Heat flow during surface melting: Effect of temperature dependent absorptivity
- PDF / 336,087 Bytes
- 3 Pages / 603.28 x 783.28 pts Page_size
- 105 Downloads / 204 Views
I I
gas
IY2 Yl ,
!
x
//
~ / "
/"
,#J/~
i
-- l ~ - ~
I
\/~7,,
AFE = 7,38MM
I
~
~-- -7~
~7~
x2 = 0
Y2 = 10,44 MM
Y
1
Fig. 5--Diagram representing Eq. [11 for pure iron in reducing atmosphere. The characteristic points of the curve are 1) vertical slope, 2) horizontal slope at y > 0.
when less oxygen is present. This is because, in that case, the smaller concentration of interdendritic liquid film due to segregation will result in a higher nonequilibrium solidus and therefore in a stronger shell? Finally, if mold cooling is more intensive, the thickness of the solid layer forming a mechanical support becomes bigger and so does the resulting depth and pitch of the folding marks. The authors would like to thank CONCAST AG for permission to publish this paper and Mr. A. Heimgartner of S U L Z E R AG for his advice on the experimental set-up. 1. 2. 3. 4.
D. R. Thornton: J. Iron Steellnst., 1956, vol. 183, pp. 300-15. H. Jacobi: StahlEisen, 1976, vol. 96, pp. 964--68. J.J. Bikerman: Physical Surfaces, Academic Press, London, 1970. M. Wolf, W. Kurz: to be published.
~5( o H2/CU
~0 2
o H2/CU
z01/ \%k ~ A I ~ T
AR ' +/CU /
~AIR/ST~T=42*C DiSCREPANCyINN}
DISCREPANCY(MM)
(a) (b) Fig. 6--Effect of discrepancy between observed and calculated shape of meniscus on (a) depth and (b) pitch of folding marks (mold material: ST = stainless st'eel, CI = cast iron. Superheat AT = 0, except when indicated.)
/
"C3
LIQUID LEVEL
/~o GAS
:-:
"
i
"/~ /
/
t1
t2
DEPT~ ~
t3
Fig. 7--Simplified model for mark formation.
d e p t h ( = d i s c r e p a n c y ) a n d p i t c h are therefore r e l a t e d as i n d i c a t e d s c h e m a t i c a l l y in Fig. 7) a n d will d e p e n d on the m e n i s c u s f o r m (surface tension, d e n s i t y of melt) resp. e x t e n t of s o l i d i f i c a t i o n ( c o n d u c t i v i t y of m o l d a n d gas). E q u a t i o n [1] d e m o n s t r a t e s that the c u r v a t u r e of the m e n i s c u s b e c o m e s s m a l l e r or its height greater for higher surface tension. A h y d r o g e n a t m o s p h e r e , therefore, leads to a larger d e p t h a n d pitch. A three-fold increase in o d u e to a h y d r o g e n a t m o s p h e r e (Table I) will result in an a p p r o x . 70 p c t increase in meniscus height. As s h o w n in Fig. 6(b), the difference in pitch b e t w e e n air a n d H 2 is a f a c t o r of a p p r o x i m a t e l y three. Therefore, o t h e r effects m u s t have p l a y e d s o m e role: T h e higher c o o l i n g effect of H 2 c o u l d have t h i c k e n e d the solidified shell. A further e x p l a n a t i o n c o u l d be that the shell which will a l w a y s d e f o r m (creep) to a certain degree d u e to ferrostatic pressure, s h o u l d d e f o r m less METALLURGICAL TRANSACTIONS B
Heat Flow During Surface Melting: Effect of Temperature Dependent Absorptivity J. A. S E K H A R A N D R. M E H R A B I A N With the acceptance of the laser as an important tool for materials processing and for the study of rapid solidification, variou
Data Loading...