Analysis of Rapid Solidification Process in the Double-Roller Method
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ANALYSIS OF RAPID SOLIDIFICATION PROCESS IN THE DOUBLE-ROLLER METHOD
F. KOGIKU, M. YUKUMOTO, K. SHIBUYA, M. OZAWA AND T. KAN High Technology Research Laboratories, Kawasaki Steel Corporation Kawasaki-cho 1,Chiba, 260, Japan ABSTRACT
High-silicon steel was rapidly solidified to thin strips by the double roller method. Two typical macrostructures were observed: one with an equiaxed zone and the other without. The formation of the equiaxed zone is caused by an excessive gap between the rollers. Heat transfer calculations and dendrite arm syacing measurements both suggested that the cooling rate is about 103 to 10 K/sec. INTRODUCTION
Production of thin sheet directly from molten metal using rapid solidification techniques has received increasing attention. These techniques offer not only cost advantages associated with streamlining of the sheet-making process, but also unique material properties brought about by the rapid solidification process itself. The crystallized thin sheets produced by rapid solidification have the following unique features: (1)Increased solid solubility (2) Decreased segregation and precipitation (3) Finer crystalline structure (4) Manufacture of thin sheets from materials difficult to shape (5) Simplification of the thin sheet making process These features are advantageous for manufacturing high-silicon steel thin sheet, which is difficult to roll but superior in magnetic and mechanical properties [1]. Kawasaki Steel is experimentally producing such high-silicon steel thin sheets by the double roller method. Examined below are the solidification characteristics of the rapidly solidified high-silicon steel strips directly cast by the double-roller method. MANUFACTURING CONDITIONS
Molten steel with silicon contents as high as 4.5-5.5 wt.% was introduced between two rollers with internal water-cooling systems. The rollers were 400-550mm in diameter and rotated at circumferential speeds of 3-12 m/sec. The rapidly solidified thin steel strip (RS strip) thus obtained measured 120-500 Pm in thickness. An example is shown in Photo. 1.
Photo. 1 High-silicon steel rapidly solidified strip
Mat. Res. Soc. Symp. Proc. Vol. 58. '1986 Materials Research Society
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roller rotation direction Photo. 2 Structure of RS strip (without equiaxed zone)
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roller rotation direction Photo. 3 Structure of RS strip (with equiaxed zone)
RESULTS AND DISCUSSION Macrostructure of Rapidly Solidified Strip
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Photos. 2 and 3 show typical examples of the mactostructure of RS strip. In Photo. 2, fine columnar crystals have developed from both surfaces, and extend almost to the center thickness. By contrast, in Photo. 3, the fine columnar crystals do not reach the center of the strip thickness, and the central area consists of equiaxed crystals [2]. The equiaxed zone is considered to be formed by roller-misalignment or roller heat crown, which are schematically shown in Fig. 1. When the gap of the rollers
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(A) uniform solidification (B) misalignment (C) heat crown
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