The strength, fracture toughness, and low cycle fatigue behavior of 17-4 PH stainless steel
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EXPERIMENTAL PROCEDURES The 17-4 PH s t a i n l e s s s t e e l used in this study was m i l l - p r o c e s s e d and annealed plate, Table I. All heat t r e a t m e n t s were p e r f o r m e d in ultrahigh p u r i t y argon. Solution annealing at 1900~ (1038~ was followed by subcooling to 32~ (0~ to a s s u r e complete f o r m a t i o n of m a r t e n s i t e . The t e n s i l e and f r a c t u r e toughness p r o p e r t i e s were e s t a b l i s h e d using a) 0.250 in. (0.635 cm) diam smooth b a r t e n s i l e s p e c i m e n s f r o m the long t r a n s v e r s e d i r e c tion, b) Charpy V-notch s p e c i m e n s with an L-S o r i e n tation 4 and c) compact tension s p e c i m e n s with a T - L orientation 4 machined in a c c o r d a n c e with ASTM Stand a r d E399-72. The Charpy s p e c i m e n s were t e s t e d at r o o m t e m p e r a t u r e in impact in the s t a n d a r d V-notch configuration and with a fatigue p r e c a r c k at the root of the notch. Charpy V-notch and p r e c r a c k e d s p e c i mens were also t e s t e d in 3-point slow bending in o r d e r to s e p a r a t e the initiation and propagation s t a g e s of f r a c t u r e . The slow bend c o r r e c t e d total f r a c t u r e
e n e r g y was taken as the sum of the c r a c k initiation e n e r g y d e r i v e d f r o m the V-notch t e s t and the c r a c k propagation e n e r g y d e r i v e d f r o m the p r e c r a c k e d t e s t s . Ronald 5 has shown that this p r o c e d u r e e l i m i n a t e s the i n e r t i a l effects n o r m a l l y a s s o c i a t e d with Charpy t e s t ing. The c h a r a c t e r i s t i c dimensions of the compact t e n sion s p e c i m e n s , in a c c o r d a n c e with ASTM E399-72, were B = 1.125 in. (2.858 cm) and W = 2.0 in. (5.08 cm). The slow bend Charpy and compact tension t e s t s e m ployed a e r o s s h e a d speed of 0.04 t n . / m i n (0.1 em/mtn) while tenstle t e s t s involved an Initial s t r a i n r a t e of 2.9 • 10-2/min; a l l t e s t s were at room t e m p e r a t u r e . Fatigue c r a c k growth r a t e s were m e a s u r e d with c o m pact tension s p e c i m e n s with a T - L orientation, a The e h a r a e t e r i s t l e dimensions were B = 0.35 in. (0.89 era) and W = 4.0 in. (10.16 cm). The t e s t s involved stnusoidal t e n s i o n - t e n s i o n loading (R = 0.1) at 10 c y c l e s p e r second. The t e s t s were p e r f o r m e d in d r y argon (99.999 pet pure) and water s a t u r a t e d argon. The d r y a t m o s p h e r e was obtained by p a s s i n g ultrahigh p u r i t y argon (dew point - 100~ through a d r y i n g agent just p r i o r to entering the specimen chamber, while water s a t u r a t e d argon was obtained by slowly bubbling the gas through boiling water. A complete d e s c r i p t i o n of the data collection and a n a l y s i s techniques ts given elsewherefl Standard techniques were used to p r e p a r e s p e c i m e n s for light and t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y . 7 The f r a c t u r e s u r f a c e
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