US3856478A - Fe-Mo-C-{8 Cr{9 {0 SINTERED ALLOYS FOR VALVE SEATS - Google Patents

Abstract

Ferrous sintered alloys adapted for use as valve seats in internal combustion engines resistive to wear and intermetallic impact wear from the heated valve associated therewith, the alloys composed essentially of from 0.4-2.0 percent of carbon, 210 percent of molybdenum, optionally containing 0.5-5.2 percent chromium, the balance being iron plus minor impurities are disclosed. The valve seats made of the novel sintered alloys are particularly suited for engines burning lead-free gasoline or engines using LPG as the fuel.

Description

United States Patent 1 Iwata et al.

1 1 Dec.24, 1974 i 1 FE-MO-C-[CR] SINTERED ALLOYS FOR VALVE SEATS [75] Inventors: Tokushige lwata; Kiyoaki Sakamoto; Teruo Nawata; Hiroyasu Endo; Masaru Nakano, all of Kyoto; Hajime Murayama, Niigata, all of Japan [73] Assignees: Mitsubishi Jidosha Kogyo Kabushiki Kaisha; Mitsubishi Kinzoku Kogyko Kabushiki Kaisha, both of Tokyo, Japan 22 Filed: Dec. 8, 1972 21 Appl. No.: 313,340

[30] Foreign Application Priority Data Dec, 22, 1971 Japan 46-104303 [52] US. Cl 29/182, 29/1567 A, 75/123 1, 75/126 C [51] Int. Cl... C22c 39/14, C22c 39/50, C22c 33/02 [58] Field of Search 29/182, 182.5, 15617 A; 252/30, 75/126 C, 123 J {56] References Cited UNITED STATES PATENTS 2,004,259 6/1935 Weiger 29/1828 X Fahrenwald 29/1567 A Koehler 29/1825 X OTHER PUBLICATIONS Chemical Abstracts, No. 378196, Volume 73, 1970.

Primary ExaminerLeland Av Sebastian Assistant Examiner-R. E. Schafer Attorney, Agent, or FirmCushman, Darby & Cushman [5 7] ABSTRACT 6 Claims, No Drawings FE-MO-C-[CR] SINTERED ALLOYS FOR VALVE SEATS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to ferrous sintered alloys for valve seats of internal combustion engines for which the so-called wet sump lubrication as by oils is impossi ble, and more particularly to ferrous sintered alloys of the type described which are resistive to intermetallic impact wear with the cooperating red-hot valve.

2. Description of the Prior Art With the trend toward smaller and higher output internal combustion engines and an increasing variety of the type of fuel used in recent years, the requirement for higher resistance to wear at high temperatures to]- erated by valve seats is becombing greater and greater, and such requirement is particularly severe in internal combustion engines using lead-free gasolines, and gas engines or high speed diesel engines using LPG.

To meet this requirement, Cr cast iron, Cr-Mo cast iron and Ni cast iron have been developed and used for valve seats, of which Crand Cr-Ni heat-resistant steels, and Co-Cr-W alloys, belonging to hard facing alloys, are representative.

Recently, piston ring materials belonging to Cr sintered ferrous alloys have been put in practical use and, Pb-Ni-Cu sintered ferrous alloys and Pb-Ni-Mo-Co sintered ferrous alloys have also been used.

However, these prior art alloys have not been entirely satisfactory. For instance, the alloy cast irons are unsatisfactory with regard to machinability due to excess carbide grains contained therein in the form ofa lattice and also in respect of wear-resistance due to precipitation of free graphite peculiar to cast iron, and therefore, the their use has been limited only to valve seats used under relatively light loads. The heat-resistant steels used heretofore have had the disadvantage that they frequently cause wear of the cooperating valve, and their use has been limited to valve seats used under relatively light and intermediate loads. Thus, either material has been unsatisfactory for application to valve seats used under high loads.

The Co-Cr-W type hard facing alloys and Ni-Cr-W type cast alloys are those of all the prior art alloys for valve seats, which are most excellent in respect of resistance to hot impact wear, but have had the defect that they promote the wear of the cooperating valve unless the valves are provided with a filling or facing of hard material, e.g., Stellite. These alloys also have had the drawback that they are expensive and difficult to ma chine and usually call for finishing operation by machining which adds to the fabrication manhours and production cost.

The present inventors have conducted various studies with a view to overcoming these disadvantages of the prior art materials for valve seats and, as a result, found that when ferrous sintered alloys are used for valve seats, the wear of the valve seat is generally greater when the surface of the cooperating valve is not provided with a filling of a nonferrous alloy such as Stellite than when it is provided with such filling, and that the surface of the valve seats, subjected to impact wear, is preferably coated with a protective oxide film which is highly stable, fastly bonded to said surface, du-

rable and excellent in self-lubricating property. or alternatively, the valve seat is preferably made of alloy compositions which encourage the formation of such film on the engaging surface thereof, and in this view. use of such sintered alloys is suitable which does not permit the formation of a free carbon or abnormally hard oxide layer which is detrimental to the formation of the above-described uniform protective film, but rather have therein suitable voids which are effective for retaining the protective film.

SUMMARY OF THE INVENTION The present invention aims to eliminate the disadvam tages of the prior art alloys for valve seats discussed above, and to provide sintered alloys which are particu larly resistive to wear even when used with valves which are not provided with a facing.

In evaluating the properties of the alloys of this invention, a repeated impact wear tester was used which was sufficiently closely simulated to the operation of a valve and valve seat in the actual engine and capable of maintaining predetermined conditions, because if the evaluation is carried out in the actual engine. a long period of time would be required before the evaluation results are obtained and further, strictly speaking. the degree ofdistortion of a valve seat and the thermal load conditions varies between different types of engines and even between the cylinders of same engine.

Namely, the properties of the alloys of this invention were ascertained by using a valve-valve seat abrasion tester simulated to create conditions occurring in the actual engine, which is equipped with an LPG flame blowing heat source provided with a fully automatic temperature control means and including an eccentric cam-driven testing mechanism for performing a hot, repeated impact test. In the testing. a valve incorporated in the tester was revolved round its own axis at the rate of 60 i 5 rpm, and the abutting and sliding conditions of the valve against and on the valve seat were made uniform. The amount of wear was by measuring the weight loss of the valve seat before and after the testing.

Because of the particularly excellent resistance to wear of the alloys of this invention and because a plurality of the evaluation testers were used to the significant difference of the subject alloys from the prior art materials for valve seats in respect of wear-resistance. the testing was carried out in all of the testers. with an uniform elevated impact seating load of about 660 kgs. In addition to the amount of wear of the valve seat. the wear on the valve side was also evaluated by measuring the total amount of displacement of the valve (the amount of valve recession shown in each Table to be given later) which corresponds to the so called valve recession attributable to the sum wear of the valve and valve seat. The testing in each of the Examples described below, was conducted under the following conditions, unless otherwise specified. The valve was operated at a temperature of 800 1- lOC.', the valve seat temperature was controlled uniformly to about 360C; the impact between the valve and valve seat was re peated at the rate of 2,000 times per minute; and the total net number of repeated impact in the testing of one valve seat was 5 X l0 times. (corresponding to a net operation time of 42 hours). Further, the weight of DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with refer- 15; the valve setting spring load was 30 kgs; and the lift ence to Examples. Table 1 shows the relationship be of the valve was 8 mm. For the valve material, an austween the amount of Mo contained in irontenite steel for valves, (consisting of 0.6% of C, 6.871 molybdenum sintered valve seats according to the inof Mn, 2.1% of Cr, 1.8% of Ni, 0.7% of Cu, 0.4% of N vention and the wear-resistances of said valve seats. and the remainder of Fe) was used. Table 2 shows the relationship between the amounts of As a result of the evaluation tests, it was found that carbon and molybdenum contained in the same sinwhen ferrous sintered alloys containing a suitable tered alloys and the wear-resistances of the valve seats. amount of carbon in the form of a solid solution or car Further, Table 3 shows the relationship between the bide and having about 2 10% of Mo incorporated amounts of carbon. molybdenum and chromium contherein or optionally containing from about 0.5-5/27r tained in valve seats according to the invention and the of Cr incorporated therein, is used for valve seats, the wear-resistances ot' the valve seats when the valve seats amount ofimpact wear can be remarkably reduced and contains both molybdenum and chromium, and Table very excellent wear-resistance can be obtained as may 4 exemplifies control alloys containing nickel. cobalt be seen from Tables 1 3 below. and/or copper in large amounts.

Table 1 Composition (7%) Hardness Amount of wear Valve No. VHN of valve seat recession Remarks C Mo Si Mn (g) (mm) 1 1.0 0.08 0.15 2.61 2.78 2 do. 0.8 0.11 0.20 137 1.10 1.11 Reference Examples 3 do. 2.0 0.12 0.20 142 0.38 0.50 4 do. 2.5 0.12 0.20 0.20 0.25 5 do. 3.2 0.13 0.22 153 0.18 0.23 26 do. 40 0.14 0.21 0.06 0.22 Examples of the 6 do. 4.4 0.14 0.21 l56 0.03 0.21 present invention 7 do. 58 0.15 0.20 182 0.03 0.20 8 do. 97 0.16 0.19 0.03 0.32

9 do. 10.5 0.20 0.20 198 0.07 0,55 10 do. 12.0 0.21 0.20 In 0.05 0515 Reference Examples Table 2 Composition (I'll Hardness Amount of wear Valve No. VHN of valve seat recession Remarks C M0 Si Mn (gl 1mm) 11 0.35 4.4 0.14 0.20 136 0.78 082 Reference Example 12 0.5 do. do. do. 142 0.35 0.49 13 0.7 do. do. do. 150 0.04 0.30 Examples of the present 14 1.5 do. do. do. 197 0.09 0.37 invention 27 0.8 5.2 do. do. 178 0.06 0.23 28 1.0 do. do. do. 100 0.05 0.22

29 0.2 6.0 0.15 do. 103 0.37 064 Reference Example 30 0.5 do. do. do. 111 0.15 0 30 31 1.0 do. do. do. 184 0.03 0.20 Examples of the present 32 1.5 do. do. do. 263 0.05 0.20 invention 33 0.0 2.0 0.16 0.10 129 0.35 054 Reference Example 34 0.4 do. do. do. 158 0.05 0 19 35 0.8 do. do. do. 177 0.03 0.22 Examples of the present 36 1.2 do. do. do. 213 0.05 0.211 invention Table 3 Composition ('7?) Hardness Amount of wear Valve No. VHN of valve seat recession Remarks C Mo Si Mn Cr lgl 10m) 15 1.0 0.15 0.20 2.0 180 1.00 1.17 Reference Example 16 do. 4.4 0.14 0.21 1.3 193 0.05 0.19 17 do. do. do. do. 1.) 195 0.03 0.10 Examples of the present 18 do. do do. do. 3.0 204 0.05 0.08 invention 19 do. do do. do. 5.2 22l 0.02 006 20 do. 15 do. do. 52 187 0.55 0.92 37 1.0 2.5 do. do. 20 195 0.36 0.43 Reference Examples 38 0.2 4.0 do. do. do. 157 0.34 n 47 Table 3 Continued Composition (9%) Hardness Amount of wear Valve N0. VHN of valve seat recession Remarks C Mo Si Mn Cr (g) inml 39 0.4 4.0 0.14 0.2 2.0 172 II 0.16 40 1.5 do. do. do. do. 2| 0 0.08 0.12 Examples of the present 41 2.0 do. do. do. do. 282 0.03 0.09 invention 42 0.8 5.2 do. do. do. 197 0.05 0.11 43 1.0 do. do. do. do. 210 0 06 0.09

44 0.2 6.0 0.15 0.20 1.5 188 0.32 0.52 Reference Example 45 0.5 do. do. do. do. 19) 0.08 0.13 Examples ofthe present 46 l.0 do. do. do. do. 215 0.02 0.08 invention 47 I do. do. do. do. 220 0.05 0.09

48 0.0 9.0 0.16 0.19 1.0 202 0.30 051 Reference Example 49 0.4 do. do. do. do. 210 0.05 (1.08 50 0.8 do. do. do. do. 212 0.05 0.12 Examples of the present 51 1.2 do. do. do. do. 2l8 0.08 0.15 invention 52 0.6 do. do. do. 0.5 2l0 0.06 0.1]

Table 4 No. Composition (K l Hardness Amount of wear Valve recession C Mo Si Cr Ni Co Cu VHN of valve seat (it) (mm) 21 1.0 0.05 I0 I64 2.60 2.18 22 do. 2.5 do. 2 5 181 0.36 0.64 23 do. do. do. 5 5 186 0.44 0.71 24 do. do. do. 5 1.5 5 235 0.35 0.61 do. do. do. 2 1.5 5 226 0.71 0.95

Each sintered alloy shown in Tables l-4 was made using l00 mesh atomized iron powder, 325 mesh carbon powder and 350 mesh ferromolybdenum. (52% Mo). For incorporating molybdenum, it is preferred for obtaining the desired wear-resistance to use a ferromolybdenum powder containing not less than about 0. 1% ofC, e.g., FMoH according to the Japanese Industrial Standards (.118), relative to the ferromolybdenum scattered in the structures of the sintered alloys of the invention as an essential ingredient. A suitable amount of metallic molybdenum powder may further be incorporated for matrix reinforcement. As a chr0- mium powder, one containing M C type chromium composite carbide is preferred. and hence 250 mesh high carbon ferrochromium alloy powder (5.3% C. 53% Cr) was used but other low carbon ferrochromium powder or chromium steel powder (7-l8% Cr for example), specified in the HS may also be used.

The sintered alloys of Reference Examples shown in Table 4 were made using l00 mesh copper powder, 250 mesh cobalt powder and -100 mesh nickel powder.

The amounts of Si or Mn shown in Tables 1-4 are those incorporated from the atomized iron powder or ferromolybdenum powder.

In each Examples shown in the Tables above, the ingredients of the alloy in amounts by weight indicated were mixed, the mixed powders were compacted into a form of a valve seat under a compacting pressure of about 7 tlcm and the resultant molded valve seat was sintered at 1.l-l,180C. for 1 hour in hydrogen. The compacted density is variable depending upon the amount of alloy used but in the range of about 6.4-7.0.

In the sintered alloys for valve seats according to the invention, the contents of the respective ingredients are restricted for the following reasons:

Carbon is necessary for reinforcing the matrix by the formation of fine carbides with iron and molybdenum incorporated and for improving the wear-resistance under pressure by the retention of the carbides formed. As may be seen, for example, from Alloy No. it in Table 2, an amount of carbon less than about 0.4 per cent is insufficient but an amount ofthe same in excess of about 2 percent is objectionable because the carbides become too large. substantially degrading the machinability of the alloy. Thus, in the present invention. the carbon content is specified within the range of 0.4 2.0 percent. Incidentally, the amount of carbon shown in the total amount of carbon contained in the respective ingredients.

Molybdenum is an essential element to impart the alloys, together with carbon. resistance to hot impact wear. Incorporation of molybdenum in an amount less than 2 percent will result in insufficient wearresistance, whereas incorporation ofthe same in excess of 10 percent will not result in further improvement in wear-resistance of the valve seats but will tend to degrade the sintering characteristics and is uneconomical. Therefore, the practically effective range of molybdenum content is 2 10 percent, preferably about 5 9 percent.

The valve seat alloys according to the invention further include about 0.5 to 5.2 percent of chromium as an optional ingredient in addition to the elements discussed above. As may be understood, for example, from the alloys of Examples Nos. 16-19. Nos. 39-43, Nos. 45-47 and Nos. 49-52 in Table 3, the incorporation of both molybdenum and chromium enables good results to be obtained. especially in respect of valve recession while maintaining the wear-resistance by molybdenum of the valve seat proper. namely in respect of wear-resistance of the valve, as compared with the incorporation of molybdenum only shown in the Examples in Table 1. It will also be understood that. as the molybdenum content increases relatively, the desired improved result can be obtained with a smaller amount of chromium incorporated. However, the incorporation of chromium in an excessive amount in combination of molybdenum will result in degradation with the sintering characteristics and hence in wear-resistance. Thus, in the present invention, the chromium content is specified up to 6 percent. A more preferable range of the chromium content is about 0.5 2.5 percent.

The alloys of the invention can contain some relatively minor amounts of Si and Mn as impurities, which are usually contained in the mixed iron powder or ferromolybdenum powder used. These elements may positively be incorporated in the alloys in the form of ferrosilicon and ferromanganese, or elementary metallic powders thereof, to obtain their deoxidizing effect or to improve the sintering property and compactability of the alloying mixture. However, the incorporation of these elements in too large amounts will rather degrade the wear-resistance of the alloys brought about by molybdenum incorporated. Therefore. the Si and Mn contents each should be usually not larger than about 1 percent.

Nickel and cobalt are effective for maintaining the wear-resistance of the valve seats only when they are present with a considerably large amount of molybdenum. Small amounts of these elements may also be incorporated in the alloys for improving the surface strength of the valve seat against pressure as well as for adjusting the dimensions of the valve seat at the time of sintering. However, if the contents of these elements are too large, the wear-resistance of the valve seat will rather be degraded than when these elements are not incorporated, as will be seen from the alloys of Reference Examples in Table 4, and therefore, should be restricted to a minimum. In the sintered alloys of the invention, copper is especially regarded as an impurity and its content should be restricted to not larger than 1 percent, because the presence of copper to such an extent that precipitation of free copper is noted through microscope, degrades the wear-resistance of the alloys. Further, the alloys of the invention may contain small amounts of carbide-forming elements such as W, V and Nb, provided that the machinability of the alloys will not be substantially degraded. Besides the elements discussed above, the incorporation ofS in the range of about 0.05 0.5 percent in the form of a simple sulfur powder, a sulfide powder or a manganese sulfide powder is effective for improving the wearresistances of the valve seat and cooperating valve when the cooperating valve is provided with a Stellite filling, as has already been found by the present inventors in other ferrous sintered alloys for valve seats.

The sintering of the alloys of this invention may effectively be carried out, not only in a hydrogen atmosphere but also in vacuum. Further, partial liquid phase sintering by ferromolybdenum at a temperature slightly higher than that for solid phase sintering may be possible, and the sintered valve seat may be subjected to forging or coining.

What is claimed is:

l. A ferrous sintered alloy valve seat having improved impact wear characteristics and having coated or having uniformly deposited on the engaging surfaces thereof stable, durable and self-lubricating protective oxide film securely bonded thereto, said surfaces and valve seat containing suitable voids therein adapted to retain said protective oxide film;

said alloy consisting essentially of 0.4-2.0 weight percent carbon, 2-10 weight percent molybdenum in the form of ferromolybdenum particles dispersed in the microscopic metallurgical structure, balance iron; said alloy having a hardness value (HvNJ of between about i l l and about 282;

said valve seat present a durable hot impact wearresistant surface in contact with the valve associated therewith without promoting substantial wearing of said valve under heated conditions. 2. The valve seat of claim I wherein said alloy additionally contains about 0.5 2.5 percent chromium.

3. A ferrous sintered alloy for valve seats of internal combustion engines, said valve seat exhibiting improved hot impact wear characteristics and having uniformly deposited on the engaging surfaces thereof a stable, desirable and self-lubricating protective oxide film securely bonded thereto. said surfaces and valve seat characterized by voids contained therein adapted to retain said protective oxide film, said alloy composed. in addition to iron, the following materials all expressed in percent by weight:

carbon 0.4 2.0 molybdenum chromium 0.5 2.5 silicon less than 1.0 manganese less than it) nickel less than l.5 cobalt less than 5 copper less than 1.0 sulfur 0.05 0 5 and having ferro-molybdenum particles dispersed throughout the microscopic metallurgical structure thereof, and a hardness value (HVN) between about 1 l l and about 282, said alloy providing a durable, hot impact wear resistant surface to the valve associated and in contact therewith whereby in operation under heated conditions substantial wearing of said valve is avoided.

4. A valve seat made of a sintered alloy consisting of 0.4 2.0 percent by weight of C, 2-l0 percent by weight of Mo and the remainder essentially of Fe, and containing finely divided ferro-molybdenum particles dispersed in the microscopic metallurgical structure of said alloy.

5. A valve seat made ofa sintered alloy consisting of 0.4-2.0 percent by weight of C, 2-10 percent by weight of Mo, 0.5-2.5 percent by weight of Cr and the remainder essentially of Fe, and containing finely divided fer ro-molybdenum particles dispersed in the microscopic metallurgical structure of said alloy.

6. The valve seat of claim 1 wherein said alloy has a hardness value (HVN) of between about 142 and about 263.

Claims (6)

1. A FERROUS SINTERED ALLOY VALVE SEAT HAVING IMPROVED IMPACT WEAR CHARACTERISTICS AND HAVING COATED OR HAVING UNIFORMLY DEPOSITED ON THE ENGAGING SURFACES THEREOF STABLE, DURABLE AND SELF-LUBRICATING PROTECTIVE OXIDE FILM SECURELY BONDED THERETO, SAID SURFACES AND VALVE SEAT CONTAINING SUITABLE VOIDS THEREIN ADAPTED TO RETAIN SAID PROTECTIVE OXIDE FILM; SAID ALLOY CONSISTING ESSENTIALLY OF 0.4-2.0 WEIGHT PERCENT CARBON, 2-10 WEIGHT PERCENT MOLYBDENUM IN THE FORM OF FERROMOLYBDENUM PARTICLES DISPERSED IN THE MICROSCOPIC METALLURGICAL STRUCTURE, BALANCE IRON; SAID ALLOY HAVING A HARDNESS VALUE (HVN) OF BETWEEN ABOUT 111 AND ABOUT 282; SAID VALVE SEAT PRESENT A DURABLE HOT IMPACT WEAR-RESISTANT SURFACE IN CONTACT WITH THE VALVE ASSOCIATED THEREWITH WITHOUT PROMOTING SUBSTANTIAL WEARING OF SAID VALVE UNDER HEATED CONDITIONS.

2. The valve seat of claim 1 wherein said alloy additionally contains about 0.5 - 2.5 percent chromium.

3. A ferrous sintered alloy for valve seats of internal combustion engines, said valve seat exhibiting improved hot impact wear characteristics and having uniformly deposited on the engaging surfaces thereof a stable, desirable and self-lubricating protective oxide film securely bonded thereto, said surfaces and valve seat characterized by voids contained therein adapted to retain said protective oxide film, said alloy composed, in addition to iron, the following materials all expressed in percent by weight:

4. A valve seat made of a sintered alloy consisting of 0.4 - 2.0 percent by weight of C, 2-10 percent by weight of Mo and the remainder essentially of Fe, and containing finely divided ferro-molybdenum particles dispersed in the microscopic metallurgical structure of said alloy.

5. A valve seat made of a sintered alloy consisting of 0.4-2.0 percent by weight of C, 2-10 percent by weight of Mo, 0.5-2.5 percent by weight of Cr and the remainder essentially of Fe, and containing finely divided ferro-molybdenum particles dispersed in the microscopic metallurgical structure of said alloy.

6. The valve seat of claim 1 wherein said alloy has a hardness value (HVN) of between about 142 and about 263.