JPS62182253A - Rust resisting cast steel for disk brake rotor - Google Patents

Abstract

PURPOSE:To obtain a material quality having superior castability similar to cast iron and rust resistance similar to stainless cast steel in addition to superior wear resistance by adjusting composition and structure of rust resisting cast steel for disk brake rotor. CONSTITUTION:As disk brake rotor material for automobile, cast steel having compsn. composed of, by weight 0.5-1.5% C, 2.5-3.5% Si, <=0.7% Mn, <=0.07% P, <=0.1% S, 5.0-10.0% Cr, 8.0-15.0% Ni, 2.0-5.0% V and the balance Fe, and structure in which hard secondary carbide of <=1.5mum particle diameter and lump and round carbonitrides of V of <=1.5mum diameter are dispersed in austenite matrix is used. The titled cast steel having both castability and productivity similar to conventional gray cast iron and corrosion resistance similar to conventional stainless steel, further superior wear resistance and weak characteristic in aggressiveness to opposite material is obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to rust-resistant cast steel used for disc brake rotors, and specifically relates to disc brake rotors that are rust-resistant and have uncertain productivity. This relates to rust-resistant cast steel for industrial use.

(Prior Art) A disc brake is a friction brake that moves a vehicle by pressing disc brake pads lined with friction material on both sides of a disc brake rotor that rotates integrally with the wheels.

In addition, this disc brake has stable braking characteristics, and there is little deterioration in braking performance due to braking at high speeds or repeated braking, that is, there is little heat fade, so it is widely used for the front brakes of passenger cars and light trucks. .

By the way, gray cast iron with excellent wear resistance and manufacturability (for example, JIS standard FC20-25) has been widely used as a material for automobile disc brake rotors, and in some cases, it has been often used as a material for disc brake rotors such as JIS standard 8450. Steel materials are also used.

However, in recent years, in coastal areas and cold regions, salt-based snow melting agents have been increasingly sprayed for the purpose of preventing freezing;
Salt damage has caused the problem of semen appearing in various parts of automobiles. Disc brake rotors are no exception to this, and rust damage frequently occurs.

For this reason, aluminum disc wheels like 3A are used recently.
In the case of a vehicle that has been damaged, the rusted disc brake rotor may be visible through the wheel opening, reducing the commercial value of the vehicle.

1. Rust on the disc brake rotor can sometimes cause the disc brake rotor and the disc brake baffle to become stuck together, impeding the vehicle's ability to start.

In addition, even if rust occurs on the friction surface of the disc brake rotor with the disc brake pad, it may be possible to use it further by polishing it again.
This polishing cannot normally be performed more than once. Therefore, the occurrence of rust shortens the service life of the disc brake rotor by two.

As described above, for disc brake rotors that have high requirements for m+ rust, attempts have been made to use rust-resistant VJ steel and cast stainless steel that have immersed l11 rust resistance. However, rust-resistant cast steel and stainless steel cast steel have poor castability and productivity, and do not have sufficient wear resistance as a single disc brake rotor.

(Problems to be Solved by the Invention) The present invention has been made in view of the problems of the prior art as described above. A disc that maintains the required characteristics such as wear resistance, has castability and productivity similar to gray cast iron, which is a conventional material for Tisfu brake rotors, and has rust resistance similar to stainless steel cast steel. The purpose is to provide a rust-resistant casting w4 for brake rotors.

(Means for solving the problem) The rust-resistant cast steel for disc brake rotors of the present invention suppresses the rotation of the disc brake rotor that moves with the wheels by pressing the disc brake pad lined with friction material in the disc brake. Rust-resistant cast steel for disc brake rotor that controls single wheels, weight ratio.

C: α5 to 1.5%, Si: 5 to 55%, M
n i 0.7% or less, P i 0.1% or less, S α
1 width or less, Cr 5.0 to 1Q, 0%, Ni aO to 15.0%, and Vi 2.0 to 5.0
%, with the remainder essentially consisting of Fe, and one structure is characterized by fine secondary carbides and massive, rounded V carbonitrides dispersed in an austenite base. shall be.

In the rust-resistant cast steel for disc brake rotor of the present invention,
The structure that can be observed with a microscope consists of secondary carbides with a grain size of 1.5 μm or less and an ostenite base with a diameter of 1.5 μm.
The reason for limiting each component element used in the present invention will be explained below (hereinafter, "I" means weight it%). ).

C is effective in increasing the strength and castability of the materials of the present invention, but if it is less than 5% α, the improvement effect on these properties is not sufficient, and if it is added in excess of 1.5%, the amount of primary carbide crystallization increases. Since this increases, heat cracking resistance, impact resistance, and machinability deteriorate, the content was set at 0.5 to 1.5%.

Furthermore, although Sl is effective in improving the castability of the materials of the present invention, if it is less than 2.5%, the effect of improving the castability is not sufficient! If L exceeds 5%, the primary carbide tends to become coarse and machinability deteriorates, so it was set at 2.5 to 55%.

In addition, Mn is not only effective as a deoxidizing agent along with the above-mentioned 81, but it is also effective because it completely alleviates the negative effects of S, such as a decrease in @ property, but when added in excess, it stabilizes carbides and embrittles the material. Therefore, it was set to 1.0% or less.

Further, if P is added in an amount exceeding α1%, it becomes easy to crystallize Steadii), so Q is set at 1% or less.

In addition, S may cause the material k to become 11M.

This was set to be [11'I) or less.

In addition, Cr is effective because it improves the rust resistance of the material of the present invention, but the rust resistance improvement effect is not sufficient at 5.0 easy grooves, and when added in excess of 100, high hardness occurs. Since it forms a large amount of carbide and deteriorates mechanical workability, it is set to 0% for 5.0 to 1Q.In addition, NI is effective for making the base assembly mirror into an austenitic structure with crushed toughness. And, moreover, Cr
Although it is effective to improve rust resistance, a (1%
If it is less than 15, the effect of improving such properties is not sufficient.
．． If it is added in an amount exceeding 0%, not only will the rust resistance improvement effect commensurate with the amount added be not obtained, but also the castability will be deteriorated.

In addition, V produces carbonitrides that are rounded and blocky with a height of 1 m1 degree and are less aggressive to the mating material, thereby improving wear resistance. However, if it is less than 2%, the effect will be small, and if it exceeds 5%, the effect will not improve, and (2) the amount of carbonitride precipitation will be excessive, making the mating material easy to wear.
．． It was set to 0%.

(Function) The rust-resistant cast steel for disc brake rotors of the present invention has excellent castability and productivity comparable to gray cast iron in terms of composition, and has rust resistance comparable to conventional stainless steel cast steel. This is within the scope that can be granted. Furthermore, it was assumed that microscopic secondary carbides and massive, rounded V carbonitrides were dispersed in the austenite matrix. Therefore, the rust-resistant cast steel for disc brake rotors of the present invention has the same castability and productivity as conventional gray cast iron, and the same rust resistance as conventional stainless steel cast steel J steel. and its aggressiveness against the mating material was weak.

(Example) Examples of the rust-resistant cast steel for disc brake rotors of the present invention will be described below based on aspect (9).

Table 1 summarizes the composition of each test material of the present invention material and comparative material of rust-resistant cast steel for disc brake rotors, which were melted on a laboratory scale.

Table 1 Note that in casting each sample material having the composition shown in Table 1, atmospheric melting was performed using a 20 kg high-frequency melting furnace, and after deoxidation treatment with Fe-8i (75N amount 'ib). The hot water was tapped at 1550°C or higher and poured at 1450°C or higher.

The mold used for casting is JIS standard A.
After melting the test materials of the present invention materials ■ to ■ and comparative materials ■ to ■ using the No. No. mold, test pieces of each test material were manufactured by machining and subjected to various evaluation tests. .

First, the rust resistance evaluation test will be explained.

As a rust resistance evaluation test, 5% saline solution at 50°C was continuously sprayed on the polished surface of the test piece for 20 hours, and then dried! 4
! The evaluation was carried out by a method of repeating the humidity cycle five times over a period of 4 hours.

The amount of rust generated on each test piece is determined by removing the rust generated on the surface of the test piece, measuring the weight, dividing the weight decreased from the weight before the test by the surface area of the test piece, and calculating the amount per unit area (
The amount of weight loss (g) of C shoulder) was calculated and used as the rust occurrence area (m7/c=1) of the sample material.

FIG. 1 shows the test results of the tit rust design test conducted after this test.

As is clear from the results of the rust resistance evaluation test shown in Figure 1, all of the materials of the present invention ■~■ are less prone to rust than gray cast iron (comparison material ■), which is a conventional material for disc brake rotors. 1/20, it has extremely rust resistance, and is almost equivalent to stainless steel cast rust (JIS standard 5C8I, i.e. comparative material ■) and Niresist cast iron (comparative material ■). It is understood that it has a rust resistance of

Next, the results of the evaluation test for the tensile strength of each sample material are shown in FIG.

As is clear from the graph in Figure 8g2, the present invention materials ■～■
Both have a slightly lower tensile strength when compared to stainless steel cast steel (JIS standard SC8I, i.e. comparative material ■), but have a high tensile strength that is approximately twice as high as that of the conventional material, gray cast iron (comparative material ■). Met.

In addition, Niresist cast iron (comparative material ■), which had good viscosity resistance,
) has a lower tensile strength than the gray cast iron (comparative material ■), and is understood to be undesirable as a rust-resistant cast steel for disc brake rotors.

Next, the results of the friction test for each sample material are shown in the graph of FIG.

This test was conducted as follows.

First, cylindrical test materials each having a diameter of 100 cm were prepared using the invention materials (1) to (2) and comparative materials (2) to (2). Then, these test materials were rotated at 1 l, 1000 rp, and a 110×10 square asbestos-based pad material was pressed onto these test materials using hydraulic pressure at a surface pressure of 50 J#/crd.

The amount of wear was measured by measuring the depth of friction for the sample material, and by the loss of friction for the mating pad material.

As is clear from the graph in FIG.
Comparative material ■, in which ■ is &0% and is out of the range of the present invention, has wear resistance equivalent to the present invention materials ■ to ■, but the amount of wear of the mating pad material is excessive, and the disc brake Not suitable as rust-resistant cast steel for rotors.

Finally, the present invention material ■ and the gray cast iron test material (comparison material ■
) was used to melt a disc brake rotor for use in a small passenger car in order to carry out boundary melting tests, and no hot water failure or shrinkage cavities occurred in either case. . Sunaichi, Mizumoto, who is involved in the present invention.

Intermediate material (■) has castability comparable to gray cast iron.

In addition, when the metal composite of the invention material (■) was observed and observed using a microscope, its composition was found to be an austenite base with fine secondary carbides and massive rounded V carbonitrides, as shown in Figure 4. were dispersed.

(Effects of the Invention) The If-resistant cast steel for tisf brake rotors of the present invention has a well-balanced composition of IC, Si, Cr, N+, and Vf, and has a rounded structure with fine secondary carbides and lumps in an austenite base. A conventional stainless steel cast steel that has castability and productivity comparable to conventional gray cast iron by dispersing V-carbonitrides.

It now has rust resistance equivalent to Niresist cast iron.

Furthermore, it has twice the strength of gray cast iron, superior wear resistance than conventional materials, and is weaker than its counterpart material.

Therefore, the rust-resistant cast steel for disc brake rotors of the present invention has become suitable as a material for disc brake rotors for automobiles and the like.

[Brief explanation of drawings]

The first figure is a graph showing the results of the W# injection property evaluation test of the inventive material and the comparative material. Figure 2 is the graph showing the tensile test results of the two inventive materials and the comparative material. FIG. 4 is a graph showing the wear test results of the invention material and comparative material. FIG. 4 is a micrograph showing the metal structure of the invention material (2). ! Applicant for the license: Toyota Motor Corporation Tsu.

Claims (1)

[Claims] Rust-resistant cast steel for disc brake rotors that controls the wheels by suppressing the rotation of the disc brake rotor that moves with the wheels by pressing the disc brake pad lined with friction material, which has a weight ratio of C. 0.5 to 1.5%, Si 2.5 to 3.5%, Mn 0.7% or less, P 0.05% or less, S 0.1% or less, Cr 5.0 or 10.0%,
Ni 8.0 to 15.0% and V 2.0 to 5
．． 0%, with the remainder essentially consisting of Fe, and the structure consists of fine secondary carbides and massive, rounded V carbonitrides dispersed in an austenite base. Rust-resistant cast steel for disc brake rotors.