JP2007247027A - HIGH HEAT RESISTANT Cr-CONTAINING STEEL FOR BRAKE DISC - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide high heat resistant Cr-containing steel for brake disc by which occurrence of defects, such as edge cracks and scabs, in a hot rolling step can be effectively prevented. <P>SOLUTION: The high heat resistant Cr-containing steel for brake disc has a composition which is composed of, by mass, 0.01 to 0.10% C, 0.3 to 2.5% Mn, ≤0.5% Si, ≤0.04% P, ≤0.008% S, 10.5 to 14.5% Cr, ≤0.10% Al, 0.030 to 0.080% N, 0.05 to 0.60% Nb, 0.1 to 1.5% Ni, further ≤0.0050% B within the range satisfying a relation of B/N≥0.030, further 0.05 to 2.5%, in total, of one or more elements selected from Cu, V, Mo, W, Ta and Ti, and the balance Fe with inevitable impurities. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used for a rotor part (brake sliding part) of a brake disk of a motorcycle, a bicycle or the like, has a suitable quenching hardness and tempering softening resistance, and has a low carbon martensite-based high heat resistance Cr content. In particular, the present invention relates to a high heat-resistant Cr-containing steel for brake disks that is excellent in hot workability.

  Rust resistance and heat resistance are required for the rotor part of a brake disc of a motorcycle or bicycle. In particular, regarding heat resistance, the temperature is repeatedly raised to a temperature range exceeding 500 ° C. due to friction between the pad and the disk at the time of brake braking. A characteristic that does not easily cause wear is required.

  As a material satisfying such characteristics, SUS410-based low carbon martensitic stainless steel containing 12 to 13 mass% of Cr has been conventionally used and is usually used in a quenched state. In the hardened state, the hardness of HRC (Rockwell hardness C scale) in the range of 30 to 45 is appropriate, and the rotor part does not soften even when subjected to tempering at 500 ° C. for 1 hour. Ingredients are designed to maintain the same level of hardness.

Furthermore, in recent years, in response to demands for improving the performance of brakes and reducing the weight of brake discs, high heat resistant steels having higher heat resistance have been developed and used. For example, as disclosed in Patent Documents 1 to 4, elements such as C, N, Nb, V, Cu, Ti, and Mo that increase temper softening resistance against heat generation during braking are added, or the amount added is increased. Thus, high heat resistant steels have been developed that can maintain HRC hardness of 30 to 45 even after quenching and after tempering at 550 to 650 ° C. for 1 hour.
JP 2001-220654 A JP 2002-121656 A Japanese Patent Laid-Open No. 2002-146489 JP 2004-346425 A

  However, as disclosed in Patent Documents 1 to 4, there is a problem that the high heat-resistant steel containing a large amount of elements that increase the temper softening resistance is extremely poor in hot workability. For this reason, in a manufacturing process such as hot rolling, defects such as ear cracks and nicks are likely to occur in the steel sheet, resulting in a decrease in manufacturing yield, and due to the defects, the disk is in use (during traveling). May break. Among them, high heat resistant steel with high N containing 0.030 mass% or more of N can stably obtain heat resistance exceeding 550 ° C. and is excellent in rust resistance, but is hot in the temperature range of 900 to 1100 ° C. It has a problem that ductility is extremely low and defects are likely to occur.

  Then, the objective of this invention is providing the high heat resistant Cr containing steel for brake discs which can prevent effectively generation | occurrence | production of defects, such as an ear crack and a baldness, in a hot rolling process.

  The high heat resistant low carbon martensitic Cr-containing steel targeted by the present invention is usually hot rolled in a temperature range of 700 to 1200 ° C. to be a steel plate. In view of this, the inventors first investigated the relationship between the cross-section reduction rate (RA) and the occurrence of defects in a hot tensile test in this temperature range. As a result, it was found that a material having an RA of less than 40% in the temperature range of 900 to 1100 ° C. has a very high rate of occurrence of ear cracks and baldness regardless of the hot rolling method.

  Therefore, as a result of studying the relationship between the component composition and hot ductility, if an appropriate amount of B is added according to the amount of N contained, hot ductility can be improved without deteriorating heat resistance and rust resistance. As a result, it has been found that the occurrence of defects during hot rolling can be prevented, and the present invention has been completed.

  That is, the present invention is C: 0.01-0.10 mass%, Mn: 0.3-2.5 mass%, Si: 0.5 mass% or less, P: 0.04 mass% or less, S: 0.008 mass% Hereinafter, Cr: 10.5 to 14.5 mass%, Al: 0.10 mass% or less, N: 0.030 to 0.080 mass%, Nb: 0.05 to 0.60 mass% Ni: 0.1 to 1. 5 mass%, further B: 0.0050 mass% or less and satisfying B / N ≧ 0.030, further containing one or more selected from Cu, V, Mo, W, Ta and Ti Is a high heat-resistant Cr-containing steel for brake discs that contains 0.05 to 2.5 mass% in total, with the balance being Fe and inevitable impurities.

  The high heat-resistant Cr-containing steel of the present invention is characterized in that the composition of Cu and Ni is Cu: more than 0.30 mass% to 2.5 mass%, Ni: 0.5 × Cumass% or more.

  ADVANTAGE OF THE INVENTION According to this invention, hot workability of the high heat-resistant Cr containing steel used for the rotor part of brake discs, such as a motorcycle and a bicycle, can be improved, and generation | occurrence | production of a defect can be prevented. Therefore, according to the present invention, the steel can be stably manufactured with a high yield, and cracks can be prevented from being generated during the running of the rotor portion, which can contribute to an improvement in safety.

An experiment that triggered the development of the present invention will be described.
C: 0.04 mass%, Mn: 1.5 mass%, N: 0.05 mass%, Nb: 0.15 mass%, Cr: 12 mass%, low carbon martensitic stainless steel having a composition substantially consisting of Fe. In this example, a steel having a B / N ratio changed by changing the addition amount of B was melted, and a hot tensile test was performed between 900 and 1100 ° C., which is a hot rolling temperature range, for this steel. The relationship between N ratio and cross-sectional area reduction rate (RA) was examined.

  FIG. 1 shows the results of the above test. When B is not added, the cross-sectional reduction rate RA decreases to a concave shape between 900 and 1100 ° C., and is below 40% in the vicinity of 1000 ° C. However, when B is added to this to increase B / N, RA increases and exceeds 40%. However, if B is added excessively, RA is decreased. That is, it can be seen that in order to improve RA, it is necessary to control B / N within an appropriate range. Therefore, the inventors completed the present invention by further studying the appropriate composition range of other components in addition to the above knowledge.

Next, the high heat-resistant Cr-containing steel for the brake disc of the present invention will be described.
The high heat-resistant Cr-containing steel targeted by the present invention has sufficient rust resistance as a material for brake disks, and is finished in a rotor (usually in a quenched state, but is subjected to strain relief annealing and slight tempering) The component was designed so that the same hardness could be maintained even after tempering treatment for 1 hour at a temperature of 550 ° C. or higher. It is a low carbon martensitic Cr-containing steel having high heat resistance.

The high heat-resistant Cr-containing steel of the present invention having the above characteristics is C: 0.01-0.10 mass%, Mn: 0.3-2.5 mass%, Si: 0.5 mass% or less, P: 0.04 mass% Hereinafter, S: 0.008 mass% or less, Cr: 10.5 to 14.5 mass%, Al: 0.10 mass% or less, N: 0.030 to 0.080 mass%, Nb: 0.05 to 0.60 mass% , Ni: 0.1 to 1.5 mass%, and B is added in an amount of 0.0050 mass% or less and B / N ≧ 0.030 is added. , Mo, W, Ta and Ti are added in a total amount of 0.05 to 2.5 mass%.
Hereinafter, the reasons for limiting the composition range of each component will be described.

C: 0.01-0.10 mass%
C is an important element that determines the hardness after quenching and tempering of steel, and in order to ensure an appropriate hardness range, it is necessary to contain 0.01 mass% or more. However, if the content exceeds 0.10%, a large number of coarse carbides are generated, which becomes a starting point of rusting, and rust resistance is lowered. Therefore, the range of C is set to 0.01 to 0.10 mass%. In addition, from the viewpoint of further improving the rust resistance, C is preferably less than 0.050 mass%.

Si: 0.5 mass% or less Si is an element added as a deoxidizing agent, and it is desirable to contain 0.05 mass% or more. However, if added in excess of 0.5 mass%, a sufficient martensite phase is not formed after quenching, leading to a decrease in hardness and a decrease in toughness after quenching.

Mn: 0.3 to 2.5 mass%
Mn is an element useful for improving the hardenability by suppressing the formation of a ferrite phase at a high temperature and stably controlling the hardness after quenching within a predetermined range. , Addition of 0.3 mass% or more is necessary. However, if added over 2.5 mass%, the workability and rust resistance are lowered, so 0.3 to 2.5 mass%. In addition, from the viewpoint of improving hardenability, 0.5 mass% or more is preferable, and from the viewpoint of improving workability and rust resistance, 2.0 mass% or less is preferable.

P: 0.04 mass% or less P is desirably reduced as much as possible in order to reduce the hot workability and toughness of steel. However, the extreme reduction of P leads to an increase in steelmaking costs, so in the present invention, it is made 0.04 mass% or less. Preferably, it is 0.03 mass% or less.

S: 0.008 mass% or less S is desirably reduced as much as possible in order to reduce the hot workability and rust resistance of steel. However, the extreme reduction of S leads to an increase in steelmaking cost, so it is set to 0.008 mass% or less. Preferably, it is 0.003 mass% or less, More preferably, it is 0.001 mass% or less.

Cr: 10.5 to 14.5 mass%
Cr is a main element for improving the rust resistance of steel, and in order to ensure sufficient rust resistance as a disc brake material, addition of 10.5 mass% or more is necessary. On the other hand, if the content exceeds 14.5 mass%, a sufficient amount of martensite phase is not generated, and appropriate hardness cannot be secured after quenching, and workability and toughness are reduced. Therefore, in this invention, Cr is taken as the range of 10.5-14.5 mass%. In addition, in order to improve rust resistance more, 11.5 mass% or more is preferable, and in order to improve workability and toughness more, less than 13.5 mass% is preferable.

Al: 0.10 mass% or less Al, like Si, is usually added as a deoxidizer, but if it is contained excessively, hard inclusions and precipitates increase, and defects such as surface marks are generated. In order to cause this, in the present invention, it is set to 0.10 mass% or less. When Si is also added as a deoxidizer, it is preferable to reduce the amount of Al added in order to suppress the increase of inclusions and precipitates, and Si should be 0.05 mass% or more and less than 0.10 mass%. For example, if Al is 0.03 mass% or less and Si is 0.10 mass% or more, Al is preferably 0.01 mass% or less.

N: 0.030-0.080 mass%
N, like C, is an important element that determines the hardness after quenching and after tempering, and in particular, the effect of forming fine nitrides and improving the temper softening resistance in the temperature range of 550 to 700 ° C. Is big. In order to maintain an appropriate hardness range, addition of 0.030 mass% or more is necessary. On the other hand, excessive addition causes a decrease in hot workability, so the upper limit is made 0.080 mass%.

Nb: 0.05-0.60 mass%
Nb forms a precipitate with N and has a great effect of improving the temper softening resistance at 550 to 700 ° C., and thus is one of the essential elements in the high heat resistant steel of the present invention. In order to obtain this effect, addition of 0.05 mass% or more is necessary. However, if added excessively, the toughness decreases, so the upper limit is made 0.60%.

Ni: 0.1 to 1.5 mass%
Ni is an element that improves the corrosion resistance of steel. In order to obtain this effect, it is necessary to add 0.1 mass% or more. However, if added excessively, a long time is required for soft annealing after hot rolling, and the productivity is lowered, so the upper limit is made 1.5 mass%.

B: 0.030 × N to 0.0050 mass%
The high heat-resistant Cr-containing steel of the present invention is characterized in that hot workability is improved by adding an appropriate amount of B in addition to the above component composition. B accumulates at grain boundaries and phase boundaries to increase their strength, while suppressing the accumulation of harmful S and P, and further suppressing the coarsening of precipitates, thereby increasing hot ductility. There is an effect to increase. In particular, when B / N is 0.030 or more in relation to N, the effect of improving hot ductility is obtained, and when B / N is 0.035 or more, the effect becomes remarkable. It is possible to reduce the occurrence of cracks and baldness. When B / N exceeds 0.050, the effect is further increased, and the occurrence of ear cracks and baldness in hot rolling is almost eliminated. However, when B / N is 0.100 or more, or the amount of B exceeds 0.0045 mass%, the effect is slightly reduced. Further, when the amount of B exceeds 0.0050 mass%, On the contrary, the ductility decreases. This is thought to be because the amount of BN deposited becomes excessive and the grain boundary strength is lowered. Therefore, in the present invention, B needs to be added in the range of B: 0.0050 mass% or less and B / N ≧ 0.030. B / N is preferably 0.035 or more and less than 0.100, more preferably more than 0.050 and less than 0.100.

0.05 to 2.5 mass% in total of one or more selected from Cu, V, Mo, W, Ta and Ti
Cu, V, Mo, W, Ta and Ti are all useful elements for enhancing the hardenability and ensuring the hardness after quenching and tempering stably, and one or more of them are 0.05 or more in total. It is necessary to add. However, if added excessively, the hardness is increased or decreased more than necessary, which causes the hardness to deviate from the appropriate range. Therefore, the total amount is 2.5 mass% or less.

Cu: more than 0.30 mass% to 2.5 mass%, Ni: 0.5 × Cumass% or more In addition, when adding Cu among the above elements, Ni should be added in combination according to the addition amount. Is desirable. This is because Cu forms a low melting point rich Cu phase in the steel slab after casting, which may significantly reduce hot workability, but Ni increases the melting point of these Cu rich phases, This is because there is an effect of suppressing a decrease in hot workability. In particular, if the amount of Cu exceeds 0.30 mass%, the amount of coarse Cu-rich phase increases and the hot workability deteriorates significantly. Is desirable.

  In the high heat-resistant Cr-containing steel of the present invention, the balance other than the above components is composed of Fe and inevitable impurities. However, within a range that does not impair the effects of the present invention, from the viewpoint of improving heat resistance, rust resistance and manufacturability, a total of 0.5 mass% of Co, Ca, Mg, Hf, Y, Zr, etc. You may add in the following ranges.

  No. having various component compositions shown in Table 1. 1 to 19 steel was melted in a high-frequency melting furnace to produce an ingot having a thickness of 170 mm. The ingot was heated at 1200 ° C. for 1 hour and hot-rolled to obtain a hot rolled sheet having a thickness of 3 to 6 mm. A board was used. About this hot-rolled sheet, the length of a crack generated at the end of the steel sheet was measured, and from this result, the hot workability was D, the 5 to 10 mm was C, the less than 5 mm was B, and further less than 3 mm. Rated A.

  In addition, from the above ingot, a test piece having a parallel part diameter of 10 mmφ was sampled separately for the hot tensile test, and a hot tensile test was performed using a Gleeble tester to evaluate the hot ductility. . In the hot tensile test, the test piece was heated to 1200 ° C. for 30 minutes, cooled to a predetermined temperature at 50 ° C./minute, held for 10 seconds, and then pulled at a speed of 100 mm / second (strain rate of 10 / Sec) under the condition of applying deformation. The test temperature was 900 ° C. to 1100 ° C. at intervals of 50 ° C., and the cross-section reduction rate was measured at each temperature, and the average value of three samples excluding the maximum value and the minimum value was obtained. As a result, the hot ductility is D if the minimum value of the cross-section reduction rate RA (minimum value of three average values at each temperature) is less than 40%, and the hot ductility is C, 45 if it is less than 45%. When it was ˜50%, the hot ductility was evaluated as B, and when it exceeded 50%, the hot ductility was evaluated as A.

  The evaluation results of the hot workability (defect evaluation) and the hot tensile test (hot ductility) are shown together in Table 1. From Table 1, No. which is suitable for the component composition of the present invention. It can be seen that the steels Nos. 1 to 12 are excellent in hot workability because the defect evaluation and the hot ductility evaluation are A or B. On the other hand, No. which does not satisfy the component composition of the present invention. It can be seen that the steels Nos. 13 to 19 have a defect evaluation and a ductility evaluation of C or D, and are inferior in hot workability.

  The hot-rolled sheet obtained by hot rolling is annealed for 4 to 20 hours at a temperature of 700 to 850 ° C., softened, and then heated at 950 to 1250 ° C. for 1 to 10 minutes. Then, it was quenched by air cooling, and the hardness was measured. As a result, it was confirmed that all the steel sheets were within an appropriate range of 30 to 45 by HRC.

It is a graph which shows the influence which ratio (B / N) of B and N has on the cross-section reduction rate RA of a hot tensile test.

Claims (2)

C: 0.01-0.10 mass%,
Si: 0.5 mass% or less,
Mn: 0.3 to 2.5 mass%,
P: 0.04 mass% or less,
S: 0.008 mass% or less,
Cr: 10.5 to 14.5 mass%,
Al: 0.10 mass% or less,
N: 0.030-0.080 mass%,
Nb: 0.05-0.60 mass%,
Ni: 0.1 to 1.5 mass%,
B: 0.0050 mass% or less and satisfying B / N ≧ 0.030,
Further, for brake discs containing 0.05 to 2.5 mass% in total of one or more selected from Cu, V, Mo, W, Ta and Ti, with the balance being Fe and unavoidable impurities High heat resistant Cr-containing steel. 2. The high heat-resistant Cr-containing steel according to claim 1, wherein the composition of Cu and Ni is Cu: more than 0.30 mass% to 2.5 mass% and Ni: 0.5 × Cumass% or more.

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