US2363947A - Alloys for cutting tools - Google Patents

Description

, applied to metal cutting and working.

Patented Nov 28, 1944 UNITED STATES PATENT OFFICE 2,353,941" annoys Foa CUTTING TOOLS Anthony GQde Golyer, om Greenwich, com,

assignor to Laurence Conm, as trustee A. Janney, Stamford,

No mattin Application March 11, 194:, Serial No. more 7 Claims. (Chili-123) drawn a second time at from about 1150' F. to

strength, stability in fabrication and use at high temperatures, and exceptional efllciency when Anillustrative embodiment, herein called for brevity "Alloy A, comprises the following -constituents, in the proportions indicated, which were ascertained by analysis of the cast product:

of manganeseand silicon Thespecinc alloy A when molten is preferably cast centritugally. 'The cast forms have a hardness or about '60, to as Rockwell 0. An illustra-- 'tive method of treating the castings is as iollows; They are annealed at a temperature range or 1800' F. to 1800' 1'. "One specific procedure istto hold the castings at about l850' I"; for two .or three hours. and-allow them to coolslowly to a temperature somewhat below 1200" I". when so annealed they show approximately 46 l'tockwell C; and are in condition to be ground or It alloy A isto be used in cutting tools or-the like, a preferred hardening procedure is as fol- 1375? F. according to the ultimate degree of hardness desired. The duration of the second draw is regulated according to thesize of the individual castings, in the range of iorty-iiveminutes to two hours for the usual rangeot sizes.-

For some purposes a single draw, to thehigher temperatures, may suiilce; but when cutting tools.

are the object the multiple drawings, approximately as above described, are preferable because they improve the distinctive characteristics of v the alloy.

vFollowing theillustratlve method, the alloy A castings exhibit a combination of properties that persede. For instance, the alloy is highly responsive to thermaltreatment by which any desired degree or hardness within the Rockwell 0. range of 60 to 72 may be developed, controlled and maintained with remarkable precision. 'Such Y ally high red hardness aswhe'n cutting metal at lows'z' The castings-are preheated at about 1100' x l". for about half an hour; and then introduced to'asecond preheatingat 1500' 1". to '1550' -1 l and heldat such ,temperaturelong enough for thorough heating. They are then transferred to; a furnace in which the temperature is from 2150 I". to 2175" I'.- When the entire body of metal has reachedthe high temperature the castings are quenched in 011.. at this stage about 62 Rockwell 'C. 4 The quenched castings are cooled to about 200 F. 300 ,I" when they are ready-tor they show Multiple drawings are desirable, e pecially for the v purpose of stabilizing the ultimate hardness oi the castingsas presentlydescribed. Castingsor ormoderate size are first .101 about one hourat 900 1?. For larger pieces a'longer period is usually desirable; After this thecastings are permittedtocool' 1 w w I slowly roomtemperature. Thereafter they are 65 tint inherent stability, the ailoy has adequateequipped with cutting tips made i'rom .the new alloy; and (b) in conditionscalling tor unusutemperatures between about 1000' I and 1250'1'.

The alloy is highly'resistant to abrasive wearat temperatures up to about lm It; and to shock andcompression'.

An outstanding characteristic otalloy A when treated as described, is its extraordinary stability. already mentioned, against permanent soften,

ing or other deterioration when reheated at tema peratures= up to 1250-.F.- or 1275' 1"...even for considerable durations, as for atimelong enough for perfecting a brazed or weldedioint, Such stability makes itgpossible-toapply the alloyj in' the temperature expected to be on re-j ati g, as in a metal-cutting orsimilar operation. .When that is done the properties 'ot'the alloy are stabilized'so thatreheating to any tem--- 01 operating wefl iciency. Along withthis imporplasticity and mechanical strength in maximum ranges of working temperatures, sufilcient to supply uncommonly long tool life under severe operating conditions. Those qualities persist throughout the wide range of secondary hardnesses, between about 60 and 70 Rockwell C., any degree of which may be selectively predetermined with surprising accurary due to the reliableresponsiveness of the alloy to the designated character of thermal treatment.

I have demonstrated that the above-described properties and characteristics of alloy A will inhere effectually, though with some absolute and relative variations in degree, in alloys composed of these ingredients within the approximate ranges stated as follows: tungsten 12.00% to 20.00%; molybdenum 1.00% to 6.00%; cobalt 20.00% to 35%; boron 0.45% to 0.95%; carbon 0.35% to 0.85%; and the remainder principally iron, in a percentage exceeding that of the peroentage of cobalt in any specific composition? The respective properties and characteristics of alloys formed within these ranges, corresponding to those of alloy A, can be developed, controlled Ind maintained 'by thermal treatment of the character I have disclosed.

It will be noted that alloy A contains a small percentage of vanadium. Vanadium, however, is not an essential component, though small amounts of it may have some beneficial influence in limitingv the grain-size of'constltuents of the alloy, especially after thermal treatment. Though the vanadium appearsto have little if any direct effect upon the novel major properties of the alloy, it is feasible to add it in the range of approximately 0.20% to 3.00% as an auxiliary alloy ele-- ,ment. 7 Small amounts of manganese and silicon may be present as incident to manufacture, for their usual purposes of aidingdeoxidation during the production of the alloy, and they are commonly present in scrap or ferro alloys. 'The ntent of manganese and silicon should not exceed about 0.70% and 0.90%, respectively, and lt is considered advisable to limit the manganese to about 0.30% and the silicon to about 0.50%. When phosphorus and sulphur are present as incidental impurities, they should be limited to about 0.030% phosphorus and 0.010% sulphur.

The valuable inherent properties that characterize the new alloy result from the novel composition of elements, within the respective ratios specified herein. I intend, therefore, to restrict v the amounts of any other elements which may be present, from any cause, to percentages which are substantially inefiectual on the valuable properties, as well as onthe chemical and physical reactions which take place within the alloy at difquite small amounts, is present in the new alloy its mainly important properties are adversely affected. As an illustration, when 1% or less of 1 chromium is present the responsiveness of' the al-' loy to heat treatment is altered to such an extent that a precise degree of hardness can not be developed, and the alloy can not be adequately stabilized against subsequent variation of hardness when heated to temperatures from 1,000

F. to 1.300 F. As a further illustration, when the amount of chromium present is in the range from 2% to the degree of red hardness is materially reduced and the general metal cutting efficiency is greatly inferior to that of the alloy which is substantially free from chromium. The adverse effects of chromium are shown by the comparative figures for alloys A and B in Table II. Therefore, the new alloy should be substantially free from chromium. I

. To exemplify the distinctiveness of the new al- -loy and technique, the following discussion and tables are presented, based upon comtive demonstrations of three alloys, that were composed as follows:

A. The alloy A already identified above. .B. A test alloy of like composition with the addition of 4.00% chromium.

C. A specimen of commercial standard 19-4-2 high speed steel with 12.00% cobalt.

The percentages given were ascertained by chemical analysis of the three alloys.

Table I Per cent Tungsten quenching according to the method disclosed.

above. Specimens of steel C were quenched in oil (125 F.) from 2425",F.,'as recommended by the producer for development of maximum hardness of this steel. Separate specimens of the respective sampleswere used for each or a series ofdrawing temperaettures. All specimens were carefully ground to remove any decarburized material before hardness determinations.

After drawing alloys A and B and steel C for one hour, except as indicated below,the Rockwell C scale hardness valueswere ascertained as follows: Table II 'Tempera ture A B C Deep scaling and demrburization required heavy grinding provide solid metal; highest reading is given.

Several specimens of each 0! the A, B and C compositions, were drawn respectively to, average hardness of 64 to 65 Rockwell C, and were brazed with silver solder to shanks x 1%" x 'l",

' followed in all cases. The brazing temperature was between 1300 Hand 1350 F. All of theB and C tips had their hardness. decreased, by the v heat, from 3 to 5 Rockwell C points. The tips of 76 s esssseeessea and 1%" 112 /2" x 14". Standard practice was.

alloy A showed no deterioration in hardness or otherwise. Equivalent'results were obtained mm like specimens whenthey were torch-brazed by a commercial tool-maker.

.Four specimens of alloys Aand B and s'teel C -were quenched, as indicated above, and, after cooling to approximately250 F., were drawn at 800 F. for one hour and allowedto cool in still air to room temperature. The. three sets of specimens were subsequently drawn and cooled irom' each of the successive ten'iperatures indicated in Table II, to and includingI135!) F. Hardness determinations after each drawing and cooling did not show any measurable diilerence from the figures in Table II, exceptin the case of steel C, the specimensof which had an average Rockwell I C hardness of 56, 52 and 48 after. drawing at 125021300" and 1350 F., respectively.

It will be apparent from Table II that; (oi

Q on appreciably higher hardness is developed in alloy A- than'in either of theother materials:-

(b) that the upper limit of maximumhardness for alloy B and steel 0 is. 1-100 F., while the maximum hardnessoi alloy A persists from 1100 F. to 1200 F., which is considered to be the upper red-hardness temperature range to whichmetal cutting-tools are subjected under more orless severe operating conditions;' (0' when alloy B and steel C are heated for one hour at 1150 new alloy, treated, as already disclosed, through V the first drawing step, may then be'iheated to progressively increased temperatures'in the second drawing, and the Rockwell C hardness at. each such temperature may be observed. Thereafter, it the same specific alloy is drawn to any said temperature, it will have inpractically ade- (mate and dependable approximation the same corresponding hardness under equivalent condi-v tions as in the specimens ilrst drawn. That is, as exemplified in Table II. the tested samples of alloy A acquired hardness of .65 points at 1300 F2; and it is safely predictable-that in all instances, under like conditions and preliminary treatment, any specimen of alloy A can be given the same hardnessiwithin permissible tolersl ces) by drawing it'to the same temperature.

, And when the drawing treatment has been carried to a given temperature to produce a cor-- responding predetermined hardness, the alloy will retain that hardness with uniquestability when reheated to any temperature at or below the maximum drawing temperature used. Thus, this invention'provides a novel alloy of peculiar responsiveness to thermal treatment, and an ac- ,curately 'regu'lable character of thermal technique, such that any example of such alloy can be hardened toany selected degree within an F. the hardness of each is permanently reduced to the degreeat which a tool will cut steel with eiilciency under favorable conditions,

whereas, the hardness of alloy A is notlowered to 62 Rockwell 0 until after the material has been heated at 1350 F. for onehoui.

This comparison demonstrates a substantial and important distinctiveness in the chemical and physical reactions which occur as a result of drawing alloy A as compared with those which take place-in the other two compositions when drawn within the same temperature range, 1. e.,,

800 F. to 1350- F. It is especially noteworthy that alloy A is conspicuously more resistant to appreciable and rapid loss of hardness at temperatures materially in excess oi" that at which maximum secondary hardness is attained.

I have found that when any desired degree of hardness (within feasible ranges above indicated) is developed in the present alloy by drawing to 'temperatures at and higherthan that required for development 01' maximum secondary hard- 1 ness, the alloy'is remarkably stabilized against measurable variaticnot such developed hardness through diffusion or atomic rearrangement whensubsequently reheated, in use or from treatment,

, to any temperature up to that at which the desired degreeoi hardness was developed.

i I have also found that the above-described drawing procedure produces an unusually high degree oi red-hardness, i. e., when a desired degree'of hardness has been attained in the manner Just illustrated, the present all'oy retains an exand that such diiierentials tully account for the exceptionally wide range, and then reheated to substantially the maximum drawingtemperature without material loss of red-hardness, or hardness at normal temperatures, and at "the same itfthe alloy is heated again for any purpose at,

any temperature up to' about 1356 F. Especially in the respects noted in this paragraph, this in vention appears to be entitled to be rated pioneer contribution to the art.

Some responses to thermal treatment manitested by alloys'oi this invention may seem analosous to similar responses that occur inhigh speed steel. My observation is, however, that the intermediate and resultant chemical compositions and physical structures of the new ,alloys are importantly diiierent from those of high speedsteel or other alloys of that general type.

unique stability against-variation oi pre-developed hardness throughdiii'usion or atomic rearrangement at temperatures in excess of 1100' ll, incontrast tothe' marked chemical and physiceptionally high percentage of such hardness at temperatures generated in .a tool during metal cutting operations.

As indicated in the first two columns ot'rabie II, each temperature in the drawing range .produced a corresponding high degree oi hardness in alloy A. -Such respective degrees of hardness may be reproduced selectively with reliable precision in the practice of this invention, sons to 'predetermine"a desired hardness ,i'or any of my newcompositions, within the percentage ranges above defined, embodying the general characteristicsot alloy A. I

Specimens of a chosen specific form of the . iting tools. The expression high degree of redcal changes which occur above that temperature in heretofore known alloys of the high speed type. In the case of the present alloy the stability at and above 1100* 1". results in aremarkably high e ree oi red-hardness in metal cuth'ardness" used herein and'in the appended claims is to be understood as meaning that the alloy.

-' retains a high percentage of pie-developed hardness when temperatures up to approximately 1250' 1". are generated in theworking portion of a tool, and thatthe actual hardness in suchportion or the alloy issuiilcientlyhizh topermit 01 efllcient' periods.

metal cutting for protracted My further observation is that boron or boron .75 compoundsare atalltimesineachmador.

constituent of the new alloys and I believe that to be a major factor contributing to the superior properties of the alloys.

The expression "the remainder principally iron when usedin the appended claims is to be understood as meaning that, besides the recited alloy elements, the balance of the alloy is iron 'whiclrmay. contain minor and not inment of a predetermined hardness between 62 and 70 Rockwell C, a relatively high degree of red hardness, and stability against permanent variation of predeveloped hardness through-diffusion or atomic rearrangement when subsequently heated to temperatures up to approximately 1275 F. for a period of time necessary to efiect emcient brazing or other fabrication.

2-. An alloy .steel comprising the components named in claim 1 within the respective ranges stated, which is characterized by responsiveness to quench hardening and by the concurrent development, during thermal treatment, of inherent properties of high red hardness and stability against permanent material variation of predeveloped hardness when heated to a temperature substantially equivalent to the drawing temperature at which the ore-developed hard- I ness was developed.

4. A heat-treated alloy steel for cutting-tools 3. An alloy steel comprising the components hardening and by the development of a relatively high degree or inherent red hardness through thermal treatment.

and the like comprising the components named in claim 1, withinthe respective ranges stated,

characterized by stability against permanent material variation of predeveloped hardness when intermittently heated and cooled, in service, within a range 'of temperatures up to the maximum drawing temperature at which the pre-developed hardness was developed.

5. An alloy comprising the following components in approximately the percentages stated: tungsten 16.00%, molybdenum 4.00%, vanadium 1.00%, cobalt 30.00%, carbon 0.70%, boron 0.75%, and the remainder principally iron, characterized by responsiveness to quench hardening and by the concurrent development, during heat treatment, of inherent properties of high red hardness and stability against permanent material variation of pre-developed hardness when reheated to a temperature approximately the maximum drawing temperature at which the hardness was developed.

6. An alloy' steel comprising the components named in claim 5 in approximately the percentages stated, characterized by responsiveness to thermal treatment for the concurrent development of inherent properties of high red hardness and stability against permanent material varl ation. of pre-developed hardness when heated,

in service, to temperatures within the range 800 mow G. or: GOLYER.