,' A‘O .‘1 ;, J N; 2:"... . ' ' , ‘5. '-.4 . ‘ _-. b . . 0" ‘1‘35: ’3’?) A‘- W';7"'. ' _—-- _ W huw-t p _‘LL’-- ._..-..._._ IRE HOT QDENCHING OP?MOLYBDENUM§TUNGSTEN'HIGH SPEED STEEL by Kenneth James Trigger A Thesis Submitted to the Graduate School of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements 'for the degree of MECHANICAL mum Department of Mechanical Engineering .19u3 'E'Hrlzifi 1. 2. 3. 1+ 5. 6. 7. 8. TABLE 01 GOHIENTS Introduction.......................... Topics for Investigation.............. Scape and.Purpose..................... Procedure............................. Calculations, Data. and.Resu1ts....... Discussion............................ conclnsj-onBOOOOOOOOO0.0...COOOOOOOOOOO Bibliography....ooooou.....o........o Page 10 11 17 33 5o 51 ACKNOWLEDGMENT The author herewith expresses his sincere appreciation for the kindly advice. criticism. and use of equipment contributed by Professor D. B. Seely. Department of Theoretical and Applied Mechanics; Professor 0. H. Casberg, Department of’Mechanical Engineering; and.Professor H. L. Walker, Department of Mining and Metallurgical Engineering - all of the University of Illinois. Ihanks is due Mr. G. G. Greanias. a senior Mechanical Engineering student. for the preparation of specimens and assistance in testing and to the Columbia Tool Steel Company, Chicago Heights, Illinois, for the tool steel used and its chemical analysis. INTBDDUCTION History and Development High Speed or "Rapid” Steels belong to that class of high alloy tool steels which have the particular property of retaining a relatively high hardness even though operating at elevated temper- ature. This characteristic is referred to as “hot hardness' and it is a necessity in tools that function at the high surface speeds used in modern metal cutting practice. The original high speed type of steel was made quite accidently by Robert F. Mushet in Sheffield. England. in 1868. After some experimenting. it was marketed as "R. Mushet's Special Steel.“ the chemistry of which was approximately: Carbon 2.0% Tungsten 5.0 Manganese 2.5 Silicon 1-1/3 Chromium 0.5 Further experiments resulted in a lowering of the carbon and silicon and in replacing most of the manganese with chromium. Mushet's steel could be hardened without the usual quench and was, therefore, called a 'selfbhardening' steel. In 189M Frederick W. Taylor began experimenting with.Mushet's and other self-hardening tool steels in an effort to improve the cutting efficiency of his tools and thereby promote his program of shcp efficiency and scientific shop management. Taylor and his associates, notably'Mannsel White. set about improving upon the then existing selfahardening steels. .After much experimenting and some failures Taylor and White in 1898 more or less stumbled.upon the "high heat'I treatment necessary to develop the maximum cutting ability in their high speed steel. To quote from (1.p-2h)‘ On The Art of Cutting Metals. paragraph 110: llThus. the discovery that phenomenal results could be obtained by heating tools close to the melting point, which was so completely revolutionary and directly the opposite of all previous heat treatment of tools. was the indirect result of an accurate scientific effort to investigate as to which brand of tool steel was, on the whole. the best to adopt as a shop standard; neither Mr. White nor the writer having the slight- est idea that overheating beyond the bright cherry red would do anything except injure the tool more and more the higher it was heated.“ In 1906 Taylor and flhite discovered "that by adding a small quantity of vanadium to tool steel to be used for making modern high chromium-tungsten tools heated to near the melting point, the hardness and endurance of tools, as well as their cutting speeds, are materially (10P011) improved.' The analysis of Taylor's most satisfactory high speed steel (determined by exhaustive and. no doubt, exhausting experimentation) was approximately: Carbon 0.7% Tungsten 18.0 Chromium 5.5 Manganese 0.1 vanadium 0.3 Marked differences between Taylor's high speed steel and Mushet's special steel are clearly evident. The carbon content was reduced markedly while tungsten and chromium were increased and manganese was all but eliminated. (The soundness of the Taylor-White research is borne out by the fact that during the following 25 years over 3/M of ‘Number of the reference in Bibliography. the high speed steel manufactured was. except for vanadium. nearly the same analysis as that recommended by Taylor.) The economic importance of high speed steel lured many tool steel manufacturers into the field. With competing companies conducting hundreds of experiments the development and treatment of high speed steel advanced rapidly. The chemical composition of modern high speed steels is the result of the years of experience in its manufacture. The alloying elements used and typical quantities are as follows: Tungsten (W) - 18% combined the best advantages of wearing properties. cutting ability, and toughness. Chromium (Cr) - h$ gives best balance between.toughness and hardening abilj-We vanadium (V) - l to 2% definitely increases cutting efficiency and improved toughness. Molybdenum (so) - 5 to 8% with 1% to 6% v has essentially the same effect as 18% w. Cobalt (Co) - h to 12% in the cobalt high speed steels. Cobalt serves to increase the red hardness and also the brittleness. Cobalt high speed steels exhibit undesirable surface decarburisation.unless protected. Manganese (Mn) - Not over approximately 0.3% to avoid grain coarsening at the high quenching temperature. Silicon (Si) - 0.3% or less is satisfactory. Prior to the present war the great number of commercial high speed steels were usually grouped into three general classifications: l) Tungsten high speed steels which are applicable to all classes of cutting tools to be used on most all materials. This type accounted for over 15% of the high speed steel used in lgho. a) 18% v; a; Cr; 1% v. ) Commonly known as ls.u-l. b) 18% w; us Or; 2% v. ) ls-h-2. and c) lufi W; h% Cr; 2% V. ) lh-h-z. respectively. 2) Cobalt type which is essentially of the tungsten type but with h to 12% Cobalt added. mess steels are exceptionally well suited to cutting hard, gritty. or scaly metals, such as sand castings,heat treated steels. and cast iron. 3) Molybdenum type usually containing 8% Mo. with 1% W in addition to the usual chromium, vanadium, and carbon. The hardness and tough- ness of this type compare favorably with the tungsten type. In the years preceding 19%. the high speed steel industry annually consumed about 3/1!» of the tungsten used in the United States. With the advent of hostilities in the Far East. one of our principal sources of imported tungsten was cut off. In order to conserve the stock of tungsten and make domestic and hemispherical supplies meet the demand. it became imperative that we introduce new or alternate high speed steels or use those of an existing type which required less tungsten and more domestically produced molybdenum. (Since as the IPB has recently stated. the 0.8. produces 85% of the world's output of molybdenum.)(2) In June 1941. the Office of Production Management issued General Preference M-lh to conserve the supply and direct the distribution and use of tungsten in high speed steel. According to the provisions of Order M-lh. users of high speed steel were required to use as much molybdenum high speed steel. by weight. as the tungsten type. Incidentally, the government now (April 198) requires that three times as much molybdenum steel be used as the high-tungsten type. It is, therefore, evident that molybdenum high speed steels are of vast current importance and a brief resume of their development is here- with presented. Taylor. White. and others.during their early researches. found that molybdenum was more effective than tungsten in its alloying effect. Indeed. around 1900 it was thought that molybdenum would become the major alloying element in high speed steel. There was. however. one serious objection to molybdenum steels—notably. the proneness to de- carburization at elevated temperatures and resultant soft spots on the hardened tool. In 1917 an attempt to utilise molybdenum was made because of the scarcity of tungsten. However. the molybdenum high speed steels produced were not seriously regarded by industry. and nothing more was done until 1930 when the Ordnance Department of the 0.8. Arm carried out investigations at Watertown Arsenal and concluded that molybdenum could replace tungsten in high speed steels if the necessity arose. In 1933 a patent was issued to J. V. Emmons and assigned to Cleveland Twist Drill Comparw on a molybdenum tungsten high speed steel containing 8% Mo.and 1% W. later known to the industry as 'Momax.‘ Decarhurization was still a problem. however. and during the period from 1933 to 1938. much research was conducted in an attempt to overcome decarburization. Boron additions were tried but brought on rolling difficulties. Boron and Cobalt used together proved satisfactory. During this period protective atmosphere furnaces and salt baths for the hardening of high speed steel were developed and did much to alleviate the decarburization problem. A recently developed high speed steel. the one used in this investigation. contains about 5% Mo. 5% w, and 1% v. in addition to the usual chromium. The decarburization tendency of this steel is not serious. being no more pronounced than in the high tungsten type. Heat Treatingjfactice for High Speed Steel Temperature ranges given are general - the actual temperature used depends upon the chemistry of the steel. the sire and shape of the section. and the use to which the tool is to be put. 1. 2. 3. Preheat Because of the low thermal conductivity of high speed steel. pre- heating is desirable to prevent undue distortion or even cracking. Also. preheating decreases the time necessary at the high hardening temperature and thereby reduces grain coarsening and brittleness. During preheating simple carbides are dissolved in the austenitic matrix. The usual preheat range is 1160 to 1600 P. In large or irregular sections. a double preheat at 1100 to 1250 1' followed by 1160-1600 I is advantageous. High Heat Imediately after preheating. the tool is transferred to the high heat furnace and brought rapidly to temperature. The object is to hold the tool for sufficient time to get proper solution of the complex carbides. without excessive grain coarsening or surface damage. Under proper conditions. most of the complex carbides are dissolved in the austenite. only the larger(or primary) carbides being undissolved. The usual temperature range is 2150 to 21150 I. and the time at temperature is measured in minutes and seconds. Qgenchipg Since the austenite contains large amounts of alloy carbides it is quite sluggish. and the tool may be hardened by quenching in oil. molten baths at 1000-1150 I. or in air if the section is small. The most common quenching medium has been. and still is. oil. The practice of quenching in molten baths (lead at 1150 I) was (1) advocated.by Taylor and White in 1906. but such hot quenching procedure has come into general use only recently. Hot quenching is important for several reasons among which are: (a) Long tools such as breaches. drills. punches. etc. may be straightened as they cool in air from 11003 to hOO I. thus reducing the necessary grinding: (b) The stresses due to quenching are less severe than during oil hardening; and (c) Less cleaning is necessary than in oil hardening. Regardless of the quenching medium used. high speed steel should cool to about 100 P‘before tempering. Te eri Quenched high speed steels contain considerable amounts of retained austenite along with the high alloy martensite and undissolved complex carbides. under such conditions rather severe stresses are present and the toughness is low. In order to develop maximum cutting efficiency and improved toughness the quenched high speed steels are tempered at 1000 to 1100 I for 2 to h hours. The tempering process has been thoroughly investigated by Cohen and Ibhs3)(83ho used X-ray. dilate-stric and electrical tests. According to them. tempering normally proceeds as follows: (a) .As the quenched specimen is reheated up to about 600 F. the martensite is tempered and softens somewhat. (b) From 600 1 to 1100: fine alloy carbides precipitate from the retained austenite so that: (c) This austenite will transform to martensite on subsequent cooling to room temperature. -8- The effect of factors (b) and (c) is to increase the hardness whereas (a) causes some softening. .As a result. the tempered hardp ness of a.properly quenched high speed steel is usually higher than the hardness ”as quenched.“ This phenomena is known.as "secondary hardening.‘I Since the austenite retained in the quench is not transformed until the cooling phase of the tempering operation. it is evident that quenched tools given a single temper may still have considerable "internal' stress due to the untempered martensite present (formed from the retained austenite). Therefore. multiple tempering is commonly practiced and is desirable from the standpoint of tool life and toughness. l. 2. 3. TOPICS TOR IIIISTIQATIOI The literature on the treatment of high speed steel contains very little information concerning the effect of holding time at the quenching temperature when hot quenching practice is used. It is felt that such information would be helpful in determining the most suitable hot quenching procedure. A comparison of hot quenching with oil quenching may shed light on the most satisfactory practice to be used for specific applications. An.investigation of hot quenching would have enhanced value if the steel used were one available for wide application at the present time. Such a steel. the author believes. is the recently developed molybdenum tungsten type. A comparison of the cutting efficiency of this new tool steel with the well known high tungsten (lS—h—l) type would.be of value. (1) (2) - 1o - SCOT! AIDIPUIPOSI The purpose of this investigation is: to determine a. effect of time in the hot quench upon the physical properties of hardened molybdenum-tungsten high speed steel and to compare hot quenching with oil quenching. to evaluate hot quenching and oil quenching by means of lathe breakdown tests on hardened tool bits. _ 11 - m Physical Test Selected In arriving at the proper type of test to evaluate the different heat treatments tension and impact tests were discarded as being subject to extreme variations due to uncontrollable factors. Torsion impact has been proposed as a means of measuring the toughness of tool steels. but equipment was not available for such tests.. The test chosen was the transverse bending of hardened.beam specimens. The transverse test is well adapted to duplication of test conditions and gives an index of toughness as well as the trans- verse bending strength and maximum deflection under load. ~Preparation and Heat Treatment of Test Beams The test pieces employed were of the molybdenum-tungsten type high speed steel of the fellowing chemical analysis: Carbon 0.82% Manganese 0.30% silicon 0.33% Chromium n.01% Tungsten 5.65% Molybdenum h.99% Vanadium 1.56% Samples approximately “Q inches long were cut from commercial § inch square annealed stock. These specimens were then.shaped equally on all sides to 0.“ inch square and surface ground to 0.385 inch square pre- paratory to heat treatment. The heat treating procedure follows: Preheat - Held 20 minutes at 1025‘1 I and then 15 minutes at 1500 I. Higp Hea - following the double preheat the specimens were transferred to an electric furnace of the "globar'l type. equipped with a carbonp aceous block for protective atmosphere. operating at 2230 1 5 I and held for h minutes. -12.. QEgnch - rive different methods of cooling to room temperature were used: 1) Quench in still all at 70 F. 2) Quench in lead at 1025 F for 2 minutes; cool in still air. 3) Quench in lead at 1025 r for 2 minutes; hold at 1025 r for 15 minutes; cool in the "holding'I furnace. M) d 5) Quench in lead at 1025 F for 2 minutes. hold at 1025 F for l and 2 hours respectively; cool in the "holding“ furnace. 'Tgmpgg.- When cool any adhering lead was removed from the quenched specimens. and they were subjected to a double tempering operation for the purpose of removing quenching stresses and improving the hard. ness and strength. The cold specimens were placed in an unheated electric furnace and heated to 1025 F for 1 hour followed by cooling in still air. When cold they were again placed in an unheated electric furnace heated to 1025 F for 1 hour and furnace cooled. The tempered specimens were carefully ground to approximately 0.375 inch square. and small. mild steel pads 1/16 inch thick were cemented to the middle of the specimen.to provide for the locating of the deflection bar on the neutral axis of the test beam. The specimens were then coated with layout dye. and their midpoint located and center punched lightly. Trom this point. the loading and supporting center lines were located and scribed. Transverse Testigg Procedure The beams were tested on a Tiniue Olsen hand operated testing machine capable of applying a maximum load of 12.800 pounds. The testing device was designed to apply the loads at the quarter points. thus subjecting the test beam to a constant bending moment between the loading points. The setup is shown in Figure 1. page 15. The method used in observing the deflection of the neutral axis is shown in - 13 - Iigure 2. page 16. The actual testing procedure consisted of locating the beams in the testing device by the use of scribed center lines and applying an initial load of 100 pounds after which the two Ames dial gages were set on zero. Deflection readings were taken.at load increments of either 500 or 1000 pounds until (and if) failure occurred. Rockwell C hardness tests were made on the'broken beam. the reported values representing the average of at least 20 tests._ Lathe Breakdown Tests The test bits were prepared from-g inch square by 3% inches long stock of the same analysis as that used in the transverse bending tests. Tour bits were double preheated at 1025 and 1500 I for-é hour at each temperature and “high! heated at 2235 for five minutes after which two were oil quenched and the other two hot quenched at 1025 I. held for 2 hours. then furnace cooled. All bits were double tempered at 1025 I. for 1 hour air cooled. followed.by 1 hour. and furnace cooled. These bits and two commerically hardened high tungsten (lS-h-l) type tool bits of the same size were surface ground on a Norton grinder to remove all decarburised skin. then carefully ground to the desired shape (as specified on the lathe test summary. page 32) on an Oesterlein Tool Grinder. The nose radius was ground off hand. After grinding all cutting surfaces were hand honed. and the nose radius honed to fit a templet of the desired radius. The test bits were rigidly supported in a heavy duty tool post and holder. The work piece was a length of railway car axle (the specifications and.physical properties of which appear on the lathe test summary.page 32). - 1h - which was mounted in a 19' x 6' LeDlond Heavy Duty Geared Head Engine Lathe. equipped with a 7% hp motor and having 12 driving speeds and 36 feeds. Surface speed of the workpiece was measured by a Schurchardt & Schutte speed indicator which had been.previously calibrated and found accurate. The tool life under cut was measured by a stop watch. a check being made by measuring the length of cut. The tool was considered as having failed when worn to the extent that the diameter of the work piece increased 0.002" to 0.003". -15.. LOADING DEV/CE —- F76. I" 5h (pa/H7; meg/75 of app/y/ng’ bend/n? women f 2-":9 @560 1’27?an f); (7/5 and def/ec- 790/) bar/x7635 x7 of J/wa/n flar- iii/wafer" (vb/I 3/ FUI/ 3.60/6 9’0 Vab/e /) ea 0’ (l) 2 ‘2‘ .. 00,0 .S‘Crcc/J — 7:3 ho/d j ,, (27/7 .Jp/‘V'Izg. I l A F 7593691 _ ' l u | ' I ' (a) \ t ( ‘1? t - ‘4) I '5‘; his; 9' ‘0 f T (2/ ‘I‘S - j - _.- i \ (57 1 .MacA/ec 6456 ‘ 4 00 ' a (/l Ml/o/ ere/ .S‘I‘oc/c: {4) 7595/“ spec/men (1.375 ”7;. AZ) (“a/ban foo/ ere/ - quencbco’ Jgrza/c (diff) 02.5“ '//95. 69/. dna’ fem/oerea' 7’22 65‘ 4?. . para/.5 a?“ 07/03/0027. (.3) 6395 3250 -~— quencnca/ and A67 JAE /04x§' 66756 a’aéWc/Ma’ fife/”per: a! 7’2) 620 afl/V 00d 7" 6197/0 creed -16- 55H. [C77 0N PEA D/Nc; —— F25. r3 .577 (so rnp’ poem f'xon 0 /' 071/7205. fr (TF7 #0 ,r'n (a, 5 )3 ‘ ‘ . 1’ s .7 I - and (/d‘d? 0 / ci/a/ / FAQ/Ir. 0 0r .5 o z) A? ~ fox/7 a’c‘.""/c?c f/cv/y 0 f. ”/76 n7 “ZS/7077 x7. 0’. // 0027 99:14 0 / / ’76 I" 9/7.» c? n #5 & /-' ,/0 ad / (ind/2737’ /7C’c70/ ”0 * 6770.127? flare. - H/a Kr" .52? a /e, flea/ freq/20 a/ b cam ./ ’L’O// Ju/QOO/‘IL 6058 0/ 0/ ”7 0? Ca fore read/03¢ 042/7492- f/o}; a 2" ’70 7‘0 .00/ ” 7670/ def/ecf/bo /5 .auer- “f"? o )0 fwo r cod/0651.5, _. _‘JL___ De f/ec. hen bar/75.5: ‘ \ uJ/ f}: beast/es: 667‘ 5C rc ed: 7‘ 0 /0cav/¢ ,7.a. I dale-97 ' — m Mac/7H7: base . \ ...N..1.FO.'\Q‘ . e. 733...,- - 17 - CALCULATIONS - DATA AND RESULTS Transverse Bending Tests Figure 3. page 19. shows the appearance of a test beam before and after application of the load. It is apparent that corrections were necessary in the beam span. the load moment arm. and deflection because of roll on the supports and under the loading head as the load was applied. These corrections were established by both graphical and analytical means. The beam was assumed to take the shape of an arc of a circle between the supporting rolls. The corrections were determined for an indicated deflection of 0.1MO inch and are linear functions of the indicated deflection. The deflection due to roll. span correction. and moment arm correction are plotted as functions of the indicated deflec- tion on Figures h. 5. and 6. pages 20. 21. and 22. Calculations of the modulus of rupture and toughness were based on corrected values of moment arm. beam span. and deflection at the mid- point of the beam. The friction couple produced by the action of the loading and supporting rolls was neglected. The modulus of elasticity was determined for each test as a check on the testing procedure. Toughness of the specimens was determined by the expression '1' . 533/]: which is strictly true only if the stress is proportional to the strain. In some tests this was not the case since the proportional limit had been exceeded. However. the method used.places the toughness on the basis of the material and its treatment and does not depend upon the size or type of loading of the specimen. Since in most tests the deviation from a straight line relationship of stress to strain was slight. the value of toughness may be considered a very close -18... approximation. Figure 7. page 2h. represents a typical load deflection curve. The value of E (modulus of elasticity) used in the toughness calculations was 30.000.000 psi since the average of all experimental values was found to be 30,021,300. -19.. FREE BODY D/AG‘IQAM —-/-"/6‘. _3__ unhOW/np acfzon ///78 of /0rc€5 06/70 ’ 0n flea/v.5 before . and arr/er app/7C0 Ion 0f /0 (70/5 17/ machine. / a, -, I. p P 2 2 - - ' - no. 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Load Pounds 100 1000 2000 3333 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000 10500 railed at 10500 pound load immediately after deflection readings were taken. - 23 - Sample Data for Transverse Bending Tee; apecimen XII-O MolybdenumnTungsten High Speed Steel Specimen eize 0.373 inch square 1 M% inches long Rockwell '6' Hardness 65.9 Quenched in oil from 2230 I Tempered 1 hour at 1025 F and air cooled followed.by 1 hour at 1025 r and furnace cooled. / Dial Readingg’ Dial Deflection Are.Deflection 1 2 0.001 inch 0.00]. inc}! 1 2 1.000 1.000 0 0 0 0.9835 0.98h0 0.0165 0.0160 0.0162 0.9665 0.9655 0.0335 0.03u5 0.03u0 0.9195 0.9h75 0.0505 0.0525 0.0515 0.9330 0.9300 0.0670 0.0700 0.0685 0.9160 0.91h0 0.08n0 0.0860 0.0850 0.9075 0.9065 0.0925 0.0935 0.0930 0.8990 0.8980 0.1010 0.1020 0.1015 0.8905 0.8895 0.1095 0.1105 0.1100 0.8820 0.8810 0.1180 0.1190 0.1185 0.8735 0.8720 0.1265 0.1280 0.12 2 0.86 5 0.86 5 0.13 5 0.1365 0.1 0.8555 0.8 35 0.1 0.1 55 0.1 50 0.8u65 0. 5 0.1535 0.15u5 0.15h0 0.8365 0.8355 0.1635 0.16u5 0.16%0 0.8270 0.8260 0.1730 0.1710 0.1735 0.8170 0.8160 0.1830 0.18h0 0.1835 -211- . 1 . 1 . . 1 1 . 1 u . 4 1 ....I. .. . 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D SR 1108801311 \K . t1 1 1. I1 ..ta-IIII I”- . II...I+IeAIII...t.I|I—.I.-.u-.I o-wIIII. .IIII. III|.10II.I.Ifile. Ileell?u.u!le...I0Ivll1 lv'ln lie-Ayn!501....OIIIWI'O'IF'YOJ1‘4‘0I'IMI' It {11*}. 1 . 1 1. . 1 . _. 11511015 £01100\\&U 1000-w .... o I . . . ..- I.. . I 1 . . I. . .inVI- TI7...II .II. ..1 ...... ~ I.|.. 9 VI..I...I 14.1rx I IIII I M . 1 1 . 1 . _.. 1 . _ .1 . 1 . 1 L. I 1| IIIIIIII. , 1 . , I I L!- . 1 .1 I 1 I ..1. . 1 1 .. 1.1.1mm2m €230“: no 2... ...). -25.. Notation AUeed in Sample Calculations ? a Total applied load. lbe L :- Corrected span length, in, a a corrected load moment arm. in. d = Indicated deflection of neutral axis of beam. in. a'. Corrected (true) deflection of neutral axis of beam. in. d' Deflection due to vertical shear at loading points. in. I a Modulus of elasticity. psi 1'. Modulus of elaeticity corrected for shear of loading points. pei 1.. Modulus of elasticity in shear, pei I n Homent of Inertia of beam cross sectional area. imu O a Distance from neutral axis to extreme fiber of beam. in. 3 a Modulus of rupture. pei T :- Toughness, in--lb/in.3 A «_- Area of beam cross section. in.2 - 26 - Calculations for Transverse Bending Test of Specimen XII-0 Data on Page 23. Modulus of rupture P 3 MC ‘2 3 ST”:— 3 ? at rupture = 10,500 pounds d at rupture a 0.1835 inch a at rupture from Figure 6 g 1.000 - .206 s 0.79h inch 1/0 for 0.373 inch square section = 0.00865 111.3 10599 s = 2 1‘ 0°79" : h82.000 p81 0.00865 Toughness r .- § 52/]: 3 taken as 30,000,000 psi since the average of all experimental values in this series of tests was fbund to be 30,021,300 psi 2 T = % ufa 0(30 2 3870 in.-l‘b/in.3 - 27 - Modulus of Elasticity Determined for a load of 6000 pounds where d a 0.1015 inch. E : Pas 3N4 Lz- 8.22 12 Id' d' from Figure u is 0.1015-0.0051 3 0.09614 inch. 1. from figure 5 is 11.00 - .126 .-. 3.87M inches. 3 from Figure 6 is 1.00 - .115 a 0.885 inch. I for 0.373 inch square section 2 0.00161 in.” 6000 x 0.88 n .8112 - 0.88"”2 I “ 12 1 0.001613: 0.09:611 " " 29'750'000 P“ Correction due to vertical shear at loading points Zn 8.35-— 2 s Ale 3 53s .L for 0.373 inch square section x 0.1391 in.2 Be 2: 12,000,000 psi 6000 x 0.885 d: I 2 x 0013§1 Z 12.0%,000 : 0.0016 inch. Modulus of elasticity corrected for vertical shear at loading points: El 2 29,750,000 2 %m e 30,300,000 p81 - 28 - RESULTS 01‘ TRANSVERSE TESTS DE EN SPECIMENS Quenching Identi- Specimen Modulus True De- Toughness Corrected Hardness Pro- fica- Size-In. of Rup- flection in Modulus of Rockwell cedurc tion Square ture, at Rup— 1b/TE;3 Elasticigy 0 ture,In. 118i 1: 10 011 111-1 0.375 276.500 0.0876 1275 30.55 66.9 Quenched 11-2 0.389 50h,000 0.1778 M233 29.80 60.7 Iv-o 0.375 061.000 0.1600 3500 30.110 65.1 veo 0.372 h02.000 0.1520 3255 30.25 60.9 Ix-o 0.375 *5h3,000 0.2185 h915 30.90 65.0 x-o 0.370 530.000 0.2115 u750 30.00 66.1 11-0 0.375 hh0.000 0.1u60 3225 31.05 65.8 XII-0 0.373 h80.000 0.17u2 3870 30.30 65.9 1111-0 0.375 533.500 0.2121 h7ho 30.5 65.6 Quenched 71—h 0.375 37.000 0.1083 1893 30.6 67.1 in.Lead VII-u 0.375 33,000 0.1h86 3125 30.25 66.1 at 1025 r Ixeu 0.375 h70,000 0.1625 3690 29.80 66.5 and Air x-n 0.367 h8h.500 0.1716 3905 29. 0 66.3 cooled xx-n 0.375 h3u.000 0.1039 3190 29. 0 66.3 III-h 00375 2893000 000899 3181 29030 6607 Quenched 11-1 0.392 hou,000 0.1256 2720 29.70 66.0 in Lead III-0 0.375 813.000 0.1381; 28140 29.70 66.». at 1025 r 17:1 0.375 293.000 0.0900 1u28 30.001 65.7 held 15 vel 0.375 h77.000 0.1755 3792 29.80 66.2 minutes. 1x21 0.375 h32.000 0.1h96 3115 29.85 66. 1hrnece x1-1 0.369 306.500 0.097u 1565 30.9 67.0 C0010 Quenched 11.0 0.389 *h27.000 0.--- 30 7 29. 0 65.7 in.Lead III-2 0.375 32u.000 0.1035 1735 30.10 67.3 at 1025 r IVLZ 0.375 387,500 0.1309 2500 29.75 66.6 1 held 762 0.372 ifiu.500 0.1037 1752 30.60 66.0 1 hour. VII-2 0.375 3.000 0.1588 3272 30.00 67.2 Furnace Ix.2 0.375 h65.000 0.1710 3805 30.10 66.5 c0010 Quenched III-3 0.375 n17.500 0.1387 2905 29.65 66.7 in.Lead 17:3 0.375 369.000 0.1259 2270 28.80 66.5 at 1025 r vz3 0.370 313.500 0.1023 1637 30.00 66.9 Held 2 hr VII-3 0.375 52.000 0.1192 2062 29.50 66.8 Ihrnnce 1xe3 0.375 9.000 0.1610 3510 29.95 66.7 cool. 1+3 0.375 098.000 0.1981 h130 29.50 65.7 x1-3 0.368 331.000 0.1069 1825 29.70 67.1 I'Unbroken Table I 0 SUMMARY OF TRANSVERSE TEST RESULTS Quenching No. of Modulus of Rupturegpsi from S = Moll. Variation _ % Procedure Tests Average Maximum Minimum variation Average 011 quenched. 9 u68.200 *5h3.000 276.500 266.500 56.9 Hot quenched. Air coal. 6 h07.900 h8h,500 289,000 195,500 h8.0 Hot quenched. - 15 mimteae 6 387.” 1477.000 293.000 lghgom ”705 Furnace cool. Hot quenched. 6 395.200 n65.000 32h.000 1h1.000 35.7 1 hour. Hot quenched. 7 391.h00 h98.000 313.500 18h,500 h7.2 2 hours. *Unbroken Quenching Io. of _Hardness - Rockwell 0 Variation - $ Procedure Tests I“werage *‘Maximum I""‘Minimum variation Average Oil 9 65.6 66.9 6h.7 2.2 3.35 'sct quenched. 6 66.5 67.1 66.1 1.0 1.50 “1' 30010 Hot quenched. 6 66.3 67.0 65.7 1.3 1.95 15 min. act quenched. 6 66.5 67.2 65.7 1.5 2.25 1 hour. Hot quenched. 7 66.6 67.1 65.7 1.h 2.20 2 hours. ...from 20 tests. *rrom 120 to 180 hardness tests. - 3o - CALCULATIONS,_DATA.AND RESULTS Lathe Breakdown Tests The relationship which exists between cutting speed and the tool life for any tool, material cut, depth of cut and feed is expressed.by the equation VT” 2 O (33ers 1': cutting speed, feet per minute T1: tool life between.grindings, minutes n.s an exponent which is the slope (negative) of the V'vs T graph on log-log coardinates. C = a constant which depends upon the tool material, tool shape, material cut, cutting speed, depth of cut and feed. From the equation VT”'- 0, when T a l, 0 = V'in feet per minute for a tool life of 1 minute. Figure 11, page N9 shows the relation between cutting speed and tool life on modified log-10g codrdinates for the three sets of tool bits tested. Determination of 'n' and Solution of the Equation VTn'a G (a) For molybdenumptungsten.bits, hot quenched at 1025 I for 2 hours, furnace cooled, then double tempered at 1025 I. From Figure 11, when T s 1 O = V': 176 {pm when T = 2.7 min V': 150 rpm wnzc 01' Tug; 2.71| a 157% from which n c 0.161 The equation, therefore, becomes VT°161 a 176 V fer a tool life of 60 minutes a éggfgi' c 91.2 1pm - 31 - (b) For molybdenum-tungsten bits, oil quenched and double tempered (c) at 1025 F. From Figure 11, when T s 1, C s V'= 168 fpm n 3 .161 as before, since the V vs T lines on Pigure 11 are parallel. The equation then becomes VT’161 3 168 V for a tool life of 60 minutes a 2:01 1 n 86.9 fpm Fer high tungsten (lS—h—l) bits commercially hardened and tempered. Tron Figure 11, when.T = 1, C = 7': 162 fpm and the equation becomes YT‘161 a 162. V for a tool life of 60 minutes 3 EggiEi-a 83.3 fpm The relative cutting efficiencies for the differently treated tool bits and tool bit materials may be (and generally are) expressed.by the cutting speed for a tool life of 60 minutes. Considering the commercially hardened 18-h-1 bit as 100$ the efficiencies become 18-h-1 3.8.8. Commercially hardened and tempered....100.0$ Molybdenum-tungsten 388 011 quenched and double temer.a...000.0000.00....OOOOOOOOOOOOOOOOOOOOOOOO0.103.” Molybdenum-tungsten HSS oil quenched, 2 hours at 1025 F and dOUbIQ temperedeeeeeeeeeuee.....e.......108.7§ - 32 - Table IIe SUMMER! OF LATHE BREAKDOWN TESTS Metal Cut: 0.h$ Carbon Steel, annealed Yield strength, h2,250 psi Tensile strength, 81,900 psi Reduction in area, 38.N$ Elongation, 25}% in 2 in. Drinell hardness, 159 Out: Dry; Roughing; Depth of cut, 1/8 in., feed 1/h5 in./rev. Tool: Material, high speed steel as noted; nose radius, 1/16 in.: side cutting-edge angle, 0 deg; end cuttingbedge angle, 6 deg; side rake, 1h deg; back rake, 8 deg; relief, 6 deg. Setting angle, 90 deg. All cutting surfaces honed; nose radius honed to a templet. Tool size 5' x-fi' x 35' long. Heat Cutting rpm of Length of T601 Life, Tbol Material Treatment §peed,£pm workjpiece Cut-in. min quenched 152% lou n; 2.01 from 2235 r in oil lung 100 6 2.66 Molybdenum Double 128 10k 11-5/8 5.12 Tungsten HSS tempered 0.1025 s 172 136 2-5/8 0.88 Re 65.9 158% 1&7 "t 1.35 quenched 152} lou 5-5/16 2.39 from 2235 r in lead inn; 10h 7-1/8 3.16 at 1025 r Molybdenum- 8 held 2 hr 137 mu ‘ 10-7/16 M55 Tungsten 888 Double 172 136 h-1/8 1.uu tempered at 1025 r 158; lh7 6 1.85 is supplied 152% 10h 3-9/16 1.58 commercially oil hardened 137 10h 6-5/16 2.76 18-34-1 a tempered Tungsten 888 2c 6h.0 118; lou 13-7/8 6.10 157 136 3—1/8 1.06 1173 1&7 5-3/8 1.65 137 135 8% 2.76 12h 136 15% 5.17 -33.. DISCUSSION Transverse Strength vs @enching Procedure Il'igure 8, page 38 and Table 1, page 29 summarisethe effect of quenching procedure upon the modulus of rupture of quenched and tempered test beams. Considering the average strength curve it is evident that on the average the strongest conditions obtain when oil quenching is used. Next in line and some 60,000 psi lower is the hot quench followed by air cooling to room temperature (i.e., O holding time). From the remaining points it is evident that hot quenching times beyond 15 minutes have little effect upon the average transverse strength. The curve showing variation in strength (maximum-minimum) is revealing. Oil quenching is indicated as causing the greatest varia- tion, the magnitude of which is, indeed, nearly equal to the minimum strength obtained. Much less variation is noted for all the conditions of hot quenching with the least variation for a 1-hour hot quench. The degree to which the variation curve approaches the minimum curve may be regarded as an index of cracking tendency during the quench. As can be observed, oil quenching procedure would be more apt to cause cracking than any of the hot quenching procedures investigated. Conversely, a 1-hour hot quench would be the least apt to cause cracking. Such tendencies would, of course, be greatly accentuated in the hardening of irregularly shaped dies and forming tools wherein cracking of a tool represents an important loss of materials and man hours. The variation in strength are high but not unexpected when testing - 3h - a material of high hardness. Theoretically, strength and hardness vary directly except at the high hardness level where 'locked upI or internal stresses bringlabout localized overstress which is not permitted to readjust itself. Surface condition was a very important factor in the beams tested. Great care was exercised in grinding the specimens prior to testing, but there was no assurance that localized overheating and consequent sub-microscopic grinding checks were absent. (Unfortunately, too, many tool grinders do not appreciate the disastrous effects of grinding a tool until discolored and then dipping in water-heinous practice.) Stress concentration under the loading and supporting rolls is of necessity high,and also localized carbide segregation in the stock may well cause large differences in strength. Examination of tested specimens is enlightening. On page 39 is a reproduction of a photoelastic study of a'beam loaded in the same manner as that used in this investigation. The photoelastic diagram illustrates the high stress concentration at the loading and supporting points and the constant bending moment existing between the loading points. Page to shows three photographs of tested beams. Beam.d deflected nearly 0.22' at the center under the maximum load of the testing machine. The extreme fiber stress was 5h3,000 psi. Hardened high speed steel is not often thought of as yielding under high stress, yet beam A.shows appreciable permanent set.' The Rockwell C hardness of 65.h is typical of high speed cutting tools. Beam 3 broke at a maximum fiber stress of 533,500 psi and virtually exploded at failure. Note the fragmentation of the entire center _ 35 - section which was subjected to the same bending moment. Evidence of longitudinal shear is clearly evident. The hardness of this sample was 65.6 He. Beam C was the weakest of the series tested, being about half as strong as beam 3. lute the relatively slight fragmentation. Ha hard- ness was 66.9, the maximum in the oil quenched series. Since toughness was determined by the expression T =-§82/B the discussion applied to transverse strength also applies to toughness. Had curves similar to Figure 8 been drawn, the slopes would have been more pronounced since toughness is a function of the square of the modulus of rupture. Hardness vs Quenching Procedure Figure 9, page #1 and Table 1, page 29 summarise the effect of quenched procedure upon the hardness of quenched and tempered test beams. ' Considering the average hardness curve, oil quenching is shown to give the lowest average hardness with the various hot quenching pro- cedures showing little effect on the hardness. In general, the hot quenched beams averaged 1 point He harder than those quenched in oil. There was very little difference in the various maxima. The curve showing the variation in hardness indicates that oil quenching is sub- Ject to the most variation and hot quenching with sero holding time, the least. 0 In general, the trend of the average strength and average hardp ness curves (Figs. 8 and 9) are reversed. Such a condition is not unusual since the harder materials are more subject to localized stress raisers. Exceptions are noted for specimens 7B0 and x-o. page 28 which - 36 - failed at hhz,000 and 53h,000 psi, respectively, though the hardnesses were 6h.9 and 66.1 He, respectively. Figure 10, page u2.depicte the effect of holding time in the hot quench.upon the as quenched and the quenched and tempered hardness. Data for Figure 10 were obtained during a preliminary search for the most suitable quenching temperature. Specimen size was 5/8” square x 3/16“ thick; high heat temperature was 2250 F (on the borderline of "burning' and too high for general recommendation), and the time at temperature was 1 minute, #5 seconds. A.hot quenching temperature of 1025 F was used, and double tempering at 1025 I was resorted to. The higher temperature and thinner samples account for the highen l Hc,hardness level of Figure 10 over*Figure 9. Considering the as quenched.hardness curve of'Figure 10, it is apparent that all hot quenching procedures result in a higher hardness than obtains in oil quenching. The effect of hot quenching time is to increase the hard» ness quite sharply up to about h hours holding time after which com- paratively little increase occurs up to and including 2N hours. The higher hardness for the increased holding time is readily accounted for. High speed steel at the high heat temperature is com- posed of a solid solution, austenite, with most of the high alloy carbides dissolved. When rapidly cooled to the hot quenching temper- ature (1025 F) by immersion the austenite comes down unchanged, and indeed, will remain essentially stable at 1025 F for more than 106 seconds,(szll§ days) before any decomposition of the austenite occurs at that temperature. During the sojourn at 1025 F,.however, alloy carbides begin to precipitate in minute particles which exert a definite precipitation - 37 - hardening effect and also decrease the alloy content of the austenite. This austenite, on cooling to room temperature, transforms more or less, depending'upon its alloy content, to hard martensite. Anstenite of’high alloy content is very apt to be retained, however, and incomplete harden. ing results. Clearly, then, an oil quenched specimen would arrive at room temperature with considerable (up to 30%)(Sltained austenite whereas hot quenched samples may have little (3 to 5%) retained austenite since appreciable carbide precipitation had occurred during the holding time. The trend of the as quenched curve, Figure 10, shows that carbide precipitation begins almost immediately during the hot quench.and.pro- coeds at a fairly uniform rate up to a holding time of some h hours with comparatively little precipitation thereafter. lvidently, little retained austenite is present after those samples hot quenched h hours or more and have cooled to room temperature, and the higher proportion of martensite together with more pronounced precipitation hardening accounts for the higher as quenched hardness. That complete austenitic transformation is not obtained even with hot quenching up to 21} hours is shown by the curve of quenched and tempered hardness, Figure 10. The increase due to tempering - i.e., secondary hardening - is considerably less for the samples hot quenched h hours or more. The final hardness is, however, not greatly affected by the quenching procedure under the specimen size and temperature comp ditions employed though the hot quenched samples retain superiority in hardness. ‘lzfliflo .2 C’) mcmnzn ORMNOmz 8. 20.. U3 - 39 - STRESS DISTRIBUTION IN PURE BEHDIFG Note: (a) Stress Concentration at the loading and supporting points. (b) Constant bending moment between the loading points. 208 ISOCLINICS AND STRESS TRAJECTORIES ’ CHAP. VI FIG. 6.35 Stress Pattern of a Straight Beam Subjeeted to Pure Bending by Means of Compressive Loads. Applied bending moment = 50.0 lb-in.; depth of beam = 0.763 in.; thick- ness = 0.250 in.; (listanee between upper loads = 3.00 in.; distance between lower loads = 4.00 in. Magnification 1—1/8 1: Reprinted by permission frothhotoelasticity, volume 1, by M. M. Frocht. published by John Wiley and Sons, Inc. EXAMPLES OF TESTED BEAMS A ,II ‘1 " ' ‘ mqnnnmilm “numb ' ' 10 ' 11;: Specimen 1X90. Magnification 1-1/8 x. Extreme fiber stress 5M3.000 psi Rockwell C Hardness 65.h . B Specimen XIII-O. Magnification 1-1/8 X. Extreme fiber stress 533,500 psi Rockwell c Hardness 65.6 ¥\. . C Specimen III-1. Magnification 1-1/8 X. Extreme fiber stress 276,500 psi Rockwell C Hardness 66.9 '._IJ.RD .1 95...). 83: 228:. 8. .8. use -hg- 'I.Za.fl° .1 C.. S. A > e 0 9 ' e mean!" 9".“sz 8. 20. U; - h} - Lathe Breakdown Tests Regardless of how carefully a tool steel is manufactured, rolled and annealed at the mill and how much time and labor is expended in the fabrication of the tool, the ultimate result will depend upon the proper heat treatment to obtain the maximum service efficiency. Tool and die breakage causes a considerable loss of man hours, material, and production and any hardening practice that would decrease cracking is highly desirable. One manufacturer of high speed steel hobs and milling cutters has reported a 35% loss due to cracking in hardening and, no doubt, many additional failures. due to the same canse, occur in service which are attributed to other faults. Tools and dies are generally of intricate shape with many abrupt sectional changes. Such conditions enhance the possibilities of cracking during heat treatment and the ideal test of the most suitable heat treating procedure would be a service test of some intricate tool or die. In the absence of such testing facilities new tool steels or heat treating procedures are frequently evaluated by lathe cutting tests of which the lathe break- down test is probably the most satisfactory. According to the Manual on Cuttipg of Metals, the lathe breakn- down test, if properly designed, gives a reliable index of the cutting ability of a specific tool material on any type of cutting operation excepting one in which tool strength and toughness is a controlling (7.po279) factor. In this investigation the lathe breakdown test was used (1) to compare two-hour hot quenching with oil quenching on molybdenum? tungsten high speed steel, and (2) to compare the molybdenum tungsten - hh - high speed steel with the more widely known lS-M—l type under similar conditions of quenching. The tool shape selected was one commonly used in lathe tests - tool contour No. 2, Manual on Cutting of Metals, page 62. l The work piece was annealed, medium carbon steel, ductile enough to give a continuous chip under the assigned cutting conditions. The continuous chip caused characteristic cratering of the tool face and subsequent breaking through at the cutting edge thereby causing failure. The cratering action of the chdp on the tool face is brought about by the high (225 .000 t psi) unit pressure of the chip on the tool together with the tendency of the chip to adhere to the tool. The high friction causes local overheating and softening of the tool material which is then washed out. The smoothness of the tool face is obviously a variable,and accordingly all cutting surfaces of the test bits were honed to a smooth finish. On page us is a.photograph of two tool bits. The one on the left shows the appearance of the tool Just prior to failure. Rots the pronounced crater, the particles of the work piece adhering to the crater, the roughened cutting edge, and discoloration caused by heat. The history of the crater is interesting. At the beginning of the test (when cutting a ductile material) the chip flows over the tool surface in a nearly straight ribbon. As cratering occurs, the chip gradually changes to a spiral of smaller and smaller radius until ’ eventually the edge of the crater breaks through the cutting edge and failure occurs suddenly. Since the crater increases the effective rake a tool rough.cutting steel is most effective Just before failure. The tool bit on the right has been completely failed. Note the partial filling of the crater by adhering metal and the dubbing of the nose radius. figure 11, page M9,and Table 11, page 32,summarise the cutting speed-tool life relationship of the three sets of bits tested. The straight line relationship is expressed by the equation VT”'- 0 in which n.= 0.161. This value agrees well with the generally accepted.value of approximately 1/7 for high speed steel tools rough. cutting a steel workpiece. In Ihgure 11, it is observed that the longest cutting life at any chosen speed was obtained for the hot quenched.Mo—M tools, with the oil quenched Mo-V bits second, and commercially hardened lS—h—l lowest of the three sets tested. It is expected that hot quenching procedures of from 15 minutes up to 2 hours would result in a gradual improvement in cutting life above that for oil quenching though no tests were conducted on bits given intervening hot quenching treatments. The tool life of the bits tested appears to be associated with the room temperature hardness. Obviously, of course, the hot hardness (or operating temperature hardness) is the important factor. Cohen and Bishop in some recent work(:lscribe a method of obtaining the hot hardness of high speed steel and present typical values. Their data indicate that there is a fairly definite relationship between hardness at room temperature and the hot hardness of high speed steel. id higher hardness would help to resist the cratering action of a continuous chip as would also the presence of abrasion resistant alloy carbides. Evidently, the two hour hot quench is advantageous both from the standpoint of higher hardness and better carbide distribution. However, the highest cutting efficiency does not necessarily require the highest hardness but rather a proper balance of hardness and toughness. Excessive hardness for a specific application may result in a crumbling of the cutting edge. Excessive abrasion results and the frictional heat soon weakens and breaks down the tool. The relative rank of the various bits may have been changed had the work piece been a hard alloy steel. The comparison‘between the oil quenched Mo-W bits and the oil quenched lS—h-l tools is subject to a limitation. Tool bits hardened in the laboratory are individually treated under carefully controlled conditions of time and temperature whereas commercially hardened bits are done in.batches and may not always be subjected to uniform time and temperature conditions. This factor may have influenced the results obtained though there is plenty of industrial evidence that the Mo-M'steel investigated is at least the equal of lS-h-l. unfortunately, the Mo-V steel was proposed as a substitute thereby implying inferiority,and.many shop men have been prejudiced against this new tool steel. Since the requirements vary when cutting different materials the application should be considered in arriving at the most suitable quenching procedure. In general, nonpferrous metals require extreme hardness and a keen cutting edge with toughness secondary. Cast iron, bakelite, plastics, certain brasses, and other materials which form well broken chips cause tool failure by abrasion on the nose or flank,and tools for such materials should have hardness at the expense of toughness. Intermittent cuts, especially on hard alloy steels, require tools of high toughness which, in general, is obtained at some sacrifice in hardness. -u7- At the eXpense of some complication, perhaps it qud be wise to specify two-hour hot quenching for lathe tools to be used on.thoss materials which cause failure by nose abrasion and on roughing cuts for medium carbon steel and oil quenching or 15 minutes hot quenching for shaper and other intermittent cutting tools or those for use on hard alloy steels. The most suitable allqpurpose treatment is that which gives the best combination of strength (toughness) and hardness with the least cracking tendency. Hot quenching at 1025 for periods of from a few minutes up to 1 hour appears to be the best compromise. TOOL BIT FAILURES Magnification 2% X. Left: Tool bit just before failure. (Not one of series tested) Right: Failed tool bit. Mo-W H.S.S. Hot quenched 2 hours. sfpm 158% Feed 1/h5"/rev Depth of cut 1/8" werkpiece -0.h$C steel annealed. Qumm. ON in.“ Qx Q. Q. n. 00. Oh. O . ON. .2 DON WON --4-———--——i "i Q: WNN j. / - _ .r._ “n"‘lF— _ ,_4r_. QNN hm; l: - -»-——-1r -—~4» re ..em “5% \ Xxx bxokeEEOD DON th \iVIQ —1}———— 1 —— --—l>- —— ~0— ————-——{r-—» l» —-——-< — ..~4 - - OVH ......Vu ———i> 0,2 T 0,..- Sx wovnh —-——«» ——-——o—-——» 4r OOH .---_-4L_. Ln bkeQLnek w to tab? an 0&0 0.: _..L- __ ___4u- §uc®\ 7/1] ea QQN Mr... .JL- __ 1H, _.._ 1i._.._h_41r L _ 'il’ __ #1 III»! ll fill on“ _—_—4p_.—_ 4? - ___. -—4>-— . ___ a} . if b! t.._.__._1> __ {F __ ___++. _ ONN L _ . t _ u. OWN NN 939K but, s also hastens - to BB: .x-o-c-c-h-1-m manna Boa the Ben 8 Beam 358 no Sci 1110’; —paadg 5U/,¢,zn3 QQHCDUSIONS (a). Transverse strength and toughness: (b) (e) l. 2. 3. The average of the oil quenched test beams is superior to that of any hot quenching procedure investigated. The greatest variation (cracking tendency) is obtained in oil quenching, whereas the least variation is noted for 1 hour hot quenching. ‘ is far as the ayerage strength is concerned, hot quenching for more than 15 minutes has no significant value. Quenched and tempered hardness: h. The lowest average is obtained in oil quenching while hot quenching for a few minutes up to 2 hours has little effect. Cutting efficiency: 5. 7. Two hour hot quenching produces more efficient tool bits than oil quenching when the work piece is annealed.medium carbon steel. Hot quenching would, in general, be more satisfactory than oil quenching with a lS—minnte hot quench proposed as an all purpose recommendation. The cutting efficiency of molybdenum-tungsten.high speed - steels is at least the equivalent of lS—h—l under similar conditions of quenching. l. 2. 3. 7. S. 9. 10. ll. 12. .-51_ BLIBLIOGRAPHY On the Art of Cutting Metals, F. W. Taylor, published by A.S.M.E., i907. W.P.B. Statement,“ p. 1201*," Metals and Alloys, Vol. 16, No. 6, Dec. l9h2. 'Tempering of High Speed Steel," Cohen and Koh, Transactions AeSeMe. Vol. 27. DOC. 1939. Metal Processi_ng, 1941 ed., 0.7!. Boston, John Wiley 8: Sons, Inc. "Kinetics and Reaction Products of the Isothermal Transformation of a Six Per Cent Tungsten - Six Per Cent Molybdenum High Speed Steel.‘I Ham, Parke, and Bernie. Transactions, A.S.M., Vol. 29, Sept. 19,41. .H_i_gh Speed Steel, 1st Ed. 1931, Grossman and Bain, John Wiley d: Sons, Inc. Manual on Cuttingqu Metals, 1939 edition, American Society of Mechanical Engineers. “Hardness Testing of High Speed Steel at High Temperatures," Cohen and Bishop, Metal Progress, Vol. 113, Ho. 3, March 1943. “Heat Treating Molybdenum High Speed Steel,‘I Breeler and Wills, Steel, Vol. 111, No. 15, Oct. 12, 19142. Metals Handbook, 1939 edition, American Society for Metals. “Rough Turning with Particular Reference to the Steel Cut," trench and Digges, gansactions, A.S.M.E., Vol. 1&8, 1926. I’hotoelasticity, Vol. I, 19141, M.M. Frocht, John Wiley and Sons,Inc. _‘t' .... .. . ..IStItIDs slit». Ill! i s purl » III), I no“ inflasshn . «the? 3 . ...? ...waa. “firearms: . flux. . r .4. . u. ..... ....J . . ‘ r a i s I. O... ‘ . b . . ......a Lo... . a. . .fiu . x9.- . . . . .. , . . . . . .. . 7s? a r e.... .. _. h . . .. ._ as,...z..... . . _ . . . . gap .. s . . v .. a . . . . i u . . . ..c . . w: . , . - . . ~ . .s .. ..vf .- \. ,.0 v u .a .1. . ...... .. . .... ..4 ...QQO,..¢s.. I am. 3 7.5““? :.\.q ....“ V. ..Wooff « ... .os Lures ’2? , f l 0 ll. J - o 9 It“ .: ...» of.» ...w _ o . ..s 73.3.. ... . V~... r..«.5_ ; .. ”BO . l a: t«.+r,. cw. ...r..l . e I . . . .. .0 ...¥ . 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