Bicycle disc brake rotors were press-molded from cold-rolled products and cold-rolled annealed pickled products. The punched holes were measured and ranked by comparative evaluation. Furthermore, after quenching under various conditions shown in Tables 3 and 4 and polishing the surface, incidental parts were attached to form a disc brake rotor for a bicycle. Brake characteristics were evaluated by actual vehicle running tests. The braking characteristics were evaluated as braking force and squeal. Further, the corrosion resistance of the disc brake rotor was evaluated in a salt spray test for 24 hours. The salt spray test was performed according to JIS Z2371. The above-described methods were used for these evaluation test methods and scoring.

  The above production conditions and evaluation results are shown in Tables 3 and 4.

  The final annealing temperatures were (1) 600 to 700 ° C and (2) 700 to 800 ° C.

  As is apparent from Tables 3 and 4, in the case of the present invention examples (test Nos. 1 to 32 and 54 to 83) manufactured with the component composition to which the present invention was applied, the brake braking performance and squeal characteristics were compared with the comparative examples. Is found to be good. It can also be seen that the disc brake has excellent corrosion resistance. In addition, in addition to the component composition of the present invention, in the examples that also satisfy the cold rolling conditions, it can be seen that in addition to brake braking performance, squealing characteristics, and corrosion resistance, there is little dripping during press molding and excellent productivity. . In other words, according to the components and manufacturing methods to which the present invention is applied, the martensitic stainless steel cold-rolled excellent in brake characteristics after quenching required for a bicycle disc brake rotor, and also in corrosion resistance and press formability. Products, cold rolled-annealed-pickled products can be obtained.

  On the other hand, in comparative examples (test Nos. 33 to 53, 84 to 96) that depart from the present invention, the hardness after quenching of cold rolled products or cold rolled-annealed-pickled products, as a disc brake rotor of a bicycle At least one of braking performance, squealing characteristics, and corrosion resistance was low. Thereby, it turns out that the performance as a disc brake rotor material of a bicycle of the martensitic stainless steel plate in a comparative example has fallen.

  Specifically, correspondence between characteristic values, components, and manufacturing conditions in the comparative example will be described.

  Test No. (Hereinafter simply referred to as No.) 33, No. No. 84 was inadequate in quenching conditions (the quenching heating time was short and the cooling rate was slow, ie, heating at 1030 ° C. for 1 second and then cooling at 0.5 ° C./s), so the amount of precipitated Fe increased and quenching occurred. The hardness became low. For this reason, brake braking performance was lowered and corrosion resistance was also lowered. No. No. 34 had a low C content, so the quenching hardness was low and the brake braking performance was lowered. No. Since 85 had a high C content, the quenching hardness was too high, and the squeal characteristics deteriorated. No. Since 35 had a low Si content, the refining time became longer and the productivity decreased. No. 36, no. No. 86 had a high Si content. 37, no. No. 87 had a low Mn content. 42, no. No. 91 had a high Cr content. 49, no. Since No. 95 had a high amount of Mo, γp decreased, ferrite remained after quenching to reduce the quenching hardness, and the brake braking performance decreased. No. Since No. 38 had a high Mn content, the squeal characteristics were lowered and the corrosion resistance was lowered. No. 39, no. Since 88 had a high P, the toughness of the hot-rolled annealed sheet was lowered. No. 40, no. No. 89 had high S and B, so the corrosion resistance decreased. No. 41, no. Since 90 had a low Cr content, the corrosion resistance was poor. Furthermore, since C + N was high, the quenching hardness was too high, and the squealing characteristics deteriorated. No. No. 43 has a high Ni content. Since 50 had high Sn, the raw material cost became high. No. 44, no. Since No. 92 had a high Al content, the basicity of the slag became high, and the water-soluble inclusion CaS crystallized in the steel, thereby reducing the corrosion resistance. No. 45, no. Since No. 93 had a high V content, the squeal characteristics were degraded by the hard V carbide. No. Since No. 46 was low in nitrogen, C + N was low, quenching hardness was lowered, and braking performance was deteriorated. No. 47, no. Since No. 94 was high in nitrogen, bubble-type defects were formed in the slab, which deteriorated the surface quality of the product. Moreover, since the amount of C + N was too high, the quenching hardness was increased and the squealing characteristics were deteriorated. No. Since No. 48 had a high amount of Cu, the squeal characteristics deteriorated. No. 51, no. No. 96 has a high Nb. No. 52 is high in Ti. Since 53 had a high Zr, squeal characteristics deteriorated.

  From these results, the above-mentioned knowledge could be confirmed, and the grounds for limiting the above-mentioned respective steel compositions and configurations could be supported.

  As is apparent from the above description, according to the steel composition and manufacturing method of martensitic stainless steel of the present invention, it becomes possible to improve the brake performance of the disc brake rotor of the bicycle, and the disc brake of the bicycle. In the rotor manufacturing process, productivity can be improved, and added value such as corrosion resistance of the disc brake rotor can be improved. That is, the present invention has sufficient industrial utility value.

[0004]
it can. However, for the technology that omits tempering, if stainless steel is used for motorcycle disc brake rotors, squealing occurs even at 38 HRC, so it is possible to find a hardness range that achieves both braking force and squeal prevention. There wasn't.
[0013]
This is similar to the problem of sliding noise (abnormal noise), called squeal, which is a problem with motorcycle disc brake rotors. In order to prevent squealing in motorcycle disc brake rotors, the hardness is generally set to 38 HRC or less, and the hardness is controlled to 32 HRC or more necessary for obtaining braking force, and the hardness is controlled to 38 HRC or less which starts to squeal. Yes.
In a bicycle, in order to obtain a required braking force, the hardness of the disc brake rotor of 38 HRC or more is required. Considering the variation in hardness after quenching, the hardness range of 38 to 43 HRC is considered necessary.
As a result of examining methods for suppressing squealing in this hardness range, the influence of the base material component through the slight oxide film formed on the disc brake rotor surface during sliding, squealing is suppressed. In addition, the present inventors have found that it is necessary to limit the Cu content of the base material to 0.1% or less and to make the Mn content in the range of 1.0 to 1.4%. Furthermore, in order to improve the corrosion resistance of the disc brake rotor, it is desirable that the structure after quenching is a structure in which carbides are slightly dispersed in the martensite matrix, and the precipitation amount is 0.04% in terms of the weight percentage of Fe. It is necessary to:
[0014]
The gist of the present invention completed based on the above knowledge resides in the following martensitic stainless steel plate for a disc brake rotor of a bicycle and a manufacturing method thereof.
[0015]
(1) In mass%,
C: 0.070 to 0.120%,
N: 0.015-0.060%,
Si: 0.10 to 0.50%,
Mn: 1.0 to 1.4%

[0005]
P: 0.035% or less,
S: 0.015% or less Ni: 0.3% or less,
Cr: 11.5 to 13.5%,
Cu: 0.1% or less V: 0.3% or less Al: 0.001% to 0.010%
And C + N: 0.09 to 0.15% is satisfied, and γp, which is an index representing the phase balance during hot rolling represented by the following formula (1), satisfies 80 to 120, and the balance is A martensitic stainless steel plate for a disc brake rotor of a bicycle comprising Fe and inevitable impurities and having a hardness after quenching of 38 to 44 in HRC.
γp = 420 [% C] +470 [% N] +23 [% Ni] +9 [% Cu] +7 [% Mn] −11.5 [% Cr] −11.5 [% Si] −52 [% Al] − 12 [% Mo] -47 [% Nb] -7 [% Sn] -49 [% Ti] -48 [% Zr] -49 [% V] +189 (1)
[% C] indicates the content (% by mass) of carbon (C).
Similarly, [% N] [% Ni] [% Cu] [% Mn] [% Cr] [% Si] [% Al] [% Mo] [% Nb] [% Sn] [% Ti] [% Zr] [% V] is N, Ni, Cu, Mn, Cr, Si, Al, Mo, Nb, Sn, Ti, Zr, V, respectively.
Content (mass%).
0 when no element is contained.
[0016]
(2) Furthermore, in mass%,
Mo: 0.05-0.5%
Sn: 0.003-0.5%,
Ti: 0.05% or less,

[0006]
Zr: 0.05% or less,
B: 0.0005 to 0.0030%,
The martensitic stainless steel plate for disc brake rotors of bicycles according to (1), characterized in that it contains one or more of the following.
[0017]
(3) When a martensitic stainless steel plate having the steel composition described in (1) or (2) above is quenched to form a disc brake rotor for a bicycle, the amount of undissolved carbide precipitated is the amount of Fe. A martensitic stainless steel plate for a disc brake rotor of a bicycle, characterized by being 0.04% or less.
[0018]
(4) After annealing the stainless steel hot-rolled sheet of the component described in (1) or (2) above, cold rolling with a total rolling reduction of 20 to 70% is performed once, or intermediate annealing is performed 2 While performing cold rolling, the cold rolling rate of finish cold rolling should be 20% or more, and the hardness of the cold rolled product or the product after annealing after cold rolling and pickling should be 220HV to 260HV. A method for producing a martensitic stainless steel sheet for a disc brake rotor of a bicycle.
Effects of the Invention [0019]
As described above, according to the present invention, a martensitic stainless steel plate for a disc brake rotor for a bicycle that is excellent in braking characteristics as a disc disc rotor for a bicycle, for example, excellent in braking force and squealing performance, and used for quenching. However, the industrial effect is very large.
BRIEF DESCRIPTION OF THE DRAWINGS [0020]
FIG. 1 is a diagram showing the influence of component C + N on brake braking performance and steel plate hardness of a bicycle disc brake rotor manufactured by quenching a martensitic stainless cold-rolled product in this embodiment. FIG. 1A is a diagram showing the relationship between C + N and Rockwell hardness, and FIG. 1B is a diagram showing the relationship between C + N and bicycle braking performance and squeal.
[FIG. 2] The effect of the finish cold rolling reduction (pressure reduction) on the Vickers hardness of the cold-rolled martensitic stainless steel product in this embodiment and the droop during press forming.

[0012]
-11.5 [% Cr] -11.5 [% Si] -52 [% Al] -12 [% Mo] -47 [% Nb] -7 [% Sn] -49 [% Ti] -48 [% Zr] −49 [% V] +189 (1)
Here, the component described in the above formula means mass% of the component contained in the steel.
Note that γp equation (1) is 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.
[0038]
In the present invention, in addition to the above elements, Mo: 0.05 to 0.5%, Sn: 0.003 to 0.5%, Ti: 0.05% or less, Zr: 0.05% or less, B: It is preferable to add one or more of 0.0005 to 0.0030%, or to perform upper limit regulation using a high-purity raw material.
[0039]
(Mo: 0.05-0.5%)
Mo may be added as necessary to enhance corrosion resistance, and the lower limit is preferably made 0.05% in order to exert its effect. On the other hand, Mo is a ferrite former like Cr, and excessive addition reduces the austenite fraction at the time of quenching heating and lowers the quenching hardness, so is 0.5% or less. However, it is an expensive element, and 0.1% to 0.3% is desirable in order to exhibit an effect of improving corrosion resistance commensurate with the addition and to suppress an increase in raw material cost.
[0040]
(Sn: 0.003-0.5%)
Sn may be added as necessary to enhance the corrosion resistance, and in order to exert its effect, the lower limit is made 0.003%, preferably 0.03%. On the other hand, Sn is a ferrite former like Cr and Mo, and excessive addition reduces the austenite fraction during quenching heating and lowers the quenching hardness, so is 0.5% or less. However, it is an expensive element and has a resistance to the addition.

[0013]
0.01% to 0.3% is desirable in order to exert an effect of improving food quality and suppress an increase in raw material cost.
[0041]
[0042]
(Ti: 0.05% or less)
In order to promote the squeal of the brake disc rotor by precipitating Ti as hard coarse nitride TiN, it is preferable to perform upper limit regulation as necessary. In order to suppress coarse TiN precipitation, the upper limit is preferably 0.05% or less. However, since it is contained as an impurity in other alloy raw materials, it is preferable to use a high-purity raw material to reduce it extremely, leading to an increase in raw material cost, so the lower limit is preferably made 0.0005%.
[0043]
(Zr: 0.05% or less)
Zr is preferably precipitated as hard coarse nitride ZrN so as to promote the squealing of the brake disc rotor, and the upper limit is preferably set as necessary. In order to suppress coarse ZrN precipitation, the upper limit is preferably 0.05% or less. However, since it is contained as an impurity in other alloy raw materials, extreme reduction makes it necessary to use high-purity raw materials and leads to an increase in raw material costs. Therefore, the lower limit is preferably made 0.0005%.
[0044]
(B: 0.0005% to 0.0030%)
B may be added as necessary in order to improve the hot ductility during hot rolling and to reduce the yield reduction due to the ear cracks of the hot-rolled sheet, and in order to exert its effect, the lower limit is 0. .0005% or more is desirable. However, excessive addition causes toughness due to precipitation of Cr2B, (Cr, Fe) 23 (C, B) 6.

[0020]
By optimizing the ductility and controlling the hardness before press forming, it becomes possible to reduce dripping during press forming, and the amount of polishing after quenching can be reduced. Further, productivity can be improved, for example, the polishing load can be leveled.
In the quenching treatment, the heating temperature range is 800 ° C. or higher, preferably 950 ° C. or higher, more preferably 1000 ° C. or higher and 1100 ° C. or lower, the holding time is 1 second to 20 minutes, and the cooling rate is 0.1 to 1000 ° C./s. This should be done under the following conditions. For example, in the case of a vacuum furnace, the cooling rate can be 0.1 to 10 ° C./s at 800 to 1100 ° C. (heating temperature) × 1 second to 20 minutes (holding time). In a continuous annealing furnace, the cooling rate can be 0.5 to 70 ° C./s at 800 to 1100 ° C. (heating temperature) × 1 to 600 seconds (holding time), or oil cooling, water cooling, or die quenching.
[0067]
The martensitic stainless steel disc brake rotor according to the present invention can increase the corrosion resistance by controlling the amount of undissolved carbide [(FeCr) ₂₃ C ₆ ], and can add value other than brake performance. Can be increased.
Example [0068]
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.
[0069]
In the present invention, first, steel having the composition shown in Tables 1 and 2 (the balance is Fe and inevitable impurities) was melted and cast into a slab. In Tables 1 and 2, examples satisfying the present invention regarding the components are examples of the present invention. In addition, steel material No. 37 to 41, 37-2, 39-2, the content of the selective element (Mo, Sn, B, Ti) exceeds the unavoidable impurity level, and also exceeds the upper limit of the content of the selective element It is. After heating this slab to 1230 degreeC, finishing temperature was made into the range of 800-950 degreeC, it hot-rolled to plate thickness 2.5-5.0 mm, and it wound up at 780 degreeC, and was set as the hot-rolled steel strip.
[0070]
Subsequently, the hot-rolled steel sheet was annealed at 850 ° C. for 4 hours, and then slowly cooled in a furnace. The hot-rolled annealed plate was shot blasted and washed with sulfuric acid to remove scale. Cold rolling was performed to obtain a 1.8 mm cold rolled product. For cold rolling

［００７４］[0022]
[Table 1]

[0074]

［００７５］[0023]
[Table 2]

[0075]

［００７６］[0024]
[Table 3]

[0076]

［００７７］
仕上げ焼鈍温度は、（１）６００〜７００℃、（２）７００〜８００℃で行った。
［００７８］
表３、４から明らかなように、本発明を適用した成分組成で製造した本発明例（試験Ｎｏ．１〜３２、５４〜８３）の場合、比較例に較べて、ブレーキ制動性、鳴き特性が良好であることが分かる。また、ディスクブレーキの耐食性に優れる事が分かる。また、本発明の成分組成に加えて、冷間圧延条件をも満足する実施例では、ブレーキ制動性、鳴き特性、耐食性に加えて、[0025]
[Table 4]

[0077]
The final annealing temperatures were (1) 600 to 700 ° C and (2) 700 to 800 ° C.
[0078]
As is apparent from Tables 3 and 4, in the case of the present invention examples (test Nos. 1 to 32 and 54 to 83) manufactured with the component composition to which the present invention was applied, the brake braking performance and squeal characteristics were compared with the comparative examples. Is found to be good. It can also be seen that the disc brake has excellent corrosion resistance. Moreover, in addition to the component composition of the present invention, in the examples that also satisfy the cold rolling conditions, in addition to brake braking performance, squeal characteristics, corrosion resistance,

[0026]
It can be seen that there is little dripping during press molding and the productivity is excellent. In other words, according to the components and manufacturing methods to which the present invention is applied, the martensitic stainless steel cold-rolled excellent in brake characteristics after quenching required for a bicycle disc brake rotor, and also in corrosion resistance and press formability. Products, cold rolled-annealed-pickled products can be obtained.
[0079]
On the other hand, in comparative examples (test Nos. 33 to 53, 84 to 95) that depart from the present invention, the hardness after quenching of a cold rolled product or cold rolled-annealed-pickled product, as a disc brake rotor of a bicycle At least one of braking performance, squealing characteristics, and corrosion resistance was low. Thereby, it turns out that the performance as a disc brake rotor material of a bicycle of the martensitic stainless steel plate in a comparative example has fallen.
[0080]
Specifically, correspondence between characteristic values, components, and manufacturing conditions in the comparative example will be described.
[0081]
Test No. (Hereinafter simply referred to as No.) 33, No. No. 84 was inadequate in quenching conditions (the quenching heating time was short and the cooling rate was slow, ie, heating at 1030 ° C. for 1 second and then cooling at 0.5 ° C./s), so the amount of precipitated Fe increased and quenching occurred. The hardness became low. For this reason, brake braking performance was lowered and corrosion resistance was also lowered. No. No. 34 had a low C content, so the quenching hardness was low and the brake braking performance was lowered. No. Since 85 had a high C content, the quenching hardness was too high, and the squeal characteristics deteriorated. No. Since 35 had a low Si content, the refining time became longer and the productivity decreased. No. 36, no. No. 86 had a high Si content. 37, no. No. 87 had a low Mn content. 42, no. No. 91 had a high Cr content. 49, no. Since No. 95 had a high amount of Mo, γp decreased, ferrite remained after quenching to reduce the quenching hardness, and the brake braking performance decreased. No. Since No. 38 had a high Mn content, the squeal characteristics were lowered and the corrosion resistance was lowered. No. 39, no. Since 88 had a high P, the toughness of the hot-rolled annealed sheet was lowered. No. 40, no. No. 89 had high S and B, so the corrosion resistance decreased. No. 41, N

[0027]
o. Since 90 had a low Cr content, the corrosion resistance was poor. Furthermore, since C + N was high, the quenching hardness was too high, and the squealing characteristics deteriorated. No. No. 43 has a high Ni content. Since 50 had high Sn, the raw material cost became high. No. 44, no. Since No. 92 had a high Al content, the basicity of the slag became high, and the water-soluble inclusion CaS crystallized in the steel, thereby reducing the corrosion resistance. No. 45, no. Since No. 93 had a high V content, the squeal characteristics were degraded by the hard V carbide. No. Since No. 46 was low in nitrogen, C + N was low, quenching hardness was lowered, and braking performance was deteriorated. No. 47, no. Since No. 94 was high in nitrogen, bubble-type defects were formed in the slab, which deteriorated the surface quality of the product. Moreover, since the amount of C + N was too high, the quenching hardness was increased and the squealing characteristics were deteriorated. No. Since No. 48 had a high amount of Cu, the squeal characteristics deteriorated. No. No. 52 is high in Ti. Since 53 had a high Zr, squeal characteristics deteriorated.
[0082]
From these results, the above-mentioned knowledge could be confirmed, and the grounds for limiting the above-mentioned respective steel compositions and configurations could be supported.
Industrial applicability [0083]
As is apparent from the above description, according to the steel composition and manufacturing method of martensitic stainless steel of the present invention, it becomes possible to improve the brake performance of the disc brake rotor of the bicycle, and the disc brake of the bicycle. In the rotor manufacturing process, productivity can be improved, and added value such as corrosion resistance of the disc brake rotor can be improved. That is, the present invention has sufficient industrial utility value.

Claims (4)

% By mass
C: 0.070 to 0.120%,
N: 0.015-0.060%,
Si: 0.10 to 0.50%,
Mn: 1.0 to 1.4%
P: 0.035% or less,
S: 0.015% or less Ni: 0.3% or less,
Cr: 11.5 to 13.5%,
Cu: 0.1% or less V: 0.3% or less Al: 0.001% to 0.010%
And C + N: 0.09 to 0.15% is satisfied, and γp, which is an index representing the phase balance during hot rolling represented by the following formula (1), satisfies 80 to 120, and the balance is A martensitic stainless steel plate for a disc brake rotor of a bicycle comprising Fe and inevitable impurities and having a hardness after quenching of 38 to 44 in HRC.
γp = 420 [% C] +470 [% N] +23 [% Ni] +9 [% Cu] +7 [% Mn] −11.5 [% Cr] −11.5 [% Si] −52 [% Al] − 12 [% Mo] -47 [% Nb] -7 [% Sn] -49 [% Ti] -48 [% Zr] -49 [% V] +189 (1)
Here, [% C] indicates the content (mass%) of carbon (C).
Similarly, [% N] [% Ni] [% Cu] [% Mn] [% Cr] [% Si] [% Al] [% Mo] [% Nb] [% Sn] [% Ti] [% Zr] [% V] represents the content (% by mass) of N, Cu, Mn, Cr, Si, Al, Mo, Nb, Sn, Ti, Zr, and V, respectively.
0 when no element is contained.
Furthermore, in mass%,
Mo: 0.05-0.5%
Sn: 0.003-0.5%,
Nb: 0.03-0.15%,
Ti: 0.05% or less,
Zr: 0.05% or less,
B: 0.0005 to 0.0030%,
The martensitic stainless steel plate for a disc brake rotor of a bicycle according to claim 1, comprising at least one of the following.
When the martensitic stainless steel plate having the steel composition according to claim 1 or 2 is quenched to form a disc brake rotor for a bicycle, the amount of precipitated undissolved carbide is 0.04% or less as the amount of Fe. A martensitic stainless steel plate for a disc brake rotor of a bicycle, characterized by
  After annealing the stainless steel hot-rolled sheet of the component according to claim 1 or 2, cold rolling with a total rolling reduction of 20 to 70% is performed once, or cold rolling is performed twice with intermediate annealing in between. In addition, the cold rolling rate of the finish cold rolling is 20% or more, and the hardness of the cold rolled product or the product subjected to the pickling after annealing after cold rolling is 220HV to 260HV, Manufacturing method of martensitic stainless steel sheet for bicycle disc brake rotor.

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