Mechanical properties of high purity Fe-26 Cr-1 Mo ferritic stainless steel
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S O M E of the b e n e f i t s which r e s u l t f r o m i n c r e a s i n g the p u r i t y of i r o n - c h r o m i u m f e r r i t i c s t e e l s were pointed out about 20 y e a r s ago b y Hochmann h z,4 and B i n d e r and Spendelow. s T h e s e w o r k e r s d e s t r o y e d the notion that f e r r i t e c o n t a i n i n g m o r e than 18 pct c h r o m i u m was i n h e r e n t l y b r i t t l e at r o o m t e m p e r a t u r e , s Using v a c u u m m e l t i n g t e c h n i q u e s , a l l o y s were produced with as much a s 35 pct c h r o m i u m and low l e v e l s of c a r b o n , n i t r o g e n and oxygen. The e a r l y w o r k e r s d i s a g r e e d s o m e w h a t as to what l e v e l s of i n t e r s t i t i a l c a r b o n and n i t r o g e n were n e c e s s a r y to p r o d u c e r o o m t e m p e r a t u r e t o u g h n e s s in i r o n c h r o m i u m f e r r i t e . However, t h e i r r e s u l t s c l e a r l y d e m o n s t r a t e d that when c a r b o n , n i t r o g e n and oxygen were r e d u c e d to low l e v e l s , r o o m t e m p e r a t u r e n o t c h e d - b a r i m p a c t v a l u e s s i m i l a r to those of a u s t e n i t i c s t e e l s w e r e obtained. D u c t i l e - t o - b r i t t l e t r a n s i t i o n s were s t i l l obs e r v e d but they o c c u r r e d well below r o o m t e m p e r a t u r e . Until r e c e n t l y , the knowledge that low i n t e r s t i t i a l e l e m e n t l e v e l s p r o m o t e toughness in high c h r o m i u m f e r r i t e has not b e e n u t i l i z e d on a l a r g e - s c a l e c o m m e r c i a l b a s i s . The r e c e n t d e v e l o p m e n t of a r e f i n i n g p r o c e s s c o m b i n i n g v a c u u m m e l t i n g , e l e c t r o n b e a m r e f i n i n g and c o n t i n u o u s casting, has made e c o n o m i c a l p r o d u c t i o n of i r o n - c h r o m i u m and other high p u r i t y alloys p o s s i b l e f i -8 E x c e l l e n t p r o p e r t i e s have b e e n shown to r e s u l t f r o m highly r e f i n e d h i g h - c h r o m i u m f e r r i t i c s t e e l s . Alloys c o n t a i n i n g up to 30 pct c h r o m i u m , v e r y low c a r b o n and n i t r o g e n , s o m e of which also contained m o l y b d e n u m for added c o r r o s i o n r e s i s t a n c e have b e e n made. 9 T h e s e s t e e l s c o n f i r m e d the e a r l y w o r k e r s '1-4 findings of high d u c t i l i t y and e x c e l l e n t r o o m t e m p e r a t u r e notch toughn e s s . Studies showed that an alloy c o n t a i n i n g 26 pct c h r o m i u m and 1 pct m o l y b d e n u m has equal or b e t t e r c o r r o s i o n r e s i s t a n c e than c o n v e n t i o n a l a u s t e n i t i c s t a i n l e s s g r a d e s . 9 - n The m e c h a n i c a l p r o p e r t i e s of c o m m e r c i a l l y produced, l a b o r a t o r y p r o c e s s e d , high p u r i t y F e 26 C r - 1 Mo s t e e l will be d i s c u s s e d h e r e i n .
I. A. FRANSON is Eastern Region SalesManger of Airco Vacuum Metals, Divisionof Airco Inc., Murray
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