United States National Museum

i!li!i! SMITHSONIAN INSTITUTION UNITED STATES NATIONAL MUSEUM Bulletin 184 THE METALLOGRAPHY OF METEORIC IRON BY STUART H. PERRY UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1944 For sale by the Superintendent of Documents, U. S. Government Printing Office Washington, D. C. - Price 60 cents ADVERTISEMENT The scientific publications of the National Museum include two series, known, respectively, as Proceedings and Bulletin. The Proceedings series, begun in 1878, is intended primarily as a medium for the publication of original papers, based on the collections of the National Museum, that set forth newly acquired facts in biology, anthropology, and geology, with descriptions of new forms and revisions of limited groups. Copies of each paper, in pamphlet form, are distributed as published to libraries and scientific organizations and to specialists and others interested in the different subjects. The dates at which these separate papers are published are recorded in the table of contents of each of the volumes. The series of Bulletins, the first of which was issued in 1875, con- tains separate publications comprising monographs of large zoologi- cal groups and other general systematic treatises (occasionally in several volumes), faunal works, reports of expeditions, catalogs of type specimens, special collections, and other material of similar nature. The majority of the volumes are octavo in size, but a quarto size has been adopted m a few instances in which large plates were regarded as indispensable. In the Bulletin series appear volumes under the heading Contributions jrom the Uinted States National Herbarium, in octavo form, published by the National Museum since 1902, which contain papers relating to the botanical collections of the Aluseum. The present work forms No. 184 of the Bulletin series. Alexander Wetmore, Assistant Secretary, Smithsonian Institution, PREFACE A systematic treatment of the metallography of meteoric iron was prompted by the author's experience in describing an iron meteorite by metallographic methods somewhat more than a decade ago. He was then unable to find that any new meteorite had been so described, and the literature bearing upon the subject was scanty. It consisted chiefly of the writings of iron and steel technicians in the books ind periodicals of that trade and a few contributions in the proceedings of scientific bodies. The work done by such investigators upon meteoric iron being incidental to their studies of artificial iron and other metals, they naturally passed over many matters of interest to students of meteorites as such. Also, in their inves- tigation of meteoric iron they did not utilize fully the methods of research that were in common use in the study of artificial metals. The present work aims to apply metallography, both theoretically and practically, to the study of iron meteorites. To that end the author has attempted to give a sufficient outline of the metallography of artificial iron and its alloys to enable the reader to interpret mete- oritic structures; the principal types and structural features are described and illustrated; methods of research are explained; and finally a somewhat comprehensive bibliography is presented. The illustrations have been selected from about 1,300 photomicrographs, covering more than a hundred meteoric irons. All these may be consulted at the United States National Museum. The author also has deposited all the negative plates in the Museum, where prints from any of them may be obtained. They were made mostly by graduate students in the engineering department of the University of Michigan, skilled in photomicrography of artificial irons, who from time to time acted as assistants in the author's laboratory work. Especially noteworthy was the work of A. W. Herbenar, his assistant for 2 years, not only in producing a large part of the photographs but also in working out details in the tech- nique of etching and in finding numerous features of interest in the specimens examined. The author's grateful acknowledgments are due to Dr. W. F. Foshag, of the United States National Museum, and to his associate, E. P. Henderson, for many courtesies and the loan of numerous specimens; to Dr. F. H. Pough, of the American Museum of Natural History, Dr. H. W. Nichols, of the Field Museum of Natural His- IV BULLETIN 184, UNITED STATES NATIONAL MUSEUM tory, Prof. Charles Palaclie, of Harvard University, and Dr. H. H. Nininger, of Denver, for the loan of specimens; to Dr. Robert F. Melil, of the Carnegie Institute of Technology, who kindly read the manuscript and made valuable suggestions; and to Prof. Clair Upthegrove, of the University of Michigan, for the use of the facil- ities of the metallographic laboratory of the university. Stuart H. Perry. Adrian, Mich., Decemher 1, 1942. CONTENTS Page Preface iii I. Introduction ' 1 Historical 1 Macroexamination ; etching 2 Microexamination 2 II. General types of meteoric iron 4 Hexahedrites 4 Octahedrites 4 Ataxites 6 Transitional forms 7 Proportions of types 7 Interpreting structures 8 Analyses 9 III. Primary constituents of meteoric iron 10 Kamacite 10 Taenite 14 Plessite 15 IV. Accessory constituents of meteoric iron 17 Troilite 17 Daubr6elite 18 Schreibersite 18 Carbon 21 Cohenite 21 Oxides 24 Silicates 25 Minor constituents 25 V. Artificial irons 25 Iron and its alloys 26 Phases of pure iron 26 Thermal critical points 27 Hysteresis 28 VI. Alloys 28 Solid solutions 28 Solidification of alloys 29 Eutectics; eutectoids 29 Phase changes in alloys 30 VII. The iron-carbon system 32 The iron-carbon diagram 32 Martensite 35 Troostite; sorbite 35 Pearlite in meteorites 36 VIII. The iron-nickel system 36 Differences in transformation 36 Early iron-nickel diagrams 37 The supposed eutectoid 38 The composition of taenite 39 V VI BULLETIN 184, UNITED STATES NATIONAL MUSEUM An eclectic iron-nickel diagram 40 Comparisons with the iron-carbon diagram 41 Hysteresis increased 42 A meteoric iron-nickel diagram 43 Bradley and Goldschmidt's diagram 44 IX. Meteoric nickel-iron 45 Structural changes 45 The trias summarized 47 Crystallization in meteorites 48 Granulation 49 Composition of kamacite 51 X. Hexahedral structures 52 Classification 52 Neumann lines 53 Taenite and plessite 53 Transitional types 54 XI. Octahedral structures 54 Genesis of the Widmanstatten structure 54 Fineness of octahedral structure 56 Vogel's theory 57 A low-temperature equilibrium 59 Cosmic heatings 60 Transformation structure 60 "Spotted" taenite and kamacite 61 The "ragged" structure 62 Granular octahedrites 63 An anomalous iron 63 Transitional octahedrites 64 XII. Plessite; nickel-rich ataxites 65 Genesis of plessite 65 Vogel's views 66 A two-phase structure 67 The nature of kamacite needles 68 Recapitulation 69 Spheroidized taenite in plessite 69 XIII, Heat alterations 70 Artificial heating 71 Natural reheating 71 Nickel-poor ataxites 75 Cosmic thermal changes 76 XIV. The role of phosphorus in meteoric iron 77 Schreibersite 77 Phosphide in taenite 78 Schreibersite and troilite 78 Diffusion of phosphide 78 Iron-phosphide eutectics 79 Effects on i)hase transformations 80 Genesis of phosphide inclusions 81 Phosphorus and plessite 81 Studies on the Cape iron 82 References 83 . CONTENTS VII XV. Carbon and sulphur in meteoric iron 83 Martensite and troostite 83 Instances of Fe-C structures 84 Ferrous sulphide 86 Reichenbach lamellae 87 Expansion of troilite 87 Swathing kamacite 87 XVI. Neumann lines and deformations 88 Occurrence 88 Neumann lines and slip bands 89 Origin 89 Resemblance to gamma twinning 90 Manner of formation 90 Thermal alteration 91 "False" Neumann lines 92 Deformations 92 Causes of displacements 92 Evidence of air pressure 93 XVII. Metallographic techniques 93 Specimens for study 93 Macroexamination 94 Macroetching 95 Micropolishing 96 Microetching 97 Preserving specimens 101 Microexamination 101 Photography 102 Other methods of study 103 XVIII. Bibliography 105 Systematic treatises 105 Descriptions and studies 106 Catalogs and lists 107 Bibliographies ; current literature 107 Illustrations 108 Metallography 108 X-ray analysis 109 Literature cited 109 Plates 114 Index 199 TEXT FIGURES 1 Solidification of pure iron 27 2. Schematic equilibrium diagram 31 3. The iron-carbon equilibrium diagram 33 4. Early iron-nickel diagram 37 5. Eclectic iron-nickel diagram 41 6. Iron-nickel constitution diagram 42 7. Bradley and Goldschmidt's iron-nickel diagram 44 8. Composition ranges of meteoric irons 48 9. The delta-gamma transformation in nickel-iron 57 THE METALLOGRAPHY OF METEORIC IRON By Stuart H. Perry I. INTRODUCTION Historical.—Before metallographic methods were applied to the study of meteoric^ iron an extensive Hterature had been built up by the work of a number of able scientists, dealing with their classification, their chemical composition, and such structural features as could be observed at moderate magnification in obhque light. The most famous of those investigators was Cohen, whose Mete- oritenkunde summarized the knowledge upon that subject up to the year 1905. Their researches, however, were limited by the imperfect methods then available; for the ordinary microscope at best could reveal only the coarser contrasts in structure. The invention of vertical illumination opened a field of research that not only laid a new foun- dation for metallurgy but also greatly extended our knowledge of meteoric iron. Vertical illumination was invented perhaps as early as 1865, and the illuminator in substantially its present form was described in the 1883 edition of W. B. Carpenter's book "The Microscope." It was used for a number of years by Sorby, whose description of the microstructure of iron and steel (1887) was the most important early contribution to that subject. Its application to the study of meteoric iron, however, was singu- larly tardy. Although Cohen (1894) cited Sorby 's work, and several others dealing with the microstructure of metals, and (1903) men- tioned Reichert's new "metal microscope," which he said made possible photomicrographs up to a magnification of 200 diameters, he apparently made no use of the device, and his works are silent on the finer microstructure of meteoric iron.

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