Ductility of stabilized ferritic stainless steel welds

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in the weld m e t a l of s t a b i l i z e d f e r r i t i c s t a i n l e s s s t e e l s , p a r t i c u l a r l y s t e e l s s t a b i l i z e d with t i t a n i u m .

EXPERIMENTAL A c o m m e r c i a l h e a t of T y p e 444 s t a i n l e s s s t e e l , a p p r o x i m a t e l y 2 m m t h i c k was u s e d t h r o u g h o u t t h i s i n v e s t i g a t i o n . T h e c h e m i c a l a n a l y s i s i s g i v e n in T a b l e I. It w i l l be n o t e d that t h i s s t e e l c o n t a i n s 18 pct C r - 2 p c t Mo, with a t o t a l C+N c o n t e n t of 460 p p m . Both T i and Nb a r e u s e d f o r s t a b i l i z a t i o n . T h e m a j o r i t y of the w e l d s w e r e m a d e by the g a s t u n g s t e n a r c p r o c e s s without the a d d i t i o n of f i l l e r m e t a l . T h e welding p a r a m e t e r s a r e g i v e n in T a b l e II. A l i m i t e d n u m b e r of v a c u u m e l e c t r o n b e a m w e l d s w e r e a l s o m a d e but w e r e not found to v a r y in e i t h e r n i t r o g e n f o r m o r content f r o m t h a t o b s e r v e d d u r i n g G T A w e l d ing. S e l e c t e d w e l d s w e r e a n n e a l e d in a v a c u u m f u r n a c e at 980~C and a i r c o o l e d . W e l d s w e r e s e c t i o n e d , and p o l i s h e d both m e c h a n i c a l l y and e l e c t r o l y t i c a l l y using a s o l u t i o n of 12 pct H2SO4 in m e t h a n o l . Q u a n t i t a t i v e m e a s u r e m e n t of the v o l u m e f r a c t i o n of i n c l u s i o n s was m a d e by a p o i n t counting t e c h n i q u e . T h e f r a c t u r e s u r f a c e s of s e v e r a l s a m p l e s w e r e o b s e r v e d in the s c a n n i n g e l e c t r o n m i c r o s c o p e . In o r d e r to d e t e r m i n e t h e f r e e n i t r o g e n content, s e c t i o n s of both b a s e m e t a l and weld m e t a l w e r e cut and s u r f a c e g r o u n d into one s q u a r e m m w i r e s of 15 c m length t a k i n g c a r e to a v o i d h e a t i n g of the s a m p l e d u r i n g p r e p a r a t i o n . T h e s e s a m p l e s w e r e then s e n t to B e t h l e hem Steel Corporation where internal friction measu r e m e n t s w e r e made using a t o r s i o n p e n d u l u m a p p a r a t u s . Soluble n i t r o g e n c o n t e n t s w e r e d e t e r m i n e d by d i g e s t i n g the s a m p l e in HC1, c e n t r i f u g i n g , and a n a l y z i n g the liquid for n i t r o g e n b y the K j e l d a h l m e t h o d . T h e i n s o l u b l e r e s i d u e f r o m the c e n t r i f u g e was then d i s s o l v e d in fuming s u l f u r i c a c i d and s o d i u m s u l f a t e , with the r e s u l t i n g s o l u t i o n a n a l y z e d by the K j e l d a h l m e t h o d . T h e s u m of the s o l u b l e and i n s o l u b l e a n a l y s e s in both the weld m e t a l and the b a s e m e t a l w a s a l w a y s within 20 p c t of the t o t a l n i t r o g e n content of the b a s e m e t a l a s d e t e r m i n e d by an i n e r t g a s f u s i o n technique; hence, a t m o s p h e r i c n i t

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