--------, Journal of Research of the National Bureau of Standards Vol. 55, No. 1, July 1955 Research Paper 2602 Thermal Expansion and Phase Transformations of Low-Expanding Cobalt-Iron-Chromium Alloys Peter Hidnert and Richard K. Kirby Coeffi cients of lineal' thermal ex pansion of some cobalt-iron-chromium alloys are reported for various tempemture ranges between - 65 0 and + 800 0 C, and the effects due to tem­ perature, chemical composition, heat treatment, etc., were determined. Some of the alloys investigated have coefficien ts of ex pansion less than t hose for fu sed quartz and ordinary inval' between - 65° and + 60 0 C. Some of the low-expanding cobalt-iron-chromium alloys have ')'--> a transformations on cooling to low temperatures, and the resulting a-phase reverted to 'Y on heating to high temperatures. AI'" temperatures were observed as high as _ 10 0 C ancl Ac, tempemtures at abou t 600 0 C. The effects of various hea t treatments from - 196° to + ] ,0000 C on t he t ransformation s were investigated, and the resultillg changes of thermal ex pansion were correlated wi t h the structlll'e of these alloys. 1. Introduction During World "Val' II, Eas tman Kodak: Co., Rochester , N . Y. , obtained a Government contract In 1934 , Masumoto [1] ' reported the res ults of his from the Office of Scientific R esearch a nd D evelop­ investigation on the linear th ermal expansion of ment to produce a low-expanding alloy having a cobalt-iron-chromium alloys co ntaining more than coeffieien t of expansion less than th at of a good 49 percent of cobalt and 5 to 20 percent of chromium. grade of invar at atmospheric temperatu res. After These alloys were prepared by mixing suitable pro­ a search of the li terature and some preliminary tests portions of electrolytic cobalt, electrolytic iron, and with the cooperation of other companies, Eastm an chromium (with 2.7 % of impurities) and melting Kodak Co. authorized th e Unexcelled Manufacturing these metals in alumina crucibles in a hydrogen Co., Cambrid ge, }.tIass. , to prepare some low-expand­ atmosphere. The melts were cast in iron molds 26 ing cobalt-iron-chromium alloys similar to those cm long and 0.6 em in diameter. Samples 10 cm in investigated by Masumoto. Peter Hidnert and length were cut from the ingots and heated for 1 hI' \iVilmer Souder of th e N'ational Bureau of Stand ard s at 1,000° C in a vacuum fmnace and then cooled made determinations of linear thermal expansion on slowly in the furnace. The chemical composi tions a number of th ese alloys over the range from - 65 ° indicated by 'Mas umoto for these alloys were not to + 60 0 C. A restrictedrepolt of the results of this obtained by chemical analyses [2] but were computed work was preps,red by Edgar D . Seymour of Eastman by him from th e initial charges. Kodak Co. for th e Office of Scientific R esea rch and Some of these alloys investigated by Masumoto D evelopment. The following summary was taken have very small coefficients of expansion. For from an unclassifi ed extract of the report : example, the coefficient of expansion of an alloy From a sea rch of t he li terature for a low-expandin g wi th a nominal composition of iron 36.5 percent and metal, Masumoto's co balt, iron, a nd chromium alloy gave chromium 9.5 per ce nt is 0.1 X 1O-6/deg C between the most promi se, if the meltin g, heat treatment, a nd a na lysis problems co ul d be solved. We beli evc these 20° and 60 ° C. This expansion coe ffwi ent is less problems have bee n solved and the techniq ue has been than those of such well-known low-expanding perfected so t hat it is possible to specify t he composition materials as fu sed quartz [3] and the usual grade of to 0.1 % in chromium and iron. An all oy has been made invar [4] . The investigation of these low-expanding with a coeffi cient of ex pa nsion of less than ± 0.5 X 10- 6/° C over t he range from - 65° to + 60 0 C wi t h the coefficient co balt-iron-chromimum alloys was made over the nearly zero from 20° to 45° C and also in t he region of range from liquid-ail' temperature to about + 250° C. - 35° C. This is from t wo to three t imes better t han Masumoto stated that the observations above room invar obtainable on t he ma rket. temperature were taken during heating, as the The data reported by Seymour 011 thermal expan­ expansion was almost reveri sble for heating and sion of cobalt-iron-chromium alloys is included in the cooli ng, and the observations below room temper­ present paper. Add itional data by th e present ature were taken during cooling. a uthors on these alloys and other cobalt-iron­ In b is paper l\l[asumoto also reported results of chromium alloys are given for various temperatures investigations on some magnetic, electrical, and between - 65 ° and + 950° C. corrosion-resisting 2 properties of one of these low­ expanding alloys. Data on Young's modulus and 2 . Alloys Investiga ted the temperature coefficien t of Young's modulus for various cobalt-iron-chromium alloys were reported The cobalt-iron-chromium alloys listed in table 1 by Masumoto and Saito [5]. were prepared by John Wulff of the Unexcelled Manufacturing Co., Cambridge, :Mass. The alloys I Figures in brackets indicate the literature references at the end of this paper. were made from cobalt, iron, and chromium powders. % 'rhis all oy res isted co rrosion in a d ilute sodium chloride solution to a much greater extent than invar, a nd t herefore IVf asumoto named it "Sta inlcss- Tn var." A master alloy of cobalt and chromium was first 29 30 .} ex pansion of cobalt-iran-chromium allays Average coetlicients of expansion per d eg C Residual change in length after 20° to 60° to JOOo to 150° to 200° to 250° to 20° to 20 ° to 20° to 20° La -60° to -60° to each test f -20° C d + 20° C • 60° C 100° C 150° C 200° C 250° C 300° C 100° C 200° C 250° C 300° C 1---------1------1----------------------------------1-----1 X 10-6 X 10- 6 X JO-6 X JO- 6 X 10- 6 X IO-6 X 10-6 X 10- 6 X 10- 6 X 10- 6 X 10-6 X 10- 6 X 10-6 X IQ-6 % 1.1 0. 000 1.2 } (1',=-67°) (Ara=- JOO) \ +.228 6.7 4.8 5. 7 J 5.2 -. 002 5.6 } .8 .000 .8 } ('1' ,=-64°) h. 1 (Ara= -35°) +- 170 6.6 3.8 5.2 } 4.3 -. 001 4.5 } 4.6 5. 4 7.7 10.6 5.0 6. 0 7. 3 9.7 +. 003 4.4 5.4 7.8 JO. 7 4. 9 6.0 7.3 9. 7 + .001 4.3 5.8 7.8 11 . 1 5. I 6. 1 7.5 9.7 .000 2. 6 4.0 3.3 6.7 -. 001 .2 1. 5.2 10.9 .8 2.5 4.8 8. 5 -. OOl -.2 1. 6 . 000 - .2 1. .7 . 000 '. 4 . 000 '. 4 (T ,=-65°) .7 (Ara= - 40°) +.019 2.5 1.0 1. 7 .8 2.0 4.9 9.8 1.4 2.8 4. 7 8.3 -.001 1.0 1.9 1. 5 .000 . 4 1.6 4.6 9.9 14. 4 15.4 1. 0 2. 4 4. 4 6.6 8. 2 -.002 .2 1.8 1. 0 .000 .2 -.OOl . 4 (1',=-64°) . 2 (Ar, =-100) +- 146 5.5 2.8 4.2 3.4 -.001 3.7 3.7 4. i 7.3 II. 2 4.2 5. 4 7. 0 9.7 +.001 3.7 4.8 7. I J I. 6 L3.7 14.9 4.2 5. a 7. I 8.5 9.6 . 000 5.5 6.4 8.5 J I. 3 13. 4 14 .6 5.9 6.9 8. 1 9.3 10_2 +.001 2.4 4. 0 3.2 6.7 .000 .3 2.0 5. 0 10.7 14.6 15.7 1. 1 2.6 4. 9 7.0 8.5 -. OO [ .3 1. 8 1.1 .000 .6 2.0 5.6 10. I 13.9 15.6 1.3 3.0 4.9 6.9 8.4 011 4.6 8.2 5.9 7. 4 6.6 8.7 10.6 276 4.5 7.3 5.9 9.3 II. 3 4. 4 7.2 5.8 II. 4 .6 2. I 1.3 .000 .6 .6 . 000 .4 .3 .4 +-004 1.2 .5 .8 .8 +.001 .7 .8 2.5 5. 6 JO.9 1.7 3.2 5.3 8.8 -. 001 1. 1 .000 1.2 } . 000 1. 3 -.2 -. 1 -.2 } +.002 . 0 . 0 . 0 1.3 } .000 1.2 1.4 4.2 2.8 .000 8.2 13.0 15.2 16.0 2.8 4.8 7. [ 8. 9 10. [ -.001 .6 . 000 .6 +- 1 -. 4 -.2 +.004 .6 -. 1 +-3 . 7 -.001 .8 1.0 2.7 6. 3 11. 9 15.0 16.2 1. 8 3.6 5.9 7.9 9.3 -.