JPH0830208B2 - Vehicle brake disc material manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a brake member, and more particularly to a method for manufacturing a vehicle brake disc material.

B. SUMMARY OF THE INVENTION The present invention relates to a method for manufacturing a vehicle brake disc material, comprising: an austempered bainite base flake graphite cast iron brake disc material obtained by subjecting pearlite matrix flake graphite cast iron to a base material and subjecting it to isothermal transformation heat treatment. Is manufactured to provide a brake disc for vehicles with excellent friction performance, material strength, and heat damage resistance.

C. Conventional technology JRS No. 12209 is the brake disc material used for the disc brakes of vehicles traveling at around 100 km / h.
Based on -1, tensile strength is 274 MPa or more and hardness HB is 183-269
Perlite base flake graphite cast iron with a maximum speed of 210k
Brake disc materials used in high-bundle vehicles with m / h are 1.0-2.0 wt% Ni-0.3-0.6 with a tensile strength of 245 MPa or more and a hardness HB of 210-280 based on JRS No. 12209-2. % By weight, Cr-0.3 to 0.5% by weight, Mo low alloy perrant matrix flake graphite cast iron (hereinafter referred to as NCM cast iron).

The characteristic of the brake disc material made of NCM cast iron is
Stable with an appropriate average friction coefficient so that the braking force satisfying the regulation can be obtained during either the normal stop braking (brake initial speed 35 km / h) or the emergency stop braking (brake initial speed maximum 210 km / h). It has a high instantaneous friction coefficient and a low wear rate, and it has a high frequency (during normal stop braking).
Also, it is superior to general-purpose perlite matrix flake graphite cast iron in terms of resistance to thermal cracks generated on the sliding surface of the brake disc even under a frictional condition of high load (during emergency stop braking).

NCM cast iron increases the shape by increasing the shape of flake graphite in the structure that has the effect of absorbing or relaxing the thermal stress, while reducing the strength due to it by the alloying of Ni, Cr, Mo Complemented by strengthening, JISF in terms of strength
Although it is a C25 grade cast iron material, it has good thermal conductivity and is extremely excellent against mechanical damage due to heat load.

D. Problems to be Solved by the Invention In recent years, a maximum speed of 240 km / h has been realized, and under the present circumstances where higher speeds are aimed at, new problems are emerging in the brake disc material of NCM cast iron. In other words, when an extremely heavy load is applied to the brake disc of such a high-speed vehicle in an emergency, NCM cast iron does not have sufficient resistance to thermal cracking of the sliding surface.

For this reason, there is an idea to suppress the occurrence of thermal cracks by using a material having higher strength and higher toughness, and a forged steel brake disc material has recently been developed and put into practical use. However, the reason why cast iron has been originally used as a brake material instead of steel is that it has excellent friction performance evaluated by a friction coefficient and a low wear characteristic that stably maintain an appropriate value during braking. Yes, this is because free graphite is included in the material constituents of cast iron. It has been pointed out that the forged steel brake disc material has a reduced friction performance, especially instability of the friction coefficient during braking, and that the permanent deformation of the material in use becomes larger than that of cast iron.

In such a situation where higher speed of the vehicle is aimed, the friction disc, the material strength, the heat damage resistance, etc. are balanced against each other as the brake disc material used for the vehicle. -There is a strong demand for the development of a high-performance, low-priced cast iron-based material that is lower in price than steel-based composite brake disc materials and does not cause an increase in unsprung weight by design.

Therefore, it is an object of the present invention to provide a method for manufacturing a vehicle brake disc material that solves such a problem.

E. Means for Solving Problems First, 2.8 to 3.7% by weight of C and 1.3 to 2.2% by weight of Si
0.2 to 1.0 wt% of Mn, 0.2 wt% or less of P, 0.1
Consists of less than S by weight and the rest of Fe, and has a tensile strength of 250.
A pearlite matrix flake graphite cast iron base material having an elongation at 330 MPa of 3% or more, a hardness HB of 180 to 260, and a U-notch Charpy impact absorption energy of 2.5 J or more is melted and then cast.

Then, this is done at a temperature of 1143-1391K (870-920 ° C)
~ 90 min treatment to austenite, then 573 ~ 6
Austempering is performed at a temperature of 48 K (300 to 375 ℃) for 60 to 90 minutes, and then air-cooled to obtain an austempered bainite base flake graphite cast iron brake disc material for high speed vehicles.

In this case, the cast iron structure has a state in which large A-shaped flake graphite is distributed in the matrix in which a small amount of retained austenite is mixed in the needle-shaped lower bainite, and the tensile strength is 350 to 600 MPa.
The elongation is 5% or more, the hardness HB is 210 to 340, and the U-notch Charpy impact absorption energy is 3.0J or more. Further, in the present invention, since the austempering treatment for the pearlite matrix flake graphite cast iron as the base material more reliably extends to the thick portion of the brake disc, 0.6% is contained in the chemical composition of the base material after casting.
~ 0.7 wt% Cu or Ni and 0.2-0.4 wt% Mo or
The composition may include V in an amount of 0.1 to 0.2% by weight.

F. Action The superiority and inferiority of the friction performance of brake disc materials for high-speed vehicles is evaluated by the suitability value of the average friction coefficient and the stability of the instantaneous friction coefficient μ during braking and the wear resistance of the disc and the mating material. According to the experience from the past, the condition of the cast iron structure of the brake disc material that should be provided for this is as follows.
It is said that it is ideal to distribute a large number and large number of A-shaped flake graphite in a matrix structure having high strength and high toughness that is more than fine perlite, and the above bainite matrix flake graphite cast iron brake disc material is This condition is met. The brake disc material is required to have sufficient strength to guarantee the centrifugal stress caused by the high-speed rotation of the brake disc and the thermal stress generated by the thermal load during braking. Austempering of graphite graphite cast iron does not significantly change the graphite morphology, that is, while effectively maintaining the effect of improving the friction performance of graphite and the action of mitigating thermal stress during braking, it is possible to bainite the base material to form a brake disc. The overall strength and toughness can be significantly improved.

It is difficult to obtain the above effects exerted by the brake disc material of the present invention by other methods. For example, even if the above-mentioned cast iron structure that satisfies the friction performance is obtained by adjusting the chemical composition by adjusting the amounts of C and Si and the addition of alloying elements during melting, on the other hand, by strengthening the matrix structure to the extent of fine pearlite, the brake disc It is difficult to raise the overall strength and toughness to a level compatible with modern braking conditions.

G. Example In order to demonstrate the above-mentioned effect of the austempered bainite matrix flake graphite cast iron as a brake disc material for high-speed vehicles, first, an austempered bainite matrix flake graphite cast iron with high strength and high toughness was firstly tested. A suitable range of chemical composition and austempering condition of pearlite base flake graphite cast iron as a base material for obtaining the austempered bainite base of high strength and high toughness obtained in the range was found in Examples. A high-load constant-speed friction test was performed on the flake graphite cast iron test material to confirm the friction performance as a brake disk material for high-speed vehicles.

Explaining the experiment, Table 1 shows the chemical composition of the three types of flake graphite cast iron that were melted for this experiment, and their mechanical properties correspond to the as cast on the horizontal axis in Fig. 1. Each value was obtained in the position. That is, this 3
The flake graphite cast iron of the type is a cast iron with a strength level equivalent to FC15, FC25, FC35 for machine structure, and the graphite morphology changes from coarse flake to slightly larger A flake graphite, Shows the change from coarse pearlite ground where ferrite is precipitated around graphite to fine pearlite ground.

Next, use the above three types of flake graphite cast iron at 1173K (900 ° C)
At 60 ° C for 60 minutes to austenite,
5 ℃), 648K (375 ℃) and 698K (425 ℃) were austempered for 60 minutes. As for these mechanical properties, respective values were obtained at positions corresponding to respective austempering treatment temperatures on the horizontal axis of FIG. The structures of the three types of flake graphite cast iron after the austempering treatment showed no significant change in the graphite morphology from that before the treatment. All bases are 598K
In the treatments at (325 ℃) and 648K (375 ℃), the retained austenite was mixed in the acicular lower bainite, and the acicular structure of the barnite became coarse and the retained austenite amount increased at higher treatment temperature. At 698K (425 ℃), a large amount of retained austenite was mixed in the feathery upper bainite. Therefore, as shown in Fig. 1, the strength is 598K.
It reached its maximum at (325 ° C) and its toughness reached its highest at 648K (375 ° C).

Here, the chemical composition of the base material and the appropriate range of the austempering treatment conditions for obtaining the austempered bainite matrix flake graphite cast iron of re-strength and high toughness are obtained by considering the recent braking conditions. Regarding the range of chemical composition of the material, the chemical composition corresponding to FC25 to FC35 is suitable from the experimental results, and this is 2.8 to 3.7% by weight of C, 1.3 to
2.2 wt% Si, 0.2 to 1.0 wt% Mn, 0.2 wt% or less P,
A pearlite-based flake graphite cast iron obtained in a composition range of 0.1% by weight or less of S and the balance of Fe, with mechanical properties having a tensile strength of 250 to 330 MPa, an elongation of 3% or more, and a hardness HB of 180 to 26.
0, U Notch Charpy impact absorption energy is 2.5 J or more. It is clear from Fig. 1 that cast iron with a chemical composition equivalent to FC15 or lower cannot guarantee high strength and high toughness even after the subsequent austempering treatment.

Next, regarding the range of austempering conditions, if the balance between strength and toughness is balanced from the experimental results, 1143 to 1193K (8
It is suitable to treat at 70-920 ° C.) for 60-90 minutes to austenite, then austemperate at 573-648 K (300-375 ° C.) for 60-90 minutes, and then air cool. As a result, the pearlite-based flake graphite cast iron selected above has a structure in which large A-type flake graphite is distributed in the matrix in which acicular lower bainite and a slight amount of retained austenite are mixed, and the tensile strength is 350 It is possible to obtain a bainite matrix flake graphite cast iron having a high strength and a high toughness, an elongation of 5% or more, a hardness HB of 210 to 340, a U-notch Charpy impact absorption energy of 3.0 J or more at 600 MPa.

Here, the heating conditions for austenitizing are 1143 to 1193K (870
The reason why the temperature is set to 60 to 90 minutes at 920 ° C.) is that the heating condition of this degree is austenite for the austenitization as the first step of the austempering of the pearlite matrix flake graphite cast iron of the base material in the above-mentioned composition range. This is because it is economically known that the optimum carbon content and its uniformity are.
Further, it is clear from FIG. 1 that an austempering temperature of 400 ° C. or higher is not preferable because it reduces both strength and toughness of the bainite matrix flake graphite cast iron.

Furthermore, in order to more easily and surely perform the austempering treatment on the thick portion of the brake disc as a cast product of the base material, 0.6 to 0.7% by weight of Cu or Ni and 0.2-0.4 wt% Mo or 0.1-0.2
In some cases, V may be contained in a weight percentage. These contents as alloy elements move the pearlite transformation region in the CCT transformation diagram to the right, so that the austempering can be performed more easily and reliably. It is empirically known that segregation of these alloy elements does not adversely affect the content of the alloy elements.

In the examples, asc of three types of flake graphite cast iron in Table 1 was used.
ast materials and austenite treated with them at 1173K (900 ℃) for 60 minutes, then 598K (325 ℃), 648 (3
A high-load constant-speed friction test was conducted on a total of 12 types of specimens, which were austempered at 75 ° C), 698K (425 ° C) for 60 minutes. In this test, the test material has a diameter of 200 mm,
A disk-shaped test piece with a thickness of 12 mm (hereinafter referred to as a disk),
The opposite material was copper-based sintered alloy lining (30 x 30 mm) for high-speed vehicles. The test conditions are three stages of friction speed 7,14,21m / s,
The lining pressing force was 0.5 MPa, the friction time for one time was 60 seconds, and the test was repeated 25 times at each friction speed. The average friction coefficient, the instantaneous friction coefficient μ, the wear rate of the disk and the lining,
The temperature rise of the disk and lining was measured. In the above constant-speed friction test, the friction load applied to the unit area of the test material for 60 seconds at a friction speed of 21 m / s is comparable to the load during emergency stop braking of a high-speed vehicle at a speed of 240 km / h. It is appropriate to evaluate the friction performance by this test.

FC25 and FC35 598K (325 ℃), 648K
(375 ℃) Austempered bainite-based flake graphite cast iron is a material whose high strength and high toughness are guaranteed in the above-mentioned experiments.
15 598K (325 ℃), 648K (375 ℃), 698K (425 ℃) austempered material and FC25, FC35 austempered material at 698K (425 ℃) are all required strength levels Although it was out of the range, it was used as a comparative material of friction performance.

FIG. 2 shows the results of a constant-speed friction test on three types of as-cast graphite cast iron and a 375 ° C. austempered material using them as a base material. In FIG. 2, the austempering treatment effect on the friction performance (average friction coefficient, wear rate of the disc and the lining) and the selection of the base material are intended. Therefore, examples of other austempering treatment materials at 325 ° C. and 425 ° C. (Test result) is omitted because it is complicated.

First, when looking at Fig. 2 for each friction velocity, the as cast material and the austempered material show symmetrical fluctuations. Of these, the austempered materials of FC25 and FC35 show the values at high speed. It is high and the variation is small, and the austempering treatment effect is clear. On the other hand, when looking at the wear rate of the disc and lining, the difference in the wear rate of the as cast material is large depending on the material, and the wear rate decreases as the strength increases. In the austempered material, the difference between the materials of the base material is small, and the wear rate increases as the friction changes from low speed to high speed, but compared with the as cast material (it decreases at high speed) despite the increase at high speed. As a result, no significant increase in the wear rate was observed, and the effect of the austempering treatment was also apparent in the wear rate. In terms of wear rate, the disk wear rate of FC15 austempered material is excellent, but considering the low strength and large fluctuations, FC25, FC3
5 austempered material is selected.

Next, Fig. 3 shows FC25 among three types of flake graphite cast iron, its as cast material and its base material 325,375,4.
It is the result of the constant velocity friction test about the 25 ° C austempered material. In FIG. 3, the purpose is to select the austempering temperature for friction performance. Regarding Fig. 3, when looking at each friction speed, the values at 325,375 ° C austempered material at high speed are high, and the fluctuations are small. On the other hand, when the wear rate of the disk and lining is overviewed, the wear rate of the 325,375 ℃ austempered material does not increase remarkably as compared with the as cast material, although it increases as the speed increases. The 425 ° C austempered material is generally low, and the wear rate increases remarkably at high speed. From the above, 325 ° C or 375 ° C is selected as the highest austempering temperature for friction performance.

From the constant-velocity friction test of the above examples, the friction performance is clearly improved by the austempering treatment, FC25 and FC35 are further selected as the base material, and 325 and 375 ° C. are selected as the austempering treatment temperature. So
It was confirmed that the high-strength, high-toughness austempered bainite matrix flake graphite cast iron based on the chemical composition of the base material and the austempered treatment conditions obtained from the above-mentioned experiment also shows excellent results in terms of friction performance. It will be.

By the way, when the austempered bainite matrix flake graphite cast iron brake disc material for high speed vehicles according to the present invention is repeatedly subjected to high load friction, the bainite matrix structure gradually collapses due to frictional heat, resulting in friction performance, material strength and heat resistance. There is a risk of damaging effects. In the constant-velocity friction test in the examples, the test was repeated 25 times at a friction speed of 21 m / s (25 tests each at 7 m / s and 14 m / s before that). However, from the hardness measurement on the disk cross section after the test and the microstructure test, the area where the vanant matrix structure was granulated or changed to the fine pearlite structure was about 4 mm from the friction surface. Therefore, the material change is limited to the vicinity of the friction surface, and the strength and toughness of the entire disc are maintained. In the case of a brake disc with a large heat capacity, this problem will be alleviated further.

On the other hand, regarding the effect of changes in the material of the friction surface on the friction performance, the structure near the friction surface (about 1 mm) has changed to a tempered troostite structure, which is a normal pearlite matrix flake graphite cast iron. Even in the case of the brake disc material, the above-mentioned change in structure gives rather good results in terms of friction performance, as compared with the fact that pearlite granulation occurs near the friction surface. In FIGS. 2 and 3, the friction performance of the austempered material is superior to that of the as cast material of pearlite base, which demonstrates this. Originally, bainite base is a structure composed of bainitic ferrite and retained austenite. Therefore, under high-speed and high-load friction conditions, the bainite structure itself cannot be said to be remarkably excellent in friction performance. It can be inferred from the experience that the friction surface of single structure of ferrite or austenite was not particularly excellent in friction performance.

H. Effects of the Invention According to the present invention as described above, austempered bainite matrix flake graphite cast iron is conventional pearlite matrix flake graphite cast iron and Ni-Cr-Mo low alloy pearlite matrix flake graphite cast iron. In comparison, it has excellent friction performance represented by the friction coefficient and the wear rate of the disc and lining, and the material strength and toughness are the bases composed of the lower bainite retained austenite by the austempering treatment. It has the highest strength and toughness of the flake graphite cast iron material, and its balance is well maintained. Further, since large A-shaped flake graphite is distributed in this tough matrix, it is also excellent in heat damage resistance. Therefore, it has effective characteristics as a brake disc material for high-speed vehicles.

In addition, 0.6 to 0.7 for the base material of pearlite base flake graphite cast iron.
The austempering treatment reliably extends to the thickened parts of the brake discs, since copper or nickel by weight and 0.2 to 0.4% by weight molybdenum or 0.1 to 0.2% by weight vanadium were included as alloying elements.

[Brief description of drawings]

Fig. 1 shows bainite-based flake graphite obtained by subjecting pearlite-based flake graphite cast iron, which has three types of base materials, to a cast material and pearlite-based flake graphite cast iron, which is the base material, at various austempering temperatures. Fig. 2 is a graph showing the mechanical properties of cast iron austempered material. Fig. 2 shows the as acst material of pearlite-based flake graphite cast iron with three types of base materials and their 3
Fig. 3 is a graph showing the results of constant-speed friction test for 75 ° C austempered material.
It is a graph which shows the result of the constant speed friction test about the 325,375,425 degreeC austempering process material which used it as a base material.

Continuation of the front page (72) Inventor Tomoji Ashikawa Kugenuma, Fujisawa-shi, Kanagawa 1-2-21 Fujigaya (72) Inventor Tatsuo Suzuki 21-1, Tennoyama, Terazu-cho, Nishio-shi, Aichi (56) Reference JP-A-61-64850 ( JP, A)

Claims (2)

[Claims] 1. A pearlite matrix flake graphite comprising 2.8 to 3.7% by weight of carbon, 1.3 to 2.2% by weight of silicon, 0.2 to 1.0% by weight of manganese, 0.2% by weight or less of phosphorus, and 0.1% by weight or less of sulfur and the balance being iron. The cast iron base material is cast after being melted, and the perlite matrix flake graphite cast iron is treated at a temperature of 1143 to 1193K (870 to 920 ° C) for 60 to 90 minutes to be austenitized.
Austempered at a temperature of 3 to 648 K (300 to 375 ° C) for 60 to 90 minutes, and then air-cooled to produce an austempered bainite matrix flake graphite cast iron, and the austempered bainite matrix flake graphite cast iron. The method of manufacturing a brake disc material for vehicles, characterized in that the structure of (1) is arranged in a state in which the A-shaped flake graphite is distributed in a matrix in which retained austenite is mixed in needle-shaped lower bainite. 2. A pearlite matrix flake graphite comprising 2.8 to 3.7% by weight of carbon, 1.3 to 2.2% by weight of silicon, 0.2 to 1.0% by weight of manganese, 0.2% by weight or less of phosphorus and 0.1% by weight or less of sulfur and the balance being iron. Cast iron base material is cast after melting,
Perlite matrix flake graphite cast iron containing ~ 0.7 wt% copper or nickel and 0.2-0.4 wt% molybdenum or 0.1-0.2 wt% vanadium as alloying elements 1143 ~
After austenitizing by treating at 1193K (870-920 ℃) for 60-90 minutes, austempering at 573-648K (300-375 ℃) for 60-90 minutes, and then air cooling A state in which A-type flake graphite is distributed in a base in which retained austenite is mixed with needle-shaped lower bainite, by making austenite-treated bainite-base flake graphite cast iron A method for manufacturing a vehicle brake disc material, comprising: