The morphology of martensite in iron alloys
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G. KRAUSS is Associate Professor, Department of Metallurgy and Materials Science, Lehigh University,Bethlehem, Pa. A. R. MARDER is Supervisor, Alloy Development Section, Homer Research Laboratories, Bethlehem Steel Corp,, Bethlehem, Pa. This paper is based on an invited talk presented at a symposium on Formation of Martensite in Iron Alloys sponsored by the IMD Ferrous Metallurgy Committee and held at the Spring Meeting of T h e Metallurgical Society of AIME, May 1 9 7 0 , in Las Vegas, Nev. METALLURGICAL
TRANSACTIONS
EXPERIMENTAL PROCEDURE Alloys w e r e m a d e f r o m pure electrolytic iron in 1 0 0 - g ingots by induction melting in a h e l i u m a t m o s phere. T h e compositions of the binary iron alloys investigated in wt pct w e r e : F e - I . 9 4 M o , F e - 2 0 . 5 Pt, F e - l . 3 Sn, Fe-0.49"V, and F e - 0 . 3 1 W . A n F e - 0 . 2 C alloy, w h i c h w a s studied in previous investigations, 2'3 w a s also used. T h e ingots w e r e h o m o g e n i z e d at 2 4 0 0 ° F (1316°C) for 24 hr p r i o r to cutting into s m a l l metallographic s a m p l e s . The s a m p l e s for light m i c r o s c o p y w e r e heat-treated in a partial a r g o n a t m o s p h e r e and after soaking at 2 1 0 0 ° F (I149°C) for 15 rain w e r e q u e n c h e d in iced brine. T h e s p e c i m e n s were s m a l l e n o u g h (0.020 in. thick) and the q u e n c h s e v e r e e n o u g h so that I00 pct martensite f o r m e d in all the alloys, e x c e p t the F e - 1 . 3 Sn, in w h i c h only partial t r a n s f o r m a tion to martensite w a s observed. S a m p l e s w e r e p r e p a r e d for transmission electron m i c r o s c o p y by grinding the metallographic s a m p l e s to 0.005 in. thickness and by jet thinning in a solution of I0 pct perchloric acid in glacial acetic acid at a 21 v potential. Replicas for m e a s u r e m e n t s of surface s h e a r s w e r e m a d e by a two-stage cellulose acetatec a r b o n technique. Cellulose acetate w a s p l a c e d on the surface and dry-stripped. P r i o r to shadowing, 0.264 polystyrene balls w e r e dispersed on the cellulose acetate. S h a d o w i n g w a s done with a 40 P d - 6 0 A u alloy at a 27 deg s h a d o w i n g angle. C a r b o n w a s then evaporated n o r m a l to the surface, and the cellulose acetate w a s dissolved with acetone. A n R C A E M U 3 E electron m i Table I. Martensite Terminology
Type I
Type iI
Schiebung Martensite Lath Martensite Self-accommodating Martensite Massive Martensite Dilute-alloy Martensite High-temperature Martensite Dislocation Martensite Cell Martensite Packet Martensite Dislocated lath Martensite Unidirectional Martensite Untwinned Martensite
Umklapp Martensite Acicular Martensite Plate Martensite High-alloy Martensite Low-temperature Martensite Twinned Martensite Twinned plate Martensite Multidirectional Martensite Twinned acicular Martensite Lenticular Martensite
VOLUME 2 , SEPTEMBER 1971-2343
Fig. 1--The s t r u c t u r e of l a t h m a r t e n s i t e s . (() F e - 0 . 2 C. Magnification 205 t i m e s . 2344-V
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