US2495731A - Stainless steel resistant to leaded fuels at high temperatures - Google Patents

Description

Jan. 31, 1950 P A. JENNINGS ,495,731

STAINLESS STEEL RESISTANT TO LEADED FUELS AT HIGH-TEMPERATURES Filed April '7, 1948 SI: 0.25% MAX FE! BALANCE INVENTOR. PAUL A. JENNINGS H IS ATTORNEY Patented Jan. 31, 1950 STAINLESS STEEL RESISTANT TO BEADED FUELS AT HIGH TEMPERATURES Paul A. Jennings, Baltimore, Md., assignor to Armco Steel Corporation, a corporation of Ohio Application April 7, 1948, Serial No. 19,480

1 11 Claim.

This invention is a continuation-in-part of my co-pending application, serial No. 786,976, filed November 19, 1947, now abandoned, which in turn is a continuation-in-part of my application, Serial No. 762,863 filed July 23, 1947, also now abandoned, and the invention relates to high temperature stainless steel articles, especially to articles in the form of valves, valve parts and other internal combustion engine components intended for use while hot in corrosive atmospheres.

Among the objects of my invention is the provision of strong, tough and durable austenitic stainless steel valves and other internal combustion engine components for elevated temperature use, which steel products, in view of the excellent properties of the particular steel employed function in a highly satisfactory manner in such fields as passenger car, truck, aircraft, Diesel and marine vessel engine use, and which offer great hardness at the high temperatures encountered in use, and substantial freedom from stretch, as well as substantial resistance, in the heated condition, to hot corrosive atmospheres such as those containing the combustion products of anti-knock gasoline illustratively of the tetra-ethyl lead variety.

Other objects of my invention in part will be obvious and in part pointed out more fully hereinafter.

The invention accordingly consists in the combination of elements, composition of materials and features of products, and in the relation of each of the same to one or more of the others as described herein, the scope of the application of which is indicated in the following claims.

The single figure of the accompanying drawing represents a specific product and steel composition thereof falling within the scope of my invention.

As conducive to a clearer understanding of certain features of my invention, it may be noted at this point that a great variety of heretofore known valves and valve parts intended for use as operating components of internal combustion engines or the like have become obsolete for such reasons as increased engine temperatures incident to greater engine power and speed. In average passenger cars, for example, the temperatures encountered by the valves frequently are as high as 700 F. or more at the fuel intake position, and as high as 1100 F. to 1450 F. or more at the exhaust position. These temperatures ordinarily are even higher in .truck, bus, marine vessel or aircraft engines, especially in the region where the exhaust valves operate.

Low-alloy steel valves, for example, which formerly operated satisfactorily in internal combustion engines now are found in most instances to be unacceptable, and particularly so on the exhaust side of these engines. The valves usually burn or warp very quickly at the high operating temperatures, thus impairing engine etliciency and requiring frequent replacement. While hot, the working parts commonly develop oxide scale which detrimentally affects proper seating. In turn, failure of the valve to seat properly allows leakage or blow-by of the hot gases, thus increasing the valve ,temperature and burning away the metal. wAn/example of this type valve is one containing'about 0.45% carbon, 8.50% chromium,

3.25% silicon, and the remainder substantially all iron.

Also, most of the low-alloy steel valves, including those having the composition just noted; are extremely susceptible to active corrosive attack by leaded fuels and particularly by the hot combustion products of these fuels. There are antiknock fuels containing lead on the market, which, when consumed, not only exert a ruinous effect upon steel valves of low-alloy content, but a great majority of relatively high-alloy steel valves and parts likewise suffer great detriment and rapid deterioration when exposed to the fuel combustion products.

A number of stainless steel valves, and valves made of other high-alloy metal, for example, have.

been introduced for better serving present-day needs. Some of these are of ferritic grade steel. Others are martensitic. In some, there is a highsilicon content and, as a result, they enjoy adequate scaling resistance. Unfortunately, however, they have poor resistance to lead compounds and are decidedly inferior in matters of hot hardness and stretch resistance under certain operating conditions.

There are still other valves in the prior art, these being of austenitic chromium-nickel stainless steel grade. The amounts of silicon in the conventional austenitic steel products range from about 0.50% to 4.0% or more. In general, the austenitic steel valves have a more favorable lattice structure for resisting stress-rupture and creep at elevated temperatures than do the ferritic or martensitic products. It is also true that the relatively high-alloy content of the chromium-nickel austenitic steel favors resistance to scaling from heat at engine temperatures. A further advantage often arising from austenitic steel valve products is their freedom from phase transformation and, in this respect, freedom from volsacs-2s:

uine changes and any resulting tendencies such as warping, sticking or cracking during the heating and cooling cycles brought about by the heat engine and its operation. The many valves of this character in the prior art, however, leave much to be desired of resistance to corrosive attack by hot lead compounds.

An outstanding object of my invention, accordingly, is the provision of high temperature heat-resistant, corrosion-resistant stainless steel valves, valve parts and internal combustion engine components having substantial strength at the temperatures of use, which are substantially free of phase transformation, are hot hard, resist stretch, and eillciently and reliably resist oxidation in the presence of heat and leaded fuel combustion products.

Referring now more particularly to the practice of my invention, I provide low-silicon, austenitic chromium-nickel-manganese stainless steel internal combustion engine valves, valve parts, and any of other internal combustion engine components made of the steel, illustratively intake or exhaust poppet valves, stems, heads, springs, casings, claddings, linings or surfacing. In preferred composition, my products include about 0.08% to 1.50% carbon, from 12% to chromium, 2% to nickel, amounts of managanese ranging from 3% to 12%, with the silicon content not exceeding 0.25%, and the remainder substantially all iron. Preferably, for desired hardness at the high temperatures encountered in actual use, the carbon content amounts to some 0.40% to 1.50%. By keeping an appreciable manganese content in the steel, and the silicon content below about the 0.25% figure, I find sharp improvement in resistance of the steel products to corrosion and attack by products of combustion resulting from the burning of leaded fuel. At about 0.15% silicon and on down to 0.10% or less, this improvement is even more pronounced, and the hot hardness is not adversely aflected. Both the hot hardness and corrosion-resistance are even more favorable where the carbon exceeds about 0.40% and the silicon ranges from about 0.15% on down substantially to zero in amount. The smaller quantities of silicon accordingly are usually preferred.

The inclusion of manganese results from my discovery that nickel in steels of the stainless grade often has an adverse aflect upon the corrosion resistance of valve products while the lat ter operate in the presence of hot lead compounds. By supplanting a substantial quantity of the nickel ordinarily required for providing a steel of austenitic quality with manganese an austenitic balance steel is had and the adverse affect of nickel upon corrosion resistance in the combustion products of leaded fuels is importantly dispelled. Moreover, it seems that the steel of high manganese content has a greater solubility for carbon and as such permits greater hot hardness as higher temperatures are achieved.

On occasions, I use the element nitrogen in amounts up to about 0.30% as a substitute for an equivalent amount of carbon or nickel in the steel. The nitrogen when used, serves the function of increasing the hot-hardness of the steel a small degree, but primarily is valuable as a partial substitute for other austenite-forming elements to maintain the austenitic balance. Also, at times, I substitute the element cobalt in discreet amounts for one or more of the austenite-forming elements, manganese, nickel and carbon. There are occasions too where my stainless steel products inciude in the alloy composition thereof, as for special purposes, one or more such elements as molyb denums, titanium, columbium, tungsten, vanadium, copper, tantalum, aluminum, zirconium, or the like, ranging from quite small amounts to substantial amounts not inconsistent with properties desired.

The stainless steel valves, valve parts, and engine components which I provide have a sulphur content which may be some quantity below about 0.04%, or even as much as 0.2% or more. The larger quantities of sulphur, and especially those between about 0.15% to 0.20%, contribute to the effect of the low-silicon content in promoting resistance to attack by the combustion products of leaded gasolines and the like. The larger quantities of sulphur, say those beyond about 0.04%. usually improve the machining properties of the steel. Amounts of sulphur much beyond 0.20% often introduce hot working difiiculties with certain of the austenitic steels which I employ; also, the rate of improvement of resistance to leadoxide corrosion usually decreases for these greater amounts. The phosphorus content of my products preferably is below about 0.04%.

The particular amounts of such elements as chromium, nickel and manganese present in the internal combustion engine products which I provide assure excellent heat resistance and resistance to oxidation at the high temperatures encountered. Also, the inclusion of manganese, and the restriction of silicon to the critically small amounts indicated, contribute to corrosion-resistance of the products in the combustion products of leaded fuels, as where the steel takes the form of an exhaust valve or part exposed to aircraft, truck or passenger car engine exhaust gases. By virtue of the austenitic quality of the steel, my valve products suffer substantially no phase transformation during heating and cooling cycles and, accordingly, are free of volume changes and difflcuities often following upon change of phase. The valves are strong, tough and hot hard at the high temperatures encountered. They resist scaling, warping and cracking at full temperature and upon being cooled and reheated.

To illustrate the eifect of silicon content on the resistance to corrosion of chromium-nickelmanganese stainless steels by lead compounds, attention is directed to Table I below. This table represents a 2l310 chromium-nickel-manganese steel subjected to molten lead oxide at 1675 F. for one hour, and to hot-hardness tests at 1400" F. The resistance to molten lead oxide is given in terms of weight-loss in grams per square decimeter per hour, and the hot-hardness in terms of Brinell values using a cold ball penetrator.

TABLE I Influence 6; silicon on corrosion-resistance to molten lead oxide of 21-3-10 chromiumnickel-manganese steel (clay crucible) 5 chromium-nickel-manganese steels of differing silicon contents were subjected to molten lead oxide at 1675 F. for one hour in a magnesia crucible with corrosion-loss results as givenin Table II below:

' TABLE II x Influence of silicon on corrosion-resistance to molten lead oxide of 21-3-10 chromiumnickel-manganese steel (magnesia crucible) Sample Cr Ni Mn Bi 3.20 10.00 l1 13. 27 3. 46 9. 89 15 10.91 3. 02 9. 89 25 18 72 3.00 10.00 .32 62.21 3.00 10.00 .66 48.33 3.00 10.00 .88 47.13

1 Nominal composition.

The data presented above shows the highly critical character of silicon content. Where the silicon content exceeds about 0.25%, corrosion by lead oxide rapidly increases. Minimum corrosion is had where the silicon content is 0.15% or less, preferably about 0.10% or less, although certain beneficial properties are had in the 21-310 chromium-nickel-manganese steel even where the silicon content is up to 0.45% as noted in Table I above and in my parent application, Serial No. 786.976.

Thus it will be seen that in this invention there are provided low-silicon austenitic chromiumnickel-manganese stainless steel articles and products, in which the various objects noted hereinbefore together with many thoroughly practical advantages are successfully achieved. It will be seen that the products are well suited for resisting corrosion in the presence of combustion products of leaded fuels.

While certain of the articles which I provide take the form of internal combustion engine valves, valve parts and other internal combustion engine components, it will be understood that certain advantages of the invention are had from other products of the low-silicon steel, among which are high-temperature gas turbine nozzles, turbine parts adjacent to the nozzle, and any of a variety of supercharger components.

As many possible embodiments may be made of my invention, and as many changes may be made in the embodiment hereinbefore set forth, it will be understood that all matter described herein is to be interpreted as illustrative and not as a limitation.

I claim as my invention:

1. Stainless steel having substantial hardness at high temperatures and substantial resistance to corrosion in the presence of leaded fuel combustion products, and containing about 0.40% to 1.50% carbon, about 12% to 35% chromium, about 2% to 35% nickel, about 3% to 12% manganese, all in such relative proportions as to assure a substantially fully austenitic structure, silicon not exceeding about 0.25%, and the remainder substantially all iron.

2. An austenitic stainless steel having great hardness at high temperatures and substantial resistance to corrosion in the presence of leaded fuels or their combustion products, and containing approximately 0.40% to 1.50% carbon, 19% to 23% chromium, 2% to 5% nickel, 7% to 11% manganese, silicon not exceeding about 0.15%, and the remainder substantially all iron.

3. Stainless steel having substantial hardness at high temperatures in the presence of leaded fuel combustion products, and containing about 0.40% to 1.50% carbon, about 12% to 30% chromium, about 2% to 35% nickel, about 3% to 12% manganese all in such relative proportions as to assure an austenitic structure, silicon not exceeding about 0.25%, about 0.04% to 0.20% sulphur, phosphorus not exceeding about 0.04%, and the remainder substantially all iron.

4. Stainless steel internal combustion engine components having substantial resistance to corrosion in the presence of leaded fuel combustion products at operating temperatures, and containing about 0.40% to 0.70% carbon, about 12% to 30% chromium, about 2% to 35% nickel, about 3% to 12% manganese, said carbon, chromium, nickel and manganese being in such relative proportions as to assure a fully austenitic structure, silicon not exceeding 0.25%, and the remainder substantially all iron.

5. Austenitic stainless steelinternal combustion engine exhaust valves having substantial resistance to corrosion in the presence of leaded fuel combustion products at operating temperatures,

and containing approximately 0.40% to 0.70% carbon, 19% to 23% chromium, 3% to 5% nickel, 7% to 11% manganese, silicon not exceeding about 0.25%, and the remainder substantially all iron.

6. Austenitic stainless steel-internal combustion engine exhaust valvescontaining about 0.40% to 1.50% carbon, about 21% chromium, about 3% nickel, about 10% manganese, silicon not exceeding about 0.15%, and the remainder substantially all iron.

7. Austenitic stainless steel having substantial hardness at high temperatures and substantial resistance to corrosion in the presence of leaded fuel combustion products at high temperatures, and containing about 0.40% to 0.70% carbon, 19% to 23% chromium, 3% to 6% nickel, 7% to 11% manganese, silicon not exceeding about 0.25%, and the remainder substantially all iron.

8. Stainless steel having great hardness at high temperatures and substantial resistance to corrosion in the presence of leaded fuel combustion products, and containing about 0.40% to 1.50% carbon, 12% to 30% chromium, 2% to 35% nickel, about 3% to 12% manganese, all in such relative proportions as to assure a substantially fully aus tenitio structure, silicon not exceeding about 0.15%, and the remainder substantially all iron.

9. Austem'tic stainless steel having hardness at high temperatures and particular resistance to corrosion at high temperatures in the presence of leaded fuel combustion products, said steel containing about 0.40% to 10% carbon, 21.0% to 23.0% chromium, 8.0% to 10.0% manganese, 3.0% to 4.25% nickel, silicon not exceeding 0.45%, and the remainder substantially all iron.

10. Austenitic stainless steel having hardness at high temperatures and particular resistance to corrosion at high temperatures in the presence of leaded fuel combustion products, said steel containing about 0.60% to 0.70% carbon, 21.0% to 22.0% chromium, 9.0% to 10.0% manganese, 3.0% to 3.7% nickel, silicon not exceeding 0.35%, and the remainder substantially all iron.

11. A low-silicon hot hard austenitic stainless steel internal combustion engine exhaust valve component having particular resistance to corrosion at operating temperatures in the presence of leaded fuel combustion products, said steel containing about 0.40% to 1.0% carbon, 21.0% to nun-mimosa cum h llowinz references up of record in the me or this mm:-

UNITED STAT BA'I'IHTB Rmnber mm; Date 2,880,821 Breele et a1. my 31;

Number gonmcm mm:

Country Date Great Britain Feb. 19, 1931 Great Britain Sept. 10, 1940 Switzerland Dec. 16, 1930 Switzerland A118. 31, 1987

Claims (1)

1. STAINLESS STEEL HAVING SUBSTANTIAL HARDNESS AT HIGH TEMPERATURES AND SUBSTANTIAL RESISTANCE TO CORROSION IN THE PRESENCE OF LEADED FUEL COMBUSTION PRODUCTS, AND CONTAINING ABOUT 0.40% TO 1.50% CARBON, ABOUT 12% TO 35% CHROMIUM, ABOUT 2% TO 35% NICKEL, ABOUT 3% TO 12% MANGANESE, ALL IN SUCH RELATIVE PROPORTIONS AS TO ASSURE A SUBSTANTIALLY FULLY AUSTENITIC STRUCTURE, SILICON NOT EXCEEDING ABOUT 0.25%, AND THE REMAINDER SUBSTANTIALLY ALL IRON.

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