JPH116026A - High hardness spheroidal graphite cast iron member excellent in fatigue strength and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the high hardness spheroidal graphite cast iron member, which has high pitting resistance, a reduced deforming rate before/after heat treatment, good machinability and excellent fatigue strength, by regulating a carbon equivalent and Cu to a specified value, essentially regulating a matrix structure around graphite to a martensitic phase and a grain size of graphite to a specified value. SOLUTION: A stock martial of the spheroidal graphite cast iron, which contains <=4.53 wt.% carbon equivalent (C+1/3 Si) and <=0.25 wt.% Cu, is heated at 850-900 deg.C with holding for >=0.1 hr, successively is held at 820-850 deg.C for <=0.1 hr to be austenitized. The cast iron is oil quenched and is tempered with holding at 200-350 deg.C for >=0.25 hr. A carbon solid solution quantity of a martensitic phase is regulated to <=0.8% and a pearite quantity of a stock is <=30% by an area rate. An average grain size of the graphite is <=20μm. The fatigue strength is >=400 N/mm<2> and the hardness is >=50 HRC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-hardness spheroidal graphite cast iron member having excellent fatigue strength and a method of manufacturing the same. More specifically, the material before heat treatment is a spheroidal graphite cast iron having good machinability, and The present invention relates to a high-hardness spheroidal graphite cast iron member excellent in fatigue strength that can be formed into a near net with a low deformation rate after heat treatment and can be manufactured at low cost, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Spheroidal graphite cast iron is known as a material having improved strength and toughness by adding spheroidizing agents such as magnesium to molten cast iron to spheroidize graphite precipitated in the form of flakes. . In recent years, various studies have been made on the improvement of the matrix structure, which are being performed to further improve the toughness of the spheroidal graphite cast iron. Among the techniques for improving the toughness of spheroidal graphite cast iron by improving the base structure, austempered spheroidal graphite cast iron has been proposed as one of the effective means.

[0003] Various proposals have also been made in the improvement technology using the austempered spheroidal graphite cast iron. For example, JP-A-61-291919, JP-A-63-1669
The technology is disclosed in Japanese Patent Publication No. 28 and the like. Austempered spheroidal graphite cast iron produced by changing the heat treatment temperature has high strength, and can be applied to members requiring high strength, such as crankshafts and gears, which could be conventionally produced only by forging. Further, by using instead of steel, it is possible to achieve weight reduction and high strength. Further, austempered spheroidal graphite cast iron is disclosed in Japanese Patent No. 26029.
As in the case of the sheave material disclosed in Japanese Patent Application Laid-Open No. 07-0707, members that require wear resistance are widely used.

According to the casting method, almost any member having a complicated shape can be formed into a near net. Therefore, it is conceivable to use a cast iron member manufactured by the casting method instead of the contact member conventionally manufactured mainly by the forging method. For example, the present invention can be applied to a component formed of the above-described hardened austempered spheroidal graphite cast iron member and a member having a higher hardness than the austempered spheroidal graphite cast iron member, which transmits force while being in contact with each other. As an example of a component that transmits a force while being in contact, a component that transmits a force by rolling a ball bearing on an austempered spheroidal graphite cast iron member or the like can be given.

[0005]

However, since the hardness of austempered spheroidal graphite cast iron is at most about 47 to 48 HRC, when applied to the above-mentioned component that transmits force while making contact, it is crushed by a high hardness counterpart. And may be deformed.

Further, if a component that transmits force while being in contact is used for a long period of time, a so-called pitting phenomenon occurs in which the surface of an austempered spheroidal graphite cast iron member peels off due to rolling fatigue with a ball bearing having higher hardness. Sometimes.

Further, the austempered spheroidal graphite cast iron has a material before the austenitizing treatment in which Cu: 0.25
Since it is a pearlite containing 0.75%, Cu
Is poor in machinability as compared with ferrites not positively containing.

The present inventors have already disclosed in JP-A-08-12023.
No. 32 has proposed a method of producing a low carbon martensitic phase matrix spheroidal graphite cast iron. That is,
A spheroidal graphite cast iron material containing 0.3% by weight or more of Mn by weight and 0.5% by weight or more of Cu is heated to a temperature equal to or higher than the austenitizing temperature, and then heated to a temperature equal to or lower than the austenitizing temperature and equal to or higher than the pearlitizing temperature for a predetermined time. After that, quenching is performed, and if necessary, tempering is performed at a temperature of 400 to 600 ° C. to reduce the carbon concentration of the martensite phase to 0.8.
This is a technique for reducing the carbon content to less than 10% by weight to increase the toughness and improve the proof stress ratio.

However, Japanese Patent Application Laid-Open No. 08-12023 discloses
In order to apply the spheroidal graphite cast iron manufactured by the technique described in Japanese Patent No. 32 to a member requiring high strength and wear resistance, it is necessary to further improve pitting resistance. In addition, there is room for technical improvement to reduce the deformation ratio before and after the heat treatment and improve the machinability so that the device can be manufactured at low cost.

The problem to be solved by the present invention is that the pitting resistance is higher, the deformation rate before and after heat treatment is small,
Another object of the present invention is to provide a high-hardness spheroidal graphite cast iron member excellent in fatigue strength, which can be manufactured at low cost because of good machinability, and a method for manufacturing the same.

[0011]

Means for Solving the Problems In order to solve the above problems, the present inventors have further developed the technique disclosed in the above-mentioned JP-A-08-120332 to improve pitting resistance and reduce fatigue strength. Excellent and high hardness, and
The spheroidal graphite cast iron member for manufacturing at low cost and the manufacturing method thereof have been earnestly studied. Carbon equivalent of spheroidal graphite cast iron material (CE value = C + ／ (Si), hereinafter simply referred to as “C
E ”) within the appropriate range, reduce Cu,
Furthermore, the average particle size is reduced by refining the graphite, the spheroidal graphite cast iron material is subjected to a two-stage austenitizing treatment, and then subjected to a special heat treatment of quenching and tempering, thereby forming a matrix around the graphite. Site phase. In the resulting spheroidal graphite cast iron material, the brittleness of the martensite phase is reduced, and the fatigue strength is 400 N / mm ² or more.
Further, it has been found that the hardness is HRC50 or more, the deformation ratio before and after the heat treatment is small, and the machinability of the material can be improved, and the present invention has been reached. This spheroidal graphite cast iron material can improve pitting resistance when applied to a part that transmits force while being in contact with a material such as bearing steel having a higher hardness than the spheroidal graphite cast iron material.

That is, the high hardness spheroidal graphite cast iron member of the first invention having excellent fatigue strength has a carbon equivalent (CE value =
C + ／ (Si)): 4.53% or less and Cu: 0.
25% or less, the matrix structure around graphite is substantially a martensite phase, and the average particle size of graphite is 20 μm or less.

[0013] Further, the present invention is characterized in that the amount of carbon solid solution in the martensite phase is 0.8% or less.

[0014] Furthermore, the present invention is characterized in that the fatigue strength is 400 N / mm ² or more and the hardness is HRC 50 or more.

Next, the method for producing a high-hardness spheroidal graphite cast iron member having excellent fatigue strength according to the second aspect of the present invention uses a carbon equivalent (C
E value = C + ／ (Si)): 4.53% or less and C
u: A material having a spheroidal graphite cast iron composition containing 0.25% or less is heated to a temperature of 850 ° C. to 900 ° C. for 0.1%.
An austenitizing step of holding for more than an hour, followed by holding for more than 0.1 hour at a temperature of 820 ° C to less than 850 ° C,
(2) a subsequent oil quenching step;
A heat treatment including a tempering step of maintaining the temperature at a temperature of 00 to 350 ° C. for 0.25 hours or more.

Further, the pearlitic graphite cast iron material is characterized in that the pearlite amount is 30% or less in area ratio.

Hereinafter, the reasons for limitation of the first invention will be described. (A) CE: 4.53% or less A spheroidal graphite cast iron member that has been subjected to a two-step austenitizing treatment and then quenched and tempered to be a martensite phase has a fatigue strength exceeding CE: 4.53%. descend. However, when the CE is 4.53% or less, the fatigue strength is 400.
N / mm ² or more. Therefore CE: 4.
Not more than 53%.

(B) Cu: 0.25% or less For a member used in the martensitic phase by subjecting a spheroidal graphite cast iron material to a heat treatment, the smaller the deformation ratio before and after the heat treatment, the better. 2%. Cu: about 0.
In the range of 5% or less, the deformation ratio before and after the heat treatment increases as the Cu content increases. This is because the increase in the Cu content increases the amount of unstable pearlite in the spheroidal graphite cast iron material, and transforms the pearlite into ferrite during heating in the austenitizing process to add expansion. In the spheroidal graphite cast iron material having a Cu content of about 0.5% or less, the deformation rate before and after the heat treatment is limited to 0.1%.
The Cu content to be 2% or less is 0.3% or less. On the other hand, if Cu is contained in an amount of 1.0% or more, the pearlite becomes extremely stable, and since the ferrite transformation does not occur during heating, the deformation ratio decreases. However, since the machinability deteriorates, the cutting time increases and the manufacturing cost increases.

Still other properties required after high hardness are tensile strength and elongation. The tensile strength and elongation also tend to depend on the added amount of Cu, and it is necessary to keep the added amount of Cu low. In order to ensure the tensile strength and elongation after the heat treatment, Cu: 0.25% or less is suitable. In this case, pearlite hardly exists in the structure. In sum, the Cu content is 0.25
% Or less.

(C) The matrix structure around the graphite is substantially a martensitic phase and the average particle size of the graphite is 20 μm or less. Fatigue strength depends on the graphite particle size, and the smaller the graphite particle size, the higher the fatigue strength. As described above, when the CE value is 4.53% or less and Cu is 0.25% or less, the matrix structure around graphite is substantially a martensite phase and the average particle size of graphite is 20 μm or less. If the fatigue strength is 400 N / m
m ² or more and a spheroidal graphite cast iron having a hardness of HRC 50 or more.

(D) a fatigue strength of 400 N / mm ² or more;
Hardness HRC50 or fatigue strength 400 N / mm ² or more, if the hardness is HRC50 or more, even when in contact with a higher hardness mating parts, may be deformed are crushed is reduced. Also,
Even if used as a component that transmits force by contact for a long time, the so-called pitting phenomenon, in which the surface of the spheroidal graphite cast iron member peels due to rolling fatigue with the mating component, is less likely to occur.

(E) When the carbon solid solution amount of the martensite phase is 0.8% or less, if the carbon solid solution amount of the martensite phase is 0.8% or less, a spheroidal graphite cast iron member having excellent fatigue strength can be obtained. it can. Ordinary heat treatment such as normalizing treatment and austempering treatment on spheroidal graphite cast iron members is usually performed at a temperature of 875 to 900 ° C. However, at this temperature, the carbon solid solution amount of the obtained martensite phase is as high as 0.9 to 1.0%, and the deformation ratio exceeds 0.2% due to the increase in the carbon solid solution amount.
As described above, when the deformation rate is large, it is necessary to perform processing after heat-treating the material, and therefore, it is preferable to reduce the carbon solid solution amount of the martensite phase and to reduce the deformation rate caused by solid solution carbon. . Therefore, the carbon solid solution amount of the martensite phase is set to 0.8% or less.

Next, the reasons for limitation of the second invention will be described. (F) Two-stage austenitizing treatment: 850 ° C to 900 ° C
Austenitizing (second stage) step of heating to a temperature of 0.1 hours or more (first stage) and then holding at a temperature of 820 ° C. to less than 850 ° C. for 0.1 hours or more The quenching and tempering treatments subsequent to the two-stage austenitizing treatment step reduce the carbon concentration of the martensite phase to 0.8% by weight or less, reduce the brittleness of the martensite phase, and reduce the tensile strength. Ensuring height and elongation. Conventional 875-900
In a single-stage austenitizing treatment at a temperature of ° C., the amount of solute carbon in the obtained martensite phase is as high as 0.9 to 1.0%, and the deformation ratio is more than 0.2%. Such a large deformation rate is not suitable as a member that makes a contact movement such as a contact member. In order to reduce the deformation due to the quenching treatment, it is desirable to minimize the amount of solute carbon as much as possible while ensuring a sufficiently high quenching temperature to increase the hardness of the spheroidal graphite cast iron. Since the carbon concentration in spheroidal graphite cast iron changes depending on the treatment temperature, when performing the two-stage austenitizing treatment of the spheroidal graphite cast iron, it is very important to determine the treatment temperature. Therefore, the temperature of the first stage is 850 to 900 ° C. Also, 1
The holding time of the stage is set to 0.1 hour or more. 0.1
If it is less than the time, complete austenitization is difficult, and it is not possible to increase the hardness of the spheroidal graphite cast iron.

Next, the austenitization in the second stage is carried out at 85%.
At 0 ° C. or higher, the amount of dissolved carbon cannot be reduced sufficiently. On the other hand, when the temperature is lower than 820 ° C., ferrite transformation starts and the deformation rate increases. Therefore, the second-stage austenitizing treatment is performed at a temperature in the range of 820 ° C. or higher, which is equal to or higher than the ferrite transformation start temperature, to less than 850 ° C.
Perform for 0.1 hours or more.

(G) Oil quenching step By performing the oil quenching treatment following the two-stage austenitizing treatment, the austenite phase becomes a martensite phase, so that a spheroidal graphite cast iron having higher hardness can be obtained. In this case, since the cooling rate needs to be increased at least to some extent, the cooling is performed at 5 ° C./min or more.

(H) Tempering step: Maintained at a temperature of 150 to 350 ° C. for 0.25 hours or more. Therefore, it is necessary to alleviate the brittleness by the tempering step and secure the tensile strength and elongation. When the tempering temperature is lower than 150 ° C., the fatigue strength is 400 N / mm ² or more, and the hardness is HR.
Although it is C50 or more, the tensile strength, elongation and impact value are reduced. On the other hand, when the tempering temperature exceeds 350 ° C,
The fatigue strength decreases, the hardness becomes less than HRC50, and the tensile strength also decreases. Combining these, tempering,
The temperature is kept at 150 to 350 ° C. for 0.25 hours or more.

(I) Perlite content: 30% or less When the Cu content is 0.25% or less, the pearlite content of the spheroidal graphite cast iron material is 30% or less. In order to obtain good tensile strength and elongation, the Cu content should be kept low,
Preferably, the pearlite content is 30% or less. Since Mn is also a pearlite forming element, Mn
n: 0.3% or less is preferable.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described in detail. The spheroidal graphite cast iron material of the present invention was prepared as follows. After melting in a 100 kg high-frequency melting furnace and adjusting components, 1.0% of a 6% Mg-based spheroidizing agent containing Ca and REM (0GRC-5H manufactured by Osaka Special Alloy) is added by a sandwich method, and spheroidizing treatment is performed at 1480 ° C. Performed and poured hot water on the ladle. Ca-Si as primary inoculation in ladle while receiving hot water
(0.2% Si equivalent), then add F
e-Si (carballoy, 0.2% Si equivalent) was added into the ladle and stirred. C and Cu were melted with the composition shown in Table 1 to obtain a sand mold having a 1-inch Y block shape.
It poured at 80-1400 degreeC. After solidification, various test pieces were prepared from the Y block.

[0029]

[Table 1]

Next, each test piece was subjected to a heat treatment such as a two-stage austenitizing treatment under the following conditions. First, the spheroidal graphite cast iron materials of Example 1, Comparative Example 1 and Comparative Example 2 in Table 1 were heated at 5 ° C. /
The temperature was raised in min, and a first-stage austenitizing treatment was performed at 875 ° C. for 0.5 hour. Next, a cooling rate of 5 ° C / m
In, Example 1 was cooled to 825 ° C., and Comparative Examples 1 and 2 were cooled to 800 ° C., and subjected to a second-stage austenitizing treatment, each of which was maintained for 0.5 hour. Example 1
Since the Cu content was small and the pearlite phase was scarcely present, the austenite holding temperature in the second stage was set to 800 ° C. as in Comparative Examples 1 and 2, so that ferrite transformation started, so that the temperature was set to 825 ° C. Next, oil quenching was applied to each of Example 1, Comparative Example 1 and Comparative Example 2, and 200 to 700
Tempering was performed for 1 hour at a temperature range of ℃. The results of examining the fatigue strength, hardness, deformation rate, machinability, tensile strength, elongation, and impact value of each test piece will be described below.

(1) CE Value and Fatigue Strength A test piece having a diameter of 10 mm had a parallel portion of 8 mm, 20 mm.
mm and 30 mm were prepared with a parallel portion of 10 mm. A 10 mm diameter test piece was subjected to a fatigue test using an Ono-type rotary bending fatigue tester, and a test piece having a diameter of 20 mm and 30 mm was subjected to a Clause type rotary bending fatigue tester. FIG.
Shows the results of the CE value and the fatigue strength of the test pieces having diameters of 10 mm, 20 mm and 30 mm. From FIG.
In any of the test pieces of 0 mm, 20 mm, and 30 mm, the fatigue strength decreases as the CE value increases. Among them, a test piece having a diameter of 10 mm had a CE value of 4.53%.
Below, no decrease in fatigue strength is observed. However, as the diameter of the test piece increases, the fatigue strength decreases.
From these results, the fatigue strength becomes 400 N / mm ² or more when the CE value is 4.53% or less.

(2) Base Structure and Fatigue Strength FIG. 4 shows the results of the respective fatigue strengths of the martensite phase, the martensite mixed phase, and the ferrite phase. FIGS. 5 to 7 show metallographic micrographs of each sample in FIG. FIG. 5 shows the martensitic phase, FIG.
FIG. 7 shows a martensite mixed phase (martensite + ferrite), and FIG. 7 shows a ferrite phase partially containing pearlite. 5 to 7, each of (a) is 100 times, and (b) is 400 times.
It is twice as large. FIG. 9 shows the results of the CE value and the fatigue strength of the martensite phase, pearlite phase, and ferrite phase. 4 and 9, the martensite phase has higher fatigue strength than the pearlite phase and the ferrite phase, and has a CE value of 4.5.
If it is 3% or less, the fatigue strength becomes 400 N / mm ² or more.

(3) Average Particle Size of Graphite and Fatigue Strength FIG. 10 shows the relationship between the average particle size of each graphite and the fatigue strength when the average particle size of graphite is changed by changing the diameter of the round bar to be cast. Is shown. The CE values are all 4.53% or less. In any of the martensite, pearlite and ferrite matrix structures, the fatigue strength depends on the graphite particle size. The higher the strength, the greater the strength. The average particle size of the graphite having the highest strength martensite phase shown in FIG. 9 and having a fatigue strength of 400 N / mm ² or more is 20 μm or less.

(4) Deformation Ratio The relationship between the deformation ratio and the amount of carbon solid solution when the martensitic transformation was performed using a spheroidal graphite cast iron material containing Cu: 0.5% and changing the austenitizing temperature was investigated. . As a result, when the austenitizing temperature increases, the amount of solute carbon increases, and the deformation ratio due to martensitic transformation also increases to 0.1.
Over 2%. Particularly, the austenitizing temperature is 8
If the temperature is higher than 50 ° C., the increase is remarkable.

(5) Machinability The machinability of the spheroidal graphite cast iron material before the two-step austenitizing treatment was evaluated. A test piece for evaluating the machinability was prepared by casting a cylindrical body having an outer diameter of 150 mm, an inner diameter of 110 mm and a length of 300 mm to remove the casting surface. A cylindrical test piece was attached to a lathe, and a TiN-coated cemented carbide for cutting cast iron (S
NMA120408) using a turning tool (bite)
Cutting speed 180m / min, feed 0.2mm / rev,
Dry turning was performed with a cut of 2 mm. The cutting time at which the maximum flank wear of the turning tool (bite) reached 0.3 mm was evaluated. FIG. 11 shows the results of evaluating the machinability of each sample. From FIG. 11, it can be seen that Example 1 containing almost no Cu (C
u: 0.04%) has a cutting time of about 77 minutes when the maximum flank wear of the turning tool (bite) reaches 0.3 mm. On the other hand, Cu of Comparative Example 1: 0.5%
About 11 minutes for the test piece containing Cu of Comparative Example 2: 1.0%
It takes about 7 minutes for the containing test piece. This result is shown in Example 1.
It can be said that the machinability is about 7 times and 11 times better than the materials of Comparative Examples 1 and 2.

(6) Tempering temperature The following shows the results of determining the relationship between the tempering temperature and each characteristic. The tempering time was all set to one hour.
FIG. 12 shows the results of the tempering temperature and the fatigue strength. From this result, the tempering temperature at which the fatigue strength is 400 N / mm ² or more is in a wide range of about 150 to 600 ° C. FIG. 13 shows the results of the tempering temperature and the hardness. From this result, the tempering temperature at which the hardness is 50 or more HRC is 3
50 ° C. or less. FIG. 14 shows the results of the tempering temperature and the tensile strength. From this result, the tempering temperature having excellent tensile strength is in the range of 200 to 400 ° C. Furthermore,
FIG. 15 shows the results of tempering temperature and elongation. From this result, the elongation increases as the tempering temperature increases. FIG. 16 shows the results of the tempering temperature and the impact value. From this result, the impact value increases as the tempering temperature increases.

In summary, the fatigue strength is 400 N /
mm ² or more, hardness is HRC 50 or more, and in consideration of tensile strength, elongation and impact value, tempering is 200 to 3
It is preferable to carry out at a temperature time of 50 ° C.

(Embodiment 2) Embodiment 2 in which a raw material having the same composition as in Embodiment 1 was subjected to two-stage austenitization.
And Comparative Example 3 subjected to ordinary one-stage austenitizing treatment
Table 2 summarizes the results. In Example 2, as shown in the heat treatment diagram shown in FIG. 3, the first stage of austenitization at 875 ° C. for 0.5 hour and the second stage of austenitization at 825 ° C. for 0.5 hour, followed by oil After quenching, tempering was performed at 280 ° C. for 0.5 hour. On the other hand, in Comparative Example 3, austenitization was performed at 875 ° C. for 1 hour, followed by oil quenching, and tempering at 280 ° C. for 0.5 hour. Table 2 shows the results of determining the characteristics of each sample.

[0039]

[Table 2]

FIGS. 1 and 2 show metallographic micrographs of Example 2 and Comparative Example 3, respectively. Each of (a) is magnified 400 times and (b) is magnified 5000 times. As can be seen from FIGS. 1 and 2, both Example 2 and Comparative Example 3 are lenticular martensite phases having a midrib. However, Example 2 in which the two-step austenitizing treatment was performed had a finer martensite structure than Comparative Example 3 in which the one-step austenitizing treatment was performed. From Table 2, Example 2 has a tensile strength of 1750 N / mm ² , an elongation of 0.9%, an impact value of 6.5 J / cm ² , and a tensile strength, an elongation and an impact as compared with Comparative Example 3. Both values are large.

[0041]

Since the present invention is configured as described above, it has excellent effects as described below. In the first invention, CE: 4.53% or less, Cu: 0.25% or less, a matrix structure around graphite is substantially a martensite phase, and an average particle size of graphite is 20 μm or less, preferably a martensite phase. Has a carbon solid solution amount of 0.8% or less, a fatigue strength of 400 N / mm ² or more, and a hardness of HRC 50 or more. The high-hardness spheroidal graphite cast iron member thus obtained has high pitting resistance, and is often used as a member that transmits force while being in contact with a member having a higher hardness than this spheroidal graphite cast iron member. Pitting phenomenon is unlikely to occur. Further, since the deformation ratio before and after the heat treatment is small and the machinability is good, it can be manufactured at low cost.

Further, the first invention is directed to the second invention, wherein CE:
A spheroidal graphite cast iron composition containing 4.53% or less and Cu: 0.25% or less.
The following materials are (1) heated to a temperature of 850 ° C. to 900 ° C. and held for 0.1 hour or more, and then 820 ° C. to 850 ° C.
An austenitizing step of holding at a temperature of less than 0.1 hours or more, (2) a subsequent oil quenching step, (4) a further 200 to
This can be achieved by performing a heat treatment including a tempering step of maintaining the temperature at 350 ° C. for 0.25 hours or more.

[Brief description of the drawings]

FIG. 1 is a metallographic micrograph of Example 2, in which (a)
Indicates 400 times and (b) indicates 5000 times.

FIG. 2 is a metallographic micrograph of Comparative Example 3, in which (a)
Indicates 400 times and (b) indicates 5000 times.

FIG. 3 is a heat treatment diagram of a two-stage austenitizing treatment in Example 2.

FIG. 4 is a view showing the results of fatigue strength in a martensite phase, a martensite mixed phase, and a ferrite phase in a matrix structure.

FIG. 5 is a diagram showing a metallographic micrograph of a martensite phase as a base structure, wherein (a) is 100 times and (b) is 40.
It is 0 times.

FIG. 6 is a diagram showing a metallographic micrograph of a martensite mixed phase (martensite + ferrite) whose base structure is 100 times and (b) is 400 times.

FIG. 7 is a metallographic micrograph of a ferrite phase having a base structure partially containing pearlite, (a) is 100 times,
(B) is 400 times.

FIG. 8 is a diagram showing results of CE value and fatigue strength of test pieces having diameters of 10 mm, 20 mm and 30 mm.

FIG. 9 is a diagram showing the results of CE value and fatigue strength in the martensite phase, pearlite phase, and ferrite phase.

FIG. 10 is a diagram showing the relationship between the average particle size of each graphite and the fatigue strength when the average particle size of graphite is changed by changing the diameter of a round bar to be cast.

FIG. 11 is a view showing a result of evaluating machinability.

FIG. 12 is a diagram showing the results of tempering temperature and fatigue strength.

FIG. 13 is a diagram showing the results of tempering temperature and hardness.

FIG. 14 is a diagram showing the results of tempering temperature and tensile strength.

FIG. 15 is a diagram showing the results of tempering temperature and elongation.

FIG. 16 is a diagram showing the results of tempering temperature and impact value.

Claims (5)

[Claims] 1. Carbon equivalent in weight% (CE value = C + ／)
(Si)): 4.53% or less and Cu: 0.25% or less, the matrix structure around graphite is substantially a martensite phase, and the average particle size of graphite is 20 μm or less. High hardness spheroidal graphite cast iron with excellent fatigue strength. 2. The high-hardness spheroidal graphite cast iron member having excellent fatigue strength according to claim 1, wherein the carbon solid solution amount of the martensite phase is 0.8% or less. 3. The high-hardness spheroidal graphite cast iron member according to claim 1, wherein the fatigue strength is 400 N / mm ² or more and the hardness is HRC 50 or more. 4. Carbon equivalent in weight% (CE value = C + ／)
(Si)): A spheroidal graphite cast iron composition material containing 4.53% or less and Cu: 0.25% or less was subjected to (1) 850 ° C.
An austenitizing step of heating to a temperature of ９００900 ° C. and holding for 0.1 hour or more, followed by holding at a temperature of 820 ° C. to less than 850 ° C. for 0.1 hour or more; (2) a subsequent oil quenching step (3) A method for producing a high-hardness spheroidal graphite cast iron member having excellent fatigue strength, which further comprises performing a heat treatment including a tempering step of maintaining the temperature at 200 to 350 ° C. for 0.25 hours or more. 5. The pearlite content of the spheroidal graphite cast iron material is 30% or less in area ratio.
3. A method for producing a high-hardness spheroidal graphite cast iron member having excellent fatigue strength according to item 1.