US2163561A - Chrome steel alloy valve element - Google Patents

Description

Patented June 20, 1939 UNITED STATES CHROME STEEL ALLOY VALVE ELEMENT Peter Payson, Neck, N. Y., Orange, N. J.,

New York, Lewis S. Bergen, Great and Walter L. Hodapp, East assignors to Crucible Steel Company of America, New York, N. Y., a corporation of New Jersey No Drawing. Application November 11, 1937, Serial No. 174,046

3 Claims.

This invention relates to a heat, oxidation and corrosion resisting alloy steel and to articles thereof, said steel containing chromium as the principal alloying element, and. providing an 6 improved steel of this character adapted primarily for use in such articles as valves, valve seat inserts and like parts of internal combustion engines.

An outstanding characteristic of the new steel,

1 as evidenced by the data hereinafter presented,

is its superior corrosion resistance to the combustion products of special motor fuels, such as the so-called anti-knock gasolines, containing lead compounds, for example, lead tetra-ethyl. An-

other outstanding characteristic of the new steel is its high strength at elevated temperatures inclusive of the highest valve operating temperature encountered in practise. The new steel, moreover, meets with outstanding degrees of effectiveness the various other criteria for a highly desirable valve steel for automotive, airplane and related uses, such as good toughness, low coeflicient of expansion, a high degree of hardenability, retention of hardness in service, etc.

A present day requirement of the airplane and automotiveindustries, and as to the latter especially as regards motors for heavy duty bus, truck and tractor service, is for a valve steel which performs effectively at valve operating temperatures in the neighborhood of 1600 F., in the presence of the extremely corrosive exhaust gases resulting from the use of ethyl gasoline and like motor ,fuels. This requirement is not met by the relatively low alloy valve steels formerly found as acceptable, such as the familiar chrome-silicon alloys, owing to their susceptibility to attack by the exhaust gases of anti-knock fuels. Some exponents have accordingly proposed substituting moderately high alloy chrome-nickel steels of the austenitic type and also those containing nickel in lesser amounts along with silicon, as constituting steels, which were believed by reason primarily of the nickel present therein to offer increased resistance to corrosion under the conditions above stated.

to attack by lead compounds even when added in amounts as low as a per cent. or so, and this irrespective of whether or not silicon is included along with the nickel. This detrimental action of the nickel increases rapidly with the quantity thereof present. We have also discovered that the presence of silicon is likewise generally detrimental and at best ineifective as regards resistance to lead compounds.

Formerly scaling tests were used to determine the suitability of steels for valve uses, and constituted the basis on which the austenitic chromenickel steels were advanced as meeting present day valve requirements more effectively than the valve steels theretofore more widely employed. Scaling tests are apt to be misleading, however, because they are conducted in an ordinary furnace atmosphere to which air is freely admitted; whereas internal combustion engine exhaust valves are exposed not to such an atmosphere, but to the combustion products of the fuel employed. The scaling test above referred to was employed for some time subsequent to the introduction of ethyl gasoline because little was then known as regards its combustion products. Subsequent investigation of the subject lead to the belief that lead oxybromlde was the determining new corrosive constitutent in the exhaust fumes of such fuels. And it was on the basis of tests for corrosion resistance to lead oxyb'romide at elevated temperatures that the aforesaid chrome steels containing lesser amounts of nickel in conjunction with silicon were proposed as best adapted to fit present day needs.

More recently the petroleum companies have, as a result of exhaustive investigation, developed a laboratory method which checks accurately with service results, for testing steels for corrosion resistance to the motor exhaust fumes derived from ethyl gasoline. This test consists in exposure or the steel to three lead compounds, present in the exhaust from ethyl gasoline, viz: lead oxide, lead oxybromide, and lead oxysulphate, the exposure being carried out at temperatures of 1800 F., 1550 F., and 1800 F., respectively. It has been found that a steel which shows superior corrosion resistance not only to one or two but to all three of these compounds at the temperatures stated, has superior corrosion resistance to exhaust gases and vapors of motor fuels in service; and that conclusions drawn from the results of tests on but one or two of these compounds, do not give results in conformity with service tests, and, therefore, are apt to lead to erroneous conclusions. I

Table III Table IV The eflect of adding nickel is shown below in Nor is the corrosion resistance of the steel im-' regards corrosion resistance to lead oxybromide and lead oxide, and a substantially ineffective addition as regards resistance to lead oxysu1- phate. Its cumulative effect is, therefore, decidedly detrimental.

Nickel is thus a highly detrimental addition as adding both nickel and silicon, as shown by:

By employing this testing technique we have discovered that straight chrome steels containing Table III.

about 18 to 30% chromium and up to about 2.0%

carbon, offer extremely high corrosion resistance 5 to the above named lead compounds as shown by 1 1 m mmm mmm can m Mu 0 0 0 0 0 0 1 3 w me H m 73 2 1 M W h mmm mmm m s mm 0 0 0 0 00 00d 1 m t h W WM 054 w m mmw man mwm m 00 0 0 0 0 0 00 .mb m m m mm mm "mad mm "la "La 1 2a P u u a a m w mun mun mam 0 0a n60 LL M P s t a t a w mmm mun mmw 0 0 11 4.5 H m mam mam w 0 0 0 0 0&0 i 0 0 .t s I. a m 2 m d 3 3 m m mmm mmm m a m can 0 00 .m m m a m r I .W. .W e e W m 7 0 7HM m M a a a t m .W. 000 000 m m t d t e m was .aaa w m a 0 0 0 LLL m 8 v b m m a m m 2 m m 3 m %n% wma H i H m wmm mum w m n m m sion increases with increasing chromium, and

that the results for high carbon are comparable with those for low carbon especially for .the higher chromium contents.

Heretofore silicon has been generally regarded as an essential constituent of valve steel, because it was believed that silicon increases the-resistance to scaling at elevated temperatures, and

that a steel found highly resistant to scaling would prove to be a superior type of valve steel proved, but to the contrary is greatly reduced, by

However, the tests on which these conclusions were based were all conducted in an ordinary furnace atmosphere having free access of air, as above stated, and do not correlate with the results of actual service tests. Based on the in service.

Weight loss in gnu/so. in.

Table V for automotive exhaust valves) with a preferred analysis in accordance with this invention.

Analysis Percent Stool w m w let-eye d 8 h S h v H r H mm mu m t m m a m i. to .2. s? m Jam 0 e b. m .mhaasvcmm m um ma w m r n mh .m mi .0. m a a m m d m us m n m mht SU m ye d nf l m m m ao me e m m t .m s e W .0 t mwe m m m mt n If. mammm n ut 3 a1. mu m 6 mm. m c r n m e P neo m a n n .m m w e ch-w s m w 6 hr. W. ...N L k flee m m m mm n. w n d l.mce 4 T m 80 T. S 6 2 e n V c n d P in m mwwSm m an t .m e a d a e e r iwn P o .m m fl s o n 1. 7 mn n 0% i M 000 t w 08 e a e m w 8W n Mm et i m 0 00 men m a dmm m m is t. a e m T u w M mm S m 000 w mm .m W as. a m 1 T a can W u 0 L2 H m n P 8 .wmw m m a 4 m m m mmm rti i m P g n 2 n o am hum a mum P tslT 55 These data-show that in general the presence of In the above table, Steel 1 typifies the relatively low alloy, chrome-silicon type of steel which has Its cumulasentative of a higher alloy austenitic chromenickel steel; Steel 3 is likewise an austenitic steel silicon is definitely detrimental as regards corrosion resistance to lead oxide, and that it is either ineffective or detrimental with respect to lead been used extensively in the past; Steel 2 is repreoxybromide and lead oxysulphate. 76 tive effect is therefore definitely detrimental.

containing silicon in addition to chromium and nickel; Steel 4 typifies the steel above referred to containing nickel in lesser amount along with silicon; Steel 5 is a heat hardenable chrome- 5 nickel-molybdenum steel of the type described in patent granted to P. Payson No. Re. 20,421; while Steel 6 'is a steel in accordance with the present invention. It will be noted that with the exception of the heat hardenable Steel 5 of the prior patent referred to, the losses for each of the above prior steels are definitely greater with respect to all of the lead compounds than those of Steel 6 according to this invention, and that even-in the case of Steel 5 the losses for lead oxide are'several times those of Steel 6. Steel 6 in accordance with this invention is thus shown to be superior to all of the above steels in current use and vastly superior to the majority of them.

To be acceptable for internal combustion engine valves, 2. steel must be sulllciently hardenable to prevent wear and abrasion of the valve stem'including the tappet end. Also, the critical point should be above any temperature which the valve may attain in service. Preferably this critical point is above 1600 F. These requirements are. fulfilled for the steels of the present invention which contain about 18 to 30% chromium. by holding the carbon content within the limits of about 0.50 and 2.0% and preferably within 0.75 and 2.0%, as shown by:

Table VI Steel analysis Peraent Rockwell C hardness after quenching from- Very high chrome steels have, heretofore, been regarded as extremely difficult to harden. The above data shows that such steels may be hardened effectively and by usual methods provided the carbon content is, in accordance with the present invention, made sufficiently high.

The steel of the invention is hardened by the conventional method of heating above the critical temperature range only for a sufficient time to insure heating throughout to the furnace temperature, following which it is subjected to an air cool, oil or water quench, or other means of rapid cooling to harden. On so heating the steel assumes an austenitic structure which on quenching is converted into the hard transition products, such as martensite, trootsite, sorbite, etc., the transformation thus stopping short of complete conversion into the relatively soft ferritic and pearlitic structures. 'The steel of the invention is thus to be distinguished from those which are precipitation hardened at elevated temperature or as a'result of maintaining them for relatively long intervals at elevated temperature, such as occurs with the so-called heat hardenable steels of the patent aforesaid.

Aside from the fact that silicon is a detrimental or ineffective addition to the steel as regards corrosion resistance to the combustion products of ethyl gasoline, it likewise materially reduces the hardenability of the steel as shown by:

Table'VII Rockwell 0" hardness Cr 21.57 Cr. 25.5

4 o 1.1% c 1.2% Air cooled from F.

Silicon Silicon The steel of the invention must, in order to meet present day requirements, be capable of withstanding heating for long periods at temperatures up to 1600" F. without transformation, since transformation causes hardness and volume changes which are apt to produce warpage of the valve with resulting improper operation or failure. To avoid this the steel should have a critical range above 1600 F. to assure which for certain analyses critical temperature raisers may be added such as Al, Be, Cb, Mo, Ta, Ti, V, W, Si and Zr in amounts up to about 2%. Also it is sometimes desirable to add up to about 2% of Co, Cu, Mo, V and W which act as "strengtheners to increase the strength of the steel at elevated temperatures. Although manganese is without effect on the corrosion resisting properties of the steel, it tends to lower the critical temperature, and hence should be held under, and preferably well under 2%. Likewise the silicon and nickel contents should each be held below 1% for reasons above stated, the nickel content lead oxysulphate, and lead oxide at elevated temperatures, said steel containing: over 20% to about 30% chromium, about 0.5 to 2% carbon, and the balance substantially iron.

2. A valve element for internal combustion engines made of an alloy steel characterized by high corrosion resistance to lead oxybromide, lead oxysulphate, and lead oxide at elevated temperatures, said steel containing: over 20% to about 30% chromium, about 0.5% to 2% carbon, under about 0.5% nickel, up to about 2% in aggregate of elements which raise the critical temperature of the steel, up to about 2% in aggregate of elements which strengthen the steel, and the balance substantially iron.

3. A valve element for internal combustion engines made of an alloy steel characterized by high corrosive resistance to lead oxybromide, lead oxysulphate, and lead oxide at elevated temperatures, said steel containing: over 20% to about 30% chromium, about 0.5 to 2% carbon, up to 2% in aggregate of elements which raise the critical temperature of the steel with silicon under 1%, up to about 2% in aggregate of elements which strengthen the steel, and the balance substantially iron.

PETER PAYSON. LEWIS S. BERGEN. WALTER L, HODAPP.