JP4315006B2 - Manufacturing method of stainless steel plate for disc brake rotor - Google Patents

Description

  The present invention relates to a method for producing a stainless steel plate for a disc brake rotor, and more particularly to a disc brake rotor that can reduce the production load of a disc brake rotor used for braking a bicycle (such as a mountain bike) that can run at high speed or a bicycle with a motor. The present invention relates to a method for producing a stainless steel sheet for use.

Bicycle disc brake materials are required to have wear resistance and rust resistance. Wear resistance, but increases the higher the general hardness, hardness of 35 ± 5 in H _{R C} is found from the relationship between the pad of the brake. In order to satisfy these requirements, a martensitic stainless steel plate such as SUS420J2 has been used as a material for a disc brake rotor. However, this stainless steel sheet has a problem that a low Cr region is generated during tempering after quenching and rust resistance is poor.

On the other hand, in a martensitic stainless steel sheet having a low C and high Mn as disclosed in Patent Document 1, a predetermined hardness is obtained only by quenching, and tempering is unnecessary. Normally, when manufacturing a disc brake rotor using this material, the steel plate manufacturer supplies the disc manufacturer with an annealed material, and the disc manufacturer quenches the annealed material, then punches and then polishes the product. .
Japanese Patent Publication No. 60-2380

When the disc brake rotor is manufactured by the method as described above, a quenching process is required to obtain a predetermined hardness. However, there are the following problems with this quenching process.
1) The disk manufacturer needs to have heat treatment equipment.
2) Since it is usually quenched after sheet processing (or further rounding), productivity is low and process load is high.
3) In order to obtain a certain hardness, it is necessary to strictly control the temperature during quenching, and the load for this is high.
4) During polishing after quenching, the load for grinding the scales produced by quenching is high.

  Therefore, the present invention eliminates the above-mentioned problems of the prior art, manufactures a steel plate that can stably obtain a predetermined hardness for a disc brake rotor during heat treatment after cold rolling, and reduces the load during disc processing. An object of the present invention is to provide a method for producing a stainless steel plate for a disc brake rotor.

The present invention contains, in mass%, C + N: 0.04 to 0.19%, Si: 0.5% or less, Mn: 0.5 to 2.5%, Cr: 10 to 14.5%, Alternatively, a stainless steel material containing one or two of Cu: 1.0% or less and Ni: 1.5% or less , the balance being Fe and inevitable impurities , was hot-rolled (hot rolled for short). After annealing, pickling, and cold rolling (cold rolling for short), the obtained cold-rolled steel strip was cooled to the austenite region after cooling in an annealing pickling facility for cold-rolled materials, and the structure was martensified. by pickling After the site tissue, the production method of the stainless steel plate for a disc brake rotor, characterized in that the hardness and H _R C30~40.

  According to the present invention, a steel strip satisfying a required hardness level can be supplied as a material for a bicycle disc brake rotor, so that the quenching process at the time of manufacturing the disc brake rotor can be omitted, which greatly improves the productivity. Can contribute.

  The reason why the composition of the martensitic stainless steel material used in the present invention is limited as described above will be described below. The unit of component content is mass% and is abbreviated as%.

C + N: 0.04 to 0.19%
C and N is an effective element to improve the wear resistance increases the hardness, is below the H _R C30 (C + N) amount quenching hardness is less than 0.04%, whereas, (C + N) amount If it exceeds 0.19%, the quenching hardness exceeds H _R C40, and an appropriate hardness for a disc brake rotor cannot be obtained. Therefore, C and N were made 0.04 to 0.19% in total.

Si: 0.5% or less Si is an element that generates ferrite at a high temperature, and addition of Si exceeding 0.5% not only lowers the quenching hardness but also adversely affects toughness, so 0.5% It was as follows.

Mn: 0.5 to 2.5%
Mn is an element that is effective in preventing the formation of δ-ferrite at high temperatures and expanding the quenching temperature range to stabilize the hardenability. However, if Mn is less than 0.5%, the prevention effect is poor, and δ-ferrite is generated in the temperature range of 900 to 1050 ° C., so that a quenching hardness of H _R C35 ± 5 cannot be obtained. In addition, if Mn exceeds 2.5%, the oxidation resistance at high temperature is reduced, the amount of scale produced in the steel plate manufacturing process is large, the surface of the plate is roughened during pickling, and the dimensional accuracy of the steel plate is significantly reduced. Let Therefore, Mn is set to 0.5 to 2.5%.

Cr: 10 to 14.5%
10% or more of Cr is indispensable for ensuring corrosion resistance. However, when Cr exceeds 14.5%, δ-ferrite is generated in the quenching temperature range of 850 to 1050 ° C. even when the upper limit amounts of Mn, Ni and Cu are added, and H _R C35 ± 5 Hardening hardness cannot be obtained. Therefore, Cr is 10 to 14.5%.

  In the present invention, in addition to the above component elements, one or two of Cu and Ni can be added as necessary.

Cu: 1.0% or less Since Cu has the same effect as Mn, it can be added as necessary in the present invention. However, if it exceeds 1.0%, hot workability is impaired, and the production of steel sheet Since the yield is lowered, it is preferably 1.0% or less.

Ni: 1.5% or less Since Ni has the same effect as Mn, it can be added as necessary in the present invention. However, since it is an expensive element, from the viewpoint of suppressing an increase in steel sheet manufacturing cost, It is preferably 1.5% or less.

  Next, the manufacturing process used in the present invention will be described. FIG. 1 is a flowchart showing all the steps from obtaining a disc brake rotor as a final product from a stainless steel material in comparison with the prior art and the present invention. In FIG. 1, a process upstream of sheet processing relates to a steel plate manufacturing method, and “” corresponds to a steel plate manufacturing process according to the present invention. After the sheet processing, it is carried out by the disk manufacturer.

  As shown in FIG. 1, conventionally, since a ferrite structure was obtained by annealing a cold-rolled sheet (as a cold-rolled steel strip), the disk manufacturer performed a quenching process as shown in step A. On the other hand, in the present invention, since the martensite structure is obtained in the heat treatment step of the cold-rolled sheet having the composition in the above-mentioned limited range, the hardness of the steel strip as the sheet processing material is necessary for the disc brake rotor. As a result, the quenching process at the disc maker can be omitted as shown in step B, so that the above-mentioned problems are solved all at once.

  In the present invention, the operation conditions of the process from hot rolling to cold rolling and the pickling process of the cold rolled sheet are not particularly limited, and may be performed under known conditions. In the heat treatment process of the cold-rolled sheet, the austenite region is heated and then cooled in order to obtain a martensite structure. If the heating temperature is too low, a martensite structure cannot be obtained, and if it is too high, a ferrite structure is generated. Therefore, the heating temperature is preferably in the range of 900 to 1100 ° C. Further, if the holding time at this heating temperature is too short, it does not become austenite, and if it is too long, a ferrite structure may be formed. The cooling rate may be equal to or higher than the cooling rate when a steel plate having a thickness of 4 mm is air-cooled.

  In order to change the hardness of the martensitic structure obtained by cold rolling heat treatment, a method of adjusting the content of (C + N) is effective.

  The martensite structure in the present invention may contain retained austenite within 5% by volume (vol.%).

  In the heat treatment and pickling after cold rolling, an annealing pickling facility for cold rolled material is used from the viewpoint of economy. The annealing pickling equipment for cold-rolled materials here refers to continuous annealing pickling equipment for stainless cold-rolled products.

  In general, a material for a bicycle disc brake rotor is required to have a good shape. For this reason, it is preferable that the stainless steel strip manufactured by the above method is subjected to skin pass rolling or tension leveler to correct the shape to be flatter.

  The structure and Rockwell hardness of the steel sheet after the cold-rolled sheet heat treatment are obtained by taking a sample after performing normal pickling or further shape correction.

  As an example of the invention (an example of the present invention), a stainless steel slab having a composition including the constituent elements shown in Table 1 and the balance of Fe and inevitable impurities was hot-rolled to a thickness of 5 mm, and then annealed at 800 ° C. × 24 h. And then pickled. The steel plate after pickling is cold-rolled to a thickness of 2 mm, and the obtained cold-rolled plate is heated at 1000 ° C. in an annealing pickling equipment for cold-rolled materials and heat-treated under the conditions of cooling (air cooling) after holding for 60 s. And then pickled to remove scale. Furthermore, skin pass rolling was performed to correct the shape.

  Further, as a comparative example (an example of the prior art), the same process as that of the inventive example was performed except that the heating temperature of the cold-rolled sheet heat treatment was changed to 800 ° C. (annealing) instead of 1000 ° C. in the inventive example.

  About the invention example and the comparative example, the structure and Rockwell hardness of the steel plate after cold-rolled sheet heat treatment and after skin pass rolling were investigated. Furthermore, using these steel plates as materials, trial manufacture of a bicycle disc brake rotor is performed by the process B of FIG. 1 in the invention example and the process A of FIG. The time required and the basic unit of whetstone were examined. In the comparative example, the hardness after quenching was also examined.

  Table 2 shows the results of investigation on these steels 1. The time required for polishing and the grinding wheel basic unit are shown as relative ratios with a comparative example of 1. As shown in Table 2, in the inventive examples, the disc brake rotor could be manufactured without any manufacturing problems, and the quenching process could be omitted. Moreover, since there is no scale caused by quenching, the time required for polishing and the grinding wheel basic unit can be greatly reduced.

In the invention example of steel 2, after the heat treatment, the hardness after the skin pass rolling is at H _{R C} = 37 together, and organization has been a martensite.

  The present invention can be applied to a bicycle disc brake rotor. In general, a disc brake rotor for bicycles having a thickness of about 2 mm is used for weight reduction. However, the present invention is not limited to the thickness range that can be manufactured by an annealing pickling facility for cold rolling materials. It is also applicable to other motorcycles, buggy cars, snowmobiles, etc.

It is a flowchart which shows all the processes until it obtains the disc brake rotor which is a final product from a stainless steel raw material by comparison with the past and this invention.

Claims (1)

In mass%, C + N: 0.04 to 0.19%, Si: 0.5% or less, Mn: 0.5 to 2.5%, Cr: 10 to 14.5%, or Cu: 1.0% or less, Ni: containing one or two of 1.5% or less, the stainless steel material consisting of the remaining Fe and inevitable impurities is hot-rolled, then annealed, pickled, and further cooled and during rolling, the resulting cold-rolled steel strip at a cold rolled material manufacturing annealing pickling by pickling after the martensite tissue by cooling after heating to the austenite region, the hardness H _R C30-40, The manufacturing method of the stainless steel plate for disc brake rotors characterized by the above-mentioned.

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