US2484903A - Heat and corrosion resisting alloy steel - Google Patents

Description

Patented Oct. 18, 1949 UNITED STATES PATENT OFFICE HEAT AND CORROSION RESISTING ALLOY STEEL No Drawing. Application September 24, 1948, Serial No. 51,127

This invention pertains to heat and corrosion resisting alloy steels, and more particularly to such as are characterized in undergoing marked hardening on heating at about 1400 F. for upwards of about one hour, and which thereafter undergo no substantial reduction in hardness on subsequent reheatings to said temperature, irrespective of the number and duration of such reheatings. Steels of this character have been heretofore disclosed in my Patents Reissue 20,421 and 2,051,415.

A primary object of the invention is to provide new and improved steels of this character which are heat hardenable in the manner aforesaid to upwards of about C 38 Rockwell, and which contain as essential alloying ingredients, only the elements chromium, manganese, nickel and silicon, these new steels having relatively high contents of chromium and manganese, together with relatively small but effective amounts of silicon, and with the nickel ranging from effective amounts up to relatively high values as set forth in detail hereinafter.

This application is a continuation-in-part of my copending application Serial No. 782,691, filed October 28, 1947, now abandoned, and is also a continuation-in-part of my copending applica' tion Serial No. 15,963, filed March 19, 1948, now abandoned.

Of the known heat and corrosion resisting steels other than the heat hardening type above referred to, the so-called martensitic varieties are hardened by quenching from above the critical temperature, and thereafter soften or temper on reheating. The so-called precipitation hardening steels may be hardened by cooling from above the solution temperature at a sufficiently rapid rate to retain the precipitation hardening constituents in solution, following which they may be precipitation hardened by reheating at some temperature up to about 1100 F. or higher, but such steels soften on prolonged heating at the precipitation hardening temperature. The so-called austenitic chromiumnickel steels, are generally speaking, quite soft and ductile and retain their initial low hardness when quenched and tempered, although certain 14 Claims. (Cl. 75128) precipitation hardening varieties have been su gested, which, however, soften on prolonged heating at the precipitation hardening temperature.

In my Patent Reissue 20,421, I have described a series of these so-called heat hardening steels to which I have above referred, such steels having heat hardening characteristics as above men tioned, and containing, as essential alloying constituents, about 18 to 35% chromium, about 1 to 10% of either or both nickel and manganese, and about 1 to 10% of either or both molybdenum and tungsten, carbon preferably under 1%, and the balance substantially iron. In my Patent No. 2,051,415 I have described another series of such steels containing, as essential alloying constituents, about 18 to 35% chromium, about 1 to 10% of either or both nickel and manganese, and about 1 to 10% silicon, or alternatively about 0.5% to 10% silicon together with about 0.5% to 10% of either or both molybdenum and tungsten, the content of silicon, molybdenum and tungsten aggregating about 1 to 10%, with the balance substantially iron except for carbon which is preferably under about 1%.

The alloying constituents of such steels are preferably so balanced that the steels consist of a mixture of austenite, ferrite, and carbides in the as cast, as forged, as rolled or as annealed conditions. The heat hardening of such steels, which is ordinarily effected by heating at about 1400 F. for about 1 to 16 hours, or more, is accompanied by a phase change to sigma, of the ferrite present in the aforesaid mixture of austenite, ferrite, and carbides. Ferrite is a magnetic phase and sigma is non-magnetic, so that, in the heat hardening operation, the steel changes from a magnetic condition to a relatively non-magnetic condition, since in the resulting mixture .of austenite, sigma, and carbides in the hardened steel, all the constituents are non-magnetic.

Although ferrite is an essential constituent in the prehardened steel for imparting heat hardenability thereto, the relative amount of ferrite in the prehardened steel is not critical and may vary from as little as about 15% to well over As shown by the test results presented below, the

degree of hardening depends not so much on the amount of ferrite in the prehardened structure as on the composition of the steel, and it has been found for example that a steel containing 22% ferrite in the prehardened condition may harden to only C 32 Rockwell whereas another steel containing 19% ferrite in the prehardened condition may harden to C 41 Rockwell. The degree of hardening is important in the steels of this invention which are intended primarily for exhaust valves in automotive engines, and it is desired that the steels have a minimum hardness of about C 38 Rockwell.

These heat hardening steels contain chromium in sizeable quantities for the purpose of engendering the hardening reaction. The chromium also contributes in marked measure to the resistance of the steel to corrosion, oxidation, andscaling, at elevated temperatures, as well as at room temperature. In consequence of these qualities these heat hardening steels are ideally adapted for such uses as valves and valve seats for internal combustion engines and related applications. The heat hardening steels in accordance with my patents aforesaid, have, in fact,

gone into wide commercial use, particularly as. valves for internal combustion automotive engines, wherein temperature and corrosion conditions are particularly severe. The one outstanding objection to the use of steels of my aforesaid patents for valves in the automotive engines of pleasure or family cars, with respect to which quantity production is greatest and competition among the various automobile manufacturers is keenest, has been the item of expense of this steel. This is due to their relatively high alloy content, particularly as regards such expensive alloys as molybdenum and tungsten.

I have, for a number of years, conducted extensive researches in an effort to devise a cheaper alloy steel having the aforesaid desirable heat hardening qualities, one, for example, which omits the relatively expensive tungsten and molybdenum. I have now discovered a series of such steels, which constitute the subject matter of the present invention. That is to say, I have now discovered that appreciable heat hardening, i. e., upwards of C 38 Rockwell, can be obtained without the use of the expensive tungsten or molybdenum, in the heat hardening type of steel of my patents aforesaid, if a high manganese is present with a high chromium content or if both nickel and manganese are present along with fairly high chromium, and if the nickel and manganese contents are properly balanced in relation to each other.

Thus I have now discovered that steels within the following range of analysis may be heat hardened to a minimum of about C 38 Rockwell, by heating at about 1400" F., for about 1 to 20 hours, viz.:

to about 8% Manganese plus nickel About 8 to 15% Carbon Up to 0.6% Balance Substantially iron Chromium vs.

manganese For manganese under about 3%, chromium should be over about. 26%.

The elements which are most effective in engendering heat hardening are chromium, manganese, and silicon. Nickel is less effective, and indeed will prevent the reaction if present in excessive amounts. Carbon also tends to prevent the reaction if present in large amounts. Both nickel and carbon are effective in establishing the austenite phase in the steel and it is desirable that this phase be present in the steel to give it adequate toughness in the hardened condition since the sigma phase is quite brittle, and the steel would be of little commercial value if it consisted altogether of sigma. The steel is therefore balanced to give an optimum combination of hardness and toughness at the lowest. alloy cost.

It should be clear from the foregoing that as the nickel and carbon are increased in the steel it is necessary at the same time to increase chromium ormanganese or silicon in order to get adequate hardening.

The new steels of the present invention possess the qualities in common with my patented, heat hardening steels aforesaid, of high strength and corrosion resistance at elevated temperatures, i. e., high resistance to stretching under stresses up to 10,000 pounds per square inch (p. s. i.) at temperatures up to about 1350 F., high hardness at temperatures up to about 1400 F.; and good resistance to corrosion in lead oxide up to about 1675" F. They are also much tougher than heat hardening steels which substitute high silicon for molybdenum and tungsten.

Although neither molybdenum nor tungsten is required in the steels of the'present-invention for imparting heat hardening qualities thereto, and

in fact are preferably omitted where the'cost item is an important" factor, nevertheless either or both of these elements may be included up to about 2 or 3% in aggregate'yw'ithcorresponding enhancement in the heat hardening properties. To this same end silicon may also be included up to about 2 or 3%.

Likewise the steels of the present invention may contain one or more of the elements cobalt, aluminum, copper and vanadium in aggregate amount to about 5% without impairing the heat hardening qualities, although such elements do not participate in the heat hardening reaction. Additions of one or more of these elements is sometimes desirable for increasing toughness, forgeability', etc.

The most commonly employed steels for automotive exhaust valves are of three types, as set forth in Table I below, namely, the austenitic, exemplified by steels A and B; the 'martensitic, exemplified by steel C; and the heat hardening or sigma phase type of my patents aforesaid, of which steel D is an example.

TABLE. I.

Steel 0 Mn" Si Ni. Cr Mo The austenitic steels are limited in their use.- fulness because they cannot be .hardened, and therefore a stem element of hardenable steel has to be welded tothe .stem of the-valve proper, so that the tappet. end of the valve will have adequate hardness for service. There are several manufacturing problems which make this twopiece welded valve less desirable than a valve comprising a single piece of steel.

The martensitic steel C has the advantages of being hardenable for adequate .wear resistance, and of being low in cost, but its usefulness for automotive valves is limited in that it has relatively low hardness and low resistance to stretching at elevated temperatures such as are encountered in the exhaust stream of modern automotive engines, wherefore it suffers excessive wear at the seat of the valve, and stretching in the upper portion of the stem of the valve, both of which make for ineflicient operation of engines in which the valves are used.

The heat hardening or sigma phase steel D in accordance with my patents aforesaid, is outstanding in performance as exhaust valves in most automotive engines, but it has, as above stated, the disadvantage of relatively high cost. It is, therefore, highly desirable for automotive engine economy in design and operation to provide a steel that has the properties of steel D, but a cost more nearly like that of steel C. Such a steel is provided by the present invention.

About C 38 Rockwell is considered adequate hardness for the tappet end of automotive exhaust valves. Since valve steel service in modern high compression engines involves temperatures up to about 1400 F. these steels should therefore be able to attain the desired minimum hardness of C 38 Rockwell by a heating at 1 F. Furthermore in order for the hardening practice to be feasible, it should not take more than about 16 hours which is an over-night period. The procedure for establishing adequate hardening of these steels therefore is a heating at 1400 F. for 16 hours followed by an air cool. In most instances the steel is heated directly from the as forged or as rolled condition, but for special tests the steel may be given an annealing treatment prior to the hardening treatment.

It will be evident from the data below that the attainable hardness is dependent on the balance of composition within the limits set forth above.

When the manganese is on the low side, i. e., under about 3%, it is necessary to raise the chromium to the high side of the range, i. e., in excess of about 26%, as shown in Table II.

TABLE II Balancing of chromium and nickel with low manganese Analysis, Per Cent Rockwell O Hardness After 16 hrs. Bar 0 Mn Si Ni Cr Ni+Mn at 1400" F.

It is clear from these results that about 26% or more chromium is required to produce adequate hardening in steels of low manganese content, i. e., under about 3%, provided the sum of nickel plus manganese is upwards of about 8%, although as shown by bar 5489 this sum may be decreased somewhat if chromium is extremely high. However, when the manganese is increased the steels harden adequately when chromium is appreciably lower than 26% as shown in Table III below.

TABLE III Effect of manganese on hardening of steel with about 3% nickel and 24% chromium Analysis, Per Cent Rockwell C Hardness After 16 hrs.

Bar 0 Mn Si Ni Or Ni+Mn at 1400 F.

These data show that manganese is quite effective in increasing the attainable hardness of the steel even though chromium is on the low side of the specified range. However, these results also show that when manganese is near the topof the specified range for this element the attainable hardness tends to decrease, and it is then necessary to balance the composition by raising the chromium as shown in Table IV below.

TABLE IV Efiect of chromium on the hardening of steels high in manganese Analysis, Per Cent Rockwell O Hardness After 16 hrs. Bar 0 Mn Si Ni Cr Ni+Mn at 1400 F.

It has been found possible to produce adequate hardening by a suitable combination of chromium and manganese and omitting nickel, as shown below but such a steel tends to be too brittle for valve service. Adequate hardness combined with good toughness is most satisfactorily obtained by a combination of manganese and nickel with chromium as is also shown in Table V.

TABLE V Attainable hardness in steels with varying proportions of manganese and nickel Analysis, Per Cent Rockwell C Hardness After 16 hrs. Bar 0 Mn Si Ni Cr Mn+Ni at 1400 F.

It will be noted that although in some of this series of steels the attainable hardness increases as the sum of manganese and nickel increases to a maximum, and then decreases, the efiect of manganese and nickel is not independent of chromium content. It is possible to cause the steel to harden adequately by raising the chromium both when the sum of manganese and nickel is high, as in the cases of steels 5588 and 5590; and 5586 and 5587; as well as when'the sum is low, as in cases of steels 5358 and 5489; and 5359 and 5491. Thus there i no simple rule for balancing the steel on the basis of the sum of manganese and nickel alone. However, chromium has to be raised to the top of the aforementioned limits both when the sum of nickel and manganese is either low or high within the percentage limits for these constituents. And since chromium is fairly expensive and .also causes fabrication difficulties when it is present in the steel in large quantities, it is desirable to balance the steel by holding the sum of manganese and nickel within limits of about 8 to which maintaining chromium over about 26% for manganese contents below about 3%.

Silicon is added to the steel for deoxidation purposes during melting. However, a certain amount beyond that necessary for 'deoxidation is desired for promoting the hardening of the steel. This is illustrated in the following Table VI.

TABLE VI Eflect of silicon on the hardening of steels with varying manganese and nickel Analysis, Per Cent Rockwell C Hardness After 16 hrs. Bar 0 Mn Si Ni Or Ni+Mn at 1400 F.

These data show that small increments in silicon greatly enhance the hardenability. It is thus desirable that silicon be present in the steel up to about 1%. Larger amounts are effective in counteracting the tendency of the steel to lose its ability to harden adequately when nickel plus manganese is below about 8% as evidenced by bars 5361 and 5619, and also when the steel is given an annealing treatment prior to hardening, the latter as shown in the following Table VII.

TABLE VII the steel, although increasing amounts of silicon tend to increase the brittleness of the hardened steel.

The effect of carbon content on the hardening of the steel containing suitable proportions of manganese and nickel is shown in Table VIlI.

TABLE VIII Efiect of carbonon hardening of steel with about -5% Mn, 3% Ni, and 24% Cr Analysis, Per Cent Rockwell O Hardness After 16 hrs.

Bar 0 Mn Si Ni Or Ni+Mn at 1400 F.

These data show that hardening decreases with increasing carbon, and that steels with carbon above about 0.60% do'not have adequate hardness after long time'he-atings at 1400 F. Furthermore, the higher carbon steels are more difficult to forge.

The steel of this invention is eminently satisfactory for automotive valves in respect to hot hardness; resistance to stretching; and resistance to corrosion in lead oxide as shown by the data in Table IX.

TABLE IX Evaluation of steel of this invention for automotive exhaust valves by comparison with properties of steels C and D 553 3 5 Steel D Steel 0 Brinell Hardness tat 1300 F--. 180 185 BrinellHardness at 1400 F. 167 1.75 120 Per cent elong. in 2 in. in 8 7 hrs. with stress of 10,000

p. s. i. at 1300 F 0.4 to 2. 2 1. 2 to 1.4 Corrosion in Lead Oxide at l675for 1hr. gms. per sq. in 2. 8 to 4. 2 4.0 to 4. 8 4.8 to 5.4

Analysis, Per Cent Rockwell C Hardness After 16 hrs.

at 1400 F., Prior Condition As Annealed Annealed Bar 0 or NHMH Forged o F. 1850 F.

For this reason it is sometimes desirable to have the silicon present in amounts up to about 3% in hardening properties of the steel, of the amount of ferrite present in relation to the austenite, of

TABLE X never encountered this type of hardening in steel having no ferrite. On the basis of the harden- Efl'ect on heat hardening of percent ferrite versus percent austenz'te in steel in the preheat hardened state Rockwell O Hardness Analysis, Per Cent Microstructure 1 After 16 hrs. at

Per Cent Per Cent As As Bar Mn Si N1 Cr Mo Ferrite Austenite Forged Hardened 5532 26 4. 68 74 3. 76 56 40 27 42 5492 36 3. 11 58 5. 38 37 57 30 45 5494 31 3. 31 52 7. 8l 39 50 33 44 5628 40 2. 26 1. 83 5. 01 19 75 34. 40. 5 5622 4O 4. 95 1. 74 3. 38 29 67 29. 5 38. 5 5612 42 7. 94 76 3. 44 28 65 31 42 5470 42 81 72 4. 65 45 48 28 39 5701 14 2. O1 1. 60 9. 98 22 75 25. 5 32 1 Balance substantially all carbides.

The data of Table X thus indicate that there is no correlation between the attainable hardness and the amount of ferrite in the as rolled or pre-heat hardened steel. Bar 5701 for example has 22% ferrite and hardens only to C 32 Rockwell; whereas bar 5628 has less ferrite, namely 19%, but hardens much better, i. e., to C 41 Rockwell. On the other hand bar 5532, which has almost three times as much ferrite as bar 5628, hardens only one point higher, namely, to C 42 Rockwell.

Since the steels of Table X vary appreciably as to composition, it is difficult conclusively to establish therefrom whether or not the hardening is dependent on the composition of the steel rather than on the ferrite content. This point is established by the data presented in the following Table XI.

ing of bars 5773 and 5628 in the tabulation above it further appears that 15% or more ferrite must be present in the steel for imparting effective heat hardenability thereto.

In order to establish that the heat hardening steels of the invention are all resistant to softening after they were hardened, disks from a wide variety of steels were hardened and reheated at 1100, 1200, 1300, and 1400 F. for intervals up to 225 hours at temperature. None of them showed any drop in hardness, and some actually increased in hardness after the long heatings at 1300 and 1400 F.

What is claimed is:

1. A heat and corrosion resisting alloy steel, consisting principally of austenite and ferrite with a minimum of about 15% ferrite, said steel being hardenable to upwards of about C 38 TABLE 2H Composition of steel versus hardening Rockwell C Amt. Ferrite Hardness Bar 0 Mn Si Ni Cr NH-Mn in As Rolled Structure As After 16 hrs.

Rolled at 1400 F.

Per cent 5771 l1 2. 5 0. 6 7. 7 24. 1 10. 2 24 32 5773 l2 4. 1 0. 7 7. 5 24. 3 ll. 6 18 31 38 5768 39 2. 2 0. 4 7. 6 27. 7 9. 8 22 31 39 5494 31 3. 3 0. 5 7. 8 27. 6 11. 1 39 33 44 5767 36 2. 2 6. 4 4. 8 23. 7 7. 0 17 31 25 5628 40 2. 3 1. 8 5. 0 24. 9 7. 3 19 41 5766 46 4. 5 0. 3 2. 9 24. 1 7. 4 30 30 27 5622 5. 0 l. 7 3. 4 25. 2 8. 4 29 30 39 In the above table, the first pair shows that bar 5773 with 4.1 manganese hardens better than bar 5771 with 2.5 manganese, even though the former has a lower amount of ferrite. The second pair also shows that manganese improves the hardening although in this case the steel with the larger amount of ferrite developed the higher hardness. The third and fourth pairs show the advantage of silicon, in each pair the higher silicon steel having appreciably higher hardness, although the amount of ferrite was the same in each steel of the pair,

It thus appears that the composition of the steel controls the attainable hardness rather than the amount of ferrite. However, I have es tablished that some ferrite must be present in the steel in order for it to harden, because I have Rockwell by heating at about 1400 F. for upwards of one hour, and of thereafter undergoing no substantial reduction in hardness after subsequent'heatings to said temperature, said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; from an effective amount to under 1% silicon; carbon up to about 0.6%; and the balance substantially iron.

2. An article made of a heat hardened alloy steel, said steel being in the condition obtained by heating at about 1400 F. for upwards of one hour, and having a hardness of upwards of about C 38 Rockwell, said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; from an effective amount up to under 1% silicon; carbon up'to about 0.6%; and the balance substantially iron.

3. A heat and corrosion resisting alloy steel, consisting principally of austenite and ferrite with a minimum of about 15% ferrite, said steel being hardenable to upwards of about C 38 Rockwell by heating at about 1400 F. for upwards of one hour, and of thereafter undergoing no substantial reduction in hardness after subsequent heatings to said temperature, said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; from an effective amount to under 1% silicon; carbon up to about 0.6%; up to about 5% in aggregate of other elements which do not impair substantially the heat hardening properties of the steel, and the remainder iron.

4. An article made of a heat hardened alloy steel, said steel being in the condition obtained by heating at about 1400 F. for upwards of one hour, and having a hardness of upwards of about C 38 Rockwell. said steel containing: from more than 22% up to about 32% chromium; amount up to about 8% nickel; from an effective about 1 to 10% manganese; from an effective amount to under 1% silicon; carbon up to about 0.6%; up to about 5% in aggregate of other elements which do not impair substantially the heat hardening properties of the steel, and the remainder iron.

5. A heat and corrosion resisting alloy steel, consisting principally of austenite and ferrite with a minimum of about ferrite, said steel being hardenableto upwards of about C 38 Rockwell by heating at about 1400 F. for upwards of one hour, and of thereafter undergoing no substantial reduction in hardness after subsequent heatings to said temperature, said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and thechromium content being in excess of about 26% when the manganese content is below about 3%; from an 'efi'ective amount to under 1% silicon; carbon up to about 0.6%; and the balance substantially iron.

6. An article made of a heat hardened alloy steel, said steel being inthe condition obtained by heating at about 1400" F. for upwards of one hour, and having a hardness of upwards of about C 38 Rockwell, said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and the chromium content being in excess of about 26% when the manganese content is below about 3%; from an effective amount to under 1% silicon; carbon up to about 0.6%; and the=balance substantially iron.

7. A heat and corrosion resisting alloy steel, consisting principally of austenite and ferrite with a minimum of about 15% ferrite, said steel being hardenable to upwards of about 0 38 Rockwell by heating at about 1400 F. for upwards of one hour, and of thereafter undergoing no substantial reduction in hardness after subsequent heatings to said temperature, said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and the chromium content bein in excess of about 26% when the manganese content is below about 3%; from an effective amount to under 1% silicon; carbon up to about 0.6%; up to about 5% in aggregate of other elements which do not impair substantially the heat hardening properties of the steel, and the remainder iron.

8. An article made of a heat hardened alloy steel, said steel being in the condition obtained by heating at about 1400 F. for upwards of one hour, and having a hardness of upwards of about C 38 Rockwell, said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and the chromium content being in excess of about 26% when the manganese content is below about 3%; from an effective amount to under 1% silicon; carbon up to about 0.6%; up to about 5% in aggregate of other elements which do not impair substantially the heat hardening proper- .ties of the steel, and the remainder iron.

9. A heat and corrosion resisting alloy steel consisting principally of austenite and ferrite, with a minimum of about 15% ferrite, said steel being hardenable to upwards of about C 38 Rockwell by heating at about 1400 ,F. for upwards of one hour, and of thereafter undergoing no substantial reduction in hardness after subsequent reheatings to said temperature, said steel containing: from more than 22% up to "about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and the chromium content being in excess of about 26% when the manganese content is below about 3%; from n effective amount to about 3% silicon; carbon up to about 0.6%; up to about 5% in aggregate of other elements which do not impair substantially the heat hardening properties of the steel, and the remainder iron.

10. A heat and corrosion resisting alloy steel consisting principally of austenite and ferrite, with a minimum of about 15% ferrite, said steel being hardenable to upwards of about C 38 Rockwell by heating at about 1400 F. for upwards of one hour, and of thereafter undergoing no substantial reduction in hardness after subsequent reheatings to said temperature,.said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and the chromium content being in excess of about 26% when the manganese content is below about 3%; from an effective amount to under 1% silicon; from an effective amount up to about 3% of metal of the group tungsten and molybdenum; carbon up to about 0.6%; up to about 5% in aggregate of other elements which do not impair substantially the heat hardening properties of the steel; and the remainder iron.

11. A heat and corrosion resisting alloy steel consisting principally of austenite and ferrite, with a minimum of about 15% ferrite, said steel being hardenable to upwards of about 0" 38 Rockwell by heating at about 1400 F. for upwards of one hour, and of thereafter undergoing no substantial reduction in hardness after subsequent reheatings to said temperature, said steel containing: from more than 22 up to about 32% chromium; about 1 to 10% manganese; from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and the chromium content being in excess of about 26% when the manganese content is below about 3%; from an effective amount up to about 3% silicon; from an efiective amount up to about 3% of metal of the group molybdenum and tungsten; carbon up to about 0.6%; up to about 5% in aggregate of other elements which do not impair substantially the heat hardening properties of the steel; and the remainder iron.

12. An article made of a heat hardened alloy steel, said steel being in the condition obtained by heating at about 1400 F. for upwards of about one hour, and having a hardness of upwards of about C 38 Rockwell, said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% of manganese; from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and

the chromium content being in excess of about 26% for a manganese content below about 3%; from an eifective amount up to about 3% silicon; carbon up to about 0.6%; up to about 5% in aggregate of other elements which do not impair 14 about 1 to 10% of manganese; from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and

the chromium content being in excess of about 26% for a manganese content below about 3%; from an effective amount up to under 1% silicon; from an effective amount up to about 3% of metal of the group molydenum and tungsten; up to about 0.6% carbon; up to about 5% in aggregate of other elements which do not impair substantially the heat hardening properties of the steel; and the remainder iron.

14. An article made of a heat hardened alloy steel, said steel being in the condition obtained by heating at about 1400 F. for upwards of about one hour, and having a hardness of upwards of about C 38 Rockwell, said steel containing: from more than 22% up to about 32% chromium; about 1 to 10% of manganese; .from an effective amount up to about 8% nickel; the sum of nickel and manganese aggregating about 8 to 15%, and the chromium content being in excess of about 26% for a manganese content below about 3%; from an effective amount up to about 3% silicon; from an efiective amount up to about 3% of metal of the group molybdenum and tungsten; carbon up to about 0.6%; up to about 5% in aggregate of other elements which do not impair substantially the heat hardening properties of the steel; and the remainder iron.

PETER PAYSON.

N 0 references cited.

Certificate of Correction Patent No. 2,484,903 October 18, 1949 PETER PAYSON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: I Columns 7 and 8, Table VII, 10th column thereof, 1st line under the heading 125 8 for the numeral 32 read 26; column 11, line 27, strike out about 1 to 10% manganese; from an effective and insert the same in line 25 after the word and semicolon chromium and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 21st day of February, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'saioner of Patents.