US3701652A

US3701652A - Valve seat inserts

Info

Publication number: US3701652A
Application number: US107667A
Authority: US
Inventors: Delmar O Stanley
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1971-01-19
Filing date: 1971-01-19
Publication date: 1972-10-31
Anticipated expiration: 1989-10-31

Abstract

A VALVE SEAT INSERT HAVING IMPROVED MECHANICAL PROPERTIES AND BEING SUBSTANTIALLY NICKEL FREE, THE INSERT HAVING A COMPOSITION CONTAINING FROM 1.00 TO 2.25% CARBON, A MAXIMUM OF 0.75%MANGANESE, A MAXIMUM OF

1.00% SILICON, FROM 28 TO 32% CHROMIUM, FROM 18 TO 30% COBALT, FROM 2 TO 8% TUNGSTEN, WITH THE BALANCE SUBSTANTIALLY IRON EXCEPT FOR INCIDENTAL IMPURITIES.

Description

Oct. 31, 1972 D. o. sTANLE 3,701,652

VALVE SEAT INSERTS Filed Jan. 19, 1971 ,3 5 2O 2 III F a: 2 g: :5-

5 I I l J I l l i 0 COBALT ,INVENTORV De/mar 0 sfaa/ey I I Q522 Q @WATTORNEYS U-S. Cl. 75-126 A 5 Claims ABSTRACT OF THE DISCLOSURE United States Patent A Valve seat insert having improved mechanical properties and being substantially nickel free, the insert having a composition containing from 1.00 to 2.25% carbon, a maximum of 0.75% manganese, a maximum of 1.00% silicon, from 28 to 32% chromium, from 18 to 30% cobalt, from 2 to 8% tungsten, with the balance substantially iron except for incidental impurities.

BACKGROUND OF THE INVENTION Field of the invention This invention is in the field of valve seat inserts which are received in the engine .block for seating an exhaust valve, the insert being composed of an iron base alloy containing substantially no nickel but having hardness, compressive yield strength and creep resistance equivalent to or greater than the more expensive nickel base alloys.

DESCRIPTION OF THE PRIOR ART A valve seat insert ring by its nature presents stringent requirements insofar as physical and mechanical properties are concerned. Since modern day engines operate at substantially elevated temperatures they must have high temperature properties in combination which are not ordinarily found in inexpensive alloys.

A description of the problems of securing adequate mechanical properties in valve seat inserts will be found in Armstrong US. Pat. No. 2,768,918 and Prasse et al. US. Pat. No. 2,805,943, both owned by the assignee of the present application. 'In the Armstrong patent, there is a description of an iron base valve seat insert containing substantial amounts of silicon (1.9 to 2.6%) and nickel (1.0 to 1.6%). The Prasse et al. patent describes a cast valve seat insert consisting of an iron base material containingfrom 27 to 33% chromium and 10 to 14% cobalt. While each of these valve seat inserts has improved mechanical properties at high temperatures, they do not retain all these properties when an operating temperature of 1,000 F. and higher is reached.

Presently, most of the valve seat insert rings used in high temperature, heavy duty engines have substantial amounts of nickel. However, the current shortage of nickel and its high cost are distinct drawbacks to the continued use of these alloys.

It was found that conventional martensitic grades of iron base alloys are not appropriate for this use because of their inherent low creep resistance at operating temperatures of 1,000 F. It was also found that conventional austenitic stainless steels would not be satisfactory because of their low hot hardness at 1,000 E, as compared to nickel base alloys. Cobalt base alloys are too expensive for this type of application.

SUMMARY OF THE INVENTION The present invention provides a valve seat insert ring which combines the better properties of austenitic "ice stainless steels with cobalt based hard facing materials and provides a cobalt containing stainless steel hardened by chromium and tungsten carbides. While the alloy materials used for the purpose of the present invention are nickel free (except as nickel may occur as an impurity in the iron) their mechanical properties at elevated temperatures are certainly comparable to and in some cases exceed the mechanical properties of the nickel alloys which are presently being used. These improvements in properties are accompanied by a significant reduction in cost. 7

The valve seat insert rings of the present invention have a composition including 1.00 to 2.25% carbon, a maximum of 0.75% manganese, a maximum of 1.00% silicon, from 28 to 32% chromium, from 18 to 30% cobalt, from 2 to 8% tungsten, with iron being substantially the balance. It has been found that the amount of cobalt present is particularly critical to achieve the improved results. At cobalt concentrations of less than 18%, the amount of martensite in the microstructure of the insert is substantially increased. However, at cobalt contents of 18% and above, the percentage of martensite in the as-cast alloy is reduced to a value below 10%. The reduction of the amount of martensite present has been found to substantially improve the creep relaxation properties of the valve seat insert.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:

FIG. 1 is a fragmentary cross-sectional view, partly in elevation, of the valve port area of an internal combustion engine employing a valve seat insert of the present invention;

FIG. 2 is a plan view of the valve seat insert on an enlarged scale; and

FIG. 3 is a graph plotting the percentage of martensite in the insert ring structure as a function of the amoun of cobalt present. 9

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 10 indicates generally an engine block composed of cast iron or the like and having a discharge port 11 in which a poppet-type exhaust valve 12 is arranged to reciprocate and thereby discharge hot combustion gases to the exhaust system. At the exhaust opening, there is provided a valve seat insert ring 13 which is press fitted in an annular recess 14 formed in the engine block 10. A valve stem guide 15 is press fitted in a bore 16 concentric with the recess 14. The valve seat insert ring 13 has a cylindrical outer peripheral wall 13a, a fiat bottom 13b, a flat top 13c and a tapered seating face 13d converging from the fiat top to a cylindrical inner peripheral wall 13a. The valve seat insert ring 13 is thus under substantial compression during operation of the engine and is further subjected to substantial pounding by the seating of the poppet valve 12 after the exhaust cycle of the engine.

Considerable experimentation has resulted in the development of a valve seat insert ring which can retain its hard hardness properties at elevated temperatures above 1,000 C., and which resists compressive creep and yielding at those elevated temperatures. The broad range of the improved alloy composition used for the insert ring is as follows:

Carbon 1.00 to 2.50% by weight. Manganese 0.75% maximum. Silicon 1.00% maximum. Chromium 28 to 32%.

Cobalt 18 to 30%.

Tungsten 2 to 8%.

Iron Substantially the balance.

Within the broader ranges set forth above, a particularly preferred alloy composition is the following:

Carbon 1.70 to 2.25%

Manganese 0.75% maximum.

Silicon 7 1.00% maximum. Chromium 28 to 32%.

Cobalt 20 to 24%.

Tungsten 6 to 8%.

Iron Substantially the balance.

The best overall balance of properties exists in an insert ring having a nominal composition including about 2% carbon, about 1% silicon, about 30% chromium, about 20% cobalt, about 7% tungsten, and the balance substantially. iron.

A series of alloys falling within the compositional ranges set forth above were compared in physical properties to those possessed by the standard nickel base alloy (VMS 434) which has a nominal analysis containing 2.50% carbon, 20% chromium, 40% nickel, 12% cobalt, 6% tungsten, a maximum of 1% silicon, and the balance substantially iron-This nickel base alloy is referred to as the control in succeeding portions of this specification.

Four alloys were made up having the following norminal analyses:

Alloy C Si Cr W Go Fe 14 0. 91 31. 54 7. 33 20. 23 39. 30 1. 31. 80 7. 12 29. 92 29. 40 0. s7 30. 95 7. 4s 20. 71 40. 0 0. s1 29. 72 7. 28 21. 19 40. 16

The following hardness and compressive yield-strengths were obtained on the alloys at various temperatures:

. Room Compressive temp. BHN BHN yield strength Alloy Rs 1,000 F. 1,200 F. at 1,000 F.

Control 35 289 225 82, 000

The compressive creep strength at 1,000 F. for the new alloys of the present invention compared very favorably with that of the control. The results are summarized in the Oxidation tests were run on alloy I 12 at 1600 F. for 120 hours. The alloy had a weight gain of only 0.0112 gram per square decimeter, an exceptionally low value.

The physical and mechanical properties achieved in the new materials is done at a substantial saving in cost. For example, the raw materials going into alloy I 12 cost about 42% less than those in the control.

The amount of martensite appears to have a definite bearing upon the retention of high temperature properties in these alloys. As evident from the curve of FIG. 3, where actual experimental results areplotte-d, there is a discontinuity in the curve at a cobalt content of approximately 18%. It will be seen that at a 10% cobalt concentration, the alloy contains about 27% martensite, whereas at cobalt contents of 18% and greater, less than 10% martensite is present.

From the foregoing, it will be understood that the valve seat inserts of the present invention provide completely satisfactory mechanical properties at elevated temperatures While achieving a substantial reduction in cost.

I claim as my invention:

1. A valve seat insert for an internal combustion engine comprising a ring having a valve seating face thereon, said ring having the following composition:

Carbon 1.00 10 2.50% by weight.

Manganese 0.75% maximum. Silicon -2 1.00% maximum. Chromium 28 tof32%. Cobalt 18 to 30%.

Tungsten 2 to 8%.

Iron Essentially the balance.

2. The valve seat insert of claim 1 in which the ring has the following composition:

Carbon 1.70 to 2.25%. Manganese 0.75% maximum. Silicon 100% maximum. Chromium 28 to 32%.

Cobalt 20 to 24%.

Tungsten 6 t0 8%. Iron Essentially the balance.

3. The valve seat insert of claim 1 in which the microstructure of said ring contains no more than about 10% martensite.

4. The valve seat insert of claim 1 which contains about 2% carbon, about 1% silicon, about 30% chromium, about 20% cobalt, about 7% tungsten, and the balance essentially iron.

5. The valve seat insert of claim 6 in the as cast con- CHARLES N. LOVELL, Primary Examiner Us. 01. X.R. -122, 126 c, 126 H, 126 R; 123-188 AA; 148.-'-31

Claims

1.00% SILICON, FROM 28 TO 32% CHROMIUM, FROM 18 TO 30% COBALT, FROM 2 TO 8% TUNGSTEN, WITH THE BALANCE SUBSTANTIALLY IRON EXCEPT FOR INCIDENTAL IMPURITIES.