Variations of nitrogen with silicon content of electrical steels
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ELECTRICAL steels are low carbon steels in which electrical properties are achieved either by .the use of silicon or special processing. A wide variety of types and grades exist to meet customer requirements for various magnetic and mechanical properties. The two broad types of silicon steels are oriented and conventional. At the teemingstage, conventionaltypes differ primarily in silicon content which may vary from 0.5 to 3.2 pet. Oriented silicon steels have 3.0 to 3.3 pet Si, lower aluminum and manganese and higher sulfur than conventionalgrades. The method of manufacture is essentially the same for the different grades. Carbonis reduced to 0.03 pet or less in a furnace by oxygen injection and the steel is then tapped into a ladle onto preweighed appropriate alloy additions. At tap time, the only change in practice which is dependent on grade is tap temperature. This is lowered for higher silicon grades since larger amounts of exothermic 75 pet ferrosilicon are subsequently added in the ladle. Because processing is similar up to the time of tapping one can assume and verify that the nitrogen content is the same for all grades. However, during the period after ladle alloying and prior to teeming, nitrogen contents of commercial heats of electrical steels have been noted to increase with decreasing silicon. This behavior is qualitatively described by a ladle nitrogen transfer model. PRESENTATION O F DATA The a v e r a g e n i t r o g e n a n a l y s e s and c o r r e s p o n d i n g c a l c u l a t e d h e n r i a n a c t i v i t i e s a r e l i s t e d in T a b l e I for s i l i c o n s t e e l s p r o d u c e d d u r i n g 1968. The g r a d e s a r e grouped in o r d e r of d e c r e a s i n g Silicon contents and the t a b u l a t i o n i n c l u d e s d e t a i l s of the c o m p o s i t i o n r a n g e s for Si, A1, Mn, S, and C. Grade A is u s e d in the m a n u f a c t u r e of g r a i n o r i e n t e d types of e l e c t r i c a l s t e e l s . The r e m a i n i n g g r a d e s a r e c o n v e n t i o n a l type e l e c t r i c a l s t e e l s which have u n d e r g o n e d e s u l f u r i z a t i o n and a l u m i n u m deoxidation t r e a t m e n t s in the ladle and a r e c h a r a c t e r i z e d by t h e i r high a l u m i n u m and low s u l f u r levels. P. KERSHAWand D. A. KRAAI are Senior Research Metallurgist and Senior SupervisingMetallurgist,respectively, Allegheny Ludlum Steel Corp., Research Center, Bfackenridge,Pa. Manuscript submitted December 9, 1969. METALLURGICALTRANSACTIONS
The n u m b e r of h e a t s a v e r a g e d for e a c h g r a d e c l a s s i f i c a t i o n was in each case g r e a t e r than 70. The s t a n d a r d deviation for n i t r o g e n is 7 ppm. The data in T a b l e I a r e plotted a s n i t r o g e n content in ppm vs wt pct Si in Fig. 1. It will be s e e n that, with the exception of G r a d e I, a close l i n e a r r e l a t i o n s h i p e x i s t s for c o n v e n t i o n a l g r a d e s whereby the n i t r o g e n l e v e l dec r e a s e s with i n c r e a s
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