US2768918A - Cast iron valve seat insert - Google Patents

Description

Oct. 30, 1956 A. A. ARMSTRONG CAST IRON VALVE SEAT INSERT Filed Sept. 16, 1953 411mmllllllll LL 40/144 4; A/MHI/QO/V IYV'ERZZUZT /ewwmmwwmm 43/ United States Patent CAST IRON VALVE SEAT INSERT Adua A. Armstrong, Mentor, Ohio, assignor to Thompson Products, Inc., Cleveland, Ohio, a corporation of Ohio Application September 16, 1953, Serial No. 380,461

Claims. (Cl. 148-31) This invention relates to cast valve seat inserts having high collapse resistance. Specifically, this invention deals with a heat-treated cast silicon-chromium steel engine valve seat insert.

It is known that when metal is heated to very high temperatures for extended periods of time, it will congeal or set in an expanded state and willnot contract as usual when cooled. Since engine valve seat inserts are press-fitted in recesses in engine cylinder heads or blocks, when heated in operation of the engine, they expand to a point where further expansion is restricted by the cylinder metal. At this point, continued expansion due to increased temperatures, will cause the inserts to bow inwardly or away from the restricting shoulder or wall of the engine head or block. Then, if the bowed inserts reach the setting temperature and are cooled from this temperature, the cylinder metal shrinks away from the insert and the insert becomes loose in the engine. The bowed and setinserts are known as collapsed inserts and the temperature at which they take the permanent set is known as the collapse temperature.

Heretofore, valve seat inserts have been produced by expensive forging, machining, and heat-treating procedures. The best of these prior known inserts had to be annealed, hardened, quenched, tempered, and drawn to a Rockwell hardness of about 35 C. The microstructure of these prior known inserts was generally an aggregate of carbides with some martensite oriented in an interdendritic pattern and having some of the carbides in the grain boundaries and scattered throughout the matrix. This microstructure, however, did not provide collapse resistance at temperatures above about 800 F.

Since the modern, high-speed, high-compression internal combustion engines frequently operate at valve seat insert temperatures above 800 F., loose-collapsed inserts have presented a seriou engine problem.

The present invention now provides inexpensive cast, heat-treated, silicon-chromium steel alloy valve seat inserts of unique microstructure and having a collapse temperature from 200 to 300 F. above the best prior known valve seat insert produced by the more expensive prior known forging and heat-treating techniques. Thus, the cast, heat-treated inserts of this invention have a collapse temperature between about 1000 to 1100 F. as compared with the maximum 800 F. collapse temperature of forged inserts. In addition, the hardness and wear resistance of the cast valve seat inserts of this invention are at least equal to or greater than the best prior known inserts produced by the more expensive forging and heat-treating processes.

Accordingly, it is an object of this invention to provide cast, heat-treated, silicon-chromium steel valve seat inserts having enhanced resistance to collapse.

Another object of the present invention is to provide a cast, silicon-chromium steel alloy for valve seat inserts having unique metallurgical properties.

A further object of this invention is to provide a "ice method of making valve seat inserts of increased collapse resistance.

A further object is to provide an inexpensive, cast, high silicon-chromium steel valve seat insert which may have a carbon content as high as 3.5% and which has metallurgical properties developed by a simplified heat treatment which omits heretofore required quenching and drawing steps and still produces a hardness of from 35 to 45 Rockwell C.

ther and further objects of this invention Will be apparent to those skilled in the art from the following detailed description of the annexed sheet of drawings which, by way of an example only, illustrates a valve seat insert of this invention.

On the drawings:

Figure l is a fragmentary, vertical cross-sectional view, with parts in elevation, of the valve port area of an internal combustion engine equipped with a valve seat insert of this invention.

Figure 2 is an enlarged, fragmentary, vertical, crosssectional view of the valve seat insert area of the valve port of Figure l on an enlarged scale and illustrating the normal condition.

Figure 3 is a view similar to Figure 2 but illustrates the insert in a collapsed condition.

Figure 4 is a top plan view of the insert.

Figure 5 is a graphic reproduction of the microstructure of the heat-treated cast alloy for the insert.

As shown on the drawings:

In Figure 1 the engine valve port assembly 5 includes an engine block 6 composed of cast iron, a cast valve seat insert 7 of the present invention press-fitted in an annular recess 8 of the block 6, a valve stem guide 9 press-fitted in a bore 10 of the engine block concentric with the recess 8 and opening into the bottomof the recess, and a valve 11 with the stem 11a thereof slidably mounted in the guide 9.

The valve seat insert 7 ha a cylindrical outer peripheral wall 7a, a flat bottom 7b, a flat top 7c, and a tapered seating face 7d converging from the fiat top 70 to a cylindrical inner peripheral wall 72.

The recess 8 in the block 6 has a cylindrical side wall or shoulder 8a and a fiat bottom 8b.

The peripheralwall 70 has a snug fitting relation with the shoulder or wall 8a of the recess and the ring 7 is preferably press-fitted into the recess with the flat bottom of the insert seated on the flat bottom 8b of the recess.

The tapered seating face 7d of the insert mates with and receives the tapered seating face 11b of the valve head 11c.

In normal operation, the valve seat insert 7 will maintain its tight fit in the recess 8 as shown in Figure 2. Thus, the expansion of the ring and cylinder block are commensurate.

When the valve seat insert 7 is excessively heated to a point where it can expand no further due to the re straining effect of the recess wall, it may become bowed asshown in Figure 3. This bowing may create a gap shown at 12 on an'exaggerated scale in Figure 3. If the insert 7 sets or collapses in the condition shown in Figure 3, then the gap 12 will not be reclaimed under lower operating temperatures. As a result, the insert 7 will be loose in the recess 8. It will, therefore, be appreciated that the temperature at which the setting or collapsing of the insert takes place, should be as high as possible to prevent looseness and permanent distortion of the insert.

In accordance with this invention, the collapse" temperature of valve seat inserts is substantially increased by utilizing a cast valve seat insert composed of a high silicon-chromium alloy of the following general composition:

Percent Carbon 0.7 to 3.5 Manganese 0.2 to 0.6 Nickel 1.0010 1:60 Chromium 19.00to 21.00 Silicon 1.90 to 2.6 Iron Balance 'While the wide carbon range of the above general formula can be tolerated, it is preferred to limit this range to about ;9% to 1.1%.

An alloy of the above composition is cast in suitable molds forproducing the insert ring 7. Preferably, shell molds composed of thermoplastic resin-impregnated sand are usedalthough any known casting technique for pro ducing smooth accurate castings free from cracks, blowholes, shrinks, and the like, is acceptable.

The cast rings are heat-treated by an inexpensive twostep process for producing the microstructure shown in Figure 5. The graphic illustration in Figure represents the general nature -of the microstructure at 500 magnification. As therein illustrated, crystals 12 are separated by grain boundaries 14. The annealed structure is an aggregate of unresolved carbides designated at 15 and the structure is generally cementitic. The general pattern is uniform and fairly free from martensite. This microstructure is materially different from the hardened and drawn structure of the prior known forged inserts which consisted of an aggregate of carbides with martensite oriented in an interdendritic pattern and with carbides definitely included in'the grain boundaries and scattered throughout the matrix. The boundaries and the matrix structure of the ring 7, however, are generally cementitic and relatively free from resolved carbides.

To produce the microstructure of Figure 5, the cast insert rings are subjected to a two-step heat treatment. The first step includes heating at temperatures from about 1500 to 1600 F., for about 1 hour. The preferred heating for this step is 1575 F. The heated rings are then slowly cooled to a range of from about 1250 to 1350 F. This temperature range is maintained for about 1 hour. Preferably, a temperature of 1300 F. is used. Heating is preferably carried out in an oven and the entire oven cycle period is about 6 to 6% hours. It is important, however, that the rings be held at the above indicated temperatures for a period of about 1 hour. The cooling rate from 1575 to 1300 F. should then be about 4 hours.

If desired, the heated rings, after being maintained at temperatures between 1500 to 1600 F. for about 1 hour, can be air-cooled to room temperature and can then be re-heated to 1250 to 1350 F. for about 1 hour and air-cooled to room temperature. This modified heat treatment is advantageous in permitting a staggering of the heat-treating steps.

By means of the simple two-step heat treatment procedures of this invention, the cast high silicon-chromium steel inserts will have a Rockwell hardness of from 28 to 45 C and a collapse temperature of from about 1000 to 1l000 F.

A convenient collapse test for the rings is accomplished by inserting a ring in a cast iron cup receiving a high-frequency induction coil into the hollow interior of the ring. A water ring surrounds the cast iron cup. The insert is then intermediately heated by the induction coil and cooled by water spray on the cast cup. The insert is heated first to 300 F. for several hundred cycles. It is then cooled and checked for looseness. The temperature is then increased in -degree increments and then cycled heating is repeated for several hundred cycles. The procedures continue until the insert, under test, loosens in the cast iron cup. The final temperature is then recorded as the loosening temperature or collapse temperature. The test is made to approximate engine conditions in the field.

From the above descriptions it will be understood that this invention now provides a cast va e 565i insert for Percent Carbon 0.9 to 1.1 Manganese 0.2 to 0.6 Nickel 1.00 to 1.60 Chromium 19.00 to 21.00 Silicon 1.90 to 2.6 Iron Balance said ring having a cementitic microstructure comprising substantially a uniform aggregation of unresolved carbides developed by a two-stage heat treatment at temperatures of from about 1500 to 1600 F. for about 1 hour followed by temperatures 'of about 1250 to 1350 F. for about 1 hour.

.2. The method of increasing the collapse resistance of cast iron valve seat insert rings which comprises heating toa temperature of about 1500 to 1600 F. for about 1 hour a cast'chromium steel alloy ring of the following analysis:

Percent Carbon 0.9 to 3.5 Manganese 0.2 to 0.6 Nickel 1.00 to 1.60 Chromium 19.00 to 21.00 Silicon 1.90 to 2.6 Iron Balance slowly cooling said ring, heating the cooled ring for about 1 hour to temperatures between about 1250 to 1350" F. and thereafter air-cooling the ring to produce a cementitic iron structure.

'3. A cast silicon-chromium steel alloy of the following formula:

Percent Carbon 0.9 to 3.5 Manganese 0.2 to 0.6 Nickel 1.00 to 1.60 Chromium 19.00 to 21.00 Silicon 1.90 to 2.6 Iron Balance said alloy having a Rockwell hardness of from about 28 to 45 C, and-a collapse temperature 'of from about 1000 to 1100 F., said alloy comprising substantially a uniform aggregation of carbides unresolved; the structure being cementitic.

4. A cast high temperature resisting iron valve seat insert for internal combustion engines comprising a ring having the following formula:

Percent Carbon 0.9 to 3.5 Manganese 0.2 to 0.6 Nickel 1.00 to 1.60 Chromium 19.00 to 21.00 Silicon 1.90 to 2.6 Iron Balance said ring having a cementitic microstructure comprising substantially a uniform aggregation of unresolved carbides developed by a two-stage heat treatment at temperatures offrom about 1500 to 1600 F. for about 1 hour followed by temperatures of about 1250 to 1350 F. for about 1 hour.

5. In a method for producinga valve seat insert ring having a collapse resistance in excess of 1000 F., the

stepscomprising: casting a valve seat insert ring from a chromium steel alloy having the following formula:

Percent Carbon 0.9 to 1.1 Manganese 0.2 to 0.6 Nickel 1.00 to 1.60 Chromium 19. 00 to 21.00 Silicon 1.90 to 2.6

Iron Balance heating the resulting cast ring to a temperature range of" from about 1500" to 1600" F. for about 1 hour; cooling said ring to a temperature range of from about 1250 to 1350 F.; and maintaining said ring at said last mentioned temperature range for about 1 hour to produce a cast valve seat insert ring having a cementitic microstructure comprising a substantially uniform aggregation of unresolved carbides and having a Rockwell hardness of from about 28 to 45 C.

Stainless Iron and Steel, vol. I, Stainless Steel in Industry, pages 38 and 39.. Edited by Monypenny. Published in 1951 by Chapman and Hall Limited, London.

Claims (1)

1. A CAST HIGH TEMPERATURE-RESISTING IRON VALVE SEAT INSERT FOR INTERNAL COMBUSTION ENGINES COMPRISING A RING HAVING THE FOLLOWING FORMULA:

Images