The effect of a rising tensile load on crack extension in a laminar composite steel
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a n n e a l , a r e s t i l l p r e s e n t in e s s e n t i a l l y the s a m e f o r m which e x i s t e d i m m e d i a t e l y a f t e r the i n i t i a l a n n e a l . F i n a l l y , the fact that the NiCrA1Y had b e e n subjected to a t e m p e r a t u r e of 2450~ (1343~ would indicate that the m i c r o s t r u c t u r e shown in F i g . 5 should be s t a ble for v e r y long p e r i o d s of t i m e in the t e m p e r a t u r e r a n g e f r o m 1800~ (980~ to 2200~ (1204~ On the b a s i s of the study d e s c r i b e d above, it s e e m s quite c l e a r that t h e r e a r e d i s t i n c t p o s s i b i l i t i e s of cold f o r m i n g l a r g e g r a i n e d , high a s p e c t r a t i o NiCrA1Y, and r e t a i n i n g this f a v o r a b l e g r a i n s i z e and shape in a f o r m which is s t a b l e at the highest use t e m p e r a t u r e of the m a t e r i a l . The p r o c e s s i n g t r e a t m e n t would have to i n c l u d e a s u i t a b l e s t r e s s r e l i e v i n g o p e r a t i o n a f t e r the cold f o r m i n g of the m a t e r i a l . As a c o n c l u d i n g r e m a r k , the a u t h o r s g r a t e f u l l y acknowledge the s u p p o r t which the National A e r o n a u t i c s and Space A d m i n i s t r a t i o n has given to the total p r o g r a m , of which the work r e p o r t e d h e r e i n is a p a r t . S p e c i a l thanks a r e due to A n n e R. K e n d r a of the NASA L e w i s R e s e a r c h C e n t e r staff for the optical m e t a l l o g r a p h y of the NiCrA1Y shown in the f i g u r e s . 1. L. J. Klingler,W. R. Weinbelger,P. G. Bailey,and S. Baranow:NASACR1211164, 1972. 2. D. L. Deadmore,C. E. Lowell,and G. J. Santoro:NASATMX-71835,1975. 3. B. A. Wilcoxand A. H. Clauer:"DispersionStrengthening",TheSuperalloys, C. T. Simsand W.C. Hagel,eds.,JohnWileyand Sons,NewYork, 1972. 4. J. J. Petrovicand L. J. Ebert:Met. Trans., 1973,vol.4, p. 1309. 5. R. D. Kaneand L. J. Ebert:Met. Trans. A, 1976,vol. 7A, p. 133.
The Effect of a Rising Tensile Load on Crack Extension in a Laminar Composite Steel S. J . ACQUAVIVA AND R. CHAIT High h a r d n e s s l a m i n a r c o m p o s i t e s t e e l c o n s i s t s of a high c a r b o n f r o n t a l p o r t i o n m e t a l l u r g i c a l l y bonded to a s o f t e r , l o w e r c a r b o n s t e e l backup by m e a n s of a r o l l bonding p r o c e s s that takes p l a c e at 1150~ to 1260~ A f t e r r o l l bonding, the m a t e r i a l is oil quenched f r o m a p p r o x i m a t e l y 815~ and t e m p e r e d at 120 to 167~ Such heat t r e a t m e n t p r o d u c e s a t e m p e r e d m a r t e n s i t i c m i c r o s t r u c t u r e and h a r d n e s s l e v e l s on the f r o n t a l and backup p o r t i o n of R c 61 and 50, r e s p e c t i v e l y . The diff e r e n c e in h a r d n e s s s t e m s m a i n l y f r o m a higher c a r bon l e v e l i n the f r o n t a l p o r t i o n t h a n i n the backup p o r tion. C a r b o n contents in the b a r d l a y e r u s u a l l y r a n g e f r o m 0.52 to 0.62 pct c a r b o n ,
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