IRON-BASED SINTERED ALLOY AND METHOD FOR PRODUCING THE SAME

Description

BACKGROUND

1. Technical Field

[0001] The present disclosure relates to an iron-based sintered alloy to be suitably used as a die material and a cutter blade material for a pelletizer of a resin extruder in pairs, and a method for producing the same.

2. Description of the Related Art

[0002] Since a cutter blade or the like for a pelletizer of a resin extruder is severely worn under a corrosive environment, excellent corrosion resistance and wear resistance are required. Also, a tool material to be used in the cutter blade and the like for a pelletizer of a resin extruder desirably has not only excellent corrosion resistance and wear resistance but also machinability for processing the material into the cutter blade or the like.

[0003] To such a request, for example, JP-A-H11-92870 proposes a material which is machinable, has a predetermined level of hardness and excellent wear resistance, and is excellent in corrosion resistance, obtainable by dispersing appropriate amounts of carbides in high strength stainless steel. That is, there is proposed a highly corrosion-resistant carbide-dispersed material in which carbides of Ti and Mo are dispersed in a matrix, wherein the carbide-dispersed material contains, in terms of weight ratio, Ti; 18.3 to 24%, Mo; 2.8 to 6.6%, C; 4.7 to 7% as the carbides and contains Cr; 7.5 to 10%, Ni; 4.5 to 6.5%, Co; 1.5 to 4.5%, and 0.6 to 1% of one or more of Al, Ti, and Nb as the matrix, the balance being Fe and unavoidable impurities.

[0004] Moreover, JP-A-2000-256799 proposes a highly corrosion-resistant carbide-dispersed material in which carbides of Ti and Mo are dispersed in a matrix, wherein the carbide-dispersed material contains, in terms of weight ratio, Ti; 18.3 to 24%, Mo; 2.8 to 6.6%, C; 4.7 to 7% as the carbides and contains Cr; 7.5 to 10%, Ni; 4.5 to 6.5%, Cu; 1 to 4.5%, Co; 0 to 4.5%, and 0.6 to 1% of one or more of Al, Ti, and Nb as the matrix, the balance being Fe and unavoidable impurities. According to the example, the highly corrosion-resistant carbide-dispersed material has a hardness of 46.0 to 49.8 HRC after sintering, is machinable, and has a hardness of 58.0 to 63.5 HRC and a bending strength of 126 to 155 kgf/mm² after an aging treatment.

[0005] However, resin materials to be used in a resin extruder are various materials and application ranges thereof have been extended, so that the tool material to be used for the cutter blade and the like for a pelletizer is required to have higher corrosion resistance, wear resistance, machinability, or mechanical strength. The highly corrosion-resistant carbide-dispersed materials proposed in JP-A-H11-92870 and JP-A-2000-256799 have a problem that they cannot always cope with such requirements sufficiently.

SUMMARY

[0006] Illustrative aspects of the present disclosure provide an iron-based sintered alloy having remarkably excellent characteristics in corrosion resistance, wear resistance, machinability, or mechanical strength according to an application target of a resin extruder. The iron-based sintered alloy may be suitably used as die and cutter blade materials for a pelletizer of the resin extruder in pairs.

[0007] According to an illustrative aspect, there is provided a method for producing an iron-based sintered alloy according to claim 5.

[0008] The area ratio of the hard particles may be 38% to 41% and standard deviation of the area ratio of the hard particles may be 2.5 to 3.5. Ti, Mo, and C forming the hard particles may be supplied as a TiC powder and a Mo powder.

[0009] The components used in pairs may be components to be used as a die and a cutter blade.

[0010] According to another illustrative aspect, there may be provided an iron-based sintered alloy that is used in sliding components in pairs according to claim 1.

[0011] The iron-based sintered alloy according to the present disclosure has remarkably excellent characteristics in corrosion resistance, wear resistance, machinability, or mechanical strength, has relatively low hardness after sintering, and has high bending strength after an aging treatment. The iron-based sintered alloy according to the disclosure has high wear resistance particularly in the case where the alloy is processed into a die and a cutter blade of a pelletizer to be provided on a resin extruder and they are used in pairs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 

FIG. 1 is a SEM photograph of an iron-based sintered alloy according to the disclosure;

FIG. 2 is a SEM photograph of a material of Comparative Example;

FIG. 3 is a graph showing maximum circle equivalent diameter and area ratio, and Rockwell hardness after sintering of an iron-based sintered alloy according to the disclosure;

FIG. 4 is a graph showing standard deviation of the maximum circle equivalent diameter and the area ratio shown in FIG. 3;

FIGS. 5A to 5C are schematic views showing a test specimen shape for a wear test and a wear testing machine portion fitted therewith;

FIG. 6 is a graph showing wear weight of a cutter blade after a wear test; and

FIGS. 7A and 7B are graphs showing a changing state of a coefficient of friction during a wear test.

DETAILED DESCRIPTION

[0013] Illustrative embodiments will now be described with reference to the accompanying drawings. FIG. 1 is a scanning electron microscope (SEM) photograph showing a structure of an iron-based sintered alloy according to the disclosure. FIG. 2 is a SEM photograph showing a structure of a commercially available carbide-dispersed iron-based sintered alloy material (material of Comparative Example) widely used in a cutter blade for a pelletizer, a punch of a punching die, and the like. In FIGS. 1 and 2, the black portions scattered in an island shape in a matrix are titanium carbide, molybdenum carbide, or a composite carbide of titanium and molybdenum and are particle (hard particle) portions having high hardness. As shown in FIG. 1, the iron-based sintered alloy according to the disclosure is characterized in that the hard particles have a fine and relatively uniform shape and are homogeneously dispersed over the whole matrix.

[0014] The present iron-based sintered alloy is manufactured by forming a mixed powder, which has been obtained by mixing a predetermined powder (e.g., the predetermined power may contain 23 to 30.8 mass% of TiC powder, 2.8 to 6.6 mass% of Mo powder, 4.5 to 6.5 mass% of Ni powder, 7.5 to 10.0 mass% of Cr powder, 1.5 to 4.5 mass% of Co powder, 0.6 to 1.0 mass% of Al powder and 40.6 to 60 mass% of Fe powder) in a wet ball mill, by a cold isostatic pressing (CIP) method (e.g., by applying a pressure of 1,000 to 4,000 kgf/cm²) and subjecting the formed compact (e.g., having a columnar shape having a diameter of 50 to 200 mm and a height of 25 to 60 mm or a cuboid shape having a length of 55 to 150 mm, a width of 100 to 275 mm and a height of 45 to 60 mm) to vacuum sintering, a solution treatment, and an aging treatment at predetermined temperatures (e.g., the vacuum sintering is performed at a sintering temperature of 1,360 to 1,400°C (preferably, 1,380 to 1,400 °C) for 4 to 6 hours), the solution treatment is performed at a temperature of 800 to 1,050 °C for 3 to 8 hours, and the aging treatment is perfomed at a temperature of 440 to 530 °C for 4 to 10 hours). As shown in FIG. 3, the iron-based sintered alloy is characterized in that it can be manufactured so that, while an area ratio of hard particles existing in the matrix is kept constant (is not changed), a maximum circle equivalent diameter (in terms of a projected area circle equivalent diameter) thereof is controlled to a predetermined value. In FIG. 3, the horizontal axis shows sintering temperature in the vacuum sintering and the vertical axis shows the maximum circle equivalent diameter (equivalent diameter) or area ratio of the hard particles after the aging treatment is performed and Rockwell hardness (hardness) after the vacuum sintering. Incidentally, FIG. 3 shows an average of 5 test specimens at each point.

[0015] As shown in FIG. 3, at a sintering temperature of 1,360 to 1,400°C, the area ratio of the hard particles (asterisk) is 38 to 41% (about 40%) and is constant and the maximum circle equivalent diameter (•) decreases in reverse proportion to the sintering temperature. In the present iron-based sintered alloy, the structure is observed like a structure formed through gradual decay from large-diameter hard particles as if the maximum diameter of the hard particles that can exist at the sintering temperature is present. This is also understood from the fact that variation (standard deviation) in the area ratio and maximum circle equivalent diameter of the hard particles shown in FIG. 4 is small. In FIG. 4, the horizontal axis shows the sintering temperature and the vertical axis shows standard deviation of the area ratio and maximum circle equivalent diameter of the hard particles. According to FIG. 4, at a sintering temperature of 1,360 to 1,400°C, the standard deviation of the area ratio is about 2% (2.5 to 3.5%) and is constant. With regard to the maximum circle equivalent diameter, the standard deviation is 12 to 11 µm at a sintering temperature of 1,360 to 1,370°C that is relatively large as compared to that at other sintering temperatures within 1,350 to 1,400°C and is small at a sintering temperature of 1,380 to 1,400°C. At a sintering temperature of 1,380 to 1,400°C, the standard deviation of the maximum circle equivalent diameter is 6 to 4 µm and is very small.

[0016] According to FIG. 3 and FIG. 4, at a sintering temperature of 1,350°C or 1,350 to 1,360°C, a singular appearance in the average and standard deviation of the maximum circle equivalent diameter is observed. The following Table 1 shows the average, standard deviation, and a coefficient of variation of the maximum circle equivalent diameter at each sintering temperature. At a sintering temperature of 1,350 to 1,400°C, a singular point is observed in the coefficient of variation (standard deviation/average) at a sintering temperature of 1,350°C. According to this, it is understood that the case where the sintering temperature is 1,350°C is structurally different from the sintering at a sintering temperature of 1,360 to 1,400°C.

[Table 1]

Sintering temperature (°C)	Average (µm)	Standard deviation (µm)	Coefficient of variation
1,350	38.64	4.57	0.12
1,360	39.87	12.52	0.31
1,370	33.87	10.71	0.32
1,380	26.77	6.21	0.23
1,390	24.78	5.39	0.22
1,400	18.67	3.9	0.21

[0017] Moreover, according to FIG. 3, Rockwell hardness (A) of the present iron-based sintered alloy after sintering increases in proportion to the sintering temperature when the sintering temperature is in a range of 1,350 to 1,380°C (31 to 46 HRC) and when the sintering temperature exceeds 1,380°C, it is observed that the hardness becomes a constant value or decreases. However, the highest value of the hardness is 46 HRC at a sintering temperature of 1,380°C and thus the iron-based sintered alloy has sufficient machinability.

[Example 1]

[0018] An iron-based sintered alloy manufactured. From the material, five disks and cutter blades were cut out and a wear test in water by a cutter blade-on-disk method was performed. FIGS. 5B and 5C show the shapes of the disk and the cutter blade used in the wear test, respectively. The disk and cutter blade were put into a wear testing machine (e.g., "EFM-III-1010-ADX", a schematic diagram of which is shown in Fig. 5A) having a rotation mechanism, pressurization mechanism and a temperature control mechanism and the wear test was performed. The hardness of the disk and the hardness of the cutter blade were both 57 HRC as hardness after an aging treatment. The wear test was performed under a contact face pressure of 5.8 kg/cm² at a peripheral speed of 5.2 m/sec and the test time was 10 hours. Volume of water bath was 1.8L and temperature of water was 30 °C. Incidentally, using the disk and cutter blade cut out from the material of Comparative Example, the same wear test as above was performed.

[0019] The iron-based sintered alloy was manufactured as shown below. That is, a compounding powder of the powders shown in Table 2 were mixed in a ball mill, the resulting mixed powder was filled into a rubber mold having a space of φ100 × 50 mm so as to be formed into a columnar shape having a diameter of 100 mm and a height of 50 mm, and, after sealing, was formed by a CIP method by applying a pressure of 1,500 kgf/cm², and the resulting compact was heated under vacuum at 1,380°C for 5 hours, thereby performing vacuum sintering. Thereafter, a solution treatment was performed under a temperature at 850°C for 4 hours and an aging treatment under a temperature at 500°C for 6 hours was conducted. Table 3 shows maximum circle equivalent diameter and area ratio of the structure of the manufactured iron-based sintered alloy (Reference Example). As shown in Reference Table 3, Example (present iron-based sintered alloy) has a maximum circle equivalent diameter of hard particles of about 16 µm and the size is 1/2 or less of that of Comparative Example and the standard deviation of the maximum circle equivalent diameter is about 2 µm and is 1/4 or less of that in Comparative Example. The reference Example has an area ratio of hard particles of 40%, which is about the same as in the case of Comparative Example (43%) but the standard deviation of the area ratio is 1.2%, which is considerably smaller than that in the case of Comparative Reference Example (4.5%). That is, Example is characterized in that small hard particles are homogeneously dispersed as a whole.

[0020] In the disclosure, with regard to the carbides, it is suitable that only TiC is supplied as a powder and the others are supplied as individual metal powders, for example, a Mo powder. As the TiC powder, a commercially available one having a particle size of 1 to 2 µm was used. Incidentally, as for materials of Comparative Example, Table 2 shows a chemical composition and Table 3 shows the maximum circle equivalent diameter and area ratio of the structure, as well.

[Table 2]

	Chemical composition (mass%)
	TiC	Mo	Ni	Cr	Co	Al	Cu	Fe
Reference - Example	27	5	5.7	8.8	2.9	0.7	-	49.9
Comparative Example	30 to 32	2 to 4	3 to 4.5	9 to 10	3 to 6.5	0 to 1	0 to I	1 to 2

[Table 3]

	Maximum circle equivalent diameter (µm)		Area ratio (%)
	Average	Standard deviation	Average	Standard deviation
Reference Example	15.9	2.01	39.58	1.21
Comparative Example	37.8	9.89	43.17	4.51

[0021] FIG. 6 shows wear weight of the cutter blade by the wear test after the passage of 10 hours and FIGs. 7A and 7B show a changing state of the coefficient of friction during the wear test. According to FIG. 6, the wear weight in Reference Example is 115 or less of that in Comparative Example. According to FIG. 7A, the coefficient of friction in Reference Example gradually increases until 1 hour from the start of the test (0.25 to 0.50), thereafter slightly decreases, after 2.1 hours, sharply decreases, subsequently fluctuates within the range of 0.15 to 0.45 until 4.2 hours, and is near to almost 0 (0.05 or less) after 4.2 hours. Incidentally, the coefficient of friction becomes about 0.1158 after 7.156 to 7.167 hours. That is, the present iron-based sintered alloy has a coefficient of friction of at least about 0.12 or less, mainly 0.1 or less and specifically, near to almost 0 in the wear test in water after passing through a certain conforming stage. On the other hand, the coefficient of friction of Comparative Example fluctuates within a certain range during the test time (0.3 to 0.6).

Claims

1. An iron-based sintered alloy that is suitable for sliding components in pairs, the iron-based sintered alloy having a composition comprising, in terms of percent by mass, Ti: 18.4 to 24.6%, Mo: 2.8 to 6.6%, C: 4.7 to 7.0%, Cr: 7.5 to 10.0%, Ni: 4.5 to 6.5%, Co: 1.5 to 4.5%, Al: 0.6 to 1.0%, the balance being Fe and unavoidable impurities,

wherein the alloy has a structure in which hard particles are dispersed in an island shape in a matrix,

characterized in that

the hard particles are formed from a carbide consisting of a TiC powder and a metal powder including a Mo metal powder,

the iron-based sintered allow is manufactured by mixing material powders consisting of TiC, Mo, Ni, Cr, Co, Al and Fe,

an area ratio of the hard particles is within a constant range,

a maximum circle equivalent diameter of the hard particles is 40 µm to 10 µm and

a standard deviation of the maximum circle equivalent diameter of the hard particles is 6 µm to 4 µm.

2. The iron-based sintered alloy according to claim 1, wherein the area ratio of the hard particles is 38% to 41% and standard deviation of the area ratio of the hard particles is 2.5 to 3.5.

3. The iron-based sintered alloy according to claim 1 or 2,
wherein a coefficient of friction after passing through a stage of fluctuation is 0.12 or less in a wear test in water by a cutter blade-on-disk method simulating a die and a cutter blade, wherein the wear test is performed under the conditions described in the description under Example 1.

4. A pelletizer of a resin extruder with a die and a cutter blade, which comprise the iron-based sintered alloy according to any one of claims 1 to 3.

5. A method for producing the iron-based sintered alloy according to any one of claims 1 to 3, the method comprising:

forming a compact by mixing material powders consisting of TiC, Mo, Ni, Cr, Co, Al and Fe and subjecting the mixture to a cold isostatic pressing method; and

subjecting the formed compact to a vacuum sintering, a solution treatment and an aging treatment, characterized in that

the vacuum sintering comprises heating the formed compact under vacuum at a sintering temperature of 1380°C to 1400°C.

Ansprüche

1. Sinterlegierung auf Eisenbasis, die zum paarweisen Gleiten von Bauteilen geeignet ist, wobei die Sinterlegierung auf Eisenbasis eine Zusammensetzung aufweist, die in Massenprozent ausgedrückt umfasst: Ti: 18,4 bis 24,6%, Mo: 2,8 bis 6,6%, C: 4,7 bis 7,0%, Cr: 7,5 bis 10,0%, Ni: 4,5 bis 6,5%, Co: 1,5 bis 4,5%, Al: 0,6 bis 1,0%, Rest Fe und unvermeidbare Verunreinigungen,

wobei die Legierung ein Gefüge aufweist, in dem harte Partikel in einer Inselform in einer Matrix dispergiert sind,

dadurch gekennzeichnet, dass

die harten Partikel aus Karbid ausgebildet sind, das aus einem TiC-Pulver und einem Metallpulver einschließlich eines Mo-Metallpulvers besteht,

die Sinterlegierung auf Eisenbasis durch Mischen von Materialpulvern aus TiC, Mo, Ni, Cr, Co, Al und Fe hergestellt ist,

ein Flächenverhältnis der harten Partikel innerhalb eines konstanten Bereichs liegt,

ein maximaler kreisäquivalenter Durchmesser der harten Partikel 40 µm bis 10 µm beträgt und

eine Standardabweichung des maximalen kreisäquivalenten Durchmessers der harten Partikel 6 µm bis 4 µm beträgt.

2. Sinterlegierung auf Eisenbasis nach Anspruch 1, bei der das Flächenverhältnis der harten Partikel 38 % bis 41 % beträgt und die Standardabweichung des Flächenverhältnisses der harten Partikel 2,5 bis 3,5 beträgt.

3. Sinterlegierung auf Eisenbasis nach Anspruch 1 oder 2,
bei der ein Reibungskoeffizient nach Durchlaufen einer Fluktuationsphase 0,12 oder weniger in einem Verschleißtest in Wasser durch ein Verfahren mit scheibenmontierter Schneidklinge, das eine Matrize und eine Schneidklinge simuliert, beträgt, wobei der Verschleißtest unter den in der Beschreibung unter Beispiel 1 beschriebenen Bedingungen ausgeführt wird.

4. Granuliervorrichtung eines Kunststoffextruders mit einer Matrize und einer Schneidklinge, die die Sinterlegierung auf Eisenbasis eines der Ansprüche 1 bis 3 umfassen.

5. Verfahren zum Herstellen einer Sinterlegierung auf Eisenbasis gemäß einem der Ansprüche 1 bis 3, wobei das Verfahren umfasst:

Formen eines Presslings durch Mischen von Materialpulvern, die aus TiC, Mo, Ni, Cr, Co, Al und Fe bestehen, und Unterziehen der Mischung einem isostatischen Kaltpressverfahren; und

Unterziehen des geformten Presslings einem Vakuumsintern, einer Lösungsbehandlung und einer Alterungsbehandlung, dadurch gekennzeichnet, dass

das Vakuumsintern das Erhitzen des geformten Presslings unter Vakuum bei einer Sintertemperatur von 1.380°C bis 1.400°C umfasst.

Revendications

1. Alliage fritté à base de fer qui est adapté pour faire glisser des composants par paires, l'alliage fritté à base de fer présentant une composition comprenant, en termes de pourcentage de masse, Ti : 18,4 à 24, 6 %, Mo : 2,8 à 6,6 %, C : 4,7 à 7,0 %, Cr : 7,5 à 10,0 %, Ni : 4,5 à 6,5 %, Co : 1,5 à 4,5 %, Al : 0,6 à 1,0 %, le solde étant du Fe et des impuretés accessoires,

dans lequel l'alliage présente une structure dans laquelle des particules dures sont dispersées dans une forme d'île dans une matrice,

caractérisé en ce que

les particules dures sont constituées à partir d'un carbure consistant en une poudre de TiC et une poudre métallique incluant une poudre métallique de Mo,

l'alliage fritté à base de fer est fabriqué en mélangeant des poudres de matériaux constituées de TiC, Mo, Ni, Cr, Co, Al et Fe,

un rapport de surface des particules durées s'inscrit dans une plage constante,

un diamètre équivalent circulaire maximal des particules dures est de 40 µm à 10 µm et

un écart standard du diamètre équivalent circulaire maximal des particules dures est de 6 µm à 4 µm.

2. L'alliage fritté à base de fer selon la revendication 1, dans lequel le rapport de surface des particules dures est de 38 % à 41 % et un écart standard du rapport de surface des particules dures est de 2,5 à 3,5.

3. L'alliage fritté à base de fer selon la revendication 1 ou 2,
dans lequel un coefficient de friction après passage par une étape de fluctuation est de 0,12 ou moins dans un test d'usure dans de l'eau par un procédé par disque de coupe simulant un moule et une lame de coupe, dans lequel le test d'usure est exécuté dans les conditions décrites dans la description sous Exemple 1.

4. Un granulateur d'une extrudeuse à résine avec un moule et une lame de coupe, qui comprennent l'alliage fritté à base de fer selon l'une quelconque des revendications 1 à 3.

5. Procédé pour produire l'alliage fritté à base de fer selon l'une quelconque des revendications 1 à 3, le procédé comprenant :

constitution d'un matériau compact en mélangeant des poudres de matériaux constituées de TiC, Mo, Ni, Cr, Co, Al et Fe et soumission du mélange à un procédé de pression isostatique à froid ; et

soumission du matériau compact constitué à un frittage sous vide, un traitement de solubilisation et un traitement anti-âge, caractérisé en ce que

le frittage sous vide comprend un chauffage du matériau compact constitué sous vide à une température de frittage de 1380 °C à 1400 °C.

Drawing