US20060201280A1

US20060201280A1 - Sinter-hardening powder and their sintered compacts

Info

Publication number: US20060201280A1
Application number: US11/308,824
Authority: US
Inventors: Kuen-Shyang Hwang; Yung-Chung Lu
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-06-10
Filing date: 2006-05-11
Publication date: 2006-09-14
Also published as: CN101069927A; DE102006027851B3; TWI294318B; TW200742623A; CN101069927B

Abstract

The present invention relates to a sinter hardening powder that can yield a sintered compact with high strength. The present invention provides a raw powder for sintering, comprising Fe as its primary component and also comprising 0.1-0.8 wt % C, 3.5-12.0 wt % Ni, 0.1-7.0 wt % Cr, and 2.0 wt % or less of Mo, wherein the mean particle size of the raw powder for sintering is 150 μm or less. The sintered compact having high tensile strength, high hardness, and good ductility can be formed without performing the quenching process.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of a prior application Ser. No. 10/907,155, filed on Mar. 23, 2005, now pending, which claims the priority benefit of Taiwan application serial no. 93116634, filed on Jun. 10, 2004 and Taiwan application serial no. 93126297, filed on Sep. 1, 2004. All disclosures are incorporated herewith by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention generally relates to raw powders, in particular, to compositions of sinter hardening powders useful for forming high hardness and high strength parts by the powder metallurgy (P/M) process.
2. Description of Related Art
As is well known in the art, the design of the alloy is always the critical starting point for the development of powder metallurgy. By combining different alloying elements and different amounts of additives, various alloy steels can be developed and applicable to diversified circumstances. In general, powder metallurgy components are required to possess high density, good dimensional control, and good mechanical properties. Thus, different alloys are developed. One example to enhance the sintered density and dimensional control of sintered compacts is described in US2005/0109157, in which a prealloyed steel powder is used, in contrast to the elemental powder or mixtures of elemental powder and ferroalloy powder of the present invention. Another example to enhance the hardness, strength, or ductility of sintered compacts is by adjusting the alloying elements, as is disclosed in U.S. Pat. No. 5,476,632. To attain better mechanical properties, most sintered components require a hardening heat treatment like quenching followed by tempering.
However, while the quenching is performed on the sintered components, several problems such as deformation, size inconsistency, or cracking may be caused by the fast cooling procedure. In addition, the heat treatment (quenching) performed on the sintered components will cause additional costs. Therefore, sinter-hardening powders have been developed by adding high hardenability alloying elements such as molybdenum (Mo), nickel (Ni), manganese (Mn) or chromium (Cr) to iron powders. The sinter-hardening powders are pressed out to form a green compact through the conventional compacting process. Thereafter, the green compact is sintered so as to obtain a sintered compact with the hardness above HRC30. Examples of alloys (i.e. sintered compacts) produced by the above-mentioned method are Ancorsteel 737SH (Fe-0.42MN-1.40Ni-1.25Mo—C) from Hoegananes Corp. and ATOMET 4701 (Fe-0.45Mn-0.90Ni-1.00Mo-0.45Cr—C) from Quebec Metal Powders Limited. The sintered components made from these sinter-hardening powders are cooled at rates of a minimum of 30° C. per minute in the sintering furnace in order to generate martensite and bainite.
Although the alloying elements in these sintered compact are still not homogenized completely using the regular sintering conditions of 1120° C. and 30-40 minutes, these sinter-hardening powders provide better mechanical properties than those possible using non sinter-hardening powders. Although the sinter-hardening powders can reduce costs due to the elimination of the quenching process, a high cooling rate system has to be installed in the sintering furnace. Furthermore, the aforementioned cooling rates, while slower than those of quenching into oil or water, are still fast enough to cause problems such as deformation, inconsistency of the dimensions, and even cracking. According to U.S. Pat. No. 5,682,588, the claimed powders are compacted by the conventional pressing process, specifically, the claimed powders are sintered between 1130-1230° C., and then cooled at rates of 5-20° C./minute in order to reach the desired sinter-hardening effects. This has improved the process by lowering the minimum cooling rate of 30′/min, as described in the previously mentioned processes. However, the mechanical properties, in particular, the ductility, are still unsatisfactory.
Concerning the press-and-sinter process, there are several material standards (the latest Year 2003 version) for sinter hardened alloys set forth by the Metal Powder Industries Federation (MPIF), for example, FLNC-4408 (1.0-3.0% Ni, 0.65-0.95% Mo, 1.0-3.0% Cu, 0.6-0.9% C, and the remaining portion is Fe) and FLC2-4808 (1.2-1.6% Ni, 1.1-1.4% Mo, 1.0-3.0% Cu, 0.3-0.5% Mn, 0.6-0.9% C, and the remaining portion is Fe). After sintering and tempering, the above-mentioned sinter hardening alloy of FLC2-4808 can reach a tensile strength of 1070 MPa under the density of 7.2 g/cm³, and the hardness can reach HRC40, while the elongation is less than 1.0%. Although this alloy is a sinter-hardening type, its mechanical properties are still not satisfactory, particularly the elongation, and the required cooling rate is still very fast.
In the field of metal injection molding process, the powders used are usually less than 30 μm in size, while the particles used in the press-and-sinter process are less than 150 μm in size. Since the diffusion distances in fine powers are shorter, the added alloying elements can be homogenized more easily in the matrix materials. Therefore, sintered compacts sintered from the fine powders possess mechanical properties better than those of the traditional pressed-and-sintered components. At present, the alloys commonly used for metal injection molding are the Fe—Ni—Mo—C alloy series, exemplified by MIM-4605 (1.5-2.5Ni, 0.2-0.5% Mo, 0.4-0.6% C, <1.0% Si, the remaining portion is Fe), which has the best mechanical properties according to the MPIF standards. This alloy, after sintering, reaches a tensile strength of 415 MPa, a hardness of HRB62, and a ductility of 15%. In order to attain the best mechanical properties, the sintered product has to be heat-treated (quenched and tempered). It then reaches a tensile strength of 1655 MPa, a hardness of HRC48, and a ductility of 2.0%.
Although excellent mechanical properties of the metal injection molded products can be obtained by heat treatment after sintering, the costs of the heat treatment accounts for a large part of the whole production cost. Hence, it is critical to lower the costs of the heat treatment, for example, by using sinter-hardening alloys. However, according to the Metal Powder Industries Federation Standards, no sinter-hardening alloys are listed for the metal injection molding process.
As mentioned above, application of fine powders improves the uniformity of the alloying elements and mechanical properties of the products. However, application of fine powders in the traditional press-and-sinter process is difficult because of the poor flowability of the powder, which in turn makes it difficult to fill the powders into the die cavity, and thus automated pressing can not be used. However, this problem can be overcome by granulating the fine powders into large spherical particles, such as by the spray drying process, and the granulated powders can then be applied in the press-and-sinter process.
The present invention was achieved in view of the problems such as those described above for press-and-sinter and metal injection molding products. An object is thus to provide raw sinter hardening powders or granulated sinter hardening powders for sintering whereby the sintered compacts can attain high hardness and high strength without any heat treatment (quenching) and with a slow cooling rate after sintering.

REFERENCE PAPERS

1. U. Engström, J. McLelland, and B. Maroli, “Effect of Sinter-Hardening on the Properties of High Temperature Sintered PM Steels”, Advances in Powder Metallurgy & Particulate materials-2002, Compiled by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I. Sanderow, MPIF, Princeton N.J., 2002, part 13, page 1-13.
2. K. Kanno, Y. Takeda, B. Lindqvist, S. Takahashi, and K. K. Kanto, “Sintering of Prealloy 3Cr-0.5Mo Steel Powder in a carbon/carbon Composite Mesh Belt Furnace”, Advances in Powder Metallurgy & Particulate materials-2002, Compiled by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I. Sanderow, MPIF, Princeton N.J., 2002, part 13, page 14-22.
3. H. Suzuki, M. Sato, and Y. Seki, “Sinter Hardening Characteristics of Ni—Mo—Mn—Cr Pre-Alloyed Steel Powder”, Advances in Powder Metallurgy & Particulate materials-2002, Compiled by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I. Sanderow, MPIF, Princeton N.J., 2002, part 13, page 83-95.
4. D. Milligan, A. Marcotte, J. Lingenfelter, and B. Johansson, “Material Properties of Heat Treated Double Pressed/Sintered P/M Steels in Comparison to Warm Compacted/Sinter Hardened Materials”, Advances in Powder Metallurgy & Particulate materials-2002, Compiled by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I. Sanderow, MPIF, Princeton N.J., 2002, part 4, page 130-136.
5. B. Lindsley, “Development of a High-Performance Nickel-Free P/M Steel”, K. Kanno, Y. Takeda, B. Lindqvist, S. Takahashi, and K. K. Kanto, “Sintering of Prealloy 3Cr-0.5Mo Steel Powder in a carbon/carbon Composite Mesh Belt Furnace”, Advances in Powder Metallurgy & Particulate materials-2004, Compiled by W. B. James, and R. A. Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page 19-27.
6. B. Hu, A. Klekovkin, D. Milligan, U. Engström, S. Berg, and B. Maroli, “Properties of High-Density Cr—Mo Pre-alloyed Materials High-Temperature Sintered”, Advances in Powder Metallurgy & Particulate materials-2004, Compiled by W. B. James, and R. A. Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page 28-40.
7. P. King, B. Schave, and J. Sweet, “Chromium-containing Materials for High-Performance Components”, Advances in Powder Metallurgy & Particulate materials-2004, Compiled by W. B. James, and R. A. Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page 70-80.
8. M. Schmidt, P. Thorne, U. Engström, J. Gabler, T. J. Jesberger, and S. Feldbauer, “Effect of Sintering Time and Cooling Rate on Sinter Hardenable Materials”, Advances in Powder Metallurgy & Particulate materials-2004, Compiled by W. B. James, and R. A. Chernenkoff, MPIF, Princeton N.J., 2004, part 10, page 160-171.
9. MPIF Standard 35, Materials standards for Metal Injection Molded Parts, 2000 edition, MPIF, Princeton N.J., pp. 12-13.
10. MPIF Standard 35, Materials standards for P/M Structural Parts, 2003 edition, MPIF, Princeton N.J., pp. 46-47.
11. K. S. Hwang, C. H. Hsieh, and G. J. Shu, “Comparison of the Mechanical Properties of Fe-1.75Ni-0.5Mo-1.5Cu-0.4C Steels made from the PIM and the Press-and-Sinter Processes”, Powder Metallurgy, 2002, Vol. 45, No. 2, pp. 160-166.
12. U.S. Pat. No. 5,876,481, 1999.
13. U.S. Pat. No. 5,834,640, 1998.
14. U.S. Pat. No. 5,682,588, 1997.
15. U.S. Pat. No. 5,476,632, 1995.

SUMMARY OF THE INVENTION

The present invention is directed to a sinter hardening powder having novel composition and sintered compact manufactured thereby.
The above-mentioned sinter hardening powder and the sintered compact prepared therefrom including iron (Fe), carbon (C), nickel (Ni), and chrome (Cr), in the ratios as follows: Ni: 3.5 wt %-12.0 wt %, carbon: 0.1 wt %-0.8 wt %, chrome: 0.1 wt %-7.0 wt %, 2.0% or less of Mo, and the remaining portion is Fe. Additionally, the mean particle size of the powder is less than 150 μm. In one embodiment of the present invention, the above composition may further contain at least one other minor strengthening elements at the amount of 0.5 wt %-5.0 wt %. The strengthening elements can be selected from the group consisting of Copper (Cu), Titanium (Ti), Aluminum (Al), Manganese (Mn), Silicon (Si), and Phosphorous (P). The element carbon mentioned above may be provided by adding graphite or using carbon-containing carbonyl iron powders. The sintered compact of the above-mentioned sinter hardening powders has a high tensile strength, high hardness, and good ductility without the use of any quenching process. Since no quenching process is required, the production cost is lower. A higher production yield is also attained due to the elimination of defects, such as cracks and distortions, which are caused by the high thermal stress during quenching.
Moreover, the sintered compact fabricated by the conventional press-and-sinter or metal injection molding processes can be sinter-hardened under the normal cooling rate (3-30° C./minute) inside the traditional sintering furnace. The sintered compact can be treated with low temperature tempering without quenching, to obtain excellent mechanical properties.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and they are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIGS. 1(a) and 1(b) show the line scan of Ni in Cr-free sintered compacts using an Electron Probe Microanalyzer (EPMA).
FIG. 2 shows that when the Cr content increases, the hardness of the sintered compact produced by using the metal injection molding process and using fine carbonyl iron powders increases slightly first, reaching a maximum at about 0.7 wt %, and then decreases.
FIG. 3 shows that when the Cr content increases, the hardness of the sintered compact produced by using press-and-sinter process and using coarse iron powders increases first, reaching a maximum at about 3 wt %, and then decreases.
FIG. 4 is a cross-sectional view of the sample in example 1, observing the ductile microstructure with dimple type fractures by the scanning electronic microscope.

DESCRIPTION OF THE EMBODIMENTS

The foregoing descriptions of specific embodiments of the invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles and the application of the invention, thereby enabling others skilled in the art to utilize the invention in its various embodiments and modifications according to the particular purpose intended. The scope of the invention is intended to be defined by the claims appended hereto and their equivalents.
The sinter hardening powder for sintering of the embodiment of the present invention includes Fe as its primary component, 0.1 wt %-0.8 wt % of C, 3.5 wt %-12.0 wt % Ni, 0.1 wt %-7.0 wt % Cr, 2.0 wt % or less of Mo, wherein the mean particle size of the sinter hardening powder for sintering is 150 μm or less.
Nickel (Ni) is an element that could yield high hardenability and could also give high toughness and elongation of sintered compacts. Thus, it is preferred to add more Ni in the sinter hardening powder for sintering. In the present invention, the Ni content preferred is between 3.5 wt % and 12.0 wt %, since the sinter-hardening characteristics are not obvious when the Ni content is lower than 3.5 wt %. Additionally, the sinter-hardening characteristics diminish when the Ni content is higher than 12 wt %. In another aspect, the sinter hardening powder becomes expensive when the Ni content is higher than 12 wt %. However, Ni has a slow diffusion rate into Fe compared to that of Cr, Mo, Cu, and Mn, which are the main alloying elements widely used in the industry. Thus, Ni is difficult to be homogenized in the Fe matrix and as a result loses its sinter-hardening benefits. Moreover, Ni-rich areas are formed. The Ni-rich areas are low in strength and hardness and become the vulnerable sites during mechanical testing and during field operations that are under high stresses.
The sinter hardening powder of the present invention may further comprise at least one other minor strengthening elements at the amount of 0.5 wt %-5.0 wt %. The strengthening elements may be selected from the group consisting of Copper (Cu), Titanium (Ti), Aluminum (Al), Manganese (Mn), Silicon (Si), Niobium (Nb), or Phosphorous (P). Specifically, the content of the strengthening elements may be listed as following: 2 wt % or less Copper (Cu), 1 wt % or less Titanium (Ti), 1 wt % or less Aluminum (Al), 1 wt % or less Manganese (Mn), 1 wt % or less Silicon (Si), 1 wt % or less Niobium (Nb), and 1 wt % or less of Phosphorous (P). In an preferred embodiment of the present invention, the content of Copper (Cu) is between 0.1 wt %-1.0 wt %, the content of Manganese (Mn) is between 0.1 wt %-0.8 wt %, and the content of Silicon (Si) is between 0.1 wt %-0.5 wt %.
In one preferred embodiment of the present invention, the content of Carbon (C) may be between 0.3 wt %-0.7 wt %, the content of Nickel (Ni) may be between 6.0 wt %-10.0 wt %, the content of chromium (Cr) may be between 0.3 wt %-6.0 wt %, and the content of molybdenum (Mo) may be between 0.1 wt %-1.0 wt %. The content of the elements of the sinter hardening powder is only for illustration. The scope of the invention is intended to be defined by the claims appended hereto and their equivalents.
In one embodiment of the present invention, the mean particle size of the sinter hardening powders is between 0.1 μm and 30 μm, and the content of chromium (Cr) is between 0.1 wt % and 2 wt %. In an alternative embodiment of the present invention, the mean particle size of the sinter hardening powders is between 30 μm and 150 μm, the content of chromium (Cr) is between 1 wt % and 6 wt %. In an alternative embodiment of the present invention, the sinter hardening powders may be elemental powders, ferroalloy powders, or a mixture thereof.
To fully take advantages of the Ni addition, we have found that Cr addition significantly improves the homogeneity of Ni. For example, the Ni distribution, as shown by the line scan of Ni in FIG. 1(a), is not uniform. When Cr is present, the Ni distribution becomes much improved, as shown by the line scan of Ni in FIG. 1(b). The addition of Cr thus improves the Ni distribution and eliminates the soft Ni-rich areas. Therefore, the overall hardness of the sintered compacts increases.
FIG. 2 shows that, using a mixture of fine carbonyl iron powders and other alloying powders according to the composition of Fe-8Ni-0.8Mo-xCr-0.5C (x varies from 0 wt %-4 wt %) and using the metal injection molding process, the hardness of the sinter hardened and tempered specimens increases first, reaching a maximum at about 0.7 wt %, and then decreases as the amount of Cr increases. This means that the amount of 3 wt % Cr is too much for the need to homogenize the Ni. However, when large iron powders are used, the homogenization becomes more difficult. Thus, the amount of Cr that is required to homogenize Ni increases. This effect is demonstrated by using a mixture of large (mean size of 72 μm) water atomized iron powders and other alloying powders according to the composition of Fe-0.5Mo-4Ni-0.5C and using the press-and-sinter process. FIG. 3 shows that the hardness increases, reaches the maximum at about 3 wt % Cr, and then decreases as the amount of Cr increases. These examples show that more Cr is required to homogenize Ni for coarse iron powders than that of using fine iron powders.
The element ingredients and the mechanical properties of the sintered compact are listed in Table 1 and Table 2, repectively, whereas examples 1-2 in Table 2 are the sintered compacts made from the metal injection molding process; examples 3-6 are the sintered compacts made from the press-and-sinter process. Table 1 and Table 2 are also used to illustrate the sinter hardening effect of the sinter hardening powder for the present invention, while examples 1-6 represent the present invention and examples A-E are used as the comparison group according to the available literatures.

EXAMPLE 1

Following the composition as shown in Table 1, the carbonyl iron powders that contain C and Si and with a mean particle size of 5 μm are mixed together with fine (with a mean particle size less than 15 μm) elemental Mo and Ni powders and Fe—Cr and Fe—Mn ferroalloy powders. The admixed powder was added with 7 wt % of the binder, kneaded in a Z type high shear rate mixer at 150° C. for 1 hour, then cooled to room temperature to obtain the granulated feedstock. Thereafter, the previously mentioned granulated feedstock is filled into the injection molding machine to produce the tensile test bar (e.g. the standard tensile bar from the MPIF-50 standard.). The tensile bar is de-bound under the procedure applied from the known arts in the industry to remove the binder, then heating the tensile bar in the vacuum furnace at 1200° C. for two hours, and then cooling to room temperature at a cooling rate of about 6° C./minute between 600° C. and 300° C., so as to reach a hardness of HRC51 and a ductility of 1.0%. The tensile bar, after being tempered at 180° C. for two hours, reaches a tensile strength of 1800 MPa, a hardness of HRC45, and a ductility of 3%, as shown in Table 2. FIG. 4 is a fracture surface of the sample in example 1. The ductile microstructure with dimple type fractures is observed using a scanning electronic microscope. This indicates that products of high hardness, high tensile strength, and high ductility can be produced from these alloying elements. Take the as-sintered MIM-4605 as an example, which is an injection molding material with the best mechanical properties listed by the MPIF. The properties are 415 MPa, HRB62, and 15% ductility, as shown in example A in Table 2. After quenching and tempering, the improved MIM-4605 will possess 1655 MPa, HRC48, and a ductility of 2%, as shown in example B in Table 2. MIM-4605 needs to be quenched and tempered to reach the mechanical properties similar to those made by the present invention. However, the sintered compact of the present invention possesses good mechanical properties without the need for quenching.

EXAMPLE 2

The same processes as disclosed in example 1 but with the compositions listed in example 2 in Table 1. After tempering, the tensile bar has a tensile strength of 1780 MPa, a hardness of HRC45, and a ductility of 4%.

EXAMPLE 3

Following the compositions listed in Example 3 in Table 1, the prealloyed Fe-3Cr-1.5Mo powders having a mean particle size of 75 μm were mixed with fine elemental Ni and graphite powders and 0.8% zinc stearate, which served as a lubricant. The mixture was compacted into tensile bars, de-bound at 550° C. for 15 minutes and then sintered at 1250° C. for two hours. After tempering, the sinter hardened tensile bar with a density of 7.2 g/cm³has a tensile strength of 1320 MPa, a hardness of HRC39, and a ductility of 2%.

EXAMPLE 4

The same processes as in example 3, but with the compositions listed in example 4 in Table 1. The Fe-3Cr-0.5Mo prealloyed powder was mixed with fine elemental Ni, Cu, and graphite powders, and 0.8% zinc stearate. After tempering, the sinter hardened tensile bar has a tensile strength of 1280 MPa, a hardness of HRC38, and a ductility of 2%.

EXAMPLE 5

The same processes as in example 3, but with the compositions listed in example 5 in Table 1. The prealloyed Fe-1.5Cr-0.2Mo powders having a mean particle size of 72 μm were mixed with fine elemental Ni and graphite powders and 0.8% zinc stearate. After tempering, the sinter hardened tensile bar has a tensile strength of 1270 MPa, a hardness of HRC31, and a ductility of 2%.

EXAMPLE 6

Following the compositions listed in example 6 in Table 1, the carbonyl iron powders that contains C and Si and with a mean particle size of 5 μm are mixed together with fine elemental Mo and Ni powders and Fe—Cr ferroalloy powder. The powder mixture was mixed together with 1.5 wt % of the binders. The powders, water, and binders (e.g.: Polyvinyl alcohol) are blended into a slurry. The slurry is then atomized from the nozzle at high speed and dried by hot air to evaporate the water within. The fine powders are thus bonded with each other by the binder to form granulated powders with good flowability. The particle size of the graduated powder is about 40 μm. The previously mentioned granulated powders are filled into the die cavity to produce the green tensile bar by the automatic compacting machine. The tensile bar is de-bound under the procedure applied from the known arts in the industry. For example, the temperature will be raised at the rate of 5° C./minute up to 400° C., and then at the rate of 3° C./minute up to 1100° C., maintained for one hour, and then raised at the rate of 10° C./minute up to 1200° C., and sintering will continue at this temperature for one hour. Afterwards, the tensile bar is cooled as the temperature of the furnace drops, and the tensile bar is tempered for 2 hours at 180° C. without the use of the quenching process. As shown in the Table 2, the sinter hardened tensile bar has a tensile strength of 1650 MPa, a hardness of HRC43, and an elongation of 4%.

EXAMPLE A

According to the standards from the MPIF-35, the elements of MIM-4605 used in injection molding are shown in Table 1, while the mechanical properties of the sintered compact produced by the elements of MIM-4605 are shown in Table 2.

EXAMPLE B

The composition of Example B is identical with the composition as in example A. After the quenching and tempering treatment, products improve enormously in terms of mechanical properties, as shown in Table 2.

EXAMPLE C

According to the MPIF-35 standards, the elements of MIM-2700 used in injection molding are shown in Table 1, while the mechanical properties of the sintered compact produced by the elements of MIM-2700 are shown in Table 2.

EXAMPLE D

According to the MPIF-35 standards, the elements of sinter-hardening alloy FLC2-4808 (the best sinter-hardened press-and-sinter work piece listed by the MPIF) are shown in Table 1. The typical mechanical properties of sinter hardened FLC2-4808 are 1070 MPa, HRC40, but with less than 1% ductility, as shown in Table 2. The low ductility makes the alloy less suitable for the application of structural parts, which usually require good ductility.

The comparison of the above examples demonstrated that the raw sinter hardening powder related to this invention makes it possible to obtain sinter hardened compacts with good mechanical properties and with low manufacturing costs.

TABLE 1


Commonly used percentages and elements for the examples 1-6 in the
present invention and for cases A-D from the industry and based on the Metal Powder
Industries Federation(MPIF) standards (weight percentage, wt %)

Element	Ex: 1	Ex: 2	Ex: 3	Ex: 4	Ex: 5	Ex: 6	Ex: A & B	Ex: C	Ex: D

C	0.36%	0.34%	0.5%	0.5%	0.6%	0.4%	0.4-0.6%	<0.1%	0.6-0.9%
Ni	8.0%	9.0%	4.0%	3.1%	4.0%	7.5%	1.5-2.5%	6.5-8.5%	1.2-1.6%
Mo	0.8%	0.8%	0.5%	0.5%	0.2%	0.8%	0.2-0.5%	<0.5%	1.1-1.4%
Cr	0.8%	0.8%	3.0%	3.0%	1.5%	0.5%	—	—	—
Mn	0.6%	—	—	—	—	—	—	—	0.3-0.5%
Cu	—	—	—	1.0%	—	—.	—	—	1.0-3.0%
Si	0.3%	0.3%	—	—	—	0.3%	<1.0	<1.0	—
Fe	the rest	the rest	the rest	the rest	the rest	the rest	the rest	the rest	the rest

TABLE 2


Comparison of mechanical properties of the alloys
among examples 1-6 and examples A-D

		Quench-
	Density	hardening	Tensile strength
Ex:	(g/cm3)	process	(MPa)	Hardness	Ductility (%)

1	7.6	None**	1800	HRC45	3
2	7.6.	None**	1780	HRC45	4
3	7.2	None**	1320	HRC39	2
4	7.1	None**	1280	HRC38	2
5	7.3	None**	1270	HRC31	2
6	7.5	None**	1650	HRC43	4
A	7.5	None	415	HRB62	15
B	7.5	Yes*	1655	HRC48	2
C	7.6	None	440	HRB69	26
D	7.2	None**	1070	HRC40	<1

*Austenizied at 860° C. and then oil quenched, then tempered at 180° C. for 2 hours.

**Sintered and then tempered at 180° C. for 2 hours.
In conclusion of the above description, compared to the best injection molding alloy, MIM-4605 (after quenching and tempering), and the best sinter-hardening alloy, FLC2-4808, for the press-and-sinter work piece, listed by the Metal Powder Industries Federation (MPIF); the sinter-hardening composition of the present invention can attain similar or even better mechanical properties without the quench-hardening process. Besides, the problems derived from quench-hardening in the prior art, including deformation, inconsistency of the dimensions, and cracking after quenching, etc, can be avoided in the present invention, and the costs from the quench-hardening process can be eliminated. Although sinter-hardening alloys have been available for the pressing process in traditional powder metallurgy, the cooling rate required for the sintered compact is much higher than that required in this study. The sintered compact of the present invention provides excellent mechanical properties, and it also provides advantages in the areas of dimensional control and lower costs.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

Claims

1. A sinter hardening powder comprising iron (Fe) as its primary composition, 0.1 wt %-0.8 wt % of Carbon (C), 3.5 wt %-12.0 wt % Nickel (Ni), 0.1 wt %-7.0 wt % chromium (Cr), and 2.0 wt % or less of molybdenum (Mo), wherein a mean particle size of sinter hardening powders is 150 μm or less.

2. The sinter hardening powder as recited in claim 1, further comprising at least one element selected from the group consisting of 2 wt % or less Copper (Cu), 1 wt % or less Titanium (Ti), 1 wt % or less Aluminum (Al), 1 wt % or less Manganese (Mn), 1 wt % or less Silicon (Si), 1 wt % or less Niobium (Nb), and 1 wt % or less of Phosphorous (P).

3. The sinter hardening powder as recited in claim 1, wherein the content of Carbon (C) is between 0.3 wt %-0.7 wt %, the content of Nickel (Ni) is between 6.0 wt %-10.0 wt %, the content of chromium (Cr) is between 0.3 wt %-6.0 wt %, and the content of molybdenum (Mo) is between 0.1 wt %-1.0 wt %.

4. The sinter hardening powder according to claim 2, wherein the content of Copper (Cu) is between 0.1 wt %-1.0 wt %, the content of Manganese (Mn) is between 0.1 wt %-0.8 wt %, and the content of Silicon (Si) is between 0.1 wt %-0.5 wt %.

5. The sinter hardening powder as recited in claim 1, wherein a source of carbon is from graphite.

6. The sinter hardening powder as recited in claim 1, wherein a source of carbon is from carbonyl iron powder.

7. The sinter hardening powder as recited in claim 1, wherein the mean particle size of the sinter hardening powders is between 0.1 μm and 30 μm, and the content of chromium (Cr) is between 0.1 wt % and 2 wt %.

8. The sinter hardening powder as recited in claim 1, wherein the mean particle size of the sinter hardening powders is between 30 μm and 150 μm, the content of chromium (Cr) is between 1 wt % and 6 wt %.

9. The sinter hardening powder as recited in claim 1, wherein the sinter hardening powders are elemental powders, ferroalloy powders, or a mixture thereof.

10. The sinter hardening powder as recited in claim 9, wherein the ferroalloy powders and the elemental powders are diffusion alloyed or chemically bonded together.

11. A granulated powder for sintering manufactured using the sinter hardening powder as recited in claim 1, wherein a mean particle size of the granulated powder is between 20 μm-150 μm.

12. The granulated powder for sintering as recited in claim 11, wherein the mean particle size of the granulated powder is between 40 μm-80 μm.

13. A sintered compact manufactured using the sinter hardening powder as recited in claim 1.

14. A sintered compact manufactured using the granulated powder as recited in claim 11.