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these applications. Although high strength steels are h i g h l y s u s c e p t i b l e to h y d r o g e n e m b r i t t l e m e n t and s t r e s s c o r r o s i o n c r a c k i n g , T R I P s t e e l s h a v e s h o w n good r e s i s t a n c e to e m b r i t t l e m e n t and d e l a y e d f a i l u r e w h e n c a t h o d i c a l l y c h a r g e d w i t h h y d r o g e n . 4'S H o w e v e r , f u r t h e r s t u d i e s have demonstrated that TRIP alloys can be embrittled by h u m i d a i r 6 o r d i s t i l l e d w a t e r . 7 T h e e m b r i t t l i n g a g e n t w a s a s s u m e d to be h y d r o g e n in b o t h c a s e s . T h e p r e s e n t e x p e r i m e n t s w e r e u n d e r t a k e n to p r o v i d e a m o r e d e f i n i t i v e d e t e r m i n a t i o n of the e f f e c t of h y d r o g e n on the m e c h a n i c a l p r o p e r t i e s of T R I P s t e e l . T e n s i l e and s t a t i c l o a d t e s t s w e r e p e r f o r m e d on u n n o t c h e d and n o t c h e d s p e c i m e n s in a h i g h - p r e s s u r e h y d r o g e n g a s e n v i r o n m e n t . G a s e o u s h y d r o g e n h a s b e e n s h o w n to s e v e r e l y e m b r i t t l e a w i d e v a r i e t y of f e r r i t i c and m a r t e n s i t i c s t e e l s a s w e l l a s one m e t a s t a b l e a u s t e n i t i c s t e e l , 304L.B T h e c o m p o s i t i o n of t h e T R I P s t e e l u s e d in t h i s w o r k was Cr-13 pct Ni-8 pct Mo-3 pct C-0.25 pct. The M D t e m p e r a t u r e f o r t h i s a l l o y i s a b o u t 150~ Test specim e n s w e r e m a c h i n e d f r o m a p l a t e t h a t had b e e n a u s t e n i t i z e d at 1200~ in v a c u u m f o r 1 h, w a t e r q u e n c h e d , r e h e a t e d to 4 5 0 ~ and w a r m r o l l e d to a f i n a l t h i c k n e s s of 0.2 c m . T o t a l r e d u c t i o n by r o l l i n g w a s 80 p c t . T h e t e s t s p e c i m e n s w e r e 6.0 c m l o n g and 1.5 c m w i d e w i t h a g a g e s e c t i o n 1.5 c m l o n g by 0.5 c m w i d e . N o t c h e d s p e c i m e n s had a 60 d e g V - n o t c h at the m i d p o i n t of the g a g e s e c t i o n . T h e n o t c h d e p t h w a s 0.06 c m and t h e r o o t r a d i u s w a s 0.005 c m . T e n s i l e t e s t s w e r e c o n d u c t e d in a i r , 10,000 p s i (7.0

kg/mm2), helium, and I0,000 psi (7.0 kg/mm 2) hydrogen. Tests in air were conducted with an Instron testing machine at a crosshead rate of 0.05 cm/min. Tests in the high-pressure gases were conducted with a pistoncylinder apparatus. Data from air tests were used as baseline tensile properties. Tests in high-pressure helium gave results under hydrostatic pressure but in a nonreactive environment. Experimental procedures for the high-pressure gas tests are described briefly below. A more detailed description of the apparatus and test techniques has been given elsewhere.9 After evacuation, an air driven diaphragm pump was used to pressurize the apparatus with high purity bottled gas. Hold time at pressure before testing was I min. The gas above the R. R.