US3410682A - Abrasion resistant chromiummolybdenum cast irons - Google Patents

Description

3 Sheets-Sheet 2 H. s. AVERY ETAL.

ABRASION RESISTANT CROMIUMMOLYBDENUM CAST IRONS .OSW oo..

Nov. 12, 1968 Filed sept. 11, 1967 3 Sheets-Sheet 3 H. S. AVERY ETAL .rzmumainzmnmo Zmummm .3.5.0.2 QN o.. Y o ma, QN m.. c.. ma n ond m oud f. n 0nd .0 OMG m 36 a M \Q 3.o u1u-z No.. n u \Q v 1 M m x mxuwm owe w .ZuSwP owo W oou mE .h ooow m .o5 R Qvd 5N m- 23 M htx ON 3.o wnwmxw w, .U No l ww3 m9242345 w Nov. 12, 1968 ABRASION RESISTANT CHROMIUM-MOLYBDENUM CAST IRONS Filed Sept. l1, 1967 @.mm mndmwm aazavj vo/swab' www zu vna 13M Inventors Howard S. Averg/ Y S'enrg J.C`.1'za|:ir1.` www, 11W 4NI/@MJ fHttorrzeas United States Patent M 3,410,682 ABRASION RESISTANT CHROMlUi MOLYBDENUM CAST IRONS Howard S. Avery and Henry J. Chapin, Mahwah, NJ.,

assgnors to Ahex Corporation, New York, N.Y., a corporation of Delaware Continuation-n-part of application Ser. No. 403,314,

0ct. 12, 1964. This application Sept. 11, 1967, Ser.

12 Claims. (Cl. 75-128) ABSTRACT 0F THE DISCLOSURE Abrasion resistant cast iron alloys consisting essentially of 2.5 to 3.4% carbon, 0.15 to 1.6% nickel, 12.5- 25.6% chromium, 0.38 to 2.90% molybdenum, and the balance iron. A second species contains 2.5 to 3.2% carbon, 0.4 to 2.1% manganese, 0.1 to 1.9% nickel, l to 23% chromium, 0.4 to 2.4% molybdenum and the balance iron. Superior abrasion resistance is achieved by restricting carbon, nickel, chromium, manganese and molybdenum contents to percentages conforming to a limiting mathematical expression of a parabolic effect.

This application is a continuation-in-part of application Ser. No. 403,314, iiled Oct. 12, 1964, and now abandoned.

This invention relates to alloys, and especially to white cast irons of a hard, abrasive-resistant type suitable for ball and rod mill liner service, and more particularly characterized as chromium-molybdenum cast irons which may or may not contain nickel.

Ball and rod mills represent processing units important to the mining industry in general, in that such units are necessary for grinding and breaking up ore as mined into finer size incidental to further processing. Such mills are equipped with replaceable liners intended to absorb the severe wear that occurs in the interior of' the mill during the course of grinding. The liners are a mosaic of heavy castings bolted or otherwise fastened to the inner surface of the mill, and the alloy of the present invention is particularly suitable as the composition for such liners.

The type of wear experienced by liners of the kind under consideration is characterized as grinding abrasion as this term is dened in the publication Wear, November-December 1961, vol. 4, No. 6. At times the Wear is.y so severe that as much as one or two pounds of liner metal may be lost by abrasion in the course of milling for every ton of ore ground.

The` liners are furnished in various shapes, and may vary in thickness from below two inches to above tive inches. Due to the differences in geometry and the severity of operating conditions encountered, including corrosion, a number of problems in metallurgy are presented. Principally, the liner should be of such metallurgical character as to possess both toughness and resistance to abrasion.

Toughness is necessary in order that the liner will withstand chipping tendencies due to the impact from the grinding medium, whether it be ore fragments, balls or rods. Strength and toughness are also required to resist the `stress imposed on the liner sections by the weight of the revolving mill load. The need for wear resistance is obvious. Unfortunately the properties of toughness and wear resistance are to a large extent opposite. Thus if an alloy displays superior resistance to wear it may be so brittle as to chip and spall under severe mill action, or the liner sections may fracture after they have worn thin. On the other hand if the alloy is treated or selected to be quite tough and resist both chipping and gross fracture it may wear so rapidly that mill operation is uneconomical.

3,410,682 Patented Nov. 12, 1968 ICC These tendencies mean that the combination that is best, or in other words, the optimum balance of toughness and abrasion resistance, is a very desirable objective. However, the way to achieve such an objective is not always clear. Hitherto, such optimum balances for mills of different severities have been approximated by selection of alloy types after considerable experience. Austenitic manganese steel and the air-hardening chromium-molybdenum steels are examples of alloys that have been accepted at the tough end of the practical range. Toward the other extreme, where less toughness is needed but where maximum abrasion resistance is economically very desirable, certain cast irons may be acceptable. However, ordinary pearlitic white cast iron seems to lack both toughness and abrasion resistance. Gray cast iron is tough enough for Such service as are the ductile irons with spheroidal graphite, but these lack enough abrasion resistance.

There are several alloys on the market which, to a greater or lesser degree, present, at least under given operating conditions, an acceptable balance between toughness and abrasion resistance properties. Toughness may be evaluated in several ways, `some of which have been standardized. Thus, the area under the stress-strain curve of a uniaxial tensile test, or the energy absorption from an impact blow (as in the Charpy and `Izod techniques), may be used to rank relative toughness. The evaluation of abrasion resistance is more difiicult as methods have not been generally standardized and there are recognizably different kinds of abrasive wear. The variables of abrasive hardness, sharpness and toughness; the stress imposed on the metal by the particles of abrasive (which depends on the character of their support); seizing and galling, which are mechanisms that operate under frictional conditions even when no abrasive is present; all contribute to the complexity of Wear studies.

Nevertheless, if quantitative evaluation of alloy merit is to be achieved it is necessary to employ a well controlled test that either involves the actual conditions of service or that simulates them satisfactorily. It has been possible to develop a simulated grinding abrasion test that has been satisfactorily validated against ball mill service and this test has been important to the evolution of this invention because it permits a scientific prediction of service performance.

Thus, critical consideration of testing for wear resistance is set forth in the above-identitied publication, reporting a laboratory test procedure which has been validated by ldata obtained from actual service testing in a ball mill. The specifications for this test are shown in FIG. 1 hereof, but briey, a copper lap in the form of a ring track is positioned in a trough that can be illed with a sand and water slurry. The alloy specimen for test is set on the track under a predetermined vertical load, and is submerged in the slurry to the extent that the test abrasive (quartz sand) is crushed between the lspecimen and the lap or ring in the course of travel of the specimen around the track. The standard for comparison is run at the same time. Weight loss of the specimen provides a measure of wear resistance, reported as wet sand. abrasion factor (WSAF) for comparison to the standard which is annealed SAE 1020 steel. A low WSAF signifies a low weight loss, evidencing high abrasion resistance. The reliabiliiy of this test has been evaluated satisfactorily many times by replicate runs, which indicate an experimental error range of about plus or minus six percent.

This test does not evaluate the factor of corrosion resistance. In `some milling operations the ore, particularly if it contains suldes, may react with the water also present and form an acid and somewhat corrosive solution. Also some waters may be unusually corrosive. If corrosive `conditions are present a high level of chromium in the alloy is an asset, since this element is the mainstay of the stainless steels and many corrosion-resistant alloys.

Among the alloys used for ball and rod mill service are the very tough austenitic manganese steels, a variety of hardenable carbon and alloy steels, and several white cast irons. Among the latter are martensitic nickel-chromium and nickel-chromium-molybdenum irons of the so-called Ni-Hard alloy type. As stated above, better wear resistance is ordinarily achieved at the sacrifice of toughness, and this is true of the following liner alloys arranged in order of increasing abrasion resistance (decreasing WSAF):

Of the allo-ys listed above, increasing popularity has favored the martensitic nickel-chromium type (No. 3 above). However, this alloy is not particularly resistant to corrosion, which is a factor to consider in ball mill service, and it is typed as a brittle material. Using a 0.7 square unnotched Charpy type impact specimen for evaluation, values around 7 foot pounds are common.

Some previous experience with a high chromium iron, using a product of tensile strength and elongation as an index of area under the stress strain curve, indicated that it was about twice as tough as the martensitic Ni-Cr iron. Values up to 29 foot pounds have been observed from 0.7 inch square unnotched Charpy specimens.

The structure of martensitic nickel-chromium irons partially accounts for their brittleness, or lack of toughness. Thus, islands or masses of austenite and its transformation products are set in a matrix of brittle iron-carbide which, as the continuous phase, presents little resistance, comparatively speaking, to the propagation of cracks. Hence, the alloy is vulnerable to impact, tension and shear.

High chromium (about l2 to 25% chromium) not only results in corrosion resistance but would reverse the structural pattern of martensitic `nickel-chromium cast irons, and yield a generally tougher iron, in that such an alloy is charactreized by hard carbides set in a matrix (continuous phase) of austenite or its transformation products which may be martensite, bainite, pearlite or mixtures thereof. A matrix of this character afforded by the high chromium content ca-n be expected to be tougher than that presented by the nickel-chromium martensitic irons. Though favored by toughness and corrosion resistance, the high-chromium irons have hitherto not been sufficiently abrasion resistant to compete economically with the lower alloy irons. This has been especially true of the castings in the heavy sections needed for ball mill liners. It is an important object of this invention to so modify the high chromium irons as to achieve abrasion resistance at least equal to and generally superior to that of the lowchromiurn or nickel-chromium cast irons, resulting in the favorable balance of properties needed.

Another object of the present invention is to afford an abrasion resistant cast iron alloy in which the resistance to abrasion in thick sections clearly excels the abrasion lresistance of alloys of the Ni-Hard type.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what is now considered to be the best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be 4used and structural changes ,may be made as desired by those skilled in the art without departing from the present invention.

In the drawings:

FIG. l is a schematic-diagrammatic showing of apparatus and test conditions for a wet sand abrasion factor test; and

FIGS. 2 through 6 are curves showing characteristic features of the alloy of the present invention.

Alloys of the character investigated are sensitive to section thickness, both as cast and after a subsequent heat treatment that may be imposed to develop the metallographic structures that are considered essential to the best abrasion resistance. Heat treatment is almost always considered to be advantageous, and hence is usually included in the foundry specification for alloys of the character involved.

As an example of the sensitivity to section, the wet sand abrasion factors for castings about one inch thick of the martensitic nickel-chromium cast iron type (No. 3 above) may be as low as 0.30, but in the heavier sections (thickness above 2`1/2 inches) despite apparently adequate hardness, the abrasion factors in several commercially produced ball mill liners were found to be as follows:

TABLE 1 [Martensitic Nickcl-Chronium Cast Iron (4.5% Nickel, 1.9% Chromium,

3.2% Carb0n)] A similar sensitivity can be seen in Table 5 for alloys of this invention. It may be stated as a caution for those who apply these alloys that hardness, as such, has not been found to be a valid index of resistance to grinding abrasion.

Such a pattern can be universally expected in alloys of the type under consideration. Accordingly, and taking into account experimental error, we consider an abrasion factor (WSAF) at or below 0.60 in a heat treated thick section (5-6") to represent the `criterion of achievement in a high chromium cast iron possessing corrosion resistance, and more toughness, in comparison to a martensitic nickel-chromium alloy of the character identified above.

Table 2 lists 113 experimental compositions determined by us as affording the basis for evaluating the alloy limits of this invention. Each heat was cast in a special mold to simulate the cooling rate of a heavy section thickness, later austenitized at 2000 F. and air cooled at rates characteristic of heavy ball mill liner sections. Abrasion factors (WSAF) and hardness values were then obtained. The WSAF values are for simulated thick or heavy casting (5l/z thick). WSAF values for sections of moderate thickness (down to about 1") would be even lower.

TABLE 2.-CoMPosiTIoN HARDNESS AND ABRASION RESISTANCE OF .ALLOYED CAST IRONS FOR BALL MILL LINE R SERVICE [Heat Treatment: Air Cool from 2,000 F. (1,093 0.)]

Percent After 2,000 F.- Hcat No 2 hours-Air Cool C Mn Si Ni Cr Mo Re B HN WSAF TABLE 2.-Continued used for 4ball mill liners have WSAF values above 0.60.) [Heat Treatment: Air C001 from 2000a F (1,0930 CJ] The WSAF value of 0.60 1s about the upper edge of the band established by the plus or minus `6% experimental Aftelloof" error of the abrasion test when appliedl to the Values in 2 hours-Au Cool R Table 1 for nickel-chromium irons.

Percent Heat No.

M0 BHN WSAF It is apparent that there is no simple correlation among 4 050714789 2140505027818807020561119 1105173552233261617792808132 75274551210943 OwwNMHWMNMWHWWWBSKUSSnQUQ 384638298331033676006893696848140323305996889848039233Mm23367636473748 2.0.ZLLLL2LLL0ZLLLL0ZLL0Z01110012010L1L22ZLLLLLn/ L00 LLLL000ZLZLLLLZ0Q LLQQLQLQLLLLLLULLLLLLLLQL1 000 5 50 000 6505 5020884005227065275022 50002O35554547082755055500005050955805230 000 7820 @.3000ao5m539wmwwoo22@0%1273305756251586364449 94919789596233324574552661829298081981098 M460m/U7952 It. 1,14 7 8347732564 .603529443026214 .0927125 0201842787897658907 019065666266 934 110001000100 111100011011 0001001000000101 0001010 000100100100000010000000100000000 000 0 8 3 150 6 50 1 www www n nnhm7 W0 m u 7 917699 H IM moo Uu 0 00 00 0000 .00 0 0 010 0 00 000 0 0 5 23h/ 756204888 1322 025 19 51212 n u O Mwmpo 555 855550424 .5556 n 551MMNMM55 @56555 000100 n "1011 u 0001 .0000 0000010110 n .0000 u n 00101000100 .000000 n 547736 0 S65 5866 999i.063720570537330844239513314616 0473934 8669476 3828 785 1A 78576A mgmOGnUmO-MWS09"Img617823788846098768g1577698648555%%4=U78666w6046n18 2 Z2.22223123222223222223223222222232222220@22h/ 9 2ZZZZZZZZZZn/ Zlllllamlllllawn/ ZZRMZZZ .2. 9 1 7 1 0/3 111 M66666777Fl7777778888888888999999 11111 |0.o8838 (Mo% M0%) Thus, it is found that when a graph of calculated versus observed WSAF is made, all of the WSAF values for the The order of experimental alloys in Table 2 is established on the basis of their Wet sand abrasion factors (WSAF) and any alloy having a WSAF above 0.60 is eighty-Six selected heats used to determine the above arbitrarily rated as unacceptable. (This is not neces formula fall within a plus or minus 22% scatter band of sarily a practical limitation because some alloys widely 75 observed WSAF, which band is merely a profile of the 7 extent of error in such factors as chemical analysis, testing for WSAF (i6%), foundry limitations, and metallurgical processing, thereby confirming Formula 1 within expected experimental error.

8 varied from about 0.4-2.0% and 0.2-1.2%, respectively. Carbon, chromium, molybdenum and nickel are calculated by means of the parabola Formula No. 1 above; but Formula No. 2, hereinafter, is also valid.

Applicability of Formula 1 to foundry specifications 5 Since the apex of the parabola represents the optimum can be visualized from the parabolas of FIGS. 4 and 5 alloy when three elements are held constant and the other (calculated) which, incidentally, are validated by the is varied, it is apparent that a great variety of alloys can parabolas of FIGS. 2 and 3, confirming Formula 1. For be calculated with the broad composition limits given and FIG. 4, the assumed cast iron composition included 2.8% that many different optimum values could be selected. In carbon, 19.00% chromium and 1.00% molybdenum as a 10 general, the optimum is selected by inspection after plotbase. WSA-F` values were then calculated by Formula l ting the calculated points from the base composition seand plotted for the nickel amounts shown. FIG. 4, then, lected to bracket the apex of the parabola. However, a indicates that for such a basic cast iron, superior wear foundry ordinarily Wishes a less mathematically involved resistance is achieved with 1.45% nickel. Below 0.6% or specification. At the same time a reasonable melting range above 2.3% nickel, the chances are poor of obtaining an is needed to allow for the production variables that canabrasion factor below 0.60. not ordinarily be avoided. Obviously, the wide limits of Similarly, according to FIG. 5, acceptable performthe broad range of this invention cannot be used for this ance can be expected from an alloy analyzing about 2.8% purpose as many of the resultant alloys, as melted in the carbon, 26.0% chromium, 0.40% molybdenum, 0.32.6% foundry, would fall outside the restrictions imposed by nickel, balance substantially iron. the formula.

The heats listed in Table 2 were experimental heats To aid the foundry that is to produce the highly abrawhich served as a basis for determination of the above sion-resistant alloys that are intended, either an aim point formula that qualifies the working foundry specification. on a production range can be specified, and a number of Actual mill liners were cast from the following heat: these aim points are specified as claims herein. Where TABLE 3 25 one element is shown .as a variable it can be aimed at the Heat 507, Percent center of the range given if the optimum p roduct is de- C 3 15 sired.' On the other hand, if a more economical specifica- Mn 076 tion is desired the variable element can be aimed within Si 0'65 the low side of the range given, but not outside the ex- Cr 19:7() 30 treme himts' Mo 1 25 If ausimple six-element production range. is desired, the Ni 0'71 following production specification is provi-ded as an ex- P III 0.614 ample one Judclously Selected to Pfmde .feasolable S n 0 012 assurance that the alloy of the present invention will be 35 realized without recourse to the rather tedious matheand resulted in the following observed data (after 2000" inatical calculations of the formula: F. for six hours, air cool): C percent 2.5 TABLE 4 Mn, percent 0.4-1.7 A Hardness WsAF 40 Si, percent 0.2-1.2 Specimen Location Re BHN (Observed) Cr, percent 17,0 210 2 n 2 o 35 Ni, percent 0.3-0.9 ii (tige oss M0 Percent 101'7 iitreiraiiiriifE/Sseeccttliiiii gli) Si; gig In practice, the foundry would aim at the approximate midpoints of these ranges. Because of normal variations The following are data pertaining to full scale producin charge make-up and melting conditions the end result tion heats for ball mill liners: of each melt will inevitably vary somewhat from this aim.

TABLE 5 Properties After Heat Treatment (2,000 F.-Air Cool) H Percent Light Section Heavy Section eat C Mn Si Ni Cr Mo Surface Interior Surface Interior Rc BHN WSAF Re BHN WSAF Re BHN WSAF Re BHN WSAF The effect of section thickness and close correspondence of calculated versus observed WSAF` values can be seen from the following data, wherein the light sections were of 2%" thickness and the heavy sections of 51/2 thickness:

Manganese and silicon may be employed in the nominal amounts oif 0.5% and 0.6% respectively, but may be If all of the elements should fortuitously fall on the low side of the ranges above, the expected abrasion factor would fall well up on the parabola away from the apex and the expected abrasion factor would be above 0.60. However, it is very unlikely that al1 elements would vary in this way. Their variation is expected to be random and if one is low, then another may Well be expected to be high. Also, the extreme variations are much less likely than small departures from the aim point.

Note that under the production specification set forth immediately above, if molybdenum should fall so low as 1.0%, it can be deduced from FIG. 4 that with the aim point of 0.6% nickel a factor of 0.60 or better is still possible. On the other hand, if nickel should fall as low as 0.3% or 0.4%, from FIG. 3 it may be deduced that the aim point of 1.35% molybdenum would still produce an expected abrasion factor of 0.51`.

This practical specification takes into account the fact that nickel and molybdenum losses in melting are usually lower than those of chromium and manganese, and thus these elements are less likely to vary much from the aim point. However, if one or more elements are outside the ranges given, the melt may be arbitrarily rejected as probably inferior unless the producer wishes to apply the formula to determine acceptability. If two of the elements (in the group of carbon, chromium, molybdenum and nickel) are below the limits shown it is not considered likely that compensation by means of the other two will be great enough to avoid inferior abrasion resistance.

The elements manganese and silicon have a somewhat different status. The ranges shown have been found by ex periment to produce acceptable results and they are given here because nearly all foundries prefer to specify and monitor these. Practically, they can be held to closer limits than the ones shown; and with good melting practice and the suggested aim points of 0.5% manganese and 0.6% silicon there is little likelihood that final results will reach the extremes of the foundry specification.

It should be apparent that many other suitable foundry speciiications can be developed with the aid of the formula and the parabolic plots that it makes possible. Narrow ranges are desirable to provide the maximum likelihood of best abrasion resistance. Where a foundry knows its own melting variations, it would be advisable to use these as the basis of limits in a practical foundry specification that is centered on the apex of the parabola, where each element in turn is plotted as the variable and the other three are fixed.

The practical foundry specification should also call for heat treat-ment at 2000 F. followed by air cooling. This :was Iused as a convenient method of microstructural control to achieve the balance discovered to be effective by abrasion testing and implied by the for-mula. However, this does not preclude the use of other temperatures for heat treatment or the use of the alloy as-cast. lIf the cooling and constituent balance are right for the section thickness involved, a desirable high level of resistance to high stress grinding abrasion is attainable, provided the alloy is made :as described by the formula. If a thermal history other than the one described `here is in prospect its merits can be evaluated by the abrasion test as embodied in FIG. 1.

It should be recognized that there are other types of abrasion. The high-chromium irons generally have been found to be resistant to erosion or low-stress scratching abrasion in both service and laboratory tests. They have also performed lwell in a test against the abrasion of an Alundum grinding wheel. The laboratory erosion tests n several alloys made according to the formula described here indicated that they had from l2 to 28 times the resistance to such wear as the standard of SAE 1020 steel. One alloy was times as resistant in the as-cast state.

While the alloy featured here was developed primarily for ball and rod mill grinding service the other tests that have been made indicate that it has fwide potential usefulness as a general purpose abrasion resistant alloy. It is not intended that its use 'will be restricted to mills. Many service environments include several types of abrasion (as well as various levels of impact or other stresses) and the alloy described here can be expected to provide superior resistance to the high-stress abrasion component as well as very good resistance to the other aspects of abrasion.

In the derivation of Formfula 1, the computer was not programmed to consider the effect of manganese, and Formula l is most valid for a manganese content of about 0.5%. However, eighty-seven additional heats were made in which manganese was deliberately varied, these heats falling within the following limits, balance su'bstantially all iron Iwith silicon at a nominal 0.6% level:

C, percent 2.5-3.2 Mn, percent 0.4-2.1 Ni, percent 0.1-,l.9 Cr, percent l5.0-23.0 Mo, percent 0.4-2.4

As to these heats, the average WSAF value was abofut 0.5366. It was found that manganese conforms to and presents substantially the parabolic effect, and in fact studies reveal that a formula which takes manganese into account as a variable subscribes to the following formula where the value for WSAF does not exceed the desired value of 0.610:

Formula 2 For-mula 2 is of particular value in determining substitutions of manganese (cheaper) for molybdenum (more expensive).

Hence, while we have illustrated and described preferred embodiments of our invention, it is to be understood that these are capable of variation and modification.

We claim:

1. An abrasion resistant cast iron consisting essentially of about 2.5 to 3.4% carbon, 0.15 to 1.6% nickel, 12.5 to 25.6% chromium and 0.38 to 2.90% molybdenum, balance substantially all iron, and in which the actual percentages of carbon, chromium, nickel and molybdenum do not produce a calculated value of more than 0.60 under the formula:

2. An abrasion resistant cast iron alloy consisting essentially of about 2.8% carbon, 19% chromium, 1.3% molybdenum, 0.5% manganese, 0.61% silicon and 0.15 to 1.16% nickel, balance substantially all iron.

3. An abrasion resistant cast iron alloy consisting essentially of about 2.6% carbon, 19% chromium, 0.4% nickel, 0.5% manganese, 0.6% silicon, and 0.7-2.9% molybdenum, balance substantially all iron.

4. An abrasion resistant cast iron alloy consisting essentially of about 2.8% carbon, 19% chromium, 1.0% molybdenum, 0.5% manganese, 0.6% silicon and 0.5- 2.4% nickel, balance substantially all iron.

5. An abrasion resistant iron alloy consisting essentially of about 2.8% carbon, 26.0% chromium, 0.4% molybdenum, 0.5% manganese, 0.6% silicon, and 0.3 to 2.6% nickel, balance substantially all iron.

6. An abrasion resistant cast iron alloy consisting essentially of about 2.8% carbon, 26.0% chromium, 0.4% molybdenum and 1.5% nickel, balance substantially all 1ron.

7. An abrasion resistant cast iron alloy consisting essentially of about 2.8% carbon, 19% chromium, 0.75% nickel, and 2% molybdenum, balance substantially all iron.

8. An abrasion resistant cast iron alloy consisting essentially of about 2.8% carbon, 19% chromium, 1.0% nickel, and 1.6% molybdenum, balance substantially all iron.

9. An abrasion resistant cast iron alloy consisting essentially of about 3.1% carbon, 0.5% manganese, 0.6% silicon, 19% chromium, 0.5% nickel and 1.2% molybdenum, balance substantially all iron.

10. An abrasion resistant cast iron alloy according to claim 1 in the form of a grinding mill liner.

11. An abrasion resistant cast iron consisting essentially of about 2.5 to 3.2% carbon, 0.4 to 2.1% manganese, 0.1 to 1.9% nickel, to 23% chromium, and 0.4 to 2.4% molybdenum, balance substantially all iron, and in which the actual percentages of carbon, manganese, chromium, nickel and molybdenum do not produce 12 a calculated value of more than 0.60 under the formula:

12. An abrasion resistant cast iron alloy according to claim 11 in the form of a grinding mill liner.

References Cited UNITED STATES PATENTS 2,253,873 8/1941 Trantin 75-126 X 2,355,726 8/1944 Hardes 75-126 2,773,761 12/1956 Fuqua 75-126 FOREIGN PATENTS 162,179 9/1964 U.S.S.R.

L. DEWAYNE RUTLEDGE, Primary Examiner'.

P. WEINSTEIN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,410,682 November l2, 196

Howard S. Avery et al.

It s certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column lO, line 20, "WSAF=4.36628l.28656xC9a" should read WSAF=5.366281.28656 X C% Column l2, line 6, "-0.94016 X M096 should read O.94015 X M095 Signed and sealed this 17th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, J r.

Attesting Officer

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