Characterization of the surfaces of good and poor paintability cold-rolled steel
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I. INTRODUCTION
THE
application of coatings to cold-rolled steel is a widely accepted method for preventing the corrosion of the steel substrate. However, the adhesion of the coating and the subsequent corrosion resistance of the system have been shown to depend on the surface characteristics of the steel.I Steel surface contamination can cause coating failure and poor corrosion resistance. The purpose of the present paper is to characterize the surfaces of cold-rolled steel samples which have good and poor painted corrosion resistance. The surface characteristics of these steels will be distinguished from those of surface graphite contamination, which is also knownto alter the quality of coated steel.2
II. EXPERIMENTAL
PROCEDURE
The s a m p l e s e x a m i n e d in this i n v e s t i g a t i o n were c o m m e r c i a l l y produced, batch a n n e a l e d , low c a r b o n c o l d - r o l l e d s t e e l . A r e a s a d j a c e n t to those e x a m i n e d had b e e n s c r e e n e d for painted c o r r o s i o n p e r f o r m a n c e in a s a l t s p r a y t e s t , p e r f o r m e d a c c o r d i n g to the method d e s c r i b e d in ASTM B l 1 7 . X - r a y d i f f r a c t i o n a n a l y s i s was p e r f o r m e d on the r e s i d u e which was s t r i p p e d f r o m the p r i m e side of 0.07 m ~ s t e e l s p e c i m e n s by i m m e r s i o n in a solution of 3 pct b r o m i n e in a n h y d r o u s m e t h a n o l for 10 to 15 s. The r e s i d u e was r i n s e d in methanol, dried, ground and its d i f f r a c t i o n p a t t e r n obtained u s i n g the D e b y e S c h e r r e r powder c a m e r a technique. P r e p a r a t i o n of s p e c i m e n s for 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 e x a m i n a t i o n c o n s i s t e d of s h e a r i n g 12 x 12 m m coupons which were r i n s e d in acetone b e f o r e mounting, p r i m e side up, on a l u m i n u m p e d e s t a l s . S p e c i m e n s were e x a m i n e d at high (20 kV) e l e c t r o n b e a m a c c e l e r a t i n g voltage to p e r m i t o p t i m u m J. A. SLANE is Research Metallurgist,MetallurgicalDivision, Republic Steel Research Center, Cleveland,OH 44131, and S. P. CLOUGH, formerly Research Metallurgist,MetallurgicalDivision, Republic Steel Research Center, is now Senior Research Engineer, Alhed Chemical Corp., Idaho National Engineering Lab., Idaho Falls, ID 83401 and J. RIKER-NAPPIERis Supervisor,Coated Products Division, Republic Steel Research Center, Cleveland, OH 44131. Manuscript submitted April 24, 1978. METALLURGICALTRANSACTIONSA
r e s o l u t i o n of t o p o g r a p h i c a l d e t a i l s , and at lower (5 kV) voltage to p r o v i d e enhanced s e n s i t i v i t y to s u r f a c e f e a t u r e s . E n e r g y d i s p e r s i v e X - r a y a n a l y s i s having a probe d i a m of a p p r o x i m a t e l y 0.5 to 2 ~tm was used to t e s t for the s e g r e g a t i o n of c h e m i c a l e l e m e n t s to v a r i ous t o p o g r a p h i c a l f e a t u r e s . A u g e r e l e c t r o n s p e
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