JPS60218452A - Alloy cast iron for brake block - Google Patents

Abstract

PURPOSE:To develop an alloy cast iron for brake block used in brake apparatus and having stable high friction coefft., wear resistance and superior strength, toughness by containing specified quantities of P, Cu, etc. into graphite flake cast iron. CONSTITUTION:The alloy cast iron of following composition is used as brake block raw material used for brake apparatus of railroad vehicle. The cast iron containing >=one among 0.02-0.10% Mg, or 0.3-2.0% Cr, 0.2-1.0% Mo, 0.1- 0.5% Ti singularly or in compounded state with Mg to graphite flake cast iron of a composition composed of 2.5-3.5% C, 1.0-3.0% Si, 0.5-2.0% Mn, 0.2- 1.5% P, <0.15% S, 3.0-8.0% Cu is used. Graphite is changed to green caterpillar or spheroidal shape from flaky shape by Mg addition, and the alloy cast iron for brake block having improved rupture strength and toughness is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new alloy cast iron for brake shoes that has excellent properties as a material for brake shoes used in brake devices for railway vehicles. The objective is to create an alloy cast iron for brake shoes that has an excellent braking effect, that is, a sufficiently high coefficient of friction and wear resistance that can be stably obtained, and is also excellent in both strength and toughness.

Conventionally, as a material for railway brake shoes for the above purpose, 0.5 to 2.0% of P is added to flake graphite cast iron containing some alloying elements.
So-called high phosphorus cast iron brake shoes containing 5% additive have been widely used. It is a well-known fact that this brake shoe has generally good friction coefficient and wear resistance, and therefore has excellent braking characteristics.

However, on the other hand, high phosphorous cast iron brake shoes containing a large amount of P have poor mechanical properties and have a disadvantage in that they are prone to damage and chipping due to their hard and brittle structures. For this reason, high phosphorus cast iron brake shoes made of materials containing a large amount of P require complicated man-hours to manufacture, such as casting a thin steel plate or lattice-shaped steel mesh wire on the back for reinforcement. Even so, the current situation is that sufficient reinforcing strength cannot be obtained, and that the products are used without being reliable enough to prevent breakage and chipping during use, and are covered by on-site maintenance.

In view of the above-mentioned current situation, the present invention is an alloy cast iron for brake shoes that eliminates the above-mentioned conventional drawbacks, and is characterized by a basic composition of C; 2.5 to 3.5% in weight percentage.
, 5iB1.0-3.0%, Mn; 0.5-2.0%,
PiO, 2-1.5%, S; <0.15%, Cu; 3
．． It is an alloy cast iron consisting of 0 to 8.0%, the balance being Fe and impurities.

The role of each element constituting the cast iron alloy of the present invention and the reasons for their limitations will be explained below.

First, C, Si, Mn, and Fe in cast iron are components for maintaining strength and toughness. The roles of the above components in the Fe-C system are as follows.

Si is effective in stabilizing graphite and improving castability, and also contributes to structural stability at high temperatures, but if it is too large, it promotes ferrite formation, that is, a decrease in pearlite, resulting in a decrease in strength. The content was set to 1.0 to 3.0%.

Mn is effective in increasing the amount of pearlite in the structure and imparting strength and toughness, but if it is too large, it forms eutectic hair mentite, which increases the hardness of the wheel tread when used as a brake shoe. 0.5 to 2 as it may cause abnormal wear and heat damage, etc.
．． It was limited to 0%.

Addition of P has the following effect on the above composition. That is,
It is a component that provides a high wear coefficient and low wear amount during braking,
If this is increased too much, the friction coefficient becomes unstable and good braking conditions cannot be obtained. Moreover, as already mentioned, the larger the amount added, the more brittle it becomes and the lower the mechanical strength. For the above reasons, the P content is limited to 0.2 to 1.5%.

S is a harmful element that significantly embrittles the material and is unrelated to braking performance, but if it becomes too low, cast iron tends to turn white, so it was limited to 0.15% or less to ensure the lowest value.

The balance being Fe and C is a typical component of high phosphorus cast iron for brake shoes, and it is generally commercially available with a thin steel plate backing etc. arranged thereon. However, as already mentioned, this alone is still fragile and unreliable.

In order to improve the above-mentioned conventional drawbacks, the present invention aims to improve the above-mentioned conventional drawbacks by adding 3.
It is added in an amount of about 0 to 8.0%, and the effects of this will be described in detail below.

Already announced Fe-C-P and Fe-C-P
The following can be said by referring to the theoretical views regarding the -Cu system. That is, in general, when P is added to Fe, about 1.7% of P is dissolved in Fe, and the tensile strength and yield point increase, but
It is said that impact value and toughness are significantly reduced, and furthermore, Fe −
In the C-P ternary system, the solid solubility limit of P is considered to be reduced to about 1%. Further, since the precipitation rate of P exceeding the solid solubility limit is slow, after other substances are precipitated, it segregates exclusively at grain boundaries as intermetallic compounds such as Fe3 PSFe2 P so as to fill the gaps of K. For this reason, toughness is further impaired.

On the other hand, when Cu is added to the Fe, -C-P system, P
Under the condition that the amount of Cu added is large relative to the content, Cu reduces the solid solubility limit of P with respect to Fe, and Cu dissolves in solid solution. Fe
When Cu is dissolved in solid solution, the strength increases without impairing the physical properties. On the other hand, regarding the relationship between Cu and P, about 3% of Po is dissolved in Cu, and when P is dissolved in Cu, the strength of Cu decreases but the elongation increases, that is, the toughness increases.

For the above reasons, it is expected that Cu in the Fe-C-Cu-P system will work exclusively to improve toughness without reducing strength, and the fact that this fully meets expectations will be described later with examples. do.

Furthermore, in the present invention, by increasing the amount of Cu added, it is expected that the thermal conductivity will be improved compared to the above-mentioned high phosphorus cast iron. That is, the L oring shown in FIG.
According to an experiment conducted by Krause et al. on the change in electrical resistance caused by the addition of Cu to a ferroalloy containing 0.6% P, the electrical resistance of the Fe-Cu-P system containing five times as much Cu as P As shown by curve 4 in the figure, a decrease in electrical resistance or an increase in electrical conductivity is observed. From this, an increase in electrical conductivity means an improvement in the thermal conductivity coefficient, so as the amount of Cu added increases, the thermal conductivity coefficient improves, which is a favorable characteristic for a brake material.

From these points of view, the lower limit for the amount of Cu added is approximately 3.0%, with reference to the dissolved amount of 3.5% during cupola operation. In consideration of solder brittleness, care should be taken not to leave any excess Cu, and the amount of Cu melted above is 3.5%.
3 Required weight percentage of Cu required to precipitate as P4
．． 5% was added to make it 8.0%.

Further, the alloy component Crs added to the basic composition of the present invention
The roles of Mo and Ti are as follows, and each has a remarkable effect on improving characteristics in a high-speed range.

Cr increases the amount of base pearlite, promotes the formation of cementite, and provides wear resistance. In particular, chromium carbide dispersed in the structure improves braking characteristics at high speeds, maintains a high coefficient of friction, and improves wear resistance. 0.2 as it plays a major role in granting
~2.0%.

Mo is an additive component that stabilizes the structure at high temperatures and is particularly effective in preventing deterioration of mechanical properties at high temperatures.
It was decided to add 0.2 to 1.0% as necessary.

Ti makes the graphite structure denser and improves mechanical properties, and C
When used in combination with r, etc., wear resistance improves, so o, i ~ 0
．． It was set at 5%.

Furthermore, M is added to the above-mentioned Cu-added high-phosphorus cast iron, which is the basic composition of the present invention, or alloy cast iron, in which one or more of Cr, Mo, and Ti, which are elements corresponding to high-speed braking, is added to the Cu-added high-phosphorus cast iron. When added, the precipitated graphite becomes worm-like or spheroidal, which significantly increases the breaking strength and
It was confirmed that toughness etc. were improved. The Mg content at this time is 0.02 to 0.10%.

Table 1 shows a comparison of the compositions of the conventional cast iron for brake shoes and three examples of the alloy cast iron for brake shoes of the present invention.

FIG. 2 shows the metal structure of the first embodiment of the present invention, and FIG. 3 shows the metal structure of the third embodiment of the present invention.
In the case of the first example, as can be seen from the photograph, graphite is flaky, the parent structure is pearlite, and steadite is dispersed in the structure. At this time, since the Cu content was 3.0%, no single Cu was precipitated in the matrix, and all of the Cu was dissolved in the matrix. In this case, molten Cu improves toughness, wear resistance, and heat cracking resistance.

In the case of the third embodiment, since the Mg content is high, the graphite becomes spherical graphite as shown in Fig. 3, and the Mg content is high.
When the content is low, graphite becomes raw. As can be seen from the photograph, the parent structure is pearlite, and steadite, cementite, and simple Cu are further dispersed in the structure.

Steadite and cementite, which are mainly composed of Fe3P and Cu3P, have a high coefficient of friction and wear resistance, and together with the Fe base containing Cu as a solid solution, they improve toughness and conformability, and have high thermal cracking resistance and a low coefficient of friction. Contributes to stabilization.

Table 2 shows the characteristic values measured for the braking characteristics of each of the cast irons in Table 1 using a full-scale inertial braking tester and a mechanical testing device. It is shown in Table 3.

The friction coefficient and wear amount listed in Table 2 show that the alloy cast iron of the present invention has a clearly higher friction coefficient and wear amount than ordinary cast iron for brake shoes.
It exhibits low wear amount and has values almost on the same level as high phosphorus cast iron.
Furthermore, even when compared with high-phosphorus cast iron brake shoes, the bending value and deflection of the brake shoes of the present invention are larger, and are higher than those of ordinary cast iron, which has a low phosphorus content. This is clearly considered to be a result of the addition of Cu. At the same time, braking from high speed
Compared to high-phosphorus cast iron brake shoes without added alloying elements such as Cr and Mo, the friction coefficient is high, and Cr
The effect of adding Mo is clear. The effect of Mg addition is expressed as the difference in tensile strength and bending load,
Although it increases fracture resistance, it does not have a large effect on braking characteristics.

As described above, the brake shoe made of alloyed cast iron of the present invention solves the problems of a lower coefficient of friction and increased wear in high-speed ranges than conventional products, and also prevents the problem of thermal cracking during use. It has increased resistance to breakage and chipping due to breakage and elongation, and is an extremely excellent braking material that overcomes the drawbacks of conventional brake shoes.The use of the alloy of the present invention improves the safety and lifespan of vehicles. It can be increased, and its industrial value is enormous.

[Brief explanation of the drawing]

FIG. 1 is an electrical resistance graph diagram, and FIGS. 2 and 3 are magnifications of metal structures according to the first and third embodiments of the present invention at a magnification of 100.
This is a microscopic photograph. Agent: Patent attorney Yuyosuke - 1 other person Figure 1 P (%)

Claims (4)

[Claims] (1) C at 31% by weight; 2.5-3.5%; St; 1.
0~3゜0%, Mn; 0.5~2.0%, PiO, 2~
1.5%, S; 0.15% or less, Cu; 3.0-8.
Alloy cast iron for brake shoes consisting of 0% Fe and impurities. (2) C72, 5-3.5% by weight, si; 1. o~
3°0%, Mn; 0.5-2.0%, P i O,2
~1.5%, Si0.15% or less, Cu;3. Q ~8
．． 0%, the balance is Fe and impurities in alloyed cast iron
Alloy cast iron for brake shoes containing 0.02 to 0.1 θ% of i O. (3) Weight% Tec: 2.5-3.5%, St: 1.0-
3゜0%, Mn; 0.5-2.0%, P; 0.2
~1.5%, S; 0.15% or less, CuH3,0-8.
The basic composition is 0% of the content, and the weight percentage is Cr: 0.2
~2.0%, j'loH, 0.2~1.0%, Ti; 0
．． An alloy cast iron for brake shoes, to which one or more components selected from 1 to 0.5% are added, and the balance is Fe and impurities. (4) C in weight%; 2.5-3.5%, St; 1.0
~3°0%, Mn; 0.5~2.0%, P, 0.2~
1.5%, Sl, 15% or less, Cu; 3.0-8.0
% of the contained components as the basic composition, Cr in weight %; 0.2 ~
2.0%, Mo; 0.2-1.0%, Ti; 0.1-0
．． Adding one or more components selected from 5% Mg; o, o
Alloy cast iron for brake shoes containing 2 to 0.10%.