JPH0860309A - Steel for motorcycle disk brake, and method for hot rolling the steel, and production of motorcycle disk brake by using the steel - Google Patents

Abstract

PURPOSE: To improve corrosion resistance, toughness, and wear resistance and to enlarge the range of hardening temp. by mutually regulating respective contents of components so that the values of γmax and Hc in a steel are in respectively specified ranges. CONSTITUTION: The steel material for motorcycle disk brake has a basic composition consisting of, by weight, 0.30-0.60% C, 0.20-0.40% Si, 0.70-1.00% Mn, <=0.040% P, <=0.010% S, 0.10-0.60% Ni, 11.50-12.10% Cr, <=0.50% Mo, 0.70-0.90% Cu, 0.O25% N, and the balance Fe with inevitable impurities. Further, respective contents of the components are mutually regulated so that the value of γmax defined by equation I and the value of Hc defined by equation II are <100 and 34.0-39.0, respectively. At the time of hot rolling a slab prepared by continuously casting a molten metal of this steel, a decarburization inhibitor is applied to the slab surface before hot rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel for motorcycle disc brakes having excellent corrosion resistance, toughness, and wear resistance, a hot rolling method for the steel, and a motorcycle disc brake manufacturing method using the steel.

[0002]

2. Description of the Related Art Corrosion resistance, toughness and wear resistance are required for components of motorcycle disc brakes. Regarding corrosion resistance, it is said that it is sufficient if it has corrosion resistance of SUS420J2 steel or more. On the other hand, the toughness and wear resistance are closely related to the hardness, and it is necessary to stably secure the quenching hardness HRC = 34.0 to 39.0 as the hardness of the disc brake. It is said that.

In order to satisfy the various characteristics required for motorcycle disc brakes as described above, low carbon martensitic stainless steel which is easy to manufacture and hardenable is used. In addition, JP-A-57-198
No. 249, C + N: 0.04 to 0.10%,
Si: 0.5% or less, Mn: 1.0 to 2.5%, Ni: 0.0.
5 or less, Cu: 0.5 or less, Cr: 10.0 to 14.5%
A low carbon martensitic stainless steel motorcycle disc brake material having the following composition and excellent in corrosion resistance and toughness has been proposed.

[0004]

However, when the hardness is controlled within a predetermined range only by quenching, the conventional steel has a significantly large change in the quenching hardness due to the difference in the quenching temperature. It is necessary to control the temperature very strictly. In addition, even slight changes in chemical composition affect quenching hardness, so it is necessary to make strict material management, and manufacturing management must be extremely complicated.
Furthermore, when hot rolling a slab made by continuously casting conventional steel,
A decarburized layer was formed on the surface layer of the hot-rolled steel strip, causing a problem that the shape was poor after quenching, that is, the amount of looseness increased. Therefore, raise the quenching heat treatment temperature more than necessary,
After quenching, I had no choice but to maintain it.

The steel described in Japanese Patent Laid-Open No. 57-198249 has a wide quenching temperature range, but since the Mn content is high, the corrosion resistance of both the raw material and the quenching material decreases, and There is a problem that toughness decreases. Further, when Mn is high, the high temperature oxidation resistance is deteriorated, the scale layer becomes thick and the pickling property deteriorates, which in turn lowers the operating efficiency and increases the cost. When the S content is high, MnS etc. However, the amount of non-metallic inclusions increases and the surface quality deteriorates.

Therefore, the present invention is disclosed in Japanese Patent Laid-Open No. 57-1982.
The Mn value is lower than that of the steel described in Japanese Patent Publication No. 49, to satisfy the above-mentioned various properties required as a material for motorcycle disc brakes.

[0007]

[Means for Solving the Problems] In order to solve the above problems, C: 0.030 to 0.060% by weight, Si:
0.20 to 0.40%, Mn: 0.70 to 1.00%, P
: 0.040% or less, S: 0.010% or less, Ni:
0.10 to 0.60%, Cr: 11.50 to 12.10%,
Mo: 0.50% or less, Cu: 0.70 to 0.90%, N
: 0.025% or less, γmax = 420C-11.5Si + 7Mn + 23
Γmax defined by Ni-11.5Cr + 9Cu + 470N + 189 is less than 100, and Hc = 218C-2.6Si + 2.9Mn + 9.2N
i-4.6Cr + 3.6Cu + 138N + 75.2 The contents of the above elements are adjusted to each other so that the Hc value is in the range of 34.0 to 39.0, and the balance is F.
Steel for motorcycle disc brakes composed of e and unavoidable impurities.

When hot rolling the slab obtained by continuously casting molten steel for motorcycle disc brake steel, a decarburizing inhibitor is applied to the surface of the continuously cast slab before hot rolling.

Further, the hot-rolled steel strip for motorcycle disc brakes obtained as described above is punched into a predetermined disc size, and the disc is quenched and heat treated at 950 to 1150 ° C. to produce a motorcycle disc brake. I decided.

[0010]

The reason for the limitation of the present invention having the above structure will be described below. First, the Hc value will be described. The quenching temperature range of conventional steel is remarkably narrow. In the case of steel that originally has the highest quenching hardness HRC: 50 to 60, conventionally, the quenching hardness increases with increasing quenching temperature. This is because trying to obtain HRC: 34.0 to 39.0 in the temperature range. Therefore, in the past, it was necessary to grasp the quenching conditions based on the composition of the material, the conditions were narrow, and it was necessary to strictly control the temperature.
On the other hand, if quenching is performed near the temperature at which the maximum quenching hardness of martensitic stainless steel is obtained, the change in quenching hardness can be reduced over a wide temperature range. That is, the maximum quenching hardness was originally HR
A martensitic stainless steel whose composition is adjusted so that C: 34.0 to 39.0 should be able to have a wide quenching temperature range.

Under the circumstances described above, the present inventor continued to study the steel composition, and as a result, the quenching hardness HRC was 34.0 by adjusting the composition of the steel of the present invention shown above.
The present invention has been completed based on the knowledge that a wide quenching temperature range of up to 39.0 can be taken.

In the present invention, the reason why γmax is limited to the range of less than 100 is that 100% martensite phase is obtained in the region of γmax> 100 and Hc is increased in that region.
To set the value to the range of 34.0-39.0, Ti or N
This is because a large amount of i, Mn, Cu, etc. must be added, which increases the material cost.

The reasons for limiting each component in the present invention are as follows. C: C is a component that gives a necessary and sufficient amount of martensite to obtain hardness during quenching, and 0.030%
The above is necessary. However, if the C content is too high, in the structure of the material ferrite phase + Cr carbonitride, Cr ₂₃
Becomes precipitate C _6, impair the corrosion resistance was precipitated at grain boundaries, also 0.060 percent to deteriorate the toughness of the material
Below.

Si: Si is an element that reduces the amount of martensite phase produced during quenching and, at the same time, solid-solution strengthens the martensite phase, increasing the hardness variation during quenching and decreasing the toughness. . However, Si is an element preferable for deoxidizing steel during steelmaking or improving the flowability of molten metal during casting, and improves operability and surface quality of the raw material. So S
The content of i was set to 0.20 to 0.40% by weight.

Mn: Mn satisfies the range of Hc value,
It exerts an important function to extend the quenching temperature range where the maximum quenching hardness HRC: 34.0-39.0 is obtained, to the low temperature side. That is, since Mn is an element that increases the amount of martensite at the time of quenching, the amount of C and N required to keep the Hc value within a predetermined range is reduced, thereby increasing the strength of the martensite phase. By making it low, the change in quenching hardness due to the variation in the amount of martensite during quenching can be reduced. In addition, the influence of the increase of C on the corrosion resistance and toughness of the material can be mitigated. Furthermore, M
n lowers the transformation temperature (A ₁ temperature) from the structure of the ferrite phase + Cr carbonitride to the structure of the austenite phase + ferrite phase + Cr carbonitride at high temperature, so the maximum quenching hardness is HRC: 34.0. It effectively works to extend the quenching temperature range satisfying 39.0 to the low temperature side.
In order to obtain such effects, the Mn content must be at least 0.70% by weight. However, if a large amount of Mn is contained, the corrosion resistance decreases, and the ductility-brittleness transition temperature of the material shifts to the high temperature side, and at the same time, the toughness of the hardened material deteriorates. Further, if Mn is contained more than necessary, the pickling property tends to be inferior, so the operating efficiency is lowered, leading to an increase in cost, and nonmetallic inclusions (MnS) are also increased, leading to a deterioration in the surface quality of the material. , Its content is 1.0
It is better to be 0% or less. Therefore, the content of Mn is set to 0.70 to 1.00% by weight.

P: P deteriorates the toughness, so the lower the better, the better, but if the content of the steel of the present invention is 0.040% or less, no particular trouble will occur. It was set to 040% or less.

S: S becomes MnS and deteriorates the corrosion resistance and the surface quality. Therefore, the lower the S content is, the better. However, if it is 0.010% or less in the steel of the present invention, there is no particular problem. Content of 0.010% by weight or less.

Ni: Ni is a substitutional austenite forming element, and like Mn, is an estimated value H of the maximum quenching hardness.
It effectively contributes to c and A ₁ temperature. However, since Ni is expensive, adding more than necessary increases the cost.
Therefore, the Ni content is set to 0.1 to 0.60% by weight.

Cr: Cr is required to be 11.50% or more in order to maintain the corrosion resistance required for the disc brake. On the other hand, in order to satisfy the range of the maximum quenching hardness Hc, it is necessary to adjust the addition amounts of other components, and if Cr is increased, Mn, Ni, and Cu must be increased, which results in cost reduction. It will be up. Therefore, the Cr content is set to 11.50 to 12.10% by weight.

Mo: Mo is an element necessary for improving the corrosion resistance, but 0.50% because it raises the cost.
Below.

Cu: Cu is an element that affects the estimated value Hc of the maximum quenching hardness and the A ₁ temperature, and its effect is larger than Mn, which is a necessary element for the steel of the present invention, but is higher than Mn. Since it is expensive, the Cu content is wt%
Was 0.70 to 0.90%.

N: N beneficially contributes to the estimated value Hc of the maximum quenching hardness and the A ₁ temperature, but since N enhances the strength of martensite similarly to C, if it is contained more than necessary, it is quenched. Increase the hardness fluctuation due to slight fluctuations in the amount of martensite. N does not have a bad effect as much as C, but it reduces the amount of solid solution Cr and reduces the corrosion resistance of the material. Therefore, the content of N is set to 0.025% or less by weight in consideration of the normal operation results.

The molten steel of the present invention having the above composition is continuously cast, and a continuously cast slab whose surface has been properly cared for is hot rolled, then diffusion annealed, pickled and hot rolled. The steel strip thus obtained is diffusion annealed in the temperature range of 760 to 790 ° C., punched into a predetermined disc size, the disc is quenched and heat treated at 950 to 1150 ° C., and surface treated to produce a motorcycle disc brake.

However, when the motorcycle disc brake is manufactured through the above steps, a defective shape may occur after quenching. As a result of studying the cause, the inventors of the present invention have found that a decarburized layer is generated in the surface layer of a continuously cast slab during hot rolling, and martensite formation due to quenching is non-uniform. It was found that the site transformation became non-uniform, resulting in a defective shape.

Therefore, in the manufacturing process in which the molten steel of the present invention having the above composition is continuously cast, the surface of the continuously cast slab is hot-rolled if necessary, and then pickled, in a manufacturing process before hot rolling. By applying a decarburization inhibitor to the surface of the casting slab, it was decided to prevent such a partial decarburization layer from occurring and prevent the defective shape after quenching.

[0026]

Embodiments of the present invention will be described below. A slab continuously cast from molten steel having the chemical composition shown in Table 1 is hot-rolled to produce a hot-rolled steel strip for motorcycle disc brakes, and then diffusion annealing is performed in a temperature range of 760 to 790 ° C.
A motorcycle disc brake was manufactured by punching into a predetermined disk size and quenching heat treatment at 950 to 1150 ° C. Steels 1 to 4 are example steels having a composition within the scope of the present invention. For these example steels, steels to which a decarburizing inhibitor was applied and steels to which no decarburizing inhibitor was applied were manufactured before hot rolling. did. Steels 5 to 11 are comparative steels, and all comparative steels were manufactured by applying a decarburizing inhibitor before hot rolling. Steel 5 has Cu content and Hc value, Steel 6 has Cu
Steel, Mn, Cu content of steel 7, C of steel 8,
The contents of Si and Cu, the contents of C, Si, Ni and Cu in steel 9 and the Hc value, the contents of steel 10 and steel 11 in C, Si, Mn,
The contents of Cr, Cu, N and the Hc value and γmax value are outside the scope of the present invention.

[0027]

[Table 1]

Table 2 shows the quenching temperature and quenching hardness HRC of each steel produced in the examples. Most of the steels of the present invention have a quenching hardness HRC in the range of 34.0 to 39.0 in the quenching temperature range of 950 ° C to 1150 ° C. In particular, they are manufactured by applying a decarburization inhibitor before hot rolling. All of the steels of the present invention that have been hardened have a quenching temperature of 950 ° C to 1150 ° C.
In this range, the quenching hardness HRC was in the range of 34.0-39.0. On the other hand, all the comparative steels have HRC: 3
A quenching hardness of 4.0 to 39.0 cannot be obtained in a wide quenching temperature range.

[0029]

[Table 2]

Table 3 shows the amount of backlash of motorcycle disc brakes manufactured from the steel of the present invention. The amount of backlash is measured by applying a load to one end of the disc brake 1 as shown in FIG. 1 and arranging a dial gauge 2 at the other end of the disc brake 1 as shown in FIG. The play amount was 3. As a result, the amount of play of the motorcycle disc brake manufactured by the steel of the present invention coated with the decarburization inhibitor was less than 0.1 mm in the quenching temperature range of 950 to 1150 ° C, but the decarburization was prevented. 950 to 1150 for products without coating
In the quenching temperature range of ℃, the amount of play is completely 0.
It was not less than 1 mm.

[0031]

[Table 3]

[0032]

According to the present invention, it is possible to obtain a motorcycle disc brake having excellent corrosion resistance, toughness, wear resistance and a wide quenching temperature range. Further, by applying a decarburizing inhibitor before hot rolling, decarburization during hot rolling can be prevented, and a motorcycle disc brake with a play of less than 0.1 mm can be manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a method for measuring a backlash amount.

FIG. 2 is an explanatory diagram of a method for measuring a backlash amount.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F16D 65/12 Z

Claims (3)

[Claims] 1. C, 0.030-0.060, by weight.
%, Si: 0.20 to 0.40%, Mn: 0.70 to 1.0
0%, P: 0.040% or less, S: 0.010% or less, Ni: 0.10 to 0.60%, Cr: 11.50 to 1
2.10%, Mo: 0.50% or less, Cu: 0.70 to 0.7.
90%, N: 0.025% or less, γmax = 420C-11.5Si + 7Mn + 23
Γmax defined by Ni-11.5Cr + 9Cu + 470N + 189 is less than 100, and Hc = 218C-2.6Si + 2.9Mn + 9.2N
i-4.6Cr + 3.6Cu + 138N + 75.2 The contents of the above elements are adjusted to each other so that the Hc value is in the range of 34.0 to 39.0, and the balance is F.
Steel for motorcycle disc brakes consisting of e and inevitable impurities. 2. A decarburization inhibitor is applied to the surface of the continuously cast slab before hot rolling when the slab obtained by continuously casting the molten steel of the motorcycle disc brake steel according to claim 1 is hot-rolled. Hot rolling method for steel for motorcycle disc brakes. 3. A motorcycle disc brake, characterized in that the hot-rolled steel strip for motorcycle disc brakes obtained by the method of claim 2 is punched into a predetermined disc size and the disc is quenched and heat-treated at 950 to 1150 ° C. Manufacturing method.