The influence of silicon on the impact and tensile properties of steels
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S I B L E Y and B r e y e r I have r e c e n t l y e x a m i n e d the i n fluence of Si on the i m p a c t b e h a v i o r and t e n s i l e p r o p e r t i e s of low C s t e e l s . R a i s i n g the Si content f r o m 0.04 to 0.7 pct i n c r e a s e d the lower yield s t r e s s , 5lyp, lowered the i m p a c t t r a n s i t i o n t e m p e r a t u r e and r e duced the value of Ky, where Ky is a constant in the equation,
5lyp = 5o + Kyd -1/2 d b e i n g the g r a i n d i a m (mean l i n e a r i n t e r c e p t ) and 5o the f r i c t i o n s t r e s s . The influence of Si on Slyp and i m p a c t t r a n s i t i o n t e m p e r a t u r e s of f e r r i t e / p e a r l i t e s t e e l s is well e s t a b l i s h e d , x'~ for h o t - r o l l e d and for n o r m a l i z e d s t e e l s , and the r e s u l t s a r e s u m m a r i z e d in T a b l e s I and II r e s p e c t i v e l y . F o r i n v e s t i g a t i o n s2,3,7 of a s - r o l l e d s t e e l s , T a b l e II, the o p t i m u m Si content above which t h e r e is no f u r t h e r l o w e r i n g of the t r a n s i t i o n t e m p e r a t u r e , and the m a x i m u m l o w e r i n g of the t r a n s i t i o n t e m p e r a t u r e , a p p e a r to be r e l a t e d to c o m p o s i t i o n . R a i s i n g the Mn content or l o w e r i n g the f r e e N conc e n t r a t i o n a p p e a r s to l e s s e n the i m p r o v e m e n t in i m pact b e h a v i o r . The a m o u n t of Si r e q u i r e d to achieve o p t i m u m i m p a c t b e h a v i o r is also lowered. T h i s can be s e e n in F i g . 1 where the M n / N r a t i o is plotted a g a i n s t o p t i m u m Si content. The i n f l u e n c e of n o r m a l i z i n g on the o p t i m u m Si content is l e s s well e s t a b l i s h e d , but f r o m T a b l e II the i n d i c a t i o n s a r e that for n o r m a l i z e d s t e e l s g r e a t e r a m o u n t s of Si a r e r e q u i r e d to a c h i e v e b p t i m u m i m p a c t p r o p e r t i e s . 4,s,9 F o r example, Sibley and B r e y e r found that the Si content to give o p t i m u m i m p a c t p r o p e r t i e s in n o r m a l i z e d s t e e l s was 0.5 pct whilst Mintz, working with a s rolled* s t e e l s , found that the o p t i m u m addition was *Rolledis usedfor hot-rolled. 0.15 pet Si, 2 Although t h e r e is r e a s o n a b l e a g r e e m e n t on the influenee of Si on Sly p arid i m p a c t p r o p e r t i e s , t h e r e is little data a v a i l a b l e on the influence of Si on Ky. B. MINTZis Section Manager, SpecializedMetallurgicalServices, Scottish Laboratory, British Steel Corporation, Motherwell, Scotland and P. J. TURNER is with VG Micromass Ltd., Winsford, Cheshire, England. Manuscript submitted May 23, 1977. METALLURGICALTRANSACTIONSA
Sibley and B r e y e r ' s r e s u l t s a r e t h e r e f o r e of p a r t i c u l a r i n t e r e s t and a r e plotted in F i g . 2 with r e s u l t s f r o m s o m e e a r l i e r work by Mintz. 2 Although a s m a l l e r a m o u n t of Si was r e q u i r e d in the l a t t e r w
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