Decarburization of 4340 steel by gaseous atomic hydrogen
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1. S. Yoda, Nobuya Kurihara, K. Wakashima, and S. Umekawa: Met. Trans. A, 1978,vol. 9A, p. 1229. 2. K. G. Kreider, L. D. Dardi, and K. Prewo: AFML-TR-70-193, 1970. 3. P. Shahinian: SAMPE QuarL, 1970, vol. 2, p. 28. 4. M. A. Wright: Met. Trans. A, 1975, vol. 6A, p. 129. 5. K. K. Chawla: J. Mater. ScL, 1976, vol. 11, p. 1567. 6. H. H. Grimes, R. A. Lad, and J. E. Maisel: Met. Trans. A, 1977, vol. 8A, p. 1999. 7. H. F. Volk, H. R. Nara, and W. H. Chang: AFML-66-310, vol. 1, Pt. V, 1971.
ELONGATION
Decarburization of 4340 Steel by Gaseous Atomic Hydrogen GOPALA KRISHNAN, ARTHUR C. SCOTT, BERNARD J . WOOD, AND DANIEL CUBICCIOTTI As p a r t of a study of the role of t r a n s i e n t g a s e o u s s p e c i e s in gun b a r r e l e r o s i o n , we have i n v e s t i g a t e d the i n t e r a c t i o n of g a s e o u s hydrogen a t o m s with s p e c i m e n s of 4340 s t e e l . The a t o m s w e r e g e n e r a t e d in a m i c r o wave d i s c h a r g e I that was excited in a flowing s t r e a m of m o l e c u l a r hydrogen in a P y r e x v a c u u m c h a m b e r at a p r e s s u r e of about 133 P a (1 t o r r ) . A r e s i s t i v e l y heated 4340 s t e e l s p e c i m e n , m e a s u r i n g 4.4 x 0.32 x 0.1 cm, was s i t u a t e d 30 c m d o w n s t r e a m f r o m the d i s c h a r g e * to i n t e r c e p t the flux of hydrogen a t o m s . *A major portion of the silica tube leading from the discharge to the specimen was kept at 195 K to minimize recombination of hydrogen atoms.
Fig. 2-Nominal tensile stress-percentageelongation curves, (a) obtained from room temperature tensile tests of an uncycled and a cycled specimen, (b) and (c) showing the respective scanning electron fractographs. m a t r i x at e l e v a t e d t e m p e r a t u r e s should be g r e a t e r in the p a r t close to the i n t e r f a c e than in the r e m a i n i n g p a r t . It is likely to c o n s i d e r that the p o r o u s m a t r i x l a y e r in contact with a fiber, whose t h i c k n e s s m a y be of the s a m e o r d e r of magnitude as the pore depth, would c o r r e s p o n d to s u c h an i n t e r f a c l a l l a y e r b e c a u s e 1 7 9 8 - V O L U M E 1 0 A , N O V E M B E R 1979
The c h a m b e r was pumped with a t r a p p e d m e c h a n i c a l v a c u u m pump, and the total p r e s s u r e was c o n t r o l l e d by t h r o t t l i n g the flow of gas at the inlet with a m e t e r i n g v a l v e . By m e a n s of a t u n g s t e n f i l a m e n t m i c r o c a l o r i m e t e r e and by t r i t r a t i o n 3 with NO2, we d e t e r m i n e d that, u n d e r our conditions of d i s c h a r g e power and total gas p r e s s u r e (133 Pa), the a t o m i c hydrogen flux at the pos i t i o n of the s p e c i m e n c o r r e s p o n d e d to about 10pct of the m o l e c u l a r hydrogen p r e s s u r e . The t e m p e r a t u r e of the s p e c i m e n was m o n i t o r e d by an i r o n - c o n s t a n t a n (ty
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