US 3827863 A
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Aug 6, 1974 KENTARO TAKAHASHI ETAL 3,827,863
' THERMAL AND ABRASION RESISTANT SINTERED ALLOY Filed Sent. 5. 1972 FIG.
0 EXAMPLE OF THIS INVENTION CONVENTIONAL SINTERED FERRO-ALLOY HARCNFLSS NORMAL IOIO 2OO 300 4OO sOO sOO (c) TEMP TRANSFORMATION TEMP.
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rates 3,827,863 THERMAL AND ABRASION RESISTANT SINTERED ALLOY Kentaro Takahashi, Ohmiya, Minoru Hasegawa, Saitama, and Kaoru Nara, Kawaguchi, Japan, assignors to Nippon Piston Ring Co., Ltd., Tokyo, Japan Filed Sept. 5, 1972, Ser. No. 286,393 Claims priority, application Japan, Sept. 2, 1971, 46/ 66,981 Int. Cl. B22f 1/00 US. Cl. 29182 1 Claim ABSTRACT OF THE DISCLOSURE An alloy prepared by molding a powdery composition comprising 0.6 to 2% of carbon, 1 to 3% of nickel, 10 to 15% of chromium, 0.3 to 1.5% of molybdenum, 5 to 15 of cobalt and 3 to 7% of tungsten, by weight, and the balance being iron, and then sintering the molded composition has large thermal resistance and abrasion resistance.
BACKGROUND OF THE INVENTION A publicly known metal such as chromium, cobalt, tungsten, etc. has not only a large abrasion resistance but also is prominent in its characteristics at elevated temperatures and is applied in various fields. However, such a metal has many problems to be solved when it is used as sintered parts for a machine. That is, such a metal has a high melting point so that the sintering temperature is, of necessity, required to be elevated and the sintering time has to be extended, and, therefore, it is naturally disadvantageous in cost.
SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the hardness at elevated temperatures of sintered alloys of Examples 1 and 2 and on a conventionally cast iron and a sintered iron alloy.
FIG. 2 is a graph showing the abrasion resistance of sintered alloys of Examples 1 and 2 and of a conventionally cast iron and a sintered iron alloy.
DETAILED DESCRIPTION OF THE INVENTION The sintered alloy of the present invention is obtained by adding 15 to 25% of special alloy powder consisting of, by weight, 1 to 3% of carbon, 55 to 65% of chrmium, 25 to 30% of tungsten and to 20% of cobalt to a powdery composition mainly composed of iron and containing carbon, nickel and molybdenum, and compression-molded the resulting powdery composition mainly composed of iron and comprising, by weight, 0.6 to 2% of carbon, 1 to 3% of nickel, 0.3 to 1.5% of molybdenum, to of chromium, 5 to 15% of cobalt and 3 to 7% of tungsten under a pressure of 3 to 6 ton/ cm. and sintering it in an atmosphere at 1120 to 1170 C. for 30 to 60 minutes.
3,827,863 Patented Aug. 6, 1974 When the carbon content is less than 0.6% by weight, the alloy changes to a ferrite-excessive structure so that high hardness cannot be expected while, with more than 2%, the alloy changes to a cementite-excessive structure which is high in brittleness.
Nickel strengthens the base structure of the alloy and improves the thermal resistance and abrasion resistance. However, the effect is small with a nickel content of less than 1%, while, when it is more than 3%, the base structure locally turns to martensite so that the hardness increases unnecessarily and the structure and the hardness lose uniformity.
Molybdenum increases the tenacity of alloy as well as the impact strength and endurance limit, and, on the other hand, improves the heat treatment property and stabilizes the structure after sintering and further possesses a synergistic effect, with other elements. However, there is no elfect with less than 0.3% of molybdenum and even with more than 1.5% no increase in eifect corresponding to the increase is not obtained.
In connection with the manufacturing of the alloy powder and structure and characteristic of sintered material, 15 to 25 of alloy powder are selected and chromium, cobalt and tungsten are established at 10 to 15%, 5 to 15% and 3 to 7%, respectively.
In the sintered alloy of the present invention, from a viewpoint of providing the material with a high density and improving the lubricating property, it is very advantageous to impregnate molten lead into the alloy after the alloy is molded and sintered. In this case, the amount of lead impregnated has been experimentally confirmed to be preferably within the range of 0.05 to 5% by weight. That is, with less than 0.05% the effect of impregnation is not remarkable and the impregnation of more than 5% of lead involves a problem in strength from the relation with the density of material before impregnation.
The present invention will be further illustrated by the following Examples by which the present invention is not intended to be limited. All percents are by weight.
EXAMPLE 1 18% of a special alloy powder (150 mesh) comprising 0.74% of graphite powder (325 mesh), 1.08% of carbonyl nickel powder (250 mesh), 0.35% (as molybdenum) of ferro-molybdenum powder (150 mesh), 55 to 65% of chromium, 25 to 30% of tungsten and 5 to 20% of cobalt were added to reduced iron powder mesh) as iron powder (at this time, the actual chromium content was 10.8%, tungsten 5.4% and cobalt 1.8% Then, cobalt powder mesh) was added thereto so that the cobalt content became 5.5% and further 1% of zinc stearate was added and mixed as a lubricant. The mixture was molded under a pressure of 4 ton/cm. and sintered at 1120 to 1170 C. in an atmosphere of decomposed ammonium gas. This sintered material had a density of 6.5 g./cm. and a hardness on the Rockwell B scale of 94'.
EXAMPLE 2 A sample was prepared by adding 2.3% of the special alloy powder under the same conditions as described in Example 1 and then the sample was impregnated with molten lead. The final composition of the sample was 1.71% of carbon, 2.83% of nickel, 1.33% of molybdenum, 14.1% of chromium, 7.0% of tungsten and 14.2% of cobalt and the lead content after lead impregnation was 3.8%. The sintered material had a density of 6.7 g./cm. and a hardness on the Rockwell B scale of 96.
FIGS. 1 and 2 show the results of measuring the hardness at elevated temperatures and abrasion using a valve sheet abrasion testing machine (number of rotation 3000 rpm, spring pressure 35 kg, valve velocity at the time of valve closing 0.5 rn./sec., width of valve 1 mm., test repeating 3 number 8x10 material SUI-1 31 B) on the sintered alloy of Examples 1 and 2 in comparison with a conventionally known cast iron and sintered ferro alloy. As is apparent from the results obtained the sintered alloy of the present invention was higher in hardness at elevated temperatures in comparison with the conventionally known cast iron and sintered ferro iron, and was excellent in hardness characteristics. In the abrasion test the conventionally known cast iron and sintered ferro alloy had peaks at 300 C. and 400 C., respectively, and the sintered alloy of the present invention was lower in abrasion and very stable at elevated temperatures. The compositions of the conventionally known cast iron and sintered ferro alloy were as follows:
Sintered ferro alloy:
Carbon 1%, copper 3%, chromium 3%, and balance 11'011. Cast iron:
Carbon 3.02%, silicon 2.11%, manganese 0.48%, chromium 0.81%.
The sintered alloy of the present invention is advantageous in cost, and excellent in thermal and abrasion resistance with improved sintering time -by alloying chromi- References Cited UNITED STATES PATENTS 3,471,343 10/1969 Koehler -125 3,495,957 2/1970 Matoba et al 29182.l 2,662,010 12/1953 Ahles 75123 J 2,562,543 7/1951 Gippert 75123 K BENJAMIN R. PADGETT, Primary Examiner B. HUNT, Assistant Examiner US. Cl. X.R.
29-1871, 156.7 A; 75128 B, 128 D, 128 W