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TABLE OF CONTENTS Page I. Continuation of Prior 'Work............... 1 II. Further Work on Heat-Treating and Processing Procedures. 11 III. Reproducibility of Data in Ru-pture Tests......... 21 IV. Effect of Chemical Composition on Properties....... 26 V. Fundamental Metallurgical SJtudies............ 38 VI. Cooperative Fatigue Test Program............ 117

PROGRESS REPORT ON METALTURGICAL RESEARCH IWORK RELATING TO THE DEVELOPMENT OF METALS AND ALLOYS FOR USE IN THE HIGH-TEMPERATURE COMPONENTS OF JETENGINE, GAS TURBINES, AND OTHER AIRCRAFT PROPULSION SYSTEMS March 13, 1918 I - CONTINUATION OF PRIOR WORK At the time work was started under contract NAw 5470 there were several investigations in progress. These investigations have been continued in order to finish the experimental work and issue reasonably complete reports. The status of this type of work is as follows: 1. Reports Prepared for Publication by NACA: The manuscripts for the following reports were reviewed, corrected, and returned to the NACA, and the reports have been published: C (1) The 1350~ F Stress-Rupture Properties of Two Wrought Alloys and Three Cast Alloys. TN No. 1380, November 1947. Xy(2) The Rupture-Test Characteristics of Heat-Resistant Sheet Alloys at 1700~ and 1800"F. TN No. 165,.February 1948. In addition the following reports have been reviewed, corrected, and returned to the NACA but have not yet been issued as Technical Notes: tL(l) A Metallurgical Investigation of Five Forged Gas-Turbine Discs of Tinken Alloy. (Tn No. 1531) < (2) A Metallurgical Investigation of Two Contour-Forged Gas-Turbine Discs of 19-9DL Alloy. (TN No. 1532) (3) A Metallurgical Investigation of Two Large Discs of CSA Alloy. (T? No. 1533)

2.: (1) A Metallurgical Investigation of a Contour-Forged Gas-Turbine Disc of EME Alloy (TN No. 153h) (5) A Metallurgical Investigation of Two Turbosupercharger Discs of 19-9DL Alloy (TN No. 1535) 2. New Reports Submitted to the NACA The following reports were issued to cover investigations completed: (1) Properties of 19-9DL Alloy Bar Stock at 12000 F. June 26, 1947. (2) A Study of the Effects of Heat Treatment and Hot-Cold Work on the Properties of Low-Carbon N155 Alloy. August 28, 19117. (3) Properties of Turbelloy-l Alloy at 12000 F in the SolutionTreated and Aged Condition. November 12, 19h7. (4) A Metallurgical Investigation of Two Large Forged Discs of S-590 Alloy. March 3, 1948. (5) A Metallurgical Investigation of a Large Forged Disc of S-816 Alloy. 3. Reports in Progress The following investigations are completed or near completion and reports are to be prepared: (1) Summary report on all work done for NACA up to July '1, 1947. (2) Effect of prior thermal history on the properties of 25-20+Si alloy sheet. The low ductility of Type 310S alloy sheet in the temperature range from 12000 to 100O F was eliminated by aging treatments at 17000 to 18000 F. Rupture strengths at 1700 F for the new heat (14998) compare with those reported for two heats of 310S in TN 1lh5 as follows:

3 i Rupture strength (psi) Heat No. Treatment 0L hour 1000 hou AF-18 Annealed + 1 cold pass 5000 3100 14626 Annealed - 1 cold pass 3600 2000 14998 Hot-rolled 3500 1600 1L998 Annealed 3900 2250 111998 Annealed + 10% cold work 3600 1700 (3) Properties of S588 alloy bar stock The rupture strengths of the S588 alloy (S590 alloy modification containing no cobalt) bar stock in the solution treated and aged condition were considerably lower than those previously obtained from S590 as is shown in the following tabulation: ~.tTe mprtr i-Rupture strength Matria Temperature ' (]Dsi) Material (F hour (our S588 1200 lh,000 30,500 1350 1 26,000 16,000 S590 1200 52,000 42,000 (Tests on discs _____1350 31 000 sto (L) Low-Carbon N155 plus boron alloy bar stock Three induction heats have been rupture tested with the following results: ~I~T prau. Rupture strength Temperature (psi) Heat ( 100 hr J597 1200 61,000 52,000 J573 1200 53,000 43,000 N175 1200 50,000 42,000 J597 1350 LOOOO, 29,500

h. The rupture strength of J597 is considerably higher than has normally been found for standard Low-Carbon Nl55, but J573 and N175 are no better than the standard alloy. A chemical analysis check by Union Carbide and Carbon Research Laboratories indicated that the boron in J573 was 0.58 percent instead of the 0.37 percent originally reported. The originally reported boron contents of J597 and N175 were 0.38 and 0.30 percent respectively. (5) Typical Low-Carbon N155 bar stock This program was originally started to obtain complete data for stress-time for total deformation curves at 12000 and rupture tests at 13500 F for three typical conditions of bar stock: hot rolled; solution treated plus hot-cold worked; and solution treated plus aged. lWerever tests units were not needed for other work, data has been obtained for this investigation. The rupture tests have been completed and were included in the report issued on August 28, 19L7. Because the design curves are still incomplete, total deformation strengths have not yet been reported. These will soon be completed, however, because they will be used as a guide in selecting tests for work in progress under Section II. The data now available indicate that the three treatments will develop total deformation strengths at 1200~ F of the following order of magnitude:

5....... Stress for indicated total deformations, (psi) 100-hours I 1000-hours Treatment _0. 0.2 0.5% 1.0 01 0.12 0..2 % 1.0% Hot rolled 16,000120,000 30,000 33,000 10,500 15,000 20,000 23,50 W.Q. 2200~ F + 50 hr at 18,500 2,500 32,000 3,000 14,000 19,000 25,000 28,500 1350~ F W.Q. 2050~ Fl + 25% hot- (1,00a (8,00a a |Cfol ork at | | 29,000 (5,000 i (15,00Oa (18,000 )a --- (35,000)a | —. cold work at 1200" F aEstimated strengths. (6) Inconel-X disc Initial work on the Inconel-X disc gave low strengths and erratic test results at 1200~ and 1350~ F. Data obtained for the Office of Naval Research at Battelle Institute from tests at 13500 and 15000 F were also not representative of the alloy. These results were discussed with representatives of the International Nickel Company, and it was concluded that the initial heat treatment of 2100~ F, h hours, W.I. plus an age of h0 hours at 1300" F did not develop the full properties of the alloy. Their subsequent work indicated that better properties would be obtained by changing the aging treatment to 24 hours at 1550" F, A.C. plus 20 hours at 13000 F. Consequently the tests are being repeated on material given the improved aging treatment. Two rupture tests have been completed at both 12000 and 13500 F. The improvement in rupture strength indicated by those tests is shown by the following tabulation:

6.I 3z~~eT~Estimated rupture Test Rupture strength elongation Aging temperature (psi) (% in 1 in.) treatment (~F) 100 hour 1000 hour 100 hour 1000 hour 300 F 40 hr 1200 57,000 6,000 1.5 1 1350 47,000 36,500 2 2 550 F 24 hr 1200 82,000a 63,000a 4 + 1300~ F 1350 54,0oOa 37,000a 17 20 hr _ aEstimated on the basis of two tests. Total deformation characteristics are being obtained but are not sufficiently complete at present to estimate time-fortotal-deformation strengths. (7) X-hO turbosupercharger buckets Investigation is nearing completion of the rupture strengths at 15000 F of X-40 turbosupercharger buckets. BJ the use of special holders in the rupture unit and with some removal of metal from the back side of the bucket in order to get a uniform cross section, satisfactory failures in tension within the gage length have been obtained. The results to date at 1500" F are as follows: Elongation Stress Rupture time in 1 in. (psi) (hours) (percent) 30,000 92 4 25,000 18b 3 17,000 In progress 1340 hours. (3-10-48) Indicated rupture strengths are 28,000 psi at 100 hours and approximately 19,000 psi at 1000 hours. This can be compared with the following previous results at 1500~ F for Vitallium turbosupercharger buckets:

7. Elongation Stress Rupture time in 1 in. (_psiJ) (hours) (percent) 25,000 13 9.1 20,000 76 9.8 17,000 298 1.0 15,000 251 3.7 Indicated rupture strengths are here 19,500 psi at 100 hours and 1,500 psi at 1000 hours. h. Continuation of the Work Covered by the Report Entitled "A Study of the Effects of Heat Treatment and Hot-Cold Work on the Properties of Low-Carbon N155 Alloy." (1) Completion of odd tests incomplete at the time the report was written have not significantly changed the trends, except for the effect of aging time. Further studies of the effect of aging time gave the results shown in figure 1. It appears that: (a) Aging at 1400 F after a 2050" F solution treatment' improved the rupture strength and ductility for 100 hours at 1200~ F but did not improve the strength at 1000 hours. A period of 8 hours at 14000 F produced nearly the maximum effect, and time periods longer than 2L hours were detrimental. (b) Aging at 1400e F after a 2050~ F solution treatment produced rupture strengths at 100 hours about equal to those similarly aged after a solution treatment at 2200~ F. The ductility in the rupture test was much higher after a 2050~ F treatment. The material solution treated at 2050~ F had somewhat lower strengths at 1000 hours than those treated at 22000 F when aged at 1400 F. (c) Apparently aging at 1350~ F for 2h hours was slightly more beneficial to 100-hour rupture strength than aging at 1400~ F. The

9. 1000-hour strength of the material solution treated at 2050~ F was also improved, but not when treated at 22000 F. Aging at 1350~ F for 50 hours did not change the properties appreciably over those aged for 50 hours at 1400~ F. (2) The influence of various typical treatments on the rupture strength of Low-Carbon N155 bar stock was extended to include 1350~ and 1500 F, with the results shown by figure 2. The results indicate that: (a) The degree of superiority of hot-cold worked material decreased as the temperature and time period increased. (b) Material solution treated prior to hot-cold work maintained strength with increasing temperature and time better than the material hot-cold worked in the as-rolled condition. (c) Material hot-cold reduced 15 percent at 1200~ F maintained higher strength with increasing temperature and time than material reduced 25 percent. (d) Solution treated and hot-cold worked stock had higher rupture strength at 1350~ F than solution treated or solution treated and aged stock, particularly at 100 hours. (e) At 15000 F solution treated and aged stock had the highest strength. The variation in strength between it and plain solution treated stock or solution treated stock hot-cold worked 15 percent was quite small. (f) The particular hot-rolled stock tested had low strength at 1350~ and 1500" F. (g) Elongation during rupture testing increased markedly with temperature.

1.1-, II - FURTHER WORK ON HEAT TREATING AND PROCESSING PROCEDURES A new lot of bar stock was obtained from the Universal-Cyclops Steel Corporation to replace the exhausted stock from Lot 30276 previously used for this type of work. The new stock was the product of one ingot from Heat A-1726 hot rolled to 675 feet of 7/8-inch broken-corner square bars. The processing conditions reported for this stock are summarized in table I. The work on this stock breaks down into two phases: (1) to determine the uniformity and properties of the stock, and (2) to extend the information regarding the effects of heat treatments and processing of Low-Carbon N155 stock to include total deformation effects and a wider temperature range. The results thus far obtained have largely been confined to determining the uniformity and properties of the stock. 1. Chemical Composition The analysis reported by the manufacturer together with the results of chemical analysis at the University on bars from the bottom, center, and top of the ingot are given in table II. In general the heat analysis agreed fairly well with the analysis of the bars and there w;asnot a significant variation between bars from the bottom, center, aid top of the ingot. 2. Hardness of Bar Stock Brinell hardness tests along the length of individual typical bars from the ingot, table III, show a range from 224 to 258 in the hot-rolled condition. Thus far all bars have been within the rarges shown in the table but apparently there is not a relationship between the hardness of the bars and the location in the ingot from which they originated0

12. TABLE I PROCESSING OF LOW-CARBON N155 7/8-INCH BROKEN CORNER SQUARE BAR STOCK FROM HEAT A-1726 (Reported by the Universal-Cyclops Steel Corporation) An ingot was hammer cogged and then rolled to bar stock under the following conditions: 1. Hammer cogged to 13-inch square Furnace temperature 2210" - 2220~ F Three heats -Starting temperature on die 2050' - 2070~ F Finish temperature on die 1830' - 1870' F 2. Hammer cogged to 10-3/4-inch square Furnace temperature 2200~ - 22200 F Three heats - Starting temperature on die 2050~ - 2070~ F Finish temperature on die 1790~ - 1800" F 3. Hammer cogged to 7-inch square Furnace temperature 22000 - 2220" F Three heats - Starting temperature on die 2050~ - 2070~ F Finish temperature on die 1790 - 18900 F Billets ground to remove surface defects.. Hammer cogged to L4-inch square Furnace temperature 2190 - 2210" F Three heats - Starting temperature on die 2010~ - 2060~ F Finish temperature on die 16800 - 1880" F Billets ground to remove surface defects. 5. Hammer cogged to 2-inch square Furnace temperature 2180" - 2210~ F Three heats - Starting temperature on die 2050" - 2065~ F Finish temperature on die 1730 - 1870~ F Billets ground to remove surface defects. 6. Rolled from 2-inch square to 7/8-inch broken corner square - one heat Furnace temperature 2100 - 21100 F Bar temperature start of rolling 2050~ - 2060~ F Bar temperature finish of rolling 1910~ F 7. Bars are numbered 1 through 56, Number 1 bar represents the extreme bottom of ingot and Number 56 the extreme top position. All billets were kept in number sequence throughout all processing, so that ingot position of any bar can be determined by its number. 8. All bars were cooled on the bed and no anneal or stress relief was applied after rolling.

TABLE II CHEMICAL ANALYSIS OF LOW-CARBON N15 7/8-INCH BROKEN CORNER SQUARE BAR STOCK FROM HEAT A-1726 Composition Percent Analysis b C C Mn I Si Cr Ni~ Co Mo NCb N Fe T Universal-Cyclops 0.13 1.64 04.2 21.22 19.00 19s70 2.90 2.6110. 8410.13 University of Michigan I~~~~~~~~~~ I Bar No. 1 0O.I^ I1.43 0.3h 20.91 18.74 1*6 3.01 2.06' 1.07 O.14 Bar No. 28 0.133 1.43 o0.3 20.73 18.92 3 4 3.05 1.98 0.98 O.1 Bar No. 56 0.149 1.41 0,37 20.87 18.91 3.01 2.05 0.97 0,13 v Note: Bar Nos. 1, 28, 56 refer respectively to the bottom, center, and top of the ingot. H'

IL. TABLE III RANGE IN HARDNESS OF AS-ROLLED 7/8-INCH BROKEN CORNER SQUARE BAR STOCK FROM HEAT A-1726 Brinell Hardness Par Position Surface. Center number iiningot Range Average Range Average *t I J1i bottom 2h5-258 253 236-246 240 J28 | center i 229-235 232 226-236 232 J56 top 239-255 250 236-239 238 Overall range j229-258 2)4 226-2116 237 Note 1.- Hardness measurements were made at 22-inch intervals alopg each bar. Center readings are for the cross section of the bar. Note.- All other bars cut to date for testing have been within this range.

i-. Rockwell hardness surveys over the cross sections of typical bars indicate that the hardness varied on a cross section at any one point to about the same degree as the variation along the length of the bars. 3. Microstructures In general the microstructure of the hot-rolled bars was remarkably uniform. Typical structures in figure 3 indicate that the grain size was more uniform and somewhat larger than that of the Lot 30276 stock used for previous work. There was very little evidence of center segregation. One end of Bar 28 (from the center of the ingot) did have some segregation, as is shown in the photomicrograph for sample J28B. This was the only example found during examination of samples from bars in several locations in the ingot. Typical structures after heat treatment are shown in figures 4 and 5. The structures are apparently similar to those which have previously been obtained for the alloy with similar treatments. The grain size after the solution treatments is not clearly defined. The grain size of the sample aged at 1000 F after solution treating is somewhat smaller than was developed by a similar treatment of Lo; 30276. 4. Rupture Properties *Tests are being run at 1200j, 1350, and 1500~ F to establish typical rupture strengths for bars from Heat A-1726. The treatments being tested are:

*( )e-V LV3H) 100MI iO MIN3D UVSN KOMJ 9? Hva XOTIV ^IN NOEm-WDOPOrf RiiToLO1-8 H do 1nIon0fluSOMIOI - a niJflD qoqa piop opmoJqo 01TO.0jo091 '9 *ON ' Rq jo pua aqtsoddo jo eJnoqanO so.Jo! 'q XOOOT XOOt A ~. ~. At~ ~ ~ P I - ' ~~ ' 'j I -.;..:~ o -.......... -~~~~~~~~~~~~~~~~~~~~~~~~V L~~ ' - "'- - ^~~~~~~~~~~ ~Xps / ^ ^k ' ^ - - o' K ~~~~~~~ 2-~~~42;~~~k~~~ < ~~~< ~~~.. 'p.-~. '.-' —~ V. }' Ill^^i ^li~ihi.~.^.^lt ^/-^ ^ ^XOO__t_____ ^/^^ XOO,~~~~~~~~~~~~ -~. 11 4.4 - 2~ ' '.. '-..'.. ~>.-. \- ~~ ^ ^,...</^ ^ ' " ~ ' ' < ~~-:~i '2 -' ~ ~.. CO ' -.,. ~i~.,~i~.~X00 ~ ~'o ",,_ "~'~~:' " ~- 'r-2!.~.. ~~'.,'.:7 #-air~~~~~~~~~~~.:,.~~.,t..,:;'.l 10~~~~ -,:'.~,,,..............i...~,.t,~~~~~~i Al~

I-If~~~,.~.. -?? --->:;...(....,~.~...::.%,~- -S - - '~~ ~ ^ - ^ 0' ' 7~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~7 ~~~~~~~~~~~-...-.,..:-.,_<~, ^......^ x.~ ~~~~~~~~~~~~~~~~.. -. - ^l^^i^~~8';" ''....~'~ 0..... ~ -7> " ' ' ' '0 -,, yrk /j~i ii - ~~ ~~~~~~~~~~~~~~~~~~~~ A~~~._ 1_/f.~ '- 1 'x ' - / '_10OOX c. Microstructure of center of bar No. 28. Electrolytic chromic acid etch FIGURE 3 (CONTINUED).* MICROSTRUCTURE OF HOT-ROLLED LOW-CARBON Nl5 ALLOY BAR 28 FROM NEAR CENTER OF INGOT (HEAT A-1726).

(9~Lt-v m1H) xoo^w Hv8 xOTIV i5tN NoHv9o-o0 ^^^"^J ~ ~ ~ 43 ppgl 01 t110J43 o^o^ioJoaig ff ^^^ew~ ~^9l^q.Ouenb J~.^ 'Jnotj i i *00j^ J^aJe nJon~zsoxOTw -q XOOOI ~~~ ~~~~~XOOt ~~~~~~~~~~... '~- ~. ~~ ^ ^ ^~~~~ ~~~ ~~~~~~~~~~~~~~~~... ^. ^ _.:___ ^~ ~ ~ ~ ~~~~~C Q ~ o14\ ~ —~'^ r'* <^<3 ^~ ^ I:.o.. ~~~~~~~~~ ~..0..,:_. v.:o, ~,l^.^ o~~~~~~~~~~~~~~~~~ ' 1^~~~~~~~~~~~~~~' 4~. ' '~-<~"^ ' ~'. '1 \ -, ' i~~~~~~ g 9 ' '~:-. ~ ~~~o, r ' ''. ^ ^.-^"'.''', ^- ~. ~^ ~ ~~~ ~ '"~ o' ~.. a.. ~~..~^<: -. I.. ^. v ' ' ''^. '~.2.x/ ~: ''." '.'> \ ' ^.%.-' ~~'., ^. ':~ '. ' - >-/ ~~'~/ k ^ ^ ^~~uupaJ'a. qouanb rQ^a 'xnoq{ i Jr *QOIe ^^Je Q onnso0Jo^y ~B) ________~______________ __ x- ^ot __:^ ' 1 ', -.. 0.....::i~:'": q~~~~~~:..,x, ' 9 ~ ' ' " ' -" '.. ' K~'i. '~~~~~~~~~~~~~~~~~~~~~~~>~~,,- ~.. o,0, -,. -~ ' ( 0** /.~~~~ ~ ~~~~~~~~~~~~~~~~~~....'.- ~, ~;..1..~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..1.,:,; ' -

t~~ ~~ ~~ ~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4' 4 ' i 1o Al 5 — -. C' - fr, E4V~~~~~~~~~~~~~~~~~~~~~~~~~~~~o i~,, lOOX 1000X a. Microstructure after 2200~ F 1 hour, water quench plus '100~ F 21 hours, air cool treatment. Electrolytic chromic acid etch FIGURE 5.- EFFECT OF AGING ON THE MIP(ROSTRUCTURE OF SOLUTION-TREATED LOWCARBON N155 ALLOY BAR STOCK (HEAT A-1726).

19. (1) As rolled (2) As rolled plus 15 percent reduction by rolling at 1200~ F (3) 2100 F for 1 hour and water quenched (4) 2200~ F for 1 hour, water quenched plus aged 2h hours at 1LOO ~ F (5) 2050~ F for 2 hours, water quenched plus 15 percent reduction by rolling at 1200 'F. A complete strese-rupture time curve will be established at 12000 F for specimens of as-rolled stock from the center of the ingot. Check tests will be made on specimens frocm bars representative of the top and bottom of the inrot. When the tests outlined above are completed, the results will be analyzed and compared with: those obtained from previous work on Lot 30276 to determine if the variability of material from the ingot has been established to a satisfactory degree. The results obtained to date are given in table IV and compared with those previously obtained for Lot 30276. The results to date indicate that: 1. The rupture strength of the new as-rolled stock from Heat A-1726 is considerably higher and the ductility considerably lower than those of the stock previously tested, particularly at 1350~ and 1500~ Fo 2. When solution treated at 2200~ F and aged at 1400 F, the two stocks have reasonably similar rupture strengths. The stock from the new heat has lower ductility, however. 3. Apparently the high rupture strength of the stock previously tested after a 21000 F solution treatment is not going to be reproduced in the new stock.

TABLE IV COMPARATIVE RUPTURE PROPERTIES OF TWO HEATS OF LOW-CARBON N155 ALLOY Rupture-test properties__ I I Heat A-1726a I Lot 30276b 'I~,I ~ ~Test Strengths Elongation Strengths Elongation temperature _ (psi)_ % in I i. (psi) % in 1 in. Treatment. (~F) 100-hr lOOO-hr 100-hr 100- 100r 1000-hr 100-hr As rolled 1200 1 o8,000 I 3,000 5 4 [9,500 37,500 17 1350 34,000.29,000 20 32,000 18,500 12. 1500 t15,500 11 13,500 7,800 4O 2200 F, 1 hr, '.Q. 1200 (9,000)C (2,O000)C (10)C 50,000 |2,000 1 + 24 hr at lt00 F 1 1350 (32,000)C (25,000)C (25)C 30,500 2l,000 7 h 1500 (21,000)C I (1,000o)C (3$)C 21,000 1,000, 5 _ _ _ _ __ _ -15 000h0';12, o 00 i,4 4: i 2100" F, hr, W.Q. j 1200 j (37,500)C1 L6,500 10,000 7 7ce aAll test specimens taken from center bar from the ingot See data given in Section I-h and the report "A Study of the Effects of Heat Treatment and Hot-Cold Work on the Properties of Low-Carbon N155 Alloy." CBased on incomplete tests. Srl, /re^e^i 5fy, ^,,,A.. 0

21 III - REFP.ODUCIBILI'TY OF DATA IN RUPTURE TESTS As work progressed for slubsequent sections of the investigation, consideration of exact reproducibility of data became necessary. This step was important in preparation for the studies on the effect of chemical composition where it was felt all other possible variables had to be controlled or eliminated. Studies made in connection with X-rayr investigations also disclosed that other variables than aging time were influencing the rupture data. As a result of this t.ype of work, it seems quitp certain that reDortdN( rupture strengths may be influerced by: (1) inherent variabilit. between different bars from one lot of stock, (2) time at temperature in a ruptulre-test uni t before applying the stress, and (3) possibly other conditions such' as slihb;t differences in heat treatment conditions between different furnace chares, variable amoints of cold wrorking of the surface of specimens during machining, variation in the rate of stress application during tosting, etc. In most cases, btlt rot ^i1, the amount of such effects is relatively small and does not change practical trends from previous tests. The maitude of these effects thus far encountered are indicated br fiaure 6 This figure shows the ranges in rupture strengths at 1200~ F for bar stock heat treated on sevoral different occasions and taker from several different bars from Lot 3027(g. The test stock was solution treated at 2200~ F for one ho-ur, water quenched ard then aged for various times at l)00 F. The ranges are due to various degrees of all of the variables listed

ovvvv F T T I T T I T\^\^ l l-hr f-r rvture _ ___ 00000 - -~ L Ul~_lAX lO-1 0-hr n 60000...... (.. cn ~ ~ _ ~-h~ ~'~ ~ ~ OL.' — ---— 100-hr 50000 ri 400000 30 00 0 10 20 30 40 50 AGING TIME AT 14000 F, HR o - Baeed on 1 str- s-ru, tu-e time curve -. rO "n 2 ee -r'tte str ss-ru:oture time curves N'"te: (1) Checks h-eve not: —en m' e -t:ll ti re.erlods. (2) RBth holding time in test units before stressing..nd non-uniform tet-t m teeri;l h ve been recor.nized as causes or variations. FIGURE K.- WVI..;ITION IU i UPITUR)E STREINCTHS AT 12000 F FOR LO'C'RBON, N15 A: LLOY BA LO0CK FHOM: LOT 30276 VATLR QUENCHED FROMI 2200~ F AiD AGED AT 1400~ F.

23. previouslr. As nearly as vcmold be judged, the primary variable was inh.erent d.i;fferences betwe-en specr.imen-s cut fr1om, dit ffre.rt, bars Troi the lrherr-rrt -S ),E —,,tes i. f lot. Jncquest1ionally, howevr,.ol' tt... it was.. ir.l Prc.n' the results for:t.-rial.a a-ed, to t eas t-hree hours at a..... 1,.7. J c r I... t,r, t ~ nc- t J I GO h 1 00 F, T, art;.lar. y for tretins t-ine per; 1iod?1 u ho usurs* W7h-en e eff..F t of holding ti~ne vWas rcogn.zised ad th.e ma - titudC 0of t e.ff e ts of coti -var l bcae ei rt a rrofrsmt un nl'r..t e(, on.-. a-n.ral from t ho e; heat to establish the effect of holding time and repro'uc iblty of t da te te- s e inen w ee as uni f orm as o siVl e. Tihe rc t l obtain.d to date ar e shonri fi ure 7, Thus far the.cecks h etw e C; co i (e>nd ' ted t.h sane way have beln excelle't. (Sim lar d li caLe c"eck est. avy- be,' Ct.de ir, the.ast with similar results.) Hldin, time at the test tempratre, owever, does have an apprecia e ef ec L on te r:'pta re tir-.e, a lIast at short time )eriOodS In settirj ^ tes- tel s a- so.ltion treac'.d. at ria' was s;.elected b ecau.se it wo'u.? pr'obab- be mos res;,ons've, i-o I v ari.abls iF test5,These- f-c,".ni:' " ind cat e t.t' ' t.e rpt:u.,: dlat. peio'i - re':rt..d ma...... J".,. ~.....,: s1!,lr i.. have o '~-'......-fl.erd r'e on..~ t;:e i.' t.he test unit before e- a.'~,,., inr. t ti. -'-... he prevo::-!da rep ort ed.', i:,e r qu itc aIScourately def ine t'no i - -' t ' r, o. part'ic;r seimes d u r e t eting ce.nFS+~-t. Thre is, "ow:v-r, apj:..?-..v little deubt tha' son'' ' o.t0.t, sho.r I'-' the re'ot rt, '. A St.' of o f c'.? ' o e 'r t-.... r' -J. o.. ren~to d t —Cold- Work or? the Propt iJo of oLow-Carto N2. A n'o v;ere di"^ t soe -tert o v: at or. i.n te bar stoc-k te-.stdt t4 ri d~r; L I., cy s cV

In view of thesse fidings considerable care is ben z used to check the uniformity of the new bar stock from Heat A-172( so as to eliminate fac2se tren)s from the experiments. Test in techniques have been modified to keep the holding time in the test units to the most practical unifcrri minirmur.

26 IV - EFFECT OF CHEMICAL COMPOSITION OPJ FRO?, LRTIES This investigation is in progress to evaluate th? effect of the various alloying elements normally present in Low-Carbon Nl1 alloy on the properties of the alloy at high temperatures. As yet the work has been confined to the development of slufficient control of a process for making the alloys so that other variables than composition will not influence the results. This has involved development of control of chemical composition during citing, a forging procedure producing a uniform structure with good quality, a heat treat.rnt+ to reduce variations due to prior processing, and a demonstration of the degree of reproducibility of properties in several standard heats, I. Procedure for Production of Test Alloys The alloys are melted as 9-pound heats in an induction furnace, poured into a 9-inch square steel ingot mold tapered from 1 1/2 inches to 1 1/h inches, hammer forged to square bar stock and heat treated to eliminate the variable effects of prior forging. Armco iron, nickel, cobalt, and ferrochromium are melted down. Shortly before pouring, the necessary additions of ferrosilicon, ferromanganese, ferro-nolybdenum, ferrotungsten, and ferrocolumLbiur are made. The bath is treated with calcium-silicon just before pouring. Pouring temperatures have been controlled by optical pyrometer and immersion thermocouple measurements. The molds are preheated to about 500~ F before.pouring. The ingots are forged byr an air hammer having a capacity equivalent to abouit 110 pounds. Forging temperatures are kept between 22000 F and about 1750O F. Much of the work to date has been carried out to develop

a satisfactory forging procedure. Most of the bars;have ben forged between flat dies to 3/8-inch to 1/2-inch square bar stock. Ehxeriments.with swaging dies indicate that thez wovOuld be preferable. On the basis of microstructural studies and previous ex-perience,with the alloyr the heat treatment seCct,'i for reducing the effects of I;rocessing conditions on properties was heat.in at?2100~ for one hour ae.d water -uenchin. 2. Resul ts T'-:e chhemical comrosi.ti onos of the eleven heats irenared to date are givern n table V. The difference in chenical comrnosition betw ne aim and actual anal..ses in the first ( heats was lar-el: due to inacclracr it tlhe rrenortced arlalvrse of melti.nC' stock and t.o ncertaini ties of mf lting l osses T'-lp rasons for the variablit of th e anal*yss of t ' last five heath are rot clear. Thtli,,acrostructures. of the e leven in.gots in fi:'ure r'f1.ect o r.arilthe pourin, temnperatlures an-d possil'r the carbon corttent and mold te'mperatures. The differenc? in pour ng temperatures between the fir.t 6 heats and the last five is probably <the result of the methoc of measuring the emper' atures and does not represert true d fferences in temperaturea. difference i:n temperatures between individual heatts measired by one methiod are, however, real. Further wor.k will be necessary to develop a method of meas:irinc true temperatures. It will be noted in each grouti that: (1) The rower nour.inr temneraturs.lroduce eq:i.axed grains ir te centPr of the in-ots andl the area of quijaxed grains decreases as the Ipour nin temperatu:re increases r;ntUi all grains are columnar.

2. TABLE V CHEMICAL ANALYSES OF ELEVEN EXPERIMENITAL hEATS OF NT55 ALLOY I-.I....... C o poshemical co nposition: Heat t.( perent) _________ percentinumnber C n Cr N Co I W C iti E i:].-L 0.,5 1.7 05 20 2 20 3 2 l 1 0.12 EN' 1.25 l. 11 8.1O 19.1 20.35 13.6 12.30.05.11 EN2.20 19. 2.95 2.?.l 1.12 fEN3.25 1.6S.60 1.?99,.60 20.6. 2.77 2.62 1.12.15 FEN4 h.30 10.17. 7).1 1.371 9.01 17 29.3 i.96.12 1 AnEN5-6 40 1.7.5 20 20 20 3 2 1.12 EN5 55: j 7 2.12 EN5.55 18..67 17.03 12.1 20. 2.33 11.75 1.00.12 EN6.53.781. 1(.27.?7 1 8.O4 il 3.32 2.50.82.10 EN6'(check) --- 1.73 --- j 1.5 70 1.03 3.1 12.45.75 - Aim EN7,.15 1.7.5 20 20 i3 12 1.12 10, ]1,. 2.. 1 EN7.16 1..66 20.64L 17.3I 20.52 3.01 2.'3 1.11.15 EN8 i.4.146.L1 21.17 20.16 i19.31 3.03 20.8.96.1 EN10. 1.40.O.2 20.9 i20.6 1 19.30 3.05 11.91 1.03.175 iEN12.161 i1.z61 e57 1 21*.0; 81.39 22.00 3.03 2.01 1.151.Il

l 3 S a. Heats EN1, 2, 3, h, 5, 6 Approximate pouring._..~&~'. ~temperatures (~F),7-r'~~ ~~B~J ~CC ~ EN1 3000 EN2 2900 EN3 2860 ENh EN5 2820 e > py..->Alsr~g ENl6 2800 Note: These temperatureswere determined with an L. and N. optical pyrometer. 2 64 b. Heats E.., 8, 10,:,: 12 Approximate pouring temperatures (OF) EN10 2660 g: 1. _-*~~~~ -- _,- ENJl 2680 -- /EN12 27,5 Note: These temperatures were determined with an immersion Pt, Pt-Rh thermocouple. I! 12.I/ / Etchant - Marble's reagent FPGUtRE 8.- MACROSTRIUCTURES O' IN't5T CROSS SECTIOnS OF ELL4VEY' EXERIIMN.TAL Hr:ATS OF N155 ALLOY.

30. (?) The fine grain size of Heats EN5 and EN6 is believed to be the result of the high carbon content. (3) Differences in grain size also mav have been caused by a difference in mold temperature, particularly between heats EN? and EN9. In experimental forming of ingots EN2, EN3, and ENh center bursts were encountered. The center porosity present in the ingots of the first six heats may have contributed to this difficulty. Heat EN1 however was forged to 1/2-inch square without difficulty. The high carbon heat EN5 was difficult to forge at 2200" F because of its higher strength at this temperature. Forging from 23000 F resulted in burning in one case. The five low carbon heats have been forged without difficulty from 2200 F, possibly because there was practically no center porosity in the ingots. As yet no difference in structure after forging attributable to the difference in ingot structure has been observed. All forged square bars have shown a variation in grain size in that grains along the line of the axes extending from the corners of the bars have been finer than the surrounding metal. This condition bears no relation to the inr ot structure because: (1) It was present in the bars from ET7 and EN8 as.well as those fr6m Heats ENIO, 11, ard 12. (2) Forging ingots fron the corners rather than the flat surfaces produced the same structure in the same location in the finished bars. (3) Forging the ingots down as octagons rather than squares merely increased the number of corners and the corresponding number of fine grains,

31 Forging the ingots as rounds eliminated these lines of fine grains but produced some gradiation of grain size from surface to center, but the difference appeared much less than in the square bars. Typical microstructures of an ingot as cast, an as-forged bar, and a solution treated bar are shown in figure 9. The interface between the fine and coarse grained areas in the as-forgcid bars is shown by photomicrograph' b of figure 9. Wher the bars were heat treated at 2100C and 2200~ F the difference in grain size disappeared. Heating at higher temperatures gave some indication that the grains would coarsen along the lines connecting the corners at the location of the finest grains in the as-forged bars. Rupture tests at 1200~ F were undertaken on the bar stock produced from Heats EN7, 8, 10, 11, and 12 for the purpose of determining the scatter in strength from the five heats made to nearly the same composition. All bars were solution treated at, 21000 F for one hour and water quenched because this treatment prodiuced a uniform grain size;and because it had produced the highes r r strentgth in previous work on solution treated Low-Carbon N155 bar stock. (See report entitled "A Study of the Effects of Heat Treatment and Hot-Cold Work on the Properties of Low-Carbon N155 Alloy.") The temperature of 21000 F was also preferred to 2200~ F because the specimens have better ductility in the rupture test, and the excessive susceptibility to stress concentration brittleness after treating at the higher temperature was avoided. The curves of solution treatment temperature versus hardness (see figure 10) indicated that the 2100~ F treatment was reasonably good so far as uniformity was concerned.

0(INS JLVSH) IOTIV 55IN NOQVO-Mo0 0 io Slvi lVNlt WIHq X3 JO S~ fJ!OniY)lV{ dVOIdoLm -'T6 VOdIq{oqa pio oumoJqo o011IOa03T uo.qoas luplpnqTJuoi *uoVoeas qSOaO - '!M I I J o0018 - Oooqs JE -p - ' m, a4 I J 00[8F - _oOqs ai ' XOOI./ —. " XOO[ JA-"-^~~ ~. ^^'~crs V;^ ~il ^ 4y^ ^^/^ ^ ^t.^^,;V. V~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~l^~~~~~, 1or ^ ^^^^^^-"111^ ''ll^>'.: 1:1,11^_ ~~~~~~~~~ 4^.J2\-~ — ^^ -t^^. ^ ' ^. —: ~UOi{Zo)s SSOJO pa^JOJ is ^o~ ~ *q *^H B ^03h11 1? XOOT XOOT ^^^ 1~~~~~~~~7 ~ ~ ~ ~ ~ ~ ^ * 0~')~~ a^ *^ ^ ^^ ~'-\^'^,'-... -' ' -' X ~, -:f '7J- 'r ' '. ' *. %' OiA ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ \r7 Iv.~~~~~~~~~~~~~~~~ UOT, -i:S SS-'1~''",,":.P.)O '. )i;4 Er.'- ~A '"on~? S',u ' -,ou #,...'.... U...':. tie-,~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~t l ^:,'- "- ~... ~'"1 ".... 4~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ '' ~ ~ ~ ~ ~ ~ ^ ^ '^ ' I '"^"- -~'? ' '~~A [\ ' ^ ' ''.... ^ Lr^^^ 'j~ ~~~~~~~~~~~~~~~~~~~ t., [' ' [1 I ' 7 ~ ~ ~ ~ ~ ~ 'J J ~ ',.?, '~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~6. ' ' ' J' '.........I' IN '( I. I, ' ' ''. w I '.-;" '!..~~~

33. 300 - ----- - 20 ~ (V ^ r^ 2^,0 ~- __ - 4 -— ~ --- —-~- - - — ~,.. -. -.~ _. ~-._ _ _ -~ _ _ ^ __ ~ _ ___ '240- K [_K____ -^ 22.^-. ---^-..-..__~ ~__ __ _~ I__. ~ ~_: ~__ ___ ^ __ ___ 200 ~ ~ - - -__ ___ L1 \0 ENI 1~~~0 I- 160 ___ ____________ ____ ___ __ ___I__ __ ___ __ Surface Cross 2000 2100 2200 2300 As f ormed Solution Temperature, F (1 hour it temp.,.Q.) Code Heat Carbon Cross section Surfaice lumber Content H rdncess ___rd Hardness ENUl 0.16 ~ EN1,25 o EN5.^; ~ FIGURE 10. - EFFECT OF S-ECTION TibT TD AND SOLUTION TREqTING TE'APSRATURE ON TBE HARDNEl OF THREE EAPERIIENTAL HEATS OF N155 ALLOY.

3h4. Surface Brinell hardness of the forged bar stock has varied from 225 to 279, as 'is shown in the, folowing smunarvr of hardness measurements: Condition EN7 227 183, 195 EN8 I 225 - 201, 205 ENO1 f 252 205, 211 ENIl 2?t7-279 198-215 EN12 2142 187, 202 Lot 30276 233 197 After solution treating at 2100 F the range was from 183 to 215. The hardness values in this t abulation merely show the results of a limited number of measurements. More tests would probably show a wider range for those whiMch appear to have a uniform hardness. The rupture strengths for 100 hours (see table VI and figure 11) at 1200" F have varied between 48,000 and 52,000 psi. The indications are that the range will be about 3000 psi at 1000 hours. All five heats were slig'htly stronger at 100 hours than the commercial bar stock from Lot 30276 used for:no-t of 'he prior work. 3. Discussion The range in rupture strengths for the five heats does not appear to b. excessive, although it had been hoped that the range would be narrower. There is a strong possibility that better uniformity could be obtained by a solution treatment at the higher temperature of 2200 F followed by a proper aging treatment. For instance: (1) The new heat of commercial bar stock (Heat A-1726), on the basis of

355. TABLE VI RUFTUREl TEST RESULTS AT 12000 F FOR FIVE EXPERIMENTAL HEATS OF LOW-CARBON N1^ ALLOY _____- ElTongation: Redlction'o Rupture strength Heat Stress Rupture t.mne in I inch of area (psi) I number (psi) (hiours) (percent) (percent) 100 hour 1000 hour EN7 $0,000 66 8 10.9 0w 1,OGO 3140 19 623.4 10000 1 1.P, - EN8 10,000 100 12 13.8 50,000 I lL,000I 2~0L 11 16.2 j hO,000 I a1l.p. 312 hours _________ _____I____________ ________________________________ ENIO 1,O000 I 12h 3 8.0 5,00 I L5,oco 318 8 19.7 hOo000 lP 168 hoiurs mil ^0,000 ^1 8 8.7 ^0,000 '39,000 50,000 9Q '10. 1O,00 276 II 17.6 1 I4 LOOOC 76u II13.1 EN12 I0,o000 69 3 5.6 14,D000) O 45,9000 305 20 19.1 1P. Test in progress 3-10-11.

70 0fj 3 o ~ ~ ~~ ~ ~ ~- _ _ _ _ __' ~ ~ ~"'~'~ ~ ~ ~ ~ " -p~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~IM I.P 10 2 46 8 H0 46 8 Q 2 TIME, HR Cod e gy-rhol~~~~~~~ He t o EN7 0 EN1 ENIO o ENII ~ EN 12 Lot 30276 (Commenrrcial heat) I.P. Test in nrogress 3-10-48 Note: Aill mate-ials were solution treated 1 hour at 21000 F aind water quenched FI7U E 11. - CURVES OF.IRELS AGINJT hUPTUO.E Tl1L iT 12000 F FOR FIVE EXPERIvENT[L HLAik OF LON-C~BON N155 ALLOY.

(Lot 30276) and the induction heats tested in this investigation. Presumably the difference was due to the lack of elimination of prior treatment effects by the 2100~ F treatment. The two lots of commercial stock have very similar properties after a 2200~ F treatment. Presumably therefore a 2200~ F treatment more comnltely removes effects of difforences in pri or treatment~ (2) The work discussed in the provfous section indicates that the rupture properties of solution treated steck can be influenced by testing conditions and that this effect would be reduced bv an aging treatment of more than three hours At lhOO~ F. The fact remains, however, that when stock from Lot 30276 (see.'section Ill);was solution treated at 2200~ F and aged for various time periods at lOO~ F considerable variability remained. The data available is therefore not conclusive and subject to many interpretations. The procedure which seems to have the most promise of reducing effects of orior treatment is: 1. Solution treat at 2200~ F for 1 hour and water quench. 2. Age at 1hOO0 F for 2h hours.

38. V - FUNDAMENTAL METALLURGICAL STUDIES Complete understanding of the fundamental reasons for the various effects measured in other parts of the program is necessary before the results can be applied generally and used to establish controlled and predetermined properties, and also to permit the most economical use of alloying elements. Such studies are therefore considered an integral and most important part of the program even though such work has been undertaken with full realization that the experimental problems would be very difficult to master. Stated in other words, the plan is to establish the fundamental processes by which treatments and composition control the properties of commercial alloys at high temperatures. Several methods of proceeding with this phase of the investigation are possible. The approach is to carry out experiments which adll: 1. Measure and determine the cause of the effect of various metallurgical treatments on the internal or atomic structure of the matrix grains; 2. Measure and determine the cause of the effect of the treatment on the grain boundaries; 3. Determine the chemical composition of the constituents which are developed by the treatments. It was early decided that in any such studies to determine the fuindamental reasons for the high temperature behavior of metals the work should be divided into two parts: (1) studies of Low-Carbon N155 alloy, since a large amount of experimental experience has been accumulated for this alloy, and (2) studies of other alloy systems for the purpose of verifying theoretical

39. findings on Low-Carbon N155 and for expansion of basic knowledge. The first division of the work is well underway with the first formal report in preparation; the latter divisions of work are just now starting to produce useable results. The studies of Low-Carbon N155 have been further subdivided in two parts: (1) studies of solution treated and aged material, and (2) studies of hot-cold rolled and hot-rolled material. This division was prompted by the rather striking difference in their high temperature properties. Under the above divisions of work, the following paragraphs summarize investigations completed or in progress and the results are to be considered tentative in nature in order to allow for changes due to further work as outlined. Studies of Low-Carbon N15 Alloy In order to achieve the three objectives as outlined in the forward of this section, the following procedures have been followed to date: 1. For a general guide to the character of aging as it affects both grain boundaries and matrix in Low-Carbon N155, a metallographic study was carried out on samples aged for various time periods at each of two different temperatures after solution treating. 2. For additional insight into the matrix changes that occur with aging after solution treating, measurement of the intensity or broadness of the X-ray diffraction lines from planes of the lattice was selected. 3. Attempts to isolate and aralyize the various constituents by selective solution of the matrix have been made, although they have not as yet produced usable data.

h o The latest theories on the creep process indicate that it is fundamentally one of shearing along certain matrix planes and that further, such creep is controlled by the perfection or lack of perfection of the atomic arrangement on these planes. To study this atomic degree of perfection several alternatives were considered. It was felt that the study of diffraction lines of the matrix, as mentioned previously, would give most directly a measure of the atomic perfection and this method was accordingly selected. It should be remembered that the diffraction phenomenon itself is based upon the regular or periodical spacing of the atoms whFich go to make up a crystal and hence any disturbance of the arrangement of the crystal or matrix atoms would show up as a change in the diffracted X-ray beams. A brief description of the experimental techniques used in the above two steps is as follows: Bar stock from Heat A-1726 was initially solution treated for 10 hours at 22000 F. The long solution treatment was for the purpose of insuring that concentration gradients on a least a small scale would be eliminated. Some indication early in the exnerimental work was found that cast doubt on the reproducibility of X-ray measurement on stock solution treated one hour. The point, however, is not as yet definitely proven. Only slight grain growth took place over the major rportion of the bar cross section, but on two diagonally opposite corners pronounced growth had taken place. A hardness survey of the as rolled bar stock showed that average hardness across one diagonal to be higher than across the other; from this the conclusion may be drawn that the last pass in the rolling operation had worked the bar across one diagonal preferentially. In any event, X-ray studies

as well as rupture and creep studies, as outlined below have been confined to the uniform small grain size areas. In the preparation of aged samples, two temperatures were chosen, 1L00 and 1600~ F. These were used in the hope that aging reactions, i.f any, would be completed within times convenient for laboratory preparationo The metallographic examination was carried out on mechanicallyr polished specimens etched electrolytically in 10 percent chromic acid. Extreme care was used to insure that identical polishing and etching conditions were used with each specimen examined. As a first attempt with X-ray diffraction work, the (11l) plane reflection of the austenite was selected for study since it gives the strongest line and conversely is the plane of most dense packing. Chronilum radiation, the logical choice for use with Low-Carbon N155 from flourescence considerations was not available, and it was decided to use copper radiation since all the heavy elements of the alloy would flouresce. This was in preference to iron radiation, for example, with which only some of the elements would flouresce. Rather lengthy study of surfaces and their preparation of austenitic alloys and of Low-Carbon N155 in particular had to be carried out, as well as development of new equipment and technriques in order to arrive at the true state of affairs in regards to matrix conditions. A detailed description of this phase of the work will be included in a formal report in preparation. The experimental results of the above outlined studies are as follows:

L2. I. Microstructural Studies From a metallographic study of material aged up to 100 hours at 1hO00 and l160D F it is believed that three processes take place. First, a development of a new l-igh:t colored phase at the grain boundaries ap)arentl occurs followed byr an In-iard diffusion and eventual disappearance. The development and disappearance of this phase is vastly accelerated at 1(00~ F age when compared to ].00O F aging, as would be normally expected. Second, upon disappearance of the above phase another phase appears at the boundaries; first, as small isaands and then as a continuous network. This develo-ment also anppeared vastly accelerated at I'OO F. Third, general precip.itatiron within the matrix appeared to be taking place while the above two phenomenon were occurring. Here an anomalous behavior was noted, for preci-itation appeared to be taking place at a more rapid rate and in greater amount at lWOO~ F age than at t100' F. This difference in rates was in reverse to the conditions holding- for the first two phel menon noted above. The general matrix precipitation there.fore appearedpat O11100 F before completion of inward diffusion of the primary grain boulndlary material and subseq-u:ent appeararnce of the scrcndary bo7undary.nater'ia and af ter such phenom.ernon had been cornpleted at 1~00~ F. It can be noted that the metallographic exmnination rr-vealeId both impt.-ctant grain boundary reactions and matrix phenomena. Imprrovd techniTques are being developedt to reveal more fulil the exact co)nd. tjons existing at the grain boundaries. At present this phase of the work is of greatest concertn in view of the indications of the important role of grain boundaries in the creep process in the work here and at other laboratories. 3Ke, T'ing-Sui, "Stress Relaxation Across Grain Boundaries of Metals',? Physical Review, vol. 72, no. 1 (July 1917).

13. 2. Intensity Studies Figure12 presents the results of the intensity studies carried out on the material aged at 1h000 and at 1600~ F. It can be readily seen that the anomalous general matrix aging behavior roted above is present in the change of intensity with time. The qualitative form of the curves is in agreement with the present theoretical knowledge of the aging mechanism.2 In short, aging takes place along certain preferred planes of near registry between the precipitating lattice and the matrix lattice. The growth of the precipitating material causes internal strain as it tries to achieve its own true atomic spacing, virichi in general is somewhat different from the atomic spacing along the preferred precipitation planes of the matrix lattice. This internal strain causes increase in hardness and distortion of the matrix lattice and consequent lowering of the line intensities, as well as broadening of the lines. Eventual breaking away of the precipitating material from the original precipitation planes reduced hardness (commonly called over-aging) and restores the matrix to an unstrained condition, thus raising the line intensities to the equilibrium or steady state value. Line broadness would also decrease correspondingly. Enough data is rot at hand to define accurately the steady state value of intensity and also the minimum point or the li}000 F curve. No data on line broadness changes with aging time is presented. The unavoidable experimental error in determining both line height and line broadness is, in the case of line half value width, sufficient to mask any changes. This is not unusual, for charges in line half value width to compensate for chansges in line height in order to keep the integrated intersities constant at any given aging time can be small in comparison to height change for small changes in h!eight.3 2Barrett, C. S., Structure of Metals, McGraw Hill book Co., 1913. 3Dehlinger, U., Z. Krist, vol. 6i, p. 615, 1927.

1.2 14000 F Are 1~00 0~ _____ ___ __.0_ ________ _____ - -— _____ ]J 10U0 F Ar-e 0, 0 0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ \ 0 ^ 0H ~ ~ --- - ~ 0.8 I- IIns rtrsity of Ina d ~~~-~r t~rtiTST-TT^ at dl^TtdlPim? 0.7 ~~ ~ -~ -~~ ~ -~~-__~~~ ~ -._ ~~~~_ 0.1 1 10 100 TIME HR FIGURF 12. - EFFECT OF AGI1uG UPON.(111)LINF INTEMIPYIT OF LOW-CARBON N155.SOLUTION TREATED 10or1i~~UB~~, 22000 F, ITER QUENCHED.~ ~ ~ ~ ~~0.8~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^ I - Rine Irte~~~~~~~~~~msity~~~

5. Additional work is being carried out on solution treated and aged Low-Carbon N155 to obtain the steady state values of intensity after aging is complete and also the time and value for the minimum point on the 1h000 F curve. Since Low-Carbon N1. cannot be considered a strongly age-hardening alloyr, it is considered desirable to study an alloy system which is a strongly age hardening type. With X-ray intensity data and correlations between such data and high temperature properties available for th+is second alloy system, worthwhile comparisons with Low-Carbon N155 can be made and fundamental knowledge both verified and expanded. Several alloy systems are under consideration and work on one of them is to be started shortly, 3. Correlation of Rupture Test Properties and Structural Studies The X-ray intensity studies indicate that various acing treatments may control,the deformation characteristics through internal strain. For this reason tests are in progress to establish accurate rupture strengths and creep characteristics for treatments Indicated by figure 12. These tests are initially being kept at rather short time periods so that the trends will primarily be those due to the heat treatment and not those duie to subsequent structural changes during long testing time periods.. Studie i s n or on Hot-Cold Rolled and Hot-Rolled Low-Carbor Nl5 1. Preliminary metallographic studies show that hot-rolled LowCarbon Nl15 alloy stock fron Heat A-1726 has a grain boundary phase similar to the second grain boundary phase which forms during aging after a

solution treatment. Unlike the solution treated and aged material, no general matrix precipitation has been observed. The matrix material, however, has been found to be greatly distorted. There is evidence in the literature to indicate that in ordinary steel the presence of a continuous grain boundary phase results in a sharp yield point at room temperature and that absence of such a grain boundary network results in a lack of a definite yield point. The possibility exists that grain boundary networks may have an analogous effect on plastic flow during creep. Attempts are therefore being made to develop techniques which will show if the grain boundary network present in the as-rolled stock from Heat A-1726 has some such effect on its creeo characterf sti cs 2. Preliminary X-ray studies have shown solution treated and hot-cold rolled stock to have a preferred grain orientation. Further studies are being made to ascertain if the preferred orientations have any bearing on the high rupture strength at 1200~ F.

h7o VI - COOPERATIVE FATIGUE TEST PROCRAM In order to carry out the cooperative fatigue testing program being sponsored by the NACA Special Panel on the Relations Between Fatigue and Static Strength of Materials at Elevated Temperatures the following steps have been taken: 1. Puichase 271 feet of 1-inch round Low-Carbon N15^ bar stock,from the Universal-Cyclops Steel Corporation. This stock was made from another ingot from the same heat (A-1726) as the new stock purchased for the work described in Section II of this report. The processing was reported to be the same as that given in table I, except for the hot-rolling of the 2-inch square billets. The following description of rolling was supplied: One-inch rounds were rolled from 2-inch square billets in one heat. The 2-inch bars were heated in a.furnace at 2100 to 2115~ F; the temperature at the start of rolling was 2050O to 20600 F; and the finishing temperatures were from 1820O to 18110~ F. The bars were numbered in order of their position in the inot. 2. Chemical aralyses, microscopic, and hardness tests are in progress to ascertain the uniformity of the stock. 3. Stock is being heat treated and machined into the necessary specimens. L. Tensile and rupture tests are in progress as part of the testing program.

UNIVERSITY OF MICHIGAN 3 9015 02654 4646