US2496246A - High-temperature article - Google Patents

Description

I. 31, I950 P. A. JENNINGS HIGH-TEMPERATURE ARTICLE Filed May 5, 1948 INFLUENCE OF SILICON CONTENT OF CHROMIUM NICKEL-COBALT STAINLESS STEEL ON CORROSION RESISTANCE IN MOLTEN LEAD OXIDE.

SAMPLES OF 20% CHROMIUM I591.- N|CKEL-'I5"/., COBALT STAINLESS OF DIFFERING SILICON CONTENTS TEMPERATURE I675 F FOR ONE HOUR SPECIMENS FLOATING IEIGHT LOSS IN GRA S/ SQ. DECJ HOUR .40 .60 .80 L00 SILICON CONTENT IN PERCENT INVENTOR. PAUL A. JNNIGS HIS ATTORNEY Patented Jan. 31, 1950 $496,246 HIGH-TEMPERATURE Paul A. Jennings,

Baltimore, Armco Steel Corporation,

MIL, Basis-nor to a corporation of Ohio Application May 5, 1948, Serial No. 25,109

7 Claims. (Cl. 75-128) I This invention relates to high temperature stainless steel articles, especially to articles in the An object of my invention is the provision of strong, tough and durable austenitic stainless Steel valves and valve parts for high temperature use,-whlch offer substantial resistance to corrosion-in the heated condition in atmospheres such tures encountered by the valves frequently are as high as 700 F. or more at the fuel intake position. and as high as 1100 F. or more at the the exhaust valves operate.

In most instances, low-alloy steel valves today are unsatisfactory in lntemal combuston engines,

components, which in view of frequent replacement. While hot, the working parts commonly develop heat oxide scale, which detrimentally afl'ects proper seating. In turn, failure to seat allows leakage or blow-by of the hot gases, thus increasing the valve temperature and burning away of the metal. An example of this type valve is one containing about 0.45% carbon, 8.50% chromium, 3.25% silicon, and the remainder substantially all iron.

A great number of the low-alloy steel valves have a low hot hardness value, and thus often are susceptible to deformation while hot as under the pounding eflects of operation. Many of the products too are highly susceptible to creep at elevated and, accordingly, introduce inditionally, a great majority of relatively highalloy steel valves and parts likewise sufler great detriment and rapid deterioration when exposed to the combustion products of leaded fuels.

Quite some few valves and other internal comappreciated more fully There are other valves in the prior art among which are those of austenitic chromium-nickel stainless steel grade. The amounts of silicon in the conventional austenitic steel products ranges from about 0.50% the austenit c stainless steel valves have a more respect, freedom from volume 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. Many valves of this 3 the prior art, however, leave much resistance to corrosive attack by lead compounds. There are many others which, despite the general merits of austenitic steels, fall on the inferior side with respect to hot hardness and resistance to creep.

An outstanding object of my invention accordingly is the prevision of high-temperature, heatresistant, corrosion-resistant stainless steel valves, valve parts, and other internal combustion engine components having substantial strength at elevated temperatures of use including resistance to creep, which are substantially free of phase transformation, are hot hard, and eihciently 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-cobalt stainless steel high temperature products, as for example internal combustion engine intake or exhaust poppet valves, valve stems or heads, seats, balls, plungers, cores and springs, valve or cylinder cladding's, linings or surfacing, or any of a host of other internal combustion engine components made of the steel. My products advantageously include about 0.05% to 1.5% carbon, from 12% to 25% chromium, 2% to 25% nickel, from 3% to 30% cobalt, and amounts of this element approximating 15% being preferred, from very small quantities up to about 0.20 silicon, and the remainder substantially all iron. By keeping an appreciable cobalt content in the steel, and the silicon content below about the 0.20% figure, I find sharp improvement in the resistance of the steel products to corrosion and attack by products of combustion resulting from the burning of leaded fuel. At about 0.10% silicon and on down substantially to zero per cent, this improvement is even more pronounced. The smallel quantities of silicon accordingly are usually preferred.

The cobalt addition importantly dispels an adverse effect of nickel on corrosion resistance in the presence of not lead compounds. In being an austenite-former, the cobalt assists the maintenance of an austenitic balance of the steel. Also, the element, in the amounts employed, im-

character in to be desired 0! proves the hot hardness and high temperature a stretch resistance of the steel products. On occasions, I use nitrogen in amounts up to about 0.30% as a substitute for an equivalent amount of carbon, nickel or cobalt in the steel. The nitrogen thus serves as an austeniteformer. It also tends to increase small degree.

The element manganese in my high temperature chromium-nickel-cobalt stainless steel products, preferably ranges from substantially zero in amount up to about 2%. The relatively large quantities within this range conveniently serve as a partial substitute for such austenite-forming elements as cobalt and nickel, thus to maintain the austenitic balance. There are occasions too where my stainless steel products include in the alloy composition thereof, as for special purposes, one or more such elements as molybdenum, 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 other internal combustion engine components which I provide have a phosphorus content prefthe metal hot hardness a about 0.04%, and a sulphur content which amounts to less than 0.04%, or even as much as 0.5% or more. The largerquantitles of sulphur, and especially those between about 0.15% to 0.50%, contribute cobalt and 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 much beyond 0.50% often introduce hot working diiilculties with certain of the austenitic steels which I employ; also, the rate of improvement in resistance to corrosion by lead oxide usually decreases for these greater amoun My internal combustion engine valve products and the like, in containing chromium, nickel. cobalt and the very small quantities of silicon below about 0.20% have excellent heat resistance and resistance to oxidation at the high temperatures of operation. Also, the presence of cobalt and the restriction of silicon to the critically small amounts indicated importantly contribute erably below to corrosion-resistance of the products in the combustion products of leaded fuels, as where the stainless steel takes the form of an exhaust valve or part exposed to aircraft, truck or passenger car anti-knock fuel exhaust gases. My stainless steel valves and other components of the steel, where made for purposes of operation under stress at high temperatures are resistant to creep. The metal is hot hard and stron and resists scour and abrasion while heated. By virtue of the austenitic quality of the steel, my valve products sufier substantially no phase transformation during heating and cooling cycles, and, accordingly, are free of volume changes and difliculties often following upon change of phase. The valves resist scaling, warping and cracking at full temperature and uponbeing cooled and re-heated.

In the accompanying drawing, the approximate effect of different amounts of silicon on corrosion-resistance of 20% chromium, 15% nickel, 15% cobalt stainless steel in molten lead oxide is graphically illustrated. The carbon content of the several steel compositions concerned, is anywhere from about 0.05% to 0.10%, manganese about 0.5%, and sulphur and phosphorus each less than about 0.04%. Thus, the curve in the drawing is directed to steels which contain chromium, nickel, cobalt, manganese, sulphur and phosphorus in substantially the constant amounts noted, but each of the steels contains a different quantity of silicon as indicated below in the table, the remainder being substantially all iron. In this table, as in the accompanying drawing, the influence of silicon content on resistance in molten lead oxide for each steel is given in terms of grams weight loss per square decimeter per hour, for a corresponding temperature of 1675 F. of the molten lead oxide.

TABLE to the effect of the v It be observed that the Steels A and B are steels falling within the scope of the present invention, the silicon content being sufliciently low,

to around 0.20%, as to the amount in the Steel B, a sharp improvement occurs in the resistance to lead oxide corrosion.

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

While certain of the steels which I provide take the form of internal combustion engine components, it will be understood that certain advantages of the invention are had with other products of the low-silicon steel, amongwhich are hightemperature gas turbine nozzles, turbine parts adjacent to the nozzle, and any of a number 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

as a limitation.

I claim:

1. Stainless steel having great hardness at high temperatures and low stretch in combination with substantial resistance to corrosion in the presence of leaded fuel combustion products, and containin about 0.05% to 1.5% carbon, 12% to chromium, Irom 2% to 25% nickel, 3% to 30% cobalt, all in such proportions as to assure a substantially fully austenitic structure, silicon not exceeding about 0.20%, and the remainder substantially all iron.

2. Stainless steel having great hardness at high temperatures and low stretch in combination with substantial resistance to corrosion in the presence of leaded fuel combustion products, and containing about 0.05% to 1.5% carbon, 12% to 25% chromium, from 2% to 25% nickel, 3% to 30% cobalt, all in such proportions as to assure a substantially fully austenitic structure, silicon not exceeding about 0.10%, and the remainder substantially all iron.

3. Stainless steel having great hardness at high temperatures and low stretch in combination with substantial resistance to corrosion in the presence, of leaded fuel combustion products, and containing about 0.05% to 1.5% carbon, 12% to 25% chromium, from 2% to 25% nickel, 3% to 30% cobalt, all in such proportions as to assure a substantially fully austenitic structure, 0.15% to 0.50% sulphur, phosphorus not exceeding 0.04%. silicon not exceeding about 0.20%, and the re mainder substantially all iron.

4. Austenitic stainless steel internal combustion engine valves having great hardness at high temperatures and low stretch in combination with substantial resistance to corrosion in the presence of leaded fuel combustion products, and containing about 0.05% to 1.5% chromium, from 2% to 25% nickel, 3% to 30% cobalt, silicon not exceeding 0.20%, up to 0.50% sulphur.,phosphorus not exceeding 0.04%, and the remainder substantially all iron.

5. Austenitic stainless steel internal combustion engine valves having great hardness at high temperatures and low stretch in combination with substantial resistance to corrosion in the presence of leaded fuel combustion products, and containing about 0.05% to 1.5% chromium, from 2% to 25% nickel, 3% to 30% cobalt, silicon not exceeding 0.20%, up to 2% manganese, and the remaindersubstantially all man.

6. Austenitic stainless steel containing at least about 0.05% to 1.5% carbon, about 20% chromium, approximately 15% nickel, about 15% cobalt, silicon not exceeding about 0.20%, and the remainder substantially all iron.

7. Austenitic stainless steel internal combustion engine valves, containing about 0.05% to carbon, about 20% chromium, approximately 15% nickel, about 15% cobalt, silicon not exceeding about 0.10%, and the remainder substantially all iron.

PAUL A. JENNDIGS.

REFERENCES CITED UNITED STATES PATEN'IS Number Name Date 1,150,113 Haynes Aug. 17, 1915 1,190,562 Henderson July 11, 1916 1,522,813 Etchells Jan. 13, 1925 2,163,561 Payson et al June 20, 1939 2,397,034 Mohling Mar. 19, 1946 FOREIGN PATENTS Number Country Date 562,102 France Nov. 5, 1923 653,900 France Mar. 28, 1929 OTHER REFERENCES Metals Handbook, 1939 edition, page 4'7. Published by the American Society for Metals, Cleveland, Ohio.

Chemical Abstracts, volume 28, column 3374. Published by The American Chemical Society at Easton, Pa.

Claims (1)

1. STAINLESS STEEL HAVING GREAT HARDNESS AT HIGH TEMPERATURES AND LOW STRETCH IN COMBINATION WITH SUBSTANTIAL RESISTANCE TO CORROSION IN THE PRESENCE OF LEADED FUEL COMBUSTION PRODUCTS, AND CONTAINING ABOUT 0.05% TO 1.5% CARBON, 12% TO 25% CHROMIUM, FROM 2% TO 25% NICKEL, 3% TO 30% COBALT, ALL IN SUCH PROPORTIONS AS TO ASSURE A SUBSTANTIALLY FULLY AUSTENITIC STRUCTURE, SILICON NOT EXCEEDING ABOUT 0.20%, AND THE REMAINDER SUBSTANTIALLY ALL IRON.

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