US2773761A - Ferrous chrome alloy - Google Patents

Description

Dec. l, 1955 .1. H. FUQUA x-:T AI. 2,773,761

FERRoUs CHROME ALLOY Filed Jan. 8, 1954 IN V EN TORS with aV steel casting.

This invention relates to iron alloys and particularly to ferrous chrome materials especially adapted for castings.

The material of our present invention is a metal alloy of the ferrous chrome class and while from an analysis of its constituents it resembles iron in some respects, likewise it approaches somewhat steel. It is our conclusion that lthe particular features and analysis of our substance places the same in a category somewhere between an iron and steel, considered from the standpoint of carbon content.

Basically our improved product comprises the combination of several ingredients, chief of which are carbon, chrome, molybdenum, silicon, manganese and iron comv bined in a designated range of proportions, as will be set forth hereinafter. Our new alloy is particularly adapted for use in castings. Generally speaking, it has been our experience that this material in its as cast condition, displays no unexpected properties, but that following special heat treating and quenching, outstanding hardness and resistance to wear are experienced. Further, it is interesting to note that the material displays a marked ability to work harden which suggests its adaptation for particular classes of cast articles which experience high abrasive wear. For example, present liners and paddles for pugmills require frequent replacement because of their inability to resist the extreme abrasive wear attending their operation. Our material when used in such 400% to 500% over previous materials used for such purposes However,fsince this material is not classified las a steel, it'does not display particularly outstanding resistance to shock or impact as is normally experienced arms, etc. which are not subject to more than average wear conditions.

The main object of our invention is to provide a new and improved ferrous-chrome alloy having outstanding resistance to abrasive wear.

Another object of our invention is to provide a new i and improved ferrous-chrome alloy which is capable of being work hardened and is particularly useful for incireasing'the life of articles used in circumstances creating high abrasive wear. A still further vobject of our invention is to provide a f new and improved ferrous-chrome alloy particularly suit-- able for castings requiring high wear resistance', as for example, for such objects .as liners, paddles, mixing arms, etc. for various types of mixers or grinding equipment.

The above and further objects and 4features of our invention will be more fully set forth in the descriptive Vmaterials hereinafter and its properties and features will vbe more fully understand with reference to the accompanying micro-structure showings as set forth in the accompanying drawings.

In the drawings: Figure 1 isaphoto-micrographic showing enlarged 50Optimes`illustrating the as cast structure of our alloy wherein the same contains a matrix of unresolved pearlite;

Figure 2 is a photo-micrographic showing, similar to.

United States Patent() 2,773,761 Patented Dec. 11, 1956 2 Figure 1, displaying the eiects of a specified ansteniz'ation treatment on the pearlitic matrix shown in the structure of Figure 1 to produce a gamma phase matrix;

Figure 3 is a photo-micrographic showing, similar to Figure '2, of our austenized alloy enlarged 100 times after a preferential etchant has been employed to illustrate the carbides of the gammannat'rix therein;

Figure 4 is a showing magnified 1000 times of a casting made from our material to illustrate the effect of abrasion on the wear surface thereof; and

Figure 5 is another enlarged showing of our alloy magnified 1800 times showing the wear resistant surface of the casting of Figure 4, and the work hardening transformations which take place therein.

Turning now to the particulars of our improved ferrous-chrome alloy we prefer that the contents thereof, other than iron, be proportioned substantially as follows:

Carbon 1.8% to 2.4% Chrome 14.0% to 17.0% Molybdenum 1.5% to 2.0% Silicon 1.0% maximum {Manganese 1.25% maximum Scale C.

instances has given increases in wearability as great as It is therefore our finding that it is best used for liners in various types of mixers or grinding equipment and for such items as paddles, mixing impact stress, but are presently short-lived from extreme -v ing a marked increase over its as cast hardness.

The alloy of this material, cast into useful objects of the nature hereinabove indicated, produces a microstructure similar to that illustrated in the photo-micrographic showing of Figure 1. From that gure it will be recognized that the cast material .contains a matrix 10 which is indicated by the darkened areas and comprises unresolved pearlite containing complex carbides of iron, chromium and molybdenum. This pearlitic matrix is found tohave an average hardness of 39.8 Rockwell In the particular sample of Figure 1, the magnification is some 500 times normal with the etching being produced by a 2% Nital etch solution.V

With regard to the structure and properties of our chrome-ferrous alloy, the same apparently displays no .surpassing property or aptitude toward wear resistance in its as cast state. As a result we have found it necessary to heat treat the same by subjecting the as cast structure of Figure l to temperatures in the neighborhood of 2020 F. followed by an air quench. This heat treatment austenizes the pearlitic matrix thereof shown in Figure 1 and transforms the same to gamma phase (retained austenite) as illustrated particularly in Figure 2 of the drawing at 11. It is found that the hardness of the matrix after the austenization treatment is altered to an approximately 57 Rockwell C, thereby demonstrat- The photo-micrographic showing of Figure 2 is an example of the austenized structure magnified 500 times and treated with a 2% Nital etch.

With regard to the gamma phase matrix of Figure 2, reference also should be had to Figure 3 of the drawings which shows the austenized structure magnified 100 times after treatment with Aqua Regia Glycerol etch to give v preferential showing of the complex carbides located in the gamma matrix, as at 12.

It is believed that the presence of these carbides, which have undergone a coalescence in the austenization phase to take on a generally spherical form, explains the abnormally highhardness obtained from the austenitic gamma phase matrix.

of the multipley carbides .present in the matrix coupled `with the stress and strain elfects experienced f working the surface pf lthe material. 'observation trated at 'or near the surface, as shown.

is borne out by examinationof theHmicro-struture of this material, which shows that the alloy contains `a ylarge percent of iron-chromium carbides of varying complexity and forms. YSince these carbides are brittle andhave full hardness by nature, the same are substantially unaffected by cold working. i i

With regard to the cold work eect, reference should now be had to Figure 4 of the drawings yfor a showing of the work hardened surface of a casting made of our improved alloy,magnied 1000ftimes and treated with an Aqua Regia Glycerol etch. It will be noted that the complex carbides 12 have "not been affected'by abrasion and that the depth of.. penetration for the abrasive effect is evidenced substantially by the darkened matrix. 13. Ithas beenestablished that the depth-of; this penetration approximates :0005 inch, as outlined by broken' line 14. This shallow surface effect is: somewhat surprising, but nds an understandable explanation as set forth-'hereinaften Y* ,Y l

The most common cause lof work hardening effect fis found in distortionv of the structure which results'in' a concentration of various complex-stresses. whichimpart increased hardness to the material. Since the hard carbides are? sof prevalent in our material andl existnear'the surface, this-distortion eect is also necessarily-concen- Aeseconda'ry veiect. causing the cold work phenomena is found in the transfer'lrnationA of any unstable fconstitlrents'iwhich imay bei present. Thus, in ourpresent material, 'ja'ny ga'im'na constituent which is prelsentinj the matrix-willtian's'form funderleold worln'ng stresses. IIoweve'r,VI this'itransforma- Vtion'effecfwhich we term fphasie'alterationmis more or less a'submicroscopic occurrence andisnot'v readily're- 'solved lby metallographic examination. vvConsequently, the resultant hardness factor caused by this phenomenon may `be said' to be proportional to the amount of cold 'work to which thematerial is subjected. From "the 'above 'it'may be concluded' that since Vthefeifect'of 'the cold working is concentrated near or at the pointof contactfthe hardness *effect is likewise necessarily re- *strictedffto a'supereial" depth as shown `in Figurerl. vIt pis' our 'belief thatin our particular material` a 'triple effect of workfstres'ses, hardcarbides rand transformationl "or 'A phase alteration 'combine'to yfurnish the extremely hat' and wear 'resistant vproperties -exliierien'ced .y Frolm Figure 5,j which is a showingmagnified 1800 l times of thecold worked surface of Figure 4 etched with qua Regia Glycerol', it willl be seen thatour above-conclusions are substantiated. Particularly, it hwill be 'noted thatthe leect 'of"abrasion^on the wear-surface appears to Ibe presentbetween' thema'ssive carbides 1 2. lFurther,

,From our above conclusionsand working'fxperince f lowing vare examples of' typical "heatsfor'=this. new

""material:

` Heat CarbonV Manga- Silicon `Chromel Molybnese '"de'num 2.25 1.10 .iis 1.94 .2.21- Y 1.00 '1; 44. .;1. ss

"is substantially lower 'than that `foun'din normal"iron analyses and likewise it is important that the silicon and manganese content be kept low as specified to obtain the desired results. As mentioned,.it has been our experience that the micro-structure of vthisl-material.demonstrates a -large percentageofthe iron, chromium and molybdenum 'caibides invaried complexity after austen'ization., Our

'examination into this material-has also shownthatathere alloy. "Thereford'even' though the transf'urination"due` to cold working is superii'ci'al the Asame is, nonetheless, very definite and benecial.

While we'have herein'shown and. described Vthe "makeup and components of 'ourfimproved ,ferrousichrome alloy,--as re'elatedvto'av preferred range of, ingredients and a certain type of austenizing heat. treatment, it willtbe understood. and appreciated that. changes, vmodilicatons and substitutions of equivalents `vmay 'bel employed/therein without necessarilydeparting from the'spirit fand'scope vof our teachings. Asr a consequence it' is not our;inten tion that we be limited to the'particular 'form' and specications for our` alloy aspresented herein exceptjas may appear in the Vfollowing claims.

We claim: Y

1. A ferrousTchrome alloy for castings, characterized by an ability to work harden to Vsubstantially 65 VRockwell C, after austenization, consisting essentially of, carbon the proportion Vof. 118%' to` 2.4%, "chromium in'i'the .proportion of 15.0% to.`l7.0%,` molybdenum inthe proportion of 1.5% to 2.0%,"silicon at a maximumv `of"'1.0%, I andm-anganese at a maximum of 1.25%; Y

2.'.A ferrous chrome'alloyfor casting purposesfcliar- 1 acterized, as cast, by arvmatrixiofunresolved pearlite having a Rockwell lC. hardness .of 'substantially 45":and lcontainingV complex carbides ofL iron, chromium^and, .molybdenum the alloy Abeing austenize'dbyV air quenching from substantially 2020"- F. after which .the same demoni'strates anA ability to work-harden'to substantiallyiGSl Rockwelll C, comprising; l1.8% to 2.4% carbon, 15%to gisting .essentially .of a

Manganese 1 n A'do 1:.00-A Silicon 0.44 Chromium do 176.4 v flVIolybde'n'u`m Y "de 2.11.88

'ti'ongbalance/tolmakeupIOO. n

l -:Rllei-encesCiteinthIeIhiSQPZtmt.

l I l2.064.155' Fahrenwald Dec/:515111936 2,199,096 1.Berglund... Apn` 30, '1'940 2,268,426 Schlumpf et al. "*Dec." 30,"1941 2,355,726 Harder et al. ..--Augfl5f1944 j FOREIGNV 'PATENTS A 5315.502

3. `A2 ferrous chrome,v alloy fonic'stingsfcharacteized bypan i' vability v:to work-harden [after ansteht'.ation,fA cony percent,...v -2.2.1

However, fthe `triple Vveif'ec't of

Claims (1)

1. 2. A FERROUS CHROME ALLOY FOR CASTING PURPOSES CHARACTERIZED, AS CAST, BY A MATRIX OF UNRESOLVED PEARLITE HAVING A ROCKWELL C HARDNESS OF SUBSTANTIALLY 45 AND CONTAINING COMPLEX CARBIDES OF IRON, CHROMIUM AND MOLYBEDNUM, THE ALLOY BEING AUSTENIZED BY AIR QUENCHING FROM SUBSTANTIALLY 2020* F. AFTER WHICH THE SAME DEMON-

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