Iron-based sintered alloy and method for producing same

Abstract

Produced is an iron-based sintered alloy in which hard particles derived from a titanium carbide powder are dispersed in the form of islands in a matrix comprising a two phase structure of austenite+martensite. The iron-based sintered alloy is obtained by mixing the titanium carbide powder, a Cr powder, a Mo powder, a Co powder, a Fe powder and a powder of Al, Ti or Nb so as to obtain a mixed powder that contains, in terms of mass %, 20-35% of titanium carbide, 3.0-12.0% of Cr, 3.0-8.0% of Mo, 8.0-23% of Ni, 0.6-4.5% of Co and 0.6-1.0% of Al, Ti or Nb, with the balance Fe, and then subjecting the mixed powder to cold isostatic compression molding, vacuum sintering and solution treatment.

Claims

1. A method for producing an iron-based sintered alloy, the method comprising: mixing a titanium carbide powder, a Cr powder, a Mo powder, a Ni powder, a Co powder, a Fe powder and a powder of any one of Al, Ti, and Nb; and subjecting a resulting mixed powder containing, in terms of % by mass, titanium carbide: 20% to 35%, Cr: 3.0% to 12.0%, Mo: 3.0% to 8.0%, Ni: 8.0% to 23%, Co: 0.6% to 4.5%, and any one of Al, Ti or Nb: 0.6% to 1.0%, with the balance Fe, to cold isostatic pressing molding, vacuum sintering, and a solution treatment, to produce an iron-based sintered alloy in which hard particles derived from the titanium carbide powder are dispersed in an island form in a matrix having a two-phase structure of austenite and martensite.

2. The method for producing an iron-based sintered alloy according to claim 1, further comprising forming at least one of a die and a cutter blade as sliding components from the iron-based sintered alloy.

3. An iron-based sintered alloy, wherein hard particles comprising titanium carbide, molybdenum carbide, and/or a composite carbide of titanium and molybdenum are dispersed in an island form in a matrix having a two-phase structure of austenite and martensite, wherein the iron-based sintered alloy contains, in terms of % by mass, titanium carbide: 20% to 35%, Cr: 3.0% to 12.0%, Mo: 3.0% to 8.0%, Ni: 8.0% to 23%, Co: 0.6% to 4.5%, and any one of Al, Ti or Nb: 0.6% to 1.0%, with the balance Fe.

4. The iron-based sintered alloy according to claim 3, wherein the composition of the matrix is a composition forming an austenite and martensite region in Schaeffler's diagram.

5. The iron-based sintered alloy according to claim 3, wherein maximum circle equivalent diameter of the hard particles is 30 m or less.

6. A die and a cutter blade as sliding components, at least one of which is comprised of the iron-based sintered alloy according to claim 3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a Schaeffler's diagram.

(2) FIG. 2 is a scanning electron microscope (SEM) photograph showing a structure of an iron-based sintered alloy according to the present invention.

(3) FIG. 3 is a photograph after etching of an iron-based sintered alloy according to the present invention.

(4) FIG. 4 is a schematic view in which a part of FIG. 3 is enlarged.

(5) FIG. 5 is a SEM photograph showing a hard particle portion and a matrix portion of an iron-based sintered alloy according to the present invention, which are subjected to fluorescent X-ray analysis.

(6) FIG. 6 are graphs showing analysis results of each portion shown in FIG. 5 by EDX.

MODE FOR CARRYING OUT THE INVENTION

(7) The following will describe modes for carrying out the present invention. The production method of the iron-based sintered alloy according to the present invention is a method for producing an iron-based sintered alloy, the method including: mixing a titanium carbide powder, a Cr powder, a Fe powder, a Mo powder, a Ni powder, a Co powder, and a powder of any one of Al, Ti, and Nb; and subjecting a resulting mixed powder containing, in terms of % by mass, titanium carbide: 20% to 35%, Cr: 3.0% to 12.0%, Mo: 3.0% to 8.0%, Ni: 8.0% to 23%, Co: 0.6% to 4.5%, and any one of Al, Ti or Nb: 0.6% to 1.0%, with the balance Fe, to cold isostatic pressing molding, vacuum sintering, and a solution treatment, to produce an iron based sintered alloy in which hard particles derived from the titanium carbide powder are dispersed in an island form in a matrix having a two-phase structure of austenite and martensite The present production method of the iron-based sintered alloy is suitably used as a production method of sliding components, particularly components such as a die and a cutter blade for a pelletizer of a resin extruder, which are processed from the same material.

(8) In the production method of the iron-based sintered alloy according to the present invention, a Cr powder, a Mo powder, a Ni powder, a Co powder, a Fe powder and a powder of any one of Al, Ti, and Nb for forming a matrix and a titanium carbide powder for forming islands dispersed in the matrix are used and they are mixed to prepare a mixed powder. As for the composition of the mixed powder, the mass ratio of titanium carbide (TiC) is 20 to 35% and, as for Cr and the like, the mass ratios thereof are determined so that Cr equivalent and Ni equivalent belong to an austenite+martensite (A+M) region in Schaeffler's diagram. That is, the region is the region of (A+M) of the Schaeffler's diagram shown in FIG. 1. As shown in FIG. 1, the Cr equivalent is determined from the mass ratios of Cr, Mo, Si, and Nb and the Ni equivalent is determined from the mass ratios of Ni, C, and Mn. For the cold isostatic pressing molding, vacuum sintering, and solution treatment, known methods can be used.

(9) According to the present production method of the iron-based sintered alloy, there can be produced an iron-based sintered alloy in which hard particles including titanium carbide, molybdenum carbide, and/or a composite carbide of titanium and molybdenum are dispersed in an island form in a matrix including a two-phase structure of austenite+martensite. FIGS. 2 to 6 show examples of the iron-based sintered alloy according to the present invention. FIG. 2 is a scanning electron microscope (SEM) photograph showing a structure of an iron-based sintered alloy according to the present invention and it is observed that black fine hard particles are dispersed in an island form.

(10) The hard particles have a size of 10 m or less and are based on aggregates of a fine titanium carbide powder having a particle diameter of about 1 m, which are used as a raw material of the aforementioned iron-based sintered alloy, or those formed by disintegration of the aggregates. According to the present iron-based sintered alloy, there can be produced those in which the area ratio of the hard particles is 30% to 40% and those having a maximum circle equivalent diameter thereof of 20 m to 30 m. Here, the maximum circle equivalent diameter means maximum sized one among projected area circle equivalent diameters.

(11) FIG. 3 shows a structure after etching of an iron-based sintered alloy according to the present invention. In the matrix, a dark portion in which etching has proceeded is a martensite phase and a white portion is an austenite phase. FIG. 4 is a schematic view in which a part of FIG. 3 is enlarged and shaded portion is a martensite phase and a white portion is an austenite phase. The proportion of the martensite phase to the austenite phase is observed to be about the same.

(12) Although it is mentioned above that the hard particles dispersed in an island form are based on aggregates of the titanium carbide powder or those formed by disintegration thereof, results of performing component analysis of the hard particles and the matrix are shown in FIG. 5 and FIG. 6. FIG. 5 is a SEM photograph showing a hard particle portion (analysis portion A) and a matrix portion (analysis portion B) of an iron-based sintered alloy according to the present invention. FIG. 6 shows spectra of the analysis portion A (FIG. 6(a)) and the analysis portion B (FIG. 6(b)), which are analyzed by an energy dispersion-type fluorescent X-ray spectrometer (EDX) equipped on SEM, and the horizontal axis shows values with the unit of key. According to FIG. 6(a), Ti, Mo, and C are detected from the hard particle portion. It is understood that Mo diffuses into TiC forming a nuclei of the hard particle to form molybdenum carbide and/or a composite carbide of titanium and molybdenum. Incidentally, Fe is present in the hard particle portion but the detail should be further analyzed.

(13) According to FIG. 6(b), Fe, Cr, Ni, Mo, Co, and Ti are present in the matrix portion. Table 1 shows results of quantitative analysis of the components of the matrix portion (analysis portion B). Table 1 also describes mass ratios of raw material powders of the sample from which the present iron-based sintered alloy is prepared. The mass ratios of the raw material powders shown in Table 1 show mass ratios when the total of the raw material powders shown in Table 1 excluding the TiC powder among the raw material powders is regarded as 100%. Moreover, Table 1 describes Cr equivalent and Ni equivalent in Schaeffler's diagram, which are determined from the data described in Table 1. When the positions of the analysis portion B and the raw material powder in Schaeffler's diagram are determined from the Cr equivalent and the Ni equivalent, as shown in FIG. 1, they belong to the austenite+martensite (A+M) region.

(14) TABLE-US-00001 TABLE 1 Schaeffler's diagram Cr Ni Chemical components (% by mass) equiv- equiv- Cr Ni Mo Ti Co Fe alent alent Analysis 5.67 14.34 2.92 2.36 4.94 69.77 8.59 14.34 portion B Raw 5.48 13.84 6.85 0.75 3.97 69.11 12.33 13.84 material powder

(15) According to Table 1, in the components Mo and Ti, a difference in mass ratio between the analysis portion B and the raw material powder is remarkable. It is understood that Mo diffuses into hard particles (TiC) diffuse in an island form to form molybdenum carbide and/or a composite carbide of titanium and molybdenum. On the other hand, it is understood that a part of TiC solid-solves in the matrix.

Example 1

(16) An iron-based sintered alloy according to the present invention was manufactured and each test specimen was manufactured. Then, a measurement of Rockwell C scale hardness, a 3-point-bending transverse rupture test, a water immersion corrosion test, and a pin-on-disk-type friction wear test were performed. In the water immersion corrosion test, each test specimen was immersed in water at room temperature for 14 days and corrosion loss was measured. The pin-on-disk-type friction wear test was performed in water at room temperature under a contact face pressure of 12.7 kgf/cm.sup.2 at a peripheral speed of 4.2 m/sec using a pin of Inventive Example or Comparative Example having an outer diameter of 8 mm and a height of 10 mm at the pin side and a disk including a commercially available carbide particle-dispersed material (55.4 HRC) having an outer diameter of 60 mm and a thickness of 5 mm at the disk side, and the test time was 1 hour. Incidentally, the above Comparative Example is an example of one based on an iron-based sintered alloy manufactured according to Examples described in Patent Document 1. The 3-point-bending transverse rupture test is based on JIS R1601.

(17) 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 10050 and the rubber mold was sealed. Thereafter, a compact was molded by a CIP method. The resulting compact was heated under vacuum at 1,400 C. for 5 hours, thereby performing vacuum sintering. Then, after a solution treatment was performed, an aging treatment was conducted. Table 3 shows composition of the compounding powder of Comparative Example. In Table 3, numerals in parenthesis of TiC and Mo.sub.2C indicate % by mass of respective constituent elements.

(18) TABLE-US-00002 TABLE 2 TiC Ni Cr Mo Co Ti Al Fe Inventive 27.0 10.1 4.0 5.0 2.9 0.55 balance Example

(19) TABLE-US-00003 TABLE 3 TiC (Ti, C) Mo.sub.2C (Mo, C) Ni Cr Co Al Fe Comparative 25 (20, 5) 5 (4.7, 0.3) 5.8 9.0 3.0 0.7 balance Example

(20) Table 4 shows test results. The iron-based sintered alloy according to the present invention (Inventive Example) has slightly lower hardness and higher transverse rupture strength as compared to that of Comparative Example. In the results of the corrosion test, no difference is observed and Inventive Example is equal to Comparative Example. In the results of the friction wear test, wear loss of Inventive Example is one sixth () that of Comparative Example and wear loss of the counterpart disk in Inventive Example is also one half () that in Comparative Example. That is, the iron-based sintered alloy according to the present invention is more excellent in wear resistance than Comparative Example and also can prevent wear of the counterpart.

(21) TABLE-US-00004 TABLE 4 Transverse Corrosion loss Wear loss in fric- Hard- rupture in water tion wear test ness strength immersion test (g) (HRC) (kgf/mm.sup.2) (g) Pin side Disk side Inventive 53.8 167 0 (no change in 0.0167 0.0336 Example appearance) Comparative 58.2 147 0 (no change in 0.1100 0.0660 Example appearance)

(22) While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. The present application is based on Japanese Patent Application No. 2016-100817 filed on May 19, 2016, and the contents thereof are incorporated herein by reference.