Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49229—Prime mover or fluid pump making
  • Y10T29/49298—Poppet or I.C. engine valve or valve seat making
  • Y10T29/49306—Valve seat making

Definitions

• 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.
• 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.
• 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-
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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
• 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).
• 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.
• 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.
• Si or Mn shown in Tables 1-4 are those incorporated from the atomized iron powder or ferromolybdenum powder.
• 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.
• 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.
• 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.
• 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.
• 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.
• chromium as an optional ingredient in addition to the elements discussed above.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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;
• 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.
• said alloy additionally contains about 0.5 2.5 percent chromium.
• 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:
• 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.
• 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.
• valve seat of claim 1 wherein said alloy has a hardness value (HVN) of between about 142 and about 263.
• HVN hardness value

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• Mechanical Engineering (AREA)
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• Powder Metallurgy (AREA)

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Citations (3)

• 1971
  • 1971-12-22 JP JP46104303A patent/JPS5130843B2/ja not_active Expired
• 1972
  • 1972-12-08 US US00313340A patent/US3856478A/en not_active Expired - Lifetime

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