JP2000273503A - Hard particle-dispersed sintered steel and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce hard particle-dispersed sintered steel excellent in reliability in the face of strength and wear resistance and to provide a method for producing it. SOLUTION: This is the sintered steel in which, into a matrix essentially consisting of Fe or an Fe alloy, hard particles contg. TiC are dispersed by 20 to 40 mass %, in which, after a sample is subjected to specular grinding, in optical microphotography of 400 magnifications in which the surface of the steel is photographed, hard particles inevitably contg. TiC are allowed to exist on an optional segment of 20 mm length. In the method for producing hard particle-dispersed sintered steel in which the raw material powder composed of Fe or Fe allay powder and carbide powder is subjected to wet blending, is subjected to compacting and is thereafter sintered in a vacuum, the wet blending is executed with a solvent (such as hexane and xylene) substantially free from hygroscopicity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hard grain dispersion sintered steel suitable for a cold working tool, a hot working tool, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Materials used for cold and hot working tools are required to have high reliability in terms of strength (high minimum strength) and excellent wear resistance. Sintered steel in which hard grains such as TiC are dispersed (hard grain dispersed sintered steel) has been developed (see, for example,
64608, JP-A-53-6207, JP-A-6-330
107, JP-A-8-253845, etc.).

[0003] In hard grain dispersed sintered steel, it is desired to disperse fine hard grains as uniformly as possible. This is because the aggregates of the hard grains serve as starting points of destruction and reduce the reliability of the material. In addition, the fact that the aggregates remain means that there are many regions where hard grains are coarse, and the abrasion resistance is deteriorated.

However, since there is a large difference in particle size and specific gravity between commercially available metal powders and hard particles such as carbides, it is difficult to uniformly mix them.
The hard particles were not always uniformly dispersed, and the reliability of strength and the wear resistance were not sufficiently high.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a hard-grain-dispersed sintered steel having excellent strength reliability and wear resistance and a method for producing the same. It is assumed that.

[0006]

Means for Solving the Problems The manufacturing method of the present invention which has solved the above-mentioned problems is that a raw material powder comprising Fe or Fe alloy powder and a carbide powder is wet-mixed, and after press molding,
A method for producing a hard-grain-dispersed sintered steel that is sintered in a vacuum, and it is intended to perform wet mixing using a solvent having substantially no hygroscopicity. Hexane or xylene may be used as the solvent having substantially no hygroscopicity. Further, it is desirable to use a powder having an average particle size of 15 μm or less as the Fe or Fe alloy powder, and to use a powder having an average particle size of 5 μm or less as the carbide powder. May be used. In performing sintering, 1300-145
It is desirable that the temperature is maintained at 0 ° C. for 1 to 10 hours.

Further, the hard grain dispersion sintered steel of the present invention which has solved the above-mentioned problems is characterized in that the hard grains containing TiC in a matrix mainly composed of Fe or an Fe alloy contain 20 to 40% by mass.
Hard particles containing TiC always exist on an arbitrary line segment having a length of 20 mm in a 400-magnification optical microscope photograph of a dispersed sintered steel, which is a mirror-polished sample of a sample, and the steel surface is photographed. The gist is that.

[0008] In addition to Fe, Ni: 3 to 20%, Co: 2 to 40%,
Mo: 2 to 15%, Al: 0.2 to 2.0%, Ti:
It is desirable to contain 0.2 to 3.0%, Cu: 0.2 to 5.0%, and further Cr: 3 to 20% and / or B: 0.
Desirably, the content is 0.01 to 0.10%.

As the hard particles containing TiC, all may be TiC, but 50% or more of the hard particles may be TiC.
Then, V, Cr, Zr, Nb, Mo, Hf,
A metal carbide selected from the group consisting of Ta and W;
One or more of iN may be used.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hard grain-dispersed sintered steels have been manufactured to disperse hard grains as much as possible, but hard grains are not uniformly dispersed. As a result of intensive studies on the dispersion of hard particles, the present inventors have found out that there was a problem with the solvent in wet mixing as a cause of insufficient dispersion of the hard particles in the conventional production method. The mixing of metal powder and hard particles is performed by wet mixing using a ball mill or attritor.
Solvents having hygroscopicity such as alcohols are used,
This hindered the uniform dispersion of the hard grains. The reason is that the powder is easily oxidized by contact with the solvent that has absorbed moisture, and if the powder surface is oxidized, the liquid phase and the hard particles become poorly wet during sintering, preventing the liquid phase from spreading uniformly. is there. Therefore, it is necessary to use a solvent having substantially no hygroscopicity, such as hexane and xylene.

Further, the present inventors examined the relationship between the dispersion state of the hard particles and the mechanical properties. As a result, as a measure of the degree of dispersion of the hard particles, a straight line having a length of 20 mm was observed in a 400-fold optical microscope photograph. If the hard particles are dispersed uniformly so as to cross the titanium carbide in any place, the reliability of the strength is high (the minimum strength is high) and the hard particles have excellent wear resistance. The inventors have found that a dispersion sintered steel can be obtained, and have reached the present invention.

That is, the hard grain dispersion sintered steel of the present invention is
Draw a straight line with a length of 20 mm in the optical microscope photograph of 0 times, and the hard grains are uniformly dispersed so that it crosses the titanium carbide everywhere, and has high minimum strength and excellent wear resistance It is a sintered steel that demonstrates its properties. The manufacturing method will be described below.

First, it is preferable to use the finest possible raw material powder. In particular, it is effective to use fine iron powder and TiC powder as main components. By using the fine powder, the liquid phase generated by the eutectic reaction between the iron powder and the hard particles can be made uniform. Specifically, it is preferable to use iron powder having an average particle size of 15 μm or less.
At this time, a method of using other components as an alloy powder obtained by alloying is also effective. The average particle size at this time is also preferably 15 μm or less. It is also preferable to use a TiC powder having an average particle size of 5 μm or less. Furthermore,
V, Cr, Zr, Nb, Mo, Hf, T
Also when using metal carbide and titanium nitride selected from the group consisting of a and W, it is preferable to use those having an average particle size of 5 μm or less.

At the time of mixing, as described above, it is necessary to use a solvent having substantially no hygroscopicity, such as hexane or xylene, as a solvent used for wet mixing. Further, if the powder is crushed or deformed during mixing to form a new surface, the amount of oxidation is increased and adversely affects uniform dispersion. For example, when mixing using an attritor, it is necessary to set the mixing time to 5 hours or less, and it is preferable to set the mixing time to about 3 hours.

Further, at the time of sintering, it is necessary to consider the atmosphere in the furnace, the sintering temperature, and the holding time. Vacuum sintering may be performed using a normal vacuum sintering furnace. At this time, the amount of the liquid phase and the spreadability of the liquid phase vary depending on the atmosphere in the furnace. Since the degree varies subtly depending on various conditions, it is necessary to carefully determine the sintering time and holding time and search for the conditions under which the hard particles are finely and uniformly dispersed. It is necessary to determine in consideration of the composition, the atmosphere in the furnace, and the like. If the sintering temperature is lower than 1300 ° C., the dispersion of the hard particles becomes insufficient due to insufficient expansion of the liquid phase. On the other hand, if the sintering temperature exceeds 1450 ° C. or the holding time exceeds 10 hours, the TiC grains grow and become coarse, and as a result, the degree of dispersion of the hard grains decreases. When TiC further increases,
It becomes the starting point of destruction and causes a decrease in strength. Therefore, as sintering conditions, it is preferable to hold at 1300 to 1450 ° C. for 1 to 10 hours.

As described above, the hard grain dispersion sintered steel of the present invention is densified by liquid phase sintering. During sintering, this liquid phase causes the hard grains to rearrange and become uniformly dispersed. Therefore, generating the liquid phase uniformly over the entire sample leads to uniform dispersion of the hard particles.

As described above, the particle size, mixing conditions, and sintering conditions of the metal powder are selected to generate a liquid phase amount capable of uniformly dispersing the hard particles, and the deformation of the sample accompanying the increase in the liquid phase amount is suppressed. By suppressing it, it is possible to obtain a sintered steel of any shape in which hard grains are finely and uniformly dispersed, and the obtained hard grain dispersion sintered steel has extremely high strength reliability and wear resistance. It is excellent.

Next, preferable components and contents in the sintered steel are shown below.

Ni is particularly necessary when forming a Ni maraging steel. However, if it is less than 3%, no martensite is formed, and if it exceeds 20%, austenite remains. It is desirable to set it to 20%.

By adding Co, the dissolution of Mo in iron is suppressed, and the precipitation of intermetallic compounds necessary for improving the hardness is enabled. If it is less than 2%, the effect of strengthening the precipitation is small, and if it exceeds 40%, a large amount of intermetallic compound is precipitated, which causes a rapid decrease in toughness.
It is desirable to set it to 0%.

Mo is an element that precipitates as an intermetallic compound necessary for improving the hardness. If it is less than 2%, the effect of strengthening the precipitation is small, and if it exceeds 15%, a large amount of the intermetallic compound precipitates and sharply increases. Since the toughness is reduced, the range of the addition amount is desirably 2 to 15%.

Al and Ti both precipitate as intermetallic compounds necessary for improving the hardness. If less than 0.2%, the effect of strengthening the precipitation is small, and if it is too large, an embrittled phase is generated. The amount is desirably 0.2 to 2.0%, and the amount of Ti is desirably 0.2 to 3.0%.

Although Cu precipitates and contributes to the improvement of hardness,
If it is less than 0.2%, the effect of the precipitation strengthening is small, and it is 5.0.
%, An embrittlement phase is generated, so that the amount of addition is 0.2 to 5.
It is desirable to set it to 0%.

Cr improves corrosion resistance.
However, if less than 3%, the effect is small, and 20%
If the ratio exceeds the above range, the sinterability will be remarkably reduced. Therefore, it is desirable to set the range of the addition amount to 3 to 20% or less.

The addition of B facilitates sintering.
If it is less than 0.01%, the effect is not obtained, and if it exceeds 0.10%, brittle borides are generated.
It is desirable to set it to 1 to 0.10%.

In addition, TiC containing 20 to 40% as hard particles is selected from the group IVA, VA and VIA (V, Cr, Zr,
Good results can be obtained even when substitution is made up to 50% with one or more compounds of carbides of Nb, Mo, Hf, Ta, W) and TiN. Some of these will form a solid solution with TiC during sintering, and form composite carbides. Although different from the composite carbide and the carbide existing alone in hardness and toughness, they play a sufficient role as a hard dispersed phase. 5
If it exceeds 0%, the sinterability is reduced, and pores and the like are generated. Therefore, the replacement amount is desirably up to 50%.

When the amount of TiC contained as hard particles is 2
If it is less than 0%, it is difficult to maintain sufficient wear resistance, and if it exceeds 40%, the strength is reduced, so the TiC content is set to 20 to 40%.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention. Are included within the technical scope of

[0029]

EXAMPLES Example 1 Co: 10%, Ni: 10%, Mo: 9%, Ti: 1
%, Al: 1%, Cu: 1%, B: 0.02%, with the sintered steel of the remainder Fe as a matrix, and hard particles dispersed and hardened with TiC in the content ratio shown in Table 1. Steel was produced under the mixing conditions and sintering conditions shown in Table 1.
The particle size of the powder used is as follows.

Fe powder (average particle size: about 5 μm), TiC powder (average particle size: about 2.5 μm), Co powder (average particle size: about 1.5 μm), Ni powder (average particle size: about 2.5 μm), M
o powder (average particle size about 4.5 μm), Ti powder (<45 μm)
m), Al powder (<45 μm), Cu powder (average particle size of about 2.5 μm)
Mix at rpm. Press molding, molding pressure: 3000k
The size was 25 × 25 × 10 mm by gf / cm ² molding.

After sintering, all the samples were heat-treated, adjusted to a hardness of 750 to 800 Hv, and used as test pieces.

First, the surface of the test piece was mirror-polished, an optical microscope photograph of 400 times was taken, and a straight line having a length of 20 mm was drawn in the photograph, and it was confirmed whether or not it crossed the hard grains at any place. did. Table 1 shows the evaluation results of the dispersion state confirmed by this method.

Using these test pieces, JIS-B-4
A bending test (20 samples) was carried out based on 104 (7.2), the minimum strength value was measured, and a wear tester shown in FIG. 1 and a test piece having the shape shown in FIG. 2 were used under the following conditions. A wear test was performed to determine the weight loss of the sample. The results are shown in Table 1. [Wear test conditions] Circumferential speed: 15 m / sec Surface pressure: 10 kgf / cm ² Lubrication: 65 ° C hot water Test time: 4.5 hours Counterpart material: SKH10

[0034]

[Table 1]

No. Nos. 1 to 4 are hard grain dispersion sintered steels according to the present invention, each having a strength of 160 kgf / mm ² or more and having excellent wear resistance.

No. Nos. 5 to 11 show that the dispersion state of the hard particles is not good (that is, 20 m in a 400 × optical microscope photograph).
This is a comparative example in which a straight line having a length of m may not cross a hard grain when a straight line having a length of m is drawn. It can be seen that the minimum strength is low and the abrasion resistance is not sufficient. Example 2 In Table 2, no. Nos. 2 to 5 used TiC and other carbon and nitride as hard particles. 6 to 13 are the same as those of Example 1 except that the composition of the matrix was changed.
o. A test piece was prepared in the same manner as in Example 1, and the minimum strength and abrasion loss were measured in the same manner as in Example 1. The average particle size of carbon / nitride other than TiC is as follows. Table 2 shows the results of TiC powder (about 2.5 μm), HfC powder (about 3 μm), TaC powder (about 1.0 μm), and Mo ₂ C powder (about 3 μm).

[0037]

[Table 2]

No. 12-15, No. 19, no. 2
Reference numerals 1 to 23 are hard grain dispersion sintered steels according to the present invention, each having a strength of 160 kg / mm ² or more and having excellent wear resistance.

No. 16-18, No. 20 is A
This is a comparative example in which the amounts of 1, B, Ti, and Cr are too large, and sufficient strength was not obtained.

[0040]

As described above, according to the present invention, it is possible to provide a hard-grain-dispersed sintered steel having excellent strength reliability and wear resistance and a method for producing the same.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a wear test device used in an example.

FIG. 2 is an explanatory view showing a test piece of a wear test used in Examples.

FIG. 3 is an example of the present invention No. 1 in Table 1. 1 is a copy of an optical microscope photograph of the steel surface of FIG.

FIG. 4 shows Comparative Example No. 1 in Table 1. 5 is a copy of an optical microscope photograph of the steel surface of No. 5.

FIG. 5 shows Comparative Example No. 1 in Table 1. It is a copy of the optical microscope photograph which image | photographed the steel surface of No. 10.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pneumatic hose 2 Air cylinder 3 Load cell 4 Roller 5 Guide block 6 Sample fixture 7 Rotating disk 8 Rotating shaft 9 Strain gauge 10 Stopper 11 Load cell

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/54 B22F 3/10 E (72) Inventor Nobuhiro Yamazaki 2-3-1, Shinhama, Araimachi, Takasago-shi, Hyogo Prefecture No. Kobe Steel, Ltd. Takasago Works (72) Inventor Shinichi Fukumi 2-3-1, Shinhama, Araimachi, Takasago City, Hyogo Prefecture F-term (reference) 4K018 AA30 AA32 AB02 AC01 BA11 BA13 BB04 BC08 BC13 BC16 CA08 CA12 DA11 DA21 DA32 FA08 KA14 4K020 AA22 AC07 BA06 BB29 BC02

Claims (10)

[Claims] 1. A method for producing a hard grain dispersion sintered steel, comprising wet mixing raw material powder comprising Fe or Fe alloy powder and carbide powder, press-molding and sintering in vacuum. A method for producing hard-grain-dispersed sintered steel, comprising performing wet mixing using a solvent having no reactivity. 2. The method according to claim 1, wherein hexane or xylene is used as the solvent having substantially no hygroscopicity. 3. The method according to claim 1, wherein a powder having an average particle size of 15 μm or less is used as the Fe or Fe alloy powder, and a powder having an average particle size of 5 μm or less is used as the carbide powder. 4. The production method according to claim 1, wherein a TiN powder having an average particle diameter of 5 μm or less is further used as the raw material powder. 5. In a temperature range of 1300 to 1450 ° C., 1
The sintering is performed by holding for 10 to 10 hours.
The production method according to any one of the above. 6. A sintered steel in which hard particles containing TiC are dispersed in a matrix containing Fe or an Fe alloy as a main component in an amount of 20 to 40% by mass. The hard grain dispersion sintered steel according to claim 1, wherein hard grains containing TiC always exist on an arbitrary line segment having a length of 20 mm. 7. The matrix comprises: Ni: 3 to 20% (meaning by mass%, the same applies hereinafter), Co: 2 to 40%, Mo: 2 to 15%, Al: 0.2 to 2.0%, The sintered steel according to claim 6, comprising 0.2 to 3.0% of Ti and 0.2 to 5.0% of Cu. 8. The method according to claim 1, wherein the matrix further comprises Cr: 3 to 2.
8. The sintered net according to claim 7, comprising 0%. 9. The method according to claim 1, wherein the matrix further comprises B: 0.01.
9. The sintered steel according to claim 7 or 8 containing 0.10%. 10. The hard grains containing TiC account for at least 50% of TiC, and V, Cr, Zr, Nb, Mo,
The sintered steel according to any one of claims 6 to 9, wherein the sintered steel is one or more of a carbide of a metal selected from the group consisting of Hf, Ta, and W and TiN.