JP2013108114A - Brake disc material and brake disc - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a brake disc excellent in resistance to thermal cracking.SOLUTION: The brake disc material used is a steel-based material which contains ≥0.15 mass% and ≤0.30 mass% C, ≥0.25 mass% and ≤1.3 mass% Si, ≥0.3 mass% Mn, ≥0.25 mass% and ≤1.0 mass% Ni, ≥0.6 mass% and ≤1.0 mass% Cr, ≥0.4 mass% Mo, ≥0.05 mass% and ≤0.22 mass% V, and ≥0.10 mass% Al and is characterized in that, based on respective mass percentages of metals, the carbon equivalent Ceq represented by formula (1) is ≥0.60 mass% and ≤0.86 mass%, the total of Mn and Ni is 1.3 mass% or less, and the balance comprises iron and impurities. Formula (1) is Ceq (wt.%)=C+Si/24+Mn/6+Cr/5+Ni/40+Mo/4+V/14.

Description

  The present invention relates to a material for a brake disc used in a railway vehicle and the like, and a brake disc using the material.

  Disc brakes used for braking railway vehicles, automobiles, airplanes, etc., press brake pads against brake discs that rotate with axles and wheels, and convert the kinetic energy of the wheels and brake discs into thermal energy generated by friction. . Therefore, since the brake disk receives a strong frictional force on the surface while rotating at high speed, it not only has the strength and toughness generally required for structural materials for vehicles, but also has excellent wear resistance and heat crack resistance. Is required. Various steel-based materials for brake discs have been proposed in which many elements are added in order to satisfy such characteristics in a well-balanced manner.

  For example, steel for brake discs as described in Patent Document 1 can be mentioned. This material is, by mass%, C 0.1-0.6%, Si 0.01-1.2%, Mn 0.2-2.0%, Ni 0.8-3.0. %, Cr 1.3-5.0%, Mo 0.1-3.0%, V 0.005-0.5%, the balance consisting of iron and impurities, and C and The amounts of Cr, Mo, and V satisfy a predetermined relational expression.

  In addition, it is required to improve the heat cracking resistance. As such a brake disc material, C is 0.15 mass% or more, 0.30 mass% or less, Si is 0.3 mass% or more, 1.3 mass% or less, Mn is 0.3 mass% or more, Cr is 0.6% by mass or more, 1.0% by mass or less, Mo is 0.4% by mass or more, Al is 0.15% by mass or less, and the carbon equivalent Ceq is 0.60% by mass or more. Patent Document 2 describes a brake disc material that is 0.86% by mass or less, the sum of Mn and Ni is 1.3% by mass or less, and the balance is iron and impurities.

  The characteristics of the material according to Patent Document 2 are based on the fact that a material containing iron as a main component may cause a transformation to a martensite structure by repeated heating and cooling. The martensite structure is higher in hardness than a structure that can be obtained by casting a steel-based material by a general method, but is brittle. Therefore, a portion where martensitic transformation has occurred is likely to crack. Also, since the brake disc is concentrated and heated at the point where it slides against the brake pad, the transformation occurs in a part near the surface of the disc, causing local plastic deformation and cracking. . Therefore, if the martensitic transformation is likely to occur, the thermal cracking property is low. Therefore, the heat cracking resistance is enhanced by finding the component ratio and other conditions that are unlikely to cause transformation to the martensite structure.

JP-A-2005-36312 JP 2010-270392 A

  By the way, especially for brake discs exposed to high temperatures at high speeds, not only wear resistance and heat cracking resistance, but also resistance to heat deformation that is difficult to deform even in a high temperature environment, it is desirable that the brake disc is not easily brittle even in a low temperature environment such as a cold region. It is. Therefore, an object of the present invention is to obtain a brake disk having not only the heat cracking resistance achieved with the material of Patent Document 2, but also high heat deformation resistance and impact resistance.

  The present invention contains a small amount of V or a small amount of V and Nb in the steel-based material described in Patent Document 2 having C, Si, Mn, Ni, Cr, and Mo as the material of the brake disk. By doing so, the above problems were solved.

Specifically, the range of steel materials that can be used is 0.15 mass% or more and 0.30 mass% or less of C, 0.25 mass% or more and 1.3 mass% or less of Si, and 0.3 Mn or less. % By mass, Ni: 0.25% by mass or more, 1.0% by mass or less, Cr: 0.6% by mass or more, 1.0% by mass or less, Mo: 0.4% by mass or more, From the value of the mass content percentage of each element, the carbon equivalent Ceq represented by the following formula (1) is 0.60 mass% or more and 0.86 mass% or less, and the total of Mn and Ni is 1.3 mass%. And
Further, V is contained in an amount of 0.05% by mass or more and 0.22% by mass or less, and Nb is less than an inevitable impurity amount, or V is contained in an amount of 0.05% by mass or more and 0.09% by mass or less, and Nb is 0.06% by mass. % Or less, and the remainder comprising iron and impurities exhibits properties suitable as a steel material according to the present invention.

  Ceq (wt%) = C + Si / 24 + Mn / 6 + Cr / 5 + Ni / 40 + Mo / 4 + V / 14 (1)

  This invention is based on the fact that, as with the alloy material described in Patent Document 2, a material containing iron as a main component may cause transformation to a martensite structure by repeated quenching of heating and cooling. In addition, in this invention, by further containing Ni and V in the above range, or by further containing Nb, the heat distortion resistance and impact resistance exceeding those of the alloy described in Patent Document 2 are exhibited. succeeded in. However, the range in which the performance is improved by the addition of V and Nb is extremely limited, and conversely, if it is excessive, the performance tends to deteriorate. Therefore, the content is adjusted to a limited range over other elements. There must be.

  In addition, the material concerning this invention may contain aluminum in 0.2 mass% or less in addition to an unavoidable impurity and said element. The amount of inevitable impurities varies depending on the element, but in most cases, it is less than 0.05% by mass, preferably less than 0.01% by mass.

  The carbon equivalent Ceq is defined by JIS G 0203 (5103), and is a value obtained by converting the degree of influence that mainly improves the hardness and strength of contained elements other than carbon into the degree of influence of carbon. In general, the higher the steel, the higher the hardness of the steel.

  The hardness of the brake disc material requires at least 300 HV or more. Preferably it is 330HV or more.

  By using the brake disc made of the alloy according to the present invention, the generation of martensite structure in the sliding portion of the brake disc is suppressed even in the heating and cooling environment generated in the environment where the disc brake is placed, and the sliding portion of the brake disc It is possible to prevent the occurrence of thermal cracks and damage caused by them. At the same time, the heat distortion resistance of the disc brake can be improved and it can be made difficult to become brittle even in a low temperature environment.

Schematic showing an example of a brake disc Example high temperature tensile test results graph Dimensional drawing of specimen Perspective view of thermal shock tester Cross section of thermal shock tester Graph showing temperature change of test piece during thermal shock test Photo as reference example for thermal shock test

Embodiments of the present invention will be specifically described below.
The material used for the brake disc according to the present invention is mainly made of iron, and specifically has the following configuration. In addition, all the following ratios are mass%, and are not the value at the time of compounding the material before casting but the value in the brake disc itself obtained after casting.

  The above brake disk material needs to contain 0.15% by mass or more of C. If it is less than 0.15% by mass, the hardness and the tensile strength are insufficient, and there is a high possibility that the mechanical properties required for the brake disk cannot be ensured. On the other hand, the C content needs to be 0.30% by mass or less. When C exceeds 0.30% by mass, a decrease in heat cracking resistance cannot be ignored. In order to more surely avoid a decrease in heat cracking resistance, the content is preferably 0.25% by mass or less. In addition to this, there is a content rate limitation in consideration of elements involved in the carbon equivalent Ceq.

  The brake disk material described above needs to contain 0.25% by mass or more of Si. Si has a deoxidizing effect, and has an effect of suppressing casting defects by depriving oxygen that is a cause of casting defects during casting. If it is less than 0.25% by mass, this effect is insufficient, and the possibility of casting defects cannot be ignored. In order to ensure the deoxidation effect more reliably, it is preferably 0.5% by mass or more. On the other hand, even if the content exceeds 1.3% by mass, the contribution to the deoxidation effect for preventing casting defects is hardly improved, and the elongation may decrease. Need to be. Preferably it is 1.0 mass% or less from the point of suppression of elongation reduction. In addition to this, there is a content rate restriction in consideration of elements involved in the carbon equivalent Ceq described later.

  The above brake disk material needs to contain 0.3% by mass or more of Mn. Mn also has a deoxidizing effect, and has the effect of more thoroughly preventing the casting defects by using it together with Si. If Mn is less than 0.3% by mass, the possibility of casting defects cannot be ignored. On the other hand, if it exceeds 1.0% by mass, there is a risk of excessive hardenability, so that it is preferably 1.0% by mass or less. Moreover, about the total amount with Ni mentioned later, there exists a virtual upper limit (1.3 mass%) from the point of provision of heat cracking property.

  The above brake disk material needs to contain Ni in an amount of 0.25% by mass or more. Ni has the effect of suppressing embrittlement at low temperatures. If it is less than 0.25% by mass, it tends to be brittle. On the other hand, it is preferable that it is 1.0 mass% or less. If it exceeds 1.0% by mass, excessive quenching occurs and embrittlement occurs. These embrittlements are particularly problematic at low temperatures. Moreover, about the total amount with Mn mentioned later, it has further limitation conditions in this range from the point of provision of heat cracking property.

  The above brake disk material needs to contain 0.6 mass% or more of Cr. When Cr is less than 0.6% by mass, the oxidation resistance becomes insufficient. On the other hand, if Cr exceeds 1.0% by mass, the hardenability increases, that is, martensite transformation is likely to occur, and the heat cracking resistance is greatly reduced. Need to be.

  The above brake disk material needs to contain 0.4% by mass or more of Mo. Mo also contributes to hardness and tensile strength, and if it is less than 0.4% by mass, these mechanical properties become insufficient. On the other hand, even if the content of Mo is increased, there is little effect of increasing the hardenability like Cr, so that the upper limit for maintaining the heat cracking resistance is not particularly specified by itself. However, since it has an effect similar to that of carbon, there is a practical upper limit as a term of the carbon equivalent. Moreover, even if it contains more than 1.5 mass% actually, the improvement effect on hardness and tensile strength will hardly appear and it will be useless, Therefore It is good that it is 1.5 mass% or less.

  The above brake disc material needs to contain V of 0.05% by mass or more. V mainly contributes to heat distortion resistance, and can be made hard to become brittle at a low temperature by addition of an appropriate amount. If it is less than 0.05% by mass, the effect is limited. However, the range of making V brittle at a low temperature by the addition of V is limited, and if V is excessive, it tends to become brittle. For this reason, content of V needs to be 0.22 mass% or less.

  In addition, when the V content is in the range of 0.05% by mass or more and 0.09% by mass or less, by adding Nb, the high temperature deformation resistance is further improved and the embrittlement is difficult to occur at a low temperature. be able to. On the contrary, if Nb is added in an environment where V is too much, it tends to become brittle. On the other hand, if V is too small, the interlocking effect with Nb may not be exhibited. The amount of Nb to be contained is preferably 0.06% by mass or less. This is because if Nb is too much, it tends to become brittle. On the contrary, when the value of V is excessive from the above range and the Nb content is more than the amount of inevitable impurities, embrittlement at low temperature cannot be ignored. The amount not more than this inevitable impurity amount is preferably less than 0.02% by mass and more preferably less than 0.01% by mass.

  The brake disc material can contain 0.02% by mass or more of Al. Al also has a deoxidizing effect and exerts its effect in a relatively small amount compared to Si. If the Al content is less than 0.02% by mass, the deoxidation effect is insufficient and the possibility of casting defects cannot be ignored. However, this can also be solved by adjusting the amount of Si or Mn contributing to the deoxidation effect or by devising a manufacturing method. For this reason, even if it does not contain Al, the requirements as a material used for this invention are satisfied. On the other hand, if Al, which is a typical element, increases too much, it may lead to a decrease in toughness, and the contribution to the deoxidation effect that prevents casting defects is almost improved even if the content exceeds 0.10% by mass. Therefore, the content is preferably 0.10% by mass or less.

  Next, among the elements constituting the brake disk material described above, the elements other than Al and Fe must satisfy the relationship in which the carbon equivalent Ceq represented by the following formula (1) is 0.60% by mass or more. There is. This carbon equivalent is a value obtained by converting the influence of elements other than carbon on the properties into the influence of carbon. If this is less than 0.60% by mass, the hardness of 300 HV required for a brake disk cannot be obtained. Moreover, it is preferable that it is 0.70 mass% or more because hardness can be stably obtained. On the other hand, it is necessary to satisfy the relationship that Ceq is 0.86% by mass or less. If this exceeds 0.86% by mass, the heat cracking resistance will be too low, as in the case where the carbon content is too high.

  Ceq (wt%) = C + Si / 24 + Mn / 6 + Cr / 5 + Ni / 40 + Mo / 4 + V / 14 (1)

  Furthermore, the total amount of Mn and Ni contained in the above brake disc material needs to be 1.3% by mass or less. Mn and Ni contribute together as to whether or not the content rate is increased and the thermal crack resistance is impaired. It is thought that these chemical properties are similar in terms of participation in heat cracking resistance.

  The elements contained in the above-mentioned brake disk material are those in which iron occupies the main component other than the above-mentioned C, Si, Mn, Ni, Cr, Mo, V, and Nb. In addition to this, it is allowed that an element which becomes an impurity which is not intentionally included but can be mixed in is contained within a range not impairing the performance required by the brake disc material according to the present invention. This impurity is left in the crucible or mold that adjusts the molten metal for casting, the elements contained in the molten metal used so far, or when scrap is made into materials from the viewpoint of environmental protection Elements that cannot be excluded.

  The content of the element serving as the impurity is preferably as follows. P is preferably 0.05% by mass or less. When it exceeds 0.05 mass%, it becomes a fracture starting point and embrittles at a low temperature. S is also preferably 0.05% by mass or less. When it exceeds 0.05 mass%, it becomes a fracture starting point and becomes brittle at a high temperature. In addition, the content of other elements in addition to Cu and Ti is preferably 0.05% by mass or less. This is because the inclusion of these elements may cause an unexpected action and hinder the properties of the brake disc material according to the present invention. In addition, the inclusion of these elements leads to unnecessary cost increase. Note that the content of these elements as impurities is preferably as small as possible, and is preferably 0% by mass.

  The content of the above element is not the compounding ratio of the elements that are the raw materials, but the content of the product that is actually obtained after casting. The specific measurement method is based on a spark emission analysis method (JIS G 1253).

  When a brake disc for a disc brake is manufactured by a general casting method using the brake disc material having the above structure, it has high heat cracking resistance, excellent mechanical properties such as hardness and tensile strength, and improved heat distortion resistance. And can be made hard to become brittle at low temperatures.

  FIG. 1 is a conceptual diagram of a brake disc for a railway vehicle that is an example of the brake disc. The brake disk 1 is used in a state where an axle 4 of a railway vehicle is fitted in a central mounting hole 2 and bolted to a wheel 5 by a plurality of bolt holes 3 around the mounting hole 2. Thereby, the brake disc 1 and the wheel 5 rotate coaxially. When the brake is operated, the brake pad 6 is pressed against the surface of the brake disc 1 opposite to the wheel 5. At this time, the brake pad 6 does not rotate and the brake disk 1 continues to rotate for a while until it stops, so that the brake pad 6 slides on the annular portion 7 on the brake disk 1. As a result, high heat is generated in the annular portion 7. After stopping by the brake, the heating stops, it is slowly cooled by air, and when the railway vehicle starts to move, it is cooled by air. The burden of receiving repeated heating and cooling and the concentration of heating especially in the annular portion 7 of the brake disc 1 can provide an environment in which thermal cracks are likely to occur. By using it, it is possible to exhibit high heat crack resistance even in such an environment.

  Further, deformation due to high heat generated around the annular portion 7 can be suppressed by using the brake disc material according to the present invention, since the strength in the high temperature range can be improved.

  Furthermore, in cold districts and the like, the brake disc may become brittle due to low temperatures and be destroyed during use, but by using the brake disc material according to the present invention, it can be made difficult to become brittle at low temperatures.

Hereinafter, an example in which the present invention is specifically examined by way of examples will be described.
<High temperature tensile test>
Each cast steel material whose components measured by spark emission analysis (JIS G 1253) after casting had the composition shown in Table 1 below was heated to 1600 ° C., then cooled to 1550 ° C., and 30 mm × 30 mm × 100 mm. After casting in a sand mold and holding at 950 ° C. for 3 hours, the furnace is once cooled to room temperature, heated to 980 ° C. and held for 3 hours, then cooled to room temperature and further heated to 650 ° C. After holding for 3 hours, heat treatment was performed to air-cool to room temperature to produce a molten test piece. In addition, less than 0.01 mass% is less than a detection limit.

  A high temperature tensile test was performed at 700 ° C. in accordance with JIS G 0567. The evaluation results are shown in Table 1. In the evaluation, a reference example not containing V and Nb was used as a reference, and the evaluation was made based on whether or not the properties of the respective test examples containing V and Nb were improved. Moreover, about Examples 1-4 which do not have a reference example and Nb, the graph which took the content rate of V on the X-axis and the yield strength measured on the Y-axis is shown in FIG. The yield strength increased to a linear function with respect to the V amount.

<Thermal shock test>
Each cast steel material whose components measured by the spark emission analysis method (JIS G 1253) after casting have the composition shown in Table 2 below are melted in the same manner as in the high temperature tensile test, and a cylindrical type having notches shown in FIG. A test piece (height 20 mm, φ25 ± 0.2) was prepared by machining. The side surface has a width of 6 mm and a depth of 3 mm, and a pair of opposed grooves are provided in the vertical direction. A hole having a depth of 5 mm and φ5 ± 0.2 is formed in the center of the upper bottom surface. The arithmetic mean roughness of the side is about 2.0.

  FIG. 4 shows a schematic diagram of a thermal shock tester 20 that rapidly heats and cools this cylindrical specimen, and FIG. 5 shows a cross-sectional view thereof. The main body 21 has a cylindrical shape with an open upper end, and the test piece 11 can be accommodated therein. A high frequency coil 31 is wound around the main body 21, and the stored test piece 11 can be heated to 1000 ° C. in 3 seconds by the high frequency coil 31.

  The upper end ring portion of the main body 21 has holes that lead to the inside at equal intervals. Half of these are air holes 22 for supplying air, and the rest are cold water holes 23 for supplying cooling water. These are provided alternately. The air supply pipe 24 and the cold water supply pipe 25 are connected to each other, and a large number of air outlets 27 and cold water outlets 28 are formed in the inner peripheral surface of the main body 21 through a hole extending inside the main body 21. And the test piece 11 can be cooled by supplying air and cold water. The supplied water is discharged through the discharge pipe 29.

  With this thermal shock tester, temperature changes consisting of rapid heating and rapid cooling as shown in FIG. 6 were repeated. This temperature change is first performed by rapid heating in which the temperature is raised to 1000 ° C. in about 3 seconds by heating from the high frequency coil 31. Next, heating by the high frequency coil 31 is stopped, cold water is supplied from the cold water outlet 28 for 20 seconds, and after cooling water is supplied, air cooling is performed for 30 seconds. Thereby, the test piece 11 heated to high temperature is rapidly cooled. The thermal cycle of repeating such rapid heating and rapid cooling was repeated 50 times, and the presence or absence of cracks was confirmed by visual inspection and penetration testing.

  Specifically, the crack was evaluated by observing the progress of the crack when the above heat cycle was repeated 10 times, 20 times, 30 times, and 50 times. FIG. 7 shows four types of reference examples based on rough criteria for the determination. In the photograph, the portion where the surface is dyed is a portion where a dye for penetrant flaw detection is attached, and indicates that the test piece is flawed. First, examples described as “x” are shown in Reference Examples 1 and 2. In Reference Example 1, scratches extend in the circumferential direction from the deepest notch at the time of 20 thermal cycles, and a line showing a clear crack is generated at 50 thermal cycles. In Reference Example 2, before reaching the thermal cycle up to 50 times, the crack was connected 20 times and the peripheral portion was peeled off. Like these, the test piece by which the clear crack was recognized by 50 heat cycles is evaluated as "x". Next, Reference Example 3 shows an example that evaluates as “Δ”. At the end of 50 thermal cycles, fine cracks are observed from the deepest part of the notch. Thus, the test piece in which the fine crack of less than 2 mm produced after 50 progresses is evaluated as "(triangle | delta)". Further, in the example evaluated as “◯”, as in Reference Example 4, at the end of 50 thermal cycles, neither a crack nor a dye for penetrant flaw detection is observed. In addition, the penetration flaw detection test was performed according to JIS Z 2343.

<Hardness criteria>
The hardness test was performed at a load of 100 g in accordance with Vickers hardness test method JIS Z 2244. When the value of HV0.10 exceeds the value 300 required as a brake disk and whether or not the value of the reference example exceeds 346.0, the hardness of the reference example is any of Examples 2 to 6. The result was excellent.

<Low temperature impact resistance test>
In order to test the degree of embrittlement at a low temperature, each cast steel material whose components measured by spark emission analysis (JIS G 1253) after casting had the composition shown in Table 3 below was melted in the same manner as in the high temperature tensile test. A V-notch test piece of a JIS Z 2202 Charpy impact test piece was machined and subjected to a V-notch Charpy impact test (−20 ° C.) described in JIS Z 2242. This temperature assumes the lower limit of the general operating temperature of the brake disc. Table 3 shows the value of the absorbed energy E at −20 ° C. and the relative evaluation which is the evaluation with respect to the reference example. In Examples 1 and 7, the amount of V was increased with a composition close to that of the reference example. In particular, Example 1 shows a significant improvement in absorbed energy E. However, when the amount of V increases further, the value of the absorbed energy E is not uniform but tends to decrease (Examples 2, 3, and 4), and V is excessive (0.43%) until Comparative Example 1. Then, the performance was worse than the reference example.

  Further, in the group containing Nb (Examples 5, 8 to 10), the absorbed energy E tends to be slightly reduced as compared with an example in which V is the same amount and Nb is not contained, but Nb is an appropriate amount. If so, the decrease is within an acceptable range. However, when V increases, the decrease in absorbed energy E due to the addition of Nb will be lower than the reference example (Comparative Example 2). Moreover, even if there is too much Nb, it will still fall below a reference example (comparative example 3).

  On the other hand, the amount of absorbed energy E also fluctuates due to fluctuations in the amount of Ni. turn into.

DESCRIPTION OF SYMBOLS 1 Brake disc 2 Mounting hole 3 Bolt hole 4 Axle 5 Wheel 6 Brake pad 7 Ring-shaped part 11 Test piece 20 Thermal shock test machine 21 Main body 22 Air hole 23 Cold water hole 24 Air supply pipe 25 Cold water supply pipe 27 Air outlet 28 Cold water Spout 29 Discharge pipe 31 High frequency coil

Claims (4)

C is 0.15 mass% or more, 0.30 mass% or less, Si is 0.25 mass% or more, 1.3 mass% or less, Mn is 0.3 mass% or more, Ni is 0.25 mass% or more, 1.0 mass% or less, Cr 0.6 mass% or more, 1.0 mass% or less, Mo 0.4 mass% or more, and Al 0.10 mass% or less,
And V contains 0.05 mass% or more and 0.22 mass% or less and the content of Nb is less than the amount of inevitable impurities, or V contains 0.05 mass% or more and 0.09 mass% or less and Nb is 0.00. Containing not more than 06% by mass,
From the value of the mass content percentage of each element, the carbon equivalent Ceq represented by the following formula (1) is 0.60 mass% or more and 0.86 mass% or less, and the total of Mn and Ni is 1.3 mass%. A brake disc material consisting of iron and impurities.
Ceq (wt%) = C + Si / 24 + Mn / 6 + Cr / 5 + Ni / 40 + Mo / 4 + V / 14 (1)   The brake disc material according to claim 1, which contains 0.02 mass% or more of Al.   C is 0.25% by mass or less, Si is 0.5% by mass or more and 1.0% by mass or less, Mn is 1.0% by mass or less, and Mo is 1.5% by mass or less. The brake disc material according to claim 1, wherein Ceq is 0.70% by mass or more.   A brake disk comprising the brake disk material according to any one of claims 1 to 3.